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 DOI: 10.1177/0040517514523176 2014 84: 1539 originally published online 21 February 2014Textile Research JournalDP Chattopadhyay and MS Inamdar

processingApplication of chitosan and its derivatives in Cu(II) ion removal from water used in textile wet

  

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Original article

Application of chitosan and its derivativesin Cu(II) ion removal from water usedin textile wet processing

DP Chattopadhyay and MS Inamdar

Abstract

The applicability of chitosan, trimethyl chitosan chloride and nano-chitosan for removal of Cu(II) ions from water used in

textile wet processing was studied. The liquor before and after treatment was analyzed iodometrically to find the

presence of Cu(II) ions, and Fourier transform infrared spectroscopy was employed for the characterization of

the chitosan–Cu(II) complex. The study included the effect of molecular weight of chitosan, particle size of chitosan

and the degree of quaternization of trimethyl chitosan chloride, pH of the medium, etc., on the sorption of Cu(II) ions.

The influence of the molecular weight of chitosan was found to be an important criterion on the rate of sorption of

Cu(II) ions. Reduction in the particle size of chitosan enhanced both the rate and amount of scavenging of metal ions.

Keywords

chitosan, chelation behavior, copper ions, nano-chitosan, trimethyl chitosan chloride

A plentiful supply of good-quality water is indispens-able for the textile wet processing industry. Water is notonly a vehicle to carry or fix the chemicals and dyes, butit is the medium for processing.1 The water employedfor various wet processing operations is nowadays lar-gely obtained from underground sources, which isaccompanied with various heavy metal ions. Therecycled water from effluent discharge also contributesto these impurities due to the inefficiency of conven-tional effluent treatment plants to remove such tracesof metal ions. The presence of these ions, even at theppm level, can have detrimental effects on processessuch as enzymatic desizing, hydrogen peroxide stabilityand its bleaching action, shade of dyes, etc.2,3

Among various metal ions, the Cu(II) ion has gainedattention due to both its beneficial and adverse effects.Use of copper compounds such as copper sulfate incertain dyeings, direct dyeing in particular, has foundto improve the fastness to washing and light. However,the presence of copper in water can seriously affect theperformance of various unit operations of textile pro-cessing, such as desizing, scouring, bleaching, dyeing,etc. Hence, it is advisable to avoid copper/brass fittings,especially in bleaching plants. Copper is found to beadsorbed by enzyme molecules to form complexes

and inactivate the enzymatic action. Copper exhibits acatalytic action on hydrogen peroxide decomposition.The presence of copper is reported to cause instabilityin peroxide bleaching baths and to damage the cottonduring bleaching. Copper is readily absorbed on wooland therefore causes damage during peroxide bleach-ing. The presence of copper ions causes a deleteriouseffect on the shades of various dyes used for cellulose,nylon and protein fibers; nevertheless, it enhances thewash and light fastness properties.2,4 The deleteriouseffect of Cu(II) ions observed on hydrogen peroxidebleaching of scoured cotton fabric and various directand reactive dyeing of cotton is presented in Table 1and Figure 1. Copper content in the textile and alliedindustries effluent was found to be approximately77mg/L5 as against the World Health Organization

Department of Textile Chemistry, The Faculty of Technology &

Engineering, The M S University of Baroda, Vadodara, India

Corresponding author:

DP Chattopadhyay, Department of Textile Chemistry, The Faculty of

Technology & Engineering, The M S University of Baroda, Vadodara,

India 390001.

Email: dpchat6@gmail.com

Textile Research Journal

2014, Vol. 84(14) 1539–1548

! The Author(s) 2014

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(WHO) norms 0.05mg/L.5 Traces of copper (5–45mg/L) in underground water and about 110 mg/kg of soil inand around Surat (India) have been detected.6

The adverse effect of such metal ions can be con-trolled either by using chelating agents such as ethylenediamine tetra acetic acid (EDTA), diethylene triaminepenta acetic acid (DTPA), nitrilo triacetic acid (NTA),etc.7 or metal ions can be chemically precipitated orcoagulated as salts or reduced to metallic form. Theycan be separated out from the liquid phase by filtration,settling, centrifuging or electro deposition.1,8,9 Variousnatural products, such as wood bark and clay,10

rice hull, cotton fibers, bamboo pulp, peanut skin,etc., and chitosan have been found to remove metalcations from streams.11–14 The detrimental effects onthe environment still persist when water is treatedthrough the first route due to the existence of metalions in discharged water, while metal ions are removedfrom discharged water by the second route, which issafer.

