CHEMICALLY MODIFIED ABSORBENT FOR EXTRACTION OF SELECTED HEAVY METAL IONS

DISSERTATION

SUBMITTED IN PARTIAL FULFILMENT OF THE REQlfTRMENT FOR THE AWARD OF THE DEGREE OF

-J of $I)tl0pound(0pf)Jgt

IN

A^CHEMISTRY

^^(~gtlt^ BY

MOHDNASIR

UNDER THE SlireRVISION OF

DR LUTFULLAH

V

DtPARTMENT OF CHEMISTRY ALICARH MUSLIM UNIVEkSITTY

ALICARH (INDIA) V

2 4 NOV 2014 DS4382

(Dr Lutfidtah (Associate Professor)

DEPARTMENT OF CHEMISTRY

ALIGARH MUSLIM LfMVERSITV ALICARH-202002 (liP) INDIA Tel +91-571-2703515 (Office) E-mail lutfullah786^gmailconi

Dated

Certifitate

This is to certify that the work embodied in this dissertation entitled

Chemically modified adsorbent for extraction of selected heavy metal

ions is original carried out by Mr Mohd Nasir under my supervision and

is suitable for submission for the award of the degree of Master of

philosophy in chemistry of this university

CANDIDATES DECLARATION

Mohd Nasir Department of Chemistry certified that the work embodied

in this MPhil dissertation is my own bonafide work carried out by me

under the supervision of Dr Lutfullah at Aligarh Muslim University

Aligarh The matter embodied in this MPhil dissertation and cited as my

own work

I declare that I have faithfully acknowledge given credit to and referred

to the research works wherever their works have been cited in the text

and the body of the dissertation I further certified that I have not wilfully

lifted up some others work para text data results etc Reported in the

journals books magazines reports dissertations thesis etc or

available at web-sites and included them in this MPhil dissertation and

cited as my own work

Date Jgti ly (Signature of the candidate)

(MOHD NASIR)

ACKNOWLEDGMENTS

In the name of ALLAH the most beneficial and roercifuF

First and foremost I bring all the praise and commendation to the ALLAH SUBHAN-

0-TALA for providing me with strength and endurance to accomplish my research

work

It will be hard to find the words to thank my supervisor Dr Lutfullah for his

excellent guidance constant support and trust throughout the course of my research

work

Research is a kind of endeavour which demands ones intellectual and emotional

involvement along with the cooperation of ones mentor and teachers In this respect 1

am deeply indebted to Prof Nafisur Rahman for his inspiration and guidance with

his profound and perceptive scientific Ideas and experience which helped me at every

step Moreover his meticulous reading and corrections led to the completion of my

dissertation 1 conceder myself very fortunate to have the opportunity of working with

him 1 am really impressed by his quality to help others without any gain

I am thankfiil to the Chairman Department of Chemistry Aligarh Muslim University

for providing the research facilities 1 am also gratefiil to Aligarh Muslim University

for providing financial assistance (Non NET Fellowship UGC) to carry out this work

I would like to thank UGC (DRS-1) DST (FIST and PURSE) for providing partial

support to complete this dissertation

1 would like to acknowledge my sincere thanks to my seniors and colleagues Dr Mohd

Kasif Uzma Haseen Mohammad Fazeel Khan Sumaiya Khan and Shahroora

Sameen for all time cooperation in my research work

My deep sense of gratitude for the guiding hand of my father Haji Naseem Ahmad

and the humble and loving care of my mother Mrs Zareena Naseem for their true

affection and love Really without them I can hardly imagine myself to be where 1 am

today I cannot forget my uncle Mr Javad Akhter for his suggestion encouragement

help and support during my research work I am also thankful to my beloved brother

Hafiz Mohd Rashid and Arslan Khan sisters Shaneela Jamsheeda and Shafeequa and

my relatives for their constant encouragement and support during my study and my

good and bad times

I would like to express my gratitude to my wife Mrs Khursheeda Nasir and son

Mohammad Arham Words fail me to express my appreciation of my wife whose

dedication love and persistent confidence in me have taken the load oflF my shoulder It was

her support and encouragement which made this dissertation possible

I have deep core in my heart for my hostel mates and friends particularly for their

supports and suggestions in my bad and good days I would like to acknowledge Dr

Mohd Asif Dr Mohd Shahid Dr Shenwaz Abbas Sadat Suhail And Faheem

Ahmad I am highly thankful to all of them for the encouragement and support

Mohd Nasir

L

CONTENTS

List of Tables

List of Figures I ^

ABSTRACT ^-^l

CHAPTER 1 General Introduction 01-20

References 21-33

CHAPTER 2 Chemically modified silica gel with thiosalicylic 34-71 acid for removal of Pb(II) Cu(II) and Cr(III)

References 72-74

LIST OF TABLES

Table 11 Modified silica gel with various functional groups for 13

separationor preconcentration of metal ions

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption 58

of Pb(II) Cu(II) and Cr(III) onto modified silica gel (Si02-

APTMS-THSA)

Table 22 Kinetic parameters for adsorption of Pb(II) Cu(II) and Cr(lll) 65

onto modified silica gel (SiOi-APTMS-THSA)

Table 23 Thermodynamic parameters for the adsorption of Pb(II) Cu(II) 70

and Cr(III) onto modified silica gel (SiOi-APTMS-THSA)

LIST OF FIGURES

Scheme 11 Preparation of 3-aniline-propyltrimethoxysilane 7

intermediate

Scheme 12 Synthesisof aniline grafted silica adsorbent 7

Scheme 13 Modification of silica surface by coupling of terminal olefin 9

presence of metal catalyst

Scheme 14 DPTH-gel formation 10

Scheme 15 TS-gel formation 11

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15 18

Scheme 17 Adsorption mechanism of Pb (II) on 19

(a) TLSG

(b) FLSG

(c) PLSG

Scheme 18 Adsorption mechanism of transition metal ions by aniline 20 grafted silica gel

Figure 21 IR Spectra of

(a) IR Spectrum of activated silica gel (Si02) 39

(b) IR spectrum of SiOi-APTMS 40

(c) IR spectrum of SiOa-APTMS-THSA 41

Scheme 21 The synthesis route of formation of Si02-APTMS-THSA 42

Figure 22 TGA and DTA Curves of Modified silica gel (Si02- 43

APTMS-THSA)

Figure 23 SEM image of 45

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 210

(a) activated Silica gel (SiOa)

(b) Si02-APTMS

(c) Si02-APTMS-THSA

(d) Si02-APTMS-RHSA loaded with Pb(Il) Cu(II) and

Cr(III)

EDX spectrum of

(a) Si02-APTMS-THSA

(b) Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III

Effect of pH on adsorption of Pb(II)Cu(II) and Cr(IIl)

Effect of contact time on adsorption of Pb(II)Cu(Il) and

Cr(III)

Effect of initial metal ion concentration on the adsorption of Pb(II)Cu(II) and Cr(III)

Effect of temperature on the adsorption of Pb(II) Cu(Il) and

Cr(III)

Langmuir isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

Freundlich isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

46

47

49

50

51

53

55

56

57

60

61

62

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) andCr(III) 64

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) 67

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III) 69

IV

ABSTRACT

The dissertation entitled Chemically modified adsorbent for extraction of selected

heavy metal ions is comprised of two chapters

The first chapter describes a general introduction of the subject matter The very

relevant matters include

bull A brief discussion of ion-exchange resin and silica gel

bull Advantages of inorganic adsorbents over polymeric resin

bull Brief discussion of modification of silica gel surface through impregnation of

organic functional groups

bull Discussion of surface modification through covalent grafting which involves

(i) Immobilization of silane reagents

(ii) Sol-gel rout of surface modification

(iii) Other routes of surface modification

bull Application of chemically modified silica gel in extraction of heavy metal ions

from wastewater

bull A list of references taken from the worlds leading scientific Journals in the

field

The last chapter deals with the synthesis of thiosalicylic acid functional ized

silica The modified silica gel was characterized by FTIR TGA-DTA and

SEM with EDX The aim of this study was to investigated the potential of the

modified silica gel as selective adsorbent for Pb(II) Cu(II) and Cr(IlI) The

adsorption of Pb(II) Cu(II) and Cr(III) on SiOs-APTMS-THSA was studied as

V

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

2 4 NOV 2014 DS4382

(Dr Lutfidtah (Associate Professor)

DEPARTMENT OF CHEMISTRY

ALIGARH MUSLIM LfMVERSITV ALICARH-202002 (liP) INDIA Tel +91-571-2703515 (Office) E-mail lutfullah786^gmailconi

Dated

Certifitate

This is to certify that the work embodied in this dissertation entitled

Chemically modified adsorbent for extraction of selected heavy metal

ions is original carried out by Mr Mohd Nasir under my supervision and

is suitable for submission for the award of the degree of Master of

philosophy in chemistry of this university

CANDIDATES DECLARATION

Mohd Nasir Department of Chemistry certified that the work embodied

in this MPhil dissertation is my own bonafide work carried out by me

under the supervision of Dr Lutfullah at Aligarh Muslim University

Aligarh The matter embodied in this MPhil dissertation and cited as my

own work

I declare that I have faithfully acknowledge given credit to and referred

to the research works wherever their works have been cited in the text

and the body of the dissertation I further certified that I have not wilfully

lifted up some others work para text data results etc Reported in the

journals books magazines reports dissertations thesis etc or

available at web-sites and included them in this MPhil dissertation and

cited as my own work

Date Jgti ly (Signature of the candidate)

(MOHD NASIR)

ACKNOWLEDGMENTS

In the name of ALLAH the most beneficial and roercifuF

First and foremost I bring all the praise and commendation to the ALLAH SUBHAN-

0-TALA for providing me with strength and endurance to accomplish my research

work

It will be hard to find the words to thank my supervisor Dr Lutfullah for his

excellent guidance constant support and trust throughout the course of my research

work

Research is a kind of endeavour which demands ones intellectual and emotional

involvement along with the cooperation of ones mentor and teachers In this respect 1

am deeply indebted to Prof Nafisur Rahman for his inspiration and guidance with

his profound and perceptive scientific Ideas and experience which helped me at every

step Moreover his meticulous reading and corrections led to the completion of my

dissertation 1 conceder myself very fortunate to have the opportunity of working with

him 1 am really impressed by his quality to help others without any gain

I am thankfiil to the Chairman Department of Chemistry Aligarh Muslim University

for providing the research facilities 1 am also gratefiil to Aligarh Muslim University

for providing financial assistance (Non NET Fellowship UGC) to carry out this work

I would like to thank UGC (DRS-1) DST (FIST and PURSE) for providing partial

support to complete this dissertation

1 would like to acknowledge my sincere thanks to my seniors and colleagues Dr Mohd

Kasif Uzma Haseen Mohammad Fazeel Khan Sumaiya Khan and Shahroora

Sameen for all time cooperation in my research work

My deep sense of gratitude for the guiding hand of my father Haji Naseem Ahmad

and the humble and loving care of my mother Mrs Zareena Naseem for their true

affection and love Really without them I can hardly imagine myself to be where 1 am

today I cannot forget my uncle Mr Javad Akhter for his suggestion encouragement

help and support during my research work I am also thankful to my beloved brother

Hafiz Mohd Rashid and Arslan Khan sisters Shaneela Jamsheeda and Shafeequa and

my relatives for their constant encouragement and support during my study and my

good and bad times

I would like to express my gratitude to my wife Mrs Khursheeda Nasir and son

Mohammad Arham Words fail me to express my appreciation of my wife whose

dedication love and persistent confidence in me have taken the load oflF my shoulder It was

her support and encouragement which made this dissertation possible

I have deep core in my heart for my hostel mates and friends particularly for their

supports and suggestions in my bad and good days I would like to acknowledge Dr

Mohd Asif Dr Mohd Shahid Dr Shenwaz Abbas Sadat Suhail And Faheem

Ahmad I am highly thankful to all of them for the encouragement and support

Mohd Nasir

L

CONTENTS

List of Tables

List of Figures I ^

ABSTRACT ^-^l

CHAPTER 1 General Introduction 01-20

References 21-33

CHAPTER 2 Chemically modified silica gel with thiosalicylic 34-71 acid for removal of Pb(II) Cu(II) and Cr(III)

References 72-74

LIST OF TABLES

Table 11 Modified silica gel with various functional groups for 13

separationor preconcentration of metal ions

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption 58

of Pb(II) Cu(II) and Cr(III) onto modified silica gel (Si02-

APTMS-THSA)

Table 22 Kinetic parameters for adsorption of Pb(II) Cu(II) and Cr(lll) 65

onto modified silica gel (SiOi-APTMS-THSA)

Table 23 Thermodynamic parameters for the adsorption of Pb(II) Cu(II) 70

and Cr(III) onto modified silica gel (SiOi-APTMS-THSA)

LIST OF FIGURES

Scheme 11 Preparation of 3-aniline-propyltrimethoxysilane 7

intermediate

Scheme 12 Synthesisof aniline grafted silica adsorbent 7

Scheme 13 Modification of silica surface by coupling of terminal olefin 9

presence of metal catalyst

Scheme 14 DPTH-gel formation 10

Scheme 15 TS-gel formation 11

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15 18

Scheme 17 Adsorption mechanism of Pb (II) on 19

(a) TLSG

(b) FLSG

(c) PLSG

Scheme 18 Adsorption mechanism of transition metal ions by aniline 20 grafted silica gel

Figure 21 IR Spectra of

(a) IR Spectrum of activated silica gel (Si02) 39

(b) IR spectrum of SiOi-APTMS 40

(c) IR spectrum of SiOa-APTMS-THSA 41

Scheme 21 The synthesis route of formation of Si02-APTMS-THSA 42

Figure 22 TGA and DTA Curves of Modified silica gel (Si02- 43

APTMS-THSA)

Figure 23 SEM image of 45

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 210

(a) activated Silica gel (SiOa)

(b) Si02-APTMS

(c) Si02-APTMS-THSA

(d) Si02-APTMS-RHSA loaded with Pb(Il) Cu(II) and

Cr(III)

EDX spectrum of

(a) Si02-APTMS-THSA

(b) Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III

Effect of pH on adsorption of Pb(II)Cu(II) and Cr(IIl)

Effect of contact time on adsorption of Pb(II)Cu(Il) and

Cr(III)

Effect of initial metal ion concentration on the adsorption of Pb(II)Cu(II) and Cr(III)

Effect of temperature on the adsorption of Pb(II) Cu(Il) and

Cr(III)

Langmuir isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

Freundlich isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

46

47

49

50

51

53

55

56

57

60

61

62

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) andCr(III) 64

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) 67

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III) 69

IV

ABSTRACT

The dissertation entitled Chemically modified adsorbent for extraction of selected

heavy metal ions is comprised of two chapters

The first chapter describes a general introduction of the subject matter The very

relevant matters include

bull A brief discussion of ion-exchange resin and silica gel

bull Advantages of inorganic adsorbents over polymeric resin

bull Brief discussion of modification of silica gel surface through impregnation of

organic functional groups

bull Discussion of surface modification through covalent grafting which involves

(i) Immobilization of silane reagents

(ii) Sol-gel rout of surface modification

(iii) Other routes of surface modification

bull Application of chemically modified silica gel in extraction of heavy metal ions

from wastewater

bull A list of references taken from the worlds leading scientific Journals in the

field

The last chapter deals with the synthesis of thiosalicylic acid functional ized

silica The modified silica gel was characterized by FTIR TGA-DTA and

SEM with EDX The aim of this study was to investigated the potential of the

modified silica gel as selective adsorbent for Pb(II) Cu(II) and Cr(IlI) The

adsorption of Pb(II) Cu(II) and Cr(III) on SiOs-APTMS-THSA was studied as

V

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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(SPIMP) and its application for solid phase extraction and preconcentration of

Fe (III) Pb (II) Cu (II) Ni (II) Co (II) and Zn (II) Ions Indian J Sci

Technol 5(2012)1893-1900

[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

benzylidene)amino]phenylethanone Synthesis characterization and

application as an efficient and reusable solid phase extractant for selective

removal of Zn(II) from mycorrhizal treated fly-ash samples JEnviron Sci25

(2013) 1252-1261

[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

Cu(lI)-Removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[84] E Akyuz M Imamoglu and H Altundag Selective determination of Cr(Vl)

by FA AS after solid phase extraction on bis(3-aminopropyl)amine- bonded

silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

(Dr Lutfidtah (Associate Professor)

DEPARTMENT OF CHEMISTRY

ALIGARH MUSLIM LfMVERSITV ALICARH-202002 (liP) INDIA Tel +91-571-2703515 (Office) E-mail lutfullah786^gmailconi

Dated

Certifitate

This is to certify that the work embodied in this dissertation entitled

Chemically modified adsorbent for extraction of selected heavy metal

ions is original carried out by Mr Mohd Nasir under my supervision and

is suitable for submission for the award of the degree of Master of

philosophy in chemistry of this university

CANDIDATES DECLARATION

Mohd Nasir Department of Chemistry certified that the work embodied

in this MPhil dissertation is my own bonafide work carried out by me

under the supervision of Dr Lutfullah at Aligarh Muslim University

Aligarh The matter embodied in this MPhil dissertation and cited as my

own work

I declare that I have faithfully acknowledge given credit to and referred

to the research works wherever their works have been cited in the text

and the body of the dissertation I further certified that I have not wilfully

lifted up some others work para text data results etc Reported in the

journals books magazines reports dissertations thesis etc or

available at web-sites and included them in this MPhil dissertation and

cited as my own work

Date Jgti ly (Signature of the candidate)

(MOHD NASIR)

ACKNOWLEDGMENTS

In the name of ALLAH the most beneficial and roercifuF

First and foremost I bring all the praise and commendation to the ALLAH SUBHAN-

0-TALA for providing me with strength and endurance to accomplish my research

work

It will be hard to find the words to thank my supervisor Dr Lutfullah for his

excellent guidance constant support and trust throughout the course of my research

work

Research is a kind of endeavour which demands ones intellectual and emotional

involvement along with the cooperation of ones mentor and teachers In this respect 1

am deeply indebted to Prof Nafisur Rahman for his inspiration and guidance with

his profound and perceptive scientific Ideas and experience which helped me at every

step Moreover his meticulous reading and corrections led to the completion of my

dissertation 1 conceder myself very fortunate to have the opportunity of working with

him 1 am really impressed by his quality to help others without any gain

I am thankfiil to the Chairman Department of Chemistry Aligarh Muslim University

for providing the research facilities 1 am also gratefiil to Aligarh Muslim University

for providing financial assistance (Non NET Fellowship UGC) to carry out this work

I would like to thank UGC (DRS-1) DST (FIST and PURSE) for providing partial

support to complete this dissertation

1 would like to acknowledge my sincere thanks to my seniors and colleagues Dr Mohd

Kasif Uzma Haseen Mohammad Fazeel Khan Sumaiya Khan and Shahroora

Sameen for all time cooperation in my research work

My deep sense of gratitude for the guiding hand of my father Haji Naseem Ahmad

and the humble and loving care of my mother Mrs Zareena Naseem for their true

affection and love Really without them I can hardly imagine myself to be where 1 am

today I cannot forget my uncle Mr Javad Akhter for his suggestion encouragement

help and support during my research work I am also thankful to my beloved brother

