Reactive & Functional Polymers 49 (2001) 133–143www.elsevier.com/ locate / react

Chemical modification of cross-linked resin based onacrylonitrile for anchoring metal ions

a , b a* ˆLuiz Claudio de Santa Maria , Marcia C.V. Amorim , Monica R.M.P. Aguiar ,a a b˜Pedro Ivo C. Guimaraes , Marcos A.S. Costa , Alcino Palermo de Aguiar ,

c c a´Paulo Roberto Rezende , Marcelo Souza de Carvalho , Flavia G. Barbosa ,a aJuliano M. Andrade , Roberto C.C. Ribeiro

a ˜´ ´Grupo de Polımeros (GPol), Instituto de Quımica, Universidade do Estado do Rio de Janeiro, R. Sao Francisco Xavier,˜524 — Pavilhao Haroldo Lisboa da Cunha, Rio de Janeiro, CEP 20559-900, Brazil

b ´ ´Departamento de Engenharia Quımica, Instituto Militar de Engenharia, Praca General Tiburcio, 80 Rio de Janeiro, CEP 22290-270,Brazil

cInstituto de Engenharia Nuclear, CNEN /RJ; C. Postal 68550 CEP 21945-970 Rio de Janeiro, Brazil

Received 7 December 2000; received in revised form 8 May 2001; accepted 14 May 2001

Abstract

Network resin based on acrylonitrile has been chemically modified through different reactions to obtain different chelatinggroups. The beads of resin were synthesized by aqueous suspension copolymerization of acrylonitrile (AN) anddivinylbenzene (DVB). The chemical modifications of these beads’ cyano groups were carried out by reaction withhydroxylamine, hydrazine and ethanolamine producing amidoxime, amidrazone and oxazoline groups, respectively. Thecopolymer and modified resins were characterized by apparent density, surface area, average pore diameter, elementalanalysis (CHN), FTIR and optical and electronic microscopies. Qualitative experiments of adsorption were conducted toevaluate the resins (modified and unmodified) on fixing Hg(II), Cd(II), Cu(II), Zn(II), Cd(II), Co(II), Ni(II) and Pb(II) fromaqueous solution using batch extractions. Based on the results obtained, it was concluded that it is possible to modifychemically a resin containing cyano groups by different routes and to use these resins as a very low cost effective sorbent formetal ions. 2001 Elsevier Science B.V. All rights reserved.

Keywords: Acrylonitrile copolymers; Cross-linked resin; Porous materials; Chemical modification; Sorbents

1. Introduction applications, which continues increasing due toseveral possibilities of modification of their

Functionalized cross-linked polymers have chemical and physical properties. Organic andgained great importance in many fields of inorganic sorbents functionalized with complex-scientific research as well as for industrial ing groups have been developed and reported in

the literature [1–7]. Preparation of pellicularresins, in which a solid is surrounded by a thin*Corresponding author. Fax: 1 55-21-587-7227.

E-mail address: lcsm@uerj.br (L.C. de Santa Maria). film of cross-linked ion-exchange material and

1381-5148/01/$ – see front matter 2001 Elsevier Science B.V. All rights reserved.PI I : S1381-5148( 01 )00068-2

134 L.C. de Santa Maria et al. / Reactive & Functional Polymers 49 (2001) 133 –143

superficially sulphonated resins, has been de- resins based on acrylonitrile. Hence, the aim ofscribed in literature [6,8]. Ion-exchange have this work is to present simple ways to chemical-provided the most universal preconcentration ly modify a resin containing pendant cyanotechnique: ions may be analyzed directly upon groups, introducing different pendant chelatingthe solid matrix using X-ray spectrometry, groups according to the chemical agent used.neutron activation analysis or isotopic batch Each modified resin can be employed to specificdilution techniques. The ions which have eluted applications as to anchoring heavy metals fromfrom the column may be analyzed using atomic aqueous solutions or as chromatograph andspectrometry or inductively coupled plasma catalyst supports.atomic emission spectrometry. On the otherhand, these materials are not selective for manykinds of metals. 2. Experimental part

Ion-exchange and adsorption are basic opera-tions in separation processes for analytical and 2.1. Materialspreparative chemistry and they are widely used

