Journal of Hazardous Materials 143 (2007) 462468

Enhanced removal of p-chloroanilinee

Kai Zh Hanu a

a ironmb En ource

Huaia

er 20er 200

Abstract

In the pre ric sochloroaniline from aqueous solution. A commercial styrene-divinylbenzene polymeric sorbent Amberlite XAD-4 was selected as the referencesorbent to evaluate the performance of CSPS. Characterization of CSPS was determined by infrared spectroscopy and pore size distribution. Ap-chloroaniline sorption enhancement on CSPS at capacity about twice of Amberlite XAD-4 was observed, which was mainly attributed to thecarboxyl group added on the polymeric matrix. Different pH-dependent sorption property of p-chloroaniline onto XAD-4 and CSPS was observedpartly due to the role of carboxyl group. Sorption isotherm of p-chloroaniline on CSPS could be represented by Freundlich model reasonably, and thaton XAD-4 wthe pseudo-removal fromimplying its 2006 Else

Keywords: Po

1. Introdu

Water pconcern in[1]. Accordby activatedevelopedthe receividemandingapplicationindustrial wbut many vered for fusorbents ha

CorresponE-mail ad

0304-3894/$doi:10.1016/jas more suitable for Langmuir model. Kinetic studies demonstrated that the uptake of p-chloroaniline on CSPS and XAD-4 followedsecond order model. Moreover, breakthrough curves on CSPS further demonstrated its better performance towards p-chloroaniline

aqueous solution. Complete regeneration of the spent sorbent CSPS was achieved by dilute hydrochloric acid for its repeated use,potential application in associated chemical wastewater treatments.vier B.V. All rights reserved.

lymeric sorbent; Carboxylation; p-Chloroaniline; Sorption; Removal enhancement

ction

ollution by chemical wastewater has been of greatmany developing countries such as India and Chinaingly, many practical processes, such as adsorption

d carbon [2,3] and low-cost sorbents [46] have beento treat chemical wastewater before discharging intong water. However, poor mechanical strength andregeneration of activated carbon hinders its wider

. Low-cost sorbents based on red mud and otherastes [46] seems more attractive in the specific field,aluable organic compounds cannot be readily recov-rther use after sorption. In recent years polymericve been emerging as a potential alternative due to

ding author. Fax: +86 25 83707304.dress: bcpan@nju.edu.cn (B. Pan).

its better mechanical strength, feasible regeneration under mildconditions, and potential recovery of chemical pollutants by fur-ther treatment of the concentrated eluate, the typical ones beingof styrene-divinylbenzene (St-DVB) matrix [7,8]. In general,many hydrophobic organic pollutants can be readily removedfrom wastewater by the St-DVB polymeric sorbents [9], whichmainly results from van der Waals interaction between the soluteand sorbent phase [10]. However, many hydrophilic or water-soluble organic compounds cannot be readily removed by thosesorbents partly due to the strong solutewater interaction [11],and how to improve the adsorption performance of the polymericsorbents is of particular significance.

In review of literatures, chemical modification of poly-meric matrix is a potential pathway to enhance sorption ofthe hydrophilic compounds from aqueous solution [12,13]. Forexample, the aminated polymeric sorbents exhibited better per-formance for removal of acidic compounds such as phenols,aromatic carboxylic acids and sulfuric acids [14].However, little

see front matter 2006 Elsevier B.V. All rights reserved..jhazmat.2006.09.052by a carboxylated polymeng a, Bingcai Pan a,, Qingjian Zhang a, Yuhua

Zhengwen Xu a, Qingrui Zhang a, Wei DState Key Laboratory of Pollution Control and Resource Reuse, School of Envgineering Technology Research Center of Organic Substance Control and Res

c Jiangsu Tasly Diyi Pharmaceutical Co., Ltd.,Received 7 June 2006; received in revised form 17 Septemb

Available online 22 Septemb

sent study a carboxylated styrene-divinylbenzene (St-DVB) polymefrom aqueous solutionric sorbent

c, Weiming Zhang a,b, Bingjun Pan a,

, Quanxing Zhang a,bent, Nanjing University, Nanjing 210093, PR ChinaReuse of Jiangsu Province, Nanjing 210038, PR Chinan 22300, PR China

