3

A final report on

 

SYNTHESIS AND PROPERTIES OF POLYMER BASED  

ION EXCHANGE MEMBRANE AND ITS APPLICATION IN  

ENVIRONMENTAL REMEDIATION 

By

Dr. JITHA KUNHIKRISHNAN M

Submitted to

University Grants Commission

South West Region

Bangalore

20th June 2019

4

Acknowledgement

I express my deep sense of gratitude to University Grants Commission for the financial assistance provided to this minor research project.

I am also thankful to Dr.Sivadasan Thirumangalath, The Principal, Sree Narayana College, Kannur for his encougement and co-operation.

I specially thank Dr. Anitha P.K., Head of the Department of Chemistry, Sree Narayana College, Kannur, and Dr.C. Reetha, The Former Head of the same, for helping me and providing the facilities.

I also thank all the faculty members of Dept. of Chemistry, Sree Narayana College, Kannur, for their kind support and co-operation.

My thanks are due to CWRDM-Calicut, Sealab-Aroor, NIT-Calicut and Nirmalagiri college -Koothuparamba for the assistance rendered for the analytical studies.

Finally, I thank my family members and all the near and dear ones for their limitless support and encouragement throughout the course of investigation.

Dr. Jitha Kunhikrishnan M

5

INDEX

1. Introduction 3

2. Review 10

3. Fabrication of zirconium tugstophosphate doped polymer 18 membrane and its application

3.1 Chemicals used 18

3.2 Characterization 18

3.3 Preparation of zirconium(IV)tugstophosphate doped membrane 19

3.4 Batch adsorption studies 20

3.5. Optimization of adsorption studies 21

3.6. Kinetics of adsorption 22

3.7. Potentiometric sensing of lead ion 25

3.8. Results and discussion

4. Fabrication of titanium dioxide doped polymer-

membrane and its application 36

4.1 Chemicals used 36

4.2 Preparation of titanium dioxide doped membrane 36

4.3 Physico- chemical characterization 36

4.4. Kinetics and thermodynamics of dye adsorption 37

4.5 Treatment of textile effluent waste 38

4.6 Results and discussion 38

5. References 48

6. List of tables 53

7. List of figures 54

8. Conclusion

6

1. INTRODUCTION

Ion exchange is a process in which ions of one substance are replaced by

similarly charged ions of another substance. In water softening, for example,

the hardness causing calcium and magnesium ions are replaced by hydrogen and

sodium ions by passing the hard water over an ion-exchange resin. The solid must

ofcourse contain ions of its own for the exchange to proceed rapidly and extensively

to be of practical value. The solid must have an open permeable molecular structure

so that ions and solvent molecules can move freely in and out. Many substances both

natural (e.g.: certain clay minerals) and artificial, have ion exchanging properties, but

for analytical work synthetic organic ion exchanger are chiefly of interest certain

inorganic materials e.g.: zirconyl phosphate, also possess useful ion exchange

capacities and have specialized application.

Ion exchange is one of the most important analytical techniques used widely for

separations involving closely related elements .The importance of this technique is

revealed from the large amount of literature accumulated during the last two decades.

Some of the book related on this area is those by Helfferich (1), Inczeddy (2), Marcus

and Kerts (3), Samuelson (4) and Riemann and Walton (5).

The phenomenon of ion exchange was first reported by two English agricultural

chemists in 1850.They proved that soil can remove potassium or ammonium ions

from water with the release of an equivalent amount of calcium and magnesium.

An important advance was made in 1935, when Adams and Holms (6)

published the first paper on the synthesis of ion exchange resins. This led to rapid

progress in research on the theoretical and practical aspects of ion exchange so that

1935 may said to mark the new beginning of ion exchange.

1.1 Ion exchange equilibrium

Ion exchange process may be represented by chemical equations. In general,

where A ion of valance ‘n’ and B ions of valance ‘z’ are exchanged on a cation

exchanger in contact with an electrolyte solution. The equation is as follows:

− + ⇆ − +

7

Where R is the equivalent amount of the ion exchange anion. The above equation

obeys the law of mass action and the thermodynamic equilibrium constant can be

derived. Applying the law of mass action to the equilibrium set up,

= ( × )( )

Where aA and aB are the activities of A and B ions measured in the liquid phase, and

arA and arB are the mean activities measured in the solid phase, K is the

thermodynamic equilibrium constant which solely depends on the temperature and not

on the change of activities.

The two quantities which are important from the point of view of separation are the

distribution coefficient Kd and the selectivity coefficient . Both can be

experimentally determined.

1.2. Theory of Ion exchange

Even now there is no fully satisfactory general theory concerning the operation of ion

exchangers and there are many questions which cannot be answered unambiguously.

The theories proposed are,

a) The double layer theory

b) The lattice exchange theory and

c) The Donnan membrane theory

According to double layer theory, an inner fixed layer is surrounded by a

diffuse and mobile outer layer of charges which owe their existence to absorbed ions.

They may be different from ions that are already present in the inner portion of the

colloidal particles. Donnan theory deals with unequal distribution of ions on both

sides of the membrane, one side contain an electrolyte, one of whose ions cannot –

penetrate the membrane. In ion exchange equilibrium, the interface between solid and

liquid phases may be considered as membranes. These theories are almost similar

since the law of electro-neutrality governs these laws. The only difference is in the

position and origin of exchange sites.

8

1.3. Types of Ion exchanger

The three important groups of ion exchanger are inorganic, natural organic base

and synthetic ion exchanger. Among inorganic ion exchangers, the aluminosilicates,

both natural and synthetic, are suitable for technical purposes. Zeolites are naturally

occurring anion exchanger .Aluminum, Iron (II) and zirconium hydroxide etc acts as

synthetic inorganic anion exchangers. Cellulose based ion exchangers containing

phosphoric, sulphonic acid and diethyl amine groups come under natural organic base

ion exchangers. Synthetic ion exchange resin consists of a large organic molecular

network to which active groups able to ionize are fixed. The active groups of cation

exchange resins can be phenolic hydroxyl(-OH),carboxyl(-COOH) or phosphoric

acid(H3PO4).While for anion exchange resins, the active groups are usually primary,

secondary, tertiary or quaternary basic groups. Ion exchanger in the liquid form is

known as liquid ion exchangers. The behavior of liquid ion exchangers is similar to

that of resin ion exchangers. In both techniques, exchange of ions of like sign occurs

between two immiscible liquid in contact with each other. Analogous to resin ion

exchangers, there are both liquid anion exchanger and liquid cation exchangers.

Liquid anion exchangers are mainly primary, secondary, tertiary amines or quaternary

ammonium salts of high molecular weight. The liquid cation exchangers are usually

phosphoric acid esters or carboxylic acids. Chelating ion exchange resins contain

various chelating groups attached to the resins matrix. Dimethylglyoxime,

iminodiacetic acid etc are the examples. An important feature of chelating ion

exchangers is greater selectivity of metal ions. The affinity of a particular metal ion

for a certain chelating resins depends mainly on the nature of the chelating groups and

the selectivity of the resin is based on the different stabilities of metal complex

formed on the resin under various pH conditions. However the exchange process in

chelating resin is slower than in the ordinary type of exchangers.

Ion exchange resins are polymers with cross-linking (connections between long

carbon chains in a polymer). The resin has active groups in the form of electrically

charged sites. At these sites, ions of opposite charge are attracted but may be replaced

by other ions depending on their relative concentrations and affinities for the sites.

Two key factors determine the effectiveness of a given ion exchange resin:

favorability of any given ion, and the number of active sites available for this

9

exchange. To maximize the active sites, significant surface areas are generally

desirable. The active sites are one of a few types of functional groups that can

exchange ions with either plus or minus charge. Frequently, the resins are cast in the

form of porous beads. The size of the particles also plays a role in the utility of the

resin. Smaller particles usually are more effective because of increased surface area

but cause large head losses that drive up pump equipment and energy costs.

