Magnetic Poly(methyl methacrylate

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Ind. Eng. Chem. Res. 2009, 48, 7616–7623

Platinum-Doped TiO2/Magnetic Poly(methyl methacrylate) Microspheres as a Novel Photocatalyst Yi-Hung Chen,*,† Matthias Franzreb,‡ Rong-Hsien Lin,§ Li-Lin Chen,§ Ching-Yuan Chang,| Yue-Hwa Yu,| and Pen-Chi Chiang| Department of Chemical Engineering and Biotechnology, National Taipei UniVersity of Technology, Taipei 106, Taiwan, Institute for Technical Chemistry, Forschungszentrum Karlsruhe GmbH, Karlsruhe 76021, Germany, Department of Chemical and Material Engineering, National Kaohsiung UniVersity of Applied Sciences, Kaohsiung 807, Taiwan, and Graduate Institute of EnVironmental Engineering, National Taiwan UniVersity, Taipei 106, Taiwan

The study focuses on the characterization of platinum-doped titanium dioxide-coated magnetic poly(methyl methacrylate) (Pt-TiO2/mPMMA) microspheres as a novel photocatalyst. The Pt-TiO2/mPMMA microspheres were prepared by a modified suspension polymerization process, followed by titania-coating and Pt-doping. The Pt-TiO2/mPMMA microspheres were synthesized with various Pt-doping levels in the range of 0.6-1.5 wt % TiO2 for comparison. The morphology, composition, Pt-doping content, and magnetic properties of the Pt-TiO2/mPMMA microspheres were characterized using scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, and superconducting quantum interference device. As a result, the superparamagnetic Pt-TiO2/mPMMA microspheres were successfully synthesized with particle sizes of 5-11 µm. The magnetite and TiO2 contents of the Pt-TiO2/mPMMA microspheres were estimated as 7.69 and 16.7 wt %, respectively, while the corresponding saturation magnetization was measured as about 4.39 emu/g. Furthermore, the doped Pt nanoparticles in the metallic state were found to have a particle density of (27.5-33.5) × 108 cm-2 on the surface of the PtTiO2/mPMMA microspheres. This density was found to increase with the synthesized Pt-doping concentration. The photocatalytic activity of the Pt-TiO2/mPMMA microspheres was further examined using the photodegradation of dimethyl phthalate in an aqueous solution. Dimethyl phthalate as one of the most common phthalic acid esters has been frequently detected in wastewater effluents and river water. Furthermore, the concentration of total organic carbons was monitored as an index of mineralization. A distinct photocatalytic efficiency improvement was shown with the employment of the Pt-TiO2/mPMMA microspheres as compared to the TiO2/mPMMA microspheres or direct photolysis. 1. Introduction Magnetic composites such as magnetic polymer microspheres have generated great interest in the biotechnology and medicine fields in recent years.1,2 These magnetic polymer microspheres can be effectively separated and collected in an applied magnetic field3 that is considered appropriate for application to the areas of cell isolation, enzyme immobilization, protein and enzyme purification, water treatment, and drug targeting.4-9 The synthesis of magnetic polymer particles has proceeded via several different polymerization processes, including emulsion,10,11 miniemulsion,12 dispersion,13 suspension,14-17 and seed18 polymerization methods. Of these, suspension polymerization is considered simpler and more feasible for the large-scale production of magnetic polymer microspheres.19 However, the magnetic polymer microspheres obtained from conventional suspension polymerization usually exhibit a relatively large particle size of ∼100 µm and a broader particle size distribution,20 which renders them less useful for certain applications. Recently, Ma et al.,19,20 Yang et al.,21 Tseng et al.,22 and Chen et al.23 proposed a modified suspension polymerization for the preparation of magnetic polymer microspheres. The novel characteristic of the modified suspension polymerization is the * To whom correspondence should be addressed. Tel.: +886-2-27712171ext. 2539. Fax: +886-2-8772-4328. E-mail: [email protected]. † National Taipei University of Technology. ‡ Forschungszentrum Karlsruhe GmbH. § National Kaohsiung University of Applied Sciences. | National Taiwan University.