Hafiz Mohd Rashid and Arslan Khan sisters Shaneela Jamsheeda and Shafeequa and

my relatives for their constant encouragement and support during my study and my

good and bad times

I would like to express my gratitude to my wife Mrs Khursheeda Nasir and son

Mohammad Arham Words fail me to express my appreciation of my wife whose

dedication love and persistent confidence in me have taken the load oflF my shoulder It was

her support and encouragement which made this dissertation possible

I have deep core in my heart for my hostel mates and friends particularly for their

supports and suggestions in my bad and good days I would like to acknowledge Dr

Mohd Asif Dr Mohd Shahid Dr Shenwaz Abbas Sadat Suhail And Faheem

Ahmad I am highly thankful to all of them for the encouragement and support

Mohd Nasir

L

CONTENTS

List of Tables

List of Figures I ^

ABSTRACT ^-^l

CHAPTER 1 General Introduction 01-20

References 21-33

CHAPTER 2 Chemically modified silica gel with thiosalicylic 34-71 acid for removal of Pb(II) Cu(II) and Cr(III)

References 72-74

LIST OF TABLES

Table 11 Modified silica gel with various functional groups for 13

separationor preconcentration of metal ions

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption 58

of Pb(II) Cu(II) and Cr(III) onto modified silica gel (Si02-

APTMS-THSA)

Table 22 Kinetic parameters for adsorption of Pb(II) Cu(II) and Cr(lll) 65

onto modified silica gel (SiOi-APTMS-THSA)

Table 23 Thermodynamic parameters for the adsorption of Pb(II) Cu(II) 70

and Cr(III) onto modified silica gel (SiOi-APTMS-THSA)

LIST OF FIGURES

Scheme 11 Preparation of 3-aniline-propyltrimethoxysilane 7

intermediate

Scheme 12 Synthesisof aniline grafted silica adsorbent 7

Scheme 13 Modification of silica surface by coupling of terminal olefin 9

presence of metal catalyst

Scheme 14 DPTH-gel formation 10

Scheme 15 TS-gel formation 11

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15 18

Scheme 17 Adsorption mechanism of Pb (II) on 19

(a) TLSG

(b) FLSG

(c) PLSG

Scheme 18 Adsorption mechanism of transition metal ions by aniline 20 grafted silica gel

Figure 21 IR Spectra of

(a) IR Spectrum of activated silica gel (Si02) 39

(b) IR spectrum of SiOi-APTMS 40

(c) IR spectrum of SiOa-APTMS-THSA 41

Scheme 21 The synthesis route of formation of Si02-APTMS-THSA 42

Figure 22 TGA and DTA Curves of Modified silica gel (Si02- 43

APTMS-THSA)

Figure 23 SEM image of 45

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 210

(a) activated Silica gel (SiOa)

(b) Si02-APTMS

(c) Si02-APTMS-THSA

(d) Si02-APTMS-RHSA loaded with Pb(Il) Cu(II) and

Cr(III)

EDX spectrum of

(a) Si02-APTMS-THSA

(b) Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III

Effect of pH on adsorption of Pb(II)Cu(II) and Cr(IIl)

Effect of contact time on adsorption of Pb(II)Cu(Il) and

Cr(III)

Effect of initial metal ion concentration on the adsorption of Pb(II)Cu(II) and Cr(III)

Effect of temperature on the adsorption of Pb(II) Cu(Il) and

Cr(III)

Langmuir isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

Freundlich isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

46

47

49

50

51

53

55

56

57

60

61

62

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) andCr(III) 64

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) 67

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III) 69

IV

ABSTRACT

The dissertation entitled Chemically modified adsorbent for extraction of selected

heavy metal ions is comprised of two chapters

The first chapter describes a general introduction of the subject matter The very

relevant matters include

bull A brief discussion of ion-exchange resin and silica gel

bull Advantages of inorganic adsorbents over polymeric resin

bull Brief discussion of modification of silica gel surface through impregnation of

organic functional groups

bull Discussion of surface modification through covalent grafting which involves

(i) Immobilization of silane reagents

(ii) Sol-gel rout of surface modification

(iii) Other routes of surface modification

bull Application of chemically modified silica gel in extraction of heavy metal ions

from wastewater

bull A list of references taken from the worlds leading scientific Journals in the

field

The last chapter deals with the synthesis of thiosalicylic acid functional ized

silica The modified silica gel was characterized by FTIR TGA-DTA and

SEM with EDX The aim of this study was to investigated the potential of the

modified silica gel as selective adsorbent for Pb(II) Cu(II) and Cr(IlI) The

adsorption of Pb(II) Cu(II) and Cr(III) on SiOs-APTMS-THSA was studied as

V

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[63] C Ekinci and U Koklu Sorption and preconcentration of vanadium silver

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[64] E G Vieiraa I V Soares N L Dias Filhoa NC da Silvaa E F Garciaa

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[67] OA Zaporozhets LS Ivanko and VV Sukhan Interaction between

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[68] M Ghaedi M Montazerozohori A Hekmati and M Roosta Solid phase

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[69] XZ Wu P Liu QS Pu QY Sun and ZX Su Preparation of dendrimer-

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[70] O H S AL- Obaidi and M N Al-Jibouri Preparation characterization

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[71] HM Marwani and AE Alsafrani New solid phase extractor based on ionic

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[72] Q Wang W Gao Y Liu J Yuan Z Xu Y Li and M Schroder

Simultaneous adsorption of Cu(II) and S04 ions by a novel silica gel

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(2014) in press ArticlepiiS 1385894714003957

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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in metal ion extraction Sep Sci and Technol 48 (2013) 1349-1355

[74] F A HarrazOE Abdel-Salam AA Mostafa RM Mohamed and M

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modified sol-gel method for cyanide degradation and heavy metals removal J

of Alloys Compd 551 (2013) 1-7

[75] Y Niu R Qu Ci Sun C Wang H Chen C Ji Y Zhang X Shao and F

Bu Adsorption of Pb(II) from aqueous solution by silica-gel supported

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[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

immobilized silica gel to flow injection on-line microcolumn preconcentration

and separation coupled with flame atomic absorption spectrometry for

interference-free determination of trace silver gold palladium and platinum in

geological and metallurgical samples J Anal Atom Spectrom 17 (2002)

125-130

[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

and mechanism of transition metal ions on silica gels functionalized with

hydroxyl- or amino-terminated polyamines Chem Eng J 221 (2013) 264-

274

[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

reduction-sorption on bi-functional silica adsorbents J Hazard Mater 250-

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[79] OA Zaporozhets LS Ivanko IV Marchenko and VV Sukhan

Determination of zirconium using morin immobilized on silica gel J Anal

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

by y-radiation synthesized silica-graft-vinyl imidazole adsorbent J Hazard

Mater 244-245 (2013) 94-101

29

[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

functionalization of silica gel with 2-((3-silylpropylimino) methyl) phenol

(SPIMP) and its application for solid phase extraction and preconcentration of

Fe (III) Pb (II) Cu (II) Ni (II) Co (II) and Zn (II) Ions Indian J Sci

Technol 5(2012)1893-1900

[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

benzylidene)amino]phenylethanone Synthesis characterization and

application as an efficient and reusable solid phase extractant for selective

removal of Zn(II) from mycorrhizal treated fly-ash samples JEnviron Sci25

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[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

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(2013)108-116

[84] E Akyuz M Imamoglu and H Altundag Selective determination of Cr(Vl)

by FA AS after solid phase extraction on bis(3-aminopropyl)amine- bonded

silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

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determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

CANDIDATES DECLARATION

Mohd Nasir Department of Chemistry certified that the work embodied

in this MPhil dissertation is my own bonafide work carried out by me

under the supervision of Dr Lutfullah at Aligarh Muslim University

Aligarh The matter embodied in this MPhil dissertation and cited as my

own work

I declare that I have faithfully acknowledge given credit to and referred

to the research works wherever their works have been cited in the text

and the body of the dissertation I further certified that I have not wilfully

lifted up some others work para text data results etc Reported in the

journals books magazines reports dissertations thesis etc or

available at web-sites and included them in this MPhil dissertation and

cited as my own work

Date Jgti ly (Signature of the candidate)

(MOHD NASIR)

ACKNOWLEDGMENTS

In the name of ALLAH the most beneficial and roercifuF

First and foremost I bring all the praise and commendation to the ALLAH SUBHAN-

0-TALA for providing me with strength and endurance to accomplish my research

work

It will be hard to find the words to thank my supervisor Dr Lutfullah for his

excellent guidance constant support and trust throughout the course of my research

work

Research is a kind of endeavour which demands ones intellectual and emotional

involvement along with the cooperation of ones mentor and teachers In this respect 1

am deeply indebted to Prof Nafisur Rahman for his inspiration and guidance with

his profound and perceptive scientific Ideas and experience which helped me at every

step Moreover his meticulous reading and corrections led to the completion of my

dissertation 1 conceder myself very fortunate to have the opportunity of working with

him 1 am really impressed by his quality to help others without any gain

I am thankfiil to the Chairman Department of Chemistry Aligarh Muslim University

for providing the research facilities 1 am also gratefiil to Aligarh Muslim University

for providing financial assistance (Non NET Fellowship UGC) to carry out this work

I would like to thank UGC (DRS-1) DST (FIST and PURSE) for providing partial

support to complete this dissertation

1 would like to acknowledge my sincere thanks to my seniors and colleagues Dr Mohd

Kasif Uzma Haseen Mohammad Fazeel Khan Sumaiya Khan and Shahroora

Sameen for all time cooperation in my research work

My deep sense of gratitude for the guiding hand of my father Haji Naseem Ahmad

and the humble and loving care of my mother Mrs Zareena Naseem for their true

affection and love Really without them I can hardly imagine myself to be where 1 am

today I cannot forget my uncle Mr Javad Akhter for his suggestion encouragement

help and support during my research work I am also thankful to my beloved brother

Hafiz Mohd Rashid and Arslan Khan sisters Shaneela Jamsheeda and Shafeequa and

my relatives for their constant encouragement and support during my study and my

good and bad times

I would like to express my gratitude to my wife Mrs Khursheeda Nasir and son

Mohammad Arham Words fail me to express my appreciation of my wife whose

dedication love and persistent confidence in me have taken the load oflF my shoulder It was

her support and encouragement which made this dissertation possible

I have deep core in my heart for my hostel mates and friends particularly for their

supports and suggestions in my bad and good days I would like to acknowledge Dr

Mohd Asif Dr Mohd Shahid Dr Shenwaz Abbas Sadat Suhail And Faheem

Ahmad I am highly thankful to all of them for the encouragement and support

Mohd Nasir

L

CONTENTS

List of Tables

List of Figures I ^

ABSTRACT ^-^l

CHAPTER 1 General Introduction 01-20

References 21-33

CHAPTER 2 Chemically modified silica gel with thiosalicylic 34-71 acid for removal of Pb(II) Cu(II) and Cr(III)

References 72-74

LIST OF TABLES

Table 11 Modified silica gel with various functional groups for 13

separationor preconcentration of metal ions

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption 58

of Pb(II) Cu(II) and Cr(III) onto modified silica gel (Si02-

APTMS-THSA)

Table 22 Kinetic parameters for adsorption of Pb(II) Cu(II) and Cr(lll) 65

onto modified silica gel (SiOi-APTMS-THSA)

Table 23 Thermodynamic parameters for the adsorption of Pb(II) Cu(II) 70

and Cr(III) onto modified silica gel (SiOi-APTMS-THSA)

LIST OF FIGURES

Scheme 11 Preparation of 3-aniline-propyltrimethoxysilane 7

intermediate

Scheme 12 Synthesisof aniline grafted silica adsorbent 7

Scheme 13 Modification of silica surface by coupling of terminal olefin 9

presence of metal catalyst

Scheme 14 DPTH-gel formation 10

Scheme 15 TS-gel formation 11

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15 18

Scheme 17 Adsorption mechanism of Pb (II) on 19

(a) TLSG

(b) FLSG

(c) PLSG

Scheme 18 Adsorption mechanism of transition metal ions by aniline 20 grafted silica gel

Figure 21 IR Spectra of

(a) IR Spectrum of activated silica gel (Si02) 39

(b) IR spectrum of SiOi-APTMS 40

(c) IR spectrum of SiOa-APTMS-THSA 41

Scheme 21 The synthesis route of formation of Si02-APTMS-THSA 42

Figure 22 TGA and DTA Curves of Modified silica gel (Si02- 43

APTMS-THSA)

Figure 23 SEM image of 45

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 210

(a) activated Silica gel (SiOa)

(b) Si02-APTMS

(c) Si02-APTMS-THSA

(d) Si02-APTMS-RHSA loaded with Pb(Il) Cu(II) and

Cr(III)

EDX spectrum of

(a) Si02-APTMS-THSA

(b) Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III

Effect of pH on adsorption of Pb(II)Cu(II) and Cr(IIl)

Effect of contact time on adsorption of Pb(II)Cu(Il) and

Cr(III)

Effect of initial metal ion concentration on the adsorption of Pb(II)Cu(II) and Cr(III)

Effect of temperature on the adsorption of Pb(II) Cu(Il) and

Cr(III)

Langmuir isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

Freundlich isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

46

47

49

50

51

53

55

56

57

60

61

62

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) andCr(III) 64

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) 67

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III) 69

IV

ABSTRACT

The dissertation entitled Chemically modified adsorbent for extraction of selected

heavy metal ions is comprised of two chapters

The first chapter describes a general introduction of the subject matter The very

relevant matters include

bull A brief discussion of ion-exchange resin and silica gel

bull Advantages of inorganic adsorbents over polymeric resin

bull Brief discussion of modification of silica gel surface through impregnation of

organic functional groups

bull Discussion of surface modification through covalent grafting which involves

(i) Immobilization of silane reagents

(ii) Sol-gel rout of surface modification

(iii) Other routes of surface modification

bull Application of chemically modified silica gel in extraction of heavy metal ions

from wastewater

bull A list of references taken from the worlds leading scientific Journals in the

field

The last chapter deals with the synthesis of thiosalicylic acid functional ized

silica The modified silica gel was characterized by FTIR TGA-DTA and

SEM with EDX The aim of this study was to investigated the potential of the

modified silica gel as selective adsorbent for Pb(II) Cu(II) and Cr(IlI) The

adsorption of Pb(II) Cu(II) and Cr(III) on SiOs-APTMS-THSA was studied as

V

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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24

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[47] A Goswami and AK Singh 18-Dihydroxyanthraquinone anchored on silica

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25

[49] MM Osman SA Kholeif NAA Al-Maaty and ME Mahmoud Metal

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[52] VN Losev EV Elsufev YV Alennikova and AK Trofimchuk Low-

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[54] F Sahina MVolkana A G Howardb and O Y Ataman Selective

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[55] ME Mahmoud AA Soayed and OF Hafez Selective solid phase extraction

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26

[57] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

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[58] D Caldarola D P Mitevb L Marline EP Nesterenkod B Paullb B

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[59] SM Zhang QS Pu P Liu QY Sun and ZX Su Synthesis of

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preconcentration and separation Anal Chim Acta 452 (2002) 223-230

[60] S Radii N Basbasl S Tighadouini and M Bacquet New polysiloxane

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graphite furnace atomic absorption spectrometry Talanta 59 (2003) 201-205

[62] N Tokman S Akman M Ozcan and U Koklu Preconcentration and

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[63] C Ekinci and U Koklu Sorption and preconcentration of vanadium silver

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[64] E G Vieiraa I V Soares N L Dias Filhoa NC da Silvaa E F Garciaa

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[67] OA Zaporozhets LS Ivanko and VV Sukhan Interaction between

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[68] M Ghaedi M Montazerozohori A Hekmati and M Roosta Solid phase

extraction of heavy metals on chemically modified silica-gel with 2-(3-

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[69] XZ Wu P Liu QS Pu QY Sun and ZX Su Preparation of dendrimer-

like polyamidoamine immobilized silica gel and its application to online

preconcentration and separation palladium prior to FAAS determination

Talanta 62(2004)918-923

[70] O H S AL- Obaidi and M N Al-Jibouri Preparation characterization

theoretical treatment and adsorption on surfacesN5 acycliclmmobilizes on

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[71] HM Marwani and AE Alsafrani New solid phase extractor based on ionic

liquid functionalized silica gel surface for selective separation and

determination of lanthanum JAnal Sci and Technol 4 (2013) 4-13

[72] Q Wang W Gao Y Liu J Yuan Z Xu Y Li and M Schroder

Simultaneous adsorption of Cu(II) and S04 ions by a novel silica gel

functionalized with a ditopic zwitterionic Schiff base ligand Chem Eng J

(2014) in press ArticlepiiS 1385894714003957

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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in metal ion extraction Sep Sci and Technol 48 (2013) 1349-1355

[74] F A HarrazOE Abdel-Salam AA Mostafa RM Mohamed and M

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modified sol-gel method for cyanide degradation and heavy metals removal J

of Alloys Compd 551 (2013) 1-7

[75] Y Niu R Qu Ci Sun C Wang H Chen C Ji Y Zhang X Shao and F

Bu Adsorption of Pb(II) from aqueous solution by silica-gel supported

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[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

immobilized silica gel to flow injection on-line microcolumn preconcentration

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interference-free determination of trace silver gold palladium and platinum in

geological and metallurgical samples J Anal Atom Spectrom 17 (2002)

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[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

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[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

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[79] OA Zaporozhets LS Ivanko IV Marchenko and VV Sukhan

Determination of zirconium using morin immobilized on silica gel J Anal

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

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Mater 244-245 (2013) 94-101

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[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

functionalization of silica gel with 2-((3-silylpropylimino) methyl) phenol

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Fe (III) Pb (II) Cu (II) Ni (II) Co (II) and Zn (II) Ions Indian J Sci

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[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

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[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

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[84] E Akyuz M Imamoglu and H Altundag Selective determination of Cr(Vl)

by FA AS after solid phase extraction on bis(3-aminopropyl)amine- bonded

silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

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Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

ACKNOWLEDGMENTS

In the name of ALLAH the most beneficial and roercifuF

First and foremost I bring all the praise and commendation to the ALLAH SUBHAN-

0-TALA for providing me with strength and endurance to accomplish my research

work

It will be hard to find the words to thank my supervisor Dr Lutfullah for his

excellent guidance constant support and trust throughout the course of my research

work

Research is a kind of endeavour which demands ones intellectual and emotional

involvement along with the cooperation of ones mentor and teachers In this respect 1

am deeply indebted to Prof Nafisur Rahman for his inspiration and guidance with

his profound and perceptive scientific Ideas and experience which helped me at every

step Moreover his meticulous reading and corrections led to the completion of my

dissertation 1 conceder myself very fortunate to have the opportunity of working with

him 1 am really impressed by his quality to help others without any gain

I am thankfiil to the Chairman Department of Chemistry Aligarh Muslim University

for providing the research facilities 1 am also gratefiil to Aligarh Muslim University

for providing financial assistance (Non NET Fellowship UGC) to carry out this work

I would like to thank UGC (DRS-1) DST (FIST and PURSE) for providing partial

support to complete this dissertation

1 would like to acknowledge my sincere thanks to my seniors and colleagues Dr Mohd

