Preparation of polysulfonebenzylthiourea-reactive ultrafiltration plate membranes and their...

Preparation of Polysulfonebenzylthiourea-ReactiveUltrafiltration Plate Membranes and Their RejectionProperties for Heavy Toxic Metal Cations

Bing Wang, Fengyun Huangfu, Wei Liu

Key Laboratory of Hollow Fiber Membrane Material and Membrane Process (Ministry of Education),School of Materials Science and Chemical Engineering, Tianjin Polytechnic University, Tianjin 300160, China

Received 15 October 2007; accepted 19 January 2008DOI 10.1002/app.28055Published online 17 March 2008 in Wiley InterScience (www.interscience.wiley.com).

ABSTRACT: The asymmetric membranes were preparedvia phase inversion method, by using chloromethyl poly-sulfone as membrane materials, polyethylene glycol (PEG)as pore forming agent to improve the morphology andfunction of resultant membranes, N,N-dimethylacetamideas solvent, and water as the extraction solvent. Then thehighly qualified polysulfonebenzylthiourea-reactive ultra-filtration plate membrane was prepared successivelythrough the reactions between the chloromethyl polysul-fone matrix membrane and thiourea. The thiourea-func-tionalized polysulfone plate reactive ultrafiltration mem-brane was used for the rejection of heavy toxic metal cati-ons such as Cd21 and Zn21 through the coordination ofthe thiourea group and heavy toxic metal cations, in whichthe effects of the morphological and the structure of the

membrane on the rejection properties were investigated.The rejection conditions, including the concentration ofheavy toxic metal cations, temperature and pH of the solu-tion had significant effects on the rejection capacity ofpolysulfonebenzylthiourea-reactive ultrafiltration membrane.The reactive ultrafiltration membrane containing thioureagroup can be conveniently recovered by dilute hydrochloricacid for coordination of heavy toxic metal cations, whichwould have wide application for the treatment of waste-water-containing heavy toxic metal cations. � 2008 WileyPeriodicals, Inc. J Appl Polym Sci 108: 4014–4022, 2008

Key words: polysulfonebenzylthiourea; phase inversion;ultrafiltration membrane; heavy toxic metal cations; sepa-ration techniques

INTRODUCTION

Heavy toxic metal cations such as Cd21 and Zn21

can cause problems to people’s health. The heavytoxic metal cations-containing industrial effluentsthat come from the plants that use or produce heavytoxic metal and heavy toxic metal compounds arethe major resource of the heavy toxic metal pollu-tion.1 The reactive ultrafiltration membrane, whichintegrates the advantages of both reactive chroma-tography and modern membrane techniques, can beused to solve separation problems in a wide rangeof applications because its energy consumption isrelatively low, it is simple to scale up, and its mem-brane properties can be kept under control easily.2–8

The reactive ultrafiltration membrane with definitemicropores has reactive functional groups on itsinner and outer surface as carrier of the reactive rea-gent. When the solution is filtered through the mem-brane, the target materials will quickly and effi-

ciently combine with the relevant functional groupsof the reactive reagent. The materials captured on thereactive ultrafiltration membrane can be soon elutedwhen an eluent passes through the membrane.

Recently, we reported the highly qualified hetero-geneous polysulfone plate filter membranes withamino group as chelating groups by phase separa-tion with the blends of the chelating resin and poly-sulfone having the highest chelating capacity of 1050lg/cm2 for mercury(II).9 In our previous work, wereported the synthesis of chloromethyl polysulfonefrom polysulfone by Friedel-Crafts reaction.10 Here,the homogeneous reactive ultrafiltration membranewith thiourea groups was obtained through the reac-tion between chloromethyl polysulfone matrix mem-brane and thiourea, and the rejection of heavy toxicmetal cations were investigated.

EXPERIMENTAL

Materials

Dichloromethane, 2,2-dichloromethane, nitrobenzene,thiourea, and polyethylene glycol (PEG 600) were ana-lytical grade and purchased from Tianjin ReagentPlant. Chloromethyl ether and ferriammonium sulfatewere analytical grade and were purchased from Nan-

Correspondence to: B.Wang ([email protected]).Contract grant sponsor: Natural Science Foundation of

Tianjin; contract grant number: 05YFJMJC04200.