Chitosan is a natural-based product derived fromalkaline deacetylation of a biopolymer, chitin. It isthe second most abundant biopolymer after cellulose.The amount of presence of primary amino groups pre-sent on the chitosan molecule is characterized by thedegree of deacetylation (DAC).15 The applicationpotential of chitosan and its derivatives for the recoveryof valuable metals or the treatment of contaminatedeffluents is well documented.16,17 Our earlier report18

has shown the scavenging property of chitosan for cal-cium ions. Karthikeyan et al.19 studied the dynamicsand equilibrium sorption of Zn(II) onto chitosan.They observed that a maximum of six minutes wererequired for complete sorption of Zn ions by chitosanobeying the Freundlich and Langmuir isotherms.Nomanbhay and Palanisamy20 used chitosan-coatedoil palm shell charcoal successfully for the adsorptionof chromium ions from water. Bioconversion of highly

CuSO4 content

in dye bath,

mg/L

C.I. Direct

Red 81

C.I. Direct

Yellow 44

C.I. Re.Red

152

C.I. Re.Blue

25

Control

50

100

200

Figure 1. Effect of Cu(II) ions in a dye bath on the shades of direct and reactive dyeing on cotton fabric.

Table 1. Effect Cu(II) ions on hydrogen peroxide bleaching of

cotton fabric

CuSO4 content in

bleach bath, mg/L

Whiteness

index

Yellowness

index

Brightness

index

Control 88.40 1.33 78.08

100 85.98 4.29 73.02

200 85.06 4.69 71.17

500 84.14 5.58 69.32

Scoured sample: W.I.¼ 78.07, Y.I.¼ 17.02 and B.I.¼ 56.91.

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toxic Cr(VI) into Cr(III) was also observed, which isessential in human nutrition, especially in glucosemetabolism. Chang and Chen21 isolated Au(III) ionsfrom water on chitosan-coated Fe3O4 nanoparticles.They found that the gold ions could be quickly andefficiently adsorbed. Guibal et al.22 synthesized thioureaderivative of chitosan for platinum and mercury recov-ery owing to the chelating affinity of sulfur ligands.Abdel-Mohdy et al.23 introduced diethyl amino ethylmethacrylate (DEAEMA) groups onto the chitosanbackbone through radiation grafting and studied thechelation property of grafted derivative on copper,zinc and cobalt ions. They reported that the extent ofmetal ions uptake by the chitosan–DEAEMA deriva-tive was preferentially higher for copper ions, followedby zinc and cobalt ions. The present investigation wasaimed at understanding the chelation property of chit-osan and its derivatives towards Cu(II) ions. Chitosanof different molecular weight, nano-chitosan of varyingparticle size and trimethyl chitosan derivative of differ-ent degrees of quaternization were taken for the study.The test sample before and after treatment was ana-lyzed iodometrically for knowing the presence ofCu(II) ions and Fourier transform infrared (FTIR)spectroscopy was employed for the characterization ofthe chitosan–Cu(II) complex.

Materials and methods

Materials

One hundred percent cotton fabric (warp and weft 40 s,ends/inch 142, picks/inch 72 and g/m2 125), at ready fordyeing stage, was procured from Mafatlal IndustriesLtd, Nadiad, Gujarat State, India. Chitosan of differentmolecular weights was obtained from MarineChemicals, Kerala State, India (CHT-MC) andMahtani Chitosan Pvt Ltd, Gujarat State, India(CHT). A low molecular weight chitosan (CHT-D)

was synthesized from CHT by depolymerization withnitrous acid as described earlier.24 The specifications ofdifferent grades of chitosan are given in Table 2.Various direct and reactive dyes namely, C.I. DirectRed 81, C.I. Direct Yellow 44, C.I. Reactive Red 152and C.I. Reactive Blue 25 were kindly supplied byColourtex Industries Ltd, Gujarat State, India. Theanionic detergent (Ezee, Godrej, India) employed wasof commercial grade.

