Preparation of Polyacrylonitrile Initiated by Modified Corn Starch and

Mar 6, 2014 - ... vacuum and nitrogen was bubbled in three times to get rid of the oxygen. ...... Levere , M. E.; Nguyen , N. H.; Sun , H. J.; Percec ...
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Preparation of Polyacrylonitrile Initiated by Modified Corn Starch and Adsorption for Mercury after Modification Yuanyaun Xu, Zhihai Hao, Hou Chen,* Jinming Sun, and Dongju Wang School of Chemistry and Materials Science, Ludong University, Yantai 264025, China ABSTRACT: Well-defined polyacrylonitrile (PAN) was precisely synthesized via a single electron transfer-living radical polymerization (SET-LRP) initiated by corn starch modified by bromoacetyl bromide (CS-Br) with La/hexamethylenetetramine (HMTA) as a catalyst system and ascorbic acid (VC) as the reductant. Amidoxime (AO) groups as adsorption functional groups were obtained via cyano groups of PAN resins modified by hydroxylamine hydrochloride. The adsorption for mercury was discussed and the maximum uptake was 4.12 mmol/g. Film diffusion and a pseudo-second-order model were better to interpret the adsorption process. The Langmuir model was appropriate to describe the adsorption isothermal process.

1. INTRODUCTION Polyacrylonitrile (PAN) resins have gained great attention in many fields of scientific research as well as industrial applications, which will continue increasing due to its light resistance, weather fastness, radiation resistance, and excellent chromaticity.1 It is particularly significant to find a suitable way to synthesize PAN resins that cater for various needs. Traditional free-radical polymerization methods have a bad control over molecular weight and macromolecular structure due to its inherent chain transfer and termination.2 Reversibledeactivation radical polymerization (RDRP) techniques for synthesizing PAN resins, in particular single-electron transfer living radical polymerization (SET-LRP),3−6 have gained much more concern and have many advantages over traditional freeradical procedures. To date, interest in SET-LRP is fueled owing to its highly robust and tolerant nature,7,8 since Percec first proposed in 2006.9 The catalyst systems composed of Cu(0) powder10−12 or Cu(0) wire13−18 combined with a suitable N-containing ligand19 in polar solvent20−22 play key roles in the intrinsic versatility of the SET-LRP process. Compared with ATRP in which Cu(I)23 acts as catalyst, SET-LRP has a good compatibility with the environment containing air. A heterolytic carbon halide bond cleavage which is catalyzed by a heterogeneous Cu(0) outer sphere single electron transfer perfectly activates these dormant chains. Hence, SET-LRP presents an ultrafast reaction rate in contrast with inner sphere single electron transfer in ATRP.24 It also makes the catalyst regeneration possible on the account of the disproportionation of Cu(I)X/N-containing ligand.17,25,26 Meanwhile, the living/ controlled feature suppresses bimolecular termination in terms of chain propagation by a persistent radical effect (PRE).19,27 This enables higher retention of chain-end functionality.19 The polymerizations with topological architecture of vinyl monomers have been performed under mild reaction conditions, such as acrylates,28,29 methyl acrylates,30,31 and methyl methacrylate.32,33 A range of different complex polymers’ structures have also been precisely obtained, like dendritic macromolecules,34 star polymers,35 and block copolymers.36 Though experiments referring to carbon/sulfate halide33 as initiators in SET-LRP were reported in the past decades, nearly © 2014 American Chemical Society

