Synthesis and Characterization of a Few Amino-Functionalized

Article pubs.acs.org/IECR

Synthesis and Characterization of a Few Amino-Functionalized Copolymeric Resins and Their Environmental Applications Muniyappan Rajiv Gandhi,† Natrayasamy Viswanathan,‡ and Sankaran Meenakshi*,† †

Department of Chemistry, Gandhigram Rural University, Gandhigram-624 302, Tamilnadu, India Department of Chemistry, Anna University of Technology Madurai, Dindigul Campus, Dindigul-624 622, Tamilnadu, India

‡

S Supporting Information *

ABSTRACT: The synthetic copolymeric resins acrylonitrile/divinylbenzene/vinylbenzyl chloride (AN/DVB/VBC), styrene/ divinylbenzene/vinylbenzyl chloride (ST/DVB/VBC), and vinylbenzyl chloride/divinylbenzene (VBC/DVB) have been prepared by suspension polymerization. These polymeric matrixes were aminated with ethylenediamine (ED) and then protonated to increase their selectivity toward Cr(VI). The experiments were carried out in batch mode to optimize various influencing parameters, namely, contact time, pH, other interfering co-ions, and temperature. The chromium removal capacity (CRC) of AN/DVB/VBC−ED resin was found to be higher than those of the other prepared copolymers. The mechanism of chromium removal was governed by electrostatic-adsorption-coupled reduction and complexation. The polymeric resins and chromium-sorbed resins were characterized by FTIR, SEM−EDAX, BET, elemental analysis, and EPR studies. The adsorption data were fitted with Freundlich and Langmuir isotherms. The calculated values of thermodynamic parameters indicated the nature of chromium sorption. from industrial wastewater. Wojcik et al.14 performed sorption studies of Cr(VI) onto a new ion exchanger with tertiary amine, quaternary ammonium, and ketone groups. Most studies have shown that Cr(VI) is removed as HCrO4− using anionic resins and reduced to Cr(III) using reducing agents and regenerated. So far, it has been reported that only the biosorbent that has plenty of lone pair of electrons reduces Cr(VI) to Cr(III). The present study shows that −NH2 groups present in the synthetic resin reduce the toxic Cr(VI) to 300-times-less-toxic Cr(III,) which is the novelty of this study. Reduction of Cr(VI) to Cr(III) was confirmed by electron paramagnetic resonance (EPR) analysis. Only a few reports are available on the removal of Cr(VI) using aminated and protonated polymeric resins. This might be the first report showing that a synthetic polymeric resin directly reduces Cr(VI) to Cr(III). The sorption capacity of the acrylonitrile/divinylbenzene/vinylbenzyl chloride− ethylenediamine (AN/DVB/VBC−ED) resin was compared with those of other reported resins/commercial resins and found to be comparable. The main aim of the present investigation was to prepare the synthetic copolymeric resins AN/DVB/VBC, ST/DVB/VBC, and VBC/DVB by suspension polymerization and modify them with ethylenediamine to introduce −NH2 groups. These resins were then used for chromium removal studies. A possible mechanism of chromium removal using the prepared synthetic resins is also proposed.