Journal of Applied Polymer Science, Vol. 108, 4014–4022 (2008)VVC 2008 Wiley Periodicals, Inc.

kai University Chemical Plant. CdCl2 and ZnCl2 werepurchased from Tianjin Chemical Reagent Plant as an-alytical grade. Sodium rhodanate was analytical gradeand purchased from Tianjin Yaohua Chemical Plant.

Main apparatuses

XL30 ESEM (environmental scanning electron micro-scope) was made by PHILIPS. VECTOR22 FourierInfrared Spectrometer (with ART appendix) wasmade by Bruker Corp., Germany. The retention mea-surement apparatus of membrane was made byTianjin Polytechnic University, China.

Synthesis of chloromethyl polysulfone

A given amount of dried polysulfone was dissolvedin dichloromethane (or 1,2-dichloroethane) and thesolution of anhydrous zinc chloride/chloromethylether was added dropwise. The reaction temperaturewas increased to 408C slowly and the reaction wascarried out at 408C for 6 h. The solution wasdropped into methanol slowly after the reaction sys-tem was cooled to room temperature. The chloro-methyl polysulfone was precipitated from the systemas lump and washed by hot distilled water repeat-edly until no bubbles. The chloromethyl polysulfonewas dried in vacuum oven at 608C, and washedwith distilled water for three times and dried in thevacuum oven at 508C till constant weight.

Preparation of polysulfonebenzylthiourea-reactiveultrafiltration plate membrane

The matrix plate membranes were prepared by thephase inversion technology. The casting solution wasformed after vacuum defoaming, using chloromethylpolysulfone as membrane materials, PEG as poreforming agent and DMAC as solvent with a certainratio with heating to form a solution. The casting so-lution was poured onto a clear and smooth glassplate at predetermined temperature. The solution wascast into thin film using blade after the evaporationin the air for definite seconds and the glass plate wasimmersed in DMAC-water solution at a certain tem-perature to let it solidify into membrane. The matrixplate membranes were soaked in a thiourea of anhy-drous ethanol solution and the reaction was carriedout at 508C for 8 h. The polysulfonebenzylthioureaplate reactive ultrafiltration membrane was affordedafter taking the membrane stripe out of the solutionand washed with distilled water repeatedly.

FTIR analysis of polysulfonebenzylthiourea-reactive ultrafiltration plate membrane

The polysulfonebenzylthiourea membranes weredried at 50–558C in vacuum oven. The dried mem-

brane was directly placed on the ART crystal andfastened firmly with clips. The metal peg should befirmly screwed when fastening. The FTIR spectra ofART annex fastened with plate membrane weredetermined on a VECTOR Fourier Infrared Spec-trometer.

Measurement of water flux

The ultra-pure water was pumped from a 2000 mLof feed reservoir and returned the feed reservoir af-ter passing through the plate membrane module.The volume of the water filtered through the mem-brane was measured by a volumetric cylinder. Theoperation pressure was 0.1 MPa. The water flux Qwas calculated according to eq. (1):

Q ¼ V

St(1)

where, V was the volume of transmitted liquid and twas the ultrafiltration time, and S was the effectivesurface area of the membrane.

Measurement of porosity

The porosity of membrane was determined bymeans of gravimetric method.11 Glycerol was usedas saturate and a definite area of wet membrane wassheared. The glycerol on the surface of membranewas wiped away to obtain the wet membrane withthe weight as Ww. Then the wet membrane wasdried in a vacuum oven till constant weight with theweight of dried membrane as Wd. The porosity ofmembrane Pr was calculated from eq. (2):

Pr ¼ Ww �Wd

S � d � q 3 100% (2)

where, d was the average thickness of membraneandq was the density of glycerol, respectively.

Measurement of membrane pore size

The membrane pore size was determined by meansof filtering velocity method.11 The membrane porediameter rf was calculated from eq. (3)

rf ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi8 3 ð2:90� 1:75PrÞ � l � L �Q

Pr � DP � S

s(3)

where, pr was porosity, L was thickness of mem-brane, l was viscosity of transmitted liquid, Q wasflux, ~p was pressure and S was filtering area,respectively.