Kasif Uzma Haseen Mohammad Fazeel Khan Sumaiya Khan and Shahroora

Sameen for all time cooperation in my research work

My deep sense of gratitude for the guiding hand of my father Haji Naseem Ahmad

and the humble and loving care of my mother Mrs Zareena Naseem for their true

affection and love Really without them I can hardly imagine myself to be where 1 am

today I cannot forget my uncle Mr Javad Akhter for his suggestion encouragement

help and support during my research work I am also thankful to my beloved brother

Hafiz Mohd Rashid and Arslan Khan sisters Shaneela Jamsheeda and Shafeequa and

my relatives for their constant encouragement and support during my study and my

good and bad times

I would like to express my gratitude to my wife Mrs Khursheeda Nasir and son

Mohammad Arham Words fail me to express my appreciation of my wife whose

dedication love and persistent confidence in me have taken the load oflF my shoulder It was

her support and encouragement which made this dissertation possible

I have deep core in my heart for my hostel mates and friends particularly for their

supports and suggestions in my bad and good days I would like to acknowledge Dr

Mohd Asif Dr Mohd Shahid Dr Shenwaz Abbas Sadat Suhail And Faheem

Ahmad I am highly thankful to all of them for the encouragement and support

Mohd Nasir

L

CONTENTS

List of Tables

List of Figures I ^

ABSTRACT ^-^l

CHAPTER 1 General Introduction 01-20

References 21-33

CHAPTER 2 Chemically modified silica gel with thiosalicylic 34-71 acid for removal of Pb(II) Cu(II) and Cr(III)

References 72-74

LIST OF TABLES

Table 11 Modified silica gel with various functional groups for 13

separationor preconcentration of metal ions

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption 58

of Pb(II) Cu(II) and Cr(III) onto modified silica gel (Si02-

APTMS-THSA)

Table 22 Kinetic parameters for adsorption of Pb(II) Cu(II) and Cr(lll) 65

onto modified silica gel (SiOi-APTMS-THSA)

Table 23 Thermodynamic parameters for the adsorption of Pb(II) Cu(II) 70

and Cr(III) onto modified silica gel (SiOi-APTMS-THSA)

LIST OF FIGURES

Scheme 11 Preparation of 3-aniline-propyltrimethoxysilane 7

intermediate

Scheme 12 Synthesisof aniline grafted silica adsorbent 7

Scheme 13 Modification of silica surface by coupling of terminal olefin 9

presence of metal catalyst

Scheme 14 DPTH-gel formation 10

Scheme 15 TS-gel formation 11

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15 18

Scheme 17 Adsorption mechanism of Pb (II) on 19

(a) TLSG

(b) FLSG

(c) PLSG

Scheme 18 Adsorption mechanism of transition metal ions by aniline 20 grafted silica gel

Figure 21 IR Spectra of

(a) IR Spectrum of activated silica gel (Si02) 39

(b) IR spectrum of SiOi-APTMS 40

(c) IR spectrum of SiOa-APTMS-THSA 41

Scheme 21 The synthesis route of formation of Si02-APTMS-THSA 42

Figure 22 TGA and DTA Curves of Modified silica gel (Si02- 43

APTMS-THSA)

Figure 23 SEM image of 45

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 210

(a) activated Silica gel (SiOa)

(b) Si02-APTMS

(c) Si02-APTMS-THSA

(d) Si02-APTMS-RHSA loaded with Pb(Il) Cu(II) and

Cr(III)

EDX spectrum of

(a) Si02-APTMS-THSA

(b) Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III

Effect of pH on adsorption of Pb(II)Cu(II) and Cr(IIl)

Effect of contact time on adsorption of Pb(II)Cu(Il) and

Cr(III)

Effect of initial metal ion concentration on the adsorption of Pb(II)Cu(II) and Cr(III)

Effect of temperature on the adsorption of Pb(II) Cu(Il) and

Cr(III)

Langmuir isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

Freundlich isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

46

47

49

50

51

53

55

56

57

60

61

62

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) andCr(III) 64

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) 67

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III) 69

IV

ABSTRACT

The dissertation entitled Chemically modified adsorbent for extraction of selected

heavy metal ions is comprised of two chapters

The first chapter describes a general introduction of the subject matter The very

relevant matters include

bull A brief discussion of ion-exchange resin and silica gel

bull Advantages of inorganic adsorbents over polymeric resin

bull Brief discussion of modification of silica gel surface through impregnation of

organic functional groups

bull Discussion of surface modification through covalent grafting which involves

(i) Immobilization of silane reagents

(ii) Sol-gel rout of surface modification

(iii) Other routes of surface modification

bull Application of chemically modified silica gel in extraction of heavy metal ions

from wastewater

bull A list of references taken from the worlds leading scientific Journals in the

field

The last chapter deals with the synthesis of thiosalicylic acid functional ized

silica The modified silica gel was characterized by FTIR TGA-DTA and

SEM with EDX The aim of this study was to investigated the potential of the

modified silica gel as selective adsorbent for Pb(II) Cu(II) and Cr(IlI) The

adsorption of Pb(II) Cu(II) and Cr(III) on SiOs-APTMS-THSA was studied as

V

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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22

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[68] M Ghaedi M Montazerozohori A Hekmati and M Roosta Solid phase

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[71] HM Marwani and AE Alsafrani New solid phase extractor based on ionic

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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[74] F A HarrazOE Abdel-Salam AA Mostafa RM Mohamed and M

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[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

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[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

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[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

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[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

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[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

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[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

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Water Air and Soil Pollution 223 (2012) 5391-5399

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[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

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[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

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128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

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preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

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gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

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[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

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from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

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Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

I would like to express my gratitude to my wife Mrs Khursheeda Nasir and son

Mohammad Arham Words fail me to express my appreciation of my wife whose

dedication love and persistent confidence in me have taken the load oflF my shoulder It was

her support and encouragement which made this dissertation possible

I have deep core in my heart for my hostel mates and friends particularly for their

supports and suggestions in my bad and good days I would like to acknowledge Dr

Mohd Asif Dr Mohd Shahid Dr Shenwaz Abbas Sadat Suhail And Faheem

Ahmad I am highly thankful to all of them for the encouragement and support

Mohd Nasir

L

CONTENTS

List of Tables

List of Figures I ^

ABSTRACT ^-^l

CHAPTER 1 General Introduction 01-20

References 21-33

CHAPTER 2 Chemically modified silica gel with thiosalicylic 34-71 acid for removal of Pb(II) Cu(II) and Cr(III)

References 72-74

LIST OF TABLES

Table 11 Modified silica gel with various functional groups for 13

separationor preconcentration of metal ions

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption 58

of Pb(II) Cu(II) and Cr(III) onto modified silica gel (Si02-

APTMS-THSA)

Table 22 Kinetic parameters for adsorption of Pb(II) Cu(II) and Cr(lll) 65

onto modified silica gel (SiOi-APTMS-THSA)

Table 23 Thermodynamic parameters for the adsorption of Pb(II) Cu(II) 70

and Cr(III) onto modified silica gel (SiOi-APTMS-THSA)

LIST OF FIGURES

Scheme 11 Preparation of 3-aniline-propyltrimethoxysilane 7

intermediate

Scheme 12 Synthesisof aniline grafted silica adsorbent 7

Scheme 13 Modification of silica surface by coupling of terminal olefin 9

presence of metal catalyst

Scheme 14 DPTH-gel formation 10

Scheme 15 TS-gel formation 11

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15 18

Scheme 17 Adsorption mechanism of Pb (II) on 19

(a) TLSG

(b) FLSG

(c) PLSG

Scheme 18 Adsorption mechanism of transition metal ions by aniline 20 grafted silica gel

Figure 21 IR Spectra of

(a) IR Spectrum of activated silica gel (Si02) 39

(b) IR spectrum of SiOi-APTMS 40

(c) IR spectrum of SiOa-APTMS-THSA 41

Scheme 21 The synthesis route of formation of Si02-APTMS-THSA 42

Figure 22 TGA and DTA Curves of Modified silica gel (Si02- 43

APTMS-THSA)

Figure 23 SEM image of 45

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 210

(a) activated Silica gel (SiOa)

(b) Si02-APTMS

(c) Si02-APTMS-THSA

(d) Si02-APTMS-RHSA loaded with Pb(Il) Cu(II) and

Cr(III)

EDX spectrum of

(a) Si02-APTMS-THSA

(b) Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III

Effect of pH on adsorption of Pb(II)Cu(II) and Cr(IIl)

Effect of contact time on adsorption of Pb(II)Cu(Il) and

Cr(III)

Effect of initial metal ion concentration on the adsorption of Pb(II)Cu(II) and Cr(III)

Effect of temperature on the adsorption of Pb(II) Cu(Il) and

Cr(III)

Langmuir isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

Freundlich isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

46

47

49

50

51

53

55

56

57

60

61

62

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) andCr(III) 64

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) 67

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III) 69

IV

ABSTRACT

The dissertation entitled Chemically modified adsorbent for extraction of selected

heavy metal ions is comprised of two chapters

The first chapter describes a general introduction of the subject matter The very

relevant matters include

bull A brief discussion of ion-exchange resin and silica gel

bull Advantages of inorganic adsorbents over polymeric resin

bull Brief discussion of modification of silica gel surface through impregnation of

organic functional groups

bull Discussion of surface modification through covalent grafting which involves

(i) Immobilization of silane reagents

(ii) Sol-gel rout of surface modification

(iii) Other routes of surface modification

bull Application of chemically modified silica gel in extraction of heavy metal ions

from wastewater

bull A list of references taken from the worlds leading scientific Journals in the

field

The last chapter deals with the synthesis of thiosalicylic acid functional ized

silica The modified silica gel was characterized by FTIR TGA-DTA and

SEM with EDX The aim of this study was to investigated the potential of the

modified silica gel as selective adsorbent for Pb(II) Cu(II) and Cr(IlI) The

adsorption of Pb(II) Cu(II) and Cr(III) on SiOs-APTMS-THSA was studied as

V

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

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[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

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[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

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Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

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32

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

CONTENTS

List of Tables

List of Figures I ^

ABSTRACT ^-^l

CHAPTER 1 General Introduction 01-20

References 21-33

CHAPTER 2 Chemically modified silica gel with thiosalicylic 34-71 acid for removal of Pb(II) Cu(II) and Cr(III)

References 72-74

LIST OF TABLES

Table 11 Modified silica gel with various functional groups for 13

separationor preconcentration of metal ions

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption 58

of Pb(II) Cu(II) and Cr(III) onto modified silica gel (Si02-

APTMS-THSA)

Table 22 Kinetic parameters for adsorption of Pb(II) Cu(II) and Cr(lll) 65

onto modified silica gel (SiOi-APTMS-THSA)

Table 23 Thermodynamic parameters for the adsorption of Pb(II) Cu(II) 70

and Cr(III) onto modified silica gel (SiOi-APTMS-THSA)

LIST OF FIGURES

Scheme 11 Preparation of 3-aniline-propyltrimethoxysilane 7

intermediate

Scheme 12 Synthesisof aniline grafted silica adsorbent 7

Scheme 13 Modification of silica surface by coupling of terminal olefin 9

presence of metal catalyst

Scheme 14 DPTH-gel formation 10

Scheme 15 TS-gel formation 11

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15 18

Scheme 17 Adsorption mechanism of Pb (II) on 19

(a) TLSG

(b) FLSG

(c) PLSG

Scheme 18 Adsorption mechanism of transition metal ions by aniline 20 grafted silica gel

Figure 21 IR Spectra of

(a) IR Spectrum of activated silica gel (Si02) 39

(b) IR spectrum of SiOi-APTMS 40

(c) IR spectrum of SiOa-APTMS-THSA 41

Scheme 21 The synthesis route of formation of Si02-APTMS-THSA 42

Figure 22 TGA and DTA Curves of Modified silica gel (Si02- 43

APTMS-THSA)

Figure 23 SEM image of 45

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 210

(a) activated Silica gel (SiOa)

(b) Si02-APTMS

(c) Si02-APTMS-THSA

(d) Si02-APTMS-RHSA loaded with Pb(Il) Cu(II) and

Cr(III)

EDX spectrum of

(a) Si02-APTMS-THSA

(b) Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III

Effect of pH on adsorption of Pb(II)Cu(II) and Cr(IIl)

Effect of contact time on adsorption of Pb(II)Cu(Il) and

Cr(III)

Effect of initial metal ion concentration on the adsorption of Pb(II)Cu(II) and Cr(III)

Effect of temperature on the adsorption of Pb(II) Cu(Il) and

Cr(III)

Langmuir isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

Freundlich isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

46

47

49

50

51

53

55

56

57

60

61

62

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) andCr(III) 64

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) 67

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III) 69

IV

ABSTRACT

The dissertation entitled Chemically modified adsorbent for extraction of selected

heavy metal ions is comprised of two chapters

The first chapter describes a general introduction of the subject matter The very

relevant matters include

bull A brief discussion of ion-exchange resin and silica gel

bull Advantages of inorganic adsorbents over polymeric resin

bull Brief discussion of modification of silica gel surface through impregnation of

organic functional groups

bull Discussion of surface modification through covalent grafting which involves

(i) Immobilization of silane reagents

(ii) Sol-gel rout of surface modification

(iii) Other routes of surface modification

bull Application of chemically modified silica gel in extraction of heavy metal ions

from wastewater

bull A list of references taken from the worlds leading scientific Journals in the

field

The last chapter deals with the synthesis of thiosalicylic acid functional ized

silica The modified silica gel was characterized by FTIR TGA-DTA and

SEM with EDX The aim of this study was to investigated the potential of the

modified silica gel as selective adsorbent for Pb(II) Cu(II) and Cr(IlI) The

adsorption of Pb(II) Cu(II) and Cr(III) on SiOs-APTMS-THSA was studied as

V

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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32

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

LIST OF TABLES

Table 11 Modified silica gel with various functional groups for 13

separationor preconcentration of metal ions

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption 58

of Pb(II) Cu(II) and Cr(III) onto modified silica gel (Si02-

APTMS-THSA)

Table 22 Kinetic parameters for adsorption of Pb(II) Cu(II) and Cr(lll) 65

onto modified silica gel (SiOi-APTMS-THSA)

Table 23 Thermodynamic parameters for the adsorption of Pb(II) Cu(II) 70

and Cr(III) onto modified silica gel (SiOi-APTMS-THSA)

LIST OF FIGURES

Scheme 11 Preparation of 3-aniline-propyltrimethoxysilane 7

intermediate

Scheme 12 Synthesisof aniline grafted silica adsorbent 7

Scheme 13 Modification of silica surface by coupling of terminal olefin 9

presence of metal catalyst

Scheme 14 DPTH-gel formation 10

Scheme 15 TS-gel formation 11

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15 18

Scheme 17 Adsorption mechanism of Pb (II) on 19

(a) TLSG

(b) FLSG

(c) PLSG

Scheme 18 Adsorption mechanism of transition metal ions by aniline 20 grafted silica gel

Figure 21 IR Spectra of

(a) IR Spectrum of activated silica gel (Si02) 39

(b) IR spectrum of SiOi-APTMS 40

(c) IR spectrum of SiOa-APTMS-THSA 41

Scheme 21 The synthesis route of formation of Si02-APTMS-THSA 42

Figure 22 TGA and DTA Curves of Modified silica gel (Si02- 43

APTMS-THSA)

Figure 23 SEM image of 45

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 210

(a) activated Silica gel (SiOa)

(b) Si02-APTMS

(c) Si02-APTMS-THSA

(d) Si02-APTMS-RHSA loaded with Pb(Il) Cu(II) and

Cr(III)

EDX spectrum of

(a) Si02-APTMS-THSA

(b) Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III

Effect of pH on adsorption of Pb(II)Cu(II) and Cr(IIl)

Effect of contact time on adsorption of Pb(II)Cu(Il) and

Cr(III)

Effect of initial metal ion concentration on the adsorption of Pb(II)Cu(II) and Cr(III)

Effect of temperature on the adsorption of Pb(II) Cu(Il) and

Cr(III)

Langmuir isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

Freundlich isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

46

47

49

50

51

53

55

56

57

60

61

62

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) andCr(III) 64

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) 67

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III) 69

IV

ABSTRACT

The dissertation entitled Chemically modified adsorbent for extraction of selected

heavy metal ions is comprised of two chapters

The first chapter describes a general introduction of the subject matter The very

relevant matters include

bull A brief discussion of ion-exchange resin and silica gel

bull Advantages of inorganic adsorbents over polymeric resin

bull Brief discussion of modification of silica gel surface through impregnation of

organic functional groups

bull Discussion of surface modification through covalent grafting which involves

(i) Immobilization of silane reagents

(ii) Sol-gel rout of surface modification

(iii) Other routes of surface modification

bull Application of chemically modified silica gel in extraction of heavy metal ions

from wastewater

bull A list of references taken from the worlds leading scientific Journals in the

field

The last chapter deals with the synthesis of thiosalicylic acid functional ized

silica The modified silica gel was characterized by FTIR TGA-DTA and

SEM with EDX The aim of this study was to investigated the potential of the

modified silica gel as selective adsorbent for Pb(II) Cu(II) and Cr(IlI) The

adsorption of Pb(II) Cu(II) and Cr(III) on SiOs-APTMS-THSA was studied as

V

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

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60(2003) 1003-1009

32

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press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

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[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

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65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

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[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

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[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

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[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

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doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

LIST OF FIGURES

Scheme 11 Preparation of 3-aniline-propyltrimethoxysilane 7

intermediate

Scheme 12 Synthesisof aniline grafted silica adsorbent 7

Scheme 13 Modification of silica surface by coupling of terminal olefin 9

presence of metal catalyst

Scheme 14 DPTH-gel formation 10

Scheme 15 TS-gel formation 11

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15 18

Scheme 17 Adsorption mechanism of Pb (II) on 19

(a) TLSG

(b) FLSG

(c) PLSG

Scheme 18 Adsorption mechanism of transition metal ions by aniline 20 grafted silica gel

Figure 21 IR Spectra of

(a) IR Spectrum of activated silica gel (Si02) 39

(b) IR spectrum of SiOi-APTMS 40

(c) IR spectrum of SiOa-APTMS-THSA 41

Scheme 21 The synthesis route of formation of Si02-APTMS-THSA 42

Figure 22 TGA and DTA Curves of Modified silica gel (Si02- 43

APTMS-THSA)

Figure 23 SEM image of 45

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 210

(a) activated Silica gel (SiOa)

(b) Si02-APTMS

(c) Si02-APTMS-THSA

(d) Si02-APTMS-RHSA loaded with Pb(Il) Cu(II) and

Cr(III)

EDX spectrum of

(a) Si02-APTMS-THSA

(b) Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III

Effect of pH on adsorption of Pb(II)Cu(II) and Cr(IIl)

Effect of contact time on adsorption of Pb(II)Cu(Il) and

Cr(III)

Effect of initial metal ion concentration on the adsorption of Pb(II)Cu(II) and Cr(III)

Effect of temperature on the adsorption of Pb(II) Cu(Il) and

Cr(III)

