the adsorption of sulphonated azo-dyes methyl orange and xylenol orange by coagulation on hollow...

The Adsorption of Sulphonated Azo-Dyes MethylOrange and Xylenol Orange by Coagulationon Hollow Chitosan Microsphere

Shan Wang,1,2 Demei Yu,1 Yi Huang,2 Jinchan Guo2

1Department of Applied Chemistry, Xi’an Jiaotong University, Xi’an 710049, Shaanxi Province,People’s Republic of China2School of Chemistry and Chemical Engineering, Xianyang Normal University, Xianyang 712000,Shaanxi Province, People’s Republic of China

Received 22 December 2009; accepted 1 June 2010DOI 10.1002/app.32919Published online 26 August 2010 in Wiley Online Library (wileyonlinelibrary.com).

ABSTRACT: Chitosan (CS) can be used as adsorbent inthe treatment of effluents from the textile industry, espe-cially for negatively charged dyes, due to its cationic poly-electrolyte nature. In this work, the adsorption of a modeldye, methyl orange, xylenol orange on hollow CS micro-sphere is analyzed. Adsorption of methyl orange, xylenolorange onto cross-linked CS is realized by means of analy-sis of pH influence, agitation time, and initial concentra-tion of the dye. The results obtained from the experimentshows that the adsorption capacities of the two dye-hollowCS microsphere systems are higher than those stated in

other literature using CS particles. The difference in thedegree of adsorption may also be attributed to the sizeand chemical structure of the dye molecule. The resultshave demonstrated that monovalent and smaller dye mo-lecular sizes have superior capacities due to the increasein dye/CS surface ratio in the system and deeper penetra-tion of dye molecules into the internal pore structure ofhollow CS microsphere. VC 2010 Wiley Periodicals, Inc. J ApplPolym Sci 119: 2065–2071, 2011

Key words: hollow chitosan microsphere; adsorption; dyes

INTRODUCTION

There are significant amounts of unused dyesremaining in the wastewater from the textile anddyeing industry. Aqueous waste and dye effluentswith persistent and high biochemical oxygendemand loading is being discharged every day inMainland. Many industries, such as dyestuffs, tex-tile, paper, and plastics, use dyes to color their prod-ucts and also consume substantial volumes of water.As a result, they generate a considerable amount ofcolored waste water. It is recognized that public per-ception of water quality is greatly influenced by thecolor. A range of conventional technologies for dyeremoval, such as carbon adsorption and photo-deg-radation, has been investigated extensively coloris the adsorption-related phenomena involved in awide range of processes used in carbohydrateresearch, such as heterogeneous catalysis,1–3 stabili-zation of colloidal dispersions, biocompatibility,4

and effluent treatment.5 Adsorption in particulatesystems has been used for heavy metal uptake, aspart of the treatment of pulp and paper mill waste-water,6 and in the treatment of effluents from thetextile industry.7 Chitosan (CS) is a biomacromole-cule obtained from the deacetylation of chitin. It canbe used as adsorbent for treatment of textile indus-try effluents as well as for metal uptaking fromwater.8–12 Apart from being biocompatible, it is apolyelectrolyte with polycationic character depend-ing on pH which be able to interact with negativelycharged molecules.13,14 Spectrophotometry has beenemployed to quantify CS, using the strong interac-tions that occur between dye molecules and this bio-polymer. Amount of works on the analysis of sorp-tion about dyes on CS has been carried out,15 whichwere usually divided into two approaches: one dedi-cated to the obtaining of adsorption isotherms andthe other one on the kinetic analysis of adsorp-tion.9,16,17 Physically and chemically modified CShas also been used in some works, for example, theauthor has employed CS/montmorillonite nanocom-posite particles in the adsorption of Congo Red,18

and Lima has used CS chemically modified withsuccinic anhydride for methylene blue adsorption.19

Some recent researches on the adsorption of methylorange as a model dye, on dry crosslinked CS par-ticles have shown that the usual kinetics description

Correspondence to: Demei Yu ([email protected]),S. Wang ([email protected]).

