Chelating resins for mercury extraction based on grafting of polyacrylamide chains onto styrene–divinylbenzene copolymers by gamma irradiation

Reactive & Functional Polymers 70 (2010) 738–746

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Chelating resins for mercury extraction based on grafting of polyacrylamide chains onto styrene–divinylbenzene copolymers by gamma irradiation Luciana C. Costa a, Ailton S. Gomes a, Fernanda M.B. Coutinho b,1, Viviane G. Teixeira c,* a

Instituto de Macromoléculas Professora Eloisa Mano, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21945-970, Brazil Departamento de Processos Químicos, Instituto de Química, Universidade do Estado do Rio de Janeiro, Rio de Janeiro 20550-460, Brazil c Departamento de Química Analítica, Instituto de Química, Universidade Federal do Rio de Janeiro, Avenida Athos da Silveira Ramos, 149 – Bloco A, sala 507, Cidade Universitária, Rio de Janeiro 21941-909, Brazil b

a r t i c l e

i n f o

Article history: Received 16 April 2010 Received in revised form 14 June 2010 Accepted 4 July 2010 Available online 8 July 2010 This work is dedicated to Professor Fernanda M.B. Coutinho who left us this year. Keywords: Chelating resins Polystyrene resins Ionizing radiation Wastewater treatment Mercury

a b s t r a c t Chelating resins for mercury adsorption were prepared by grafting polyacrylamide chains onto styrene– divinylbenzene (Sty–DVB) copolymers by applying gamma radiation. Sty–DVB copolymers were synthesized by aqueous suspension polymerization employing different synthesis conditions. The copolymers were characterized by apparent density, surface area, pore size distribution and swelling capacity. The copolymers were irradiated using a 60Co-c source at room temperature in the presence of acrylamide solution in methanol. The grafting reaction was evaluated with the aid of elemental analysis, FTIR and thermogravimetric analysis (TGA). Hg(II) uptake measurements were carried out in batch experiments. The results showed that these resins can be successfully used for Hg(II) adsorption at ppm levels. The porosity degree of the copolymers influences the grafting yield as well as the Hg(II) complexation capacity of the chelating resins. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction In recent years, increased concern about the toxic effects of mercury species on human health, especially methyl mercury, has resulted in an intensive effort to develop methods for their measurement and removal from aqueous solutions. Mercury is emitted to the atmosphere mainly as vapor by natural or anthropogenic sources. It is the only metal that biomagnifies through aquatic food chains. The bioaccumulation of mercury in aquatic systems mainly starts with the presence of free mercury(II) ions, which undergo methylation reaction to form highly toxic free methyl mercury compounds. These species are easily incorporated into the aquatic food chain, reaching higher concentrations in the tissue of fish species at the top of the chain. This problem mainly affects the river-dwelling population, such as in Amazon region, where fish is a main source of protein [1–3]. Several chelating resins based on styrene–divinylbenzene (Sty– DVB) copolymers containing different electron donor groups have been evaluated for removing Hg(II) from wastewater [4–6]. * Corresponding author. Tel.: +55 21 2562 7548; fax: +55 21 2562 7262. E-mail address: [email protected] (V.G. Teixeira). 1 In memoriam. 1381-5148/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.reactfunctpolym.2010.07.003

Although Hg(II) has a strong affinity for ligands containing soft atoms such as thiol [7,8] and dithiocarbamate [9], several studies have demonstrated that anchoring polyacrylamide chains onto Sty–DVB copolymers is a good way to provide an efficient material for mercury removal from aqueous solutions. The amide group does not show a very high tendency to form complexes with metal ions because the basicity of the amide nitrogen is reduced due to the resonance effect with the carbonyl group. However, mercury ions are soft acids with a high tendency to receive electrons. The synergy of these properties enables the occurrence of a selective reaction between Hg(II) and the amide group [10–16]. Most of the routes for functionalizing polymers with grafted polyacrylamide chains have been based on radical polymerization, using an oxidation–reduction initiation system (using ceric ions as oxidant) or a living radical polymerization (LRP) by coppermediated atom transfer radical polymerization (ATRP) [11–13]. Sty–DVB copolymers are generally chlorosulfonated and then a sequence of reactions are carried out to introduce a functional group capable of undergoing oxidation reactions. The oxidation forms polymer radicals that initiate the acrylamide polymerization. The high number of synthesis steps is a serious disadvantage of these routes. The possible formation of a mixture of functional groups in the final product due to the incomplete conversion of each

