Synthesis and Selective Sorption Behavior of Pt (IV) Ion-Imprinted

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Synthesis and Selective Sorption Behavior of Pt(IV) Ion-Imprinted Polymer Particles Yang Jiang†,‡ and Dukjoon Kim*,† †

School of Chemical Engineering, Sungkyunkwan University, Suwon, Kyunggi 440-746, Korea College of Materials and Textile Engineering, Jiaxing University, Jiaxing City, Zhejiang 314001, China

‡

ABSTRACT: Pt(IV) ion-imprinted polymer (Pt(IV)-IIP) was synthesized in the form of porous particles with dimensions of 100−400 μm by the copolymerization of divinylbenzene and styrene in the presence of self-assembled chelates of 4-vinylpyridine and dimethylglyoxime functional monomers along with Pt(IV) ions. The chemical structure of Pt(IV)-IIP was identified by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectroscopy. The pore size and structure of Pt(IV)-IIP was characterized by Brunauer−Emmett−Teller analysis and scanning electron microscope. The effects of pH and the initial concentration of Pt(IV) on the selective adsorption behavior for the template ion was investigated using flame atomic absorption spectroscopy. Compared to nonimprinted polymer particles, the Pt(IV)-IIPs illustrated excellent selectivity toward the template ion, Pt(IV), over other competitive ions such as Ni(II), Cu(II), and Pd(II). The selectivity coefficients (α) of Pt(IV)/Ni(II), Pt(IV)/Cu(II), Pt(IV)/Zn(II), and Pt(IV)/Pd(II) were 330.27, 359.89, 463.91, and 4.85, respectively. The study on the selective separation of Pt(IV) from the spent catalyst solution revealed the potential application of Pt(IV)-IIP particles in the practical industry.

1. INTRODUCTION Although platinum group metals (PGMs) are precious and noble with high cost, they are widely used in many manufacturing industries such as jewelry, medical and electrical contacts, and biomedical devices. Particularly, platinum (Pt) is one of the typical PGMs consumed in many industries, and its demand is still increasing and expanding.1 Natural resources of PGMs are limited (and highly centralized in South Africa and Russia). They are generally produced in complex forms with other metals, including palladium, nickel, copper, arsenide, and sulfides.2,3 Because of this, the effective extraction and recovery of PGMs from source materials such as ores and industrial wastes may have potential importance, both economically and in environmental protection. In general, PGMs are difficult to separate from source materials.4 To separate and recover PGMs from complex metal sources, several methods have been employed, including coprecipitation, fire-assay, biosorption, ion exchange, solvent extraction, solid-phase extraction, cloud-point extraction, reverse osmosis, membrane separation, and evaporation.5−13 Each method has distinguishable advantages, but a common drawback lies in the poor selectivity of the separation. The separation of a specific metal from complex metal sources is hard to establish by a single unit operation, so numerous secondary unit operations are frequently needed. In recent years, molecular imprinting techniques have been applied to the separation of metal ions via adsorption.13−21 The synthesis of molecularly imprinted polymers (MIP) is based on a self-assembled complex formed by an interaction between functional monomers and a template prior to polymerization. After polymerization of a self-assembled complex in the presence of comonomers and cross-linker, the removal of templates provides polymers with specific recognition sites. MIPs synthesized by this method have superior selectivity due © XXXX American Chemical Society