Langmuir isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

Freundlich isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

46

47

49

50

51

53

55

56

57

60

61

62

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) andCr(III) 64

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) 67

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III) 69

IV

ABSTRACT

The dissertation entitled Chemically modified adsorbent for extraction of selected

heavy metal ions is comprised of two chapters

The first chapter describes a general introduction of the subject matter The very

relevant matters include

bull A brief discussion of ion-exchange resin and silica gel

bull Advantages of inorganic adsorbents over polymeric resin

bull Brief discussion of modification of silica gel surface through impregnation of

organic functional groups

bull Discussion of surface modification through covalent grafting which involves

(i) Immobilization of silane reagents

(ii) Sol-gel rout of surface modification

(iii) Other routes of surface modification

bull Application of chemically modified silica gel in extraction of heavy metal ions

from wastewater

bull A list of references taken from the worlds leading scientific Journals in the

field

The last chapter deals with the synthesis of thiosalicylic acid functional ized

silica The modified silica gel was characterized by FTIR TGA-DTA and

SEM with EDX The aim of this study was to investigated the potential of the

modified silica gel as selective adsorbent for Pb(II) Cu(II) and Cr(IlI) The

adsorption of Pb(II) Cu(II) and Cr(III) on SiOs-APTMS-THSA was studied as

V

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

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Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

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32

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

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[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

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[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

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[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

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[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

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[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

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Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 210

(a) activated Silica gel (SiOa)

(b) Si02-APTMS

(c) Si02-APTMS-THSA

(d) Si02-APTMS-RHSA loaded with Pb(Il) Cu(II) and

Cr(III)

EDX spectrum of

(a) Si02-APTMS-THSA

(b) Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III

Effect of pH on adsorption of Pb(II)Cu(II) and Cr(IIl)

Effect of contact time on adsorption of Pb(II)Cu(Il) and

Cr(III)

Effect of initial metal ion concentration on the adsorption of Pb(II)Cu(II) and Cr(III)

Effect of temperature on the adsorption of Pb(II) Cu(Il) and

Cr(III)

Langmuir isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

Freundlich isotherm for Adsorption of

(a) Pb(II)

(b) Cu(II)

(c) Cr(III)

46

47

49

50

51

53

55

56

57

60

61

62

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) andCr(III) 64

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) 67

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III) 69

IV

ABSTRACT

The dissertation entitled Chemically modified adsorbent for extraction of selected

heavy metal ions is comprised of two chapters

The first chapter describes a general introduction of the subject matter The very

relevant matters include

bull A brief discussion of ion-exchange resin and silica gel

bull Advantages of inorganic adsorbents over polymeric resin

bull Brief discussion of modification of silica gel surface through impregnation of

organic functional groups

bull Discussion of surface modification through covalent grafting which involves

(i) Immobilization of silane reagents

(ii) Sol-gel rout of surface modification

(iii) Other routes of surface modification

bull Application of chemically modified silica gel in extraction of heavy metal ions

from wastewater

bull A list of references taken from the worlds leading scientific Journals in the

field

The last chapter deals with the synthesis of thiosalicylic acid functional ized

silica The modified silica gel was characterized by FTIR TGA-DTA and

SEM with EDX The aim of this study was to investigated the potential of the

modified silica gel as selective adsorbent for Pb(II) Cu(II) and Cr(IlI) The

adsorption of Pb(II) Cu(II) and Cr(III) on SiOs-APTMS-THSA was studied as

V

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

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60(2003) 1003-1009

32

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

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[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

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65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

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[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

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[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

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[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

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[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

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[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

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73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

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[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

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[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) andCr(III) 64

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) 67

adsorption onto modified silica gel (Si02-APTMS-THSA)

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III) 69

IV

ABSTRACT

The dissertation entitled Chemically modified adsorbent for extraction of selected

heavy metal ions is comprised of two chapters

The first chapter describes a general introduction of the subject matter The very

relevant matters include

bull A brief discussion of ion-exchange resin and silica gel

bull Advantages of inorganic adsorbents over polymeric resin

bull Brief discussion of modification of silica gel surface through impregnation of

organic functional groups

bull Discussion of surface modification through covalent grafting which involves

(i) Immobilization of silane reagents

(ii) Sol-gel rout of surface modification

(iii) Other routes of surface modification

bull Application of chemically modified silica gel in extraction of heavy metal ions

from wastewater

bull A list of references taken from the worlds leading scientific Journals in the

field

The last chapter deals with the synthesis of thiosalicylic acid functional ized

silica The modified silica gel was characterized by FTIR TGA-DTA and

SEM with EDX The aim of this study was to investigated the potential of the

modified silica gel as selective adsorbent for Pb(II) Cu(II) and Cr(IlI) The

adsorption of Pb(II) Cu(II) and Cr(III) on SiOs-APTMS-THSA was studied as

V

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

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32

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

ABSTRACT

The dissertation entitled Chemically modified adsorbent for extraction of selected

heavy metal ions is comprised of two chapters

The first chapter describes a general introduction of the subject matter The very

relevant matters include

bull A brief discussion of ion-exchange resin and silica gel

bull Advantages of inorganic adsorbents over polymeric resin

bull Brief discussion of modification of silica gel surface through impregnation of

organic functional groups

bull Discussion of surface modification through covalent grafting which involves

(i) Immobilization of silane reagents

(ii) Sol-gel rout of surface modification

(iii) Other routes of surface modification

bull Application of chemically modified silica gel in extraction of heavy metal ions

from wastewater

bull A list of references taken from the worlds leading scientific Journals in the

field

The last chapter deals with the synthesis of thiosalicylic acid functional ized

silica The modified silica gel was characterized by FTIR TGA-DTA and

SEM with EDX The aim of this study was to investigated the potential of the

modified silica gel as selective adsorbent for Pb(II) Cu(II) and Cr(IlI) The

adsorption of Pb(II) Cu(II) and Cr(III) on SiOs-APTMS-THSA was studied as

V

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

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Water Air and Soil Pollution 223 (2012) 5391-5399

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[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

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extraction and preconcentration of Sc(III) from environmental samples

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preconcentration and determination of trace heavy metal ions in water samples

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[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

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[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

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Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

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[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

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32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

a function of pH contact time initial metal ion concentration and temperature

All these parameters proved to be useful in the description of the adsorption

process An optimum pH for the adsorption of Pb(II) Cu(II) and Cr(III) was

found to be 4 Equilibrium isotherm data for Pb(Il) Cu(ll) and Cr(lll) were

analyzed by Langmuir and Freundlich models The Freundlich adsorption

isotherm described the adsorption data very well at all studied temperatures

The kinetic of metal ion adsorption followed a pseudo-second-order rate

equation Thermodynamic parameters ie change in free energy (AG )

enthalpy (AH) and entropy (AS) were also evaluated The thermodynamic

analysis showed that the adsorption process for all metal ions studied was

endothermic and spontaneous in nature

VI

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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22

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[58] D Caldarola D P Mitevb L Marline EP Nesterenkod B Paullb B

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[63] C Ekinci and U Koklu Sorption and preconcentration of vanadium silver

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[68] M Ghaedi M Montazerozohori A Hekmati and M Roosta Solid phase

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[70] O H S AL- Obaidi and M N Al-Jibouri Preparation characterization

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[71] HM Marwani and AE Alsafrani New solid phase extractor based on ionic

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[72] Q Wang W Gao Y Liu J Yuan Z Xu Y Li and M Schroder

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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modified sol-gel method for cyanide degradation and heavy metals removal J

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[75] Y Niu R Qu Ci Sun C Wang H Chen C Ji Y Zhang X Shao and F

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[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

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geological and metallurgical samples J Anal Atom Spectrom 17 (2002)

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[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

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[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

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[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

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[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

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[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

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[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

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145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

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[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

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[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

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[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

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128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

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gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

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from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

CHAPTER 1

GENERAL INTRODUCTION

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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24

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[53] V N Losev V Kudrina N V Maznyak and A K Trofimchuk Use of

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[54] F Sahina MVolkana A G Howardb and O Y Ataman Selective

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[55] ME Mahmoud AA Soayed and OF Hafez Selective solid phase extraction

and preconcentration of heavy metals from seawater by physically and

chemically immobilized 4-amino-3-hydroxy-2-(2-chlorobenzene)-azo-l -

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[56] MM Osman SA Kholeif NA Abou-Almaaty and ME Mahmoud

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26

[57] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

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[58] D Caldarola D P Mitevb L Marline EP Nesterenkod B Paullb B

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[59] SM Zhang QS Pu P Liu QY Sun and ZX Su Synthesis of

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[60] S Radii N Basbasl S Tighadouini and M Bacquet New polysiloxane

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[61] N Tokman S Akman and M Ozcan Solid-phase extraction of bismuth lead

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[62] N Tokman S Akman M Ozcan and U Koklu Preconcentration and

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[63] C Ekinci and U Koklu Sorption and preconcentration of vanadium silver

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[64] E G Vieiraa I V Soares N L Dias Filhoa NC da Silvaa E F Garciaa

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[67] OA Zaporozhets LS Ivanko and VV Sukhan Interaction between

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[68] M Ghaedi M Montazerozohori A Hekmati and M Roosta Solid phase

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[69] XZ Wu P Liu QS Pu QY Sun and ZX Su Preparation of dendrimer-

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preconcentration and separation palladium prior to FAAS determination

Talanta 62(2004)918-923

[70] O H S AL- Obaidi and M N Al-Jibouri Preparation characterization

theoretical treatment and adsorption on surfacesN5 acycliclmmobilizes on

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[71] HM Marwani and AE Alsafrani New solid phase extractor based on ionic

liquid functionalized silica gel surface for selective separation and

determination of lanthanum JAnal Sci and Technol 4 (2013) 4-13

[72] Q Wang W Gao Y Liu J Yuan Z Xu Y Li and M Schroder

Simultaneous adsorption of Cu(II) and S04 ions by a novel silica gel

functionalized with a ditopic zwitterionic Schiff base ligand Chem Eng J

(2014) in press ArticlepiiS 1385894714003957

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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in metal ion extraction Sep Sci and Technol 48 (2013) 1349-1355

[74] F A HarrazOE Abdel-Salam AA Mostafa RM Mohamed and M

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modified sol-gel method for cyanide degradation and heavy metals removal J

of Alloys Compd 551 (2013) 1-7

[75] Y Niu R Qu Ci Sun C Wang H Chen C Ji Y Zhang X Shao and F

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[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

immobilized silica gel to flow injection on-line microcolumn preconcentration

and separation coupled with flame atomic absorption spectrometry for

interference-free determination of trace silver gold palladium and platinum in

geological and metallurgical samples J Anal Atom Spectrom 17 (2002)

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[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

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[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

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[79] OA Zaporozhets LS Ivanko IV Marchenko and VV Sukhan

Determination of zirconium using morin immobilized on silica gel J Anal

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

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Mater 244-245 (2013) 94-101

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[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

functionalization of silica gel with 2-((3-silylpropylimino) methyl) phenol

(SPIMP) and its application for solid phase extraction and preconcentration of

Fe (III) Pb (II) Cu (II) Ni (II) Co (II) and Zn (II) Ions Indian J Sci

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[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

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[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

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[84] E Akyuz M Imamoglu and H Altundag Selective determination of Cr(Vl)

by FA AS after solid phase extraction on bis(3-aminopropyl)amine- bonded

silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

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[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

The rapid industrialization and urbanization have resulted in the deterioration of

water air and soil quality Environmental pollution by toxic heavy metals arises from

industrial agricultural effluents and water disposal from various sources The toxic

heavy metals damage the fauna and flora of lakes and streams One of the potential

remedies to this problem is the use of adsorption technologies A number of

inexpensive adsorbents such as agricultural residues and peat have been used for the

removal of heavy metal ions from wastewater However major disadvantages of these

adsorbents are their low loading capacities and their relatively weak interactions with

metallic cations as evidenced by low metal ion binding constants [1 2] To overcome

this drawback many investigators have developed modified adsorbents such as

aminopropylcorboxylic acid functionalized adsorbents [3] thiol functionalized

adsorbents [4] and aminofunctionalized magnetic cellulose composite [5] for removal

of heavy metal ions from the aqueous media A process for the separation of metals

that can be operated simply without the requirement of organic solvents is therefore

required Various investigations have been reported on the separation of metals by the

use of various kinds of organic materials modified with several chelating agents

Ion-exchange materials are commonly used for separation of metal ions

comparatively than preconcentration The elution of metal ions causes the dilution

which decreases the sensitivity of analysis These facts lead to development of solid

phase extraction by modified solid sorbent for removal of heavy metal ions Solvent

impregnated resins and chelating polymeric resins were used with substantial

attention for extractive concentration of metal ions from aqueous solution and

wastewater The solvent extractants or chelating groups are either impregnated into

the pores of the solid polymeric matrix of the resin or covalently bonded to the

polymeric surface The chelating groups are built-in into the ion-exchange resin or

other polymeric surfaces to improve the specificity of the resin or polymeric surface

An important characteristic of the chelating ion-exchanger is the greater selectivity as

compared to the usual type of ion-exchanger A series of chelating resins [6-8] were

prepared for the removal of heavy metal ions from the aqueous solution but the main

disadvantages of polymeric resins are slow kinetics irreversible adsorption of

organic swelling sensitivity towards many chemical environments and loss of

mechanical stability in modular operation These troubles suggest the use of inorganic

supports in place of polymeric resin Some of the advantages of inorganic supports [9]

are

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[68] M Ghaedi M Montazerozohori A Hekmati and M Roosta Solid phase

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[69] XZ Wu P Liu QS Pu QY Sun and ZX Su Preparation of dendrimer-

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[70] O H S AL- Obaidi and M N Al-Jibouri Preparation characterization

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[71] HM Marwani and AE Alsafrani New solid phase extractor based on ionic

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[72] Q Wang W Gao Y Liu J Yuan Z Xu Y Li and M Schroder

Simultaneous adsorption of Cu(II) and S04 ions by a novel silica gel

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(2014) in press ArticlepiiS 1385894714003957

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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in metal ion extraction Sep Sci and Technol 48 (2013) 1349-1355

[74] F A HarrazOE Abdel-Salam AA Mostafa RM Mohamed and M

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modified sol-gel method for cyanide degradation and heavy metals removal J

of Alloys Compd 551 (2013) 1-7

[75] Y Niu R Qu Ci Sun C Wang H Chen C Ji Y Zhang X Shao and F

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[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

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interference-free determination of trace silver gold palladium and platinum in

geological and metallurgical samples J Anal Atom Spectrom 17 (2002)

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[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

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[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

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[79] OA Zaporozhets LS Ivanko IV Marchenko and VV Sukhan

Determination of zirconium using morin immobilized on silica gel J Anal

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

by y-radiation synthesized silica-graft-vinyl imidazole adsorbent J Hazard

Mater 244-245 (2013) 94-101

29

[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

functionalization of silica gel with 2-((3-silylpropylimino) methyl) phenol

(SPIMP) and its application for solid phase extraction and preconcentration of

Fe (III) Pb (II) Cu (II) Ni (II) Co (II) and Zn (II) Ions Indian J Sci

Technol 5(2012)1893-1900

[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

benzylidene)amino]phenylethanone Synthesis characterization and

application as an efficient and reusable solid phase extractant for selective

removal of Zn(II) from mycorrhizal treated fly-ash samples JEnviron Sci25

(2013) 1252-1261

[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

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[84] E Akyuz M Imamoglu and H Altundag Selective determination of Cr(Vl)

by FA AS after solid phase extraction on bis(3-aminopropyl)amine- bonded

silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

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determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

gt good selectivity

gt no swelling

gt rapid sorption of metal ions and

gt good mechanical stability

The literature survey revealed that inorganic adsorbents have received great attention

for extraction of metal ions from the aqueous envirormient [10] Recently selective

adsorbents have been developed involving inorganic solid surfaces modified with

chelating groups Among the different adsorbents silica gel especially immobilized

with various organic compounds with metal chelating ability has received great

attention [11-13] Immobilization of organic functional groups on a siliceous surface

has been successfully employed to produce varieties of modified silica In this

process organic reagent or synthesized organic molecule containing the desired

organic functional group is directly attached to the support or to the original chain

bonded to the support via sequence of reactions to increase the main chain where

other basic centres can be added to ensure the enhancement of a specific adsorption

[14] The advancement in this field is associated with silylization process which is

employed to generate products of coupling agents to permit the fixation of a reagent

that is able to fulfil predetermined specific applications The silylated

organofunctional groups play an important role in coordination chemistry as a

possibility of synthesis of new ligands with muhi coordinafing capabilities Silica

surface interacts with the silane reagent to form a covalent bond with the surface [15]

By the introduction of organic functional groups to silica surface there is a partial

conversion of surface silanol to a new organofunctional surface that acquires

organophilic properties Thus ligand-grafted silica gives a set of properties to the

surface which differs considerably from the original matrix [16]

Surface modification of silica gel

Modification of silica surface relates to all the processes that lead to change in

chemical composition of the surface Surface can be modified either by physical

treatment (thermal or hydrothermal) that leads to change in ratio of silanol and

siloxane concentration of the silica surface or by chemical treatment that leads to

change in chemical characteristics of silica surface By the modification the

adsorption properties are significantly affected Chemisorptions of chelating

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

molecules on silica surface provides immobility mechanical stability and water

insolubility thereby increases the efficiency sensitivity and selectivity of the

analytical application Silica gel surface can be modified by two distinct processes

(I) Organofunctionalization In which the modifying agent is an organic group and

(II) Inorganofunctionalization In which the group anchored on the surface can be

an organometallic composite or a metallic oxide

The possibilities of target directed variation of the chemical and analytical properties

of the sorbent by modifying them is almost limitless Chemical modification of silica

surface by organic chelating group acts as ion-exchanger which provides greater

selectivity for the analyte than that offered by traditional ion-exchanger The most

convenient way to develop a chemically modified surface is achieved by simple

immobilization (or fixing) of the group on the surface by adsorption or electrostatic

interaction or hydrogen bond formation or other type of interaction [17] Simple

impregnation of the solution of modifiers or covalent binding so called covalent

grafting of the chelating molecule to the silica matrix is the common practice of

developing a functionalized silica surface

Modification through impregnation

Impregnation deals with physical interactions between the modifier and solid support

by either inclusion in the pores of the support material or adhesion process or

electrostatic interaction [18] 8-Hydroxyquinoline was immobilized onto silica gel for

extractive concentration of metal ions by simply stirring with the activated silica [14]

Modification of silica gel with Eriochrome black T (ECB-T) was reported by stirring

a mixture of ethanolic solution of ECB-T and silica gel for 30 min Silica gel

immobilized with the ECB-T has been used as a solid phase extractor for Zn(II)

Mg(II) and Ca(II) ions [19] The sorption of some metal ions on silica gel

impregnated with a mixture of Zincon and Aliquat 336 was investigated [20] The

sorbent was used for the preconcentration of trace amounts of some metals from

aqueous solution before their determination by atomic absorption spectrometry for the

separation of metal ion mixtures by column-extraction chromatography and additional

purification of some salt solution from trace amount of Zn(II) Pb(II) Cd(II) and

Cu(II) Mahmoud [21] used metal chelating agent 1-aminoanthraquinone (AAQ) for

the surface modification of silica gel by covalent grafting as well as physical sorption

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

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Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