Other reagents, such as acetic acid, acetone, methylalcohol, methyl iodide, EDTA, sodium thiosulfate,potassium iodide, sodium iodide, sodium hydroxide,soda ash, sodium sulfate, copper sulfate, N-methyl-2-pyrrolidone (NMP), etc., used were of analytical grade.

Synthesis of trimethyl chitosan chloride

Trimethyl chitosan chloride (TMCHT) was synthesizedas follows: purified chitosan (CHT) (1 g) was treatedwith the required amount methyl iodide (5 and 15 gfor two different levels of degree of quaternization) inthe presence of sodium iodide 2.4 g and sodium hydrox-ide (2 g) dispersed in NMP(40mL) in a stainless steelreaction vessel at 50�C for 24 h. Trimethyl chitosaniodide was recovered from using acetone then subjectedto ion exchange by treatment with sodium chloride(10%, 50mL) for 1 h. TMCHT was then recoveredfrom acetone with repeated washings and oven driedat 55�C.

Synthesis of nano-chitosan dispersions

The method for synthesis of nano-chitosan dispersionswas followed as discussed elsewhere.18 The preparednano-chitosan (CHTN) from the starting materialCHT was stored in refrigerator. The particle size andsize distribution of the chitosan were analyzed using aparticle size analyzer (Zetasizer Nano ZS90, MalvernInstruments Ltd, UK).

Table 2. Chitosan derivatives employed for chelation study

Sample code Chemical name

Properties

DAC, % Molecular weight Particle size, nm DQ, %

CHT-MC Chitosan 89.03 654,127 – –

CHT Chitosan 90 135,839 4014 –

CHT-D Chitosan 90 38,733 – –

CHTN1 Nano-chitosan – – 408.73 –

CHTN2 Nano-chitosan – – 534.2 –

TMCHT1 Trimethyl chitosan chloride – – – 13.41

TMCHT2 Trimethyl chitosan chloride – – – 50.92

DAC: degree of deacetylation; DQ: degree of quaternization.

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Hydrogen peroxide bleaching

of cotton fabric

Scoured cotton fabric was treated with solution con-taining hydrogen peroxide (30%, 10 g/L), soda ash(10 g/L), sodium silicate (10 g/L) and detergent (1 g/L)at about 85�C for 60 minutes. The material-to-liquorratio was maintained at 1:30. After bleaching was over,the fabric was washed at 80�C for 20 minutes and thenrinsed.

Dyeing with direct dyes

The cotton fabric was dyed with direct dye (1% o.w.m.)in the presence of Glauber’s salt (20% o.w.m.) and sodaash (5% o.w.m.) at temperature 90�C for 60 minutes.The material-to-liquor ratio was maintained at 1:40.The dyed sample was then rinsed with cold waterthree times, air dried and hot pressed. The dyedsamples were evaluated for color strength in terms ofK/S values on a computer color matching system(Spectroscan 5100A, Premier Colorscan, India).

Fourier transform infrared analysis

FTIR spectra of CHT and TMCHT derivatives weretaken on a Thermo Nicolet iS10 Smart ITR spectro-photometer (Thermo Fisher Scientific, USA) in thewavenumber between 4000 and 500 cm–1.

Treatment of Cu(II) ions containingwater with chitosan derivatives

The required quantity of chitosan or chitosan deriva-tive (e.g. 1 g/L) was treated with copper sulfate solutioncorresponding to a Cu(II) ions concentration of394.32mg/L in the presence of acetic acid (0.7mL/Lfor pH 5.5 and 1.5mL/L for pH 3.5) with occasionalstirring. After the prescribed reaction time is over, chit-osan was precipitated out by the addition of a fewdrops of sodium hydroxide (10%) solution. The solu-tion was then filtered, the filtrate was analyzed forCu(II) ions content iodometrically and the residuewas analyzed for FTIR spectroscopy.