no research initiated by modified macromolecules, except cellulose and chitosan, have been shared with the public until now. To the best of our knowledge, corn starch is a natural polymer material, containing a quantity of bare hydroxyl which can be chemically modified conveniently. Thus, corn starch will play a significant role owing to its biodegradation, regeneration properties, and wide range of sources.37 A well-defined and functional PAN can be achieved using acrylonitrile (AN) and a macroinitiator by the “grafting from” route via SET-LRP. The excellent adsorbent with amidoxime (AO) groups can be yielded via modifying cyano (CN) groups as well. It is known to all that heavy metal ions tend to cause a bad influence on our surrounding environment, in particular mercury compounds, and they must be removed thoroughly. This advanced method provides a potential application in effluent treatment, recycling noble metals, and separating metal ions.38,39 To solve the toxicity problem caused by halohydrocarbon and obtain a high grafting ratio, here corn starch is first modified by bromoacetyl bromide (CS-Br) and used as the macroinitiator. In our research group, lanthanum (La) power instead of copper powder has been successfully utilized to synthesize PAN with a high grafting rate. As a result, the optional range of the catalyst system in SET-LRP is broadened. The addition of ascorbic acid (VC) as the reductant weakens the sensitivity upon oxygen. AO groups are obtained from CN groups of PAN reduced with NH2OH·HCl. The resin possesses chelating ability with metal ions, and Hg(II) adsorption is discussed in detail.

2. EXPERIMENTAL SECTION 2.1. Materials and Methods. Corn starch (CS) (Beijing Chenxing Starch Co., Beijing, China) was dried out before it was used. Acrylonitrile (AN) (Tianjin Fuchen Chemical Reagent Co., Tianjin, China) was purified via atmospheric Received: Revised: Accepted: Published: 4871

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distillation prior to conserving at 5 °C. Ascorbic acid (VC) (Tianjin Jinruite Chemical Reagent Co. Tianjin, China) was stored at 5 °C. La/HMTA (Guoyao Group Limited Co., Tianjin, China), N,N-dimethylformaide (DMF) (Tianjin Chemical Reagents Co., Tianjin, China), methanol (Tianjin Damao Chemical Reagent Co., Tianjin, China), ammonium acetate (Tianjin Jinruite Chemical Reagent Co., Tianjin, China), hydroxylamine (Tianjin Jinruite Chemical Reagent Co., Tianjin, China), concentrated hydrochloric acid (Laiyang Economic and Technologic Development Zone Refined Chemical Reagent Co., Yantai, China), concentrated nitric acid (Laiyang Economic and Technologic Development Zone Refined Chemical Reagent Co., Yantai, China), sodium hydroxide (Tianjin Chemical Reagent Co., Tianjin, China) were directly used. 2.2. Synthesis of CS-Br Macroinitiator. The macroinitiator which was modified by bromoacetyl bromide can be obtained according to the following process. In total, 2.5 g of corn starch (CS) in N,N-dimethylacetamide (DMAC)/LiCl (5% w/w) was added to a 250 mL flask with three necks. The slurry in the flask was put in an oil bath at 80 °C. The mixture was stirred under reflux of the solvent for 2 h and then cooled down at ambient temperature. Pyridine (4 mL) and bromoacetyl bromide (4 mL) were added into the flask for reacting for 24 h at 20 °C. A volume of 200 mL of hydrochloric acid (2 mol/L) was mixed with the resulting solution and the mixture was filtrated. The modified product (CS-Br) was washed thoroughly with water and methanol (v/v = 1:1) for three times and dried at 50 °C. 2.3. Polymerization of AN Grafted from the Surface of CS-Br (PAN-g-CS-Br). In total, 1 g of CS-Br in 10 mL of dimethyl formamide (DMF) was added into a 50 mL twonecked flask. The reactants were stirred for 60 min to yield a dispersion medium phase at room temperature. La (0.0527 g), HMTA (0.2662 g), VC (0.0308 g), and AN (10 mL) were finally mixed in the flask prior to immersing in a mixture of ice and water. The reaction system was under vacuum and nitrogen was bubbled in three times to get rid of the oxygen. The solution was sealed under nitrogen and was in the oil bath maintained 65 °C for 12 h. A volume of 100 mL of water, 100 mL of methanol, and 2 mL of concentrated hydrochloric acid were added successively after the solution was poured into a neat beaker. The product was extracted 24 h later. The production was dried at ambient temperature and filtrated via a Soxhlet extraction apparatus for 12 h. The product (PAN-g-CSBr) was dried until at constant weight. 2.4. Modification of Cyano Groups of PAN with NH2OH·HCl. In total, 3 g of NH2OH·HCl in 15 mL of methanol and 2 g of PAN-g-CS-Br were added to a 50 mL bottle with two necks. The reaction was performed with a magnetic stirrer and reflux. A volume of 7.5 mL of NaOH (1.95 g) aqueous solution was added to the mixture system to adjust pH at 9.0 2 h later. The experiment was performed for 20 h at 70 °C with stirring. The resin (AO PAN-g-CS-Br) was purified via ethanol and dried under vacuum at 50 °C until at constant weight. 2.5. Adsorption Capacity of Hg(II). 2.5.1. Effect of pH on Adsorption. Effect of pH on adsorption was conducted at 25 °C for 24 h by adding 10 mg of AO PAN-g-CS-Br resin and 20 mL of Hg(II) solution (0.005 moL/L) in seven iodine flasks in a shake. The blank experiment was also performed. The pH of buffer solution varied from 1.0 to 7.0 by adding nitric acid solution. A volume of 4 mL of solution was extracted and