06; accepted 18 September 20066

rbent (CSPS) was prepared for enhanced removal of p-

K. Zheng et al. / Journal of Hazardous Materials 143 (2007) 462468 463

ted p

was availabamine commatic aminare ubiquitlutants in a

In the cusorbent toChloroanilwidely useof dyes, phchloroanilihematoxici[17,18], anbe harmfulby carboxypost-cross-tion runs inwere perfo

2. Materia

2.1. Mater

Zinc chbenzene, nfrom Shangused withoin double-dorous St-DRohmHaaSt-DVB cois 17.3%) b(Hebei pro

2.2. Prepa

As showboxylationof the carboswollen ove28.0 g of 4mechanicachloride waand the reacfiltered to rwere extrac

ylateing phe poloringht in, 6.0e flapeross-g angot

atch

ch sof

onta00 tmodt a pn eqductlowi

1(C

V1 (lt; C0tratistudg antervs.

ixed-

umndiaScheme 1. Preparation procedures of the carboxyla

le in open literature on how to enhance sorption ofpounds from aqueous solution, among which aro-es should gain more attention because most of themous in chemical wastewater and listed as priority pol-quatic systems [15,16].rrent study we aimed at preparing a new polymeric

gain sorption enhancement of aromatic amines. p-ine was chosen as a target solute because it wasd as a chemical intermediates for manufacturingarmaceuticals and other compounds. Moreover, p-

ne is a well-known priority pollutant in terms of itsty, splenotoxicity, hepatoxicity, and nephrotoxicityd its presence in water even at a low level (mg/l) wouldto aquatic life and human health. This was achievedlation of a St-DVB polymeric matrix followed bylinking of the carboxylated derivative. Batch sorp-cluding isotherm, kinetics and column sorption testsrmed to evaluate the new sorbents.

ls and methods

ials

loride, 4-methylbenzoic acid, ethanol, 2,4-dichloro-itrobenzene, p-chloroaniline (A.R.) were purchasedhai Chemical Reagent Plant (Shanghai, China) and

ut further purification. p-Chloroaniline was dissolvedistilled water for batch sorption runs. A macrop-

VB sorbent Amberlite XAD-4 was obtained froms (Philadelphia, PA, USA). The chloromethylatedpolymer (denoted CSC, the chloro content in masseads were kindly provided by Langfang Resin Co.

vince, China).

ration of the new sorbent

n in Scheme 1, the new sorbent was prepared by car-of the CSC particles followed by post-cross-linking

carboxfollow

In t(the chovernistirringinto thent tempost-crfilterinand we

2.3. B

Bat0.100 gflask cfrom 1a G25Inc.) asorptioby conthe fol

qe = V

wheresorbenconcen

kineticas 0.50time inkinetic

2.4. F

Col(12 mmxylated derivatives. First, 30.0 g of CSC beads werernight by 250.0 g of o-dichlorobenzene together with

-methylbenzoic acid in a 500 ml flask. Under a mildl stirring (at about 60 rpm), 6.0 g of anhydrous zincs gradually added as catalyst into the flask at 298 Ktion lasted about 12 h. The reaction mixture was thenemove the liquid moiety and the rest solid particlested with ethanol for 4 h in a Soxlet apparatus. The

to maintainused to assformed undliquid velowere identi

Concentrophotomeeter (Unicaolymeric sorbent CSPS.

d particles (designated CCSC) were obtained for theost-cross-linking reaction.st-cross-linking procedure 30.0 g of CCSC particlese percent content decreased to 12.6%) was swollen100.0 g of nitrobenzene in a flask. Under mechanicalg of anhydrous zinc chloride was gradually added

sk at 298 K, followed by an increase of the ambi-ature from 298 to 405 K within 1 h. After 8 h of thelinking reaction at 405 K, the mixture was treated byd extracting in the similar manner for CCSC particlesthe new sorbent CSPS.