1. INTRODUCTION The extensive use of heavy metals has resulted in an increased fluctuation of metallic compounds in different environmental segments. Once heavy metal ions enter the environment, their chemical form largely determines their potential toxicity. It is well-established that heavy metals obstruct the functional groups of essential enzymes even at very low concentrations.1 Chromium is one of the most toxic heavy metals, causing health problems such as stomach irritation or ulceration; skin irritation and dermatitis; liver, kidney, and nerve tissue damage; and even death in large doses.2 The maximum permissible limit of chromium content in drinking water is 0.05 mg/L.3 Ion exchange/adsorption seems to be the most effective and promising technique for chromium removal. Adsorption to chelating resins is a common method for recovering heavy metals from wastewater containing very small concentrations of heavy metals. A variety of polymeric adsorbents, including synthetic polymers4−6 and polymeric resins,7−9 have been reported to reduce the concentration of metal ions in water. Synthetic resins are adaptable to continuous processes involving columns and chromatographic separations. Their insolubility renders them environmentally compatible because the cycle of loading, regeneration, and reuse allows them to be used for many years. In a review, Dabrowski et al.10 explained the removal of Cr(III) and Cr(VI) by various commercial resins. Saha et al.11 investigated the removal of Cr(VI) from aqueous solution using solvent-impregnated Amberlite XAD-7 resin with Aliquat 336. Batch adsorption experiments were carried out by Rengaraj et al.12 to evaluate the performance of the ion-exchange resins 1200H, 1500H, and IRN97H in the removal of chromium from aqueous solutions. Rajesh et al.13 prepared trialkylamine-impregnated macroporous polymeric sorbent and utilized it for the effective removal of chromium © 2012 American Chemical Society

Received: Revised: Accepted: Published: 5677

January 9, 2012 March 22, 2012 March 25, 2012 March 25, 2012 dx.doi.org/10.1021/ie3000503 | Ind. Eng. Chem. Res. 2012, 51, 5677−5684

Industrial & Engineering Chemistry Research

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2. MATERIALS AND METHODS 2.1. Materials. Styrene (ST), divinylbenzene (DVB), and poly(vinyl alcohol) (PVA) were purchased from Fluka; vinylbenzyl chloride (VBC) was supplied by Aldrich; and gelatin, N,N′-azo-bis-isobutyronitrile (AIBN), boric acid, acrylonitrile (AN), benzoyl peroxide, ethylenediamine (ED), 1,2-dimethylformamide (DMF), K2Cr2O7, calcium chloride, sodium hydroxide, toluene, 1,4-dioxane, acetone, and n-heptane were purchased from Merck. All other chemicals and reagents were of analytical grade. 2.2. Synthesis of Various Polymeric Matrixes. Acrylonitrile/divinylbenzene/vinylbenzyl chloride (AN/DVB/VBC), styrene/divinyl benzene/vinylbenzyl chloride (ST/DVB/ VBC), and vinylbenzyl chloride/divinylbenzene (VBC/DVB) polymeric matrixes were prepared by suspension polymerization.15−17 These polymeric matrixes were aminated with ethylenediamine (ED), and the amine groups were then protonated using HCl. The detailed synthetic procedures for these polymeric resins and relevant schemes are provided in the Supporting Information. 2.3. Sorption Experiments. Sorption studies were carried out with the synthetic polymeric resins to assess the suitability of their use for chromium removal from water.18 The two most important physicochemical aspects for the evaluation of sorption processes are sorption equilibrium and sorption kinetics.19,20 An equilibrium analysis is the most important fundamental information required to evaluate the affinity or capacity of a resin. However, thermodynamic data can reveal only the final state of a system from an initial nonequilibrium mode.12 Studies were also performed to assess how the sorption rate depends on the concentration of sorbate in solution and how the rate is influenced by various parameters such as contact time, dosage, pH, presence of other co-ions, and temperature.18 The sorption efficiency of the resins was studied under laboratory conditions. The experiments were carried out according to a batch equilibration method as described below. In a typical case, 0.1 g of resin, fixed as the optimum dosage, was added to 100 mL of fixed initial metal ion concentration. The effects of the pH of the medium, time of contact, and co-ions that are normally present in water on the sorption capacity were investigated. The adsorption of metal ion on the sorbent was studied at different initial metal ion concentrations and different temperatures, namely, 303, 313, and 323 K. During the optimization of each parameter, the other equilibrium parameters were kept constant. The contents of the experimental system were shaken thoroughly using a shaker rotating at a speed of 200 rpm. The solution was then filtered, and the metal ion concentration was measured. The chromium removal capacity (CRC or qe, mg/g) of the sorbent was calculated as qe =