introduction of nanosized oleic acid-coated magnetite (Fe3O4) particles (OMP) into the suspension polymerization system for the production of magnetite-encapsulated polymer particles. The magnetic polymer microspheres thus obtained would have a particle diameter of several micrometers along with a narrow size distribution and high magnetite content. With these advantages, the resulting magnetic polymer microspheres can be used as an ideal magnetic adsorbent or carrier after further surface modification.19-22,24,25 The usability of these magnetic polymer microspheres is significantly improved through the employment of magnetic separation. Titanium dioxide (TiO2) pigment is a fine white powder that creates excellent whiteness and opacity for paints, plastics, and paper. In addition, TiO2 is known to be a promising and practical photocatalyst in the removal of organic pollutants.26,27 However, the commercial TiO2 photocatalyst usually exhibits a small particle size and is hard to recover after use. It tends to accumulate or cause blockages in instruments, thus limiting its practical use. The TiO2-coated magnetic poly(methyl methacrylate) (TiO2/mPMMA) microspheres that can be applied in the slurry photocatalytic reactor and overcome the difficulty in recovering by the magnetic separation have been synthesized.28 Nevertheless, there is still room for improvement in the photocatalytic activity of the commercial TiO2 particles. Many studies have attempted to improve the photocatalytic activity of TiO2 by doping with noble metals such as platinum (Pt), which acts as an electron acceptor.29-31 The capture of photogenerated electrons by the doped Pt particles is postulated

10.1021/ie900509t CCC: $40.75  2009 American Chemical Society Published on Web 07/09/2009

Ind. Eng. Chem. Res., Vol. 48, No. 16, 2009

to suppress the recombination of electron-hole pairs and facilitate the transfer of holes on the TiO2 surface. Thus the photocatalytic efficiency can be enhanced in the context of a longer electron-hole pair separation lifetime. This study investigates the characteristics of a novel photocatalyst, namely, Pt-doped TiO2/mPMMA (Pt-TiO2/mPMMA) microspheres. The Pt-TiO2/mPMMA microspheres were prepared using a modified suspension polymerization followed by titania-coating and Pt-doping processes. The Pt-TiO2/mPMMA microspheres were synthesized with various Pt-doping concentrations in the range of 0.6-1.5 wt % TiO2. The morphology, composition, doped Pt content, and magnetic properties of the Pt-TiO2/mPMMA microspheres were characterized. Furthermore, the photocatalytic activity of the Pt-TiO2/mPMMA microspheres under UV radiation illumination was evaluated in terms of the removal and mineralization rates of dimethyl phthalate (DMP) in an aqueous solution. DMP is one of the most common phthalic acid esters. The chemical structure of DMP is composed of a benzene ring with methyl ester groups attached at the ortho-positions. DMP has been used as a plasticizer in tools, automotive parts, toothbrushes, food packaging, cosmetics, and insecticide, etc. DMP has been frequently detected in wastewater effluents and river water because of its high mobility in the aquatic system.32 2. Materials and Methods 2.1. Materials. Ferric chloride hexahydrate (FeCl3 · 6H2O, 99%), ferrous chloride tetrahydrate (FeCl2 · 4H2O, 99%), ammonium hydroxide (NH4OH, 25%), and methyl methacrylate (MMA), all reagent grade, were purchased from Merck (Darmstadt, Germany). Oleic acid was obtained from Nacalai Tesque (Kyoto, Japan). Poly(vinyl alcohol) (PVA; molecular weight, 22000 g/mol) was obtained from Acros (Geel, Belgium). Methylene blue trihydrate was purchased from MP Biomedicals (Irvine, CA). Divinylbenzene (DVB) was purchased from Tokyo Chemical Industry (Tokyo, Japan). Benzoyl peroxide (BPO) was obtained from Fluka (St. Gallen, Switzerland). Hexane was purchased from Hayashi Pure Chemical Industries (Osaka, Japan). Degussa P25 TiO2 (Dusseldorf, Germany) with a primary particle size and specific surface area of 21 nm and 50 m2/g, respectively, was used. Methanol (methyl alcohol, ACS certified) was obtained from Mallinckrodt Chemicals (Phillipsburg, NJ). Dihydrogen hexachloroplatinate hexahydrate (IV) (H2PtCl6 · 6H2O) with a purity of 99.9% was purchased from W. C. Heraeus GmbH (Hanau, Germany). 2.2. Preparation of OMP. The co-precipitation method is used to create nanosized OMP. A 23.5 g amount of FeCl3 · 6H2O and 8.6 g of FeCl2 · 4H2O were dissolved in 500 mL of deionized water under a continuous nitrogen purge. The temperature of the solution was maintained at 85 °C, and 27.8 mL of NH4OH was added rapidly. Subsequently, 15 mL of oleic acid was added dropwise into the solution over 10 min. The stirring speed was controlled at 600 rpm until the blocklike magnetite gel appeared. The resulting magnetite gel, the aggregate of the OMP, was cooled to room temperature and washed several times with deionized water. 2.3. Preparation of Pt-TiO2/mPMMA Microspheres. First the mPMMA microspheres were prepared by modified suspension polymerization. BPO (2 g) used as an initiator for the polymerization, 95 mL of MMA, 10 mL of DVB used as the cross-linker, and 30 mL of hexane used as the solvent were mixed with 15 g of OMP to form the organic phase, which was strongly agitated and subjected to ultrasonication for 3 min to ensure a homogeneous dispersion of the OMP. The water phase