Temperature and pH also affect the effectiveness of ion exchange, since pH is

inherently tied to the number of ions available for exchange, and temperature governs

the kinetics of the process. The rate-limiting step is not always the same, and

temperature's role is still not thoroughly understood.

For technical purposes thin plates or membranes are produced from ion

exchange materials. The main characteristic of ion exchange membrane in contrast

with conventional semi permeable membrane is that, they are selective for one type of

ion. The use of ion exchangers as ion selective electrodes is a new field in which

works are rapidly progressing.

1.4. Ion exchange membrane

Today, separation membranes have become essential materials not only in

industries, but also in day-to-day life. Thus, innumerable membranes have been

developed for the use in reverse osmosis, nanofiltration, ultra filtration,

microfiltration, pervaporation separation, electrodialysis and in medical use such as

artificial kidney .Among these membranes, ion-exchange membranes are one of the

advanced separation membranes. Basic applications of the ion-exchange membrane

process are based on the Donnan membrane equilibrium principle and have been paid

attention to solve two important environental problems: (i) recovery and enrichment

of valuable ions, and (ii) removal of undesirable ions from wastewater, especially to

extract toxic metal ions. Basically, the ion-exchange membranes separate cations from

anions and anions from cations, so they should have a high transport number for

counter ions. Such membranes with high transport number have the potential

applications in new field’s such as separation of ionic materials, mostly used in the

solutions containing multi-components, such as electrodialytic concentration of

seawater to produce sodium chloride, demineralization of saline water, desalination of

cheese whey, demineralization of sugarcane juice, etc. In some cases, specific ions

10

have been used industrially: monovalent selective ion exchange membranes and

proton selective ion-exchange membranes are important. Apart from these

applications, several trials have been carried out to be used as sensors such as

humidity sensor ,carbon monoxide sensor , drug sensor, carriers for enzymes, solid

polyelectrolyte’s, a carrier for functional materials, generation of photo voltage and

photocurrent, etc. The generation of photo voltage from anion exchange membranes is

a new phenomenon and might lead to a new application of the ion-exchange

membranes.

In the past, excellent review articles appeared on different aspects of ion-

exchange membranes. However, none of the articles was dedicated to compile the

different methods for the preparation of ion-exchange membranes. Most commercial

ion-exchange membranes can be divided, according to their structure and preparation

procedure, into two major categories, either homogeneous or heterogeneous.

According to Molau, depending on the degree of heterogeneity of the ion-exchange

membranes, they can be divided into the following types: (a) homogeneous ion-

exchange membranes, (b) inter polymer membranes, (c) micro heterogeneous graft-

and block-polymer membranes, (d) snake-in-the-cage ion-exchange membranes and

(e) heterogeneous ion-exchange membranes. All the intermediate forms are

considered as the polymer blends from the viewpoint of macromolecular chemistry

1.5. Classification of Ion exchange membranes

There are different methods of classifying ion-exchange membranes:

Classification based on function is clear; ion-exchange membranes have an electrical

charge, which is positive or negative. The function of ion-exchange membranes is

determined from the species of the charge of the ion-exchange groups fixed in the

membranes and their distribution:

1. Cation exchange membranes, in which cation exchange groups (negatively

charged) exist and cations selectively permeate through the membranes.

2. Anion exchange membranes, in which anion exchange groups (positively charged)

exist and anions selectively permeate through the membranes.

3. Amphoteric ion exchange membranes, in which both cation and anion exchange

groups exist at random throughout the membranes.

4. Bipolar ion-exchange membranes which have a cation exchange membrane layer

11

and anion exchange membrane layer (bilayer membranes).

5. Mosaic ion exchange membranes, in which domains having cation exchange

groups exist over cross-sections of the membranes and domains of anion exchange

groups also exist.

Basically, three basic properties are required for ion-exchange membranes:

(1) to exist as a membrane;

(2) to be insoluble in solvents; and

(3) to have fixed charges in the membrane.

To achieve these properties, many methods have been developed: after ion exchange

groups are introduced in a polymer, the polymer is changed into an insoluble

membrane; a polymeric membrane is produced and ion-exchange groups are then

Introduced in the membrane, etc.

1.6. Ion exchange properties

1.6.1 Ion exchange capacity

Ion exchange capacity of an exchanger means the total amount of the

exchangeable ions of unit weight. Salt splitting capacity is measured when, for

instance the amount of sodium ions absorbed by the cation exchange resin in the

hydrogen form, from a sodium chloride solution, and for anion exchange it is the

amount of base from salt by unit weight or unit volume of the hydroxyl form anion

exchanger. For mono functional strongly basic or acidic exchanger, the salt splitting

capacity is identical with the total capacity.

The apparent capacity may differ from the theoretical values, when the ions

examined cannot occupy every exchange site because of their greater size. The

apparent capacity called the break through capacity is not a constant and it depends on

the condition under which it is determined.

1.6.2. Disitribution coefficients

It is the ratio of concentrations of the substance measured in the exchanger and

in the solution phase respectively. The distribution coefficient Kd is a measure of the

extent to which an ion is removed from solution and is defined as the number of

12

milliequivalent of an ion absorbed per gram of the exchanger divided by the number

of milliequivalent of that ion per ml remaining in the solution at equilibrium.

13

2.REVIEW

The last year or so have seen a great upsurge in the researches on synthetic

inorganic ion exchangers as they are stable towards heat and radiation. The main

emphasis has been given to the development of new materials possessing chemical

stability, reproducibility in ion exchange behavior and selectivity for certain metal

ions are important from analytical point of view. Important advances in this field have

been reviewed by a number of workers at various stages of its development.

According to Vesely and Pekarek (7) synthetic inorganic ion exchangers can be

classified in to following categories,

(1) Oxides and hydrous oxides.

(2) Heteropoly acid salts.

(3) Acid salts of polyvalent metals.

(4) Aluminosilicates synthetic zeolites and clay.

(5) Insoluble hydrated metal ferro and ferricyanide.

(6) Miscellaneous.

2.1. Oxides and Hydrous oxides

In 1972 Vesely and Pekarek (7) have given an exhaustive survey covering the

preparation, properties, uses and theory of hydrous oxides of bivalent, trivalent,

quadrivalent, quinquivalent and sexivalent ions. De and Sen (8) gave synthesis,

properties and analytical application of the hydrated oxides of metals such as Al, Si,

Sn, Zr, Ce and Tungsten oxides. Hydrous alumina sample are constantly used in

analytical separation as adsorbent and desorbent.

2.2 Acid salts of polyvalent metals

Vesely and Pekarek (7) De and Sen (8) have given details of various acidic salts

of polyvalent metals having different anionic part such as phosphate, arsenate,

antimonite, selenate, ferrocyanides, molybdate, tungstate etc. In 1980 Walton(9) has

reviewed bismuth tungstate, cobalt arsenate, and antimonates of thorium and nickel.

14

Industrial application of ion exchangers, ways of increasing efficiency of ion

exchange method for mixture separation, substance purification and preparation,

characteristics and properties of group(IV) acid salt as ion exchangers have been

discussed. Ruvarac and Howe(10), Clearfield(11), Besse(12), Garicia(13),

Laginestra,(14) Alberti(15) have discussed the catalytic properties and application of

ion exchangers and super ionic conductivity in cubic potassium- antimonate(V),

zirconium phosphate and exchange of alkali metals, thermal, redox and catalytic

characterization of inorganic ion exchange membrane and recent trends in inorganic

ion exchangers.

A new exchanger thorium tellurite act as a cation exchanger in alkaline medium

and anion exchanger in acidic medium another thorium based ion exchanger thorium

iodate was synthesized and characterized by C.Janardanan and Jitha (16). It was found

to be selective towards Pb (II).

Chromatographic and proton conduction behavior of 44 metal ions on thin

layers of stannic phosphate have been described. Selectivities of alkali metals on

stannic antimonate, prediction of Ksp from Rf values and of thin layer chromatography

of 47 metal ions in H2O-HCl system in stannic pyrophosphate and poly phosphate

were synthesized and planar chromatography of 36 metal ions on tin(IV)phosphate,

tin(IV)molybdate and tin(IV)tungstate impregnated papers were carried out.