Contract grant sponsor: Shaanxi Province (People’sRepublic of China’s Scholarship Council); contract grantnumber: 08JK482.

Journal ofAppliedPolymerScience,Vol. 119, 2065–2071 (2011)VC 2010 Wiley Periodicals, Inc.

as pseudo-second-order kinetics is not adequate todescribe this particular sorption process. It has alsobeen found that diffusion-related phenomena governthe kinetics of sorption in these systems.20 The aimof the proposed work is to conduct experiments oncrosslinked hollow CS microsphere and compare thecapacity of hollow CS microsphere with conven-tional CS about the adsorption of two acid dyes,methyl orange, and xylenol orange.

METHODS

Materials

CS (Mw ¼ 750,000) was made and the degree ofdeacetylation is 55%.21 The preparation of the hollowCS microsphere has been reported.22 The adsorbentwas applied directly in this project without anyprior purification and pretreatment processes. Twodifferent commercially available textile dyestuffswere used in this study and they are both azo dyes:methyl orange and xylenol orange. The selected dye-stuffs are commonly used in dye houses nowadaysand are regarded as dye contaminants in the dis-charged effluents. All dye stuffs were obtained fromAldrich Chemical and used without any further pu-rification process. The characteristics of the selecteddyestuffs are listed in Table I.

Concentration measurement and calibration

To calculate the concentration of sample from eachexperiment, a calibration curve of each dye was firstprepared. For each dye, different concentrations (0–50 mg/L) were prepared and the absorbance wasmeasured using a Perkin–Elmer UV/VIS Spectro-photometer. The calibration checks maximumabsorption occurs, kmax were carried out repeatedlyin Figure 1. Then, the maximum absorbance of eachdye was plotted against a range of dye concentra-tion. From the results, the concentrations of the dyesamples can be calculated with the following equa-tion Type (1) and the constants for calculations aresummarized in Table I.

Qe ¼ VðCo � CeÞ=W (1)

where Qe ¼ the dye concentration on the adsorbentat equilibrium , Co ¼ the initial dye concentration

(mg of dye/g�1 of CS microsphere), Ce ¼ the liquid-phase dye concentration at equilibrium (mg of dye),V ¼ the total volume of dye-hollow CS microspheremixture, and W ¼ mass of adsorbent used (g).

Adsorption experiments

The adsorptions of the dyes were performed usingbatch procedures,23 where the CS quantities speci-fied by the adsorption factorial design were placedin contact with 50 mL of aqueous solutions in 100 mLpolyethylene flasks. The suspensions were agitatedfor sufficient time to reach equilibrium.

pH effects

The hollow CS microspheres were investigated todetermine the pH effects of their adsorption ofmethyl orange and xylenol orange. These wereadjusted to pH 2 and 11 with 1.0 M HCl solutionand 1.0 M NaOH solution, and then by stirring forsufficient time at room temperature. Their solutionswere filtered and their concentrations of methyl

TABLE IPhysical and Chemical Characteristics of the Dyestuffs

Being Investigated in This Project

Generic name ChromophoreFormulaweigh

kmax

(nm) R2

Methyl orange AN¼¼NA 327 505 0.9992Xylenol orange AN¼¼NA 738 480 0.9990

Figure 1 UV spectra of the wavelength of dyes (a, methylorange; b, xylenol orange).

2066 SHANWANG ET AL.

Journal of Applied Polymer Science DOI 10.1002/app

orange and xylenol orange were measured on a Per-kin–Elmer UV/VIS spectrophotometer. The adsorp-tion capacity (Qe) was calculated by the eq. (1).

Effect of initial concentration

The hollow CS microspheres were investigated todetermine the initial concentration effects of theiradsorption of methyl orange and xylenol orange.These were adjusted to methyl orange and xylenolorange solution in the range of 0–600 mg/L at pH 5,and then by stirring for sufficient time at room tem-perature. Their solutions were filtered and their con-centrations of methyl orange and xylenol orangewere measured on a Perkin–Elmer UV/VIS spectro-photometer. The adsorption capacity (Qe) was calcu-lated by the following eq. (1).