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consisted of 25 g of PVA used as a stabilizer, 5 mL of methylene blue trihydrate, and 1000 mL of deionized water. MMA and DVB were purified by vacuum distillation prior to use. Other chemicals were used without further purification. Then the two phases were mixed at a stirring speed of 600 rpm in a reactor equipped with four vertical baffles under continuous nitrogen purge. The temperature of the synthetic solution was increased from 45 to 55 °C within 1 h, maintained at 60 °C for 2 h, and finally held at 70 and 80 °C for 1 h each. The temperature program of the polymerization is considered appropriate for the initiation by the BPO.20 After the synthesis process, the mPMMA microspheres were separated from the solution by a magnet and washed with deionized water and acetone in turn to remove the attached stabilizer and other impurities from the surface of the particles. The nonporous surface of the mPMMA particles has been demonstrated by using the mercury porosimeter23 that is advantageous to the titania-coating. Dried mPMMA microspheres (15 g) were thoroughly mixed with 45 g of TiO2 in a 500 mL beaker. The mixture was then placed in a high-temperature oven at 220 °C, which is close to the glass transition temperature of the mPMMA microspheres, to promote the adhesion of TiO2 particles onto the softened surface of the mPMMA microspheres. After 2 h at 220 °C, the beaker containing the TiO2/mPMMA microspheres and excess TiO2 particles was removed and cooled at room temperature. The TiO2/mPMMA microspheres were washed with deionized water and separated with a magnet to remove any nonadhered TiO2 particles. In the Pt-doping process, a 3.7 L aqueous solution consisting of three different weights (6, 10, or 15 g) of TiO2/mPMMA microspheres and 150 mL of methanol was held in a reactor and then purged with nitrogen to remove dissolved oxygen while being stirred by a mechanical stirrer at 300 rpm. The 15 mL H2PtCl6 · 6H2O solution with the Pt concentration of 1 g/L was then added into the solution. The pH of the solution was controlled at 3 ( 0.5 by using 0.1 M HNO3 solution and continuously purging with nitrogen. Afterward the mixed solution was irradiated by low-pressure mercury lamps (model PL-S 9W, Philips, Eindhoven, The Netherlands) at 365 nm for 24 h. The Pt-TiO2/mPMMA microspheres were subsequently separated by a magnet and washed with deionized water three times. The Pt-TiO2/mPMMA microspheres were dried and stored for subsequent analyses and applications. The Pt-TiO2/ mPMMA microspheres were synthesized with three Pt-doping contents based on TiO2 contents of 0.6, 0.9, and 1.5 wt %, which were denoted as 0.6, 0.9, and 1.5 wt % Pt-TiO2/mPMMA microspheres, respectively. The Pt-doping content was calculated, assuming the complete photoreduction of Pt ions on the surface of the TiO2/mPMMA microspheres. 2.4. Characterization of Pt-TiO2/mPMMA Microspheres. The morphology and elemental composition of the Pt-TiO2/ mPMMA microspheres were observed by scanning electron microscopy (SEM, Hitachi, model S-3000N, Tokyo, Japan) and energy dispersive spectrometry (EDS, Horiba, model EX-250, Tokyo, Japan), respectively. In addition, transmission electron microscopy (TEM, JEOL, model JEOL-2000EX, Tokyo, Japan) was utilized to investigate the structure of the microtomed PtTiO2/mPMMA microspheres. The crystal structure and X-ray photoelectron spectroscopy (XPS) profiles of the Pt-TiO2/ mPMMA microspheres were analyzed using wide-angle X-ray diffraction (XRD, Bruker AXS, model D8-Advance, Karlsruhe, Germany) and a Kratos Analytical spectrometer (model Axis Ultra DLD, Manchester, England), respectively. XPS was

