CHAPTER IV

RESULTS AND DISCUSSIONS

4.1 FUNCTIONAL CHARACTERIZATION OF CHITOSAN MEMBRANE

Among the novel families of biological macromolecules, whose relevance is

becoming increasingly evident are chitin and its main derivative, chitosan. Potential and

usual applications of chitin, chitosan and their derivatives are estimated to be more than

200 (Kumar, 2000). Chitosan is derived from chitin, by a deacetylation reaction using an

alkali. Chitosan is therefore a copolymer of glucosamine and N-acetyl glucosamine. It is

composed of β-(1, 4)-2–amino-2-deoxy-D-glucopyranose (glucosamine units) and β-(1,

4)-2-acetamido-2-deoxy-Dglucopyranose (acetyl glucosamine units). The term

“chitosan” refers to chitin that has been deacetylated to greater than 60%. Chitosan has

many properties that have generated interest in its use such as biodegradability,

biocompatibility and its nontoxic nature (Varma, 2004).

The deacetylated product, chitosan, has an amine functional group, which is

strongly reactive with metal ions. This has initiated research into the use of chitosan in

metal uptake. The deacetylation degree will control the content of glucosamine and

therefore the fraction of free amine groups available for metal binding. These reactive

amine groups interact with the metal ions in different ways, such as by chelation or

electrostatic attraction depending on parameters such as pH, and total composition of the

solution. These groups are more reactive than the acetamide groups present on chitin. A

complete Physical, Chemical and Physiochemical characterization of chitosan and its

complexes are not possible without using spectroscopic techniques like FTIR, XRD, UV-

Vis, SEM etc., (Kumirska et al., 2010).

4.1.1 Fourier Transform Infrared (FTIR) Spectroscopy

Infrared (IR) spectroscopy is one of the most important and widely used analytical

techniques available to scientists working on chitin and chitosan. It is based on the

vibrations of the atoms of a molecule. The infrared spectrum is commonly obtained by

passing infrared electromagnetic radiation through a sample that possesses a permanent or

62

induced dipole moment and determining what fraction of the incident radiation is

absorbed at a particular energy (Stuart 2004). The energy of each peak in an absorption

spectrum corresponds to the frequency of the vibration of a molecular part, thus allowing

qualitative identification of certain bond types in the sample. An IR spectrometer usually

records the energy of the electromagnetic radiation that is transmitted through a sample as

a function of the wavenumber or frequency. Fourier-transform infrared (FTIR)

spectroscopy has dramatically improved the quality of infrared spectra and minimized the

time required to obtain data (Smith 1996, Stuart 2004).

The infrared spectrum is commonly plotted in one of three formats such as

transmittance, reflectance, or absorbance. If a fraction of light is transmitted through the

samples, then the transmittance of the sample at frequency ω (Tω) is defined as

where It is the intensity of transmitted light and I0 is the intensity of the incident light. In

the present work, absorbance spectra were used to quantify the characteristic peaks of

Chitosan in the middle infrared region (4000 cm-1 to 400 cm

-1) with a resolution of 2 cm

-1

for 8 to 128 scans at room temperature using a Bruker IFS - 66V spectrometer. Since all

the samples under study were transparent and freestanding films, the samples were placed

directly on the sample holder for the analysis.

The analyses were carried out in the three regions (600 – 1200, 1200 - 1800

and 2800 – 3600 cm-1) of the pure chitosan (CHP) and chitosan acetate (CHA) spectra

(Fig 4.1.1). Pure chitosan means, chitosan membranes / films free from solvent or

dopant molecules and chitosan acetate means, chitosan membranes / films in the

presence of acetic acid (solvent). There are no significant peaks observed in the

range of 1800 – 2800 cm-1. The first region (600 – 1200 cm

-1) has no significant

peaks except small peaks at 1153 cm-1(C-O-C vibrations), 900 cm

-1 and 647 cm

-1

(NH wag primary and secondary amines) found in pure chitosan, which is gradually

broadened and obscured when it is dissolved in acetic acid. The peak positions

and the corresponding band assignments of pure chitosan film / membrane are

shown in table 4.1.1.

