174 Chiang Mai J. Sci. 2014; 41(1)

Chiang Mai J. Sci. 2014; 41(1) : 174-183http://epg.science.cmu.ac.th/ejournal/Contributed Paper

Utilization of Chitosan/Bamboo Charcoal Compositeas Reactive Dye AdsorbentWalaikorn Nitayaphat*Department of Home Economics, Faculty of Science, Srinakharinwirot University, Bangkok, 10110, Thailand.*Author for correspondence; e-mail: walaikorn@swu.ac.th

Received: 7 November 2012Accepted: 27 February 2013

ABSTRACTChitosan/bamboo charcoal composites were prepared by blending chitosan with

bamboo charcoal and forming composite beads. The composites were used as reactive dyeadsorbents. Adsorption equilibrium experiments were carried out as a function of contacttime, bamboo charcoal concentration, pH value, and adsorbent dosage level. The equilibriumtime of dye adsorption was found to be 8 h. Composite adsorbent had the highest adsorptionefficiency when the weight ratio was 50/50. The maximum dye removal took place at theinitial pH value of 4.0. The optimum adsorbent dosage for dye removal was 6.0 g. Underabove optimal conditions the maximum dye removal was 98.4%. The adsorption isothermof chitosan and chitosan/bamboo charcoal composite beads agreed well with the Langmuirmodel. The maximum adsorption capacity was 3.47 mg/g for chitosan bead and 4.32 mg/gfor chitosan/bamboo charcoal composite bead, respectively. SEM micrographs confirm thatafter adsorption the pores were packed with Reactive Red 152.

Keywords: chitosan, bamboo charcoal, composite, reactive dye, adsorbent

1. INTRODUCTIONThe textile industry is one of the most

important and rapidly expanding industrialsectors in developing countries. Among thevarious processes in the textile industry, thedyeing process uses large volumes of waterfor the dyeing, fixing and washing processes.Therefore, the wastewater generated form thetextile processing industries contains suspendedsolids, high amounts of dissolved solids,un-reacted dyestuffs and other auxiliarychemicals which are used in the various stagesof dyeing and with other processing [1].The water coloration from the presence ofdyes, even in small concentrations, is highlyvisible and affects the esthetics, water

transparency and the gas solubility of waterbodies [2]. Among several classes of textiledyestuffs, the reactive dyes represent about50% [3] of the total market share due to theiradvantages, such as with a wide variety ofcolor shades, bright colors, excellent colorfastness, easy application, and minimal energyconsumption [4]. A large fraction, typicallyabout 30%, of applied reactive dye is wastedbecause of the dye hydrolysis in the alkalinedyebath.

Several wastewater treatmenttechnologies have been applied for colorremoval, including physical, chemical andbiological processes. In the past years,

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adsorption processes have been shown to beeffective along with economical treatmentprocesses, thus many low-cost adsorbentshave been investigated, such as clay minerals,rice husk, leaf powder, fly ash, and bacterialbiosorbents [5-11]. However, low adsorptioncapacities of these adsorbents toward dyeslimit their applications in practical fields.

Chitosan, the deacetylated product ofchitin, which are extracted from variousanimals and plants, are the second mostabundant natural biopolymers found on earth,next to cellulose. Due to its biocompatibility,biodegradability, antimicrobial activity,non-toxicity, and exhibits a high adsorptioncapacity, chitosan has been extensivelyinvestigated for several decades for use inwastewater treatment towards many classesof dyes, such as reactive dyes [12-15], aciddyes [16-17], and direct dyes [18]. Chitosancontains high contents of amino functionalgroups, which might form electrostaticattraction between chitosan and solutes toadsorb the dyes [19]. Nevertheless, the marketcost of chitosan is relatively high and

its specific gravity should be improvedwith practical operations. Bamboo charcoalpowder contains many pores and gaps in itsstructure, making it excellent for adsorption.

In this study, chitosan/bamboo charcoalcomposite beads were used to removereactive dye from an aqueous solution bybatch adsorption process and the parametersaffecting the adsorption capacity of thechitosan/bamboo charcoal composite beads,including bamboo charcoal concentrationvariation and pH, were investigated.

2. MATERIALS AND METHODS2.1 Materials

Chitosan powder with an averagemolecular weight of 150 kDa and adeacetylation degree of 90% was purchasedfrom Seafresh Chitosan (Lab) Co., Ltd.(Thailand). Bamboo charcoal powder, witha particle size range of 40-45 micron andspecific surface area about 743 m2/g, used asfiller. C. I. Reactive Red 152 (Figure 1) wasused as a model anionic dye. Glacial aceticacid was purchased from J.T. Baker (Thailand).