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Figure 1. SEM images of magnetic TiO2/mPMMA and Pt-TiO2/mPMMA microspheres: (a) TiO2/mPMMA and (b) 0.60, (c) 0.90, and (d) 1.5 wt % PtTiO2/mPMMA microspheres.

employed to determine the chemical composition and oxidation state of the doped Pt. The magnetite and TiO2 contents of the Pt-TiO2/mPMMA microspheres were measured using thermogravimetric analysis (TGA, DuPont, model SDT2960, Wilmington, DE). The magnetization curves of the samples were recorded with a superconducting quantum interference device (SQUID, Quantum Design, model MPMS-XL7, San Diego, CA). 2.5. Photocatalytic Experiments of DMP in Aqueous Solution. The removal and mineralization of DMP in an aqueous solution were studied under different photocatalytic conditions. The photocatalysis of DMP with the 0.90 wt % Pt-TiO2/ mPMMA microspheres was compared with direct photolysis and with the TiO2/mPMMA microspheres. The initial concentration of DMP (CBLb0) was 0.15 mM (29.1 mg/L) with an initial concentration of total organic carbons (CTOC0) of about 18 mg/ L. The UV radiation intensity of 0.499 W/L at 254 nm was adopted as the average applied power of UV radiation per unit volume of the well-mixed reaction system.33 The applied dosage of the photocatalysts was 0.4 g/L in the reaction solution. The diffuse reflectance spectra of platinized and nonplatinized samples would show no differences in the UV range.34 Therefore, the Pt-TiO2/mPMMA microspheres can absorb the UV radiation at 254 nm as Degussa P25 TiO2. The concentration of DMP (CBLb) was analyzed using a highperformance liquid chromatography (HPLC) system with a 250 mm × 4.6 mm column (model ODS-2, GL Sciences Inc., Tokyo, Japan) and a diode array detector (model L-2455, Hitachi, Tokyo, Japan) at 230 nm.35 The HPLC solvent, at a flow rate of 1.0 mL/min, was composed of methanol/water at a 50:50 ratio. The injection volume of the analytical solution was 40

µL, while the detection limit of the DMP concentration was 0.01 mg/L. The TOC value of the solution (CTOC) was monitored by the TOC analyzer (model 1030W, OI Corp., College Station, TX). 3. Results and Discussion 3.1. Morphology of Pt-TiO2/mPMMA Microspheres. The morphology of the TiO2/mPMMA and Pt-TiO2/mPMMA microspheres with different Pt-doping contents is illustrated by the SEM micrographs (Figure 1). The TiO2/mPMMA and Pt-TiO2/mPMMA microspheres were found to have a roughly spherical shape. Compared with both the magnetic and nonmagnetic polymer microspheres prepared by the conventional suspension polymerization with the particle size distribution of 100-370 µm,36,37 the particle size of the TiO2/ mPMMA and Pt-TiO2/mPMMA microspheres prepared by the modified suspension polymerization is smaller and with a narrower distribution of 5-11 µm. In addition, the TiO2/ mPMMA and Pt-TiO2/mPMMA microspheres showing no significant size differences between the two groups exhibited a rougher surface than the original mPMMA microspheres23 due to the TiO2 particles that were coated on the mPMMA surface. The distribution patterns of the magnetite and TiO2 nanoparticles were assessed using the TEM images of the microtomed Pt-TiO2/mPMMA microspheres in Figure 2a, b. It is apparent that the magnetite nanoparticles are dispersed and encapsulated inside the Pt-TiO2/mPMMA microspheres. The shape of the OMP is close to a sphere with a particle diameter of about 8 nm.23 The Pt-doped TiO2 particles that cover the surface of the mPMMA microspheres form a


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Figure 2. TEM images of microtomed 0.90 wt % Pt-TiO2/mPMMA microspheres at magnifications of (a) 2k, (b) 10k, and (c) 100k.