measurements were done with an EA 940 expandable ion analyzer with a pH electrode.21 Fourier transform infrared (FTIR) spectra of the samples as solids diluted in KBr pellets were recorded on an FTIR spectrophotometer (JASCO-460 Plus) with a resolution of 4 cm−1 in transmittance mode with 16 scans. The FTIR spectra were used to confirm the functional groups present in the resins. The surface morphologies of the sorbents before and after treatment with metal ions were visualized by scanning electron microscopy (SEM) using a Hitachi-S-3000H instrument fitted with an energy-dispersive analysis by X-rays (EDAX) attachment allowing the qualitative detection and localization of elements present in the sorbents. Surface area measurements were obtained using a Micromeritics-Tristar 3000 instrument and a NOVA 1000 high-speed gas sorption analyzer. Elemental analysis was carried out using an Elementar Vario EL III-CHN element analyzer. EPR spectra were recorded on a JEOL JES-FA200 EPR spectrometer. Differential scanning calorimetry (DSC) measurements were carried out on a TA Instruments model Q20 V24.2 Build 107 instrument. 2.5. Computational Analysis. Computations were performed using Microcal Origin (version 6.0) software. The significance of trends in the data and the goodness of fit are discussed in terms of the correlation coefficient (r), standard deviation (sd), and chi-squared (χ2) analysis.

3. RESULTS AND DISCUSSION 3.1. Characterization of the Synthetic Resins. The characteristics of the synthetic resins are shown in Table 1. The elemental analyses of the synthetic resins before and after Table 1. Characteristics of the Synthetic Resins polymeric matrix particle size (mm) density (g/cm3) BET surface area (m2/g)

ST/DVB/VBC−ED

AN/DVB/VBC−ED

ST/DVB/VBC 0.80 0.601 0.025

AN/DVB/VBC 0.27 0.699 0.007

amination are reported in Table 2. After amination of the synthetic resins, the percentage nitrogen content was found to Table 2. Elemental Analysis of the Synthetic Polymeric Resins

(C i − Ce) V m

synthetic resin

N (%)

C (%)

H (%)

VBC/DVB ST/DVB/VBC AN/DVB/VBC VBC/DVB−ED ST/DVB/VBC−ED AN/DVB/VBC−ED

0.06 0.05 2.45 0.16 5.12 7.66

89.67 86.62 75.86 90.70 77.28 62.77

11.60 9.95 9.85 9.11 12.60 10.91

increase. This confirms that amination of the polymeric resin occurred. Figure S1 in the Supporting Information shows FTIR spectra of ST/DVB/VBC and ST/DVB/VBC−ED resins. The band at 1265 cm−1 indicates the presence of −CH2Cl groups in the resin matrix (cf. Figure S1a, Supporting Information). The disappearance of the band at 1265 cm−1 (indicative of the presence of −CH2Cl groups) along with the appearance of a new wide broad band at 1650 cm−1 are attributable to the formation of amino groups and the displacement of −Cl groups on the polymeric matrix (cf. Figure S1b, Supporting Information).

where Ci is the initial chromium ion concentration (mg/L), Ce is the equilibrium chromium ion concentration (mg/L), m is the mass of the sorbent (g), and V is the volume of the solution (L). 2.4. Analysis. The chromium ion concentration was measured by UV−visible spectrometry (PHARO 300, Merck) at 540 nm, according to the 1,5-diphenylcarbazide method.21 Duplicate measurements were made so that the residual concentration values were reproducible to within ±2%. pH 5678

dx.doi.org/10.1021/ie3000503 | Ind. Eng. Chem. Res. 2012, 51, 5677−5684


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Figure 1. SEM images of (a−c) AN/DVB/VBC−ED resin at different magnifications and (d) chromium-sorbed AN/DVB/VBC−ED resin.