ω

ω

=

0I

IT t (4.1.1)

63

The spectra of pure chitosan (CHP) and chitosan acetate (CHA) films in the

region between 1200 and 1800 cm-1 show (Fig. 4.1.1) significant peaks for analysis. This

is the region where the carbonyl, C – O–/NHR, amine, NH2 and ammonium, NH3+ band,

OH and CH deformation are situated. The band at 1380 cm-1 is due to the –CO stretch of

the primary alcoholic group (CH2-OH) and at 1262 cm-1 represents free primary amino

group (NH2). The band at 1153 cm-1 and 1082 cm

-1 are due to the anti-symmetric

stretching of C-O-C bridge and skeletal vibrations involving C-O-C stretching. The band

at 1650 cm-1 represents acetylated amino group, which is due to the C=O stretching

vibrations of (Amide I) O-C-NHR. The band at 1590 cm-1 is assigned to NH2 bending

vibrations (amide II) (Osman 2003).

Fig. 4.1.1 FTIR spectra of Chitosan pure (CHP) and Chitosan acetate (CHA)

The NH2 bending vibrations (1590 cm-1) for CHP disappeared and new

absorption band characteristic of NH3+ bending vibrations appeared at 1630 cm

-1

and 1568 cm-1. These results suggest that the NH2 groups in the chitosan chains

were protonated by the H+ supplied by acetic acid. In this work, the carbonyl band for

the pure chitosan (CHP) spectrum is observed at 1650 cm-1, the amine (NH2) band at

1590 cm-1 and OH and CH deformation band at 1420 cm

-1.

4000 3600 3200 2800 2400 2000 1600 1200 800 400

CHA

1262

1630

1568

1410

2878 1650

1590

1420 1380 1323

1153

1080 Transmittance (Arbitrary Units)

Wave Number (cm-1)

900

CHP

64

Table 4.1.1 Infrared band assignment for pure Chitosan membrane

Peak Position (cm-1)

Assignment

900

NH wag primary amine

1153

C-O-C vibrations

1262

CH wag (ring)

1323

OH and CH deformation ring

1380

CH symmetrical deformation bend

1420

OH and CH deformation ring

1590

NH2 deformation

1650

Amide I (C=O)

2878

C-H asymmetrical stretching

2913

C-H symmetrical stretching

3317

N-H2 asymmetrical stretching

3369

N-H2 symmetrical stretching

3441

O-H Stretching

65

Due to some interaction between the acetic acid and the nitrogen donors of the

chitosan polymer, the carbonyl band has shifted to 1630 cm-1, the amine band to 1568

cm-1and OH and CH deformation moved to 1410 cm

-1 in the chitosan acetate film

(CHA). This is due to the formation of salt (chitosan acetate) produced due to a reaction

between the acetic acid and chitosan as have been reported (Kaneko, 1997), where the H+

of acetic acid has formed a dative bond with nitrogen of the chitosan functional group.

This is in good agreement with the literature survey (Yahya et al., 2002].

In the third region of the spectra (Fig.4.1.1 - 2800 – 3600 cm-1), the broad

band around 3200 cm-1, confirms the conversion of NH2 groups into NH3

+groups

by the protonation. It is seen from various reports (Miya et al., 1980., Mima et al.,

1983 Brugnerotto et al., 2001) that the infrared C-H stretching bands shift to lower

wave number and became sharper as crystallinity increases. However, the peak

position of aliphatic C-H stretching band in this study (2878 cm-1) remains same,

but its sharpness is reduced when it is dissolved in acetic acid. This property

indicates that the acetic acid alter the crystallinity of the pure chitosan film.

4.1.2 X- Ray Diffraction (XRD) Spectroscopy

X-ray spectroscopy is a powerful and flexible tool and an excellent complement to

many structural analysis techniques such as UV-Vis, IR, NMR or Raman. It is unarguably

the most versatile and widely used means of characterizing materials of all forms (Guo

2009). There are two general types of structural information that can be studied by X-ray

spectroscopy: electronic structure (focused on valence and core electrons, which control

the chemical and physical properties, among others) and geometric structure (which gives

information about the locations of all or a set of atoms in a molecule at an atomic

resolution).