to their specific binding affinity toward the target molecule (template).19−21 Because of this dominant property, MIP techniques have been used in diverse applications, such as the extraction and cleanup of organic compounds,22 bioseparation,23 chemical sensing,24 and sensors on quartz crystal microbalance electrodes.25 Although there have been many studies on the synthesis and adsorption behavior of MIPs for a number of metal ions, such as Cu, Pb, Cd, Zn, Hg, Cr, and Ni, with excellent adsorption capacities and selectivity having been demonstrated,19−21,26−32 only one report has been released so far for Pt ions.18 Lesniewska et al.18 used acetaldehyde thiosemicarbazone (AcTSn) and benzaldehyde thiosemicarbazone (BnTSn) as chelating agents for Pt ions, and methacrylic acid and ethylene glycol dimethacrylate cross-linker as a monomer and crosslinker for synthesis. Even though the MIPs prepared exhibited fairly good selective adsorption behavior toward Pt ions over other metal ions, poor selectivity over Pd ions was still observed. Pt/Pd metal alloy is an important material used in many industries. One important application is as an automobile catalytic converter material. Since massive Pt/Pd wastes are produced from used vehicles, selective separation is of real commercial value. In this study, Pt(IV) ion-imprinted polymers were synthesized, and their selective separation behaviors were characterized. The adsorption capacity and kinetics of ionimprinted polymers were analyzed for Pt(IV) ions and several industrially important metal ions, including Pt(IV) ions. Dimethylglyoxime and 4-vinylpyridine were selected as PtReceived: March 1, 2014 Revised: July 29, 2014 Accepted: August 9, 2014

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particles (NIP) were also prepared by the same method as that for Pt(IV)- IIPs in the absence of the template. 2.4. Adsorption Experiments. The adsorption behavior of Pt(IV) ions on both the imprinted and nonimprinted polymeric particles was investigated in a batch operation mode. In a typical adsorption experiment, 0.1 g of Pt(IV)-IIP particles were placed in 100 mL of aqueous medium containing Pt(IV) ions, with magnetic agitation. The effects of pH and initial Pt(IV) concentrations of the ion-containing medium on the adsorption capacities of adsorbents were studied. The pH of the medium was adjusted to a range of 0.5−4.5 at room temperature by adding HCl and NaOH solution at the beginning of the experiment. The initial concentration of Pt(IV) was in the range of 10−80 mg L−1. Adsorption experiments were conducted in a 250 mL glass bottle with stirring at room temperature. After equilibrium, the particles contained in the mixture were filtered out by filter paper, and the ion concentration was measured using AAS. The feed flow rates and pressures of fuel (acetylene) and oxidant (air) were 1.7 L min−1 at 20 kPa and 15 L min−1 at 160 kPa, respectively. The amount of Pt(IV) ions adsorbed onto the particles was calculated using the following equation:

chelating monomers with reference to the report on Pdchelating ones,17 and divinylbenzene and styrene were used as comonomers for synthesis via bulk polymerization.