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Nomenclature Sty styrene DVB divinylbenzene PVA polyvinyl alcohol rpm rotations per minute lm micrometer kGy kilogray Gy min 1 gray per minute FTIR Fourier transform infrared spectroscopy DD dilution degree Sty/DVB percentage of styrene/divinylbenzene in monomers mixture

reaction step and the inherent problem of intermediate products removal lead to contamination of the final chelating resin, which affects its complexation capacity and selectivity [17]. In our last work [18], we verified that macroporous Sty–DVB copolymers can be functionalized with polyacrylamide chains using c-rays (60Co source) by applying the simultaneous method. The main advantage of this method is the direct way that polyacrylamide chains are introduced onto the copolymers. This route generates chelating resins with a high content of polyacrylamide chains and a low level of contamination because the high number of synthesis steps is eliminated. Moreover, this more direct route reduces reagent consumption and residue production. In this work, different synthesis conditions were employed to obtain Sty–DVB copolymers with varied morphological structures. Polyacrylamide chains were grafted onto copolymers by applying gamma radiation in the best conditions, already established in our previous work [18]. The Hg(II) complexation capacity of the chelating resins produced were investigated. In addition, we tried to establish the relationship between morphology characteristics of the Sty–DVB copolymers and the complexation capacity of the final chelating resins.

dap S Vp CR N Hg nd nm

apparent density surface area determined by BET method fixed pore volume determined by BJH method chelating resin nitrogen content determined by elemental analysis mercury complexation capacity not determined non-measurable

which already contained the aqueous phase consisting of a solution of PVA and NaCl, both 0.5% w/v. The volumetric ratio between the aqueous and organic phase was 4:1 (v/v). The system was maintained under stirring (500 rpm) at 90 °C during 10 or 30 h (Table 1). The beads obtained were washed several times with hot water and sieved. The 50–106 lm fraction was collected and washed with hot ethanol and methanol and finally dried for 48 h at 60 °C. This fraction was used for the further modification reactions. 2.3. Grafting procedure The grafting reaction was carried out by applying the best condition established in our last work [18]. The copolymers were weighed in glass tubes and imbibed in a 7.5 mol L 1 acrylamide solution in methanol. The tubes were sealed with rubber septa and nitrogen was bubbled through the solution for 10 min to create an inert atmosphere. The samples were irradiated in an MDS Nordion, Gammacell 220 Excel gamma ray source at room temperature using a dose of 33 kGy by applying a dose rate of 56 Gy min 1. Afterwards, the copolymers were washed several times with hot water to remove the homopolymer (polyacrylamide) also produced.

2. Experimental part 2.1. Chemicals Commercial styrene (Sty) and divinylbenzene (DVB) were donated by Nitriflex Indústria e Comércio S.A. (Rio de Janeiro, Brazil) and used after washing with 5% w/v NaOH aqueous solution followed by water until neutral pH in order to remove the inhibitor. Commercial divinylbenzene is a mixture of meta and para divinylbenzene (55–60%) [19]. Acrylamide (PA grade) was purchased from Aldrich Chemical Co. (St. Louis, USA) and used without further purification. Poly(vinyl alcohol) (PVA) (88% hydrolysis degree) and 1000 ppm Hg(NO3)2 standard solution were purchased from Kurary Company (Umeda, Japan) and Spectrum Chemical Mfg. Corp. (Gardena, CA, USA), respectively, and used as received. Other reagents and solvents were purchased from Vetec Química Fina Ltda. (Rio de Janeiro, Brazil) and used as received. 2.2. Preparation of Sty–DVB copolymers The Sty–DVB copolymers were synthesized by aqueous suspension polymerization in a 1 L three-necked round bottomed reactor flask equipped with a mechanical stirrer and a reflux condenser containing a silicon oil seal at its top. The organic phase, composed of Sty and DVB in different proportions (Table 1), benzoyl peroxide 1% molar of total monomers and a diluent mixture composed of different toluene/n-heptane ratios (in varied relations to monomer mixture, according to Table 1), was prepared and transferred to the flask