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32

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

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[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

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[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

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[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

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Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

By covalently binding nitrogen or oxygen atom of the organic modifier to the surface

of silica gel two different immobilized silica phases were synthesized Physical

adsorption of AAQ on the surface of silica gel developed another silica phase The

stability of the three newly synthesized silica gel phases were performed in different

buffer solutions in pH range 1-6 It was found that physically adsorbed silica gel

phase exhibited maximum hydrolysis while covalently grafted phases were to be

fairly resistant to hydrolysis

Modification through covalent grafting

(I) Immobilization of silane reagent

lon-chelating organic molecules are usually bound to silica surface via silanization

procedure that involves covalent grafting [22] However a number of desirable ion-

chelating groups do not contain a reactive functional group suitable for chemical

bonding to the silanized surface In such a case physical adsorption of the chelating

agent on the solid support is useful which can be achieved through hydrophobic

attraction such as van der Waals interaction between the methyl groups on the

silanized surface and the carbon chain of the chelating agent For example

hydrophobic attractions between the methyl groups of the dichlorodimethyl silane or

chlorotripropyl silane immobilized silica and the carbon chain of Alamine 336 or 2-

hydroxy-5-nonylacetophenoneoxime (HNAOX) or Cyanex 272 (di-244-

trimethylpentyl phosphonic acid) developed modified silicas [23 24]

R

N

R ^ R

R = C 8 - C 8 -10

Alamine 336

NOH

CH

H3C H2

H3C-^ C

H3C ^ c -H 3 C H

H 3 C H3C

H 3 C ^ ^ H3C 2

Cyanex

P

-H2C

272

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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24

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[54] F Sahina MVolkana A G Howardb and O Y Ataman Selective

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[55] ME Mahmoud AA Soayed and OF Hafez Selective solid phase extraction

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26

[57] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

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[58] D Caldarola D P Mitevb L Marline EP Nesterenkod B Paullb B

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[59] SM Zhang QS Pu P Liu QY Sun and ZX Su Synthesis of

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[60] S Radii N Basbasl S Tighadouini and M Bacquet New polysiloxane

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[63] C Ekinci and U Koklu Sorption and preconcentration of vanadium silver

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[67] OA Zaporozhets LS Ivanko and VV Sukhan Interaction between

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[68] M Ghaedi M Montazerozohori A Hekmati and M Roosta Solid phase

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[69] XZ Wu P Liu QS Pu QY Sun and ZX Su Preparation of dendrimer-

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preconcentration and separation palladium prior to FAAS determination

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[70] O H S AL- Obaidi and M N Al-Jibouri Preparation characterization

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[71] HM Marwani and AE Alsafrani New solid phase extractor based on ionic

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[72] Q Wang W Gao Y Liu J Yuan Z Xu Y Li and M Schroder

Simultaneous adsorption of Cu(II) and S04 ions by a novel silica gel

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(2014) in press ArticlepiiS 1385894714003957

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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[74] F A HarrazOE Abdel-Salam AA Mostafa RM Mohamed and M

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modified sol-gel method for cyanide degradation and heavy metals removal J

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[75] Y Niu R Qu Ci Sun C Wang H Chen C Ji Y Zhang X Shao and F

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[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

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geological and metallurgical samples J Anal Atom Spectrom 17 (2002)

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[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

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[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

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[79] OA Zaporozhets LS Ivanko IV Marchenko and VV Sukhan

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

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Mater 244-245 (2013) 94-101

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[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

functionalization of silica gel with 2-((3-silylpropylimino) methyl) phenol

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Fe (III) Pb (II) Cu (II) Ni (II) Co (II) and Zn (II) Ions Indian J Sci

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[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

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[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

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silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

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Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

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[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

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gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

In covalent grafting the active H atoms of the surface silanol groups dispersed on

silica gel surface react with organosilyl groups to give some organic nature to the

inorganic matrix of silica gel The organo-functionalization of silica surfaces is

normally used to introduce basic groups through an anchored pendant chain The

advantages of the immobilization of a desired organic compound onto the silica gel

are the great versatility arising from the various functionalities of the bonded groups

which should be resistant to removal from the surface by organic solvent or water [25

26] Conventional methods of silica surface modification by chemical routes involve

reaction of surface hydroxyl group with commercial silane coupling reagents that act

as precursors for further immobilization of organic molecules Normally these

silylating agents react with the surface silanol groups in one step allowing the surface

to embrace desirable terminal functional group In this route of surface modification

Si-O-Si-C moiety so formed has bifunctional nature (provides firm attachment to

silica matrix and allows further modification) and high chemical stability FTIR and

solid-state Si NMR studies have revealed the possibilities of direct attachment of

alkoxysilane reagent to Si-O-Si sites [27 28]

Jacques and co-workers [29] have synthesized aniline grafted silica gel The

procedure involves the mixing of aniline and sodium hydride in a mixture of toluene

and THF and stirred for 30 min 3-Chloropropyltrimethoxysilane was added to the

resulting mixture followed by silica gel Finally it was stirred for 72 h under argon at

solvent reflex temperature The modified silica was filtered and dried The grafting

reaction for obtaining the modified silica is shown in Scheme 11 and 12

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

NH NHNa^

+ NaH

^ ^

+ H

^ ^

OCH3

NH Si-OCH

OCH

OCH

^ ^ OCH

^ ^ ^ H3CO o ^ = ^

+ NaCI

Scheme 11 Preparation of 3-aniIine-propyltrimethoxysilane intermediate

i -OH H3CO

A

-OH + HjCO-Si

H3CO -OH ^

HN

Silica surface

7 -^

-OH

OH

^ ^ HN

^ ^

V-

Scheme 12 Synthesis of aniline grafted silica adsorbent

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[2] V Ravindran MR Stevens BN Badriyha and M Pirbazari Modeling the

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[3] E Repo JK Wachol A Bhatnagar A Mudhoo and M Sillanapa

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[4] J Bao Y Fu and Z Bao Thiol-functionlized magnetitegrapheme oxide

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[5] X Sun L Yang Q Li J Zhao X Li X Wong and H Liu Amino-

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[6] AF Shaaban DA Fadel AA Mahmoud MA Elkomy and SM Elbahy

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[7] M Monier and DA Abdel-Latif Preparation of cross-linked magnetic

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[8] C Xiong XChen and X Liu Synthesis characterization and application of

ethylenediamine functionalized chelating resin for copper preconcentration in

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[9] NV Deorkar and LL Tavlarides Zinc cadmium and lead separation from

aqueous streams using solid-phase extractants Ind Eng Chem Res 36

(1997)399-406

21

[10] M Dogan Y Turhan M Alkan H Namli P Turan and O Demirbasect

Functionalized sepiolite for heavy metal ions adsorption Desalination 230

(2008)248-268

[11] A Tong Y Akama and S Tanaka Preconcentration of copper cobalt and

nickel with 3-methyl-l-phenyl-4- stearoyl-5-pyrazolone loaded on silica gel

Analyst 115(1990)947-979

[12] R Kocjan Retention of some metal ions and their separation on silica gel

modified with acid red 88 Microchim Acta 131 (1999) 153-158

[13] S Radi S Tighadouini M Bacquet S Degoutin F Cazier M Zaghrioui and

YN Mabkhot Organically modified silica with pyrazole-3-carbaldehyde as a

new sorbent for solid-liquid extraction of heavy metals Molecules 19 (2014)

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[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

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[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

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[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

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preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

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32

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

(II) Sol-gel route of surface modification

Sol-gel process often invites much attention for the formation of organically modified

silicas (Ormosils) The most common approach has involved the preparation of sol-

gel hybrids including the combination of inorganic oxides (particularly silica) with

alkylalkoxysilanes [30] Non-hydrolytic sol-gel method was reported for the

preparation of hybrid ormosils with a variety of organic groups starting from

organically modified precursors [31] A method for the preparation of surface-

modified silica particle is described as hydrolyzing a tetraalkoxy silane compound in a

medium of an alcohol containing 25-60 moles of water and 01-30 moles of an

alkaline compound as a catalyst each per mole of the tetraalkoxy silane compound to

form an alcosol of silica particles having alkoxy groups and hydroxy groups bonded

to the silicon atoms on the surface and then admixing the alcosol of silica particles

with an organosilicon compound [32] Using sol-gel process synthesis of an

inorganic-organic hybrid material is reported [33] where an amino-silica intermediate

was obtained on stirring a mixture of tetraethoxysilane and 3-

trimethoxysilylpropylethylenediamine in presence of HCl in an ice bath for 10 min

followed by addition of ethanol and 5 NaHCOs solution The silica particles thus

obtained after drying were treated with 15 glutaraldehyde solution Subsequently

glutaraldehyde modified silica when treated with ethylenediamine and NaBH4

resulted in the desired modified silica [34]

(III) Other routes of surface modification

Besides the covalent grafting of silane reagent or sol-gel process few other methods

are also reported as potential routes for modification of silica surface Preparation of

alkyl bonded silica phase includes halogenation of silanol group by reaction of the

surface hydroxyl groups of the silica with a halogenating agent in anhydrous aprotic

solvent followed by reaction with Grignard reagent or organolithium compound

Halogenation of the surface hydroxyl groups of the silica in an anhydrous aprotic

solvent replaced the surface hydroxyl groups with a halogenated surface which was

isolated from the solvent and excess of the halogenating agent was removed by

washing Treatment of the washed halogenated silica material with group consisting

of unsaturated Grignard reagents (eg CH2=CH-(CH2)bdquoMgBr) and organolithium

reagents (eg CH2=CH-(CH2)bdquoLi) resulted in direct covalent attachment of carbon to

silicon atom

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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28

[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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[74] F A HarrazOE Abdel-Salam AA Mostafa RM Mohamed and M

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[75] Y Niu R Qu Ci Sun C Wang H Chen C Ji Y Zhang X Shao and F

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[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

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[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

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[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

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[79] OA Zaporozhets LS Ivanko IV Marchenko and VV Sukhan

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

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Mater 244-245 (2013) 94-101

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[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

functionalization of silica gel with 2-((3-silylpropylimino) methyl) phenol

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Fe (III) Pb (II) Cu (II) Ni (II) Co (II) and Zn (II) Ions Indian J Sci

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[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

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[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

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[84] E Akyuz M Imamoglu and H Altundag Selective determination of Cr(Vl)

by FA AS after solid phase extraction on bis(3-aminopropyl)amine- bonded

silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

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[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

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[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

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from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

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by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

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[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

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Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Conversion of surface silanol to surface hydride followed by coupling of terminal

olefins in presence of metal catalyst has also modified the silica surface (Scheme 13)

Success of synthesis of such a modified surface depends on successful conversion of

surface silanol to surface hydride which can be achieved through either chlorination

of surface silanol by SOCb followed by reduction with LiAlH4 [35] or controlled

chemisorption of silanetriol (HSi(0H)3) in which the silanetriol is covalently attached

to silica surface as well as adjacent silanol via formation of siloxane linkage [36]

This method provides an extremely high surface coverage of Si-H

2

A Rh Catalyst I ^ ^ H

J I

Schemel3

The synthesis of l5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-

gel) [37] and methylthiosalicylate silica gel (TS-gel) [38] have been reported which

involved two steps In the first step activated silica gel was suspended in 3-

aminopropyltrimethoxysilane in dry toluene and the mixture was refluxed for 10 h in

a nitrogen atmosphere with constant stirring to obtain aminopropyl silica gel (APSG)

while in the second step APSG was reacted either with DPTH or methylthiosalicylate

to get modified silica gel The reactions for DPTH-gel and TS-gel are shown in

Scheme 14 and 15

A new ion-imprinted amino-functionalized silica gel sorbent was synenthesized by

hydrothermal assisted surface imprinting technique using Cd(II) as template 3-[2-(2-

aminoethylamino)ethylamino] propyl-trimethoxysilane as the functional monomer

and epichlorohydrin as the cross linking agent The adsorption capacity of the sorbent

for Cd(II) was found to be 574 mg g [39] The adsorption of Cd(II) onto sorbents

was best described by Langmuir isotherm model The kinetic adsorption data were

well represented by pseudo second order kinetic model and the rate limiting step of

Cd(II) onto sorbent could be chemical sorption

R

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[2] V Ravindran MR Stevens BN Badriyha and M Pirbazari Modeling the

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[3] E Repo JK Wachol A Bhatnagar A Mudhoo and M Sillanapa

Aminopropylcorboxylic acid functionalized adsorbents for heavy metal

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[4] J Bao Y Fu and Z Bao Thiol-functionlized magnetitegrapheme oxide

hybrid as reusable adsorbents for Hg(II) removal Nanoscale Res Lett 8

(2013)486-492

[5] X Sun L Yang Q Li J Zhao X Li X Wong and H Liu Amino-

functionalized magnetic cellulose nanocomposite as adsorbent for removal of

Cr(IV)Synthesis and adsorption studies Chem Eng J 41 (2014) 167-174

[6] AF Shaaban DA Fadel AA Mahmoud MA Elkomy and SM Elbahy

Removal of Pb(II) Cd(II) Mn(II) and Zn(II) using iminodiacetate chelating

resin by batch and fixed-bed column methods Desalination and Water

Treatment 51 (2013) 5526-5536

[7] M Monier and DA Abdel-Latif Preparation of cross-linked magnetic

chitosan-phenylthiourea resin for adsorption of Hg(II) Cd(II) and Zn(II) ions

from aqueous solutions J Hazard Mater 209-210 (2012) 240-249

[8] C Xiong XChen and X Liu Synthesis characterization and application of

ethylenediamine functionalized chelating resin for copper preconcentration in

tea samples Chem Eng J 203 (2012) 115-122

[9] NV Deorkar and LL Tavlarides Zinc cadmium and lead separation from

aqueous streams using solid-phase extractants Ind Eng Chem Res 36

(1997)399-406

21

[10] M Dogan Y Turhan M Alkan H Namli P Turan and O Demirbasect

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[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

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[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

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[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

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32

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

OH

OH

OH

H3COC O

NH

O COCH3

NH J

O

H

AP-gel

H

O O

H

O

O ^yj

H

H

Glut AP-gel

chemel4 DPTH-gel formation

10

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

HCOC O

I ^ ^

Scheme 15 TS-gel formation

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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24

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[54] F Sahina MVolkana A G Howardb and O Y Ataman Selective

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[55] ME Mahmoud AA Soayed and OF Hafez Selective solid phase extraction

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26

[57] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

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[58] D Caldarola D P Mitevb L Marline EP Nesterenkod B Paullb B

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[59] SM Zhang QS Pu P Liu QY Sun and ZX Su Synthesis of

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[60] S Radii N Basbasl S Tighadouini and M Bacquet New polysiloxane

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[63] C Ekinci and U Koklu Sorption and preconcentration of vanadium silver

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[67] OA Zaporozhets LS Ivanko and VV Sukhan Interaction between

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[68] M Ghaedi M Montazerozohori A Hekmati and M Roosta Solid phase

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[69] XZ Wu P Liu QS Pu QY Sun and ZX Su Preparation of dendrimer-

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[70] O H S AL- Obaidi and M N Al-Jibouri Preparation characterization

theoretical treatment and adsorption on surfacesN5 acycliclmmobilizes on

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[71] HM Marwani and AE Alsafrani New solid phase extractor based on ionic

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determination of lanthanum JAnal Sci and Technol 4 (2013) 4-13

[72] Q Wang W Gao Y Liu J Yuan Z Xu Y Li and M Schroder

Simultaneous adsorption of Cu(II) and S04 ions by a novel silica gel

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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[74] F A HarrazOE Abdel-Salam AA Mostafa RM Mohamed and M

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modified sol-gel method for cyanide degradation and heavy metals removal J

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[75] Y Niu R Qu Ci Sun C Wang H Chen C Ji Y Zhang X Shao and F

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[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

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geological and metallurgical samples J Anal Atom Spectrom 17 (2002)

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[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

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[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

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[79] OA Zaporozhets LS Ivanko IV Marchenko and VV Sukhan

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

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Mater 244-245 (2013) 94-101

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[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

functionalization of silica gel with 2-((3-silylpropylimino) methyl) phenol

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Fe (III) Pb (II) Cu (II) Ni (II) Co (II) and Zn (II) Ions Indian J Sci

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[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

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[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

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[84] E Akyuz M Imamoglu and H Altundag Selective determination of Cr(Vl)

by FA AS after solid phase extraction on bis(3-aminopropyl)amine- bonded

silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

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Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Functionalized silica gel in extractive concentration of metal ions

Extraction of metal ions using chelating sorbents has several advantages over the

conventional methods

1 Selective determination of metal ions will be possible by using a chelating sorbent

having a ligand possessing high selectivity to the targeted metal ion

2 It is free from difficult phase separation which is caused by the mutual solubility

between water and organic solvent layers

3 The chelating sorbent method is an economical method since it uses only a small

amount of ligand

4 Trace metal ions at concentrations as low as parts per billion (ppb) can be

determined because the targeted ion is enriched on the solid phase

5 The concentration of metal ion can be visibly estimated from the colour intensity of

the solid phase if the metal complex formed absorbs radiation in the visible

wavelength region

6 Use of carcinogenic organic solvents is avoided and thus the technique is

ecofriendly

The interest in chelating sorbents based on silica gel for preconcentrationseparation

and determination of metal ions has received considerable attention in recent years

Development of silica supported molecular traps through covalent grafting of organic

molecules on silica surface plays important role in elimination of toxic heavy

elements from wastewater Again there is a decrease in detection limit due to

extraction of the analyte component from a relatively large volume of solution into

the phase of the sorbent Better selectivity results from the geometrical features of

fixing chelating groups on silica surface and complex forming properties of the

chelating group The representative contributions relating to

preconcentrationseparation of metal ions are reported in Tablel 1

12

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

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Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

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32

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press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

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[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

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(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Table 11 Modified silica gel with various functional group for

preconcentrationseparation of metal ions

Functional group Metal ions Refrences

l5-Bis(di-2-pyridyl)methylene Zn(II) Cd(II) Co(II) [40-45] thiocarbohydrazide Pb(II) Ni(II) Pt(IV)

18-Dihydroxyanthraquinone Fe(III) Co(II) Ni(II) [4647] Cu(II) Pb(II) Zn(II) Cd(II)

1 -Aminoanthraquinone

1 -Nitroso-2-naphthol

2-Hydroxy-1 -naphthaldehyde

Cu(II) Cr(III) [21]

Co(II) [48]

Cu(II) Zn(II) Cd(II) [49] Hg(II) Pb(II)

2-Mercaptobenzothiazole Hg(II) [50]

3-Hydroxy-2-methyl-l4-naphthoquinone Co(n) Cu(II) Zn(II) [51] Fe(III)

3-Mercaptopropyl group Hg(II) Au(III) Pd(II) [52-54] Se(IV) As(IV)

4-Amino-3-hydroxy-2-(2- Cr(III) Ni(II) Cu(II) [55] chlorobenzene)-azo-l Naphthalene Zn(II) Cd(II) Pb(II)

4-Aminoantipyrene Hg(II) Cd(II) Pb(II) [56] Cu(II) Zn(II)

8-Hydroxyquinoline Cd(II) Pb(II) Zn(ll) [57] Cu(II) Fe(III) Mn(II) Ni(II) Co(II)