sorption runs

orption experiments were performed as follows:each sorbent was introduced into a 250 ml conicalining 100 ml of the p-chloroaniline solution rangingo 500 mg l1. The flasks were sealed and shaken inel incubator shaker (New Brunswick Scientific Co.reset temperature under 120 rpm for 24 h to ensureuilibrium. The p-chloroaniline uptake was calculateding a mass balance before and after adsorption usingng equation:

0 Ce)W

(1)

) is the volume of solution andW (g) is the mass of dryand Ce (mg l1) denote the initial and equilibrium

on of p-chloroaniline in aqueous solution. As for they, the amount of sorbent and solution was determinedd 500 ml, respectively, and 0.5 ml solution at various

als was sampled from the flasks to determine sorption

bed sorption

experiments were carried out with a glass columnmeter and 230 mm length) equipped with a water bath

a constant temperature. A HL-2B pump (China) wasure a constant flow rate. All column runs were per-er the same hydrodynamic conditions: the superficialcity (SLV) and the empty bed contact time (EBCT)cal and equal to 1.0 m/h and 4 min, respectively.trations of p-chloroaniline were determined spec-trically by using a Helious Betra UVvis spectrom-m Co., UK) at wavelengths of 238 nm.

464 K. Zheng et al. / Journal of Hazardous Materials 143 (2007) 462468

Table 1Characteristics of the polymeric sorbents in the present study

Sorbent XAD-4 CSPS

Matrix PolystyrenePolarity Nonpolar ModerateBET surface area (m2 g1) 908 1000Micropore surface area (m2 g1) 115 587Micropore volume (cm3 g1) 0.033 0.27Average pore diameter (nm) 5.64 2.31Functional group None COOHAmount of functional group (mmol g1) 0 1.32

3. Results and discussion

3.1. Sorbent characterization

Table 1 listed some characteristics of XAD-4 and CSPS sor-bents. No significant difference of both sorbents in the BETsurface aremicropore4. It coulddistributionThe averagof CSPS. Tther provedspectrum (iof 673.9 cmCSC becaution, and thbonyl grouwere strengtence of ca

3.2. Effect

Fig. 1 ilsorption oncapacities obut they exSorption ca

Fig. 1. Correof XAD-4 anchloroaniline

Fig. 2. Sorption isotherms of p-chloroaniline onto XAD-4 and CSPS at differenttemperatures.

n pH values were larger than 6, and decreased as the solu-decreased. It was consistent with the protonation curve of

roanto X

e prosurfS de

enerd fro

4CO

4CO

R rbenzsimu

offfecsic cuirea was observed, however, micropore surface area andvolume of CSPS was much larger than that of XAD-also be concluded by comparison with the pore size

(PSD) of both sorbents (in supporting materials).e pore diameter of the XAD-4 was almost twicehe presence of carboxyl groups on CSPS was fur-by the strong band at 3446, 1607.5 cm1 in the IR

n supporting materials). The strong absorbance band1 (chloromethyl group) in CSPS was weaker than

se of the decrease of chlorine content after carboxyla-e bands of about 3446 (hydroxyl group), 1607.5 (car-p), 1510.5 and 1450.2 cm1 (carboxyl ester group)thened accordingly, which further testified the exis-

rboxyl groups.

of solution pH

lustrated the effect of solution pH on p-chloroanilineto XAD-4 and CSPS at 298 K. Maximum sorptionf both sorbents was observed at neutral pH (about 6),hibited different pH-dependent sorption properties.pacity of XAD-4 approached to a plateau when the

solutiotion pHp-chlotion onand thon theof CSP6. In ginferre

RC6H

RC6H

wherechlorooccur

mation[21]. Eand ba(3) reqlation of solution pH with sorption capacity in equilibrium (Qe)d CPCS (left) and the proportion of the molecular state of p-and 4-methylbenzoic acid (right).

