Enhancement of the Visible Light Photocatalytic Activity of C-Doped

ARTICLE pubs.acs.org/JPCC

Enhancement of the Visible Light Photocatalytic Activity of C-Doped TiO2 Nanomaterials Prepared by a Green Synthetic Approach Fan Dong,†,‡,§ Sen Guo,*,†,§ Haiqiang Wang,†,§ Xiaofang Li,†,§ and Zhongbiao Wu†,§ †

Department of Environmental Engineering, Zhejiang University, Hangzhou 310027, People’s Republic of China College of Environmental and Biological Engineering, Chongqing Technology and Business University, Chongqing, 400067, People’s Republic of China § Zhejiang Provincial Engineering Research Center of Industrial Boiler & Furnace Flue Gas Pollution Control, Hangzhou, 311202, People’s Republic of China ‡

bS Supporting Information ABSTRACT: Mesoporous C-doped TiO2 nanomaterials with an anatase phase are prepared by a one-pot green synthetic approach using sucrose as a carbon-doping source for the first time. A facile post-thermal treatment is employed to enhance visible light photocatalytic activity of the as-prepared photocatalyst. The enhancement effect of post-thermal treatment between 100 and 300 °C is proved by the photodegradation of gas-phase toluene, and the optimum temperature is 200 °C. Physicochemical properties of the samples are characterized in detail by X-ray diffraction, Raman spectroscopy, N2 adsorption desorption isotherms, transmission electron microscopy, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy, UV vis diffuse reflectance spectroscopy, and photoluminescence. The results indicate that the promotive effect of the postthermal treatment can be attributed to the changes of the catalysts’ surface and optical properties. The results also show that the recombination of electron hole pairs is effectively inhibited after thermal treatment due to the reduction of surface defects. The facile post-thermal treatment provides a new route for potential industrial applications of C-doped TiO2 nanomaterials prepared by a green approach owing to its low cost and easy scale-up.

1. INTRODUCTION Visible light photocatalysis has become the current topic of intensive interest due to its potential applications in solar energy conversion and environmental purification by utilizing visible light in a solar or indoor light source.1 8 The leading candidate photocatalyst, TiO2, however, requires ultraviolet light (about 5% of natural solar light) to initiate photocatalytic reaction due to its relatively wide band gap (ca. 3.2 eV for anatase TiO2). An effective approach to tackle this challenge is to dope TiO2 with nonmetal elements, such as C, N, S, and I, to extend the light absorbance of TiO2 into visible light.9 25 Numerous contributions have been devoted recently to developing effective nonmetal-doped TiO2 photocatalysts with visible light activity.9 25 Specially, carbon doping can significantly stabilize the anatase TiO2 and improve the adsorption of organic pollutant molecules on the catalyst surface.26,27 Besides, carbon doping can enhance the conductivity of TiO2, as it could facilitate the charge transfer from the bulk of the TiO2 structure to the surface region where the desired oxidation reactions take place.28,29 However, the doping of nonmetals into the lattice of TiO2 usually results in the formation of oxygen vacancies in the bulk. These defects can act as massive recombination centers of photoinduced electron hole pairs, which largely limit the visible light photocatalysis efficiency of r 2011 American Chemical Society

C-doped TiO2 for industrial applications.30 32 From the viewpoint of practical application, higher photocatalytic reaction efficiency is required because the photocatalytic efficiency of nonmetal-doped TiO2 under visible light is still low.33 35 The preparation method is another crucial factor that should be considered for applications. Traditional methods to prepare C-doped TiO2 include (1) high-temperature sintering of a carbon-containg TiO2 precursor, (2) CVD or pyrolysis, and (3) sol gel methods.36 41 Usually, for these methods, high-temperature treatment (400 850 °C) is required; expensive, toxic, or unstable precursors are used; undesirable gaseous byproducts are usually produced in the preparation process; and the procedures are somewhat tedious, which, in all, make the preparation cost high and large-scale application difficult.42 A green synthesis approach is efficient in scale-up and benign to human health and the environment, which is based on minimizing the number of preparation steps without utilizing either excessively harmful reagents or unstable precursors and without generating particularly toxic byproducts.42 Received: December 15, 2010 Revised: May 30, 2011 Published: June 08, 2011 13285