2-[(Phosphonomethyl)-amino]aceticacid Be(II) Zn(II) Pb(II) [58] Cd(II)

Amidinothiourea Ag(II) Au(III) Pd(II) [59]

o-Nitrophenyl Cu(II) [60]

Aminopropyltriethoxysilane Bi(III) Pb(II) Ni(II) [61-63] Cu(II) Cd(II) Cr(IIl) V(III) Mn(II)

13

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[68] M Ghaedi M Montazerozohori A Hekmati and M Roosta Solid phase

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[69] XZ Wu P Liu QS Pu QY Sun and ZX Su Preparation of dendrimer-

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[70] O H S AL- Obaidi and M N Al-Jibouri Preparation characterization

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[71] HM Marwani and AE Alsafrani New solid phase extractor based on ionic

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[72] Q Wang W Gao Y Liu J Yuan Z Xu Y Li and M Schroder

Simultaneous adsorption of Cu(II) and S04 ions by a novel silica gel

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(2014) in press ArticlepiiS 1385894714003957

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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in metal ion extraction Sep Sci and Technol 48 (2013) 1349-1355

[74] F A HarrazOE Abdel-Salam AA Mostafa RM Mohamed and M

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modified sol-gel method for cyanide degradation and heavy metals removal J

of Alloys Compd 551 (2013) 1-7

[75] Y Niu R Qu Ci Sun C Wang H Chen C Ji Y Zhang X Shao and F

Bu Adsorption of Pb(II) from aqueous solution by silica-gel supported

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[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

immobilized silica gel to flow injection on-line microcolumn preconcentration

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interference-free determination of trace silver gold palladium and platinum in

geological and metallurgical samples J Anal Atom Spectrom 17 (2002)

125-130

[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

and mechanism of transition metal ions on silica gels functionalized with

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[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

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[79] OA Zaporozhets LS Ivanko IV Marchenko and VV Sukhan

Determination of zirconium using morin immobilized on silica gel J Anal

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

by y-radiation synthesized silica-graft-vinyl imidazole adsorbent J Hazard

Mater 244-245 (2013) 94-101

29

[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

functionalization of silica gel with 2-((3-silylpropylimino) methyl) phenol

(SPIMP) and its application for solid phase extraction and preconcentration of

Fe (III) Pb (II) Cu (II) Ni (II) Co (II) and Zn (II) Ions Indian J Sci

Technol 5(2012)1893-1900

[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

benzylidene)amino]phenylethanone Synthesis characterization and

application as an efficient and reusable solid phase extractant for selective

removal of Zn(II) from mycorrhizal treated fly-ash samples JEnviron Sci25

(2013) 1252-1261

[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

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[84] E Akyuz M Imamoglu and H Altundag Selective determination of Cr(Vl)

by FA AS after solid phase extraction on bis(3-aminopropyl)amine- bonded

silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

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determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

22-Dipyridylamine Fe(II) Ni(II) Zn(II) [64]

Bis(244 trimethylpentyOphosphonic Zn(II) [65] acid

N-(Aminothioxomethyl)-2-thiophen Cu(II) Cd(II) [66] arboxamide

Crown ether carboxylic acid Tl(III) [67]

2-(3-Silylpropylimino)methyl)-5- Fe(III) Pb(II) Cu(Il) [68] bromophenol Ni(II) Co(II) Zn(II)

Dendrimer-like polyamidoamine Pd(II) [69]

26 Diacetal pyridine Zn(ll) Cd(II) Cr(II) [70] Pb(II)

N-Phenacylpyridinium bromide bis Fe(II) Fe(III) Co(II) [71] (trifluoromethyane) sulfonimide lithium Ni(II)

Ditopiczwitterionic Schiffbaseligand Cu (II) [72]

l-(Pyridin-2-yl)imine Hg(II) Cd(II) Pb(II) [73] Zn(II)

TiCb Cr(lll) Cu(II) Ni(n) [74]

Polyamidoamine dendrimers Fe(II) Co(II) Ni(II) [75] Co(II) Zn(II) Cd(II)

Isodiphenylthiourea

Hydroxy- or amino-terminated polyamines

Mercaptopropyl ethylenediaminetriacetate

Morin

Vinyl imidazole

2-((3-Silylpropylimino) methyl) phenol

Au(III) Ag(II) Pd(II)

Ag(I) Hg(II) Cu(II)

Cr(IV)

Zr(IV)

Hg(II)

Pt(IV)

Au(III)

Fe(III) Pb(II) Cu(II) Ni(II) Co(II) Zn(II)

[76]

[77]

[78]

[79]

[80]

[81]

l-4-[(2-Hydroxy- Zn(ll) [82] benzylidene)amino]phenylethanone

14

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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21

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22

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[27] LH Debois and BR Zagarski Reaction of alkoxysilane coupling agents with

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23

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[58] D Caldarola D P Mitevb L Marline EP Nesterenkod B Paullb B

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[63] C Ekinci and U Koklu Sorption and preconcentration of vanadium silver

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[68] M Ghaedi M Montazerozohori A Hekmati and M Roosta Solid phase

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[71] HM Marwani and AE Alsafrani New solid phase extractor based on ionic

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[72] Q Wang W Gao Y Liu J Yuan Z Xu Y Li and M Schroder

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

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geological and metallurgical samples J Anal Atom Spectrom 17 (2002)

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[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

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[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

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[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

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[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

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[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

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[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

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145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

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[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

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Water Air and Soil Pollution 223 (2012) 5391-5399

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[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

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[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

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128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

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preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

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gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

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from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

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press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Phenylamine and phenyldiamine

Bis(3-aminopropyl)amine

Xylenol

Quaternary ammonium salts

N-(2-Aminoethyl)-salicylaldimine

Triethylentetramine

246-Trimorpholino-l35- triazin

l-(2-Aminoethyl)-3- phenylurea

N-( 1 -Carboxy-6-hydroxy) Benzylidenepropylamine

3-[2-(2-Aminoethylamino)ethylamino]propyl-trimethoxysilane

3-Mercaptopropyltrimethoxysilane

23-Dimercaptosuccininc acid

Cu(II)

Cr(VI)

Hg(II)

Bi(III) Fe(II)

Cu(II) Ni(II) Zn(II)

Au(III) Pd(II)

Ag(II)

Sc(III)

Pd(II) Cu(II) Cd(II) Zn(II)

Cd(II)

Ni(II)

[83]

[84]

[85]

[86]

[87]

[88]

[89]

[90]

[91]

Cd(II)

Ag (II)

[92]

[93]

As(IV) Cd(II) Hg(II) [94] Pb(II)

4-Amino-5methyl-l24-triazol-3(4H)- Hg(II) thion

[95]

15

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

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60(2003) 1003-1009

32

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

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[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

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65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

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[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

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[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

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[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

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[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

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[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

8-Hydroxyquinoline has been immobilized on various solid matrices The adsorption

capacities have been determined for some metals For example the adsorption

capacities of 8-hydrpxyquinoline functionalized controlled pore glass porasil C

porous silica and silica gel for Cu(II) were found to be SS imoleg 104|imoleg and

216nmoleg respectively [96] The silica gel modified with 3-

aminopropyltriethoxysilane was reacted with 5-formyl-8-hydroxysilane to anchor 8-

hydroxyquinoline on the silica gel It was further characterized and used for the

preconcentration of Cu(II) Pb(II) Ni(II) Fe(III) Cd(II) Zn(II) and Co(II) prior to

their determination by flame atomic absorption spectrometry [97] Mercapto-modified

silica gel has been used by many workers for preconcentration of some trace metals

[53-55] Bifunctional porous silicas functionalized via the introduction of chelating

ligands such as mercaptopropyl and aminopropyl groups were synthesized for use in

the removal of heavy metal ions from aqueous solution The adsorbents showed high

loading capacities and selectivity for mercury ions in aqueous solutions [98]

Silica gel functionalized with 3-aminopropyltriethoxysilane was used for separation

and preconcentration of Cu(II) Cd(II) and Cr(III) from seawater [99] as well as

determination of vanadium manganese silver and lead [100] from aqueous solution

Silica gel modified with 3-aminopropyltrimethoxysilane was reported to adsorb

copper and cobalt in the form of their chlorides or acetylacetonates or

dipivaloylmethanoates from ethanolic solution [101] 3-(2-Aminoethyl-

amino)propyltrimethoxysilane was loaded onto mesoporous silica via covalent

grafting in order to extract Cu(II) ions from aqueous solutions The extraction

capacity was found to be 10 times more than that of a commercial silica gel [102]

Silica gel modified with 3-mercaptopropyltrimethoxy silane was used for selective

separation and preconcentration of selenite Se(IV) from aqueous mixture of Se(IV)

andSe(V)[103]

Recently Huang and co-workers [104] have synthesized EDTA-modified mesoporous

silica SBA-15 and explained its application for the removal of Pb (II) from aqueous

solutions It was suggested that removal of Pb(II) from the aqueous solution by

adsorption onto EDTA-SBA-15 was a multiplex process which involved ion exchange

as well as complexation The mechanism of Pb(II) adsorption onto EDTA-SBA-15 is

shown in Scheme 16 Kushwaha and coworkers [105] have synthesized

functionalized silica gel by loading with 2-thiophenecorbonyl chloride 2-furoyl and

L-proline The adsorption properties of activated silica gel (ASG) 2-

16

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

thiophenecorbonyl loaded silica gel (TLSG) 2-furoyl loaded silica gel (FLSG) and L-

proline loaded silica gel (PLSG) were investigated with Pb(II) as target pollutant from

aqueous solution The percent removal of Pb(II) by adsorption was found to be 76

85 89 and 95 by ASG TLSG FLSG and PLSG respectively The highest

percent removal shovm by PLSG was due to the presence of nitrogen as donor atom

having a lone pair of electron which was freely available for chelation with Pb(II) but

in case of TLSG and FLSG a lone pair of electron of sulphur and oxygen was

conjugated with double bond and used to stabilize aromatic ring which reduced its

availability for chelation and adsorption capacity The mechanism of adsorption

Pb(II) by the modified adsorbents is given in Scheme 17

17

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

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Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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Preconcentration and determination of metal ions from Fuel methanol with

73

T3 X

XI

T3 X

I

(^ p

HN-C COOH gt gt N - ( C H 2 ) 2 - N

HOOC COOH

p l 2 S8A15

HN-C COOH gt gt N-(CH2)2-N

HOOC Pb COOH

O HI 0

sSA-i

H N - C COOH f l HN-C COOH gt gt D K Z ^ SBA16 gt gt N-(CH2)2-N - - NHCH2)2-N + Na

HOOC COONa HOOC Pb C

V^O

HN-C SSA-t6 ) )

N - (CH2)2 - N gt gt

0 W N COOH 0 HN-C

Pb2

NaOOC COONa 0 cr O

COOH

N-(CH2)2-N + 2Na

C ^ P b - ^ C

o o 0 0

0 HN 0 O

HN-C OC SBA 15 ) )

N - (CH2)2 - N 4- Na

gtX gt^gt C Pb-OH C

O ^ V 0

Pb= + 20H - Pb(0H)2 (Ksp -1 2x10 )

Scheme 16 The mechanism for Pb(II) adsorption onto EDTA-SBA-15

18

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

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extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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73

SiOo -HO

Pb

(a)

SiO -HO

(b)

SiO -HO

(c)

Scheme 17 Adsorption mechanism of Pb (II) on TLSG (a) FLSG (b) and PLSG (c)

19

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

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at pH gt 6 these transition metal ions may undergo hydrolysis forming species such as

Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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73

Aniline grafted silica gel has been used for the removal of Cu(II) Fe(II) and Cr(lII)

from aqueous solution [29] It was observed that the maximum adsorption occurs at

pH 45 At pH lt 4 the excess of H could make it difficult for the adsorption of

Cu(ll) Fe(II) and Cr(III) ions onto chemically modified sorbents On the other hand

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Cu(OH) Fe(OH)^ and Cr(OH) ^ which promotes the diminulation of adsorption

capacity The possible adsorption mechanism is shown in Scheme 18

t -OH

OH

v ^ M

(n-l)H

Scheme 18 Adsorption mechanism of transition metal ions by aniline grafted silica

gel

20

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[84] E Akyuz M Imamoglu and H Altundag Selective determination of Cr(Vl)

by FA AS after solid phase extraction on bis(3-aminopropyl)amine- bonded

silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

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with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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anchored to silica gel via new moderate size linker Synthesis and applications

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[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

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[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

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press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

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isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

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[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

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extraction and preconcentration of Sc(III) from environmental samples

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[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

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[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

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[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

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[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

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[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

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[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

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Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

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Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

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32

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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26

[57] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

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[58] D Caldarola D P Mitevb L Marline EP Nesterenkod B Paullb B

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[59] SM Zhang QS Pu P Liu QY Sun and ZX Su Synthesis of

amidinothioureido-silica gel and its application to flame atomic absorption

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preconcentration and separation Anal Chim Acta 452 (2002) 223-230

[60] S Radii N Basbasl S Tighadouini and M Bacquet New polysiloxane

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adsorption J Surf Eng Mater Adv Technol 4 (2014) 21-28

[61] N Tokman S Akman and M Ozcan Solid-phase extraction of bismuth lead

and nickel from seawater using silica gel modified with 3-

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graphite furnace atomic absorption spectrometry Talanta 59 (2003) 201-205

[62] N Tokman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374 (2002) 977-980

[63] C Ekinci and U Koklu Sorption and preconcentration of vanadium silver

manganese and lead in aqueous solution with silica gel chemically modified 3-

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[64] E G Vieiraa I V Soares N L Dias Filhoa NC da Silvaa E F Garciaa

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[65] L Giraldo J C Moreno-Pirajan Study on the adsorption of heavy metal ions

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[66] L Geogescu M Mureseanu G Carja and V Hulen Adsorptive removal of

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[67] OA Zaporozhets LS Ivanko and VV Sukhan Interaction between

thallium(III) bromide and dicyclohexano-18-crown-6 immobilized on silica J

Anal Chem 55 (2000) 130-134

[68] M Ghaedi M Montazerozohori A Hekmati and M Roosta Solid phase

extraction of heavy metals on chemically modified silica-gel with 2-(3-

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Anal Chem 93 (2013) 843-857

[69] XZ Wu P Liu QS Pu QY Sun and ZX Su Preparation of dendrimer-

like polyamidoamine immobilized silica gel and its application to online

preconcentration and separation palladium prior to FAAS determination

Talanta 62(2004)918-923

[70] O H S AL- Obaidi and M N Al-Jibouri Preparation characterization

theoretical treatment and adsorption on surfacesN5 acycliclmmobilizes on

silica gel for removal of some toxic metals InterJ Biochem Res 4 (2014)

28-42

[71] HM Marwani and AE Alsafrani New solid phase extractor based on ionic

liquid functionalized silica gel surface for selective separation and

determination of lanthanum JAnal Sci and Technol 4 (2013) 4-13

[72] Q Wang W Gao Y Liu J Yuan Z Xu Y Li and M Schroder

Simultaneous adsorption of Cu(II) and S04 ions by a novel silica gel

functionalized with a ditopic zwitterionic Schiff base ligand Chem Eng J

(2014) in press ArticlepiiS 1385894714003957

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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in metal ion extraction Sep Sci and Technol 48 (2013) 1349-1355

[74] F A HarrazOE Abdel-Salam AA Mostafa RM Mohamed and M

Hanafy Rapid synthesis of titania-silica nanoparticles photocatalyst by a

modified sol-gel method for cyanide degradation and heavy metals removal J

of Alloys Compd 551 (2013) 1-7

[75] Y Niu R Qu Ci Sun C Wang H Chen C Ji Y Zhang X Shao and F

Bu Adsorption of Pb(II) from aqueous solution by silica-gel supported

hyperbranched polyamidoamine dendrimers J Hazard Mater 244-245

(2013)276-286

[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

immobilized silica gel to flow injection on-line microcolumn preconcentration

and separation coupled with flame atomic absorption spectrometry for

interference-free determination of trace silver gold palladium and platinum in

geological and metallurgical samples J Anal Atom Spectrom 17 (2002)

125-130

[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

and mechanism of transition metal ions on silica gels functionalized with

hydroxyl- or amino-terminated polyamines Chem Eng J 221 (2013) 264-

274

[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

reduction-sorption on bi-functional silica adsorbents J Hazard Mater 250-

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[79] OA Zaporozhets LS Ivanko IV Marchenko and VV Sukhan

Determination of zirconium using morin immobilized on silica gel J Anal

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

by y-radiation synthesized silica-graft-vinyl imidazole adsorbent J Hazard

Mater 244-245 (2013) 94-101

29

[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

functionalization of silica gel with 2-((3-silylpropylimino) methyl) phenol

(SPIMP) and its application for solid phase extraction and preconcentration of

Fe (III) Pb (II) Cu (II) Ni (II) Co (II) and Zn (II) Ions Indian J Sci

Technol 5(2012)1893-1900

[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

benzylidene)amino]phenylethanone Synthesis characterization and

application as an efficient and reusable solid phase extractant for selective

removal of Zn(II) from mycorrhizal treated fly-ash samples JEnviron Sci25

(2013) 1252-1261

[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

Cu(lI)-Removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[84] E Akyuz M Imamoglu and H Altundag Selective determination of Cr(Vl)

by FA AS after solid phase extraction on bis(3-aminopropyl)amine- bonded

silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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[70] O H S AL- Obaidi and M N Al-Jibouri Preparation characterization

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[71] HM Marwani and AE Alsafrani New solid phase extractor based on ionic

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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[74] F A HarrazOE Abdel-Salam AA Mostafa RM Mohamed and M

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[75] Y Niu R Qu Ci Sun C Wang H Chen C Ji Y Zhang X Shao and F

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[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

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geological and metallurgical samples J Anal Atom Spectrom 17 (2002)

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[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

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[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

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[79] OA Zaporozhets LS Ivanko IV Marchenko and VV Sukhan

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

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[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

functionalization of silica gel with 2-((3-silylpropylimino) methyl) phenol

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Fe (III) Pb (II) Cu (II) Ni (II) Co (II) and Zn (II) Ions Indian J Sci

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[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

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removal of Zn(II) from mycorrhizal treated fly-ash samples JEnviron Sci25

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[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

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[84] E Akyuz M Imamoglu and H Altundag Selective determination of Cr(Vl)

by FA AS after solid phase extraction on bis(3-aminopropyl)amine- bonded

silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

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[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

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[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

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128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

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by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

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[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

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press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

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extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

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[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

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[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

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(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

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[73] S Radi Y Toubi M Bacquet S Degoutin and F Cazier 1-(Pyridin-2-yl)

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[74] F A HarrazOE Abdel-Salam AA Mostafa RM Mohamed and M

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[75] Y Niu R Qu Ci Sun C Wang H Chen C Ji Y Zhang X Shao and F

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[76] P Liu ZX Zu XZ Wu and QS Pu Application of isodiphenylthiourea

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[77] M Wang R Qu C Sun P Yin and H Chen Dynamic adsorption behavior