2.4. Characterization of Sty–DVB copolymers and modified copolymers (chelating resins) The Sty–DVB copolymers were characterized by determining: apparent density by the graduated cylinder method [20], surface area and pore volume distribution by nitrogen adsorption measurements following the BET and BJH methods, respectively (Micromeritcs, ASAP 2010 apparatus), swelling capacity in toluene and n-heptane, optical appearance and morphology by optical (Olympus SZ10) and scanning electron (JEOL-JSM 6460 LV) microcopies. The FTIR spectra of the copolymers were recorded in a Perkin– Elmer Spectrum One spectrometer (4 scans and 4 cm 1 resolution) as KBr discs. TG and DTG curves of the copolymers were obtained using a TA Q50 instrument in a temperature range of 30–650 °C at a constant heating rate of 20 °C min 1 under nitrogen atmosphere and a flow rate of 60 mL min 1. Elemental analyses of the copolymers were carried out in a GE instrument (EA 1110 CHN-O). The grafting degree was calculated on the basis of the nitrogen content determined by elemental analysis. 2.5. Mercury uptake Mercury uptake measurements were carried out in batch experiments. About 0.2 g of the chelating resin was put in contact

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Table 1 Porous characteristics of Sty–DVB copolymers, nitrogen content, grafting degree and mercury adsorption efficiency of the chelating resins (CR). Copolymer StyDVB-1 StyDVB-2 StyDVB-3 StyDVB-4 StyDVB-5 StyDVB-6 StyDVB-7 StyDVB-8 a b c d e f g h i j k l m n o

Ta (h)

DDb (%)

Sty/DVBc (%)

Tol/Hepd (%)

dape (g cm

10

50

90/10

80/20 20/80 80/20

0.72 0.65 0.60 0.46 0.25 0.65 0.52 0.20

40/60 150 30

50 150

90/10 40/60

20/80 80/20 20/80

3

)

Sf (m2 g 0.05 0.14 0.40 349.7 353.9 0.1 110.7 278.3

1

)

Vp g (cm3 g nmo nm nm 0.4 0.9 nm 0.12 0.6

1

)

SD Tolh (%)

SDHepi (%)

CRj

132 151 51 152 89 141 146 56

7 10 52 133 89 12 80 35

CR-1 CR-2 CR-3 CR-4 CR-5 CR-6 CR-7 CR-8

Nk (mmol g nm nm 1.28 5.28 6.56 nm 4.53 6.28

1

)

GDl (%)

Hgm (lmol g

nm nm 9.1 37.5 46.6 nm 32.2 44.6

nm nm 1.7 52.7 42.6 7.0 51.6 32.2

1

)

En (%) 0 0 1.4 42.4 34.3 5.6 41.5 25.9

Polymerization time. Dilution degree of monomers in the diluent mixture. Styrene/divinylbenzene ratio in the monomer mixture. Toluene/n-heptane ratio in the diluent mixture. Apparent density. Surface area of the copolymers (BET method). Pore volume (BJH method). Swelling degree in toluene. Swelling degree in n-heptane. Chelating resin. Nitrogen content determined by elemental analysis. Grafting degree. Mercury uptake. Efficiency of mercury extraction. Non-measurable.

with 10 mL of a 2.4856  10 5 mol L 1 Hg(NO3)2 aqueous solution. The pH of the solution was kept at 5.0 with the aid of an acetic buffer. The mixture was stirred for 24 h at room temperature. Then, an aliquot was taken for analysis by cold vapor atomic absorption spectroscopy (CVAAS) (HG 3500 Automatic Mercury Analyzer – KKSanso SS – LD: 2 ng mL 1).

3. Results and discussion The complexation capacity of a chelating resin produced by chemical modification of a polymer support is governed by the characteristics of its two components: the chelating group and the polymer matrix. Thus the properties of both components have to be taken into account when synthesizing a chelating resin [17]. Many of the works on the synthesis of chelating resins do not consider in detail the relationship between their chelating capacity and the characteristics of the polymer matrix [11–16]. The porosity degree of the polymer influences the process of reagents diffusion, and consequently the extent of the reactions that promote the immobilization of functional groups on this matrix, as well as the accessibility of metal ions to these groups [21]. Thus, in this work we tried to establish the relationship among three parameters: the morphological characteristics of Sty–DVB copolymers, the efficiency of the grafting reaction and the complexation efficiency of the final chelating resins. The mechanisms proposed to explain the porous structure formation of Sty–DVB copolymers are based on a phase separation process between the growing polymer chains and the diluent mixture during the conversion of the system from a liquid to a solidlike state (the gel point). This process can occur in different stages of the polymerization reaction, depending on the synthesis conditions (type and amount of diluent, crosslinker concentration, etc.) and determines the type of pore structure of the copolymer [21– 24]. Therefore, to prepare copolymers with different porous structures, the copolymerization of Sty and DVB was carried out using different DVB concentrations and monomer dilution degrees. Different mixtures of toluene and n-heptane were used as pore forming agents. The polymerization time was also varied in order to evaluate the influence of residual double bonds on the graft