dx.doi.org/10.1021/jp111916q | J. Phys. Chem. C 2011, 115, 13285–13292

The Journal of Physical Chemistry C Therefore, it is of particular worth to develop an energyefficient and environmentally friendly approach to synthesize visible-light-active C-doped TiO2 from the viewpoint of energetic or environmental applications. At the same time, it is also significant to develop a facile method to enhance the visible light photocatalytic activity of C-doped TiO2, such as methods to reduce the number of defects for inhibiting the electron hole pair recombination or methods to further broaden the spectrum of visible light absorbance for utilizing more photoenergy. Previously, we prepared C-doped TiO2 with high visible light activity by a green synthetic approach using glucose as carbon doping source.42 A facile method was also developed to enhance the visible light activity of C-doped TiO2 by surface modification with V2O5.32 To make the green approach to synthesize C-doped TiO2 general, another kind of carbohydrate (sucrose) as a new carbon-doping source was used in the green synthetic route, which resulted in the successful preparation of mesoporous C-doped TiO2. However, for the large-scale applications of visible light photocatalytic materials, the activity of the as-prepared C-doped TiO2 needs to be further enhanced. In the present study, post-thermal treatment was carried out on the as-prepared C-doped TiO2 in order to improve the visible light activity. It was found that the visible light absorbance of the thermally treated sample can be broadened due to the increased doped carbon content and the recombination of electron hole pair can be effectively inhibited due to the reduction of defects. These promotive effects in all contributed to the significantly promoted visible light photocatalytic activity of C-doped TiO2. By combination of the green approach to prepare C-doped TiO2 and the facile route to enhance the visible light activity, a new effective route is already developed for large-scale applications of C-doped TiO2 nanomaterials owing to its low cost and easy scale-up.

2. MATERIALS AND METHODS 2.1. Photocatalyst Preparation. Chemicals used in the experiment were titanium sulfate, Ti(SO4)2 (CP, Sinopharm Chemical Reagent Co., Ltd., China), and sucrose, C12H22O11 (AR, Sinopharm Chemical Reagent Co., Ltd., China). Distilled water was used in all experiments. In a typical synthesis, appropriate amounts of Ti(SO4)2 and C12H22O11 were mixed with 70 mL of H2O in a 100 mL autoclave Teflon vessel and hydrothermally treated at 180 °C for 12 h. The sample obtained was filtered, washed with water three times, and dried at 60 °C to get the final C-doped TiO2 with no further treatment. The molar ratio of Ti(SO4)2 to C12H22O11 was controlled at 25:1. The resulting sample was labeled as C-TiO2. Undoped TiO2 was synthesized accordingly without addition of sucrose. To investigate the effect of post-thermal treatment on C-TiO2, the asprepared C-TiO2 was treated in air at 100, 200, and 300 °C for 2 h in a muffle furnace. The corresponding samples were labeled as C-TiO2-100, C-TiO2-200, and C-TiO2-300. 2.2. Characterization. The crystal phase of the samples was analyzed by X-ray diffraction with Cu KR radiation (XRD, model D/max RA, Rigaku Co., Japan). The accelerating voltage and the applied current were 40 kV and 150 mA, respectively. X-ray photoelectron spectroscopy with Al KR X-rays (hν = 1486.6 eV) radiation operated at 150 W (XPS, Thermo ESCALAB 250, USA) was used to investigate the surface properties and to probe the total density of states (DOS) distribution in the valence band. The shift of the binding energy due to relative surface charging was corrected using the C 1s level at 284.8 eV as an internal