Iodometric method for determinationof Cu(II) ions

One hundred milliliters of aliquot (sample solution) wastaken in a conical flask and mixed with 10mL of 10%liquor ammonia to obtain a dark blue color. The solu-tion was then neutralized with acetic acid; a slightexcess acid was added, followed by 2 g of potassiumiodide. The flask was placed in the dark for about15minutes for complete liberation of free iodine and

then titrated against 0.1N sodium thiosulfate usingstarch as the indicator. Ammonium thiocyanate (2 gin 10mL water) was then added and titration contin-ued. The amount of Cu(II) present in the given solutionwas calculated using the following equation:24

CuðIIÞ ions content; mg=L ¼A� 6:36� 1000

V

where A is the amount (mL) of 0.1N Na2S2O3 takenin the burette and V is the volume (mL) of aliquottaken for titration (100 mL).

Chelation efficiency in terms of sorption of Cu(II)

ions by chitosan (mg/g) ¼I0 � IFM

Chelation efficiency in terms of copper ions removal

from water (mg/L) ¼ I0 � IF

where I0 is the initial concentration (mg/L) of Cu(II)ions and IF is the concentration (mg/L) of Cu(II) ions intreated water. M is the mass (g) of chitosan.

Results and discussion

Characterization and mechanism of chelationof copper (II) ions on chitosan

The important ligands on chitosan macromoleculesthat form a complex with metal ions are oxygen per-taining to primary and secondary hydroxyl groups andnitrogen belonging to amino and acetamido groups.The structural changes in chitosan occurred due to che-lation with Cu(II) ions; they can be conveniently stu-died using FTIR spectra analysis. The FTIR spectra ofCHT and the CHT–Cu complex are presented inFigures 2 and 3.

The broad bands at wave numbers 3355, 3284 cm–1

of the FTIR spectrum of chitosan (Figure 2) may beattributed to O-H, NH and NH2 stretching. Theabsorption band at 1651 cm–1 was due to C¼O (car-bonyl) stretching of the secondary (amide I) amidebond, a characteristic of the N-acetyl group, and themedium peak at 1585 cm–1 appeared due to bendingvibrations of N-H of the amide II bond (N-acetyl resi-due) and the primary amine. Another medium absorp-tion peak at 1374 cm–1 was attributed to the N-Hlinkage of amide III. A strong absorption peak at1025 cm–1 was due to the primary hydroxyl group, acharacteristic peak of -CH2OH in primary alcohols,arising from C-H stretching.25,26 The structural changesin chitosan arose due to complex formation withcopper ions that were observed in the spectrum,

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Figure 2. Fourier transform infrared spectrum of CHT.

Figure 3. Fourier transform infrared spectrum of CHT–Cu complex residue.

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as shown in Figure 3. The broadening of the peakat 3355 cm–1 and progressive reduction of the peak atthe wave number at 1025 cm–1 indicated the involve-ments of amino and hydroxyl groups in the scavengingof the Cu(II) ions. Formation of a new peak at1392 cm–1 and modifications in peaks due to variousamide groups characterized interaction of thesegroups with Cu(II) ions.27 The complex formation ofchitosan with copper ions may be explained with thehelp of its electronic configuration of copper ions.Copper, although not strictly termed as a transitionmetals as its d orbitals are complete, still forms anumber of complexes when its ions have incomplete dorbitals, for example in the case of Cu(II) ions havingthe co-ordination numbers usually 2, 4 and 6 facilitateco-ordinate bond formation.28 The possible ways inwhich Cu(II) ions become bound to chitosan are illu-strated in Figure 4.

In order to understand the chelation property, chit-osans in various forms and grades were employed aslisted in Table 2 and the performances were comparedwith tetra sodium salt of Na4EDTA.

Effect of structural modification of chitosanon chelation of Cu(II) ions

The extent of copper ions binding chitosan is believedto be dependent on the availability of a number of elec-tron donating ligands, such as O and N. The state ofthese ligands on chitosan macromolecules is anticipatedto be altered due to chemical modifications, such asquaternization. The Cu(II) ion sorption by various chit-osan derivatives at pH 5.5 is shown graphicallyin Figure 5.

