Carbon-Deposited TiO2: Synthesis, Characterization, and Visible

Dec 16, 2009 - Ewelina Kusiak-Nejman , Agnieszka Wanag , Łukasz Kowalczyk , Joanna Kapica-Kozar , Christophe Colbeau-Justin , María G. Mendez ...
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J. Phys. Chem. C 2010, 114, 933–939

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Carbon-Deposited TiO2: Synthesis, Characterization, and Visible Photocatalytic Performance Jing Zhong, Feng Chen,* and Jinlong Zhang Key Laboratory for AdVanced Materials and Institute of Fine Chemicals, East China UniVersity of Science and Technology, 130 Meilong Road, Shanghai 200237, China ReceiVed: October 13, 2009; ReVised Manuscript ReceiVed: NoVember 28, 2009

Carbon-deposited TiO2 (TiO2@C) was prepared with a one-pot hydrothermal process by using glucose as a carbon source. The physical properties of TiO2@C were studied by XRD, TG-DTA, HRTEM, and UV-vis diffuse reflectance spectra (DRS), while the chemical states of carbon were discussed via X-ray photoelectron spectroscopy (XPS). A graphite carbon layer was formed out of the TiO2 grain during the hydrothermal process via the dehydration of glucose, which consisted of not only Cn but also CsOH (and CsOsC) and CdO (and COO). TiO2@C has remarkable light absorption in the visible region. It was found that the photocatalytic activity of TiO2@C was greatly enhanced compared to noncarbon-TiO2 under visible irradiation. The photocatalyst with the highest photocatalytic activity for the degradation of Acid Orange 7 (AO7) was G15 TiO2@C, while that for the degradation of 2,4-dichlorophenol (2,4-DCP) was G5 TiO2@C. Two kinds of sensitization processes, carbon sensitization and dye sensitization, are responsible for the visible lightinduced photocatalysis of TiO2@C. Carbon sensitization reached its optimal condition in G5, while dye sensitization occurred in its maximum efficiency in G15. Introduction TiO2, as a cheap, nontoxic, and highly efficient photocatalyst, has been extensively studied and applied for degradation of organic pollutants, air purification, sterilization, and as a demister.1,2 Generally, TiO2, with a band gap of 3.2 eV, can only be excited by a small UV fraction of solar light, which accounts for only 3-5% of the solar energy.3-5 In the past decade, many works have been done to extend the photoresponse of the TiO2 to the visible region.3-16 Among these attempts, TiO2 doping, either with main group elements or transition metals, has been the most important approach for improving the photocatalytic performance of the catalyst.2-9 The dopants, such as C,2,6,12 N,3,5,15 B,8,9 and Fe3+,7 can produce new hybrid states in the band gap, which narrow the band gap and bestow significant visible light absorbance to the TiO2. Nonmetal elements such as N were always suggested permeating to the lattice of TiO2 and form O-Ti-N, Ti-ON, and Ti-NO species,3,5 which construct a hybrid orbital just above the valence band of TiO2. However, another explanation, which involves surface modification and interfacial sensitization, was also suggested by H. Kisch et al. based on their recent work.17 Melamine, in their work, was condensed stepwise to form a large conjugated structure, which acts as a visible-light sensitizer and confers visible light photocatalytic reactivity to TiO2 via an interfacial charge transfer process. The meaningful work17 initiated another possible strategy for shifting the photoresponse of TiO2 photocatalyst into the visible region. Some materials, such as graphite carbon materials, have a very similar large conjugated structure as above; thus, they should take a similar role in a graphite covered TiO2 (TiO2@C). Functional carbonaceous materials have been a hot topic because of their wide applications as adsorbents, catalysts, electrode materials, and others. Recently, several works have * To whom correspondence should be addressed. E-mail: fengchen@ ecust.edu.cn. Phone/Fax: +86-21-6425 2062.