Clark and Smith (1937) were the first to make crystal studies of chitin and

chitosan using X-ray diffraction (XRD). Main parameter that determines properties of

chitosan, apart from molecular mass and deacetylation degree is polymer crystallinity.

The chitosan is a semi-crystalline material shows polymorphism depending on its

physical state. Recently, true crystal structure and configuration of chitosan is intensively

66

investigated. The structures for different forms including an anhydrous form, a hydrated

form and various salts were obtained by X-ray diffraction analyses (Ogawa et al., 1992,

1993, 2004; Yawo-Kuo Twu et al., 2005; Trang Si Trung et al., 2006). The small angle

X-ray diffraction study carried out on chitosan powder obtained from crab shells, show

regular packing of the molecules in parallel bundles. The data indicate that the

interactions of chitosan macromolecules along the b-axis give rise to a fibrous structure

(Ogawa et al. 2004). The XRD study on chitosan and its complexes will reveal many

important parameters that characterize the polymer and show significant information

about the physicochemical properties of these materials.

Fig. 4.1.2 XRD spectrum of pure Chitosan (CHP)

10 15 20 25 30 35 40

100

200

300

400

(020)

(110)

10.3o,20.2

0

Chitosan

Two theta ( degrees)

Intensity (cps)

67

X-ray diffractograms of pure chitosan film measured in the range of 2θ=10˚-40˚

(Fig. 4.1.2) showed two characteristic reflections at 10.3˚ and 20.2˚ that are typical

fingerprints of semi crystalline Chitosan indexed as (020) and (110) known as hydrated

crystalline structure and an amorphous structure of chitosan, respectively (Ogawa et al.

1984, Wang et al., 2005). In 1990, Focher et al., used XRD to study chitin and

postulated the following equation for determining the crystallinity index (CI):

����� � ����� � ������

� 100

where I110 (arbitrary units) is the maximum intensity of the (110) peak at around 2θ = 20°,

and Iam (arbitrary units) is the amorphous diffraction at around 2θ = 12.6°. This

expression had in fact been employed three years earlier by Struszczyk (1987) to

determine the CI of chitosan. Currently this equation is routinely applied during

investigations of chitin, chitosan and their derivatives (Kumirska et al., 2010). The

degree of crystallinity for pure chitosan film in the investigated range through X-ray

diffractometry using the equation 4.1.2, which was employed to determine the

crystallinity index (CI) for chitin and chitosan (Zang et al., 2005, Serkan Keleolu 2007,

Kumirska et al., 2010) was found to be CI110 = 56.25%.

On the basis of X-ray powder diffractograms of chitin and chitosan with different

degrees of N-acetylation, Zhang et al., (2005) noted two maximum peaks of the

following intensities: one at the (020) reflection and the other at the (110) reflection and

postulated a crystallinity index (CI) expressed by equations 4.1.2 and 4.1.3.:

����� � ����� � ������

� 100

Further chitin and chitosan studies indicated that crystallinity could also be assigned from

an X-ray diffractogram by dividing the area of the crystalline peaks by the total area

under the curve (background area) (Kumirska et al., 2010). The calculated value of CI020

is 8.75% for pure chitosan membrane. In these calculations, the crystallinity percentage

supplied information based on relative crystallinity. Studies of Yawo-Kuo Twu (2005)

refer to crystallinity of the chitosan formed as scaffolds. The scaffolds were formed by

4.1.2

4.1.3

68

electrolysis of chitosan using different solvents (acetic and formic acid). Crystallinity of

the chitosan scaffolds is lower than crystallinity of initial polymers and it drops with an

increase of the acid concentration.