2. EXPERIMENTAL SECTION 2.1. Materials and Instrument. The salt form of the template ion, H2PtCl6, and the functional monomers of 4vinylpyridine (4-VP) and dimethylglyoxime (DMG), were supplied from Sigma−Aldrich (St. Louis, MO, USA). Divinylbenzene (DVB) and styrene (St) were supplied for copolymerization from Sigma−Aldrich and Duksan Pure Chemicals (Ansan, Korea), respectively. Azobis(isobutyronitrile) (AIBN) was used as an initiator, and all other chemicals, such as dimethyl sulfoxide (DMSO) and toluene, were purchased from Daejung (Inchon, Korea). To investigate the chemical and physical structure of the Pt(IV) ion-imprinted polymers (IIPs), Fourier transform infrared spectroscopy (Bruker IFS-66/S, FTIR, Bruker, Ettlingen, Germany), field emission scanning electron microscope (FESEM) (JSM7000F, JEOL, Tokyo, Japan) attached with energy dispersive X-ray spectrometer (EDX, EDAX USL 30 analyzer), and X-ray photoelectron spectroscopy (XPS, Phi5000versapro, Ulvca-PHI, Kanagawa, Japan) were employed along with Brunauer−Emmett−Teller (BET, ASAP 2010, Micromeritics, Norcross, GA, USA) analysis. The adsorption characteristics of Pt(IV)-imprinted polymers were tested using flame atomic absorption spectroscopy (FAAS, Z-6100, Hitachi, Japan). 2.2. Formation of Pt-DMG-VP Ternary Complexes. PtDMG complexes were first prepared. Five mmol H2PtCl6 and 10 mmol DMG were separately dissolved in 100 mL of DI water and 100 mL of ethyl alcohol/DI water (30/70 wt %) at room temperature. An aqueous solution of DMG and ethanol was slowly added to the Pt(IV)/DI water mixture when H2PtCl6 was completely dissolved. The temperature was increased to 90 °C, and stirring was performed for 3 h until dark brown precipitates were obtained. The Pt-DMG complex precipitates were filtered off and sequentially washed three times with methanol and acetone, and then dried under vacuum for 24 h. Five mmol Pt-DMG complexes were dispersed in 100 mL of DMSO, and then 10 mmol 4-VP was dropped into the solution. This mixture was stirred for 3 h at 90 °C using a magnetic bar. The product was washed three times with methanol and acetone, and then dried under vacuum for 24 h. 2.3. Preparation of Pt(IV)-Imprinted Microporous Particles. Pt(IV) ion-imprinted polymers (Pt(IV)-IIPs) were synthesized by bulk-polymerization. A 1.5 mmol sample of PtDMG-VP complex, 30 mmol of DVB and St comonomers at 1:1 molar ratio, 0.05 g of AIBN, and 10 mL of toluene were added one-by-one to a 100 mL three-neck flask. The mixture was stirred at 200 rpm using a mechanical agitator at room temperature under N2 atmosphere. The polymerization reaction was conducted for 15 min at room temperature, followed by increasing the temperature to 70 °C for 6 h. After polymerization, the IIP particles were ground by a mortar and sieved into 100−400-μm particles. The products were washed with methanol and acetone to remove impurities and unreacted monomer, and then dried under vacuum for 24 h. Pt(IV) ions were removed by washing polymer particles with 1 M HCl aqueous solution containing 1 wt % thiourea. Finally, the Pt(IV)-IIP produced was washed with methanol and acetone, and then dried in vacuum. Nonimprinted polymer

Q = (CA − C B)v /m

(1)

where Q is the adsorption capacity of the polymer (mg g−1), CA and CB are the initial and equilibrium concentrations of ions after adsorption, respectively (mg L−1), v is the volume of the solution (L), and m is the mass of polymer (g). 2.5. Selectivity Experiments. The selective separation properties of Pt(IV)-IIP and NIP were studied at varying pH values in a batch system. Cu(II), Zn(II), Ni(II), and Pd(II) were used as competitive ions with Pt(IV) at a solution concentration of 50 mg L−1. After equilibrium, the concentration of metal ions in the remaining solution was measured using AAS. The distribution ratio (D) and the selectivity factor α for Pt(IV) were calculated according to the following equations: D=

CA − C B υ CA m

(2)

Here, v is the volume of the solution (L), m is the mass of the polymer (g), and CA and CB are the initial and final concentrations of metal ions (mg L−1), respectively. α=

DPt DM

(3)

DPt and DM represent the distribution ratios of Pt(IV) and other metal ions, respectively. 2.6. Selective Separation of Pt(IV) Ions from the Spent Catalyst Solution. The separation of Pt(IV) ions from the spent catalyst solution in the catalytic reforming process of petrochemical industries was studied using Pt(IV)-IIP particles. As the typical spent catalysts solution in the catalytic reforming process contains 0.00025 M Pt(IV), 0.0015 M Fe(III), and 0.1 M Al(III) ions along with a negligible amount of Ni(II) ion, the simulated spent catalyst solution composed of Pt(IV), Fe(III), and Al(III) in the same concentration was synthesized and employed.33 Pt(IV)-IIP particles, 0.1 g, were placed in 100 mL of the simulated spent catalyst solution. After magnetic agitation in pH 0.5 for 1 h, each ion concentration was measured using FAAS. B

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Figure 1. Schematic representation of the synthetic process of Pt(IV)-IIP particles.