multilayer coating with a thickness of about 100-160 nm. Moreover, the doping of the Pt nanoparticles for the TiO2 particles is shown in Figure 2c, revealing that the Pt nanoparticles are spherical in nature and exhibit a particle diameter of about 2 nm. Furthermore, the magnetite and TiO2 contents were estimated from the residual mass percentages of the dehydrated mPMMA and Pt-TiO2/mPMMA microspheres in the TGA runs at a heating rate of 20 °C/min under an air atmosphere. The organic materials and magnetite content were completely incinerated to generate gas products and iron oxides, respectively, at the elevated temperature (roughly over 500 °C).38,39 Accordingly, the magnetite and TiO2 contents of the Pt-TiO2/mPMMA microspheres are estimated as 7.69 and 16.7%, respectively. Moreover, the titania-coating and Pt-doping for the mPMMA microspheres can also be observed by the color change. The color of the mPMMA microspheres changed from light brown to red brown after the titania-coating process and became dark brown after the Pt-doping process. 3.2. Characterization of Pt-TiO2/mPMMA Microspheres. Figure 3 represents the elemental mappings of Pt for the aggregated TiO2/mPMMA and Pt-TiO2/mPMMA microspheres from the SEM/EDS analyses. Dots of Pt which were not apparent in the case of the TiO2/mPMMA microspheres would appear on the Pt-TiO2/mPMMA microspheres. As shown in Figure 3, the Pt nanoparticles are uniformly distributed on the surfaces of the Pt-TiO2/mPMMA microspheres. Furthermore, the Pt particle density can be calculated by counting the Pt dots on the elemental mapping images. The relationship between the Pt particle density and the Pt-doping content for the Pt-TiO2/ mPMMA microspheres is illustrated in Figure 4. Note that the

Pt particle density of (27.5-33.5) × 108 cm-2 increases with higher Pt-doping content. However, the ratio of the Pt particle density to the Pt-doping content decreases with higher Pt-doping content, thus showing an exponential relationship. The nonlinear relationship between the Pt particle density and Pt-doping content may be a result of the incomplete reduction or significant aggregation of Pt nanoparticles. To confirm the structure of the synthesized Pt-TiO2/ mPMMA microspheres, the XRD patterns of the TiO2/ mPMMA and Pt-TiO2/mPMMA microspheres are illustrated in Figure 5. In comparison with standard XRD patterns, the peaks of the four samples match the peaks of the reference crystalline metals obtained from the Joint Committee on Powder Diffraction Standards. The results demonstrate that the Pt-TiO2/mPMMA microspheres contain the expected components including the crystalline magnetite, TiO2 and Pt. Figure 6 shows the high-resolution XPS spectra of Pt 4f for the TiO2/mPMMA and Pt-TiO2/mPMMA microspheres. In these spectra, the XPS binding energies of the Pt 4f photoelectrons are distinctly present in terms of the chemical bonding states as Pt 4f7/2 (71.3 eV) and Pt 4f5/2 (74.9 eV) peaks. This confirms the existence of pure metallic Pt in agreement with the findings of the previous studies.30,40-42 One should note that metallic Pt has a higher activity than the oxidized Pt species such as PtII and PtIV.41 The magnetic properties of the Pt-TiO2/mPMMA microspheres were characterized by a SQUID magnetometer at room temperature, as shown in Figure 7. The magnetization of the samples would approach saturation when the applied magnetic field increased to 15000 Oe. All of the magnetization curves suggest typical superparamagnetic behavior

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Figure 3. Elemental mapping of Pt dots for aggregated mPMMA and Pt-TiO2/mPMMA microspheres from SEM/EDS analyses: (a) TiO2/mPMMA and (b) 0.60, (c) 0.90, and (d) 1.5 wt % Pt-TiO2/mPMMA microspheres.

Figure 4. Variation of Pt particle density with Pt-doping content for PtTiO2/mPMMA microspheres.

without the hysteresis loop. Furthermore, the values of the saturation magnetization (Ms), residual magnetization (Mr) per gram, remanence-to-saturation magnetization ratio (Mr/ Ms), and coercivity (Hc) of the samples are listed in Table 1. The superparamagnetic properties of the Pt-TiO2/mPMMA microspheres are also reflected in the small Mr/Ms and Hc values (Table 1). The Pt-TiO2/mPMMA microspheres have an Ms value of about 4.39 emu/g, which is smaller than that for the TiO2/mPMMA microspheres. However, one may address that the Ms of the synthesized Pt-TiO2/mPMMA microspheres is still of the same order of magnitude as those of the magnetic polymer carriers in the previous studies.20,36,43 The recovery efficiency of such microsized Pt-TiO2/mPMMA microspheres can be significantly enhanced with the use of magnetic separation instead of gravity separation that has