Fig. 3. Determbent CSPS aniline as shown in Fig. 1. In fact, p-chloroaniline sorp-AD-4 was driven mainly by van der Waals interactiontonated p-chloroaniline cannot be effectively loadedace of XAD-4. On the other side, sorption capacitycreased whether solution pH was less or larger than

al, effect of carboxyl group on amine sorption can bem the following equation [11,19] (Figs. 2 and 3):OH + RNH2 RC6H4COOH NH2R (2)O + RN+H3 RC6H4COON+H3R (3)

epresents the polymeric matrix, and R is the p-yl group. Effective sorption of p-chloroaniline canltaneously on the introduced carboxyl group by for-acidbase complex [20] or electrostatic interactiontive interaction depicted in Eq. (2) required the acidicompounds both at molecular state while that in Eq.d both at ionization state. In fact both requirementination of isosteric enthalpy of p-chloroaniline sorption on sor-d XAD-4.

K. Zheng et al. / Journal of Hazardous Materials 143 (2007) 462468 465

could not be met simultaneously and a maximum sorption wouldbe reached under a specific condition As illustrated in Fig. 1,solution pH larger or less than the optimal one (around 6) wasunfavorable for one or both interactions and therefore resulted ina decrease of sorption capacity. Anyway, different pH-dependentsorption onto CSPS by comparison with XAD-4 indicated thatthe carboxyl group introduced on the polymeric sorbent takesan important role in p-chloroaniline removal from aqueous solu-tion.

3.3. Sorption isotherm

Sorption isotherms of PCA on XAD-4 and CSPS at 298 K areshown in Fig. 2. It is very clear that sorption capacity of CSPSis much larger than the typical polystyrene sorbent XAD-4.The semi-etion [22] wp-chloroan

ln Qe = ln

1Qe

=KLQ

where KFneous sorbeand KL (l malways takrelated tothe sorbentvalues werequation fiequation isdepends upthe Langmonto a homuniform stythe contrarresulting frtribution. Ais an exotheperature ondiscussed i

3.4. Thermodynamic aspects

The free energy change for sorption process is given by

G = H TS (6)At low solute concentration, Goverall can be determined as fol-lows [23]:

G = RT Ce

0 Q(Ce)d ln CeQ(Ce)

(7)

where x is the mole fraction of the sorbate in the solution. Whenthe sorption capacity Q (Ce) follows the Freundlich equation,incorporating Eq. (4) into Eq. (7) yields [11]:G = nRT (8)

otheget

:

R

tericroxim

e)) =

T iscom

). Pinedalorainecan

ld b3 mrben

stilled tondenloro

ributrptio

inter

Table 2Isotherm para

Sorbent

XAD-4

CSPSmpirical Freundlich equation and Langmuir equa-ere employed to describe the sorption isotherms ofiline on CSPS and XAD-4:

KF + 1n

ln Ce (4)

1mCe

+ 1Qm

(5)

and n is the Freundlich constants for a heteroge-nt, Qm (mmol g1) is the maximal sorption capacity,mol1) is a binding constant. The constant KF is

en as a relative indicator of sorption capacity, n isthe magnitude of the sorption driving force and to

site energy distribution. All the related parametere listed in Table 2. It can be seen that the Langmuirt the sorption on XAD-4 well while the Freundlichmore representative for that on CSPS sorbent, whichon their different sorption mechanism. In general,

uir equation originates from the ideal sorption modelogeneous sorbent, an example being XAD-4 of arene-divinylbenzene matrix and pore structure. On

y, CSPS presented a heterogeneous surface propertyom the uneven functional group and its pore size dis-nother observation is that sorption on both sorbentsrmic process inferred from the effect of ambient tem-sorption. Detailed thermodynamic properties will be

n the forthcoming section.

On thewe can

Eq. (7)

G =

If isosbe app

d(ln Cd(1/T

wherecan be(Fig. 3determmicrocbe obtbutionIt shouTableboth socouldassum

indepeof p-chbly attpart sostatic

meters of p-chloroaniline sorption onto XAD-4 and CSPS

T (K) Freundlich modelKF n R2

298 0.85 2.49 0.967308 0.63 1.59 0.873318 0.49 2.02 0.996

298 2.34 3.02 0.986308 2.06 3.57 0.978318 1.83 3.70 0.976r side, when Q (Ce) follows the Langmuir equation,the following equation by incorporating Eq. (5) into