Separation follows the order tin (IV) molybdate > tin (IV) tungstate > Tin (IV)

phosphate.

Cerium (IV) tellurite was prepared and characterized as a new inorganic cation

exchanger by Nabi et al(17). Ceric phosphate was used in the separation of carrier

free Bismuth-210 from Lead-210, Yttrium-90 from Strontium-90.Thin layer

chromatography of ten previous metal ions and separation of Zn (II), Cd (II), and Co

(II) on Cerium metaphosphate were conducted. Cerium phosphate was characterized

and synthesized, by Nilchi et.al (18).Cerium (IV) selenite, cerium (IV) arsenite,

cerium (IV) vanadate etc were extensively studied as ion exchangers by Hussein(19),

C.Janardanan(20) and their coworkers. Study of selectivity of certain metal ions Cs

(I), Sr (II), Co (II) etc. and kinetic study of alkali metals on Ceric antimonate have

been reported. Cerium silicate was synthesized and used by Maragch for the sorption

studies of radinuclei on it.

15

Varshney and his co-workers conducted cation exchange study, effect of

gamma-irradiation on ion exchange behavior and separations on thermally stable

phase of antimonysilicate. A new exchanger antimony(V)tungstate was synthesized

and was used to remove chromium(VI), mercury(VI), lead(II) etc. C.Janardanan(20)

and co-workers synthesized many antimony based exchangers such as

antimony(III)arsenate, antimony(III)molybdate, antimony(III)vanadate,

antimony(III)tungstate, antimony(III)selenite and explored their ion exchange

properties.

Bismuth antimonate was synthesized and its ion exchange properties were

extensively studied by Janardanan et.al (20) Bismuth tungstate was used as an

absorbent for thin layer chromatography of organic acid by Kulshrestha et.al (21)

Abou Mesalam et.al (22) studied the retention behavior of Nickel, Copper, Cadmium

and Zinc ions from aqueous solution on silicotitanate and silicoantimonite.

Silver ion selective Lithium titanium phosphate glass-ceramic cation exchanger

was synthesized and latter was applied to the bacteriostatic materials. Ion exchange

properties of Tin(IV) iodate were studied by Janardanan et.al(20) and separation of

Pb(II) and Cu(II) from industrial waste was successfully carried out on it.

Thorium phosphosilicate – a new mercury selective ion exchanger was

synthesized and the effect of gamma irradiation on its ion exchange property was

reported.

Lead selective cerium (IV) phosphomolybdate and antimony (III)

molybdotungstate were studied in detail by Janardanan et.al (20). They also made a

comparative study of the ion exchange property of antimony (III) tungstoselenite with

antimony (III) tungstate and antimony (III) tungstovanadate.

Titanium(IV)arsenophosphate,Titanium(IV)tungstoarsenate,Titanium(IV)molyb

doarsene, Titanium(IV)vanadophosphate were synthesized and characterized.

Titanium (IV) molybdoarsenate has been used for the separation of Pb (II) and Hg (II)

from lanthanum and cerium.Titanium tungstopyrophosphate, Titanium

tungstophosphate and Titanium tungstosilicates were prepared by Zhang (23) et.al and

Siddiqi et.al (24).The latter conducted the separation of methylamine from ethylamine

by GC on a column packed with Titanium (IV) tungstophosphate.

16

2.3. Ion exchange membrane

Traditionally, ion exchange membranes are classified into anion exchange

membranes and cation exchange membranes depending on the type of ionic groups

attached to the membrane matrix. Cation exchange membranes contain negatively

charged groups, such as –SO3−, –COO−, –PO3

2−,–PO3H−, –C6H4O

−, etc., fixed to the

membrane backbone and allow the passage of cations but reject anions. While anion

exchange membranes contains positively charged groups, such as –NH3+, –NRH2

+, –

NR2H+, –NR3

+, –PR3+,–SR2

+, etc., fixed to the membrane backbone and allow the

passage of anions but reject cations (25,26). According to the connection way of

charge groups to the matrix or their chemical structure, ion exchange membranes can

be further classified into homogenous and heterogeneous membranes, in which the

charged groups are chemically bonded to or physically mixed with the membrane

matrix, respectively.

However, most of the practical ion exchange membranes are rather homogenous and

composed of either hydrocarbon or fluorocarbon polymer films hosting the ionic

groups (27)

The development of ion exchange membrane-based process began in 1890 with the

work of Ostwald (28) who studied the properties of semi permeable membranes and

discovered that a membrane can be impermeable for any electrolyte if it is

impermeable either for its cation or its anion. To illustrate this, the so-called

“membrane potential” at the boundary between a membrane and its surrounding

solution was postulated as a consequence of the difference in concentration. In 1911,

Donnan (29) confirmed the existence of such boundary and developed a mathematical

equation describing the concentration equilibrium, which resulted in the so-called

17

“Donnan exclusion potential”. However, the actual basic studies related ion exchange

membranes were firstly begun in 1925 and carried out by Michaelis and Fujita with

the homogeneous, weak acid collodium membranes (30). In 1930s, Sollner presented

the idea of a charge-mosaic membrane or amphoteric membrane containing both

negatively and positively charged ion exchange groups and showed distinctive ion

transport phenomena (31). Around 1940, interest in industrial applications led to the

development of synthetic ion exchange membrane on the basis of phenol-

formaldehyde-polycondensation(32).Simultaneously, Meyer and Strauss proposed an

electrodialysis process in which anion exchange and cation exchange membranes

were arranged in alternating series to form many parallel solution compartments

between two electrodes (33).It was hard to go into the industrial implications because

commercial ion exchange membranes with excellent properties especially low electric

resistance were still not available at that time. With the development of stable, highly

selective ion exchange membrane of low electric resistance in1950 by Juda and

McRae of Ionics Inc. (34)and Winger et al. at Rohm in 1953 (35), electrodialysis

based on ion exchange membranes rapidly became an industrial process for

demineralizing and concentrating electrolyte solutions. Since then, both ion exchange

membranes and electrodialysis have been greatly improved and widely used in many

fields. For example, in 1960s, first salt production from sea water was realized by

Asahi Co. with monovalent ion perm selective membranes (36); in 1969, the

invention of electrodialysis reversal (EDR) realized long-term run without salt

precipitation or deposition on both membranes and electrodes (37); in 1970s, a

chemically stable cation exchange membrane based on sulfonated polytetra-

fluorethylene was first developed by Dupont as Nafion, leading to a large scale use of

this membrane in the chlor-alkali production industry and energy storage or

18

conversion system (fuel cell) (38); simultaneously, a composition of cation exchange

layer and an anion exchange layer into a bipolar membrane in 1976 by Chlandaet al.

(39) brings many novelty in electro dialysis applications today (40). Also, stimulated

by the development of new ion exchange membranes with better selectivity, lower

electrical resistance and improved thermal, chemical and mechanical properties, other

applications of ion exchange membranes apart from the initial desalination of

brackish water have recently gained a broader interest in food, drug, chemical process

industry as well as biotechnology and waste water treatment nowadays (40-47).