The ESEM characterization was performed on acoating film by ion-sputtering after the membrane

POLYSULFONEBENZYLTHIOUREA-REACTIVE ULTRAFILTRATION PLATE MEMBRANE 4015

Journal of Applied Polymer Science DOI 10.1002/app

was frozen in liquid nitrogen and fasten on the sam-ple table. The pore size and size distribution of themembrane was obtained from the observation ofthe morphological structure of the cross section ofthe matrix membrane with a XL30 ESEM

The determination of chloromethyl polysulfonechlorinity was performed by Woolhad method.11

The concentration of Cd21 and Zn21 were deter-mined with dithizone method.12

Rejection of polysulfonebenzylthiourea-reactiveultrafiltration plate membrane for Cd21 and Zn21

The rejection of polysulfonebenzylthiourea-reactiveultrafiltration membrane for Cd21 and Zn21 weredetermined with the experimental apparatus formeasurement of water flux (made in Tianjin Poly-technic University, China). The properties of themembrane can be described by the rejection capacityof the membrane for Cd21 and Zn21 was calculatedfrom eq. (4):

C ¼ C0 � Ct

S(4)

where, C0 is original concentration of Cd21 andZn21, Ct is the residual concentration of Cd21 andZn21 after the Cd21 and Zn21 were through themembrane, and S was membrane area.

RESULTS AND DISCUSSION

Preparation of polysulfonebenzylthiourea-reactiveultrafiltration plate membrane

The chloromethyl polysulfone was afforded by Frie-del-Crafts electrophilic substitution reaction underanhydrous conditions using polysulfone as startingmaterial, dichloromethane as solvent, chloromethylether as chloromethyl reagent and anhydrous zincchloride as catalyst. The specific reactions were asScheme 1:

The reaction was carried out at 408C for 5 h. Itwas observed that the amount of the catalyst hadsignificant effect on the chloromethylation of poly-sulfone. The chlorinity of chloromethyl polysulfoneincreased considerably with the increase amount ofzinc chloride. However, the reaction system wouldfreeze if the amount of zinc chloride was in large

excess. The chlorinity of chloromethyl polysulfonealso increased with the increase amount of chloro-methyl ether. The chloromethyl polysulfone matrixplate membranes were prepared via phase inversionmethod. The structure and property of membranewere determined not only by the nature of the mem-brane materials and membrane-forming process con-ditions but also by the thermodynamic conditions ofcasting solutions, such as concentration of polymer,the concentration of additive and temperature forcasting solutions. Table I shows the relationshipbetween chloromethyl polysulfone concentration andthe properties of matrix membrane. It could beobserved that water flux, pore size, and porosity ofchloromethyl polysulfone matrix membrane alldecreased significantly and the dense layer becamemore compact with increasing concentration ofchloromethyl polysulfone in casting solution. Fur-thermore, as chloromethyl polysulfone concentrationincreased, the viscosity of casting solution increased,which caused to decrease the diffusion rate betweensolvent and coagulating agent and gradually todecrease the phase inversion rate and coagulatingrate. Table II showed the effect of the concentrationof the polymer additive PEG (Mw 5 600) on matrixmembrane structure. It could be observed that waterflux, pore size, and porosity of matrix membrane allincreased significantly with increase of the concen-tration of the polymer additive in casting solution.

The polysulfonebenzylthiourea-reactive ultrafiltra-tion membrane was obtained through the reaction

Scheme 1 The synthesis of chloromethyl polysulfon.

TABLE IThe Effect of the Concentration of Chloromethyl

Polysulfone on the Properties of the Matrix Membrane

Chloromethylpolysulfonecontent (%)

Water flux(L/m2 h)

Porediameter (nm)

Porosity(%)

10 64.2 6 0.1 38.5 6 0.2 61.3 6 0.212 51.8 6 0.2 31.2 6 0.1 52.4 6 0.114 45.3 6 0.1 27.1 6 0.1 48.4 6 0.216 40.7 6 0.2 23.2 6 0.2 45.7 6 0.118 37.6 6 0.2 22.1 6 0.1 43.2 6 0.220 34.3 6 0.1 20.6 6 0.1 42.6 6 0.2

TABLE IIThe Effect of the Amount of Polymer PEG on the

Properties of the Chloromethyl PolysulfoneMatrix Membrane

PEG content(%)

Water flux(L/m2 h)