been carried out to develop an easy hydrothermal approach for the synthesis of carbon spheres.18-21 X. Huang19 and Y. Li et al.20 prepared perfect spherical carbon with uniform nanopores by a hydrothermal route in 2001 and 2004, in which sugar and glucose were used as carbon sources. After their publications, many studies were done to prepare carbon spheres via a similar method.18,21,22 Further, some works began to combine the similar carbonaceous material with metal oxide hydrothermally, in which the resulting carbon acted either as a spherical shell or core.22-24 A. Thomas et al.22 prepared carbon spheres via a simple hydrothermal approach and then coated a metal oxide layer on the carbon sphere. Metal oxide hollow spheres were thus synthesized by removing the carbon cores via calcination. Y. Li et al.24 later developed a one-pot hydrothermal method to prepare core-shell nanostructures with carbonaceous shells and oxide cores (oxides@C). This work was thus carried out based on the latest progress in hydrothermal preparation of oxides@C. Using glucose, one of the common carbohydrates, as a carbon source, a carbonaceous shell was coated on TiO2 nanoparticles through a onepot hydrothermal method. The chemical state of carbon in the carbonaceous layer and the visible light photocatalytic activity of this TiO2-carbonaceous composite on both dye and colorless pollutants were studied, from which the role of the carbonaceous shell was supposed in the text. Experimental Section Catalyst Preparation. Carbon-deposited TiO2 (TiO2@C) nanoparticles were prepared by a one-pot hydrothermal method: A certain amount of glucose was dissolved in 78 mL of doubledistilled water to form a clear solution. A 2 mL portion of TiCl4 (0.018 mol) was added dropwise to 78 mL of the above glucose solution. After vigorous stirring for 10 min, the suspensions were transferred into autoclaves and kept at 180 °C for 4 h. After reaction, the autoclaves were cooled naturally in air, and the suspensions were isolated by filtration and washed with

10.1021/jp909835m  2010 American Chemical Society Published on Web 12/16/2009

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water several times. According to different concentrations of glucose solutions (0.0, 5.0, 15.0, 25.0, and 30.0 g/L), the corresponding product Gx series (G0, G5, G15, G25, G30) TiO2@C were obtained. In order to observe whether the chloride ion (byproduct) and the pH value would affect the photocatalytic activity of the final products, two referential TiO2 (GA15, g15) were prepared. GA15 was prepared with a very similar process as that of G15, except that TiCl4 was replaced by Ti(OC4H9)4 as the titanium source. In the case of g15, an additional modification was introduced into the GA15 synthesis process: 7.7 mL of HCl (37%, amount of Cl- was equivalent as that hydrolyzed from TiCl4 in G15 synthesis) was added into the glucose solution before Ti(OC4H9)4 was dropped. Catalyst Characterization. X-ray diffraction (XRD) analysis of the prepared photocatalysts was carried out at room temperature with a Rigaku D/max 2550 VB/PC apparatus using Cu KR radiation (λ ) 0.15406 nm) and a graphite monochromator, operated at 40 kV and 30 mA. Diffraction patterns were recorded in the angular range of 10-80° with a step width of 0.02° s-1. The surface morphologies and particle sizes were observed by high-resolution transmission electron microscopy (HRTEM, JEM-2011), using an accelerating voltage of 200 kV. To analyze the light absorption of the photocatalysts, UV-vis diffuse reflectance spectra (DRS) were obtained using a scan UV-vis spectrophotometer (Varian Cary 500) equipped with an integrating sphere assembly, while BaSO4 was used as a reference. Thermogravimetric and differential thermal analysis (TG-DTA) curves were recorded on a Rigaku TG8120 instrument at a heating rate of 10 °C min-1 under air using R-Al2O3 as the standard material. X-ray photoelectron spectroscopy (XPS) was recorded with a PerkinElmer PHI 5000C ESCA System with Al KR radiation operated at 250 W. The shift of binding energy was corrected using the C 1s level at 284.6 eV as an internal standard. Photoluminescence (PL) emission spectra were measured on a luminescence spectrometer (Cary Eclips) at room temperature under the excitation light at 550 nm. Photocatalytic Activity Test. The photocatalytic activity was evaluated by measuring the decomposition of the aqueous solution of Acid Orange 7 (AO7, 20 mg/L) and 2,4-dichlorophenol (2,4-DCP, 50 mg/L). A 1000 W halogen lamp was used as the light source of the homemade photoreactor, cooled with flowing water in a quartz cylindrical jacket around the lamp. The short wavelength components (λ < 420 nm) of the light were cut off using a glass optical filter. The distance between the lamp and the center of the quartz tube was 10 cm. For a typical photocatalytic experiment, a total of 0.06 g of catalyst powders was added to 60 mL of the above AO7 solution or 2,4-DCP solution in the quartz tube. Prior to irradiation, the suspensions were magnetically stirred in the dark for 30 min to ensure the establishment of an adsorption/desorption equilibrium. The above suspensions were kept under constant airequilibrated conditions before and during the irradiation. At given time intervals, about 4 mL aliquots were sampled, and centrifuged to remove the remaining particles. The residual AO7 or 2,4-DCP solution was then analyzed by recording variations in the UV-vis absorption of AO7 or 2,4-DCP using a Cary 100 ultraviolet-visible spectrometer. Results and Discussion Characterization of the Photocatalysts. The XRD patterns of the Gx series TiO2@C are shown in Figure 1. All samples are composed of anatase and rutile. The predominant phase for G0 is rutile, while those for G5, G15, and G30 are anatase.