Apart from polymeric ion exchange membranes, an ion exchange membrane can also

be prepared from inorganic material, such as zeolites, betonite or phosphate salts (48-

50).However, these membranes are rather unimportant due to their high cost and other

disadvantages, such as relative bad electrochemical properties and too large pores

though they can undergo higher temperatures than organic membranes(51). It can be

expected that ion exchange membranes prepared from polymers can possess both

chemical stability and excellent conductivity if the membranes were incorporated into

inorganic components, such as silica. So inorganic–organic ion exchange membrane

were development in late of 1990s by sol–gel for applications in severe conditions,

such as higher temperature and strongly oxidizing circumstances (51–53). Thus, till

now, various ion exchange membranes including inorganic–organic (hybrid)ion

exchange membranes, amphoteric ion exchange membranes, mosaic ion exchange

membranes, bipolar membranes(ion exchange composite membranes) are available

.Though ion exchange membranes and the related processes has received

multidiscipline attention in both theoretical investigations and industrial applications

nowadays, a more recently informative review including all the ion exchange

membrane types and synthesis or novel ion exchange membrane-based processes is

19

still insufficient except some reviews on specific aspects, such as modifications of ion

exchange membranes (54,55). Electro-catalytic membrane reactors (56), radiation-

induced graft copolymerization for ion exchange membrane preparation (57,58), ion

exchange membrane applications (44) or bipolar membrane process and applications

in environmental protection (47) and in food industry (48). Furthermore, ion exchange

membrane related processes are gradually considered less important than pressure-

driven membrane processes, such as RO due to the commercial interests. But they are

actually indispensable for separation of ionic species, especially in environmental

protection and clean production and in many applications, ion exchange membrane-

related processes are in direct competition with other separation techniques, such as

distillation, ion exchange and various chromatographic procedures. Therefore, to

awaken researcher’s interest in this field and also to understand the present states ion

exchange membrane research, this review is to give a summary of what have been

accomplished in ion exchange membranes and development of novel ion exchange

membrane processes.

2.4. Membrane Adsorption Technology

Membrane separation has been increasingly used recently for the treatment of

inorganic effluent due to its convenient operation. Membrane adsorbent technology

is a membrane integration technology that was developed in the mid-1980s

.(49)Adsorption is a mass transfer process by which a substance is transferred from

the liquid phase to the surface of a solid, and becomes bound by physical and/or

chemical interactions. The heavy metal ions in the aqueous solution can be captured

by the adsorbent though the physical or chemical adsorption. Generally, chemical

adsorption is more popular for heavy metal removal because it has stronger

interactions and higher adsorption capacity towards heavy metals. The special

20

functional groups on the surface of the adsorbents provide significant interactions

with heavy metals, resulting in the adsorptive separation of heavy metals from

water.

Adsorption is a very significantly economic, convenient and easy operation

technique. It shows high metal removal efficiency and is applied as a quick method

for all types of waste water treatment. A membrane adsorbent is made by

connecting functional groups to the surface and pore wall of polymer membranes;

the target pollutants are selectively adsorbed to the functional group. The membrane

adsorbent effectively combines the filtration performance of the membrane. When

the contaminated water flows through the membrane, the functional active binding

sites will combine with the target pollutants to remove contaminants from drinking

water with a high adsorption rate and capacity because of the very short contact

distance at a submicron-scale level between the target pollutants to the adsorbed

active binding site of the membrane adsorbents ( 50).

21

3. FABRICATION OF ZIRCONIUM(IV) TUNGSTOPHOSPHATE

DOPED POLYMER MEMBRANE AND ITS APPLICATION

3.1 Chemicals used :

Poly styrene sulphonic acid, poly vinyl alcohol, and maleic acid used for the

preparation of membrane were of analytical grade and was purchased from Alfa aeser.

Salts of heavy metals such as lead, copper, cadmium, mercury, cobalt etc. were from

Loba chemie. Zirconium oxy chloride, sodium tungstate, sodium phosphate etc were

from Merck.

3.2. Preparation of Zirconium(IV)tungstophosphate doped

polymer- membrane

3.2.1. Preparation of the ion exchanger.

Zirconium tunsgstophosphate (ZWP) was prepared by mixing desired

concentration of zirconium oxychloride to a mixture of solution of sodium tungstate

and sodium phosphate. The slurry obtained was kept overnight and filtered. The

exchanger was converted into H+ form by transferring it into 1.0M HCL in a 100 ml

beaker and shaken occasionally. It was filtered , washed was then dried at room

temperature.

3.2.2. Fabrication of membrane.

Membrane of different compositions were made by mixing polystyrene

sulphonic acid, poly vinyl alcohol and ZWP gel, in different proportions. Maleic acid

was added as a cross-linker.

A definite amount of poly vinyl alcohol(PVA) dissolved in hot water was

boiled with maleic acid in dil.H2SO4. To this poly styrenesulphonic acid(PSSA)

dissolved in distilled water was added carefully and heated. Zirconium

tungstophosphate suspended in distilled water was then slowly added to the above

mixture in drop wise manner and homogenized using vortex mixer.

Different composition membranes were prepared by mixing different ratios of

the components and it was spin coated on a Table - Top Spin-Coating Unit (Spektron

22

Instruments).(Fig.2)To get thick membranes mutliple layer coating was done.

Different samples were analysed for their maximum performance.

3.3. Physico-chemical Charcterisation

3.3.1. Instrumental Analysis:

Thermal stability (TGA) of PVA- PSSA-ZWP membrane was determined using

NETZSCH STA 449F5 Thermogravimetric analyzer under N2 atmosphere. Samples

were heated up to 900oC at the rate of 30oC/min. X-ray diffraction (XRD) is used to

study the crystal structure of prepared composite membrane. The structural analysis

was performed using X-ray diffractometer (Rigaku Miniflex 600) equipped with

CuKα radiation (λ= 1.54056A°) at 2θ angles between 5° and 80°. Mechanical strength

was measured using Universal testing machine.

3.3.2. Determination of Ion exchange capacity(IEC) of the ion exchanger.

The total ion exchange capacity of the exchanger was determined as follows.

1.0g of the exchanger was taken in H+ form in a 100 ml beaker. It was then

equilibrated with 20 ml 1.0 M NaCl solution for 24 hours. The solution was decanted

into conical flask, diluted to 50 ml. The hydrogen ion eluted from the exchanger was

determined titrimetrically with standard NaOH. From the titre value the ion exchange

capacity of the exchanger was determined using the following equation: IEC = (Volume of NaOH × Molarity of NaOH)(Weight of exchanger taken) 3.3.3. Determination of temperature stability

Several 1.0 g portions of the sample were heated at various temperatures in air

oven for 3h and the ion exchange capacities were determined by usual process after

cooling to the room temperature.

3.3.4. Determination of percentage water uptake and IEC of the membrane

For the water uptake measurement, a sample of the dry membranes were

weighed and immersed in distilled water for 24 hours, then excess water was removed

23

with absorbent paper and the wet sample was weighed. The water uptake was

calculated according to the following equation.

% Water uptake = (Ww − Wd)Wd × 100

Where Ww is the wet sample weight and Wd is the dry sample weight.

3.4. Batch adsorption studies of heavy metal ion on the

membrane

For adsorption studies standard solutions of Ni(II), Co(II), Cd(II), Pb(II) and

Cu(II) were prepared carefully by dissolving the desired amount of respective metal

nitrate salt.

3.4.1 Adsorption procedure

The adsorption equilibrium experiments of Ni(II), Co(II), Pb(II), Cu(II), and

Hg(II) were performed using a batch process to determine the amount of metal ion

adsorbed.

Membrane samples were equilibrated in a series of aqueous solution of

different metal ions. The solutions were kept overnight with intermediate shaking.

The membrane samples were then removed and the concentrations of metal ions in

the remaining solutions were determined using AAS (Agilent technologies). The

amount of metal ions adsorbed per unit mass of the adsorbent and the percentage of

adsorbed metal ions were obtained using equations given below.

qe =

VW

CeCo , where q is the amount of adsorbed metal ion at

equilibrium in mg/g. It is called metal adsorption capacity. V is the volume of the

adsorption medium, C0 is the initial metal ion concentration in mg/L. Ce is the

equilibrium metal ion concentration in mg/L and W is the dry weight of the

membrane in grams.

24

% adsorbed metal ion =Co

CfCo ,where, Cf is the final metal ion concentrations in

adsorption medium in mg/L.

3.5. Optimization of adsorption studies on the membrane

The studies were optimized for maximum sorption under different conditions

like effect of initial feed concentration, effect of pH, effect of membrane thickness.