A broad band observed in the region between 3347 and 3507 cm−1 is due to the vibrations of N−H bonds in −NH2 groups.15−17 Figure S2 (Supporting Information) shows the FTIR spectra of AN/DVB/VBC, AN/DVB/VBC−ED, and chromium-sorbed AN/DVB/VBC−ED resins. The band at 1265 cm−1 indicates the presence of −CH2Cl groups in AN/DVB/VBC resin; this band vanished in AN/DVB/VBC−ED resin, and a band at 1650 cm−1 appeared due to formation of amino group. In chromium-sorbed AN/DVB/VBC−ED resin, a new band at 550 cm−1 indicates Cr−O bonds and the presence of chromium in the sorbed resin.2,18 The widening of the broad band in the region between 3087 and 3598 cm−1 in the spectrum of chromium-sorbed AN/DVB/VBC−ED resin is due to the interaction of amine and hydroxyl groups with chromate ion.8 Figure S3 (Supporting Information) shows a DSC thermogram of AN/DVB/VBC−ED resin, which has peaks at 122.14 and 198.8 °C corresponding to the melting and degradation temperatures, respectively, of the resin. 3.2. SEM−EDAX Studies. SEM images of AN/DVB/ VBC−ED resin and chromium-sorbed AN/DVB/VBC−ED resin are shown in Figure 1. Parts c and d of Figure 1 clearly show the difference between the metal-free resin beads and the Cr(VI)loaded resin beads. In Figure 1d, the surface of the resin shows glowing metallic spots that are absent in Figure 1c. From these two images (Figure 1c,d), it can be concluded that Cr species adsorbed on the resin surface. This is further supported by EDAX analysis. Figure 2 shows EDAX spectra and quantitative elemental compositions of ST/DVB/VBC−ED and AN/DVB/ VBC−ED resins, along with chromium-treated ST/DVB/VBC−ED

and AN/DVB/VBC−ED resins. The EDAX spectrum of chromium-sorbed ST/DVB/VBC−ED confirms the sorption percentage of chromium was 7.39% (cf. Figure 2c). Higher chromium sorption occurred on AN/DVB/VBC−ED resin, as confirmed by the presence of chromium as 22.42% in the EDAX spectrum of chromium-treated AN/DVB/VBC−ED resin (cf. Figure 2d). 3.3. EPR Analysis. Liyuan et al.22 studied the detoxification of chromium-containing slag by Achromobacter sp. CH-1. They recorded EPR spectra for powders of K2CrO4 and CrCl3 used as standards and pointed out that there is no signal for the Cr(VI) solution, as no single electron is present. However, a broadened EPR spectrum centered at 3500 Gs in the Cr(III) standard solution was obtained. The reduction product of Cr(VI) by Achromobacter sp. strain CH-1 exhibited a strong signal similar to that of the Cr(III) standard solution. A similar result was obtained in this work for Cr(VI)-adsorbed AN/ DVB/VBC−ED resin. In chromium-sorbed AN/DVB/VBC− ED resin, Cr(VI) was adsorbed and then reduced to less toxic Cr(III). The presence of Cr(III) in the AN/DVB/VBC−ED resin was confirmed by the g value. The EPR spectrum of Cr(VI)-adsorbed AN/DVB/VBC−ED resin at pH 4 showed a g value of 1.91, which is close to the standard value of 1.98 for Cr(III), as shown in the Supporting Information (Figure S4). Cr(III) is not in free form, but rather is bound to the polymeric matrix, which might be the reason for the small reduction in the g value. This result was further supported by Nakajima and Baba,23 Albino Kumar et al.,24 Miretzky and Fernandez Cirell,25 and Suksabye et al.26 5679



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Figure 2. EDAX spectra of resins (a) ST/DVB/VBC−ED, (b) AN/DVB/VBC−ED, (c) chromium-treated ST/DVB/VBC−ED, and (d) chromium-treated AN/DVB/VBC−ED.