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Figure 1. XRD patterns of Gx series TiO2@C: (a) G0; (b) G5; (c) G15; (d) G30.

TABLE 1: Average Crystal Sizes and Weight Percentage of Carbon Species of Different Samples sample

average crystala (nm)

carbon species contentb (wt %)

G0 G5 G15 G30

13.8 11.1 9.3 9.0

2.0 4.3 8.9 14.6

a Determined by XRD using the Scherrer equation. b Determined by TG/DTA.

The hydrolysis of TiCl4 presented an extremely acidic condition for TiO2 crystallite formation; therefore, rutile TiO2 was constructed prior to anatase TiO2 as for G0.25,26 The presence of glucose surely changed the phase formation process of TiO2 and preferred the construction of anatase. Glucose, as a multihydroxyl compound, tends to replace the water molecule and/or hydroxyl anion to chelate the titanium atom, which should take the responsibility for the formation of anatase. In our previous works, the presence of Ti chelator such as sulfate ion during the condensation process of [TiO6] octahedra led to the formation of anatase.27,28 The crystallinity of TiO2, however, was inhibited with the increase of the glucose dosage. A similar result was also reported by L. Zhang et al.;29 the presence of glucose promoted the formation of anatase but deteriorated the crystallinity. The average crystal sizes of all of the samples are estimated using the Scherrer equation:

D)

Kλ β cos θ

where β is the half-height width of the diffraction peak of anatase or rutile, K ) 0.89 is a coefficient, θ is the diffraction angle, and λ is the X-ray wavelength corresponding to the Cu KR radiation. The crystallite sizes of G0, G5, G15, and G30 are shown in Table 1, with the corresponding weight percentage of practical deposited carbon. It is suggested that the average grain size decreased with the increase of deposited carbon species, indicating that carbon depositing had a depression effect on the grain growth. Figure 2 presents the TEM and HRTEM images of asprepared TiO2 sample G0 and carbon-deposited samples G5, G15, and G30. The as-prepared G0 photocatalyst was nanorod, G15 and G30 were nanospheres, and G5 gave an interim

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Figure 3. UV-vis DRS of Gx series TiO2.

Figure 2. TEM images of (A) G0, (B) G5, (C) G15, and (D) G30. Insets: corresponding HRTEM images.