Studies were also carried out to find the selectivity of membrane in presence of

different metal ions.

3.5.1. Effect of initial feed concentration on adsorption

Different initial concentration of the metal ions for which the membrane

showed higher affinity were prepared and equilibrated. The %adsorption were

determined for different initial concentrations.

3.5.2. Effect of membrane thickness on the adsorption percentage

Membrane of different weights were prepared by mixing the components in

same proportion ratios. The membrane samples of different thickness were then

equilibrated with metal ion solution and % adsorption for different samples were

calculated.

3.5.3. Effect of sorption medium pH

PH dependence of metal ion adsorption was performed by equilibrating

adsorbed samples in a series of solutions of different pH. The pH of the solution was

adjusted to a desired value by adding 1M HNO3 and 1M NaOH solution and noted

using Cole parmer pH meter(model: P200).

3.5.4. Selectivity studies

Affinity of membrane towards a particular metal ion in presence of other metals

was determined. This was done by equilibrating mixture solution of different metal

ions.

25

3.6. Kinetics of adsorption

Lagergren's pseudo first order and Ho's pseudo second order kinetic models were used

to investigate the mechanism of adsorption process.

Lagergren's equation can be expressed as

= k1(qe-qt)

where k1 is the pseudo first order adsorption rate constant.

by integrating above equation, for the condition that t=0 to t=t and qt=0 to qt = qt.

Therefore the linear form of equation obtained become,

ln(qe-qt) = lnqe - k1t ............................(1)

log(qe-qt) = logqe - . ..............................(2)

where qe and qt are the amount adsorbed at equilibrium, at time ‘t’ in minutes.

when log(qe-qt) is plotted against t, straight line is obtained. The slope gives the value

of rate constant k1.

Ho's pseudo second order equation can be expressed as

= k2(qe-qt)2 .............................(3)

where k2 is the pseudo second order rate constant.

by integrating equation (3) for the condition t=0 to t=t and qt=0 to qt = qt. therefore the

linear form of equation become,

= +

3.6.1. Adsorption isotherm

Langmuir, Freundlich, Dubinin-Radushkevich (D-R), Temkin isotherm models were

used to plot adsorption isotherms, which express the equilibrium relationship between

adsorbent and adsorbate (51).

Langmuir adsorption

26

Langmuir adsorption assumes monolayer adsorption in which the extent of adsorption

takes place on the surface of solid and is represented as,

= + (52)

Ce (mg/L) and qe (mg/L) are the equilibrium concentration and equilibrium adsorption

capacity. qm and KL are langmuir constants related to adsorption capacity (mg/g) and

energy of adsorption (L/g) respectively. Plot of Vs Ce gives straight line with slope

and intercept . The important characteristics of langmuir isotherm can be expressed in terms of RL, a

dimensionless constant, separation factor and can be written as,

= 11 + Co

where Co (mg/L) is the initial concentration of adsorbate.

According to the value of RL, four possibilities are there, RL>1.0 for Unfavourable

adsorption, RL=1.0 for Linear adsorption, 1>RL>0 for Favourable adsorption and

RL=0 for Irreversible adsorption (52,53).

Freundlich adsorption isotherm

Freundlich adsorption isotherm assumes multilayer adsorption and it is used to

describe the adsorption characteristics for the heterogeneous surface (54). The

logarithmic form of freundlich adsorption isotherm is written as

logqe = logKF + logCe (55)

Where qe is the amount of adsorbate per unit mass of adsorbant (mg/g). Ce is the

equilibrium concentration of adsorbate (mg/l). n and KF are Freundlich constants. Plot

of logqe Vs logCe gives a straight line with slope , which is ranging between 0 and 1.

It is a measure of not only surface homogeneity but also measure of adsorption

intensity. If the value of is closer to zero, it indicates the surface become more

heterogeneous. Value of below 1 indicates a normal langmuir isotherm while

above 1 indicates co-operative adsorption.

27

Dubinin-Radushkevich isotherm

It is generally used to express the adsorption behaviour on the heterogeneous surface

and their linear form is expressed as

lnqe = lnqs -Kad �2

where qe is the amount of adsorbate (mg/g), qs is the monolayer adsorption capacity

(mg/g), � is the polanyi potential, kad is the Dubinin-Radushkevich isotherm constant

(mol2/KJ2) related to mean free energy of adsorption. ie

E = 1/(√−2 )

B is the isotherm constant. If E value is in between 8 and 16 KJ/mol, adsorption

mechanism follows chemical adsorption and E<8 KJ/mol indicates that adsorption

mechanism is physical in nature [14]. Polanyi potential can be expressed as,

ℇ = 1 + 1 Where R is the gas constant (J/K/mol) and T is the absolute temperature.

The plot of lnqe Vs �2 gives a straight line with negative slope –Kad and intercept of

lnqs. The values of Kad and qs will be obtained.

Temkin isotherm

It expresses the effect of adsorbent - adsorbate interaction. By ignoring extremely low

and large value of concentration, this model assumes the heat of adsorption of

molecule decreases linearly with coverage due to adsorbate - adsorbent interaction.

Temkin isotherm can be written as,

= ( ) Here = B

Where R is the universal gas constant (8.314J/K/mol), T is the temperature at 298K, b

is the Temkin isotherm constant, A is the equilibrium binding constant (L/g). B is the

constant related to heat of adsorption (J/mol). The plot of qe against lnCe gives the line

with slope and intercept lnA.

28

3.7.Potentiometric sensing of lead ion using the membrane.

3.7.1. Preparation of ion selective electrode:

The prepared membrane was fixed to one end of a glass tube of diameter 1.5cm.

Then it was activated with 0.1M lead ion solution for 24hrs.

3.7.2. Calibration of the ion selective electrode:

SCE was used as internal reference electrode for the ion selective electrode. It

was then coupled with another SCE, the whole unit was then immersed in test

solution. EMFs were measured for varying lead ion concentration using a digital

potentiometer (Scientific Tech., model: ST DPS-01)

3.8 Result and discussions

Various samples of zirconium tungstophosphate obtained were white in

colour. The sample having higher ion exchange capacity (0.80meq/g) was used for

systematic study (Table1). The exchanger was found to be stable in 1.0 M mineral

acid and 1.0M salt solution.

Fig 1: PVA- PSSA- ZPW Membrane

29

Table 1: Preparation conditions and ion exchange capacities of various samples

The Na+ ion exchange capacity of zirconium tungstophosphate at room

temperature was found to be 0.80meq/g. The effect of heating on the ion exchange

capacity shows an abrupt decrease on ion exchange from 200° C (Table.2)

Temperature (℃) Duration (hr) Na+ I.E.C

50 3 0.77

100 3 0.70

200 3 0.60

300 3 0.25

400

3 0.15

Table 2: Effect of temperature on the ion exchange capacity of the exchanger

A stable zirconium tungstophosphate doped poly-vinyl alcohol-polystyrene

sulphonic acid membrane was obtained using spin coater (Fig.2). Sample-3 having

high IEC was used for futher studies.(Table.3). The membrane was found to be stable

in 1M HCl and NaOH.