3.4. Effect of Contact Time. The chromium removal capacities (CRCs) of synthetic resins can vary with the period of contact with the sorbate solution. Therefore, experiments were carried out with different contact times in the range of 30−420 min with a 0.1-g dosage of sorbents at 303 K using an initial chromium concentration of 100 mg/L for AN/DVB/ VBC−ED and 10 mg/L for ST/DVB/VBC−ED and VBC/ DVB−ED. Figure 3 shows that all of the resins reached saturation at 240 min, and hence, for further studies the contact time was fixed at 240 min. The CRCs of AN/DVB/VBC−ED, ST/DVB/VBC−ED, and VBC/DVB−ED were found to be 96.12, 6.8, and 4.25 mg/g, respectively. 3.5. Effect of pH. Cr(VI) can exist in several forms such as Cr2O72−, HCrO4−, HCrO7−, and CrO42−, and the relative

abundance of each particular complex depends on the concentration of chromium ion and the pH of the solution. Sorption of chromium ions onto the synthetic resins was carried out at five different initial pH levels, namely, 2, 4, 6, 8, and 10, while keeping other parameters constant as follows: contact time, 240 min; dosage, 0.1 g; initial chromium concentration, 100 mg/L; and temperature, 303 K. The pH of the working solution was controlled by adding HCl/NaOH solution. Figure 4 shows the CRCs of the resins as a function of pH, which indicates that the CRCs of all of the resins were influenced by the pH of the medium. The maximum CRC for all of the resins was observed between pH 2 and 4, and a minimum CRC was observed at pH 10. It is obvious that, in acidic media, where the H+ concentration is higher, the surface 5680



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CRC of AN/DVB/VBC−ED resin was not significantly altered except in the presence of SO42− and NO3− ions, which showed slight interference, as these ions have ionic radius similar to that of HCrO4−.27 3.7. Sorption isotherms. To quantify the sorption capacities of the synthetic resins for the removal of chromium, two commonly used isotherms, namely, the Freundlich28 and Langmuir29 isotherms, were employed. 3.7.1. Freundlich Isotherm. The linear plot of log qe versus log Ce indicates the applicability of the Freundlich isotherm. The values of 1/n, n, and kF of AN/DVB/VBC-ED resin are listed in Table 3. The values of 1/n lie between 0 and 1, and the n value lies in the range of 1−10, confirming the favorable conditions for adsorption. With an increase in temperature, the kF values were found to increase for AN/DVB/VBC−ED resin, which indicates that the chromium uptake by this resin is an endothermic process. 3.7.2. Langmuir Isotherm. A linear plot was obtained for the sorbent when Ce/qe was plotted against Ce, which gave Qo and b values from the slope and intercept, respectively; the calculated results are listed in Table 3. For AN/DVB/VBC− ED resin, the Qo and b values increased with increasing temperature, indicating that the sorbate uptake increased with the rise in temperature. The RL values30 lying between 0 and 1 for AN/DVB/VBC−ED resin indicate favorable conditions for adsorption at all of the temperatures studied (cf. Table 3). 3.7.3. Chi-Squared Analysis. The results of the chi-squared analysis31 of AN/DVB/VBC−ED resin are presented in Table 3. The lower χ2 values for the Freundlich isotherm indicate that this isotherm is the best fitting model for the sorption of chromium on AN/DVB/VBC−ED resin. 3.7.4. Thermodynamic Treatment of the Sorption Process. The values of the thermodynamic parameters are listed in Table 4.

Figure 3. Effect of contact time on the CRCs of the synthetic resins.