Porediameter (nm)

Porosity(%)

0 41.2 6 0.1 24.0 6 0.2 46.3 6 0.12 170.1 6 0.2 34.8 6 0.2 60.1 6 0.24 180.4 6 0.1 37.2 6 0.1 61.3 6 0.16 194.5 6 0.2 38.4 6 0.2 62.7 6 0.38 201.1 6 0.1 40.1 6 0.2 65.7 6 0.2

10 208.4 6 0.2 42.1 6 0.1 67.8 6 0.1

4016 WANG, HUANGFU, AND LIU


between chloromethyl polysulfone matrix platemembrane and thiourea. The synthetic route wasshown as in Scheme 2:

The polysulfonebenzylthiourea-reactive ultrafiltra-tion membrane successively through the thioureareaction to incorporate the thiourea groups werecharacterized with FTIR spectra as shown in Figure1. The successful thiourea reaction was confirmed bythe FTIR spectra in Figure 2(a,b) with complete dis-appearance of the peak at 1246 cm21 correspondingto the stretching vibration of chloromethyl group forchloromethyl polysulfone matrix membrane and thepresence of new peaks at 1402 cm21 assigning tothe vibration of C��S bond, 1640 cm21 attributing to

the vibration of C¼¼N, and the wide strong peakaround 3134 cm21 contributing to the NH3\plus ofthe thiourea group on methyl(iso-thiourea) polysul-fone plate (MTUPSF), respectively. In other words,the chloromethyl groups were quantitatively con-versed into the thiourea groups with estimationfrom the complete disappearance of peak at 1246cm21 of the chloromethyl group in the FTIR spectra.

Figure 2 was the ESEM of the cross section of thepolysulfonebenzylthiourea-reactive ultrafiltration mem-brane with different concentration of PEG (Mw

5 600). Figure 3 showed that the cross-section struc-ture of the membrane changed from dense to loosegradually, the pore size of membrane increased con-siderably and the structure from compact to loosegradually while the amount of PEG increased. It wasfound from SEM micrograph of membrane that thepore size of the membrane increased, which wasshown in Table II, with increase the concentration ofpolymer additive. This was attributed not only tothe increase of pore size but also to the connectionextent of the membrane pores. The formation pro-cess of micropore on the membrane was a liquid–liq-

Scheme 2 The synthesis of polysulfonebenzylthiourea.

Figure 1 FTIR spectra of membrane. (a) Chloromethylpolysulfone; (b) Polysulfonebenzylthiourea.

Figure 2 Scanning electron micrographs of the cross sec-tion of membranes with different concentration of PEG(Mw: 600). (a) PEG: 6%; (b) PEG: 4%.



uid phase inversion process. The structure of themembrane was mainly determined by the composi-tion of the local field of the casting solution duringthe phase inversion. After the phase inversion of thecasting solution, the rich phase of chloromethyl poly-sulfone was continuous and gelled, then solidifiedinto a continuous membrane phase with micropores.When the solvent (DMAC) and the additive (PEG)scattering in the polymer as poor phase werewashed away, the poor phase grew larger and largerand then intercrossed the micropores during casting.The prerequisite for the continuous growth of poorphase was that the vicinities could continuously pro-vide solvent for poor phase before the solidificationof the rich phase. In the casting system, when waterwas used as gel reagent, the diffusion rate of DMACsolvent towards water was faster than that of waterto casting solution. The further the casting solutioncomposition away from cloud point composition, thelater the phase inversion occurred and the more thesolvent (DMAC) overflowed. When the concentra-tion of the additive PEG was low, the compositionof the casting solution was far away from the cloudpoint and the overflowing amount of solvent waslarge. The chloromethyl polysulfone concentrationwas high before phase inversion to form a dense toplayer structure and small pore size. The dense layersprevented the solvent DMAC from further inter-changing with water, which was good for the forma-tion of micropore with finger shape. With increase ofthe additive PEG concentration in the casting solu-tion, the composition of the solution was approach-ing the cloud point. The rate of phase inversionincreased and the solvent overflowed less before thephase inversion. The excessive amount of solventwas good for poor phase growth. The connectionsamong membrane micropores increased to form aloose top layer. The hindrance of loose top layer tonext layers decreased and formed an intercrossedfinger shape structure. Although there was littlechange for pore sizes, the finger shape connections

were good, osmosis resistance decreased and flux ofthe membrane increased obviously.