Figure 5 illustrates that EDTA attained the equilib-rium rapidly for the copper ion binding and the chela-tion capacity was maximum. The prolonged treatmentshowed little improvement in chelation efficiency after

an initial 15 minutes of treatment. The chelation behav-ior of chitosan was comparatively slower. The molecu-lar weight of chitosan was found to have a little effecton its chelation behavior. At the onset and during thefirst hour of treatment, the rate of chelation was slightlyhigher for low molecular weight chitosan. When thetreatment was continued for a longer time the copperion sorption leveled off for different molecular weightchitosans. With an increase in molecular weight of chit-osan (CHT-MC), the rate of sorption of copper ionswas slowed down, but the absolute adsorption afterprolonged treatment (>3 h) was higher. Thus, the influ-ence of the molecular weight of chitosan, in the firsthour of treatment, seemed to be more pronounced onthe rate of sorption than on the absolute sorption ofcopper ions. Modification of chitosan by the

O

O

O

HH

H

H

OH NH

H

O

H

NH2H

OH

H

CH2

H

O

H CH2

OH

COOH

CH3

O

O

O

HH

H

H

OH NH

H

O

H

NH2H

OH

H

CH2

H

O

H CH2

OH

COOH

CH3

OHH

Cu

Cu(II)

CHT-Cu ComplexCHT

Figure 4. Chelation of Cu(II) ions by chitosan.

0

50

100

150

200

250

300

350

400

0

15 m

ins

30 m

ins

45 m

ins

60 m

ins

90 m

ins

2 h 3 h 4 h 24 h

Che

lati

on e

ffec

ienc

y, m

g/g

EDTA CHT-MC CHTCHT-D TMCHT1 TMCHT2

Figure 5. Chelation behavior of chitosan derivatives for Cu(II)

ions. (Concentration of chelating agent 1 g/L; initial concentration

of Cu(II) ions 394.32 mg/L; pH 5.5.)

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quaternization process was found to reduce its metalbinding capacity. The chelation capability of TMCHTwas decreased with increase in the degree ofquaternization.

The substantially higher chelation power of EDTAmay be attributed to the combined effect of ionic link-ages of Cu(II) cations with anionic carboxylate groupsand the co-ordinate bonds with amino groups. Theelectrostatic attraction between EDTA and metal cat-ions may be the driving force for the attachments.Chitosan, on the other hand, is a polymeric materialhaving rigid conformation. When dissolved in water inthe presence of acid, most of the amino groups areprotonated and therefore are incapable of bondingwith copper cations. The only possible route of inter-action is through unprotonated amino groups, hydro-xyl groups and/or N-acetyl groups. Further, thesepolycationic macromolecules in solutions are mostlyswollen entangled bunches exposing a very small sur-face area and hence provide fewer ligands for inter-action with metal ions. The chitosan molecules,therefore, are slower in chelation compared withEDTA. The latter inactivates metal ions but does notremove them. On the other hand, chitosan, a bio-degradable chelating agent, removes metal ions evenwhen present in traces. The process can be madefaster by using nano-chitosans, chemical modificationsof parent chitosan, etc. It is a better choice for medicalusage.

Being a polycationic polymeric material, chitosancan easily undergo sedimentation due to nucleationand can be removed simply by decantation or bysand filtration. On account of this unique property,chitosan can be used to minimize the turbidity inwater treatment. Since the treatment is done prior tofinal filtration, no additional filtration is required.

The availability of accessible interactive ligands forchelation is determined by the physical state of macro-molecules in solvent, which in turn is determined byits molecular size and hence the molecular weight.Low molecular weight chitosans (CHT-D) in solutionare comparatively more extended and mobile due toless intra and intermolecular forces and thus providemore surface area for chelation reactions and there-fore show an enhanced rate of sorption. Conversely,high molecular weight chitosan (CHT-MC) moleculesin solution are more entangled and compact withlesser accessibility of ligands, which led to a lowerrate of sorption of Cu(II) ions. On prolonged treat-ment, large-sized chitosan molecules slowly undergodepolymerization due to hydrolysis, which results ina fall in viscosity as was observed earlier,18 leadingto the opening of sites and continued chelation. Thechelation property of TMCHT, however, was reducedas some of the amino groups were engaged in forming

bonds with methyl groups, which consume the lonepair of electrons of nitrogen and, also, the presenceof bulkier methyl groups restricts the diffusion ofmetal ions.