Sample

No

Molar Ratio Volume

Ratio

pH Appearance I.E.C

(meq/g) Zr2+ WO3- PO42-

1

2

3

0.1

0.2

0.05

0.05

0.2

0.05

0.05

0.2

0.05

1:1:1

1:1:1

1:1:1

1

1

1

White

amorphous

solid

0.60

0.80

0.35

30

Fig 2: Spin coating unit with IR currer

Sample

No:

Weight % of RPM

TemperatureOC

PSSA PVA ZWP

1 50 40 10 5000 45

2 50 45 5 5000 60

3 40 50 10 10000 60

Table 3: Spin coating parameters and composition of different membrane samples

5 10 15 20 25 30 35 40 45 50

0

200

400

600

800

1000

1200

1400

Inte

ns

ity

(a

.u)

(degree)

Fig 3: XRD data Fig 4: TG curve

31

Fig 5: IR spectrum

XRD data shows a crystalline nature for the polymer membrane,this may be mainly

attributted to the presence of ZWP.(Fig.3)

The broad strong peak at 3231cm-1 in the IR data indicates the OH stretching of

structural hydroxyl group. The strong peak at 2901cm-1 can be attributed to carboxylic

hydroxyl group. The medium peak at 1644cm-1 is due to the C=O stretching of the

ester group formed as a result of esterification between polyvinyl alcohol and maleic

acid. The peak at 1416cm-1 may be due to the free carboxylic acid which did not take

part in the esterification reaction, showing lower extend of cross linking. The peaks at

1324 and 1076cm-1 can be attributed to S=O stretching of sulphonic acid group. The

weak peak at 2094cm-1 is due to aromatic C-H bending. The peaks at 912 and 823cm-1

can be assigned to C-H bending of cross linked poly vinyl alcohol.((Fig.5)

As per thermogravimetric analysis, the polymer shows three step degradation.

The first weight loss observed in the temperature range 1000C could be due to the loss

of physically bound water molecules. The second weight loss ranging from 200-

3700C may be due to the condensation of structural hydroxyl group and

desulphonation of sulphonic acid group. By 4300C, the polymer degrades.(Fig.4)

32

The affinity of membrane towards different heavy metal ions was found to be in

the order Pb>Cu>Cd>Co>Hg. Metal adsorption capacity for Pb(II) was 60mg/g. The

membrane showed least affinity towards Hg(II).(Fig.6)

Cu(II) Pb(II) Cd(II) Co(II) Hg(II)

0

20

40

60

80M

eta

l A

dso

rpti

on

%

Metal ions

Fig 6: % removal of various heavy metals

A study on effect of membrane thickness on adsorption was done by varying the dry

weight of membrane and the result showed that for initial concentration of 500mg/L

of Pb(II). The adsorption increased until a maximum value was reached at a

membrane thickness corresponding to 1.0g dry weight of membrane (Fig.7). Increase

in adsorption is attributed to the increase in the sorption sites available. But as the dry

weight increased to 1.2g the % adsorption decreased. This may be due to the non-

availability of sorption sites for the Pb(II) ions as a result of change in pore size

.

0 .2 0 .4 0 .6 0 .8 1 .0 1 .2

76

78

80

82

84

86

88

90

92

94

96

Met

al A

dso

rpti

on

%

M em brane Th ickn ess (g )

Fig 7: Effect of membrane thickness on adsorption

33

Study on the effect of initial feed concentration shows that as the

concentration increased % adsorption decreased. This may due to the saturation of

available sites (Fig.8).

500 600 700 800 90064

66

68

70

72

74

76

78

80

82

84M

etal

Ad

sorp

tio

n %

Initial metal concentration (mg)

Fig 8: Effect of initial metal ion concentration on adsorption

Study on the effect of pH on the adsorption capacity shows that the %

adsorption increased as the pH increased and a maximum was reached when the pH of

the medium was equal to 7.0 (Fig.9). The low adsorption capacity of all metal ions at

lower pH can be ascribed to competitive adsorption of H3O+ ions and metal ions for

the same active adsorption sites.

Selectivity of membrane towards Pb(II) in presence of other metal ions like Cd,

Zn, Cu, Hg, and Co were determined and the studies showed that though the

membrane was selective towards Pb(II), the % adsorption decreased. This may be

probably due to the competitive adsorption of Pb(II) and other heavy metal ion.

Optimisation studies of membrane adsorption for Pb(II) shows that an effective

adsorption can be attained by a membrane of thickness corresponding to 1.0g dry

weight of membrane at a pH of 7.0 at a lower concentration range of 200ppm.

34

3 4 5 6 750

55

60

65

70

75

80

85

Met

al A

dso

rpti

on

%

pH

Fig 9: Effect of pH on adsorption of heavy metals

Calibration plot of potentiometric sensing of lead ion using the membrane was

not satisfactory with an average linear regression coefficient 0.78. So further studies

on sensing behavior of the membrane were not carried out.

Results of kinetic study reveal that the linear regression coefficient of second order is

higher than that of first order kinetic model. In pseudo second order model, the

experimental and calculated values are more agreeable to each other(Table.4). This

indicates that second order kinetic model is best model to explain the mechanism of

adsorption of lead ions onto the membrane.(Fig.10,11)

35

Kinetic parameters

Heavy metal

Pb2+

First order kinetics (lagergren’s)

qe (exp)

(mg/l)

0.4861

qe (calc)

(mg/l)

0.1961

K1

(min-1)

0.0184

R2 0.9059

Second order kinetics (Ho’s)

qe (exp)

(mg/l)

0.4982

qe (calc)

(mg/l)

0.5859

K2

(g/mg.min)

0.3484

R2 0.9905

Table 4: Pseudo first order and second order kinetic

parameters

36

Fig 10: Lagergren’s pseudo first order

kinetic model for Pb2+ ions

Fig 11: Ho’s pseudo second order kinetic

model for Pb2+ ions

The distribution of heavy metals between solid and liquid phase was studied using

Langmuir, Freundlich, Dubinin and Temkin isotherm models( Fig: 12-15). From

linear regression coefficient values, it is clear that Langmuir isotherm model is the

better one to explain the adsorption. From the slope and intercept obtained from

graph, monolayer adsorption capacity (qm), separation factor (RL), energy of

adsorption (KL) were calculated. The negative RL values indicates that the adsorption

of heavy metals onto the membrane is a feasible one.

Freundlich isotherm constant n and Kf correspondsing to adsorption intensity

and adsorption capacity are given in (Table.5). Freundlich constant n value smaller

than 1 indicates that the adsorption is a chemical process.

Monolayer adsorption capacity (qs), mean free energy of adsorption (E),

Dubinin isotherm constant (Kd) values were obtained from D-R isotherm plot. Mean

free energy of adsorption of Pb2+ ion is 0.4454, indicates that mechanism of

adsorption is physical in nature.

37

Temkin constant related to heat of adsorption (b) obtained from graph is negative

for Pb2+ ions and reveals that the adsorption of Pb2+ onto the membrane was

endothermic in nature

Table 5: Langmuir, Freundlich, Dubinin, Temkin isotherm parameters

Isotherm parameters

Heavy metal

Pb2+

Langmuir constants

qm (mg/g) 0.3728

KL -0.3761

RL -0.0790

R2 0.9906

Freundlich constants

n -2.7670

KF 1.1863

R2 0.9678

Dubinin isotherm constants

qs 0.4385

Kad -2.5209x10-6

E (KJ/mol) 0.4454

R2 0.8378

Temkin isotherm constants

A (l/g) 6.4904x10-3

B -0.1897

b -13060.4744

R2 0.9827

38

Fig 12: Freundlich isotherm Fig 13: Langmuir isotherm

Fig 14: Dubinin isotherm Fig 15: Temkin isotherm

39

5. Fabrication of Titanium dioxide doped polymer

membrane and its application

5.1 Chemicals used:

Poly vinyl alcohol, carboxymethyl cellullose and maleic acid used for the preparation

of membrane were of analytical grade and was purchased from Alfa aeser. Malachite

green and methylene blue congo red rhodamine blue etc. were from Loba chemie.

Titanium dioxide, was from Merck.

5.2 Preparation of titanium dioxide doped polymer membrane:

Membrane of different compositions were made by mixing poly vinyl alcohol,

carboxymethyl celluose and titanium dioxide, in different proportions. Maleic acid

was added as a cross-linker.

A definite amount of poly vinyl alcohol dissolved in hot water was boiled with

maleic acid in dil.H2SO4. To this carboxymethyl cellulose dissolved in distilled water

was added carefully and heated. Titanium dioxide suspended in distilled water was

then slowly added to the above mixture in drop wise manner and homogenized using

vortex mixer.

Different composition membranes were prepared by mixing different ratios of

the components and it was spin coated on a Table - Top Spin-Coating Unit (Spektron

Instruments). To get thick membranes mutliple layer coating was done. Different

samples were analysed for their dye removing capacities.