Figure 5. XRD patterns of TiO2/mPMMA and Pt-TiO2/mPMMA microspheres: (a) TiO2/mPMMA and (b) 0.60, (c) 0.90, and (d) 1.5 wt % PtTiO2/mPMMA microspheres.

been observed in the separation of the Pt-TiO2/mPMMA microspheres from the solution. 3.3. Photocatalytic Activity of Pt-TiO2/mPMMA Microspheres. The variations of CBLb/CBLb0 and CTOC/CTOC0 with time for the photodecomposition of DMP under different experimental conditions are shown in Figures 8 and 9, respectively. The direct UV photolysis of DMP is slow; by contrast, the photocatalysis with the TiO2/mPMMA or Pt-TiO2/mPMMA microspheres shows remarkably enhanced performance. Furthermore, the use of the Pt-TiO2/mPMMA microspheres achieves


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Figure 8. Variations of CBLb/CBLb0 with time for photodecomposition of DMP under different experimental conditions: (4) direct photolysis; photocatalysis with (0) TiO2/mPMMA and (O) 0.90 wt % Pt-TiO2/mPMMA microspheres.

Figure 6. XPS spectra of Pt 4f5/2 and Pt 4f7/2 for TiO2/mPMMA and PtTiO2/mPMMA microspheres.

Figure 9. Variations of CTOC/CTOC0 with time for photodecomposition of DMP under different experimental conditions. Notations and experimental conditions are the same as those specified in Figure 8.

Figure 7. Magnetization curves of (0) TiO2/mPMMA (obtained from Chen et al.28) and (O) 0.90 and (4) 1.50 wt % Pt-TiO2/mPMMA microspheres measured by SQUID. Table 1. Magnetic Properties of TiO2/mPMMA and Pt-TiO2/ mPMMA Microspheres samples a

TiO2/mPMMA 0.90 wt % Pt-TiO2/mPMMA 1.50 wt % Pt-TiO2/mPMMA a

Ms (emu/g) Mr (emu/g) Mr/Ms (-) Hc (Oe) 4.81 4.40 4.38

0.202 0.136 0.162

0.0421 0.0307 0.0368

13.1 10.5 11.1

be attributed to an enhancement of the quantum yield, thus producing greater oxidative species for the purpose of pollutant elimination. Apparently, the CTOC/CTOC0 value slightly varies in the initial photocatalytic stage, implying that the initial intermediates from the decomposition of DMP still contribute high TOCs relative to the initial value. The CTOC/CTOC0 would start to significantly decrease with time after the inactive stage. In addition, the PtTiO2/mPMMA microspheres have good stability in the photocatalytic experiments, while the leaching of the magnetite is insignificant. As a result, this study provides useful information about the preparation and characterization of the Pt-TiO2/ mPMMA microspheres.

Obtained from Chen et al.28

4. Summary the highest DMP removal and mineralization rates. The pseudofirst-order reaction rate constant of DMP (kB) in the expression of CBLb/CBLb0 ) e- kBt, which is applied to describe the elimination rate of DMP, is determined from the experimental data in Figure 8. The kB values in the photocatalytic processes with the TiO2/mPMMA and Pt-TiO2/mPMMA microspheres are 0.0066 and 0.015 min-1, respectively. It suggests that the doped Pt nanoparticles of the Pt-TiO2/mPMMA microspheres make a significant contribution to the photocatalytic activity. This can

Platinum-doped titanium dioxide-coated magnetic poly(methyl methacrylate) (Pt-TiO2/mPMMA) microspheres were successfully synthesized by a modified suspension polymerization followed by titania-coating and Pt-doping processes. Furthermore, the Pt-TiO2/mPMMA microspheres are characterized by the scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, and superconducting quantum interference device. The photocatalytic experiment of dimethyl