For unmodified chitosans, recycling of the usedproduct would be difficult as the attachment of metalions to chitosan is accomplished by the co-ordinatelinkages. However, chemical modification of chitosanby introducing anionic groups, such as carboxyl, sul-fonate, etc., can impart an ion exchange property. Thetreatment of chitosan is effective in removing traces ofmetal ions and hence can be beneficial in the isolationof precious metals.

Effect of pH on chelation of Cu(II) ions

An important parameter that alters the state of ligandson chitosan and its derivatives is the pH of the medium.Acidic pH is required for dissolution of chitosan inaqueous medium; however, it leads to protonation ofamino groups. In order to understand the effect of pHon the chelation behavior of CHT and its quaternizedderivative of maximum degree of quaternization, thatis,TMCHT2, two different pH values were selected,namely pH 3.5 and pH 5.5. Higher pH (pH �7) wasavoided due to the formation of hydroxides of coppercausing precipitation.29 The sorption of Cu(II) ions byCHT and TMCHT2 as a function of pH is presented inFigure 6. CHT was found to be more efficient in com-plex formation with Cu(II) ions at pH 5.5. Similarresults were observed in the case of TMCHT2,although it was found to be less efficient comparedwith CHT. It is known that the attachment of Cu(II)

0

50

100

150

200

250

300

350

0

15 m

ins

30 m

ins

45 m

ins

60 m

ins

90 m

ins

2 h 3 h 4 h 24 h

Che

lati

on e

ffic

ienc

y, m

g/g

pH 3.5 (CHT Treated) pH 5.5 (CHT Treated)pH 3.5 (TMCHT2 Treated) pH 5.5 (TMCHT2 Treated)

Figure 6. Effect of pH of the medium on the chelation behavior

of chitosan derivatives at different time intervals. (Concentration

of chelating agent 1 g/L; initial concentration of Cu(II) ions

394.32 mg/L.)

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ions with chitosan is possible through co-ordinatebonds by the donation of a lone pair of electrons ofamino, acetamido and hydroxyl groups. In highlyacidic medium, that is, at pH 3.5, most of the aminogroups are protonated and therefore they do notremain available for co-ordinate bond formation. Inthat case the scavenging of Cu(II) ions would beassigned to hydroxyl and N-acetyl groups. At a slightlyhigher pH (pH 5.5), some of the amino groups remainunprotonated or free. The free amino groups, due tothe presence of the lone pair of electrons, are capable offorming co-ordinate linkages with copper ions andhence an improvement in chelation was observed atpH 5.5. TMCHT exerts ionic repulsion to copper cat-ions and, in addition, the bulkier side methyl groups actas a barrier and lead to the reduction in chelationefficacy of trimethyl chitosan.

Effect of concentration of chitosan derivativeson chelation of Cu(II) ions

An important parameter that influences the sorption ofmetal ions is the concentration of the chelating agent.The aqueous behavior of chitosan was found to be gov-erned by the storage time and the behavior of chitosanin solution, which may affect the chelation capacity.20

Thus, in order to understand the chelation behavior,the effect of different concentrations and molecularweights of chitosan on the removal of copper ionsfrom water for two different durations of treatment,namely, short (1 h) and long (24 h) treatment times,respectively, was studied. The results are shown inFigures 7 and 8.

It is observed from Figures 7 and 8 that the sorptioncurves for EDTA followed linearity with respect to con-centration and almost the same level of chelation effi-cacy was observed for both the durations of treatment.The amount of Cu(II) ions removed from treated liquorwas found to be increased with an increase in concen-tration of chitosan derivatives. The sorption curve forlow molecular weight chitosan (CHT-D), when treatedfor a short time (1 h), was found to be linear within thechosen concentration range, while high molecularweight chitosans showed some deviations at higher con-centrations (Figure 7).The chelation efficiency of differ-ent forms of chitosan was found to follow the followingtrend CHT-D>CHT>CHT-MC. On prolonged treat-ment, that is, when the treatment was extended to 24 h(Figure 8), the chelation behavior of chitosan wasaltered particularly for high molecular weight chito-sans. The chelation behavior of low molecular weightchitosan (CHT-D) was not much influenced. The che-lation efficiency of chitosans was, however, reversed asagainst short duration of treatment, that is, CHT-MC>CHT>CHT-D. The linearity observed for low

molecular weight chitosan (CHT-D) can be ascribed tothe presence of its molecules in solutions in compara-tively free and more extended form due to less intra andintermolecular forces. These molecules provide, in thechosen concentration range, a uniform number of sitesproportional to the concentration of chitosan. Duringthe short treatment time, high molecular weightchitosan (e.g. CHT-MC) molecules in solution stillremain entangled due to overlapping of macromol-ecules, as revealed by the viscosity measurementreported elsewhere.18 Therefore, they provide fewersites for the interaction with Cu(II) ions, resulting in