ARTICLE

standard. Ar+ sputtering was applied to clean the surface of the samples. The morphology, structure, and grain size of the samples were examined by transmission electron microscopy (TEM, JEM2010, Japan). The UV vis diffuse reflection spectra were obtained for the dry-pressed disk samples using a Scan UV vis spectrophotometer (UV vis DRS, TU-1901, China) equipped with an integrating sphere assembly, using BaSO4 as the reflectance sample. The spectra were recorded at room temperature in air in the range from 230 to 800 nm. The photoluminescence (PL) spectra were measured by a fluorospectrophotometer (PL, Fluorolog-3-Tau, France) using a Xe lamp as the excitation source at room temperature. Raman spectra were recorded at room temperature using a micro-Raman spectrometer (Raman, RAMANLOG 6, USA) with a 514.5 nm Ar+ laser as the excitation source in a backscattering geometry. The incident laser power on the samples was less than 10 mW. The time of acquisition was varied according to the intensity of the Raman scattering. Nitrogen adsorption desorption isotherms were obtained on a nitrogen adsorption apparatus (ASAP 2020, USA). All the samples were degassed at 100 °C prior to measurements. 2.3. Photocatalytic Activity Tests. Photocaytalytic degradation of toluene in air is chosen as the probe reaction to test the activities of the as-prepared samples, as toluene is considered as a typical indoor pollutant.43,44 The photocatalytic activity tests were performed at room temperature using a 1.8 L photoreactor. The catalyst was prepared by coating an ethanol suspension of the catalyst onto a dish with a diameter of 12.5 cm. The weight of catalyst used for each test was kept at 0.20 g. The dish containing catalyst was dried at 60 °C for 1 h to evaporate the ethanol and then cooled to room temperature before being used. After the catalyst-coated dish was placed in the reactor, a small amount of toluene was injected into the reactor with a microsyringe. The analysis of the toluene concentration in the reactor was conducted with a GC-FID (FULI 9790, China). The toluene vapor was allowed to reach adsorption equilibrium in the reactor prior to irradiation. The initial concentration of toluene after adsorption equilibrium was controlled at 150 mg/m3. A 150 W Xe lamp with an IR cutter and a UV-cut optical filter (λ < 425 nm) was placed above the reactor as the light source. The temperature of the reactor was controlled at 25 ( 1 °C by continuous cooling air. The initial relative humidity was controlled at 60% by a CaCl2 dryer connected to the photoreactor. The photocatalytic activity of the catalyst samples can be quantitatively evaluated by comparing the apparent reaction rate constants (k). The photocatalytic oxidation of toluene is a pseudo-first-order reaction, and its kinetics can be expressed as follows: ln(C0/C) = kt, where C0 and C are the initial concentration and the reaction concentration of toluene, respectively.45,46

3. RESULTS AND DISCUSSION 3.1. Effect of Post-Thermal Treatment on the Photocatalytic Activity of C-Doped TiO2. The photocatalytic activity of

the as-prepared samples is evaluated by degradation of toluene in gas phase under visible light irradiation (λ > 425 nm). Figure 1a shows the change of the relative concentrations of toluene with irradiation time for C-doped TiO2 treated at different temperatures. It can be seen that undoped TiO2 (anatase, 3.2 eV) shows almost no activity. C-TiO2 prepared by green synthesis exhibits decent visible light photocatalytic activity (k, 0.026 min 1). As shown in our previous study, carbon doping could reduce the band gap of TiO2 and increase absorption in the visible region, 13286

dx.doi.org/10.1021/jp111916q |J. Phys. Chem. C 2011, 115, 13285–13292

The Journal of Physical Chemistry C

ARTICLE

Figure 1. (a) Visible light photocatalytic activities of C-doped TiO2 treated at different temperatures in the degradation of gaseous toluene. (b) The comparison of the corresponding reaction constants (min 1).