morphology between nanorod and nanosphere. Hydrothermal synthesis of TiO2 from TiCl4 usually results in anisotropic growth and gives nanorod, which had been observed in our previous work and A. Testino’s literature.26,28 The average grain size of TiO2 decreased with the increase of the carbon deposition, which confirmed the results calculated from XRD data. The HRTEM image of G0 shows clear rutile (110) lattice fringes with long order, which confirmed that the nanorod of G0 was composed of rutile crystallite. However, the TiO2 lattice fringes of G5, G15, and G30 are relatively dim, which is probably because of the interference of the deposited carbon layer on the TiO2 grain. Some new lattice fringes are observed at the edge of TiO2 grains for G5-G30, which are most likely to be (101) and (002)30,31 lattice fringes of graphite carbon. Other lattice fringes of graphite are, however, close to that of TiO2 in size, and thus cannot be distinguished from each other from HRTEM. It seems that the condensation of glucose resulted in carbon deposition on the TiO2 grains during the hydrothermal process. The lattice fringes of TiO2 with different orientations mean the aggregation of TiO2 grains, around which carbonaceous materials, observed as either disordered lattice fringes or the lattice fringes ascribed to graphite, are possibly presented. Hydrothermal preparation of TiO2 with glucose leads to the colorization of the TiO2. Although carbon itself can absorb visible light,32-34 the colorization of TiO2 was sometimes suggested as the C-doping in TiO2 and consequent forbidden gap narrowing to TiO2.6,33 The UV-vis DRS spectra of the Gx series TiO2 are thus shown in Figure 3. G5, G15, and G30 show significant enhancement of light absorption at a wavelength of 400-800 nm. Further, their absorbance is enhanced in sequence from G5 to G30 following with the increase of carbon content. As a result, TiO2@C should most probably have visible light photocatalytic reactivity for organic degradation. The Chemical States of Ti, O, and C in TiO2@C. Confused suggestions about the relationship of C and metal oxide (TiO2) through the hydrothermal treatment using glucose as the carbon source have been reported in the literature.22,23,29,35 A. Thomas et al. concluded that the condensation of glucose resulted in the generation of carbonaceous species, containing some hy-

Figure 4. TG curve of G30 for representation.

droxyl and carbonyl groups in the case of incomplete condensation.22,23 X. Lou et al.35 prepared carbon-coated SnO2 hydrothermally, finding that a glucose-derived, carbon-rich polysaccharide coating was formed on the SnO2 nanocores. However, L. Zhang et al.29 suggested that carbon element was diffused into the lattice of TiO2 and formed C-doped TiO2. A crude estimation on the state of carbon obtained from the TG curve of Gx series TiO2 in this work shows most of the carbon element here was not likely to be doped into the TiO2 lattice, as the burning of the carbon species burst at only 220 °C (Figure 4). In order to reveal the very essential part of the Gx series TiO2, the chemical states of as-prepared samples were carefully checked with XPS spectra. C1s fine XPS spectra of Gx series TiO2 are shown in Figure 5. The adsorbed carbon contaminants from the ambience were used as an internal standard to correct the binding energy in the spectra.36 The classification and amount of the deposited carbonaceous materials in the Gx series TiO2 were analyzed semiquantitatively with the XPS results. The C 1s signal is well fitted with three contributions. A main contribution at 284.6 eV was ascribed to Cn, while contributions at 286.4 and 288.4 eV were due to the CsOH (and CsOsC) and CdO (and COO),36-38 respectively. The C1s signal for G0 was ascribed to the adsorbed carbon contaminants from the ambience, which could be some hydrocarbons and carbonates. The significant increases of the C1s signals for G5, G15, and G30 were due to the deposited carbonaceous materials during the hydrothermal process. Figure 6A presents relationships of the total integrated area of C1s signal in XPS spectra and relative mass loss in TG/ DTA measurement with the glucose concentration. Both the

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Figure 5. C1s fine XPS spectra of (a) G0, (b) G5, (c) G15, and (d) G30.

Figure 6. (A) Total integrated area of the C1s signal in XPS spectra and relative mass loss in TG/DTA measurement vs the glucose concentration. (B) The integrated areas of Cn, CsOH, and CdO and the relative content of Cn vs the glucose concentration.

integrated area of C1s and the relative mass loss of samples were increased in direct proportion to the concentration of glucose. After deducting the peak area of the C1s signal for G0, i.e., signal for the adsorbed carbon contaminants, the integrated area of C1s signal for each sample was fitted strictly with the corresponding relative mass loss. Therefore, it is reasonable to semiquantify the deposited carbonaceous materials with XPS spectra. Y. Zhu and M. Titirici suggested previously that a two-stage reaction occurs during the hydrothermalization