3. RESULTS AND DISCUSSION 3.1. Synthesis of Imprinted Polymers. The synthetic procedure of Pt(IV)-IIPs is schematically depicted in Figure 1. H2PtCl6 is first ionized in the aqueous phase to provide [PtCl6]2− ions (six-coordinated compound ions). When DMG (C4H8O2N2) and 4-VP (C7H7N) are added in turn, the -N groups act as the coordinating sites for chelation, so that the Cl ligand is gradually replaced by -N group due to the weaker electronegativity of N than Cl. After that, the Pt-DMG-VP complex is polymerized with the DVB and St comonomers. While Pt(IV) was removed by washing, the functional monomers were trapped, and acted as binding sites for the template ion inside the polymer matrix. 3.2. IR Spectra, EDX, and XPS Analysis. The IR spectra of Pt(IV) ion-containing polymers, Pt(IV) ion-removed (imprinted) polymers (Pt(IV)-IIP), and nonimprinted polymers (NIP) are shown in Figure 2 for comparison. All polymers show similar IR spectra, indicating similarity in the backbone structures, except for the binding groups to the Pt(IV) ion. The CN stretching of the pyridine ring at 1255 cm−1 in the Pt(IV)-containing polymers was shifted to 1220 cm−1 in the Pt(IV)-IIPs and nonimprinted polymers (NIPs), indicating the involvement of the -N group of the pyridine ring in the binding with Pt(IV) ions. Pt(IV)-IIP and NIP have exactly the same IR spectra. EDX and XPS measurements were performed to determine the elemental composition of the Pt(IV)-containing polymer

Figure 2. FTIR spectra of nonimprinted polymer (NIP), Pt(IV)containing polymer, and Pt(IV)-IIP samples.

and Pt(IV)-IIPs. In EDX spectra, Pt signals are clearly observed around 2 keV in Figure 3a before the removal of the Pt(IV), but not in Figure 3b. In XPS spectra, the Pt signals from Pt(4f), Pt(4d3/2), and Pt(4d5/2) observed in the 0−450 binding energy in Figure 4a are not seen anymore in Figure 4b. Those EDX and XPS analyses indicate that the Pt(IV) ions were completely removed during the extraction process. 3.3. Particle Size and Morphology. The surface morphology of the Pt(IV)-IIPs particles was analyzed using a C

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Figure 4. XPS analysis of polymer samples (a) before and (b) after Pt(IV) washing process in the synthesis of Pt(IV)- IIP particles. Figure 3. EDX analysis of polymer samples (a) before and (b) after Pt(IV) washing process in the synthesis of Pt(IV)- IIP particles.

platinum species are attracted to the adsorbent. As the adsorbent becomes neutralized with increasing pH, however, the electrostatic interactions between the adsorbent and the anionic platinum species decrease, and hence, the adsorption capacity also decreases. There is a precipitation by the formation of Pt(OH)4 over pH 4.5, so further adsorption tests were difficult to perform. 3.4.2. Maximum Adsorption Capacity of Pt(IV)-IIPs for Pt(IV) ions. The equilibrium adsorption capacity of Pt(IV)imprinted polymer particles was measured in Pt(IV) ioncontaining aqueous solution at pH 0.5. In Figure 7, the equilibrium adsorption capacity is illustrated as a function of Pt(IV) concentration. It initially increased with Pt(IV) ion concentration, followed by saturation at 50 mg L−1. This means that the Pt(IV) ions are bound to pore surfaces of imprinted polymers until the active binding vacant sites are completely occupied by ions. Thus, the plateau value corresponds to the maximum adsorption capacity of the imprinted polymers. In this study, the maximum adsorption capacity was 38.89 mg g−1 (ion/polymer) at 50 mg L−1. 3.4.3. Selective Separation Behavior. The selectivity coefficients of Pt(IV) ions over other metal ions that coexisted with Pt(IV) ions in solution were studied in batch adsorption experiments at different pH. As the maximum adsorption