Figure 1. Structure of C. I. Reactive Red 152.

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2.2 Preparation of Chitosan /BambooCharcoal Composite Beads

Pure chitosan beads were prepared bydissolving 2 g of chitosan powder in 50 mlof 2% (v/v) acetic acid solution and stirringfor 3 h at room temperature. This mixturewas dropped through a syringe into aprecipitation bath containing 1 dm3 of analkaline coagulating mixture (H2O: EtOH:NaOH = 4:5:1, w/w) gave rise to the chitosanbeads. The beads were extensively washedwith de-ionized water and preserved in anaqueous environment for future use.

Different weights of bamboo charcoalpowder (0.2, 0.6, and 1.0 g) were added into50 ml of 2% (v/v) acetic acid solutiontogether with 1.8, 1.4, and 1.0 g of chitosan,respectively. The mixtures were stirred for3 h at room temperature. Then, the mixtureswith different ratios by weight (chitosan/bamboo charcoal: 90/10, 70/30, and 50/50)were dropped through a syringe into aprecipitation bath containing 1 dm3 of analkaline coagulating mixture gave rise to thechitosan/bamboo charcoal composite beads.

2.3 Surface Area and Porosity AnalysisThe specific surface area and pore size

distribution were determined by surfaceanalyzer (Autosorb-1, Quantachrome) usingN2 as adsorbate. The diameter (D) andporosity (ε) of the chitosan and chitosan/bamboo charcoal composite beads weredetermined by the amount of water withinthe pores of the chitosan and chitosan/bamboo charcoal composite beads [20]. Thediameter (D) and porosity (ε) can be calculatedusing these equations:

D = 6

ε =

where WW (g) is the wet weight of the beadsbefore drying; WD (g) is the wet weight ofthe beads after drying; ρw is the density ofwater, 1.0 g/cm3; and ρMat is the density ofmaterial.

2.4 Adsorption ExperimentsAdsorption experiments were carried

out by using chitosan and chitosan compositesamples (with different bamboo charcoalpowder content) as adsorbents. Batchadsorption experiments were carried outusing a water bath shaker (Model RAPID).For a typical adsorption experiment, 1.0 gadsorbent was dispersed in 50 mL of 50 mg/L aqueous Reactive Red 152 solution withoutadjusting the pH value. The dispersion wasstirred at a speed of 120 rpm at 30°C. Thedye concentrations were determined bymeasuring the absorbance at the maximumabsorption of Reactive Red 152 (520 nm)using spectrophotometer (Model ICS-TEXICON).

The effect of pH on adsorption capacitieswas determined in the pH range from 3 to 9.The pH was adjusted with 0.1 mol/L NaOHor 0.1 mol/L HCl. Different amounts ofadsorbent in the range of 1.0 to 6.0 g wereused to examine the effect of an adsorbentdosage on adsorption of Reactive Red 152.

2.5 Adsorption IsothermsAdsorption isotherms were obtained by

using 1 g of adsorbent beads and 50 mL ofdye solution with different concentrations(10-100 mg/L). These solutions werebuffered at an optimum pH (pH 6.0) foradsorption and stirred in a water bath shakeruntil they reached adsorption equilibrium, i.e.,8 h. The quantity of dye adsorbed was derivedfrom the concentration change.

2.3.1

2.3.2

WD/ρMat+(WW-WD)/ρW

(WW-WD)/ρW

1/3[ ]

WD/ρMat+(WW-WD)/ρW

π

x 100%

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2.6 Scanning Electron Micrograph(SEM) Study

Morphological features and surfacecharacteristics of chitosan/bamboo charcoalcomposite beads were obtained from thescanning electron microscopy (SEM) usinga JEOL JSM-5400 microscope. Beforeobserving the SEM, all the samples were fixedon aluminum stubs and coated with gold.

3. RESULTS AND DISCUSSION3.1 Surface Area and Porosity Analysis

The porosity and diameter of chitosanand chitosan/bamboo charcoal compositebeads are shown in Table 1. The porosity ofchitosan/bamboo charcoal composite beadswas significantly higher than of the chitosanbeads due to the presence of bamboocharcoal. The diameter of chitosan/bamboocharcoal composite beads was less than

that of chitosan beads, indicating bamboocharcoal addition makes chitosan/bamboocharcoal composite beads smaller thanchitosan beads. Table 2 shows the specificsurface area and the pore size distributionof chitosan and chitosan/bamboo charcoalcomposite beads. The total porosity isclassified into three categories according tothe pore diameter (d). The categories are:macropores (d>50 nm), mesopores (2<d <50nm), and micropores (d<2 nm) [21]. Basedon Table 2, chitosan and chitosan/bamboocharcoal composite beads are mesopore. It isclear that with the addition of bamboocharcoal, the surface areas of chitosan/bamboo charcoal composite beads becamelarger than that of chitosan beads, resultingthat the chitosan/bamboo charcoal compositebeads might be able to enhance the reactivedye adsorption.