T (1 + KLCe)KLCe

[ ln(1 + KLCe)|Ce0 ] (9)

sorption enthalpy change (H) can be assumed toately constant, the vant Hoff equation gives:

H

R(10)

the absolute temperature in K. The enthalpy changeputed from the slope of the lnCe versus 1/T plot

revious study indicates that enthalpic change thusagrees well with that obtained independently using

imetric technique [24]. The free energy change cand from Eqs. (8) and (9), and the entropic contri-be subsequently determined according to Eq. (6).e noteworthy that different Qe values selected inainly lay on their distinct sorption capacity ontots. However, the thermodynamic results listed there

be taken for comparison because XAD-4 could bebe a homogenous sorbent, implying its capacity-

t enthalpy changes. Higher absolute enthalpy changeaniline sorption onto XAD-4 than CSPS was possi-ed to their different sorption mechanisms. Generally,n of p-chloroaniline onto CSPS driven by electro-

action was an endothermic process [25,26], which

Langmiur model

KL (l mmol1) Qm (mmol g1) R2

2.43 0.995 0.9981.72 0.885 0.9971.31 0.873 0.999

2.38 2.38 0.9802.11 2.11 0.9691.96 1.96 0.969

466 K. Zheng et al. / Journal of Hazardous Materials 143 (2007) 462468

Table 3Thermodynamic parameters of p-chloroaniline sorption onto XAD-4 and CSPS under different conditions

Sorbent Qe (mmol g1) T (K) H (kJ mol1) G (kJ mol1) S (J mol1 K1)CSPS 1.5 298 4.59 7.53 9.87

1.5 308 9.14 14.81.5 318 10.5 14.3

XAD-4 0.5 298 35.6 3.50 1080.5 308 2.56 1030.5 318 2.15 100

required absorption of heat and resulted in a lower value ofenthalpy change. Similarly, the positive entropy change value ofCSPS sorption was also possibly related to the sorption driven byelectrostatic interaction, where the p-chloroanilne and the func-tional group on the polymeric matrix may be partly dehydratedbefore the effective sorption occurs. Additionally, the free energychanges for XAD-4 decreased but that for CSPS increased as theambient temperature increased, which might also be related totheir different sorption mechanism.

3.5. Sorpti

The inflXAD-4 anrium of PCCSPS, depXAD-4 thafirst order athe experim

Pseudo-firs

Pseudo-sec

where Qe ithe sorption

Fig. 4. Effectat 298 K.

Table 4Kinetic parameters of p-chloroaniline sorption onto CSPS and XAD-4 for thepseudo-first order model and the pseudo-second order model

Sorbents Pseudo-first order model Pseudo-second order model

k1 (min1) R2 k2 (g mmol1 min1) R2

XAD-4 0.0159 0.731 0.0740 0.998CSPS 0.0107 0.970 0.0184 0.995

the pseudo-ord

ted tA sudoat oder.

olum

s neehaved a

wininged en ent, whbatch runs. After column sorption both spent sorbentson kinetics

uence of contact time on p-chloroaniline sorption byd CSPS were illustrated in Fig. 4. Sorption equilib-A on XAD-4 was achieved in a shorter time thanending upon the larger average pore diameter ofn CSPS (in Table 1). Here the widely used pseudo-nd pseudo-second order model were employed to fitental data

t order model : lnQe

Qe Qt = k1t (11)

ond order model :1Qt

= 1k2Q2e t

+ 1Qe

(12)

s the equilibrium sorption capacity (mmol g1), Qt iscapacity (mmol g1) at the contact time t (min), k1 is

secondindicathe PCthe psethan thsize or

3.6. C

It ition bdepictpackedcontaioccurr

sorptiosorbeniors inof contact time on p-chloroaniline sorption onto CSPS and XAD-4Fig. 5. Breakfirst order rate constant(min1), and k2 is the pseudo-er rate constant(g mmol1 min1). Results in Table 4hat the pseudo-second order model could representorption kinetics onto CSPS and XAD-4 better than-first order model. The K2 value of XAD-4 four timesf CSPS was also consistent with their average pore

n sorption tests

cessary to test the column sorption and desorp-ior of PCA on CSPS before its application. Fig. 5complete effluent history of a fixed-bed column

th either XAD-4 or CSPS for a feeding solution500 mg l1 PCA at pH 6.0. Earlier breakthrough

xpectedly for XAD-4 than CSPS demonstrated thehancement of p-chloroaniline onto the carboxylatedich is consistent with their different sorption behav-through curves of p-chloroaniline on XAD-4 and CSPS at 298 K.