Effect of the loading of thiourea groups onchelating capacity of polysulfonebenzylthioureamembranes

The chloromethyl polysulfone matrix membranes withdifferent chlorinity were prepared with 4% PEG (Mw 5600) as pore forming agent and the entire solid contentof 15% in the casting solution. Then the polysulfoneben-zylthiourea-reactive ultrafiltration membrane with dif-ferent amount of thiourea were prepared by the reac-tion between chloromethyl polysulfone matrix mem-brane and thiourea with the total conversion higherthan 90% from chloromethyl group. The chelatingcapacity of polysulfonebenzylthiourea membrane forCd21 and Zn21 were determined by soaking the mem-brane in 500 lg/mL Cd21 and Zn21 solution at pH 2–5for 24 h and the results were shown as in Figure 3. Theresults indicated that the chelating capacity of the poly-sulfonebenzylthiourea membranes increased rapidlywith the increasing thiourea from 0 to 1%, and thenincreased considerably with the thiourea increasing fur-ther till 8%. The chelating capacity for Cd21 and Zn21

on polysulfonebenzylthiourea membranes increasedwith higher loading of thiourea groups. The polysulfo-nebenzylthiourea membrane with high thiourea load-ing (from the chloronity of 5.4%) in the present workwas utilized for investigation, as the chlorinity of chlor-omethyl polysulfone matrix material had little influenceon the formation of chloromethyl polysulfone matrixmembrane. These results further proved the successfulincorporation of thiourea groups on the porous polymermembrane successively through the thiourea reaction.

Effect of the thiouriuming conditions on chelatingcapacity of polysulfonebenzylthiourea membranes

The chloromethyl polysulfone matrix membraneswere soaked in saturate solution of thiourea in anhy-drous ethanol for 5 h at different temperatures, i.e.,20, 30, 40, and 508C to afford the polysulfoneben-zylthiourea membranes. The effect of the thiourium-ing temperature on the chelating properties of poly-sulfonebenzylthiourea membranes was shown inFigure 4. The results indicated that the chelatingcapacity increased considerable with the increasingreaction temperature, which was due to the higherconversion of methyl chloride to the methyl thiou-rium chloride under higher reaction temperature.

The chloromethyl polysulfone matrix membraneswere soaked in saturate solution of thiourea in anhy-drous ethanol for different time at room temperatureto afford the polysulfonebenzylthiourea membranes.The effect of the thiouriuming time on the capacityof the polysulfonebenzylthiourea membrane was

Figure 3 The effect of the loading of thiourea of polysul-fonebenzylthiourea on the chelating capacity of polysulfo-nebenzylthiourea membrane.



shown in Figure 5. The capacity of polysulfoneben-zylthiourea with the pore size of 40 nm for Cd21

and Zn21 increased rapidly with the increasing thio-uriuming time till 8 h and then leveled off at 12 htill a constant value. While the pore size was 35 nm,the capacity increased rapidly with the increasingthiouriuming time till 12 h and then leveled off at16 h till a constant value. The results showed thatthe thiouriuming reaction of the chloromethyl poly-sulfone matrix membrane with bigger pore size wasmuch faster than that of the membrane with thesmaller size.

The effect of the thiourea concentration on thecapacity of polysulfonebenzylthiourea membranewas shown in Figure 6. The results indicated thatthe chelating capacity increased considerably withincreasing the concentration of thiourea during thethiouriuming reaction.

All these results demonstrated that the best thiour-iuming temperature was 508C, the best thiouriumingtime was 12 h, and the best concentration of thioureawas saturated solution, respectively.

Effects of the porosity and pore size on chelatingcapacity of polysulfonebenzylthiourea membranes

The chloromethyl polysulfone matrix membraneswith different porosity and pore size were preparedby utilization of either different amount (2%, 4%,6%, 8%) of PEG (Mw 5 600) as the additive, whilethe total solid content in the casting solution waskept at 15%. The effects of the pore size and porosityon the chelating capacity of the polysulfonebenzylth-iourea membranes for Cd21 and Zn21were shown inFigure 7 and Figure 8, respectively. The results indi-cated that the chelating capacity of the polysulfone-benzylthiourea membranes increased both with theincreasing pore size and porosity, which was origi-nated either from the different amount of PEG addi-tive. With bigger size and higher porosity, the areaof the porous polymer polysulfonebenzylthioureamembrane increased and the fraction of the accessi-ble thiourea groups on the wall of the membraneincreased. In this way, the chelating capacity of thepolysulfonebenzylthiourea membrane increased withlarger pore size and porosity of the membrane.