diluted to 25 mL colorimetric tubes, and the Hg(II) concentration was measured via atomic absorption spectrophotometer. The resin adsorption capacity was calculated using the following equation,

Q=

(C0 − Ce)V W

(1)

where Q is the amount of metal ions adsorbed per unite amount of adsorbents (mmol/g); C0 means the initial concentration of Hg(II); Ce (mmol/mL) is the equilibrium concentration of Hg(II); V (mL) stands for solution’s volume; and W (g) is the weight of the adsorbent, i.e., AO PAN-g-CSBr. 2.5.2. Adsorption Kinetics. A mass of 10 mg of AO PAN-gCS-Br and 20 mL of 0.005 mol/L Hg(II) (pH = 4.0) were mixed in a series of iodine flasks to perform kinetics experiments under various temperatures. A 4 mL solution was withdrawn and diluted with deionized water to a 25 mL colorimetric tube. The method of calculating concentration and adsorption amount obeyed the above-mentioned way. 2.5.3. Adsorption Isotherms. In order to investigate adsorption isotherms, 10 mg of AO PAN-g-CS-Br and a series of different Hg(II) concentrations from 0.001 to 0.005 mol/L were placed into iodine flasks, respectively. The original pH was adjusted to 4.0. Then the supernatant was collected after 4 h with a temperature scope varied from 15 to 45 °C. 2.5.4. Adsorption Selectivity. In terms of adsorption selectivity for Hg(II), the experiments were performed in the condition of 10 mg of AO PAN-g-CS-Br adsorbents and 20 mL solutions of a equal initial concentration (0.1 mol/L) of Hg(II) and another coexisting metal ions for 6 h. 2.6. Characterization. The comparisons of functional groups were conducted by infrared spectra Perkin-Elmer Spectrum 2000 FTIR. The surface of the resins was characterized using high and low vacuum scanning electron microscopy (SEM), running at 20 kV. The yield of AO PAN-gCS-Br and percentage of AO in AO PAN-g-CS-Br was calculated according to nitrogen content determined by the Elementar VarioEL III instrument, Elementar Co., Germany. The concentration of Hg(II) was determined via an atomic adsorption spectrophotometer.