Acrylonitrile and divinylbenzene were kindlyin technical plants. The main fields of applica-offered by Nitriflex (Brazilian) and used astion of them are the removal of undesired ionsreceived; a,a9-azo-bis-isobutyronitrile (AIBN)and molecules from solutions and the extractionwas donated by Metacril do Brasil and wasof useful substances. In addition, the use ofrecrystallized in methanol; hydroxylamine hy-functional polymers as catalysts in organicdrochloride, hydrazine sulphate, gelatin,chemical reactions and for the chromatographicmethylethylketone (MEK), propanone, NaCl,separation of metals (e.g. rare earth, and organicNaOH, heptane, toluene, methanol, chloro-compounds, such as sugars and amino acids) hasbenzene, cadmium acetate; standard solution ofbeen known for a long time but has only comeheavy metals [Hg(II), Cd(II), Cu(II), Zn(II),into general use on a technical scale in the lastCd(II), Co(II), Ni(II) and Pb(II)] from Merckfew years [9–11].(Titrisol) and ethanolamine were purchasedEnvironmental and industrial problems aris-from Vetec (Brazilian) with P.A. degree anding from polluted waters markedly influence theused as received.relevance of the identification of trace metal

ions and their species. Industrial requirements ofhigh purity materials and environmental prob- 2.2. Preparation of resin based onlems have stimulated the development of new acrylonitrilematerials and techniques suitable for trace metalion recovery and enrichment from several liquid In a typical glass reactor (1000 ml) with asources (polluted waters, liquids for biological mechanical stirrer, aqueous phase (AP) wasand medical treatments, industrial waters, sur- prepared by addition of gelatin (0.2% w inface waters, gallium recovery from Bayer liquor relation to water) and NaCl (2% w in relation toetc.) [12–18]. water) solutions. The organic phase (OP) pre-

Resin based on acrylonitrile is easy to prepare pared with monomers mixture (0.28 mol ofand presents a reactive pendant group (cyano acrylonitrile and 0.42 mol of divinylbenzene),group), which can be modified by different diluents (heptane and toluene, volume ratio 5

kinds of reagent through nucleophilic addition 70/30 and 100% dilution) and initiator (AIBN)and cycloaddition reactions. Although these was added slowly to aqueous phase previouslyreactions are well known with low molecular prepared under stirring at room temperature,weight compounds [19–21], they have not been employing AP/OP ratio 5 4/1. These tworeported in literature for modifying cross-linked phases were maintained under stirring (400

L.C. de Santa Maria et al. / Reactive & Functional Polymers 49 (2001) 133 –143 135

Table 1Properties of poly(acrylonitrile-divinylbenzene) copolymer beads

bCopolymer type Average Swelling ratio (%) Apparent Acrylonitrile Surface Averagea c dsize density content area pore

3 2 d(mm) MEK Toluene (g /cm ) (mol%) m /g diameter

Acrylonitrile /DVB 210–250 8 5 0.32 10 440 96Non-modified copolymer

a More than 50% of beads remained between sieves of 210–250 mm (granulometric analysis).b Described as follows: % 5 [(V 2V ) 3V 3 100], where V and V are the volume of swollen beads (ml) (in methylethylketone — MEKs d d s d

or toluene) and volume of dry beads (ml), respectively.c Described as follows: %5[(elemental analysis results)353/14].d Determined by BET.

rpm) at room temperature for 10 min. Hence, they have presented a narrow particle sizedistribution (150–210 mm).the suspension copolymerization system was

kept under stirring at 708C for 24 h. The resin2.3. Chemical modifications of resinbeads was thoroughly washed with hot water

(eight volumes of 500 ml) and with ketone in aThe chemical modifications of beads basedSoxhlet extractor and dried at 608C. The yield

on copolymer of acrylonitrile were carried outof these copolymers beads was 80–95% andby different routes which are described below.

2.3.1. Modification with hydroxylamineFifteen grams of NH OH.HCl in 70 ml of2

methanol and 10 g of resin were added to areactor equipped with a magnetic stirrer andreflux condensator. After 2 h, about 14 ml ofNaOH (9.5 g) aqueous solution were added tothis mixture and the pH was kept at 9. Thereaction was performed for 20 h at 708C understirring. The modified resin was washed thor-oughly with hot water and MEK and dried at608C.

2.3.2. Modification with hydrazineThirty-three grams of NH NH .H SO in 1602 2 2 4

ml of methanol and 10 g of resin were added toa reactor equipped with a magnetic stirrer andreflux condensator. About 26 ml of NaOHaqueous solution were added to this mixture andthe pH was kept at 9. The reaction was per-formed for 20 h at 808C under stirring. Themodified resin was washed thoroughly with hotwater and ethanol and dried at 608C.

2.3.3. Modification with ethanolamineA volume of 6.3 ml of ethanolamine wereFig. 1. Optical microscopy of unmodified resin based on

added to a reactor equipped with magneticacrylonitrile (703).