Zhong et al. of glucose: formation of carbon species involves the dehydration of the carbohydrate and subsequent carbonization of the soformed organic compounds.22,23 Thus, OH and CdO groups observed in XPS were from non- or just partially dehydrated carbohydrates. The integrated areas of the three different species Cn, CsOH, and CdO were all increased with increasing glucose concentration (Figure 6B). However, the percentage of Cn in the total deposited carbonaceous was decreased with the deposited amount of carbonaceous species. As a kind of dehydration catalyst, TiO2 has a positive effect on the dehydration of glucose,39,40 which results in a relatively entire dehydration process near the TiO2 surface and a corresponding lower content of CsOH (and CsOsC) and CdO (and COO). The above results are also supported by FT-IR spectra of Gx series TiO2, in which a new peak appeared compared to G0 and increased from G5 to G30 at 1705 cm-1, which is attributed to CdO vibrations.20 With respect to the XPS spectra of O1s in Figure 7, four peaks of 529.6, 531.3, 532, and 533.5 eV have been fitted, which should be ascribed to TisOsTi (lattice O), CdO (and COO), TisOH, and CsOH (and CsOsC) species, respectively.37,41 According to Figure 8, the oxygen signals attributed to lattice O and TisOH decreased with increasing glucose concentration. The abrupt reduction of TisOH from G0 to G5 suggested the esterification of a surface hydroxyl group of TiO2 at the beginning of the carbon deposition. The intensifying of CdO and CsOH signals suggested a more limited dehydration with the increase of deposited carbon content, which was consistent with the results observed in C1s fine XPS spectra. The Ti 2p binding energies (Figure 7) of all of the samples are located at around 458.4 eV (Ti 2p3/2) and 464.4 eV (Ti 2p1/2) without any shift, which are in good agreement with pure TiO2.29,42 Although previous literature suggested a possible C-doping during the hydrothermal process,29 the main form of carbon element here should be deposited carbonaceous species on the surface of TiO2. The carbon element in the form of doping, if existing, must be limited to a very low extent, as neither Ti2p binding energy shift29,42 nor carbon species with binding energy around 282 eV (C-Ti)43,44 was observed. Visible Light Photocatalytic Performances of TiO2@C. Photocatalytic activity tests were investigated by the degradation of an aqueous solution of AO7 and 2,4-DCP under visible light irradiation. Figure 9A shows the degradation rate of AO7 in the presence of G0, G5, G15, G25, and G30 and two reference TiO2 (GA15, g15). The visible light photocatalytic degradation of AO7 was greatly improved with carbon depositing. Compared to the AO7 degradation rate of 23% with G0, 80, 99, and 66% were found with G5, G15, and G30, respectively. G15 presented the highest photocatalytic reactivity for the AO7 degradation among all samples, which demonstrates an optimum glucose concentration of 15 g/L for TiO2@C composite by hydrothermal preparation. The degradation rate of reference TiO2 (GA15, g15) was also studied, for inorganic anions (Cl- in this system) may be adsorbed on the surface active site45,46 to affect the reactivity of the catalyst. It is found in Figure 9A that G15 has obviously the highest photocatalytic activity, while the degradation rates of GA15 and g15 are 49 and 59%, respectively. The higher activity of G15 may be due to the different hydrolytic and condensation kinetics of TiCl4 from that of Ti(OC4H9)4. The relatively close value of the degradation rate of AO7 with GA15 and g15 shows that Cl- has limited influence on the photocatalytic performance of the TiO2@C photocatalyst in this work.

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Figure 7. O1s and Ti2p fine XPS spectra of (a) G0, (b) G5, (c) G15, and (d) G30.

Figure 8. Integrated areas of Ti-O-Ti, C-O-C, Ti-OH, and C-OH species vs the glucose concentration.

Surely, TiCl4 is a better titanium source than Ti(OC4H9)4 for the preparation of TiO2@C photocatalyst. Visible light-induced photocatalytic degradation of colorless 2,4-DCP is also shown in Figure 9B. Different from that in the degradation of colored AO7, G5 showed the highest photocatalytic activity in this case, although undeposited TiO2 G0 still had the lowest photocatalytic activity.