which provides C-doped TiO2 with an efficient visible light photocatalytic activity.42 The photocatalytic activities under UV and UV vis light irradiation are also tested (see the Supporting Information). Figure S1a (Supporting Information) shows that C-doped TiO2 exhibits higher activity under both UV and UV vis irradiation than that of undoped TiO2, although the specific surface areas (SBET) of undoped TiO2 are 118.97 m2/g higher that that of C-doped TiO2 (96.86 m2/g). If the reaction constant k is normalized by SBET, the increase of the activity under UV and UV vis irradiation is more significant, as shown in Figure S1b (Supporting Information). Thus, the carbon doping not only makes TiO2 visible-light-sensitive but also promotes the activity under UV and UV vis irradiation. For C-TiO2 treated at 100 300 °C, the visible light activity is markedly enhanced, although the specific surface area and the pore volume of the sample are decreased slightly (Table 1). Under the optimized treating condition, the sample C-TiO2-200 exhibited the highest activity (k, 0.007 min 1), which is nearly 3 times higher than that of the pristine C-doped TiO2. 3.2. Phase Structure. Figure 2 shows the XRD patterns of C-doped TiO2 treated at different temperatures. For each sample, all peaks can be indexed to the anatase phase of TiO2 (JCPDS file No. 21-1272). The average crystallite sizes are calculated according to the Debye Scherer equation, as shown in Table 1. It can be seen that thermal treatment between 100 300 °C has no obvious effect on crystal sizes. Figure 3 shows the Raman spectra of C-doped TiO2 treated at different temperatures. Raman peaks at 146 cm 1 (Eg), 199 cm 1 (Eg, weak), 399 cm 1 (B1g), 516 cm 1 (A1g), and 640 cm 1 (Eg) can be attributed to the characteristic peaks of the anatase phase.47,48 As the treating temperatures increases, the main peak at around 146 cm 1 shifts to lower wavenumber (inset) and the peak intensity increases. The shifting of the Raman peak position toward lower wavenumber indicates that thermal treatment could reduce the number of surface defects.49 The increase of peak intensity can be ascribed to the increase of crystallinity during thermal treatment. 3.3. Microstructure and Morphology. Figure 4a shows the nitrogen adsorption desorption isotherms of C-TiO2 and C-TiO2-200. The two samples exhibit a Type IV adsorption isotherm with a H2 hysteresis loop in the range (P/P0) of 0.6 1.0, which is a typical characteristic of a mesoporous structure.50 The pore size distribution was calculated from the desorption branch of a nitrogen isotherm by the

Table 1. Phase Structure, BET Surface Area, Pore Parameter, and Band Gap of Different Samples phase

crystal size (nm)

SBET (m2/g)

pore volume (cm3/g)

band gap (eV)

C-TiO2

anatase

12.9

96.86

0.306

2.74

C-TiO2-100

anatase

13.1

85.04

0.251

2.74

C-TiO2-200

anatase

13.2

79.11

0.246

2.30

C-TiO2-300

anatase

13.3

77.98

0.243

2.93

samples

Figure 2. XRD patterns of C-doped TiO2 treated at different temperatures.

Barret Joyner Halenda (BJH) method using the Halsey equation, as shown in Figure 4b.50 The mesopores between 2.0 and 5.5 nm can be observed for both samples, which can be ascribed to intra-agglomerated primary particles.46 A TiO2 cluster or crystal nucleus is first formed by the slow hydrolysis and condensation of Ti(SO4)2 in aqueous solution. The nucleus is then agglomerated and grows into larger particles with framework confined small mesopores. The physical properties of different C-doped TiO2 samples are summarized in Table 1. It can be seen that the surface areas and the pore volume decreased when the treatment temperature increased from 100 to 300 °C due to the collapse of some pores during thermal treatment. The 13287


The Journal of Physical Chemistry C sample without post-treatment was a mesoporous material with a high specific surface area of 96.9 m2/g, which decreased slightly to 79.1 m2/g after treating at 200 °C. To further investigate the morphological structure, TEM analysis was conducted for C-TiO2 and C-TiO2-200, as shown in Figure 5. Figure 5a,c indicates that both samples consist of large amounts of monodispersed particles with a size of around 10 12 nm, which is consistent with the XRD result. The intraaggregation of particles could form the mesoporous structure. HRTEM images (Figure 5b,d) show that both samples have a cubic shape and are highly crystallized with a well-resolved lattice structure. The observed spacing between the lattice planes of both samples is obtained as 0.35 nm, corresponding to the (101) plane of the anatase crystal.51 Figure 5 indicates that the thermal treatment of C-TiO2 at 200 °C has no obvious influence on the particle morphology and crystal size. 3.4. FT-IR and XPS Analyses. The FT-IR spectra of C-TiO2 and C-TiO2-200 samples are shown in Figure 6. The peaks at about 3400 and 1630 cm 1 with similar intensities are associated with the stretching vibrations of water molecules, including hydroxyl groups and molecular water.41 No peaks corresponding to CH, CH2, or CH3 bonds can be observed, indicating that it is free of organic species on the surface of C-doped TiO2.

Figure 3. Raman spectra of C-doped TiO2 treated at different temperatures.