Figure 4 The effect of the thiouriuming temperature onthe chelating properties of polysulfonebenzylthioureamembranes.

Figure 5 The effect of the thiouriuming time on thecapacity of the polysulfonebenzylthiourea membrane.

Figure 6 The effect of the thiourea concentration on thecapacity of polysulfonebenzylthiourea membrane.

Figure 7 The effect of the pore size on the chelatingcapacity of polysulfonebenzylthiourea membrane.



Effect of pH of the Cd21 and Zn21 solution onchelating capacity of thepolysulfonebenzylthiourea membranes

Figure 9 showed the effect of the pH of Cd21 andZn21 solution on the chelating capacity of the poly-sulfonebenzylthiourea membranes. The results indi-cated that the capacity of the membrane was muchhigh in the range of pH 2–5 and the capacityincreased slightly with the increasing pH of Cd21

and Zn21 solution. However, the pH of the solutionshould be in acidic state because Cd21 and Zn21

react with hydroxide anion to precipitate from thesolution under basic environment, which wouldcause it impossible to selective separation Cd21 andZn21 from the pollution with the polysulfoneben-zylthiourea membrane. Naturally, the low pH solu-tion was not favorable for such chelating adsorption.

Effect of temperature on the chelating capacity ofpolysulfonebenzylthiourea membranes

Figure 10 showed the effect of the chelating tempera-ture on the chelating capacity of the polysulfoneben-zylthiourea membrane. The results indicated that thecapacity increased slightly with increasing chelatingtemperature. The processes for the chelating adsorp-

tion of the polysulfonebenzylthiourea membrane forthe metal cations included the following three steps:(i) The diffusion of the metal cations to the surfaceof the membrane; (ii) The diffusion of the metal cati-ons in the pore of the membrane; (iii) Chemicaladsorption through the ion-exchanges between themetal cations and the chelating groups on the mem-brane. The high temperature was good not only tothe diffusion of the metal cations but also for the dis-sociation of the thiourea group to chelate with themetal cations. The mobility of the metal cationsincreased with higher chelating temperature to over-come the hindrance of the membrane to enhance thechelating rate and the chelating capacity. Therefore,it was better to perform the chelating adsorptionbetween polysulfonebenzylthiourea membrane andCd21 and Zn21 with a little higher temperature.

Effect of concentration of Cd21 and Zn21 on thechelating properties of polysulfonebenzylthioureamembranes

The polysulfonebenzylthiourea membranes weresoaked in 400, 800, 1000 lg/mL of Cd21 and Zn21

solution at pH 2–3 to determine the chelatingcapacity. The relationship between the chelatingamount of the polysulfonebenzylthiourea membraneand the adsorption time was shown in Figure 11.The results indicated that the chelating amountincreased rapidly in the first 3 h and then leveled offwith the increasing adsorption further till a saturatevalue after 16 h for all the four samples. The saturateadsorption amount of the polysulfonebenzylthioureamembrane increased with the increasing concentra-tion of Cd21 and Zn21 in the solution. The adsorp-tion properties of the polysulfonebenzylthioureamembrane for metal cations were mainly determinedby the nature of the chelating groups on the mem-brane and the electronic structure of the metalcations.

Figure 8 The effect of the porosity on the chelatingcapacity of polysulfonebenzylthiourea membrane.

Figure 9 The effect of the pH of Cd21 and Zn21 solutionon the chelating capacity of the polysulfonebenzylthioureamembrane.

Figure 10 The effect of the chelating temperature on thechelating capacity of the polysulfonebenzylthiourea mem-brane.