Possible Mechanism in Visible Light Photocatalysis with TiO2@C. Chemical species, such as polymer, fullerene, and doped carbon, sometimes can be photosensitizers.32,47,48 R. Qiu47 et al. also prepared a polymer [poly(fluorene-co-thiophene)] sensitized TiO2 and proved that electron transfer took place between the polymer and TiO2. E. Hotze et. al48 described photosensitive reactive oxygen species generation by a hydroxylated C60 fullerene (fullerol). Lettmann32 suggested that carbon residues formed during calcination are responsible for the photosensitization of TiO2, and confirmed this by testing the photocurrent generated by visible light irradiation. Therefore, carbon species coating on the surface of TiO2 are likely to carry out a charge transfer process and responsible for the photosensitized photocatalysis. Except for the sensitization effect of carbon itself, dye sensitization can also be an important factor on photocatalytic activity. The electron transfer from dye molecule to TiO2 would induce a fluorescence quenching of the dye, which was studied in Figure 10A. According to the photoluminescence intensity of rhodamine B (RhB, 5 mg/L) solution with different concentrations of samples (0, 0.3, 1, and 1.5 mg/mL), the value of -ln(I/I0) was calculated and shown in Figure 10A. Figure 10B shows adsorption of RhB on the surface of TiO2@C. The adsorption of RhB increased in sequence from G0 to G30; however, the highest photoquenching of RhB was carried out

Figure 9. (A) Photocatalytic degradation rate of AO7 for 4 h. (B) Photocatalytic degradation rate of 2,4-DCP for 5 h under visible light illumination.

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Figure 10. (A) Fluorescence intensities of Gx in different concentrations. (B) Adsorption rate of RhB (1.0 mg of catalyst/mL of RhB solution) for 4 h.

with G15. Therefore, the high photoquenching of RhB with G15 was not just because of the adsorption, as RhB adsorbed more on G30. The charge transfer process from the excited dye molecules to TiO2@C should play an essential role for the photoquenching of RhB. In a word, the photoexcited RhB molecule has the fastest charge transfer on the surface of G15, which agreed well with the photocatalytic degradation of colored AO7. Thus, two kinds of sensitization processes, carbon sensitization and dye sensitization, could occur in the visible lightinduced photocatalytic reaction of TiO2@C. Carbon sensitization can take place in the degradation of either colorless or colored targets, in which the excited deposited carbon transfers electrons to the conductive band of TiO2 to initiate the reaction. Carbon sensitization confers an inherent visible light photocatalytic activity to TiO2@C. G5 TiO2@C reaches the optimal condition for the carbon sensitization. A further carbon deposition seems adverse for the carbon sensitization, which may be due to the more limited dehydration of carbohydrates at the place away from the surface of TiO2, as shown in XPS and FTIR spectra. Dye sensitization takes place in the case of dye degradation with TiO2@C. The recombination of injected electron with dye cation radical is the main problem to be solved for increasing the photon efficiency in either the dye-sensitized photocatalysis or dye-sensitized solar cell. It had been reported previously that an inert interlayer with a limited thickness (0.7-1 nm) between the adsorbed dye and TiO2 increased the electron transfer efficiency under irradiation.49 It seems a carbon layer with a limited thickness also benefits the dye-sensitization process, and the optimal thickness of the carbon layer could be calculated as 0.27 nm (D ) 9.3 nm for G15 and assuming a homogeneous coating thickness) in the dye-sensitization photocatalysis for TiO2@C in this work. However, dye sensitization can only be raised in the presence of colored target organics. Conclusions TiO2@C was prepared with a one-pot hydrothermal process by using glucose as a carbon source. The presence of glucose inhibits the formation of rutile in strong acidic conditions, resulting in the generation of anatase. HRTEM and XPS results showed that a graphite carbon out-layer was formed on the TiO2 grain surface during the hydrothermal process via the dehydration of glucose. TiO2@C has remarkable light absorption in the visible region. The photocatalyst with the highest photocatalytic activity in the degradation of AO7 was G15 TiO2@C, while