Table 4. Thermodynamic Parameters of AN/DVB/VBC−ED Resin in the Removal of Chromium Figure 4. Influence of pH on the CRCs of the synthetic resins.

thermodynamic parameter

value

−1

ΔG (kJ mol ) 303 K 313 K 323 K ΔHo (kJ mol−1) ΔSo (kJ mol−1 K−1) o

acquires more positive charge and, hence, chromium sorption is higher. At alkaline pH, the OH− is present at higher concentration and will compete with anionic chromate ions for the sorption sites of the resin, hence resulting in a low CRC. In all of the pH ranges studied, AN/DVB/VBC−ED resin found to have higher a CRC than ST/DVB/VBC−ED and VBC/ DVB−ED resins, as the number of −NH2 groups available for the removal of chromium is higher in AN/DVB/VBC−ED resin. Therefore, further studies were focused only on AN/ DVB/VBC−ED resin. 3.6. Effect of Co-Ions. Figure S5 (Supporting Information) shows the behavior of the CRC of AN/DVB/VBC−ED resin in the presence of co-ions such as Cl−, SO42−, HCO3−, NO3−, Ca2+, and Mg2+ at a fixed initial concentration of 500 mg/L for a constant 100 mg/L initial chromium concentration and 0.1 g dosage of sorbent. From the graph, it is evident that the overall

−6.10 −6.18 −6.27 3.59 0.008

The negative values of ΔG° for the resin confirm the spontaneous nature of chromium sorption. The value of ΔH° is positive for AN/DVB/VBC−ED, indicating that the sorption process is endothermic. The resin showed a positive value of ΔS°, which is a measure of randomness at the solid/liquid interface during chromium sorption, indicating that chromium sorption is irreversible and stable.32 3.8. Comparison of Cr(VI) Removal with Different Polymeric Adsorbents Reported in the Literature. The adsorption capacities of the adsorbents studied for the removal

Table 3. Freundlich and Langmuir Isotherms for the AN/DVB/VBC−ED Resin Freundlich isotherm

Langmuir isotherm

temp (K)

1/n

n

kF [(mg/g) (L/mg) ]

r

χ

Q (mg/g)

b (L/g)

RL

r

χ2

303 313 323

0.121 0.236 0.261

8.26 4.24 3.83

74.13 64.71 63.10

0.983 0.992 0.974

0.0321 0.0125 0.0421

125.51 140.85 145.56

0.397 0.599 3.81

0.113 0.161 0.011

0.998 0.997 0.993

0.0317 0.0256 0.0550

1/n

2

5681

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positively charged groups on the resin, namely, NH3+, attract chromium ions, which exist as chromate anions in aqueous medium, by means of electrostatic attraction through hydrogen bonding. Moreover, the resins can be considered as hard acids because they contain H+ ions, and hence, they prefer to bind with hard bases, most preferably with HCrO4− ions. At acidic pH, the resin acquires a positive charge due to the protonation of the amino groups, which removes hydrogen chromate ion by means of electrostatic attraction/complexation. This results in increased chromium sorption at low pH. The −NH2 groups present in the resin reduce the toxic Cr(VI) to Cr(III), as confirmed by EPR studies.22−24 Chromium sorption was further supported by the presence of a chromium peak in the EDAX spectra of chromium-sorbed resins (cf. Figure 2c,d). The higher enhancement in CRC of AN/DVB/VBC−ED resin compared to ST/DVB/VBC−ED resin and VBC/DVB−ED resin is mainly because it has more −NH3+ groups available for chromium sorption.

of Cr(VI) in the present study were compared with those of other polymeric adsorbents reported in the literature, and the values of adsorption capacities are presented in Table 5. The Table 5. Comparison of the SCs of Various Polymeric Sorbents Toward Cr(VI) Ions sample no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