field emission scanning electron microscope (FESEM) (JSM7000F, JEOL, Tokyo, Japan). Figure 5 shows the shape and pore structure of Pt(IV)-IIPs particles. This porous structure plays an important role in the enhancement of the adsorption capacity in association with increased surface area. BET analysis resulted in a surface area of 42.62 m2 g−1, with a total pore volume and pore width of 0.2985 cm3 g−1 and 31.612 Å, respectively for Pt(IV)-IIP particle. The nonimprinted polymer particles possessed a surface area of 40.02 m2 g−1 and pore volume of 0.2912 cm3 g−1, which were very similar to the imprinted ones. 3.4. Adsorption Behavior. 3.4.1. Effect of pH. The pH dependence of the adsorption capacity of Pt(IV)-IIPs is shown in Figure 6. At low pH in the range of 0.5 to 3, Pt(IV)-IIPs exhibit a high affinity toward Pt(IV) ions. When pH was increased to the range of 3−4.5, however, the adsorption capacity was rapidly reduced. The higher adsorption capacity at lower pH can be explained by the electrostatic interactions between the adsorbent and the Pt(IV) ions. The active platinum species are present in the form of form [PtCl6]2− in acidic conditions. As the functional ligand groups of Pt(IV)IIPs start protonation in acidic solution, [PtCl6]2− anionic D

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Figure 7. Effect of the Pt(IV) ion initial concentration on the adsorption capacity of Pt(IV)-IIP particles.

capacity of Pt(IV)-IIPs was obtained at 50 mg L−1, this concentration was used on this selectivity study. The selective separation behavior of the IIP particles for Pt(IV) ions was tested with aqueous solutions containing Cu(II), Zn(II), Ni(II), Pd(II), and Pt(IV) ions. In Figure 8, there is a clear distinction in adsorption capacity between Pt(IV) ions and other competitive ions. The IIPs demonstrated much higher adsorption capacity for Pt(IV) ions over Cu(II), Zn(II), Ni(II), and Pd(II) ions, while the nonimprinted polymer had no selective separation behavior for Pt(IV) ions. This high separation selectivity of IIPs is due to the imprinting effect of the polymers toward Pt(IV) ions associated with the specific interaction force, coordination number, and geometry, and the cavity size inside the imprinted polymer. Above pH 4.5, the selective adsorption property decreases because of the precipitation tendency mentioned above. The distribution ratios (D) and selectivity factors (α) of imprinted particles for several Pt(IV) related metal pairs are shown in Table 1. The selectivity coefficients of the imprinted particles for Pt(IV)/ Ni(II), Pt(IV)/Zn(II), Pt(IV)/Cu(II), and Pt(IV)/Pd(II) pairs were 330.27, 463.91, 359.89, and 4.85, respectively, which are much greater than those of nonimprinted polymers even if the similar surface area (40.02 m2 g−1) and pore volume (0.2912 cm3 g−1) of the nonimprinted polymer particles are quite similar to those of imprinted ones. The selectivity coefficient for Pt(IV)/Pd(II) pair, 4.85, is still higher than that of the previously reported imprinted system, 0.03.18 3.4.5. The Selective Separation of Pt(IV) from the Spent Catalysts Solution. Figure 9 shows the separation behavior of Pt(IV) from the spent catalyst solution using Pt(IV)-IIPs particles. Pt(IV)-IIPs exhibited excellent selective separation property toward Pt(IV) ion over other ions form this study. The presence of other interfering ions had no effect on selective sorption property of Pt(IV)-IIPs, and it showed their potential industrial applications. In this experiment, the adsorption experiment was conducted in the batch mode. The equilibrium adsorption capacity was measured from the sorption amount of each metal ion which was actually determined from the difference between initial and equilibrium ion concentrations in the mixture using FAAS. Thus, all experimental data about % recovery (based on this difference between initial and equilibrium ion concentration in mixture) are kept in our file. As this % recovery, however, is totally dependent on the

Figure 5. SEM images of particle and pore structures of Pt(IV)- IIPs.

Figure 6. Effect of pH on the adsorption capacity of Pt(IV)-IIP particles.

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Figure 9. Selective adsorption behavior of Pt(IV)- IIP particles for the spent catalysts solution.

determines the effectiveness of adsorbents in the industrial separation process. If the adsorption takes place too slowly, the packed column efficiency in a continuous process is so low that the column height must be very tall, and enough to establish long residence time. In the Pt(IV)-IIP cases examined, almost all Pt(IV) ions were adsorbed on polymer adsorbents within 40 min in Figure 10.