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phthalate (DMP) is employed to test the photocatalytic activity of the Pt-TiO2/mPMMA microspheres. The Pt-TiO2/mPMMA microspheres have a particle diameter of 5-11 µm, and the coated TiO2 layer exhibits a thickness of about 100-160 nm. The encapsulated magnetite and coated TiO2 contents of the Pt-TiO2/mPMMA microspheres are estimated at 7.69 and 16.7 wt %, respectively. The saturation magnetization of the Pt-TiO2/ mPMMA microspheres was recorded as about 4.39 emu/g. The Pt nanoparticles doped onto the TiO2 particles are in the metallic state, with particle diameters of about 2 nm. The Pt nanoparticles were incorporated at a particle density of (27.5-33.5) × 108 cm-2 on the surface of the Pt-TiO2/mPMMA microspheres that increased with increasing synthesized Pt-doping content. Furthermore, the Pt-TiO2/mPMMA microspheres present higher photocatalytic activity for both the elimination and mineralization of DMP in an aqueous solution compared to the direct photolysis and the use of TiO2/mPMMA microspheres. Consequently, the manufactured Pt-TiO2/mPMMA microspheres with good magnetic and photocatalytic properties can be used as a promising photocatalyst in the water treatment and effectively recovered through magnetic separation after use. In the future, the magnetic particles with the coating of composite catalysts may be synthesized to have the multifunctions or synergistic effect that can be applied in catalytic and/or adsorption processes. Acknowledgment This study was supported by the National Science Council of Taiwan under Grant No. NSC 96-2221-E-027-140-MY2. Literature Cited (1) Olsvik, Ø.; Popovic, T.; Skjerve, E.; Cudjoe, K. S.; Hornes, E. Magnetic Separation Techniques in Diagnostic Microbiology. Clin. Microbiol. ReV. 1994, 7, 43. (2) Landfester, K.; Ramı´rez, L. P. Encapsulated Magnetite Particles for Biomedical Application. J. Phys. Condens. Matter 2003, 15, 1345. (3) Hatch, G. P.; Stelter, R. E. Magnetic Design Considerations for Devices and Particles Used for Biological High-gradient Magnetic Separation (HGMS) Systems. J. Magn. Magn. Mater. 2001, 225, 262. (4) Kronick, P.; Gilpin, R. W.; Biochem, J. Use of Superparamagnetic Particles for Isolation of Cells. J. Biochem. Biophys. Methods 1986, 12, 73. (5) Li, X. H.; Sun, Z. G. Synthesis of Magnetic Polymer Microspheres and Application for Immobilization of Proteinase of Balillus Sublitis. J. Appl. Polym. Sci. 1995, 58, 1991. (6) Abudiab, T.; Beitle, R. R. Preparation of Magnetic Immobilized Metal Affinity Separation Media and Its Use in the Isolation of Proteins. J. Chromatogr., A 1998, 795, 211. (7) Kim, D. K.; Zhang, Y.; Voit, W.; Kao, K. V.; Kehr, J.; Bjelke, B.; Muhammed, M. Superparamagnetic Iron Oxide Nanoparticles for BioMedical Applications. Scr. Mater. 2001, 44, 1713. ¨ ztu¨rk, E. Magnetic (8) Denkbas¸, E. B.; Kiliçay, E.; Birlikseven, C.; O Chitosan Microspheres: Preparation and Characterization. React. Funct. Polym. 2002, 50, 225. (9) Dahlke, T.; Chen, Y. H.; Franzreb, M.; Ho¨ll, W. H. Continuous Removal of Copper Ions from Dilute Feed Streams Using Magnetic WeakBase Anion Exchangers in a Continuous Stirred Tank Reactor (CSTR). React. Funct. Polym. 2006, 66, 1062. (10) Kondo, A.; Kamura, H.; Higashitahi, K. Development and Application of Thermosensitive Magnetic Immunomicrospheres for Antibodies Purification. Appl. Microbiol. Biot. 1994, 41, 99. (11) Li, P.; Zhu, A. M.; Liu, Q. L.; Zhang, Q. G. Fe3O4/Poly(Nisopropylacrylamide)/Chitosan Composite Microspheres with Multiresponsive Properties. Ind. Eng. Chem. Res. 2008, 47, 7700. (12) Ramirez, L. P.; Landfester, K. Magnetic Polystyrene Nanoparticles with a High Magnetite Content Obtained by Miniemulsion Processes. Macromol. Chem. Phys. 2003, 204, 22. (13) Hora´k, D. Magnetic Polyglycidylmethacrylate Microspheres by Dispersion Polymerization. J. Polym. Sci., Part A: Polym. Chem. 2001, 39, 3707.

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ReceiVed for reView March 29, 2009 ReVised manuscript receiVed June 23, 2009 Accepted June 23, 2009 IE900509T

Magnetic Poly(methyl methacrylate

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