content. The morphological characteristics of Sty–DVB copolymers are given in Table 1. The eight Sty–DVB copolymers synthesized with different pore structures were submitted to reaction with acrylamide initiated by gamma radiation, as described in our previous work [18]. Table 1 also presents the nitrogen content, grafting degree and mercury extraction efficiency of the chelating resins (CR) produced from these copolymers. Occurrence of the grafting reaction was evidenced by elemental analysis and FTIR spectroscopy. In general, the FTIR spectra of all chelating resins (Fig. 1 is a typical example) show a strong absorption band, which is a doublet near 1660 and 1603 cm 1 involving the C@O stretching and NH2 deformation (amide I and amide II bands), and a broad absorption band at 3400 cm 1, ascribed to the asymmetric and symmetric NH2 stretching [25]. Considering the influence of the synthesis conditions on the copolymers porosity, we can say that an increase of the n-heptane proportion in the diluent mixture caused the formation of more porous structures. However, this effect is more pronounced at higher dilution degrees and DVB concentrations (Table 1). The higher apparent density, the lower surface areas and the swelling data for StyDVB-1 and StyDVB-2 reveal the gel like structures of these materials. In this case, the increase of the n-heptane proportion led to a slight increase in porosity degree, as demonstrated by the values of surface area and apparent density. However, for StyDVB-4, StyDVB-5, StyDVB-7 and StyDVB-8 the increase of the nheptane content led to a significant increase on the porosity degree, as demonstrated by the values of pore volume and apparent density. The swelling capacity of StyDVB-5 and StyDVB-8 are lower in both solvents, confirming the more entangled structure of these copolymers [21]. A comparison of the electron micrographs of those four materials (Fig. 2) shows that an increase in the n-heptane content led to an increase of the pore diameter as well as of the polymer domains. The pore size distribution curves of these four copolymers (Fig. 3) shifted to higher diameters as the n-heptane content in the diluent mixture increased. The grafting degree of the chelating resins was dependent on the porosity degree of the copolymer supports (Table 1). The nitrogen content of the chelating resins CR-1 and CR-2, derived from StyDVB-1 and StyDVB-2 was not measurable, indicating that the

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Sty-DVB copolymer

1602 1451

2922

700

%T Chelatin resin

1603

3398

1661

-1

cm

Fig. 1. Typical FTIR spectra of a Sty–DVB copolymer and chelating resin.

Fig. 2. Electron micrographs of the external region of copolymers StyDVB-4 (a), StyDVB-5 (b), StyDVB-7 (c) and StyDVB-8 (d).

grafting reaction did not occur or occurred with very low conversion. As observed before, StyDVB-1 and StyDVB-2 presented low

porosity (Table 1). The absence of fixed pores restricts the access of the reagent solution through the polymer matrix, making the

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StyDVB-5

3 -1

Pore Volume (cm g )

StyDVB-4

StyDVB-7 StyDVB-8

Pore Diameter (Å) Fig. 3. Pore size distribution curves of copolymers StyDVB-4 and StyDVB-5, StyDVB-7 and StyDVB-8.

reactivity of these materials dependent on their swelling capacity in the reaction medium. However, according to the Hildebrand solubility parameter theory [26], methanol is not a good solvent for polystyrene chains. This means that polymers with low porosity do not swell in methanol. As a result, the reagent solution (acrylamide in methanol) cannot access the internal structure of these polymers, so probably these materials were functionalized only on the external surface, resulting in a non-measurable grafting degree. Comparing the nitrogen content of the CR-4, CR-5, CR-7 and CR8, the increase of n-heptane proportion resulted in enhancement in the grafting degree of the chelating resins. This was also confirmed by the thermoanalysis data (Fig. 4). The unmodified Sty– DVB copolymers degradation curves show only one significant weight loss step, around 400 °C, and a single DTG peak, related to the decomposition of the main chain of the Sty–DVB copolymer. However, the chelating resins presented two degradation steps. The first thermal decomposition step is around 250 °C, attributed to the decomposition of the amide groups, and the second decomposition stage at 400 °C is due to the degradation of the carbon chains of the polyacrylamide and Sty–DVB copolymer [27]. The DTG curves show two peaks related to these degradation stages. The DTG peak associated with the degradation of the polyacrylamide is more intense for the chelating resins produced from the