Fig. 4.1.3 XRD spectrum of Chitosan acetate (CHA)

Fig. 4.1.3 shows the X-ray diffractogram of chitosan acetate film (i.e.) chitosan

scaffold, which exhibit two sharp peaks at 11.5˚ and 15.7˚, and a suppressed amorphous

hump (indicated in dotted line) exhibit many minor peaks around 18.4˚-23.65˚ as reported

earlier (Puteh et al., 2005, Modrzejewska et al., 2006). It is clearly observed that the peak

positions of pure chitosan membrane were shifted to new position (10.3˚ 11.5˚,

12.6˚ 15.7˚ and 20. 2˚ distributed over a range) when chitosan converted to chitosan

acetate (Fig 4.1.2 and 4.1.3). When chitosan films were formed with acetic acid as

solvent, the peak intensity ratio of pure chitosan membrane is reduced (comparing

intensity ratio of Fig. 4.1.2 and 4.1.3).

10 15 20 25 30 35 4020

40

60

80

100

120

Chitosanacetate

Two theta ( degrees)

Intensity (cps)

11.50,15.7

0,18.4

0-23.65

0

69

Table 4.1.2 Crystal Index of pure chitosan and chitosan acetate films

Film Type

Crystal Index

CI110 CI020

CHP 56.25% 8.75%

CHA 16.12% 32.24%

The above result is an indication of reduction of crystallinity of chitosan. The

decrease in the crystallinity of chitosan acetate films are due to the formation of hydrogen

bonding between acetic acid that leads to their good compatibility. The changes in the

crystal index as shown in table 4.1.2 informed the reduction of CI110 and raise in CI020

explains reordering of glucosamine molecules in the chitosan acetate which is different

from the initial polymer. However, the total crystal index (CI) of chitosan scaffold

calculated as per the equations 4.1.2 and 4.1.3 are lower than the pure chitosan due to the

fact that when chitosan dissolved in acetic acid the interaction between the acetic acid

and the nitrogen donors of the chitosan polymer (NH2 groups in the chitosan chains

were protonated by the H+ supplied by acetic acid results in the formation of NH3

+)

disrupt the crystallinity of the pure chitosan.

4.1.3 Ultra Violet and Visible (UV-Vis) Spectroscopy

The steps in the structural analysis of chitosan and its complexes by UV-Vis

spectroscopy are very similar to those in the FTIR methodology (Section 4.1.1). The main

difference is connected with the aim of these analyses. IR spectroscopy is used mostly for

determining the molecular structure of chitosan and its complexes, whereas UV-Vis

spectroscopy is more often applied to the study of covalent and non-covalent interactions.

Since certain functional groups present in organic molecules absorb light at characteristic

wavelengths in the UV-Vis region, this technique is applied qualitatively to identify the

presence of these groups in samples, supporting structural information obtained from

other spectroscopic methods, especially IR. As mentioned, one of the most important

applications of UV-Vis techniques is the characterization of interactions between chitosan

and its solvents or dopants.

70

Chitosan has two far-UV chromophoric groups namely, N-acetylglucosamine

(GlcNAc) and glucosamine (GlcN), since chitosan cannot be deacetylated completely.

The UV-Vis spectra obtained for pure chitosan (CHP) and chitosan acetate (CHA) films

showed (Fig. 4.1.4 transmittance spectra and inset show the absorbance spectra) two

characteristic absorptions at circa 210 and 260 nm revealing the presence of pure chitosan

(Tyagi et al., 1996). The spectrum of the chitosan acetate (CHA) exhibited a new

absorption centered at circa 320 nm indicates the conversion of glucosamine (GlcN) into

glucosamine acetate unit. The λmax of CHP (260 nm) shifts to longer wavelength

demonstrated the chemical interaction between chitosan and acetic acid even at room

temperature. A similar effect was reported by Sharma et al., (2003) who had studied the

interaction of chitosan with ammonium sulfate and t-butanol.