ARTICLE

Besides, the two samples display two additional absorbance peaks at 1130 and 1050 cm 1, indicative of the sulfate ions from the Ti(SO4)2 precursor.52 The XPS measurements are carried out to determine the chemical state of the elements and total density of states (DOS) of the valence band (VB) in C-doped TiO2. Figure 7a,b shows the C 1s spectra of C-TiO2 and C-TiO2-200 samples. A broad energy range from 291 to 282 eV can be observed. The peaks at 284.8, 286.3, and 288.8 eV for both samples can be assigned to adventitious carbon species from the XPS measurement. The different peaks at 282.3 and 282.5 eV of C-TiO2 and C-TiO2-200 are close to the C 1s peak (281.8 eV) of TiC.53 Accordingly, the C 1s peaks at 282.3 and 282.5 eV can be ascribed to carbon substituting for the oxygen atom in the lattice of TiO2, forming the O Ti C bond.41,53 As the electronegativity of oxygen is larger than that of carbon, the binding energy of titanium in the O Ti C bond increased compared with that in the Ti C bond in TiC. The content of doped carbon in C-TiO2 and C-TiO2-200 is determined to be 0.19 and 0.28 at. %, indicating that thermal treatment of C-TiO2 could increase the doped carbon content through surface reconstruction. The carbon on the C-TiO2 surface could be doped into the lattice during thermal treatment. Figure 7c shows the O 1s spectra of C-TiO2 and C-TiO2-200 samples. The binding energy at 530.6, 531.7, and 532.9 eV can be ascribed to Ti O, surface OH, and adsorbed H2O, respectively.46 The VB XPS spectra are shown in Figure 7d. The observed new widely dispersed electronic states below 3.0 eV that are observed above the valence band edge for both samples can be attributed to the contribution of C 2p orbitals in C-doped TiO2.54,55 This evidence directly supported the previous theoretical DFT predictions and experimental results that the substitutional carbon shifts the valence band top upward.54,55 The new states are directly responsible for the electronic origin of the band-gap narrowing and visible light photoactivity of the C-doped TiO2.54,55 3.5. UV vis DRS and PL. Figure 8a shows UV vis DRS for undoped TiO2, C-TiO2, and samples treated at different temperatures. It can be seen that undoped TiO2 absorbs only UV light and C-TiO2 shows a huge optical absorbance in the visible light region. The band-gap energies can be estimated from the intercept of the tangents (inset) to the plots of (Ahν)1/2 versus photoenergy (hν), as shown in Figure 8b.16 The band-gap narrowing can be attributed to the substitutional carbon for the oxygen site (C 1s peak at 282.4 eV), which results in the upward shift of the valence band top. The visible light absorbance and band-gap narrowing due to carbon doping are consistent with the

Figure 4. Nitrogen adsorption desorption isotherms (a) and pore size distribution (b) of C-TiO2 and C-TiO2-200 samples. 13288



ARTICLE

Figure 5. TEM and HRTEM images of C-TiO2 (a, b) and C-TiO2-200 (c, d) samples.

observed new electronic states above the valence band edge from VB XPS. Under the treatment at 100 °C, the visible light absorbance intensity of sample C-TiO2-100 increased slightly compared with that of C-TiO2. At 200 °C, more carbon enters into the TiO2 lattice and the doped carbon content increases (see Figure 7a,b). Consequently, the absorbance of visible light increases significantly and the band-gap energy reduces to 2.30 eV. When increasing the treating temperature to 300 °C, the doped carbon was released, resulting in the decreased visible light absorbance. Generally, the photocatalytic activity is proportional to (IRΦ)n (n = 1 for low light intensity and n = 1/2 for high light intensity), where IR is the photonumbers absorbed by photocatalyst per second and Φ is the efficiency of the band-gap transition.56 The increase of visible light absorbance could contribute to the increase of IRΦ, thus improving the photocatalytic activity. Therefore, the enhanced visible light activity of thermally treated C-doped TiO2 can be partly explained by the broadened light absorbance. The PL process is closely related to surface states and stoichiometric chemistry, which generally would be altered by a thermal treatment.49 Figure 9 shows the PL spectra of C-TiO2 and C-TiO2-200. A broad visible PL band centered at 570 nm can be observed for both samples. There may be multifold PL processes contributing to the broad nature of the visible PL band. According to previous study, the visible PL band is related to shallow traps associated with oxygen vacancies and the visible PL is a surface phenomenon. It is known that, for anatase TiO2, the oxygen vacancy states are below the lower end of the