5.3 Physico - chemical characterization:

5.3.1 Instrumental Analysis:

Thermal stability (TGA) of PVA- PSSA-ZWP membrane was determined

using NETZSCH STA 449F5 Thermogravimetric analyzer under N2 atmosphere.

Samples were heated up to 900oC at the rate of 30oC/min. IR spectrum of composite

membrane was recorded using agilent cary 630 FTIR spectrometer with KBr pellet

technique.The surface morphology of the PVA-CMC-TiO2 membrane was examined

using scanning electron microscopy.

40

4.3.2. Ion exchange capacity of TiO2 and the membrane:

Ion exchange capacity of TiO2 and PVA-CMC-TiO2 membrane was determined

by titrimetric method as described in Chapter 3.

4.3.3. Degree of swelling:

Degree of swelling of PVA-PSSA-ZPS membrane was measured by immersing

membrane in distilled water at room temperature for 24 hours. The membrane was

then removed, surface water was wiped and subsequently weighed. It was then dried

in an air oven at 55°C and weighed again. Net weight loss (degree of swelling) was

calculated using the expression,

W = x 100

Wdry and Wwet are weight of dry membrane and weight of water absorbed membrane

respectively.

4.3.4.Chemical stability of the membrane:

Chemical stability of PVA-CMC-TiO2 membrane was investigated by soaking the

membrane into different solvents and dilute acid solution for 24 hours at room

temperature.

4.3.5. Dye adsorption studies on the membrane:

Different dyes were made to adsorb on the the membrane and the result was

analysed using UV-Visible spectrophotometer. Effect of contact time, initial feed

concentration, pH and temperature on adsortion of dyes were studied. Kinetic studies

on adsorption were then carried out for the dye that was adsorbed to a greater extend..

5.4 Kinetics and thermodynamics of dye adsorption

Kinetics of membrane adsorption was done by adding the prepared membrane

in 20ml, 10ppm MB and MG dye solutions. Adsorption at different time intervals

were determined. A water bath shaker was used for the purpose. The resulting sample

after the removal of membrane was analysed on UV-Visible spectrophotometer.

Theoretical calculations were done as described in chapter 3. For thermodynamic

studies adsorptions were carried out for different temperature.

41

5.5 Treatment of textile effluent waste using the membrane

Efficiency of the membrane was tested for the treatment of textile effluent

waste collected from the nearby loom unit. The sample dye waste was analysed on

UV- Visible spectrophotometre for its intial concentration.

An effluent treatment column was made, by carefully embedding the

membranes in an ion exchange column. Effluent waste was directly poured onto the

coulmn and the flow at the outlet was maintained at 0.1ml per minute. After the

treatment the eluted waste water was analysed on UV- Visible spectrophotometer.

6. Results and discussion

Fig 16: PVA-CMC-TiO2 Membrane in wet and dry form

Polymer membranes obtained were of different compositions. One sample out

of three showed good dye adsoprtion poperty. The composition ratio for PVA, CMC

and TiO2 for this membrane was 50:20:30 by weight percentage (Fig.16). So this

membrane was used for further analysis.The SEM image of PVA-CMC-TiO2

composites is depicted in (Fig.17). Heterogeneous surface is observed which indicates

good interfacial adhesion between TiO2 and polymer matrix. Aggregation of TiO2

particle on the surface of polymer matrix was also observed.

42

Fig 17: SEM image of PVA-CMC-TiO2 membrane

IR spectrum clearly shows the presence of esteric bonds confirming

crosslinking and it also shows some structural hydroxyl grops are still present where

the exchange takes place(Fig 18). Tg curve shows that three step degradation process

and presence of TiO2 incearses thermal stability to a little extend(Fig.19).

Fig 18: IR spectrum Fig 19: TG curve

It was observed that IEC value of TiO2 was 3.2meqg-1 and that of PVA-CMC-

TiO2 membrane was found to be 6.436 meqg-1. Results show that composite

membrane has high capacity to exchange H+ ions than the inorganic counter part. It

may be due to large number of movable H+ ions as well as high water uptake of

polymer matrix.

The results show that swelling degree of membrane is less as compared to

polymer matrix without TiO2. The percentage degree of swelling of PVA-CMC

membrane was found to be 215% and the TiO2 doped membrane was found to be

186.22 ± 5% . Crosslinking decreased the swelling degree. When crosslinking agent,

maleic acid was added to PVA matrix, esterification reaction occured within the

matrix. Addition of TiO2 to the polymer matrix, reduced the free volume in the blend

and this also decreased the water uptake capacity of the membrane

43

Chemical stability of PVA-CMC-TiO2 membrane was investigated by soaking

the membrane into different solvents and dilute acid solution for 24 hours at room

temperature. Sample did not show any physical change and there was also no

noticeable weight change .

The membrane was found to adsorb malachite green(MG) and methylene blue

(MB)in a very efficient manner. The Fig.20,21 shows the dye content before and after

adsorption on the membrane. Almost complete removal can be noticed distinctly from

the UV-visible spectrum. So further studies were carried out for the adsorption of

these two dyes.

The effect of time on adsorption was investigated. The adsorption of dyes onto

the membrane at different time interval ranging from 10min to 90minute is shown in

(Fig.22) Adsorption initially increased and then reached an equilibrium. Dye

adsorption onto the membrane increased with increase in time. Observation shows

that equilibrium was reached at 90min for MB and 80min for MG by using 10ppm

dye solution. A rapid decolorisation occurred after 50 minutes for MB and after

30min for MG. Percentage of dye removal using PVA-CMC-TiO2 membrane is in the

order of MG > MB.

Fig 20: UV-Visible spectrum of MG

before and after adsorption

Fig 21: UV-Visible spectrum of MB

before and after adsorption

44

Fig 22: Effect of time on dye adsorption

The effect of temperature on dye adsorption on the membrane was conducted at

318K, 328K and 338K using 10ppm dye solutions. Adsorption capacity increased

with increase in temperature. (Fig23) The temperature dependence on adsorption was

measured using van’t Hoff plot. From the slope and intercept, spontaneous nature of

the process was confirmed.

Fig 23: Effect of temperature on dye adsorption on MG and MB

Initial concentration is an important factor in dye adsorption process.

Optimisation studies were done with initial concentration ranging 20ppm to 100ppm.

Observations show that as the initial concentration increased, the dye adsorption also

increased.(Fig 24)

45

Fig 24: Effect of initial concentration on the removal of dyes

pH dependence is also an important parameter in membrane adsorption studies.

The effect of pH on adsorption was studied at pH ranging from 3 to 10. Maximum

adsorption capacity has been observed at pH 6 for MB and pH 10 for MG. In the case

of MB, percentage of dye removal increased initially upto pH 6 and then decreased.

(Fig .25)

Fig 25: Effect of pH on dye adsorption

46

Kinetic studies of membrane adsorption were done by equilibrating the

prepared membranes in 20ml, 10ppm MB and MG dye solutions. Adsorption studies

were carried out at different time intervals. The dye solutions after adsorption were

analysed using U-Vvisible spectrophotometer.( Fig. 26,27)

Results reveal that the second order kinetics and intra-particle diffusion model

are the most fitted ones(Table.6)

Fig 26: Lagergren’s pseudo first order

kinetic model for MB and MG

Fig 27: Ho’s pseudo second order kinetic

mode for MB and MG

Kinetic parameters

MB

MG

First order kinetics

(lagergren’s)

qe (exp)

(mg/l)

1.2693 1.3097

qe (calc)

(mg/l)

0.8991 0.0594

K1

(min-1)

0.0849 0.2796

R2 0.9811 0.9435

47

Table 6: Pseudo first order and second order kinetic parameters

Langmuir, Freundlich, Dubinin and Temkin isotherm models were used to

study the adsorption properties of prepared membrane. From linear regression

coefficient values, it is observed that Langmuir isotherm was the best fitted model for

explaining adsorption of both MB and MG dyes on the surface of PVA-CMC-TiO2

membrane. From slope and intercept obtained from graph, monolayer adsorption

capacity (qm), separation factor (RL), energy of adsorption (KL) were calculated.