Table 1. Porosity and diameter of chitosan and chitosan/bamboo charcoal composite beads.

Adsorbent

CTS90:10 CTS/BC composite70:30 CTS/BC composite50:50 CTS/BC composite

Wet weight(WW, mg )

7.377.127.297.15

Dry weight(WD, mg )

0.230.230.250.26

Porosity(ε, %)

86.4490.9494.3594.58

Diameter(D, mm)

4.874.844.794.53

Table 2. Specific surface area and pore size distribution of chitosan and chitosan/bamboocharcoal composite beads.

Adsorbent

CTS90:10 CTS/BC composite70:30 CTS/BC composite50:50 CTS/BC composite

Specific surface area(m2/g)2.6323.1728.3632.52

Average pore diameter(nm)3.553.472.662.43

Pore volume(cm3/g)0.0310.0340.0390.048

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3.2 Adsorption Studies3.2.1 Effect of contact time and bamboocharcoal concentration in beads

The effect of contact time and theinclusion of different bamboo charcoalconcentration on the removal of ReactiveRed 152 are summarized in Figure 2. It canbe observed that the chitosan bead has goodadsorption for Reactive Red 152. Adsorptionsof anionic dyes occur mainly due to theelectrostatic interactions between theprotonated amine groups on the chitosan(-NH3

+) and the SO3- groups of the anionic

dyes structures [12]. All of the studied chitosanand chitosan/bamboo charcoal composite

beads presented similar trends. The ReactiveRed 152 was rapidly adsorbed in the first 1 h,and then the adsorption rate decreasedgradually from 1 h to 7 h and finally reachedequilibrium in 8 h. This observation could beexplained as at the very beginning of theadsorption process, abundant active sites areavailable on the surface of chitosan/bamboocharcoal composite bead, which makes theadsorption process easier. As time went by,the adsorption sites become scarce, thusresulting in a decrease of adsorption efficiency.Thus, in the following experiments theequilibrium time was fixed at 8 h.

Figure 2. Effects of contact time and bamboo charcoal concentration in beads on ReactiveRed 152 removal (adsorbent dosage = 1.0 g, dye concentration = 50 mg/L, volume = 50 mL,pH = 6.0).

The dye removal of the chitosan/bamboo charcoal composite beads increasedwith the increasing bamboo charcoalconcentrations in the composite beads.The maximum dye removal (84.4%) wasobserved at the weight ratio of 50/50 ofchitosan to bamboo charcoal in chitosan/bamboo charcoal composite beads. Bamboocharcoal is already reported as goodadsorbents for various materials due to itslarge specific surface area, and porous

structure [22]. It is clear that with the additionof bamboo charcoal, the surface areas ofchitosan/bamboo charcoal composite beadsbecame larger than that of chitosan beads,resulting that the chitosan/bamboo charcoalcomposite beads might be able to enhancethe dye removal. However, the dye removalof the chitosan/bamboo charcoal compositebeads increased with increase in bamboocharcoal concentration up to a certain level(weight ratio of chitosan to bamboo charcoal

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= 50/50). However, the higher bamboocharcoal concentrations in the chitosan/bamboo charcoal composite beads (weightratio of chitosan to bamboo charcoal lessthan 50/50) appear to induce the formationof larger aggregates of bamboo charcoal,which obstruct the formation of the chitosan/bamboo charcoal composite beads.

3.2.2 Effect of pHThe effect of the initial solution pH on

Reactive Red 152 adsorption is shownin Figure 3. The maximum dye removalwas 87.5% at pH 4 followed by a slightdecrease from pH 5 to 9. During adsorption,

protonation of amine groups is necessaryfor its interaction with negatively chargedReactive Red 152 molecules. At lowerpH levels more protons will be availableto protonate amine groups of chitosanmolecules, thereby increasing the electrostaticattraction of dye molecules to active sitesand causing the observed increase in dyeadsorption [23-24]. On the other hand, inalkaline conditions of pH (>7), the aminogroups are not protonated, and the interactionbetween the dye and the adsorbent occurs byvan der Waals forces. The adsorption occurspreferentially for physical interaction,decreasing the dye removal.

Figure 3. Effect of initial solution pH on Reactive Red 152 removal (weight ratio of chitosanto bamboo charcoal = 50/50, adsorbent dosage = 1.0 g, dye concentration = 50 mg/L,volume = 50 mL).