Figure 8. Selective adsorption behavior of (a) Pt(IV)- IIP and (b) NIP particles.

Table 1. Distribution Ratio (D), Selectivity Factor (α) of Pt(IV)-IIP and NIP Particles distribution ratio and selectivity coefficient

Pt(IV)-IIPs

NIPs

DPt DPd DCu DNi DZn α(Pt/Pd) α(Pt/Cu) α(Pt/Ni) α(Pt/Zn)

802.56 165.58 2.23 2.43 1.73 4.85 359.89 330.27 463.91

86.65 78.41 2.25 2.89 2.43 1.01 38.51 29.98 35.66

Figure 10. Adsorption kinetics for Pt(IV)- IIP particles.

The reutilization of Pt(IV) imprinted particles is also very important in industrial applications, as the Pt(IV) imprinted particles can be regenerated after all binding sites are occupied by metal ions. Figure 11 shows the adsorption−desorption cycle tests using the same IIPs for evaluating their adsorption capacity and selectivity. The recycled particles can still accommodate the ions to a high degree (up to 32 mg g−1) after 10 cycles, even though their capacities are gradually reduced by repeated utilization. This result demonstrates the good reutilization property of the Pt(IV) -IIPs. In order to regenerate Pt(IV)-IIP particles, the Pt(IV) adsorbed polymer particles, 0.1 g, were placed in 100 mL of 1 M HCl aqueous solution containing 1 wt % thiourea for at least 1 h under stirring.

amount (mass) of IIP particles or concentration of ion mixtures, we think it does not have such importance in scientific and technological meaning. If we increase the amount of IIP particles, the % recovery increases, but if we decrease it, vice versa. Also, the overall % recovery can be changed if there is a regeneration step of IIP particles. This is usually possible in continuous operation mode. 3.4.6. Adsorption Kinetics and Regeneration. The adsorption kinetics, characterized by the adsorption time to reach equilibrium, is a very important parameter that F