3. RESULTS 3.1. Preparation and Characterization of AO PAN-gCS-Br. CS was modified by bromoacetyl bromide to obtain CSBr. CS-Br was used as a macroinitiator for SET-LRP to prepare PAN-g-CS-Br. After modification with hydroxylamine hydrochloride, AO PAN-g-CS-Br was obtained. The preparation process of AO PAN-g-CS-Br is shown in Scheme 1. The nitrogen contents of PAN-g-CS-Br and AO PAN-g-CS-Br determined by element analyzer were 13.39% and 18.73%, respectively. The yield of AO PAN-g-CS-Br copolymer was 69.94% and AO in AO PAN-g-CS-Br was 3.81 mmol/g. The surface-initiated SET-LRP of AN was conducted in DMF using La powder as a catalyst and CS-Br as an initiator. An obvious first-order linearity manifestation of the semilogarithmic plot of ln[M]0/[M] versus time (ln[M]0/[M] = kp[R• ]t), as assessed by Figure 1, indicated that the concentration of active species was kept constant and the number of dead chains was negligible. The above result verifies that the polymerization perfectly possessed living characteristic. 4872

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which were the feature of the stretching vibration of C−N and N−O bonds in AO groups, respectively, assigned to succeeding in the modification of AN with hydroxylamine hydrochloride. Figure 3c shows that the proportion of surface became rougher than the bare CS (Figure 3a) and the modified CS

Scheme 1. Preparation of AO PAN-g-CS-Br

Figure 1. Semilogarithmic kinetic plots for SET-LRP of AN catalyzed by La/HMTA in the presence of VC at 65 °C.

The presence of the organic groups grafted from CS was confirmed via the infrared spectra as exhibited in Figure 2. With comparison of parts a and b of Figure 2, a new peak at 1750 cm−1 turned up, which was ascribed to the stretching vibration of carbonyl groups, indicating that CS was modified successfully with bromoacetyl bromide. In Figure 2c, a new peak at 2246 cm−1 appeared compared with b, which was attributed to the stretching vibration of CN groups in PAN. It demonstrates that the surface-initiated SET-LRP of AN was successfully grafted from CS-Br. In Figure 2d, the peak at 2246 cm−1 vanished and two new wide peaks at 1648 cm−1 and 930 cm−1 appeared,

Figure 3. SEM photographs of CS (a), CS-Br (b), PAN-g-CS-Br (c), and AO PAN-g-CS-Br (d).

(Figure 3b). Furthermore, products in Figure 3d changed a lot contrasted with that in Figure 3c. A conclusion could be drawn that the modification process successfully fulfilled

Figure 2. FTIR spectra of CS (a), CS-Br (b), PAN-g-CS-Br (c), and AO PAN-g-CS-Br (d). 4873

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3.2. Adsorption Capacity. 3.2.1. Effect of pH on the Adsorption. pH plays a key role in the adsorption process, because functional groups’ dissociation and surface charge in the adsorbent are prone to be affected. Furthermore, pH affects the existent state of metal ions in solution to a certain extent. From Figure 4, we can see that pH had remarkable influence on the adsorption quantity and the optimal pH was found to be 4.

When the adsorbents expose themselves to the low metal ions and high metal ions concentrations, according to theories proposed by Boyd41 and Reichenberg,42 the adsorption process is considered to occur through two patterns, i.e., film diffusion and particle diffusion. The data were calculated by equations put forward by Reichenberg42 and Helfferich.43 F=1−

F=

∞

6 2

∏

∑ n=1

2 2 1 ⎡ −Dit ∏ n ⎤ ⎢ ⎥ ⎥⎦ n2 ⎢⎣ r0 2

(2)

qt q0

(3)

where qt, q0 represent the adsorption quantity at time t and the maximum adsorption quantity when the adsorption process achieves the equilibrium state, respectively. 2

B= Figure 4. Effect of pH on adsorption of Hg(II).