Effect of the chelating reagent in the solution onthe chelating capacity ofpolysulfonebenzylthiourea membrane

To determine the competitive coordination effect ofthe ligand on the chelating capacity, the chelatingcapacity of polysulfonebenzylthiourea membranewas determined in the presence of reagent EDTA inthe introductory solution as shown in Figure 12. Theresults indicated that the chelating capacity of thepolysulfonebenzylthiourea membrane decreased sig-nificantly with the increasing concentration of EDTAin the solution. It is well known that EDTA has astrong chelating ability with Cd21 and Zn21, whichis much stronger than that between polysulfoneben-zylthiourea membrane and Cd21 and Zn21. Suchcompetitive coordination prevented polysulfoneben-zylthiourea chelating with Cd21 and Zn21 todecrease the capacity of the polysulfonebenzylth-iourea membrane for Cd21 and Zn21.

The rejection and the recycle of thepolysulfonebenzylthiourea membrane

The rejection of polysulfonebenzylthiourea mem-brane was determined from the relationship between

the concentration of Cd21 and Zn21 in the eluted so-lution and the volume eluted through the membraneunder 0.1 MPa with 100 lg/mL of Cd21 and Zn21

as the elution, which was shown in Figure 13. Theresults indicated that the concentrations of Cd21 andZn21 were below 30 lg/mL in the initial 150 mL ofeluted solution and then increased abruptly tillthe same level as the starting solution after eluted200 mL and 230 mL of Cd21 and Zn21. It meant thatthe chelating adsorption of the polysulfonebenzylth-iourea membrane reached a saturate state aftereluted 200–230 mL of the solution and the rejectioncapacity were 420 lg/cm2�memb for Cd21 and 403lg/cm2�memb for Zn21, which were much similar asthe static adsorption capacity of 417 lg/cm2�memb.for Cd21 and 400 lg/cm2�memb for Zn21. The con-centration of Cd21 and Zn21 in the eluted solutiondecreased slightly after the eluted volume largerthan 300–310 mL and the eluted solution was a littleturbid maybe due to the precipitation of Cd21 andZn21 from the elution on the chelating membrane.The polysulfonebenzylthiourea membrane wasrecycled by soaking in 250 mL of 0.1M dilute HClsolution for 6–8 h at room temperature and the con-centration of Cd21 and Zn21 in HCl was 30–32 lg/mL. The recycled polysulfonebenzylthiourea mem-brane was used to remove Cd21 and Zn21 and therejection capacity was 310–315 lg/cm2�memb, whichwas little smaller than that of the brand new mem-brane. This showed that the polysulfonebenzylth-iourea membrane can be easily and convenientlyrecycled in dilute HCl solution, which will play animportant roll for the utilization of such polysulfone-benzylthiourea plate reactive ultrafiltration mem-brane in the treatment of Cd21 and Zn21 in theindustrial wasted-water.

CONCLUSIONS

The highly qualified polysulfonebenzylthiourea-reac-tive ultrafiltration membranes with high rejection

Figure 12 The chelating capacity of polysulfonebenzylth-iourea membrane which was determined in the presenceof reagent EDTA in the introductory solution.

Figure 13 The dynamic rejection of polysulfonebenzylth-iourea membrane.

Figure 11 The relationship between the chelating amountof the polysulfonebenzylthiourea membrane and theadsorption time.



capacity for heavy toxic metal cations Cd21 andZn21 were prepared through the reaction betweenthe chloromethyl polysulfone matrix membrane andthiourea. The results indicated that the rejectioncapacity of polysulfonebenzylthiourea membranewith increasing the thiourea loading, the pore sizeand porosity due to the larger accessible number ofthiourea groups for chelating adsorption. The chelat-ing capacity of polysulfonebenzylthiourea membraneincreased with increasing the reaction time, tempera-ture, concentration of thiourea for the thiouriumreaction. The chelating capacity also increased withthe adsorption temperature, the concentration ofCd21 and Zn21 in the introductory solution and theadsorption time. The optimum pH for the adsorptionof Cd21 and Zn21 is in the range of 4–5. The dy-namic rejection capacity of the polysulfonebenzylth-iourea-reactive ultrafiltration membrane for Cd21

and Zn21 was much the same as that of the staticadsorption chelating capacity. The polysulfoneben-zylthiourea-reactive ultrafiltration membrane can be

easily and conveniently by soaking in dilute HCl so-lution with high chelating capacity.

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