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274

[78] N Zaitseva V Zaitsev and A Walcarius Chromium(VI) removal via

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251(2013)454^61

[79] OA Zaporozhets LS Ivanko IV Marchenko and VV Sukhan

Determination of zirconium using morin immobilized on silica gel J Anal

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[80] J Sun Z Chen Mi Ge L Xu and M Zhai Selective adsorption of Hg(II)

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Mater 244-245 (2013) 94-101

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[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

functionalization of silica gel with 2-((3-silylpropylimino) methyl) phenol

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Fe (III) Pb (II) Cu (II) Ni (II) Co (II) and Zn (II) Ions Indian J Sci

Technol 5(2012)1893-1900

[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

benzylidene)amino]phenylethanone Synthesis characterization and

application as an efficient and reusable solid phase extractant for selective

removal of Zn(II) from mycorrhizal treated fly-ash samples JEnviron Sci25

(2013) 1252-1261

[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

New amine-modified silicas Synthesis characterization and its use in the

Cu(lI)-Removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[84] E Akyuz M Imamoglu and H Altundag Selective determination of Cr(Vl)

by FA AS after solid phase extraction on bis(3-aminopropyl)amine- bonded

silica gel Atomic spectroscopy 34 (2013) 146-153

[85] J Fan C Wu Y Wei C Peng and P Peng Preparation of xylenol orange

functionalized silica gel as a selective solid phase extractor and its application

for preconcentrationmdashseparation of mercury from waters J Hazard Mater

145(2007)323-330

[86] Nagtigo Nuryono Narsito and B Rusdiarso Synthesis of silica gel modified

with quaternary ammonium salts and its application for solid phase extraction

of Au(IIl) ion 4 International conference on Biology Environment and

Chemistry 58(2013)

[87] G Ozcelik M Imamoglu S Z Yildiz and DKara Chemically modified

silica gel with N-(2-aminoethyl)-salicylaldimine for simultaneous solid phase

extraction and preconcentration of Cu(II) Ni(II) Cd(II) and Zn(Il) in waters

Water Air and Soil Pollution 223 (2012) 5391-5399

30

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

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[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

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[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

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[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

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[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

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[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

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[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

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[81] K Mortazavi M Ghaedi M Roosta and M Montazerozohori Chemical

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[82] RK Sharma Aditi Puri Anil Kumar and Alok Adholeya Chemically

modified silica gel with l-4-[(2-hydroxy-

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[83] S Radi N Basbasi S Tighadouini M Bacquet SDegoutin and F Cazi

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[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

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33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

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[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

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[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

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[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

[88] M Imamoglu and V Gunes Solid phase exraction of Au and Pd by silica gel

functionalized with triethylentetramine for determination by FAAS Atomic

Spectroscopy 33 (2012) 205-211

[89] T Madrakian A Afkhami MA Zolfigol and M Solgi M Separation

preconcentration and determination of silver ion from water samples using

silicagel modified with 246-trimorpholino-135- triazin J Hazard Mater

128(2006) 67-72

[90] Z Tu Z Hu X Chang L Zhang Q He Q J Shi and R Gao Silica gel

modified with l-(2-aminoethyl)-3- phenylurea for selective solid-phase

extraction and preconcentration of Sc(III) from environmental samples

Talanta 80(2010) 1205-1209

191] ME Mahmoud IMM Kenawy MAH Hafez and RR Lashein Removal

preconcentration and determination of trace heavy metal ions in water samples

by AAS via chemically modified silica gel N- (l-carboxy-6-hydroxy)

benzylidenepropylamine ion exchange Desalination 250 (2010) 62-70

[92] H Fan J Li Z Li and T Sun An ion-imprinted amino-fiincfionalized silica

gel sorbent prepared by hydrothermal assisted surface imprinting technique for

selective removal of cadmium (II) from aqueous solution Applied Surface

Science 258 (2012) 3815-3822

193] DV Quang JE Lee J Kim YN Kim GN Shao and HT Kim A

gentle method to graft thiol-functional groups onto silica gel for adsorption of

silver ions and immobilization of silver nanoparticles Powder Technology

235(2013)221-227

[94] W Yantasee R D Rutledge W Chouyyok V Sukwarotwat G Orr CL

Warner MG Warner GE Fryxell RJ Wiacek C Timchalk and RS

Addleman Functionalized nonporous silica for the removal of heavy metals

from biological system Adsorption and application Appl Mater

Interfaces 2 (2010) 2749-2758

[95] F Tadavon MS Tehrani and S Mothar Selective removal mercury (II) from

aqueous solution using silica gel aerogel modified with 4-amino-5methyl-

l24-triazole-3(4H)-thion Korean J Chem Eng 30 (2013) 642-648

31

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

[96] M Daye B Ouddane J Halwani and M Hamzeh Solid phase extraction of

inorganic mercury using5-phenylazo-8-hydroxyquinoiine and determination

by cold vapor atomic fluorescence spectroscopy innatural water samples The

Scientific World J 2013 (2013) Article ID 134565

[97] A Goswami AK Singh and B Venkataramani 8-Hydroxyquinoline

anchored to silica gel via new moderate size linker Synthesis and applications

as a metal ion collector for their flame atomic absorption spectrometric

determination Talanta 60 (2003) 1141-1154

[98] B Lee Y Kim H Lee and J Yi Synthesis of functionalized porous silica via

templating method as heavy metal ion adsorbents the introduction of surface

hydrophobocity onto the surface of adsorbents Microporous and Mesoporous

Mater 50(2001)77-90

[99] N Takman S Akman M Ozcan and U Koklu Preconcentration and

separation of copper(II) cadmium(II) and chromium(III) in a syringe filled

with 3-aminopropyltriethoxysilane supported on silica gel Anal Bioanal

Chem 374(2002)977-981

[100] CE Kinci and U Koklu Determination of vanadium manganese silver and

lead by graphite furnace atomic absorption spectrometry after

preconcentration on silica-gel modified with 3-aminopropyltriethoxysilane

Spectrochim Acta B Atomic Spectr 55 (2000) 1491-1495

[101] JGP Espinola SF Oliverira WES Lemus AG Souza C Airoldi and

JCA Moreira Chemisorption of Cu(II) and Co(II) chlorides and beta-

diketonates on silica gel functionalized with 3-aminopropyltrimethoxysilane

Colloids Surf A Physicochem Eng Aspects 166 (2000) 45-50

[102] H Lee and J Yi Removal of copper ions using functionalized mesoporous

silica Sep Sci Technol 36 (2001) 2433-2448

[103] F Sahin M Volkan AG Howard and OY Ataman Selective preshy

concentration of selenite from aqueous samples using mercapto-silica Talanta

60(2003) 1003-1009

32

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

[104] J Huang M Ye Y Qu L Chu R Chen Q He and D Xu Pb(II) removal

from aqueous media by EDTA-modified mesoporous silica SBA-15

JColloidal Interface Sci385 (2012) 137-146

[105] AK Kuswaha N Gupta and MC Chattopadhyaya Adsorption behavior of

lead onto a new class of functionalized silica gel Arabian J chem (2012) in

press DOIorg101016jarabjc201206010

33

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

r

CHAPTER 2

CHEMICALLY MODIFIED SILICA GEL WITH

THIOSALICYLIC ACID FOR REMOVAL OF Pb(II) Cu(II) and

Cr(III)

34

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

INTRODUCTION

Excessive release of heavy metals into the environment is a great threat to humans

animals and plants The heavy metals such as Pb(II) Hg(II) Ni(II) Cu(ll) Cd(II)

Zn(II) and Cr(III) are introduced in ecosystem through wastewaters originating from

metal plating mining activities smelting battery manufacture tanneries petroleum

refining paint manufacture pesticides pigment manufacture painting and

photographic industries etc [1-4] Among these Pb(II) Cu(II) and Cr(III) are common

contaminants of industrial wastewater These metal ions even at low concentration

have deteriorated water resources and drinking water They are easily accumulated in

the human body and thus causes a variety of diseases and disorders When the copper

is in excess in the body then a wide array of psychological and physiological

symptoms can develop that include Touretts syndrome schizophrenia mania

anemia etc [5 6] Extremely high copper levels can result in a psychotic break [6]

Cr(III) is an essential trace element that is involved in the metabolism of glucose and

fats [7] but can have large effect on ecological environment when present in large

amount [8] Pb(II) is a well known toxic metal ion and is considered as priority

pollutant Exposers to lead can have a wide range of effects on a childs development

and behaviour Blood lead levels less than 10|ig dL are associated with increase

behavioural effects delayed puberty and decreases in hearing cognitive performance

and postnatal growth or height [9 10] A study [11] showed that lifetime Pb(II)

exposure may increase the risk of developing cataracts In view of these it is required

to remove heavy metal ions from industrial wastewater for their subsequent safe

disposal The major techniques employed for heavy metal removal from industrial

wastewaters include precipitation reduction ion-exchange and adsorption

Adsorption is a well known separation method and now a days considered as one of

the efficient and economic methods for water decontamination applications The

advantage associated with this technology is that the adsorbents can be regenerated

by suitable desorption processes for multiple applicafions [12] Generally the

desorption processes are of low maintenance cost high efficiency and ease of

operation [13] Activated carbon [14 15] and a number of low cost adsorbents such as

Fava beans [16] tobacco stems [17] peanut husk charcoal fly ash and natural zeolites

[18] have been used for removal of heavy metal ions Some of these materials possess

35

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

low selectivity and low removal capacity Recently preparation of silica based

adsorbent has generated considerable interest owing to large surface area and well

modified surface properties Radi and coworkers [19] have synthesized amine-

modified silica that have been used for removal of Cu(II) from aqueous solutions

Literature review revealed that silica surface was chemically modified with 22-

dipyridylamine molecules [20] Aguado and coworkers [21] have prepared amino

functional mesoprous silica SBA-15 materials for effective removal of heavy metal

ions from wastewater Functionalization with amino groups has been carried out by

grafting and co-condensation methods Metal removal from aqueous solution has been

examined for Cu(II) Ni(II) Pb(II) Cd(II) and Zn(II)

This chapter reports the synthesis of thiosalicylic acid flinctionalized silica gel The

modified silica gel was characterized by FTIR TGA DTA and SEM with EDS The

modified silica gel was used as an adsorbent for removal of Pb(II) Cu(II) and Cr(III)

from aqueous solutions

EXPERIIMENTAL

Materials and Reagents

Silica gel (Merck India ) used for surface modification was 230-400 mesh with a

surface area of 550m g and 08 cm g pore volume Thiosalicylic acid and 3-

aminopropyltrimethoxysilane were obtained from SiscoChem Industries (Mumbai

India) and Alfa Aesar (England UK) respectively and used without further

purification Metal ions solutions for adsorption studies were prepared by dissolving

appropriate amount of metal salts such as CrClaHaO (Central Drug House PLtd

New Delhi India) Pb(N03)2 (Merck India) or CUSO45H2O (S D Fine Chem Ltd

Biosar India) in distilled water and standardized with standard methods [22] The pH

of the solution was adjusted to the desired value using HNO3 or NaOH solution

Preparation of silica gel-supported 3-aminopropyltrimethoxysilane (Si02-

APTMS)

Silica gel (50 g) was mechanically stirred with excess amount of IM HCl for 24 h

then filtered off and washed with distilled water until filtrate was neutralized

Acfivated silica gel was dried in an oven at 110 degC for 24 h Activated silica gel (5 g)

was transferred into a round bottom flask containing 25 ml toluene then 3 ml of 3-

aminopropyltrimethoxysilane was added drop wise in order to prevent self

36

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

polymerization with vigorous stirring followed by 015 ml glacial acetic acid and kept

for 12 h under continuous stirring at room temperature Then 015 ml glacial acetic

acid was added to the reaction mixture and refluxed at 60 C for 2 h The suspension

was filtered and the solid obtained was washed with excess amount of toluene and

ethanol Finally the modified adsorbent was dried in an oven at 80 degC for 8 h

Preparation of silica- supported thiosalicylic acid (Si02-APTMS-THSA)

SiOi-APTMS (20g) was added to 25 ml toluene Then thiosalicylic acid (05g)

dissolved in 10 ml ethanol was added to the reaction mixture and refluxed at 60 ^C for

8 h The yellow coloured solid was filtered and washed with excess amount of toluene

and ethanol Finally it was dried in an oven at 80 ^C for 8 h

Characterization

Infrared adsorpfion spectra of Si02 Si02-APTMS and SiOs-APTMS-THSA were

recorded with FTIR spectrophotometer (FT-IR Spectrophotometer Perkin Elmer

USA) using KBr disk method The thermal stability of the modified silica gel was

investigated by thermal analysis using DTG60H Shimadzu thermal analyzer at a rate

of 10 ^C min in nitrogen atmosphere The SEM images of the silica gel (SiOi) SiOi-

APTMS Si02-APTMS-THSA and SiOz-APTMS-THSA loaded with metal ion were

recorded using JEOL scarming electron microscope (Model No-JSM- 6510LV)

Batch Adsorption Studies

Adsorption experiments were conducted for the adsorption of Pb(II) Cu(ll) and

Cr(III) on the modified silica gel Si02-APTMS-THSA as a function of adsorbent

dose contact time temperature and initial metal ion concentration The experiment

was carried out in the pH range 1-7 initial Pb(II) ion concentrafion (20-100 mgL)

contact time (5-60 min) and temperature range (25-60 degC ) 02g of the adsorbent was

contacted with 20 ml of a given solution in a thermostated water bath for temperature

regulation At the end of the given contact time the solution was filtered and the

filtrate was analysed for the concentration of metal ion remaining in the aqueous

phase by atomic absorption spectrometer

The amount of the adsorbed metal ion onto the modified silica gel was calculated

using the equation

qe = (Co-Ce)Vm (1)

37

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Where qe (mgg) is the adsorption capacity of the modified silica for metal ion Co

(mgg) and Ce (mgL) are the initial and equilibrium metal ion concentrations in

solution respectively V (L) is the volume of solution used and m (g) is the mass of

adsorbent

RESULTS AND DISCUSION

Infrared spectroscopic studies

The IR spectrum of silica gel (Figurela) shows a broad band in the region 3600 -

3200 cm which is due to the Si-OH stretching vibration The adsorption band

appeaimg 2A W cm s assigned to the Si-O stretehiirig mcde Additionai barids aie

found at 801 cm and 467 cm Figure (21b) shows the IR spectrum of intermediate

ie aminopropyl modified silica gel The bands appearing at 3421 cm and 2934 cm

are assigned to -NH2 stretching and - CH2 stretching modes Moreover two bands at

1567 cm and 1412 cmare also observed These bands are assigned to C-N

stretching and C-H bending vibrations Figure (21c) shows the IR spectrum of Si02-

APTMS-THAS The peaks appearing at 2510 cm and 1633 cm belong to S-H and -

N-C=0 groups respectively [23] The above points confirm the functionalization of

silica gel with thiosalicylic acid The synthesis routes of the functionalized silica with

thiosalicylic acid are shown in Scheme 21

Thermal Analysis

The thermogravimetric curve (Fig 22) showed that the initial loss of mass of up to 97

degC is 585which corresponds to physically adsorbed water [24] The second loss of

mass (5217) occurred in the range 98 to 210 degC which is due to decomposition of

thiol group DTA curve also shows the same observation ie an endothermic peak

occurs in the same region The last stage of loss of mass of (1835) occurred in the

range 210 to 600 degC this loss in mass is due to the decomposition of remaining

organic groups anchored on the silica surface and condensation of silanol groups [25]

38

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

1-

58 55

50-

45-

401

20-

1JH

10

-O 4000

345310cm-1

3500

2raquo897cm-l

3000 2500

188134cm-1

2000

cm-1

l635 95cm-1

110023cm-1

1500

8mo0oiraquo-t

lt67 74cm-1

1000 SOiWOO

Figure 21 (a) IR Spectrum of activated silica gel (Si02)

39

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

50

4S-

40- 699 49OT-1

-ic 2137 16cm 1 ^^ 569 75011-1

H 793 28c~i 1 SS 30 |

2 C 456 36cn--1 34228cm-1 93lt3cm-i

20- 1567 67cfn-M12 27cm-1

10- 110-CScm-1

Figure 21 (b) IR spectrum of SiOi-APTMS

4000 3500 3000 2500 2000 1500 1000 50O40O cmraquo1

40

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

t -0

70

65

60

55

50

45

40

35

30

25

20

16-

10--4000

iV

3500

-6ci bull

^q-iT c mdash bull

a30o 2500 2000 cm-1

bullbullbull

15Claquo 1000

r

50C40C

Figure 21 (c) IR spectrum of SiOa-APTMS-THSA

41

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Step I

SKgt

OM OH OM

Hj(^

SI

gtraquoeurolt1 bivic OlVIr

raquobull

SIOj-AFTMS

IH

Step II

SiO-APTMS-THSA

Scheme 21 Synthesis route of formation of Si02-APTMS-THSA

42

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

TGA mg

SOOO

800O V-

40001

i

2 000 0 00 10000 20000 30000

Temp [CJ 4OO00 50000

DTA uV

2000

000

bull - mdash -20 00

1 - 4 0 0 0

60000

Figure 22 TGA and DTA curves of modified silica gel (Si02-APTMS-THSA)

43

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Scanning Electron Microscopic Studies

The SEM images of silica gel (SiOa) SiOa-APTMS SiOz-APTMS-THSA and metal

absorbed on SiOi-APTMS-THSA are shown in Figure 23 (a-d) The SEM image of

silica gel (Figure 23a) shows that the material is porous in nature but the particle size

is not regular in shape The morphological differences among the silica gel Si02-

APTMS and SiOa-APTMS-THSA in SEM images indicate that the flinctionalization

has taken place The reaction of metal ions which diffuse through the chaimels with

the functional groups of modified silica surface change the morphology of the final

product EDX spectra(Flgure 24a) confirms the loading of the thiol group on the

amino functionalized silica whereas Figure (24b) shows the adsorption of Pb(II)

Cu(ll) and Cr(II) on the thiol functionalized silica gel

44

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

bull -

^^A ^

i W ^ k

Figure 23 (a) SEM image of the activated Silica gel (Si02) (b) SEM image of the

Si02-APTMS (c) SEM image of the Si02-APTMS-THSA and (d) SEM image of

Si02-APTMS-THSA loaded with Pb(II) Cu(II) and Cr(III)

45

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

2 4 6 8 Ful Scale 7S4 cts Cursor 0000

Figure24 (a) EDX spectrum of Si02-APTMS-THSA

46

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Figure24 (b) EDX spectrum of Si02-APTMS-THSA loaded with Pb(II) Cu(II) and

Cr(III)