that in the degradation of 2,4-DCP was G5 TiO2@C. Two kinds of sensitization processes, carbon sensitization and dye sensitization, are responsible for the visible light-induced photocatalysis of TiO2@C. Carbon sensitization reached its optimal condition in G5, while dye sensitization occurred in its maximum efficiency in G15. Acknowledgment. This work was supported by the National Science Foundation of China (20777015). References and Notes (1) Hoffmann, M. R.; Martin, S. T.; Choi, W.; Bahnemann, D. W. Chem. ReV. 1995, 95, 69. (2) Khan, S. U. M.; Al-Shahry, M.; Ingler, W. B., Jr. Science 2002, 297, 2243. (3) Cong, Y.; Zhang, J. L.; Chen, F.; Anpo, M. J. Phys. Chem. C 2007, 111, 6976. (4) Cong, Y.; Zhang, J. L.; Chen, F.; Anpo, M.; He, D. N. J. Phys. Chem. C 2007, 111, 10618. (5) Xing, M. Y.; Zhang, J. L.; Chen, F. Appl. Catal., B 2009, 89, 563. (6) Kang, I. C.; Zhang, Q. W.; Yin, S.; Sato, T.; Saito, F. Appl. Catal., B 2008, 80, 81. (7) Aran˜a, J.; Dı´az, O. G.; Saracho, M. M.; Rodrı´guez, J. M. D.; Melia´n, J. A. H.; Pen˜a, J. P. Appl. Catal., B 2001, 32, 49. (8) Bettinelli, M.; Dallacasa, V.; Falcomer, D.; Fornasiero, P.; Gombac, V.; Montini, T.; Romano`, L.; Speghini, A. J. Hazard. Mater. 2007, 146, 529. (9) In, S.; Orlov, A.; Berg, R.; Garcı´a, F.; Pedrosa-Jimenez, S.; Tikhov, M. S.; Wright, D. S.; Lambert, R. M. J. Am. Chem. Soc. 2007, 129, 13790. (10) Irie, H.; Kamiya, K.; Shibanuma, T.; Miura, S.; Tryk, D. A.; Yokoyama, T.; Hashimoto, K. J. Phys. Chem. C 2009, 113, 10761. (11) Abe, R.; Takami, H.; Murakami, N.; Ohtani, B. J. Am. Chem. Soc. 2008, 130, 7780. (12) Sakthivel, S.; Kisch, H. Angew. Chem., Int. Ed. 2003, 42, 4908. (13) Neumann, B.; Bogdanoff, P.; Tributsch, H.; Sakthivel, S.; Kisch, H. J. Phys. Chem. B 2005, 109, 16579. (14) Sakthivel, S.; Kisch, H. ChemPhysChem 2003, 4, 487. (15) Sakthivel, S.; Janczarek, M.; Kisch, H. J. Phys. Chem. B 2004, 108, 19384. (16) Lindgren, T.; Mwabora, J. M.; Lindquist, S.-E. J. Phys. Chem. B 2003, 107, 5709. (17) Mitoraj, D.; Kisch, H. Angew. Chem., Int. Ed. 2008, 47, 9975. (18) Demir-Cakan, R.; Baccile, N.; Antonietti, M.; Titirici, M. Chem. Mater. 2009, 21, 484. (19) Wang, Q.; Li, H.; Chen, L. Q.; Huang, X. J. Carbon 2001, 39, 2211. (20) Sun, X. M.; Li, Y. D. Angew. Chem., Int. Ed. 2004, 43, 597. (21) Titirici, M.; Thomas, A.; Antonietti, M. AdV. Funct. Mater. 2007, 17, 1010. (22) Titirici, M.; Antonietti, M.; Thomas, A. Chem. Mater. 2006, 18, 3808. (23) Shen, W. H.; Zhu, Y. F.; Dong, X. P.; Gu, J. L.; Shi, J. J. Chem. Lett. 2005, 34, 840. (24) Sun, X. M.; Liu, J. F.; Li, Y. D. Chem. Mater. 2006, 18, 3486.