∏ Di r0 2

(4)

where Di means the metal ion’s effective diffusion coefficient; r0 stands for the adsorbent particle’s radius, provided that the adsorbent is spherical; and n, as an integer, defines the infinite series solution. Values of Bt were acquired according to corresponding values of F given by Reichenberg.42 If the linearity relationship between Bt and t passes through the origin, it demonstrates the adsorption process is controlled via particle diffusion, whereas it is regulated by film diffusion. As Figure 6 shows, all the lines concerning Bt versus t possessed a good linear relationship without passing through

Adsorption sites provide a place where the surface net charge of adsorbents and the H+ ions has a competition. The competing reaction could best account for this phenomenon. At low pH, most amidoximation groups are converted to the protonated form as a result of the ultrahigh concentration of H+ in the solution so that the adsorbent was full of positive charge forming repulsive interaction on Hg(II) adsorption. The adsorbent gradually deprotonated leading to more bare adsorptive groups emerging with diminishing concentration of H+. While pH went beyond 4, Hg(II) would be hydrolyzed to Hg(OH)3(I), giving rise to declining adsorption capacity. The optimal condition for maximum adsorption was pH = 4 for that the effect of H+ could be neglected. The solution with pH = 4 was used in the following experiment. 3.2.2. Adsorption Kinetics. From Figure 5, we can see that adsorption rate was rapid at first, then the curves became mild

Figure 6. Bt versus time plots for AO PAN-g-CS-Br.

the origin, suggesting that film diffusion was fit to the adsorption procedure. It was also consist with the early design attributing to the modified PAN grafting from the surface of CS-Br. The linear equations and correlation coefficients R2 are listed in Table 1. Pseudo-first-order44 and pseudo-second-order45 are used to illustrate adsorption mechanism and interpret the experimental data. The equations were expressed as follows

Figure 5. Adsorption kinetics of AO PAN-g-CS-Br for Hg(II) at different temperatures.

for reaching equilibrium and the maximum adsorption capacity increased with temperature increasing. The result suggested that Hg(II) was easy to solvate by water molecule forming hydrated ions, making it difficult to diffuse onto the surface of AO PAN-g-CS-Br at low temperature.40 While the bare Hg(II) was obtained from dehydration of hydrated Hg(II) so that the chances of combining the active site was amplified giving rise to shortening the equilibrium time with higher temperature. Thus the kinetics adsorption provided a powerful basis to define the optimum contact time.

Table 1. Bt Versus Time Linear Equations and Coefficients R2 T (°C) 15 25 35 45 4874

linear equation Bt Bt Bt Bt

= = = =

0.0141t 0.0216t 0.0195t 0.0199t

+ + + +

0.5891 0.5736 0.7631 0.8888

R2 0.9570 0.9294 0.9435 0.9546

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(qe − qt) qe

Article

= −k1t

(5)

t 1 t = + qt qe k 2qe 2

(6)

where k1 stands for the rate constant of pseudo-first-order (min−1), k2, the pseudo-second-order rate constant (g(mmol min)−1) of adsorption, qe and qt, the equilibrium capacity and adsorption amount at time t, respectively. Comparing Figures 7 and 8, the linear fitting of the pseudosecond-order was better than that of the pseudo-first-order. As

Figure 9. Isotherm of AO PAN-g-CS-Br for Hg(II) at different temperatures.

conclusion could be drawn that adsorption for Hg(II) in this paper was endothermic within the scope of given temperatures. To deal with the isotherm data, the Langmuir model and Freundlich46,47 model were used. The equations of them are as follows Ce C 1 = e + qe q qK L ln qe = ln KF +

Figure 7. Pseudo-first-order kinetic plots for adsorption of Hg(II).

(7)

ln Ce n

(8)

where qe and Ce stand for adsorption capacity (mmol/g) and concentration of metal ions in a state of equilibrium, respectively. q is the maximum adsorption amount (mmol/g), KL, an empirical constant, n, the constant of Freundlich, KF, the combination ability of the chemical bond between adsorbent and metal ions. Figures 10 and 11 clearly show that the Langmuir model fitted the isotherm adsorption better than the Freundlich

Figure 8. Pseudo-second-order kinetic plots for adsorption of Hg(II).