Fig. 4.1.4 UV-Vis Spectra of Chitosan Pure (CHP) and Chitosan acetate (CHA)

200 300 400 500 600 700 800 900

200 300 400 500 600 700 800 900

320

absorbance (a.u)

Wave length (nm)

260

320 nmCHA

CHP

Wave length (nm)

Transmittance (a.u)

260 nm

71

The shifts to longer wavelength in UV spectra are known to be associated with

increase in hydrogen bonding. Both inter- and intra-molecular hydrogen bonding are

possible in these cases. It is already observed that the IR bands of chitosan acetate are

shifted to lower frequency (Section 4.1.1). This again fits in well with increase in intra- or

inter-molecular hydrogen bonding which decreased the frequency of amine and hydroxyl

bonds. The XRD result also showed the reordering of glucosamine (GlcN) unit under the

action of solvent. Therefore, the FTIR, XRD and UV-Vis spectroscopic methods

characterize the interaction between chitosan and ions of solvents or dopants leads to

various applications to be discussed in the later part of the thesis.

4.1.4 Optical Absorption Analysis of Heavy Metal Ions

The problems of the ecosystem are increasing with developing technology. Heavy

metal pollution is one of the main problems. Toxic metal compounds coming to the

earth's surface not only reach the earth's waters (seas, lakes, ponds and reservoirs), but

can also contaminate underground water in trace amounts by leaking from the soil after

rain and snow. Therefore, the earth's waters may contain various toxic metals. Drinking

water is obtained from springs which may be contaminated by various toxic metals. One

of the most important problems is the accumulation of toxic metals in food structures. As

a result of accumulation, the concentrations of metals can be more than those in water and

air.

The contaminated food can cause poisoning in humans and animals. Although

some heavy metals are necessary for the growth of plants, after certain concentrations

heavy metals become poisonous for both plants and heavy metal microorganisms.

Another important risk concerning contamination is the accumulation of these substances

in the soil in the long term. Heavy metals are held in soil as a result of adsorption,

chemical reaction and ion exchange of soil. In recent years, chitosan and agar have been

commonly used to remove heavy metals and organic compounds from water and waste

water (Muzzarelli, 1977; Knorr, 1991; Taguchi et al., 1999; Yuh – Shan Ho, 2004) in

bulk and film forms.

72

Fig. 4.1.5 Linear variation of Fe2+

ions absorption by the chitosan films

Fig. 4.1.6 Linear variation of Cu2+

ions absorption by the chitosan films

4 6 8 10 12 140.08

0.12

0.16

0.20

0.24

300 400 500 600 700

0.08

0.12

0.16

0.20

0.24 λmax=514 nm

Absorbance

Wave length (nm)

Absorbance

[Fe]/µg

5 10 15 20 25

0.05

0.10

0.15

0.20

0.25

0.30

300 400 500 600 7000.08

0.12

0.16

0.20

0.24

Absorbance

Wave length (nm)

λmax=455nm

Absorbance

[Cu] /µg

73

Fig. 4.1.7 Linear variation of Co2+

ions absorption by the chitosan films

The purpose of this preliminary study is to investigate the heavy metal absorbing

capacity of pure chitosan in film form with specific thickness and to study its variation of

absorption with concentration. The optical absorption analysis of the chitosan films of

typical thickness (50 µm) coated with Iron (II), Copper (II) and Co (II) solutions were

carried out using UV-Vis spectrophotometer in the wavelength range of 200 – 900 nm.

The absorption spectra for different concentrations of metal ions (Fe2+, Cu

2+ and

Co2+) were taken and the maximum absorptions were measured from its characteristic

peaks. The insets show the absorption spectrum of Fe2+, Cu

2+ and Co2

+ metal ion

adsorbed in chitosan films at maximum metal ion concentration. The figures 4.1.5 - 4.1.7

show the linear variation of metal ions absorption for various concentrations by the pure

chitosan films. The absorption values get saturated at higher concentration and it limits

the analysis. The preliminary experiments on higher thickness improve the absorption

capacity. However, interest is taken to study the absorption property in thin film form.

Therefore the study is limited and reported only for the optimized thickness, which gives

the preliminary support for fabrication of heavy metal sensor for effluent and water

treatment.