Carbon-Deposited TiO2 (25) Li, G. H.; Gray, K. A. Chem. Mater. 2007, 19, 1143. (26) Testino, A.; Bellobono, I. R.; Buscaglia, V.; Canevali, C.; D’Arienzo, M.; Polizzi, S.; Scotti, R.; Morazzoni, F. J. Am. Chem. Soc. 2007, 129, 3564. (27) Yan, M. C.; Chen, F.; Zhang, J. L.; Anpo, M. J. Phys. Chem. B 2005, 109, 8673. (28) Tian, B. Z.; Chen, F.; Zhang, J. L.; Anpo, M. J. Colloid Interface Sci. 2006, 303, 142. (29) Ren, W. J.; Ai, Z. H.; Jia, F. L.; Zhang, L. Z.; Fan, X. X.; Zou, Z. G. Appl. Catal., B 2007, 69, 138. (30) Dobb, M. G.; Guo, H.; Johnson, D. J. Carbon 1995, 33, 1115. (31) Oshida, K.; Nakazawa, T.; Miyazaki, T.; Endo, M. Synth. Met. 2002, 125, 223. (32) Lettmann, C.; Hildenbrand, K.; Kisch, H.; Macyk, W.; Maier, W. F. Appl. Catal., B 2001, 32, 215. (33) Kuo, C. S.; Tseng, Y. H.; Huang, C. H.; Li, Y. Y. J. Mol. Catal. A: Chem. 2007, 270, 93. (34) Naoe, H.; Hasegawa, S.; Heintzenberg, J.; Okada, K.; Uchiyama, A.; Zaizen, Y.; Kobayashi, E.; Yamazaki, A. Atmos. EnViron. 2009, 43, 1296. (35) Lou, X. W.; Chen, J. S.; Chen, P.; Archer, L. A. Chem. Mater. 2009, 21, 2868. (36) Rockafellow, E. M.; Fang, X. X.; Trewyn, B. G.; Schmidt-Rohr, K.; Jenks, W. S. Chem. Mater. 2009, 21, 1187.

J. Phys. Chem. C, Vol. 114, No. 2, 2010 939 (37) An, G. M.; Ma, W. H.; Sun, Z. Y.; Liu, Z. M.; Han, B. X.; Miao, S. D.; Miao, Z. J.; Ding, K. L. Carbon 2007, 45, 1795. (38) Choukourov, A.; Grinevich, A.; Polonskyi, O.; Hanus, J.; Kousal, J.; Slavinska, D.; Biederman, H. J. Phys. Chem. B 2009, 113, 2984. (39) Kim, K. S.; Barteau, M. A. J. Catal. 1990, 125, 353. (40) Bowker, M.; Stone, P.; Bennett, R.; Perkins, N. Surf. Sci. 2002, 511, 435. (41) Zschoerper, N. P.; Katzenmaier, V.; Vohrer, U.; Haupt, M.; Oehr, C.; Hirth, T. Carbon 2009, 47, 2174. (42) Song, Z.; Hrbek, J.; Osgood, R. Nano Lett. 2005, 5, 1327. (43) Chen, L. C.; Ho, Y. C.; Guo, W. S.; Huang, C. M.; Pan, T. C. Electrochim. Acta 2009, 54, 3884. (44) Wang, X. X.; Meng, S.; Zhang, X. L.; Wang, H. T.; Zhong, W.; Du, Q. G. Chem. Phys. Lett. 2007, 444, 292. (45) Abdullah, M.; Low, G. K. C.; Matthews, R. W. J. Phys. Chem. 1990, 94, 6820. (46) Wang, K.; Zhang, J. Y.; Lou, L. P.; Yang, S. Y.; Chen, Y. X. J. Photochem. Photobiol., A 2004, 165, 201. (47) Zhang, D. D.; Qiu, R. L.; Song, L.; Eric, B.; Mo, Y. Q.; Huang, X. F. J. Hazard. Mater. 2009, 163, 843. (48) Badireddy, A. R.; Hotze, E. M.; Chellam, S.; Alvarez, P.; Wiesner, M. R. EnViron. Sci. Technol. 2007, 41, 6627. (49) Palomares, E.; Clifford, J. N.; Haque, S. A.; Lutz, T.; Durrant, J. R. J. Am. Chem. Soc. 2003, 125, 475.

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