3.2.3 Effect of adsorbent dosageAdsorbent dosage is an essential

parameter which must be carefully adjustedduring wastewater treatment. The effect ofadsorbent dosage (varying from 1.0 g to6.0 g) on Reactive Red 152 dye removal ispresented in Figure 4. Initially, a rapidincrease of adsorption with the increasingadsorbent dosage was attributed to the

availability of a larger surface area andmore adsorption sites [25]. A furtherincrease of the adsorbent dosage from2.0 g to 6.0 g didn’t increase dye removaltoo much (only from 93.8% to 98.4% atan equilibrium time of 8 h). It was alsonoted that the equilibrium time decreasedwith the increasing adsorbent dosage.

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3.3 Adsorption IsothermsThe linear form of the Langmuir

isotherm is expressed as:

= +

where qe is the amount of dye adsorbedper unit mass of adsorbent (mg/g) and Ce isthe equilibrium concentration of dye insolution (mg/L). The constant Xm is themonolayer adsorption capacity (mg/g) andb is the Langmuir constant. The Langmuirisotherms of chitosan and chitosan/bamboo

charcoal composite beads are shown inFigure 5 for chitosan and chitosan/bamboocharcoal composite beads, the absorptioncapacity (Xm), and the Langmuir constantderived from the linear regression plots areshown in Table 3.

The adsorption isotherms of chitosanand chitosan/bamboo charcoal compositebeads could be described very well by theLangmuir equation. The chitosan/bamboocharcoal composite beads had a higheradsorption capacity (Xm=4.32) than that ofchitosan (Xm=3.47).

Figure 4. Effect of adsorbent dosage on Reactive Red 152 removal (weight ratio of chitosanto bamboo charcoal = 50/50, pH = 4, dye concentration = 50 mg/L, volume = 50 mL).

2.3.2Ce

qe

1bXm

Ce

Xm( ) ( )

Figure 5. The Langmuir adsorption isotherm of chitosan and chitosan/bamboo charcoalcomposite (weight ratio of chitosan to bamboo charcoal = 50/50) beads for Reactive Red152.

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3.4 Scanning Electron Micrograph (SEM)Study

The SEM micrograph of the freshchitosan/bamboo charcoal composite beadand Reactive Red 152 dye adsorbed chitosan/bamboo charcoal composite bead werepresented in Figure 6(a) and (b), respectively.After adsorption the pores were packed withReactive Red 152. The micrograph showed

that the heights of heterogeneous pores withinchitosan particle were decreased whereadsorption could occur. The dye had denselyand homogeneously adhered to the surfaceof the adsorbent, as a result of physicaladsorption onto chitosan due to electrostaticforces and natural entrapment in to theporous bamboo charcoal material.

Table 3. Parameter of the Langmuir isotherm and the relative correlation coefficients forchitosan and chitosan/bamboo charcoal composite (weight ratio of chitosan to bamboocharcoal = 50/50).

4. CONCLUSIONSChitosan/bamboo charcoal composites

were made by adding bamboo charcoal intoa chitosan solution and forming the compositebeads. The adsorption of the reactive dye(Reactive Red 152) from an aqueous solutionby using composite beads was investigated.Adsorption equilibrium experiments werecarried out as a function of contact time,bamboo charcoal concentration, pH value,and adsorbent dosage level. The equilibriumtime of dye adsorption was found to be 8 h.

Composite adsorbent had the highestadsorption efficiency when the weightratio was 50/50. The maximum dye removaltook place at the initial pH 4.0. The optimumadsorbent dosage for dye removal was6.0 g. Under above optimal conditionsthe maximum dye removal was 98.4%.The adsorption isotherm of chitosan andchitosan/bamboo charcoal composite beadsfollowed the Langmuir isotherm modelvery well. The chitosan/bamboo charcoalcomposite beads had a higher adsorption

Figure 6. SEM micrograph of chitosan/bamboo charcoal composite (weight ratio of chitosanto bamboo charcoal = 50/50) beads (a) before and (b) after the adsorption of Reactive Red152.

Type of adsorbent

CTSCTS/BC composite

Xm (mg/g)3.46864.3215

b0.07270.1188

R2

0.98640.9904

Langmuir equationCe/qe = (1/bXm)+(Ce/Xm)

182 Chiang Mai J. Sci. 2014; 41(1)

capacity than that of chitosan. SEMmicrographs confirm that after adsorptionthe pores were packed with Reactive Red152.

ACKNOWLEDGEMENTSThis research is financially supported by

the Faculty of Science, SrinakharinwirotUniversity Fund. The author would like tothank the Department of Anatomy, Facultyof Medicine, Srinakharinwirot University forthe Scanning Electron Microscope.

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