0 5 10 15 20 25 30 35 40 450.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

300 400 500 600 700

0.02

0.04

0.06

0.08

0.10

0.12

0.14 λmax=414 nm

Absorbance

Wave length (nm)

Absorbance

[Co]/µg

74

. 4.1.5 Selective Adsorption Property of Chitosan Membrane

Rapid industrialization, large scale urbanization involves the use of chemicals

containing toxic elements and heavy metal ions that resulted in the increased

contamination of our environment. Metallic pollution specifically caused potential

danger to the mankind as the heavy metal ions are dumped into the surroundings in

the form of industrial effluents. A lot of research has been carried out to alleviate or at

least minimize the effect of the heavy metal ions from industrial waste waters in

environmental pollution. Several ways and means including filtration, chemical

precipitation, ion exchange, adsorption, electro deposition and the use of membrane

systems have been developed (Taguchi et al., 1999; Yuh – Shan Ho, 2004). Each of the

above methods has its own advantages and disadvantages. Any method chosen for that

matter need to be environment friendly as the method itself should not be counter-

productive to the surroundings.

Adsorption method is found to be relatively convenient and economical in addition

to our prime objective of not to affect the environment. In recent years, studies on

chitin and chitin derivatives, which adsorb metal ions, have increased substantially

and that attract greater interest in terms of their efficiency, wider availability and

environmental safety. The effectiveness of chitosan to remove lead and cadmium in

drinking water has been demonstrated by Knorr, (1991). Chitosan from treated crab

shells have also been used effectively to treat effluents from electroplating industry

and for the removal of hexavalent chromium (Muzzarelli, 1977). Therefore, studies on

the interaction of ions with chitin and chitosan are of importance in ecology not only

in connection with water pollution but also with ionic equilibria in uncontaminated

natural waters.

A systematic analysis of literatures reveals that studies on heavy metal adsorption

by chitin and chitosan are plenty. However the cost involved in this process is heavy,

since it requires materials in bulk form. At the same, time for certain specific

applications, chitin and chitosan in bulk form is unsuitable (Meyers et al., 2000).

Therefore, preparing this material in thin film form is valuable and improves its

physical and chemical character.

75

Fig.4.1.8 Absorbance peaks of the effluent sample

Fig. 4.1.9 Absorbance peaks of the chromium solution

200 300 400 500 600 700 800 9000.0

0.2

0.4

0.6

0.8

1.0 326

415

578

Absorbance

Wavelength (nm)

200 300 400 500 600 700 800 900

0.0

0.2

0.4

0.6

0.8

1.0

414 585

Wavelength (nm)

Absorbance

76

Fig.4.1.10 Optical absorbance spectra of pure and chromium adsorbed chitosan

membranes

Fig. 4.1.11a Optical spectra of pure and 30 min. immersed chitosan membranes

200 300 400 500 600 700 800 900

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

120 90

60

30

Absorbance

Wavelength (nm)

0

Time in minutes

240 260 280 300 320 340 3600.4

0.5

0.6

0.7

0.8

0.9

1.0

30 min

0 min

CHP+(Cr-VI)

Wavelength (nm)

Absorbance

CHP

329 nm

77

Fig.4.1.11b Optical spectra of 60, 90 and 120 min. immersed chitosan membranes

Fig.4.1.12 Variation of absorbance maximum with time

250 275 300 325 3500.95

0.96

0.97

0.98

0.99

1.00

1.01

CHP+(Cr-VI)

120 min.

90 min.

Wavelength (nm)

Absorbance

60 min.

0 20 40 60 80 100 120

0.0

0.2

0.4

0.6

0.8

1.0

Absorbance

Time (min)

78

It is very difficult to dissolve chitin to make it as thin films. Therefore chitosan is

selected as a suitable candidate, which can be easily dissolved in organic solvents and

can be made as free standing film, which can act as membrane for metal adsorption.

The chitosan membranes thus prepared were subjected to selective adsorption

property of chromium ions present in the leather effluents.