K. Zheng et al. / Journal of Hazardous Materials 143 (2007) 462468 467

Fig. 6. Desorchloroaniline.

were subjeof hydrochwater at 33of more themployed fisfactory sous to believwastewater

4. Conclu

A new cprepared fophase. p-Chprocess anboxyl grourole in p-cwith a typof p-chloroand a satisbent was osecond ordtion enhanby comparXAD-4. Thby dilute hyresults demchloroanili

Acknowled

This resence FundiScience FuWe gratefuversity forUniversity

Appendix A. Supplementary data

Supplemin the onlin

nce

. Zhaource

ogy a5, pp

Bautisovalsolu

Laszled car39.. Jain

ustria. Gup

ng bo. Gup

ng re04) 4. Xu,ustria. Tech. Pan

in adsInternn and. Leeo a hy. He,

in. U.. Panancemymer,

. Liberli

(2001. Cai,

n of anorben. Pan

n of aemospption curves of the spent XAD-4 and CSPS loaded with p-

cted to a separate elution using 1 bed volume (BV)loric acid (2 M) followed by 1.5 BV of deionized3 K. Similarly to XAD-4, an entire elution efficiencyan 99% indicated that the sorbent CSPS could beor repeated use after regeneration (Fig. 6). The sat-rption and regeneration behavior of CSPS promotede it is a potential candidate for treatment of chemicalcontaining aniline compounds.

sion

arboxylated polymeric sorbent (denoted CSPS) wasr enhanced removal of p-chloroaniline from aqueousloroaniline sorption onto CSPS was a pH-dependent

d the optimal solution pH is around 6. The car-p introduced on the polymeric matrix takes a positivehloroaniline sorption enhancement by comparisonical polymeric sorbent XAD-4. Sorption isothermsaniline onto CSPS followed Freundlich model wellfactory sorption kinetic property of the new sor-

bserved, which could be represented by the pseudo-

Refere

[1] Q.Xres

nol200

[2] I.rem

and[3] K.

vat32

[4] A.Kind

[5] V.Kusi

[6] V.Kusi(20

[7] Z.YindSci

[8] B.Cres

in:tio

[9] J.Wont

[10] B.LCh

[11] B.Cenhpol

[12] A.MAm49

[13] J.Gtioads

[14] B.CtioCher model. Column test results suggested that sorp-cement of p-chloroaniline on CSPS was validatedison with a typical polystyrene sorbent Amberlitee spent CSPS beads could be readily regenerateddrochloride solution for repeated use. All the aboveonstrated that CSPS is a potential candidate for p-

ne removal from industrial wastewater.

gements

earch was financially funded by National Natural Sci-ng of PR China (Grant no. 20504012) and Naturalnding of Jiangsu Province (Grant no. BK 2004415).lly acknowledge the analytical center of Nanjing Uni-IR analysis and Dr. Zong in Jiangsu Polytechnic

for characterization of the associated sorbents.

[15] M. Kada2,4-dichtrochim.

[16] W.M. Zhof the suof 1-nap(2005) 7

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[18] F. Bhunisome fre

[19] H.M. Anresins in

[20] H. Borneand PH3(2002) 1

[21] P.K. Dasble layercapillaryentary data associated with this article can be found,e version, at doi:10.1016/j.jhazmat.2006.09.052.

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Enhanced removal of p-chloroaniline from aqueous solution by a carboxylated polymeric sorbentIntroductionMaterials and methodsMaterialsPreparation of the new sorbentBatch sorption runsFixed-bed sorption

Results and discussionSorbent characterizationEffect of solution pHSorption isothermThermodynamic aspectsSorption kineticsColumn sorption tests

ConclusionAcknowledgementsSupplementary dataReferences