0

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0

0.50 g

/L1 g

/L

1.5 g/

L2 g

/L

Che

lati

on e

ffic

ienc

y, m

g/L

EDTA CHT-MC CHT CHT-D

Figure 7. Effect of concentration and molecular weight

of chitosan on chelation efficiency for 1 h treatment.

(Initial concentration of Cu(II) 754.93 mg/L; pH 5.5.)

0

100

200

300

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500

600

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0

0.50 g

/L1 g

/L

1.5 g/

L 2 g

/L

Che

lati

on e

ffic

ienc

y, m

g/L

EDTA CHT-MC CHT CHT-D

Figure 8. Effect of concentration and molecular weight of

chitosan on chelation efficiency for 24 h treatment.

(Initial concentration of Cu(II) 754.93 mg/L; pH 5.5.)

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decreased chelation. On prolonged treatment, highmolecular weight chitosans may undergo depolymeriza-tion due to hydrolysis and may also display moreopened conformation due to disentanglement leadingto opening up of more sites for chelation, which ismore prominent at higher concentration.29,30 Thus,the depolymerization leading to opening up of molecu-lar conformation is comparatively more prominent inhigh molecular weight chitosan than in low molecularweight chitosan on prolonged treatment and what wevirtually see is the reversal in chelation efficiency onprolonged treatment.

Effect of particle size of chitosan on chelationof Cu(II) ions

The reduction in particle size of chitosan macromol-ecules to the nano level can furnish increased surfacearea and hence a greater number of reactive sites (lig-ands) for metal scavenging. The particle size of chitosanwas reduced by ionotropic gelation with sodium tripo-lyphosphate (TPP), as described earlier.31 The varyinglevels of particle size of nano-chitosan, for a givenmolecular weight chitosan, were obtained by varyingthe concentration of chitosan. Two different nano-chit-osans of average particle sizes 408 and 534 nm wereobtained from CHT from initial concentrations of 1.5and 2 g/L. These stock solutions were employed for thechelation study of copper ions at a concentration of1 g/L, obtained by dilution. The effect of particle sizeon the chelation efficiency of chitosan is shown graph-ically in Figure 9. The results revealed that the rate ofchelation was enhanced by the reduction in particlesize of chitosan, indicating faster establishment of

equilibrium with higher equilibrium chelation effi-ciency. Besides the increased surface area due to reduc-tion in particle size, the presence of TPP can also act asa ligand for scavenging the copper ions.28

Conclusion

The presence of excessive copper ions adversely affectsthe bleaching efficiency and dyeing results. Chitosan ofdifferent molecular weights and quaternized derivativesof varying degrees of quaternization were employed inthe present experiment. The effect of particle size ofchitosan on scavenging efficiency was also studied.

The binding of copper ions to chitosan was con-firmed by FTIR spectroscopy. The chelation efficiencyof trimethyl chitosan (TMCHT) was reduced with anincrease in the degree of quaternization. A highly acidicpH was not found to be suitable for chelation of metalions. A milder acidic condition (pH 5.5) showed betterresults. The sorption of copper ions was increased withincrease in the concentration of chitosan/chitosanderivatives. The extent of chelation was found to behigh for low molecular weight chitosan when treatedfor a shorter time and decreased with increase in themolecular weight, whereas for higher sorption time areverse trend was noticed. Reduction in particle size ofchitosan enhanced both the rate and amount of scaven-ging metal ions.

Funding

This research received no specific grant from any fundingagency in the public, commercial or not-for-profit sectors.

References

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Figure 9. Effect of particle size on chelation efficiency of CHT

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