copolymers with a higher proportion of n-heptane. These results can be explained considering that the increase of n-heptane increased the porosity degree (Table 1) and pore diameter of the copolymers (Fig. 3). Although the swelling capacity of these more porous structures was reduced (Table 1), the diffusion of the reagent through the larger pores was favored. In order to evaluate the efficiency of the chelating resins for trace amounts of Hg2+, the chelating resins were put in contact with a 2.4856  10 5 mol L 1 Hg(NO3)2 aqueous solution. The solution’s pH was adjusted in the range from 4.0 to 6.0. More acidic or basic solutions were not studied due to the undesirable protonation of the amide nitrogen and Hg(OH)2 precipitation phenomena respectively. Data of mercury retention behavior as a function of pH are show in Table 2. The chelating resins CR-1 and CR-2, with a non-measurable nitrogen content, did not retain Hg(II) (Table 1). This behavior indicates that the unmodified copolymers were not able to adsorb this metal ion. On the other hand, the chelating resins with a measurable nitrogen content retained Hg(II), which demonstrates that this adsorption ability is related to the presence of polyacrylamide chains grafted onto Sty–DVB copolymers. For CR-4, CR-5, CR-7 and CR-8, although the increase of n-heptane proportion increased the grafting degree, the complexation efficiency was reduced. This leads us to the conclusion that copolymers with narrower pores

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dWeight/dT (%/°C)

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T(°C) Fig. 4. DTG curves of the chelating resins CR-4 and CR-5, CR-7 and CR-8.

Table 2 Mercury retention as a function of pH. pH

Hga (lmol g

4.0 5.0 6.0

55.2 96.9 77.3

1

Eb (%)

)

44.4 78.0 62.2

a

Mercury uptake. Efficiency of mercury extraction (2.4852  10 resin). b

5

mol L

1

Hg2+ solution, 0.2 g of

produced more efficient chelating resins. This unexpected behavior is opposite to the findings reported in our previous works [9,23]. In those works, copolymers with higher pore diameters produced resins with a large proportion of active groups and higher complexation efficiency. For the copolymers grafted with polyacrylamide, the pores were filled with polymer chains. Those copolymers with lower pore diameters produced smaller polyacrylamide domains distributed throughout the matrix. This arrangement may permit a higher contact area between the hydrophilic polymer and Hg(II)

ions. Probably in this case the complexation reaction was not governed by the diffusion of the metal ions through the porous Sty– DVB matrix, but rather by the contact area between the ionic solution and the polyacrylamide chains. The grafting degree and the efficiency of Hg(II) extraction for CR-1 and CR-3 show that the increase of the DVB content in the monomer mixture resulted in an increased grafting degree of the chelating resins, and this resulted in a measurable Hg2+ adsorption. This can be explained considering that the copolymer StyDVB-3, in opposition to StyDVB-1, probably has a higher content of fixed pores due to the higher DVB proportion used in its synthesis. This was sufficient to permit the access of the reagent solution to the inner structure of this material. The increase of the dilution degree also led to the increase of porosity degree. Comparing StyDVB-3 and StyDVB-4 (Table 1), it is possible to observe that an increase in the dilution degree caused a decrease in the apparent density and an increase in the surface area and fixed pore volume. The electron micrographs of these two copolymers (Fig. 5) also confirm the higher porosity of the materials synthesized with higher dilution degrees. In addition,

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Fig. 5. Electron micrographs of the inner region of copolymers StyDVB-3 (a) and StyDVB-4 (b).

polymer substrate. However, this occurs randomly on a molecular scale. On the other hand, the subsequent chemical changes are not random. Some chemical bonds, such as double bonds, are particularly sensitive to radiation [29]. Thus, we expected the presence of residual DVB vinyl groups could make the grafting reaction onto Sty–DVB copolymer via gamma radiation much easier. Comparison of the FTIR spectra of copolymers StyDVB-4, StyDVB-7, StyDVB-5 and StyDVB-8 (Fig. 7) shows that the bands at 985 and 1630 cm 1, characteristic of the C@C bond, are more intense for the copolymers polymerized for 10 h, indicating their higher content of vinyl groups [25]. Therefore, the FTIR spectra of the copolymers StyDVB-1 and StyDVB-6 are similar. This indicates that for low DVB concentrations 10 h is time enough to polymerize even the second vinyl bond of this monomer. Thus, the increase of the polymerization time did not cause a change in these absorption bands. An increase in the polymerization time resulted in a decrease in the porosity degree, as can be observed by the decrease of the surface area and pore volume. However, this change was not pronounced at lower dilution degree and DVB content either. Probably long periods of polymerization permit the formation of more closely packed microspheres, leading to the formation of more continuous structures with lower surface areas. The results shown in Table 1 suggest that the grafting degree decreased as the polymerization time increased. This behavior