was shown in Table 2, R2 of the pseudo-second-order equaled almost 1, while R2 of the other team showed more deviation from 1. Moreover, the calculated qe of pseudo-second-order was preferable in accordance with the experimental qe. Hence, the pseudo-second-order model was more favorable than pseudofirst-order model to describe the adsorption kinetics process of AO PAN-g-CS-Br for Hg(II). It reveals that the ratedetermining step may be chemical adsorption containing a valency force via exchange or sharing electrons between the amidoxime group and Hg(II). 3.2.3. Isotherms Adsorption. Figure 9 shows that the uptake capacity increased with concentration and temperature rising. A

Figure 10. Langmuir isotherm of AO PAN-g-CS-Br for Hg(II) at different temperatures.

model. It also can be seen from Table 3 that the regression coefficients RL2 was closer to 1 (>0.98) obtained from the Langmuir model, indicating that the Langmuir model was more

Table 2. Maximum Adsorption Capacities (qe(exp), qe(cal)) and Parameters (k, R2) of Pseudo-First-Order and Pseudo-SecondOrder at Different Temperatures pseudo-first-order kinetics

pseudo-second-order kinetics

T (°C)

qe(exp) (mmol g−1)

k1 (min−1)

qe(cal) (mmol g−1)

R12

k2 (g mmol−1 min−1)

qe(cal) (mmol g−)

R22

15 25 35 45

3.71 3.88 3.96 4.07

0.0178 0.0218 0.0197 0.0219

1.39 1.34 1.13 0.94

0.8999 0.9741 0.9450 0.9306

0.032 0.042 0.046 0.065

3.80 3.95 4.02 4.12

0.9999 0.9997 0.9998 0.9998

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ACKNOWLEDGMENTS This study was supported by the Program for New Century Excellent Talents in University (Grant No. NCET-11-1028), the Natural Science Foundation for Distinguished Young Scholars of Shandong province (Grant No. JQ201203), and the Program for Scientific Research Innovation Team in Universities of Shandong Province.

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(1) Belousova, T. A. IR Spectroscopic characteristics of polyacrylonitrile copolymer fibres. Fibre Chem. 2002, 34, 146. (2) Hong, H. K.; Mays, J. W. Synthesis of block copolymers of styrene and methyl methacrylate by conventional free radical polymerization in room temperature ionic liquids. Macromolecules 2002, 35, 5738. (3) Liu, X. H.; Zhang, G. B.; Li, B. X. Copper(0)-mediated living radical polymerization of acrylonitrile: SET-LRP or AGET-ATRP. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 5439. (4) Liu, D. L.; Chen, H.; Yin, P. Synthesis of polyacrylonitrile by single-electron transfer-living radical polymerization using Fe(0) as catalyst and its adsorption properties after modification. J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 2916. (5) Ma, J.; Chen, H.; Zhang, M. Cu powder-catalyzed single electron transfer-living radical polymerization of acrylonitrile. J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 2588. (6) Rosen, B. M.; Percec, V. Single-electron transfer and singleelectron transfer degenerative chain transfer living radical polymerization. Chem. Rev. 2009, 109, 5069. (7) Nguyen, N. H.; Percec, V. Disproportionating versus nondisproportionating solvent effect in the SET-LRP of methyl acrylate during catalysis with nonactivated and activated Cu(0) wire. J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 4227. (8) Nguyen, N. N. H.; Percec, V. Dramatic acceleration of SET-LRP of methyl acrylate during catalysis with activated Cu(0) wire. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 5109. (9) Percec, V.; Guliashvili, T.; Ladislaw, J. S.; Wistrand, A.; Stjerndahl, A.; Monika, J.; Monteiro, M. J.; Sahoo, S. Ultrafast synthesis of ultrahigh molar mass polymers by metal-catalyzed living radical polymerization of acrylates, methacrylates, and vinyl chloride mediated by SET at 25 °C. J. Am. Chem. Soc. 2006, 128, 14156. (10) Percec, V.; Popov, A. V.; Castillo, E. R.; Weichold, O. Living radical polymerization of vinyl chloride initiated with iodoform and catalyzed by nascent Cu0/tris(2-aminoethyl)amine or polyethyleneimine in water at 25 °C proceeds by a new competing pathways mechanism. J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 3283. (11) Ding, W.; Lv, C. F.; Sun, Y.; Liu, X. J.; Yu, T.; Qu, G. M.; Luan, H. X. Synthesis of zwitterionic polymer by SET-LRP at room temperature in aqueous. J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 432. (12) Levere, M. E.; Nguyen, N. H.; Sun, H. J.; Percec, V. Interrupted SET-LRP of methyl acrylate demonstrates Cu(0) colloidal particles as activating species. Polym. Chem. 2013, 4, 686. (13) Nguyen, N. H.; Rosen, B. M.; Lligadas, G.; Percec, V. Surfacedependent kinetics of cu(0)-wire-catalyzed single-electron transfer living radical polymerization of methyl acrylate in DMSO at 25 °C. Macromolecules 2009, 42, 2379. (14) Nguyen, N. H.; Rosen, B. M.; Xuan, J.; Fleischmann, S.; Percec, V. New efficient reaction media for SET-LRP produced from binary mixtures of organic solvents and H2O. J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 5577. (15) Nguyen, N. H.; Rosen, B. M.; Percec, V. SET-LRP of N,Ndimethylacrylamide and of N-isopropylacrylamide at 25 °C in protic and in dipolar aprotic solvents. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 1752. (16) Nguyen, N. H.; Jiang, X.; Fleischmann, S.; Rosen, B. M.; Percec, V. The effect of ligand on the rate of propagation of Cu(0)-wire catalyzed SET-LRP of MA in DMSO at 25 °C. J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 5629.