Effect of agitation time

The hollow CS microspheres were investigated todetermine the agitation time effects of their adsorp-tion of methyl orange and xylenol orange. Thesewere adjusted to methyl orange and xylenol orangesolution stirring for period time at room temperatureat pH 5. Their solutions were filtered and their con-centrations of methyl orange and xylenol orangewere measured on a Perkin–Elmer UV/VIS spectro-photometer. The adsorption capacity (Qe) was calcu-lated by the following eq. (1).

RESULTS AND DISCUSSION

Mechanism of adsorption

The mechanisms of the adsorption process of aciddye on hollow CS microsphere are likely to be theionic interactions of the colored dye ions with theamino groups on the CS in Figure 2.

Preparation and characterization

Presence of CS in the microspheres has been con-firmed by FTIR measurements. Curves a–c in Figure 3are the FTIR spectra of the CS, CS microsphere,and CS microsphere after adsorption xylenol or-ange. The FTIR spectra (4000–400 cm�1) of the CSflakes and CS microspheres are shown in Figure3(a,b). Usually, the major peaks of the CS flakes arelocated at around 3400 cm�1 for OH stretchingvibration and 1650 cm�1 for NH2 stretching vibra-tion. The band observed at 1320 cm�1 and 1380cm�1 are assigned to the CH3 deformation andCAN bond. The broad band at 3433 cm�1 wasAOH stretching, which overlapped the NH2 stretch-ing in the same region. The shifts at 1660 and1597 cm�1 were the bands of amide I and II,respectively. For CS microspheres, a new peak at1635 cm�1 can be observed [Fig. 3(c)], which corre-sponded to stretching vibrations of C¼¼N bond. Itindicated that the reactions occurred.

Solubility and surface morphology

The CS’s microspheres were found to be insoluble inacid and alkaline media as well as distilled water incomparison with native CS. It is well known thathigh hydrophilicity of CS with the primary aminogroup makes it easily soluble in dilute organic acidsto yield a hydrogel in water. Therefore, the cross-linking treatment of CS reinforces its chemical stabil-ity in organic acidic media, making it useful for theremoval of chemical pollutants from wastewaters inacidic solution. The SEM of CS microsphere wereshown in Figure 4. It shows typical SEM images ofthe CS microsphere prepared under the standard

Figure 2 Mechanism of anionic dye adsorption by chito-san under acidic conditions.

Figure 3 FTIR spectra (a, chitosan; b, chitosan micro-sphere; c, chitosan microsphere after adsorption xylenolorange). [Color figure can be viewed in the online issue,which is available at wileyonlinelibrary.com.]

ADSORPTION OF SULPHONATED AZO-DYES 2067


preparative condition,22 and its enlarged surfacestructure. It can be seen that the microsphere isspherical, and its diameter is about 74 lm [Fig. 4(a)].The CS microspheres were found to have regularspherical geometry [Fig. 4(b)]. Further study that themicrosphere contracts with drying and is swollenafter being immersed in water. What’s more, thecontraction and swelling processes could be re-peated for a number of times. The average value is9/SD. In addition, the size distribution of the com-posite microspheres is narrow. Figure 4(c) shows thebroken CS spherical particle, in which the contrastacross the diameter reveals that the thickness of theshell wall is about 2 lm. the comparative analysis ofSEM images [Fig. 4(c)] demonstrate that the particlesare hollow. What’s more, CS microspheres exhibit asmooth surface morphology [Fig. 4(d)]. Figure 4(e)were the CS microsphere after adsorption xylenol or-ange. It can be found the microspheres have regularspherical geometry, whose diameter is about 74 lm.But the microsphere exhibit a roughness surfacemorphology and the CS microsphere after adsorp-tion methyl orange were shown in Figure 4(f).