dWeight/dT (%/°C)

an increase in dilution degree caused an increase on the polymers swelling capacity in both solvents (toluene and n-heptane). This can be explained because the increase of the dilution degree favors the separation between the growing polymer chains during their polymerization, resulting in a more elastic polymer structure [23]. The nitrogen content of the chelating resins CR-3 and CR-4 increased as the dilution degree increased. As observed in Table 1, the increase of the dilution degree increased the porosity degree and the swelling capacity of the copolymers. In StyDVB-4, with higher porosity and swelling capacity, the reagent mixture could reach the inner regions of the polymer beads, resulting in an increase of the grafting yield. These results were also confirmed by the thermogravimetric analysis and the complexation efficiency. Fig. 6 shows that the DTG peak related to the degradation of the polyacrylamide chains is more intense for the chelating resin prepared from the copolymer with higher dilution degree. The mercury uptake efficiency also increased when the dilution degree was increased. This behavior supports the results of the elemental and TG analysis. The copolymerization time of styrene and divinylbenzene was varied in order to increase the content of vinyl groups in the Sty– DVB copolymers. The second DVB vinyl group is less reactive than the first one [28], therefore the amount of unreacted double bonds in the final Sty–DVB copolymer can be controlled by the polymerization time. It has been established that the absorption of high-energy radiation depends on the electron density of the

T(°C) Fig. 6. DTG curves of the chelating resins CR-3 and CR-4.

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Fig. 7. FTIR spectra of the Sty–DVB copolymers StyDVB-1 (a), StyDVB-4 (b), StyDVB-5 (c), StyDVB-6 (d), StyDVB-7 (e) and StyDVB-8 (f).

can attributed to the higher residual double bond content allied to the higher porosity degree of the copolymers synthesized for 10 h. The chelating resins produced from these copolymers were more efficient, a behavior that agrees with their nitrogen content.

4. Conclusions The extent of the polyacrylamide grafting reaction onto Sty–DVB copolymers was governed by the diffusion of the reagent

solution through the bulk material, by its swelling capacity in the reagent mixture and by the residual double bond content. Thus, the synthesis parameters that contributed to increase the porosity degree or swelling capacity in methanol increases the polyacrylamide content. On the other hand, the mercury uptake efficiency of the chelating resins was determined by the association of two factors: polyacrylamide graft content and contact area available for the complexation reaction. When copolymers with distinct porosity degrees are compared, it was possible to observe that an increase in porosity degree led to an increase in the grafting degree

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and complexation efficiency. However, the mercury uptake efficiency was not only dependent on the number of functional groups introduced, but also on the disposition of these groups onto the polymeric matrix. Acknowledgements We thank the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Fundação de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ) for financial support. We would also like to express thanks to Nitriflex Indústria e Comércio S.A. for donating the reagents. References [1] M.E. Mahmoud, Anal. Chim. Acta 398 (1999) 297. [2] C. Sun, R. Qu, C. Ji, Q. Wang, C. Wang, Y. Sun, G. Cheng, Eur. Polym. J. 42 (2006) 188. [3] J. Rutkowska, K. Kilian, K. Pyrzynska, Eur. Polym. J. 44 (2008) 2108. [4] S.D. Alexandratos, M.A. Strand, D.R. Quillen, A.J. Walder, Macromolecules 18 (1985) 829. [5] S.D. Alexandratos, S. Natesan, Eur. Polym. J. 35 (1999) 431. [6] N. Kabay, J.L. Cortina, A. Trochimczuk, M. Streat, React. Funct. Polym. 70 (2010) 484. [7] A. Lezzi, S. Cobianco, A. Roggero, J. Polym. Sci.: Polym. Chem. 32 (1994) 1877. [8] Z. Hubicki, M. Leszczynska, B. Lodyga, A. Lodyga, Desalination 207 (2007) 80. [9] P.A. Costa, V.G. Teixeira, J. Appl. Polym. Sci. 116 (2010) 3070. [10] N. Biçak, D.C. Sherrington, B.F. Senkal, React. Funct. Polym. 41 (1999) 69.

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