19 20 21 22

23 24 25 26

27 28 29 30 31

adsorbent Amberlite XAD-7 resin impregnated with Aliquat 336 Lewatit MP 64 anion-exchange resin Lewatit MP 500 anion-exchange resin acrylic strong-base anion exchanger Lewatit MP 62 Lewatit M 610 D 314 glycidyl methacrylate resin bearing quaternary ammonium chloride Dowex resin ion-exchange resin 1200H Dowex M4195 chelating resin Amberlite (XAD-4) resin impregnated with p-tert-butylcalix[8]areneoctamide Purolite CT-275 Purolite MN-500 Mowital B30H resin immobilized activated sludge poly(ethylene glycol) methacrylate-covinylimidazole (PEGMA-VI) poly(ethylene glycol) methacrylate 4-vinylpyridine (4-VP)−divinylbenzene (DVB) copolymer functionalized with benzyl chloride Amberlite XAD-7 resin impregnated with brilliant green cellulose-based anion exchanger bearing −N+H(CH3)2Cl− functional groups toluidine blue o-impregnated XAD-7 resin magnetic methyl methacrylate (MMA)/ glycidyl methacrylate (GMA)/DVB terpolymer functionalized with ethylenediamine (EDA) amino-functionalized poly[GMA-co-ethylene glycol dimethylacrylate (EGDMA)] polyaniline (PANI)/poly(ethylene glycol) (PEG) composite 4-vinylpyridine−divinylbenzene copolymer functionalized with 2-chloroacetamide cellulose modified with β-cyclodextrin (β-CD) and quaternary ammonium groups (cellg-GMA-β-CDN+) poly(styrene-co-EGDMA) microcapsules loaded with Aliquat 336 polyaniline (PANI)/zeolite nanocomposite Lewatit FO36 nano ion-exchange resin Amberlite IRA 743 AN/DVB/VBC−ED resin

adsorption capacity (mg/g)

ref

50.43

11

20.79 21.31 88.4 20.79 21.31 120.48 48.0

33 33 14 34 34 35 36

109.32 84.0 29.7 87.7

37 12 38 39

89.29 126.5 18.9

40 40 41

108.7

42

2.0 113.63

42 43

5.58

44

126.87

45

18.18 61.35

46 47

4. CONCLUSIONS AN/DVB/VBC−ED resin exhibited a higher CRC than ST/ DVB/VBC−ED resin, which, in turn, exhibited a higher CRC than VBC/DVB−ED resin, because of the presence of higher numbers of protonated amine groups. The sorption capacities of the synthetic resins were influenced by the pH of the medium and slightly decreased in the presence of co-ions. The sorption of chromium on the synthetic resins was found to follow the Freundlich isotherm. The positively charged groups on the resins, namely, NH3+, attract chromium ions. Chromium removal by the synthetic resins was found to be governed by electrostatic-adsorption-coupled reduction and complexation. AN/DVB/VBC−ED resin reduces toxic Cr(VI) to 300-timesless-toxic Cr(III). The sorption process is spontaneous and endothermic in nature.

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ASSOCIATED CONTENT

* Supporting Information S

110.0 68.97

49

74.62

50

61.05

51

44.56

52

25.0 15.0 20.41 125.6

Synthesis of polymeric resins, FTIR spectra of resins, DSC thermogram of AN/DVB/VBC−ED resin, EPR spectra of chromium-sorbed AN/DVB/VBC−ED resin, effect of co-ions on CRC of AN/DVB/VBC−ED resin, and proposed mechanism of chromium sorption. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +91-451-2452371. Fax: +91-451-2454466. E-mail: drs_ [email protected].

53 54 18 present work

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS S.M. is grateful to the Defence Research and Development Organization (ERIP/ER/0703670/M/01/1066), New Delhi, India, for the provision of financial support to carry out this research work. M.R.G. thanks CSIR, New Delhi, India, for awarding an SRF.

sorption capacity of AN/DVB/VBC−ED resin is higher than the reported values in many cases. The adsorption capacity depends on the characteristics of the individual adsorbent, the extent of surface/surface modification, the pH, and the initial concentration of the adsorbate. 3.9. Sorption Mechanism. The chromium removal by the synthetic resins was governed by electrostatic-adsorptioncoupled reduction and complexation,18 and the relevant schemes are shown in the Supporting Information. The

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REFERENCES

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