136 L.C. de Santa Maria et al. / Reactive & Functional Polymers 49 (2001) 133 –143

stirrer and reflux condensator containing 35 ml was conducted at 1208C for 24 h under stirring.of chlorobenzene; 5 g of resin and 0.5 g of The modified resin was washed thoroughly withcadmium acetate (used as catalyst). The reaction ethanol and dried at 608C.

Fig. 2. Scanning electron microscopy of unmodified resin: (a) external part detail; (b) internal part detail.

L.C. de Santa Maria et al. / Reactive & Functional Polymers 49 (2001) 133 –143 137

2.4. Resin characterization ing concentration of metals in solution wasdetermined by atomic spectroscopy using an

2The specific surface area (in m /g), and inductively coupled plasma atomic emission˚average pore diameter (A) were determined by spectrometer (Optima 3100 by Perkin–Elmer).

the BET method from low-temperature nitrogenadsorption isotherms (ASAP Micromeritics2010) which were obtained at 77 K using ahigh-vacuum volumetric apparatus. The samples 3. Results and discussionwere degassed at 1008C/1 mPa for 3 h. Carbon,hydrogen, nitrogen and oxygen contents were Milky white beads of poly(acrylonitrile-di-determined by elemental analysis (CHN Perkin– vinylbenzene) copolymer were produced byElmer 2400). The chemical modification of aqueous suspension copolymerization. Thenitrile groups was investigated by infrared tech- characteristics of this copolymer are shown onniques (FTIR — Perkin–Elmer 1720 3 ) in Table 1 where it can be seen that the copolymerKBr. The morphological characteristics were beads produced have mesoporous characteris-observed with a stereo optical microscope tics. The resin has presented low swelling in(Olympus SZ10). Resins were also character- MEK and toluene, low apparent density, highized by a scanning electron microscope (Zeiss surface area and large average pore diameterDSM 960). The beads were coated with carbon which are characteristics of mesoporous materi-film and their external and internal parts were als. The sphere shape of the beads was verifiedobserved using a 15 kV acceleration electron by optical microscopy (Fig. 1). Another mor-beam. Qualitative experiments were conducted phological features were observed by scanningto evaluated the resins (modified and un- electron microscopy where it could be observedmodified one) on fixing Hg(II), Cu(II), Zn(II), that the resin has presented superficial porousCo(II), Ni(II), Cd(II) and Pb(II) from aqueous (Fig. 2a). On the other hand, internally thesolution of these metal ions mixture. Batch structure resin presents some microporous (Fig.extractions were employed using 1 g of resin, 2b). This result could be confirmed by the large10 ml of metals solutions (80 ppb of each) at surface area verified by the BET analysis (Table308C under magnetic stirrer. After 30 min of 1).contact time, the beads were separated by Mesoporous resins with pendant cyanocentrifugation and filtration. Then, the remain- groups can be chemically modified by different

Fig. 3. Reactions on the resin based on acrylonitrile /divinylbenzene.

138 L.C. de Santa Maria et al. / Reactive & Functional Polymers 49 (2001) 133 –143

reactions. Depending on the starting resin and with hydroxylamine to introduce pendantreactions used, the porous structure is can be amidoxime groups; (c) reaction with ethanol-retained. There is a broad spectrum of type of amine to introduce pendant oxazoline groupsreaction which can involve cyano groups. Three (Fig. 3).kind of reactions were performed using the resin It was observed that after the modificationprepared and characterized previously. These reaction, the beads became yellowish for thereactions were conducted to introduce three resins modified with hydroxylamine and hy-different pendant complexing groups, described drazine and dark yellow for the resin modifiedas follow: (a) reaction with hydrazine to intro- with ethanolamine. By microscopical observa-duce pendant amidrazone groups; (b) reaction tion, it was observed that the surface texture of

Fig. 4. Spectrum of FITR of unmodified resin and modified resin with hydroxylamine.

L.C. de Santa Maria et al. / Reactive & Functional Polymers 49 (2001) 133 –143 139

the resin modified with hydroxylamine was changes indicated that the modification re-rougher than the unmodified resin. It was also actions were done. The similar results wereconcluded that the chemical treatment had not achieved in the resin modified with hydrazine.caused the break of the beads, had not affected On the other hand, the resin treated withthe morphological characteristics but had ethanolamine became powder, showing that thechanged chemical features only. These two chemical treatment conditions were drastic. The

Fig. 5. Spectrum of FITR of unmodified resin and modified resin with hydrazine.