Adsorption experiments

The adsorptions of the dyes were performed usingbatch procedures,23 where the CS quantities speci-fied by the adsorption factorial design were placedin contact with 50 mL of aqueous solutions in

100 mL polyethylene flasks. The suspensions wereagitated for period of time, sufficient time to reachequilibrium.

Effect of pH

Figure 5 shows the effect of pH on the adsorption ofmethyl orange and xylenol orange by hollow CSmicrosphere. The adsorption of the dyes increases(i.e., the difference in absorbance increases) withincreased pH of the solution. This could be ex-plained by the fact that at low pH (acidic solution),amine groups in the beads easily form protonation.Therefore, competition existed between protons andthe dyes for adsorption sites and adsorption capacitywas decreased. As pH value was increased, theamino group was free from the protonation forthe adsorption behavior in the dyes. At the sametime, they were found to be the largest adsorptioncapacity of methyl orange and xylenol orange atpH 5.0.

Effect of initial concentration

Figure 6 shows the effect of concentration on theadsorption of methyl orange [Fig. 6(a)] and xylenolorange [Fig. 6(b)] by hollow CS microsphere. Theadsorption of methyl orange and xylenol orangeincreases with concentration and attains equilibriumat an initial methyl orange and xylenol orange

Figure 4 SEM of the CS microsphere (a, �100; b, �1200; c, �1500; d, �10000; e, �1200; f, �1200).



concentration of 200 mg/L, 32 mg/L for hollow CSmicrosphere, respectively.

Effect of agitation time

The optimum period (Fig. 7) for the adsorption ofmethyl orange and xylenol orange on hollow CSmicrosphere can be observed at the different time.The adsorption of methyl orange and xylenol orangeincreases with agitation time and attains equilibriumat about 40 mins, 120 mins for CS microsphere foran initial methyl orange and xylenol orange concen-tration of 200 mg/L and 32 mg/L. It shows that theadsorption of methyl orange and xylenol orangeremains constant after 40 mins, 120 mins for hollowCS microsphere, implying that equilibrium has been

reached. Therefore the optimum agitation time foradsorption of methyl orange and xylenol orange wasabout 40 min and 120 mins, respectively.

Effect of inorganic salts

Apart from dyes, the waste waters from textile man-ufacturing also contain various types of dissolvedcompounds, such as acids, alkalis, salts, surfactants,etc. Anions such as chloride, sulphate, carbonateand nitrate, etc. are the most common ions presentin textile effluents. An experiment was carried outon the effect of Cl�, NO�

3 , SO2�4 , and HCO�

3 on theadsorption of methyl orange and xylenol orangeby a coagulation flocculation process. A quantity of1 g/L of an appropriate salt was added to the dye

Figure 5 The effect of pH to the adsorption (a, methyl orange; b, xylenol orange).

Figure 6 The initial concentration effect to the adsorption (a, methyl orange; b, xylenol orange).



solution under optimal experimental conditions (ini-tial dye concentration: 200 mg/L, 32 mg/L) at pH 5(Fig. 8). Since the common cation of all the addedsalts, i.e., Naþ, did not react with CS or with thedyes, only relevant anions were involved in the inhi-bition effect. As shown in Figure 8, the addition ofsuch anions as Cl� and NO�

3 to the solution did notinfluence the removal of the studied dyes. The per-centage of removal remained constant at a high saltconcentration, 10-fold exceeding the concentration ofthe dyes. On the other hand the removal of methylorange and xylenol orange was more influenced bythe SO2�

4 . In this case, the efficiency decreased about30% in the presence of Na2SO4. The removal ofmethyl orange and xylenol orange was significantlylower in the presence of Na2SO4 than in the pres-ence of NaCl and NaNO3. The impact of sulphateanions may be explained by the precipitation effectof these ions on CS: the interactions of the sulphateanions with protonated amine groups contributed toreducing the polymer solubility (dehydrating effect)and decreasing the availability of protonated aminegroups. In the case of NaHCO3, a drastic increase ofthe pH was observed (up to 7.1 for methyl orangeand up to 8.8 with and xylenol orange). Thisincrease of the pH entrained a significant decreasein the protonation of the amine groups and conse-quently also their affinity for the sulphonic groupsof the dyes was reduced. In addition, the increase in

ionic strength may affect the distribution of thecharge on the CS molecules due to a charge screen-ing effect24 or the contraction of the thickness of thedouble layer surrounding the CS molecules. This, inturn, has an influence on the interaction of CS mole-cules with the dyes. In a different field, Tixier et al.investigated the effect of the ionic strength on theviscosity of an activated sludge suspension25 andobserved that the simultaneous decrease in the par-ticles’ double layer thickness and surface charge con-tributed to the decrease in intraparticle interactions.

Comparison of adsorption capacities

The adsorption capacities of the two dye-hollow CSmicrosphere systems are higher than those stated inother literature using CS particles26 because of theincreased surface area available for adsorption as aresult of using hollow CS microsphere. The particlediameter of hollow CS microsphere as measured bySEM and it is found to be average 74 lm. The differ-ence in the degree of adsorption may also be attrib-uted to the size and chemical structure of the dyemolecule. Methyl orange has the smallest molecularsize which implies smaller surface area and proto-nated amino groups of the adsorbent being occupiedby each dye molecule. The small molecular size notonly increases the concentration of dye on the sur-face of the CS particle but also enables a deeper

Figure 7 Effect of agitation time to the adsorption. [Colorfigure can be viewed in the online issue, which is availableat wileyonlinelibrary.com.]

Figure 8 Influence of the presence of inorganic salts (1 g/L)on the adsorption of methyl orange, xylenol orange underoptimum experimental conditions. [Color figure can beviewed in the online issue, which is available atwileyonlinelibrary.com.]

TABLE IIComparison of Chitosan Microsphere for Acid Dyes

Dye Adsorption ratio General conditions Reference

Methyl orange 95% 25�C, pH ¼ 4.9, 45 mins 2474 lm, 200 mg/100 mL

Xylenol orange 93.6% 25�C, pH ¼ 4.9, 2 h,74 lm, 32 mg/100 mL

25



penetration of dye molecules into the internal porestructure of CS microsphere. The monovalent natureof methyl orange dye molecules makes more proto-nated amino groups on the CS particle available foradsorption of xylenol orange. It also reduces theelectrostatic repulsion of adjacent dye molecules,which is significant in hollow CS microsphere, onthe adsorbent surface when compared with xylenolorange, enabling dye molecules to be packed moreclosely on the CS surface. The possible reason forthe inconsistent results in the present study is theinaccurate initial pH adjustment, which will beexplained further in the recommendations and sug-gestions section. As the hollow CS microsphereavailable for the experiment was in suspensionform, the initial pH adjustment had to be carriedout after the mixing of suspended hollow CS micro-sphere and dye solution. The pH adjustment had tobe performed as soon as possible because once HClwas added into the mixture, the amino group on theCS particles were immediately protonated by the Hþ

ions added. Although problems can be minimizedby rapid pH adjustment, the experimental errorcaused cannot be eliminated completely. A compari-son of the adsorption capacities of the hollow CSmicrosphere is shown in Table II.

CONCLUSION

The performance of hollow CS microsphere(withparticle size average 74 lm) as an adsorbent toremove acid dyes: methyl orange, xylenol Orangefrom aqueous solution has been investigated. Thedifferences in capacities may be due to the differen-ces in the particle size of dye molecules and thenumber of sulfonate groups on each dye molecule.The results have demonstrated that monovalent andsmaller dye molecular sizes have superior capacitiesdue to the increase in dye/CS surface ratio in thesystem and deeper penetration of dye molecules

into the internal pore structure of hollow CSmicrosphere.

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the adsorption of sulphonated azo-dyes methyl orange and xylenol orange by coagulation on hollow...

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