Malachite green showed high adsorption capacity than MB. The negative RL values

indicates that the adsorption of dyes on to the membrane is a favourable one.

Freundlich isotherm constant n and Kf corresponding to adsorption intensity

and adsorption capacity resp. are given in(Table.7 ). Freundlich constant n is less than

one and indicates that the adsorption is a chemical process.

Monolayer adsorption capacity (qs), mean free energy of adsorption (E),

Dubinin isotherm constant (Kd)etc. were obtained from D-R isotherm plot shown in .

Mean free energy of adsorption of MB is 3.92 and MG is 5.11 indicating that

mechanism of adsorption is physical in natureFig( 28-31).

Second order kinetics (Ho’s)

qe (exp)

(mg/l)

1.2693 1.3097

qe (calc)

(mg/l)

1.3978 1.3671

K2

(g/mg.min)

0.2055 0.5774

R2 0.9996 0.9999

48

Table 7: Different isotherm parameters

Temkin constant related to heat of adsorption (b) obtained from graph is

negative for MB and MG dyes and it reveals that the adsorption of MB and MG dye

on to the membrane was endothermic in nature.

Isotherm parameters

MB

MG

Langmuir constants

qm(mg/g) 1.0965 1.1578

KL -25.4743 -53.9817

RL -3.9409x10-3 -1.8559x10-3

R2 0.9960 0.9992

Freundlich constants

n -23.5849 -49.5049

KF 1.2167 1.2788

R2 0.8739 0.8732

Dubinin isotherm constants

qs 1.1118 1.1877

Kad -0.0325 -0.0191

E 3.9223 5.1164

R2 0.7966 0.6477

Temkin isotherm constants

A (l/g) 5.9774x10-8 1.7851x10-11

B -0.0716 -0.0494

b -3.4602x104 -5.0153x104

R2 0.8441 0.7716

49

Fig 28: Langmuir isotherm Fig 29: Freundlich isotherm

Fig 30: Dubinin isotherm Fig 31: Temkin isotherm

The spontaneous nature of adsorption onto the membrane was proved by

adsorption thermodynamics. Adsorption studies were carried out at different

temperatures such as 318K, 328K and 338K using 10ppm MB and MG solutions.

Temperature dependence on adsorption constant was obtained from Van’t Hoff plot,

which is given in Fig.32. Table.8 shows the thermodynamic parameters like ∆H°, ∆S°

and ∆G° for adsorption. From the results, it is clear that the positive value of ∆H°

indicates that the adsorption of dyes onto the PVA-CMC-TiO2 membrane is

endothermic. The positive value of ∆S° indicates that the dye molecules adsorbed

50

onto the membrane surface are organised. The ∆G° values were obtained by

substituting the values of ∆H° and ∆S° in Gibbs free energy equation. Here negative

value of ∆G° indicates that adsorption of MB and MG dyes onto the membrane is

spontaneous in nature(Table.8).

Fig 32: Van’t Hoff plot for adsorption of Dyes onto the membrane

DYES

∆H

(J/mol)

∆S

(J/mol.K)

∆G

(KJ/mol)

MB

37.0197

128.3416

-3.8208x104

MG

20.9829

83.8284

-2.4959x104

Table 8: Thermodynamic parameters for the

adsorption of dyes onto the membrane

51

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56

6. List of figures

Fig 1: PVA- PSSA- ZPW Membrane

Fig 2: Spin coating unit with IR currer

Fig 3: XRD data

Fig 4: TG curve

Fig 5: IR spectrum

Fig 6: % removal of various heavy metals

Fig 7: Effect of membrane thickness on adsorption

Fig 8: Effect of initial metal ion concentration on adsorption

Fig 9: Effect of pH on adsorption of heavy metals

Fig 10: Lagergren’s pseudo first order kinetic model for Pb2+ ions

Fig 11: Ho’s pseudo second order kinetic model for Pb2+ ions

Fig 12: Freundlich isotherm

Fig 13: Langmuir isotherm

Fig 14: Dubinin isotherm

Fig 15: Temkin isotherm

Fig 16: PVA-CMC-TiO2 Membrane in wet and dry form

Fig 17: Sem image of PVA-CMC-TiO2 membrane

Fig 18: IR spectrum

Fig 19: TG curve

Fig 20: UV-Visible spectrum of MG before and after adsorption

Fig 21: UV-Visible spectrum of MB before and after adsorption

Fig 22: Effect of time on dye adsorption

Fig 23: Effect of temperature on dye adsorption on MG and MB

Fig 24: Effect of initial concentration on the removal of dyes

Fig 25: Effect of pH on dye adsorption

Fig 26: Lagergren’s pseudo first order kinetic model for MB and MG

Fig 27: Ho’s pseudo second order kinetic mode for MB and MG

Fig 28: Langmuir isotherm

Fig 29: Freundlich isotherm

Fig 30: Dubinin isotherm

Fig 31: Temkin isotherm

Fig 32: Van’t Hoff plot for adsorption of Dyes onto the membrane

57

7. List of tables

Table 1: Preparation conditions and ion exchange capacities of various

samples

Table 2: Effect of temperature on the ion exchange capacity of the exchanger

Table 3: Spin coating parameters and composition of different membrane

samples

Table 4: Pseudo first order and second order kinetic parameters

Table 5: Langmuir, Freundlich, Dubinin, Temkin isotherm parameters

Table 6: Pseudo first order and second order kinetic parameters

Table 7: Different isotherm parameters

Table 8: Thermodynamic parameters for the adsorption of dyes onto the membrane

58

Conclusion

A novel cross linked polyvinyl alcohol-poly styrenesulphonic acid- zirconium

tunstophosphate(ZWP) membrane was prepared by dispersing ZWP gel into PVA-

PSSA blend by spin coating method. It was proved to be an effective adsorbent for the

removal of heavy metal Pb2+ ion from aqueous solutions. The incorporation of

Zirconium tungstophosphate gel into PVA-PSSA blended solution improved the

thermal properties, as well as selectivity of heavy metals towards the membrane.

Characterisation of membranes was done by XRD, FTIR, TGA etc. Adsorption

studies were carried out by batch adsorption process. Effect of pH, contact time,

initial concentration etc. were studied. It showed maximum selectivity towards lead

ion .Optimisation studies of membrane adsorption for Pb2+ shows that an effective

adsorption can be attained by a membrane of thickness corresponding to 1.0g dry

weight of membrane at a pH of 7.0 at a lower concentration range of 200ppm. Kinetic

studies were used to explain the mechanism of adsorption process. Pseudo second

order kinetic model and Langmuir isotherm models are more fitted. Potentiometric

lead ion sensing was tested on ion selective electrode fabricated using the membrane.

A new polymeric membrane doped with titaniun dioxide was also prepared.

Instrumental characterization like TGA, XRD, SEM etc. were done. The new polymer

matrix was polyvinyl alcohol and carboxymethyl cellulose. Ion exchange properties,

degree of swelling and dye adsorption studies were carried out. The membrane was

found to adsorb malachite green (MG) and methylene blue (MB) in a very efficient

manner. The effect of different parameters on adsorption was investigated.

Observation shows that equilibrium was reached at 90min for MB and 80min for MG

by using 10ppm dye solution. A rapid decolorisation occurred after 50 minutes for

MB and after 30min for MG. Percentage of dye removal using PVA-CMC-TiO2

membrane was found to be in the order of MG > MB. Kinetic and thermodynamic

studies were carried out. Langmuir, Freundlich, Dubinin and Temkin isotherm etc.

were the theoretical models used. The negative value of ∆G° indicates that adsorption

of MB and MG dyes onto the membrane is spontaneous in nature. Effective dye

removal was also done with textile effluent waste.

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