Figure 11. Freundlich isotherm of AO PAN-g-CS-Br for Hg(II) at different temperatures.

Table 3. Langmuir Parameters and Freundlich Parameters at Different Temperatures Langmuir parameters −1

Freundlich parameters 2

T (°C)

q0 (mmol g )

KL

RL

15 25 35 45

4.80 4.62 4.56 4.45

1465 2142 2631 3796

0.9899 0.9933 0.9954 0.9920

KF

n

RF2

68 31 73 45

2.21 3.01 2.04 0.4067

0.8440 0.9503 0.9710 0.9826

suitable to interpret the isotherm adsorption as well. In other words, the adsorption process complied with a homogeneous surface belonging to monolayer adsorption. 3.2.4. Adsorption Selectivity. A conclusion can be drawn from Table 4 that AO PAN-g-CS-Br shows excellent adsorption Table 4. Adsorption Selectivity of AO PAN-g-CS-Br system Hg(II)−Ag(I) Hg(II)−Pb(II) Hg(II)−Ni(II)

metal ion

adsorption capacity (mmol g−1)

selective coefficient

Hg(II) Ag(I) Hg(II) Pb(II) Hg(II) Ni(II)

4.11 0.36 4.09 0.41 4.03 0.33

11.42 9.98 12.21

ability for Hg(II) in different mixed metal ions. These findings suggest that resin with AO groups can probably be used to selectively adsorb Hg(II) from the mixed metal ions system.

4. CONCLUSIONS PAN-g-CS-Br resin was successfully synthesized via SET-LRP with La(0) as a catalyst and CS-Br as a macroinitiator. SETLRP displayed the characteristic of well-controlled radical/ living polymerization. The maximum adsorption capacity for Hg(II) of AO PAN-g-CS-Br was 4.12 mmol/g. Film diffusion was the dominant mechanism during the Hg(II) adsorption process, and the process was chemical uptake and monolayer adsorption.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest. 4876

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dx.doi.org/10.1021/ie404365h | Ind. Eng. Chem. Res. 2014, 53, 4871−4877