47

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Adsorption Studies

Parameters which influence the extent of adsorption such as pH initial metal ion

concentration contact time and temperature were investigated by batch method In

this study 02 g modified silica gel was equilibrated with 20 ml of metal ions (20-100

ppm) such as Pb(Il) Cu(ll) and Cr(IIl) for different time intervals The concentration

of metal ions remaining in the solution was determined by atomic absorption

spectrometer

Effect of pH

The adsorption behaviour of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was

examined in the pH range 1 - 7 The resuhs are presented in Figure (25) As can be

seen from the Figure that the uptake of Pb(Il) Cu(ll) and Cr(IlI) by the modified

material varies significantly as pH changes At pH lt 4 the uptake of all the metal ions

studied is lower since the pH of medium is not favourable for chelation of the metal

ion with the functional groups present on the surface of silica gel The maximum

sorption occurs at pH 4 and remains unchanged upto pH 7 At pH gt 7 the retention of

metal ions was not studied because of possible hydrolysis of metal ions Therefore

adsorption of all metal ions was studied at pH 4

Effect of contact time

The uptake of metal ions at pH 4 was studied as a function of contact time and the

results are shown in Figure 26 As can be seen from the figure that the uptake was

rapid in first 10 minute and then gradually increased upto 60 minute Therefore in the

present work 60 minute was chosen as equilibrium time

Effect of initial metal ion concentration

The adsorption of particular metal ion onto an adsorbent depends on the initial

concentration of metal ion in solution Keeping this in view the adsorption of Pb(II)

Cu(II) and Cr(III) onto the modified silica gel was studied as a function of initial

metal ion concentration and results are shown in Figure 27 The sorption capacity

increases with increase in concentration This is due to fact that at higher

concentration metal ions are available for binding to the surface sites of the adsorbent

48

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

25 n

2

1

05

(

fj^ ^^^^^^

1 1

) 2 4

PH

- bull -PMI I )

- B - r r d l l )

1 p --Cu(ll)

1

6

1

8

Figure 25 Effect of pH on adsorption of Pb(II) Cu(II) and Cr(III)

49

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Figure 26 Effect of contact time on adsorption of Pb(II) Cu(II) and Cr(III)

50

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Figure 27 Effect of initial metal ion concentration on the adsorption of Pb(n)

Cu(II) and Cr(III)

51

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Effect of temperature

Temperature has important effect on adsorption process The effect of temperature on

the adsorption of metal ions was studied in the range 25 - 60 C The resuhs are

shown in figure 28 It was found that the uptake increases with increase in

temperature This may be due to the increase of intra particle diffusion rate of the

metal ion into the interior sites of the sorbent

52

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Figure 28 Effect of temperature on the adsorption of Pb(II) Cu(II) and Cr(III)

53

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Adsorption Isotherm

The adsorption isotherm study was carried out at 25 C 40 degC 50 degC and 60 C

Adsorption isotherm indicates the partition of adsorbent between solution and

adsorbent at equilibrium Therefore for the designing of a sorption system to remove

the metal ion from the aqueous solution it is required to establish the most

appropriate correlation for the equilibrium curve In this study Langmuir and

Freundlich isotherm models have been tested for the removal of Pb(II) Cu(II) and

Cr(III) ions from the aqueous medium

Langmuir Isotherm

Langmuir isotherm describes the adsorption of adsorbate onto the surface of

adsorbent [26] This model is based on three assumptions (i) the adsorbate is strongly

attracted to the surface of the adsorbent (ii) the surface has fixed number of well

defined sites all sites are energetically equivalent and (iii) the maximum adsorpfion

occurs when only one layer of molecules is attached to the surface ie monolayer

adsorption The linearized form of Langmuir isotherm is represented as

C e q e = l ( q m b ) + Ceqm (2)

Where qe is the amount adsorbed per gram of adsorbent at equilibrium (mgg) Ce is

the equilibrium concentration (mgL) qm is monolayer (maximum) adsorption

capacity (mgg) and b is the Langmuir constant related to energy of adsorption

(Lmg) A linear plot of Ce qe against Ce suggests the applicability of the Langmuir

isotherm The maximum adsorption capacity qm and Langmuir constant can be

calculated from the slope and intercept of the linear plot In this study Ce qe vs Ce

was plotted for the adsorption of Pb(II) Cu(II) and Cr(III) at 25 degC 40 degC 50 C and

60 C respectively (Figure 29 a-c) Langmuir parameters were calculated and

summarized in Table 21 As can be seen from the table that the value of R is very

low which indicated non applicability of this model

54

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Figure 29 (a) Langmuir isotherm for Adsorption of Pb(II)

^^^aAzadLx

5gtflaquo-

55

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

3

25

05

0

6 8 10

CeltiiifL)

12 14

bull 25oC

bull 40 OC

ASOoC

X60oC

16

Figure 29 (b) Langmuir isotherm for Adsorption of Cu(II)

56

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

25

15

9

O 1

05

X bull 25oC

bull 40oC

ASOOC

bull 60 OC

6 8 10 12 14

Figure 29 (c) Langmuir isotherm for Adsorption of Cr(III)

57

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Table 21 Langmuir and Freundlich isotherm parameters for the adsorption of Pb(II)

Cu(II) and Cr(III) onto modified siUca gel (SiOa-APTMS-THSA)

Temperature

(V)

Pb(III)

25

40

50

60

Freundlich isotherm

kf

1513

2071

399

2600

parameters

n

1474

1605

1584

1506

R^

0957

0983

0987

0994

Langmuir isotherm

qm

15625

15625

15873

15625

parameters

b

0083

0123

0185

0193

R^

0434

0730

0975

0931

Cu(n)

25

40

50

60

Cr(III)

25

40

50

60

0220

0392

1207

0893

0453

0879

1999

1241

0755

0813

1116

1007

09115

1082

1422

1091

0974

0989

0996

0973

0967

0980

0997

0992

-10869

-1666

-4166

3448

-2941

111111

1754

-58823

-0029

-0028

0028

0023

-0016

0007

0116

-0013

0887

0876

0861

0029

0332

0065

0921

0126

58

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Freundlich Isotherm

The Freundlich isotherm [27] describes the heterogeneous system and gives an

expression encompassing the surface heterogeneity and the exponential distribution of

active sites and their energies The Freundlich isotherm is expressed by the equation

qe = KfCe (3)

The equation is conveniently used in the linear form as

logqe = logKf+lnlogCe (4)

Where qe is the amount of metal ion adsorbed per unit mass of adsorbent (mgg) at

equilibrium Ce is the equilibrium concentration of metal ion (mgL) Kf and n are

Freundlich isotherms constant related to adsorption capacity and adsorption intensity

respectively

In this study log qe against log Ce was plotted for Pb(II) Cu(II) and Cr(III) at 25 C

40 V 50 degC and 60 degC (Figure 210 a-c) The values of n and Kf were calculated from

the slope and intercept respectively The results are reported in Table 21 As can be

seen from the table that the values of R^ are falling in the range 0957-994 0973-

0996 and 0967-0997 for Pb(II) Cu(II) and Cr(III) respectively The higher value of

R indicated that the adsorption data obey the Freundlich isotherm

59

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

12

E

1 T -1 1 1 r-

-06 -04 -02 0 02 04 06 08

log ce (mgL)

bull 25oC

bull 40 oC

bull SOoC

x60oC

1 12

Figure 210 (a) Freundlich isotherm for Adsorption of Pb(II)

60

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Figure 210 (b) Freundlich isotherm for Adsorption of Cu(II)

61

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

12

4

bull02 02 04 06 08

bull 25oC

bull 40oC

ASOOC

X60oC

12

Figure 210 (c) Freundlich isotherm for Adsorption of Cr(III)

62

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Kinetic Study

Kinetic models have been exploited to test the experimental data and to find the

mechanism of adsorption and its potential rate controlling step In addition

information on the kinetics of metal ion uptake is required to select the optimum

conditions for full scale batch or continuous metal ion removal processes In this

study Pseudo-first-order and pseudo-second-order kinetic models have been used

Pseudo-first-order kinetic model

The pseudo-first-order kinetic model is based on assumption that the rate of uptake of

adsorbate with time is directly proportional to the amount of available active sites on

the adsorbent surface The differential equation is given as

dqtdt = k(qe-qt) (4)

Where qe and qt are the amount taken (mgg) at the equilibrium and timet

respectively ki is the pseudo-first-order adsorption rate constant (min) The

integration of equation (4) under boundary conditions t = 0 to t = t and qt= 0 to qt = qt

yields the equation

log(qe-qt) = logqe-kt2303 (5)

The log (qe-qt) vs t was plotted for the adsorpfion of Pb(II) Cu(II) and Cr(III) at 50 C

(Figure 211) The values of k] and qe were calculated from the slope and intercept

respectively The results are reported in Table 22

63

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

05 -

0

(

-05

or 1

-1 -O

-15

-2

-25

g

1 ^

i

bull^

1 1 1 1 1

^^^ 20 30 40 50 60

^~-~-s^^ y=-0019x +0002 ^ ^ -gt^ R = 0953

y = -0033X 4 0 0 4 7 ^ ^ ^ ^~^-~~~A R = 0964 ^ ^

y = -0009X -1435 - ^ R = 0989

Tiiiie(iiiiii)

1

70

bull Pb(il)

bull Cr(lll)

bull Cu(ll)

Figure 211 Pseudo-first-order kinetics of Pb(II) Cu(II) and Cr(III) adsorption onto

modified silica gel (Si02-APTMS-THSA)

64

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

lt t3

ffi H t5

2 H amp lt

(N

o bull 1-H

Ol ^ gt mdash ^ i ^

ltu bO c3 O

bull t-H

IZl

T3 D

ta ^ o e o c o

t mdash lt t -H

^ O T3

- i

ltU O

V i O

T3

o o en

o T3 3

OH

u

c o

o

-T3

o

I

-5

CO

C O

tti

u

B bull i-H

C3

5 1 M

^ S ^^ oa

~5) c

(N (N O O

0 0 as ON ON

o

T^ ^ t~~ ON

raquoo VO o ON

VO m ^ -

ON Tf 00 ON

o

ON ON VO bull mdash I

o

0 0 O 00

m 00 r H o ^ ON ON

O

o rn rlt-i

O ON ON

^

s B

1^ ou

B^

1

i n (N

CO

00 ON

ON 00 ON

O

o o

oo (N o o

ON

o o

i n iri

i n ON

O

NO O O

O o

o

oo

00

00 o

o

NO ON

o

gtn

^

ON in r-o o

o NO

ON

3 u

65

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Pseudo-second-order kinetic model

The pseudo-second-order kinetic model is expressed as

dqtdt = k2 (qe-qt)^ (6)

The integration under the boundary conditions t = 0 to t = t and qt = 0 to qt = qe the

above equation becomes

tq= lk2qe^+lqe (7)

Where k2 is the pseudo-second-order rate constant (1 mg min) The plot of tqtvs t

yields a straight line if pseudo-second-order kinetic model is obeyed The value of k2

can be calculated from the intercept of the plot To investigate the applicability of

pseudo second order kinetic model tqtagainst t was plotted for adsorption of Pb(II)

Cu(II) and Cr(III) at 50 degC (Figure 212) The values of K2 and R^ are reported in

Table 22

The applicability of the kinetic model was evaluated by calculating the percent

relative deviation (P) using the following equation

P = 100N [ Zqe (exp) - qe (sim) qe (exp)] (8)

Where qe (exp) is the experimental value of qe at any value of Ce qe (sim) is the

corresponding simulated value of qe and N is the number of observations Literature

survey revealed that when p lt 5 the simulated data fitted will with the

experimental data The value of P is given in Table 22 As can be seen from the table

that the qe (sim) value calculated from the pseudo-first-order kinetic model differed

appreciably from the experimental value Moreover the value of P is greater than

45 The qe (sim) value calculated from the pseudo-second-order kinetic model is

close to qe (exp) value The percent relative deviation (P) is less than 278

Moreover the correlation coefficient value (R^) is greater than 098 which is also very

high when compared with the pseudo-first-order kinetic model These suggest that the

adsorption of Pb(II) Cu(II) and Cr(III) onto Si02-APTMS-THSA is governed by the

pseudo-second-order kinetic model

66

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

120 n

100

80

^ 60 bulllaquoi

40 -

20 -

(

bull Pb(n)

bull Cr(ll)

bull Cu(ll)

1

) 50

bull

r

100

Time (min)

1

150 200

Figure 212 Pseudo second order kinetics of Pb(II) Cu(II) and Cr(III) adsorption

onto modified silica gel (SiOz-AFTMS-THSA)

67

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Thermodynamic Studies

Thermodynamic parameters such as Gibbs free energy change (AGdeg) (Jmole)

enthalpy change (AH ) (Jmole) and entropy change (AS ) (JKmole) for the

adsorption can be evaluated from the following equations [28-30]

Ko = Csolid Ciiquid (9)

AGdeg=-RTlnKo (10)

AGdeg = AHdeg-TASdeg (11)

lnKo=-AGdegRT (12)

lnKo=ASR-AHRT (13)

Where KQ is the equilibrium constant Csoiid is solid phase concentration at equilibrium

(mgg) Ctiquid is the equilibrium concentration in solution (mgL) T is absolute

temperature (K) and R is gas constant (8314 Jmole K) Plot of In KQ VS 1T is used to

found the values of AHdeg and ASdeg from the slope and intercept respectively (Figure

213) The calculated thermodynamic parameters are summarized in Table 23 The

negative values of AGdeg and positive values of AHdeg and ASdeg indicated that the

adsorption of Pb(II) Cu(II) and Cr(III) onto the modified silica gel was favourable

68

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

3 1

25

2

bull

1

05

u

^~i-~~~~-

1 1 1

000305 00031 000315 00032

y=-4261JJ+1592 R = 0999

y=-3334x 4 1266 gt--laquo ^ R = 0997

---l-- ^ ^ bull PNII)

A Cu(ll)

V=-3021x+1146 R^r 0980

1 i f 1 1

000325 00033 000335 00034 000345

1T

Figure 213 VontHoff plot for adsorption of Pb(II) Cu(II) and Cr(III)

69

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

lt

H I

GO

H lt

I

O C5

3 K3

o

o

s o o

U

03

3

OH

o c

amp o 13

(U

c2

o

XI

g

raquolaquo

^^^^ u o a ^

a lt

f^ fS f l

IT) l-H

f 1mdash1

ON ON

IT) 1 mdash I

f^

1mdash(

ON ON

e 2

1

ON in

ON

o 00

CO 00

ON

00

00 CN

irl ON

NO

(N 00

in

00 ON

NO 00 in

o

i n ltN o NO

ro m t ^ ^

^ o en -^ in ^

ON ON ro m

ON

00

NO

CO

NO

NO

oo

s

m in (N in

o

00 m m NO (N

in ON r-NO 00 (N NO

in

(N

(N in

in

o NO

ltN

m

o in

u U

H

70

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

Conclusion

In this study the surface of silica gel was modified with 3-

aminopropyltrimethoxysilane and then functionalized with thiosalicylic acid The

adsorbent was tested for the removal of Pb(II) Cu(II) and Cr(III) The operating

parameters such as pH contact time initial metal ion concentration and temperature

were studied to find the maximum efficiency for removal of Pb(II) Cu(II) and Cr(lll)

The Langmuir and Freundlich isotherm models were used for description of the

adsorption of Pb(II) Cu(II) and Cr(III) onto SiOi-AFTMS-THSA and isotherm

constant were evaluated Results indicated that the adsorption equilibrium data fitted

well Freundlich isotherm model The result shows that the pseudo second order

mechanism is predominant and the chemisorptions may be the rate controlling step

Negative Gibbs free energy values (AGdeg) indicate the feasibility and spontaneous

nature of the process Experiments clearly indicated that the SiOi-APTMS-THSA is

an effective adsorbent for the removal of higher concentration of Pb(II) Cu(II) and

Cr(III) from wastewater

71

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

characteristics Chin J Southwest InstNationalaties 34 (1998) 283

[9] M Nadeem R Nadeem H N Nadeem S S Shah Accumulation of lead

and cadmium in different organs of chicken Pak J Sci Res 57 (2005) 71-

73

[10] H A Godwin The biological chemistry of lead Current opinion in Chemical

Biology 5(2001)223-227

72

[11] DA Schaumberg F Mendes M Balaram MR Dana D Sparraw and H

Hu Accumulated lead expouse and risk of age related cataract in men

JAMA 292 (2004) 2750-2754

[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

[13] B Samiey C Cheng and J Wu Organic-Inorganic hybrid pokymers as

adsorbents for removal of heavy metal ions from solutions a reviw

Materials 7 (2014) 673- 726)

[14] AK Meena C Rajagopal Kiran and GK Mishra Removal of heavy metal

ions from aqueous solutions using chemically (Na2 S) treated granular

activated carbon as an adsorbent J Sci Ind Res 69 (2010) 449-453

[15] I Sharma SK Sharma and SS Sambi Cadmium and Chromium adsorption

on activated carbon Indean Chem Eng 56(2014) 97-105

[16] AM Etorki M El-Rais MT Mahabbis and NM Moussa Removal of

some heavy metals from wastewater by using of Fava beans Am J Anal

Chem 5(2014)225-234

[17] W Li L Zhang J Peng N Li S Zhang and S Guo Tobacco stems as a low

cost adsorbent for the removal of Pb(II) from wastewater Equilibrium and

kinetics studies Industrial Crops and Products 28 (2008) 294-302

[18] OEA Salam NA Reiada and MM Elshafei A study of the removal

characteristics of heavy metals from wastewater y low-cost adsorbents J

Adv Res 2 (2011) 297-303

[19] S Radi N Basbas S Tighadouini M Bacquet S Degoutin and F Cazier

New amine-modified silcas Synthesis characterization and its use in the

Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

(2013)108-116

[20] EG Vieira IV Soares NLD Filho NC da Silva EF Garcia AC

Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

73

REFERENCE

[1] U Forstner G T W William Metal Pollution in the Aquatic Environment

Springer-Verlag Berlin 1983

[2] P E Warwik I W Croudace A G Howard Solid-Phase extraction of

Technetium-Amine complexes onto Cig silica and its application to the

isolation of ^^Tc Anal Chem 72 (2000) 3960-3963

[3] K Karivelu K Thamaraiselvi and C Namasivayam Removal of heavy

metals from industrial wastewaters by adsorption onto activated carbon

prepared from an agricultural solid waste Bioresour Technol76 (2001a) 63-

65

[4] J Williams D Aderhold and GJ Edyvean Comparison between biosorbent

for the removal of metal ions from aqueous solutions Water Res 32 (1998)

216-224

[5] RGundogan B Acemioglu and MH Alma Copper (II) adsorption from

aqueous solution by herbaceous peat J Colloid Interface Sci 269 (2004)

303-309

[6] A Kamaria And W S W Ngha Isotherm kinetic and thermodynamic

studies of lead and copper uptake by H2SO4 modified chitosan Colloids Surf

B Biointerferences 73 (2009) 257-266

[7] Z Hubicki and D Kolodynskka Selective removal of heavy metal ions from

water and waste water using ion exchange method Intech

doiorg10577251040 (2012) 195

[8] M H Liu J S Zhang Y C Fang Y Deng An advanced Cr(III) selective

nanocomposite cation exchanger Synthesis characterization and sorption

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[12] N Rahman U Haseen and M Rashid Synthesis and characterization of

polyacralamide Zirconium (IV) iodate ion-exchanger Its applications for the

selective removal of Lead (II) from wastewater Arabian J Chem http

dxdoiorg1010I6jarabj 201306029

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adsorbents for removal of heavy metal ions from solutions a reviw

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Adv Res 2 (2011) 297-303

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Cu(II) removal from aqueous solutions Prog Nanotechnol Nanomater 2

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Bastos SD Perujo TT Ferreira AH Rosa and LF Fraceto

Preconcentration and determination of metal ions from Fuel methanol with

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