Leather industrial effluent mainly contains chromium III (Cr-III), chromium VI (Cr-

VI), proteins and some minerals. Out of these various components Cr-VI is the

carcinogenic species that cause cancer in living beings. In order to study the selective

adsorption property, the chitosan membranes were immersed in the effluent samples for

different time intervals (0, 30, 60, 90 and120 minutes) collected in a leather industry

(NMZ Tanners - Ambur). The optical absorption properties of the effluent (Fig.4.1.8)

samples show peaks at 326, 415 and 578nm. The peak at 326nm is due to chromium –VI

species that was well documented in several literatures (Muzzarelli, 1977; Knorr, 1991;

Taguchi et al., 1999; Yuh – Shan Ho, 2004). The peaks 415 and 578nm are due to

chromium –III species which was verified with the help of standard chromium solution

(Fig 4.1.9). The complete absorption spectra of chitosan membranes show the absorption

peak around 330nm as shown in Fig. 4.1.10. This indicates that the chitosan films

selectively adsorbed the dangerous species of the chromium (Cr-VI) in the effluent.

Fig 4.1.11a and 4.1.11b show the selective part of the graph drawn to show the correct

peak positions. Since the instrument used is having an accuracy of ± 2nm, the error in

the measurement of the peak positions are within the limits. The absorption starts

immediately after the immersion of the chitosan films in the effluents. The absorption

gets saturated around two hours. The maximum absorption found within 30 minutes as

shown in Fig.4.1.12. The SEM image shows porous nature of the chitosan membrane

(Fig. 4.1.13) which is the pre-requisite for membrane filtration (Serkan Keleolu,

2007). Figure.4.1.14 shows Cr-VI adsorbed chitosan membrane surface.

The absorption mechanism of chitosan can be explained as follows. Chitosan have

different functional groups, such as hydroxyls and amines (anions) to which the

chromium metal ions (cations) can bind either by chemisorptions or by physi-sorption

process. Since the chitosan is fabricated in thin film form provide enormous surface area

79

per unit volume which enhances the capacity for attachment of the chromium metal ion

on the surface of the film. If a stack of chitosan films arranged in an effluent unit may

facilitate the removal of this carcinogenic Cr-VI species completely from the effluent.

Further studies on various parameters of heavy metal absorption in chitosan films both

qualitatively and quantitatively will throw more light on this material.

Fig.4.1.13 Scanning Electron Micrograph of the porous surface of pure

chitosan membrane

Fig.4.1.14 Scanning Electron Micrograph of the Cr-VI adsorbed surface of

chitosan membrane

80

4.1.6 Permeability and Porosity of Chitosan Membrane

Permeability is the most important physical property of porous medium, while

porosity is the most important geometric property. Permeability describes the

conductivity of the porous medium with respect to fluid flow, whereas porosity is a

measure of fluid storage capacity of a porous material. The permeability coefficient of

any porous medium can be directly obtained from Darcy’s law, which states that

� � �

�∆�∆� �

where Q – Flow rate, K – permeability coefficient, n – fluid viscosity, ∆P – Pressure

difference, ∆L – Flow length or Thickness of the test sample and A – Area of the sample.

The porosity can be calculated from the formula

�������� ����%� � !"#!$!"

� 100 � !" #%"/'!"

where Vt is the total volume of chitosan (cm3), Va the actual volume of chitosan (cm

3)

and Wt is the mass of chitosan (g) and ρ is the density of chitosan (1.342 g/cm3).

A fully automated Gas Permeability Tester (GPT – LYSSY – L100-5000) was

used to analyze the permeability and porosity of pure chitosan (CHP) samples of

thickness 40 µm with the CO2 flow rate of 100 bars on an area of 56.716 cm2. The

permeability and porosity was calculated using equations 4.4 and 4.5 and corresponding

values are 2.337 ×10-12 cm

3/ (m s Pa) or 205 ml / m

2 day and 0.8783. Similar results were

reported for chitosan by Wen-Chuan Hsieh et al., (2007) who studied the microporous

structure for the development of cell culture. It should be noted that the porosity does not

give any information concerning pore sizes, their distribution, and their degree of

connectivity. However, the porosity value indicates that 88% of the membrane area is

porous as seen from the SEM image (Fig. 4.1.12). From the SEM image it was found that

the pore size ranges from 0.2 – 1 µm suitable for water and effluent filtration. The

maximum capacity of single membrane to withstand the gas pressure was 800 bars.

Therefore stack of chitosan membrane may be arranged for the removal of Cr-VI in an

effluent unit.

4.1.4

4.1.5