140 L.C. de Santa Maria et al. / Reactive & Functional Polymers 49 (2001) 133 –143

swellings in MEK and toluene and apparent were increased compared to the non-modifiedresin (2.5% of nitrogen content). Figs. 4–6density of the modified resins did not change,show the IR analysis of unmodified and modi-showing that the reticular structure was notfied resins. Bands of acrylonitrile and di-affected. CHN analysis and IR spectra of un-vinylbenzene units were observed for bothmodified and modified resins were carried out to

21resins (unmodified and modified): 2238 cmcertify that the modification reactions has pro-21(CN); 1488 and 1450 cm (CH of aliphaticduced the desire pendant groups on the resin 2

21surface. The nitrogen contents of the modified compounds); 1615–1590 cm (benzene ring).21resin with hydroxylamine and hydrazine (2.9% The presence of a band at 2238 cm related to

and 3.1% of nitrogen content, respectively) the CN group on the modified resins spectrum

Fig. 6. Spectrum of FITR of unmodified resin and modified resin with ethanolamine.

L.C. de Santa Maria et al. / Reactive & Functional Polymers 49 (2001) 133 –143 141

showed that the modifications of cyano groupswere not complete. The IR spectrum of modi-fied resin with hydroxylamine (Fig. 4) exhibited

21a broad band observed in the 3650–3340 cm(O–H of oxime group) [22]. The C 5 N of the

21oxime group was observed at 1655 cm . The21band observed at 910 cm is assignable to the

N–O bond of the oxime group [19,22–25]. Thespectrum of modified resin with hydrazine (Fig.5) showed bands which are characteristics of the

21amidrazone group (3470 and 3024 cm region21due to NH and NH; strong band at 1697 cm2

21assigned to C 5 N; 1654 cm assigned toNH ) [19,22,25]. The oxazoline ring was ver-2

ified on the resin modified with ethanolamine21(Fig. 6) by the bands at 1655 cm of the

21C 5 N bond and at 1251 cm of the C–O–Cbond [22,25].

The modified and unmodified resins wereFig. 8. Effect of pH in heavy metals sorption on modifiedevaluated on fixing different metal ions —acrylonitrile AN resin by hydrazine.

Hg(II), Cu(II), Cd(II), Zn(II), Co(II), Cd(II),Ni(II) and Pb(II) — from aqueous solution. Theresults are shown on Fig. 7 (non-modified resin), results have shown that the chemical modi-Fig. 8 (resin modified with hydrazine), Fig. 9 fications of the resin based on acrylonitrile have(resin modified with ethanolamine) and Fig. 10 provoked an increase of metal ion fixing capaci-(resin modified with hydroxylamine). These ty depending upon the pH employed. It seems

Fig. 7. Effect of pH in heavy metals sorption on acrylonitrile AN Fig. 9. Effect of pH in heavy metals sorption on modifiedunmodified resin. acrylonitrile AN resin by ethanolamine.

142 L.C. de Santa Maria et al. / Reactive & Functional Polymers 49 (2001) 133 –143

sible to control the surface area, porosity,structural integrity, content and distribution ofthe pendant cyano groups by reaction parame-ters of suspension polymerization. The pendantcyano groups can act as sites for modificationby nucleophilic addition and cycloaddition re-actions. These modified resins present a po-tential application regarding the removal ofmetal ions from a mixture of other metal ions.

Acknowledgements

F.G. Barbosa, J.M. Andrade and R.C.C.Ribeiro acknowledge the financial support ofSR1/UERJ and PIBIC/UERJ/CNPq. The au-thors also thank the CNPq, CNEN, FAPERJ andPRONEX (IMA/UFRJ, COPPE/UFRJ, IQ/UERJ and UFSC) for financial support. We aregrateful to Metacril do Brasil and Nitriflex formonomers and initiator donation. Thanks alsoFig. 10. Effect of pH in heavy metals sorption on modified

ˆgo to Maria F.S. Lopes (Dep. De Ciencia dosacrylonitrile AN resin by hydroxylamine.

Materiais e Metalurgia — PUC-Rio) for theelectronic microscopy.that the optimum pH for extracting metal ions is

around 9 for the majority of the cases. It ispossible that in this pH range, the majority of Referenceschelating groups is free to complex the metalions. Fig. 8 shows that the resin modified with [1] R.A. Beauvais, S.D. Alexandratos, React. Funct. Polym. 36hydrazine was selective at pH range of 2–4 for (1998) 113.

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59 (1992) 343.and Pb(II) at pH 5 and between 2 and 4, [6] V. Bulmus, K. Kesenci, E. Piskin, React. Funct. Polym. 38respectively. (1998) 1.

[7] O. Okay, Prog. Polym. Sci. 25 (2000) 711.The high efficiency of these modifications to[8] F.M.B. Coutinho, D.L. Carvalho, M.L.L. Aponte, C.C.R.introduce complexing groups on the surface of Barbosa, Polymer 42 (2001) 43.

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