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(3) Kielhorn, J.; Melber, C.; Keller, D.; Mangelsdorf, I. PalladiumA review of exposure and effects to human health. Int. J. Hyg. Environ. Health 2002, 205, 417−432. (4) Hartley, F. R. The Chemistry of Platinum and Palladium; John Wiley & Sons: New York, 1973. (5) Ozturk, N.; Bulut, V. N.; Duran, C.; Soylak, M. Coprecipitation of palladium(II) with 1,5-diphenylcarbazite−copper(II) and determination by flame atomic absorption spectrometry. Desalination 2011, 270, 130−134. (6) Suvardhan, K.; Babu, S. H.; Kumar, K. S.; Krishnaiah, L.; Reddy, A. V. R.; Chiranjeevi, P. Inductively coupled plazma-optical emission spectrometry for on-line determination of multitrace elements in environmental samples after preconcentration by using Borasus flabellifer inflorescence loaded with 2-propylpiperidine-1-carbodithioate. Chem. Biodivers. 2005, 2, 477−486. (7) Ramakul, P.; Yanachawakul, Y.; Leepipatpiboon, N.; Sunsandee, N. Biosorption of palladium(II) and platinum(IV) from aqueous solution using tannin from Indian almond (Terminalia catappa L.) leaf biomass: Kinetic and equilibrium studies. J. Chem. Eng. 2012, 193, 102−111. (8) Chassary, P.; Vincent, T.; Marcano, J. S.; Macaskie, L. E.; Guibal, E. Palladium and platinum recovery from bicomponent mixtures using chitosan derivatives. Hydrometallurgy 2005, 76, 131−147. (9) Ghaedi, M.; Shokrollahi, A.; Nikham, K.; Nikham, E.; Najibi, A.; Soylak, M. Cloud point extraction and flame atomic absorption spectrometric determination of cadmium(II), lead(II), palladium(II), and silver(I) in environmental samples. J. Hazard. Mater. 2009, 168, 1022−1027. (10) Hoffman, J. E. Recovering platinum-group metals from auto catalysts. J. Met. 1988, 40, 40−44. (11) Patthaveekongka, W.; Vijitchalermpong, N.; Pancharoen, U. Selective recovery of palladium from used aqua regia by hollow fiber supported with liquid membrane. Korean J. Chem. Eng. 2003, 20, 1092−1096. (12) Brooks, C. S. Metal Recovery from Industrial Waste; Lewis Publishers: Chelsea, MI, 1991. p 267. (13) Rao, T. P.; Daniel, S.; Gladis, J. M. Tailored materials for preconcentration or separation of metals by ion-imprinted polymers for solid-phase extraction (IIP-SPE). Trends Anal. Chem. 2004, 23, 28−35. (14) Daniel, S.; Gladis, J. M.; Rao, T. P. Synthesis of imprinted polymer material with palladium ion nanopores and its analytical application. Anal. Chim. Acta 2003, 488, 173−182. (15) Daniel, S.; Babu, P. E. J.; Rao, T. P. Preconcentrative separation of palladium(II) using palladium(II) ion-imprinted polymer particles formed with different quinoline derivatives and evaluation of binding parameters based on adsorption isotherm models. Talanta 2005, 65, 441−452. (16) Daniel, S.; Rao, P. P.; Rao, T. P. Investigation of different polymerization methods on the analytical performance of palladium(II) ion imprinted polymer materials. Anal. Chim. Acta 2005, 536, 197−206. (17) Godlewska-Zyłkiewicz, B.; Lesniewska, B.; Wawreniuk, I. Assessment of ion imprinted polymers based on Pd(II) chelate complexes for preconcentration and FAAS determination of palladium. Talanta 2010, 83, 596−604. (18) Lesniewska, B.; Kosinska, M.; Zylkiewicz, B. G.; Zambrzycka, E.; Wilczewska, A. Z. Selective solid phase extraction of platinum on an ion imprinted polymers for its electrothermal atomic absorption spectrometric determination in environmental samples. Microchim. Acta 2011, 175, 273−282. (19) Dam, H. A.; Kim, D. Metal ion imprinted polymer microspheres derived from copper methacrylate for selective separation of heavy metal ions. J. Appl. Polym. Sci. 2008, 108, 14−24. (20) Hoai, N. T.; Kim, D. Synthesis, structure, and selective separation behavior of copper-imprinted microporous polymethacrylate beads. AIChE J. 2009, 55, 3248−3254.

Figure 11. Reutilization behavior of Pt(IV)-IIP particles in adsorption of P(IV) ions.

4. CONCLUSION The selective adsorption behaviors of Pt(IV)-IIP particles toward Pt(IV) ions were investigated. Pt(IV)-IIPs were prepared by St and DVB in the presence of Pt(IV)/DMG/4VP self-assembled complexes by bulk polymerization method. The maximum adsorption capacity of Pt(IV) on IIP particles was about 38.89 mg g−1, and the acidic condition was favorable for quantitative enrichment. In comparison with the nonimprinted polymers, the ion-imprinted polymers prepared show enhanced selectivity toward Pt(IV) ions over several other competitive metal ions, including Pd(IV) ions. The selectivity coefficients of ion-imprinted particles for Pt(IV)/Ni(II), Pt(IV)/ Zn(II), Pt(IV)/ Cu(II), and Pt(IV)/Pd(II) systems were 330.27, 463.91, 359.89, and 4.85, respectively, which were much greater than those of nonimprinted particles. The time to reach equilibrium adsorption was very short, at 40 min. The study on the selective separation of Pt(V) from the spent catalyst solution also showed the potential industrial application of Pt(IV)-IIP particles. The Pt(IV) ion-imprinted particles can be repeatedly used after regeneration without considerable loss of adsorption capacity.

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AUTHOR INFORMATION

Corresponding Author

*Tel:+82-31-290-7250. Fax: +82-31-299-4700. E-mail: djkim@ skku.edu. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) Grant (NRF-2010-0027955) and NRF2012R1A2A1A05026313.

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