Figure 6. FT-IR spectra of C-TiO2 and C-TiO2-200 samples.

conduction band at 0 1 eV.49 Oxygen vacancies can form both in the bulk and on the surface of TiO2. The post-thermal treatment at 200 °C for C-TiO2 led to significant quenching of PL, as shown in Figure 9. The lower intensity of the visible PL band suggests that the post-thermal treatment resulted in the enhanced separation of electron hole pairs. As the visible PL band is associated with 13289



ARTICLE

Figure 7. XPS spectra of C 1s for C-TiO2 (a), C 1s for C-TiO2-200 (b), O 1s for C-TiO2 and C-TiO2-200 (c), and VB-XPS for C-TiO2 and C-TiO2-200 (d).

Figure 8. UV vis DRS (a) and plots of (Ahν)1/2 vs photon energy (b) of C-doped TiO2 treated at different temperatures.

electrons trapped at surface defect sites, the quenching of the PL of C-TiO2-200 indicates a decrease in the number of surface defects, which is also consistent with the Raman result (Figure 3).49 Zhang et al. also reported that the visible PL of TiO2 is strongly weakened after thermal treatment, suggesting the removal of defects associated with oxygen defects.57 Wang et al. conducted the calcination of a photocatalyst by treatment at elevated temperature in N2, and the resulting sample showed enhanced photocatalytic activity for water splitting due to the reduction of the density of surface defects in the catalyst

material.58 The reduction of defects indicated the decrease of recombination centers, thus improving the electron hole pairs separation. Therefore, reduction of defects is considered to be another important contributing factor to the enhanced photocatalytic activity of C-doped TiO2. As the thermal treatment induced little change in crystal sizes of C-TiO2-200 and decreased the specific surface areas and pore volumes, the excellent activity of C-TiO2-200 can be ascribed to the following other factors. First, the visible light absorbance of C-TiO2-200 is the strongest (Figure 8a). As known, the increased 13290



ARTICLE

’ ACKNOWLEDGMENT This research is funded by the Zhejiang Provincial Engineering Research Center of Industrial Boiler & Furnace Flue Gas Pollution Control (No. 2010B01), the National High Technology Research and Development Program (863 Program) of China (2010AA064905), Changjiang Scholar Incentive Program (Ministry of Education, China, 2009), and the National Natural Science Foundation of China (NSFC-50808156). This work is also supported by The Program for Chongqing Innovative Research Team Development in University (KJTD201020), The Chongqing Key Natural Science Foundation (CSTC, 2008BA4012), and Research Grants of Chongqing Technology and Business University (2010-56-13). ’ REFERENCES Figure 9. PL spectra of C-TiO2 and C-TiO2-200 samples (light source: 280 nm).

visible light absorbance could make the sample utilize more photoenergy taking part in the photocatalytic reaction and generate more photocarriers, thus enhancing the visible light activity.56 Second, the post-thermal treatment could reduce the number of defects, which inhibits the recombination of electron hole pairs, thus promoting the photocatalytic activity (Figure 9).41,49 The result indicates that facile thermal treatment of C-doped TiO2 is an effective and novel method to promote the visible light activity.

4. CONCLUSION A mesoporous C-doped TiO2 photocatalyst was prepared by a one-pot green synthetic approach using sucrose as a new carbondoping source for the first time. Post-thermal treatment was found to be an effective, facile method to promote the visible light activity of C-doped TiO2. The thermal treatment of the asprepared C-doped TiO2 has little influence on the crystal size and could decrease the specific surface areas and pore volumes slightly. However, the optical and surface properties could be improved significantly, which might be caused by the changes of doped carbon element. For the sample treated at an optimum temperature of 200 °C, the visible light absorbance was broadened due to the increased content of doped carbon and the recombination of electron hole pairs was suppressed due to the reduction of surface defects, which, in all, contributed to the promoted visible light photocatalytic activity. Our result could provide a feasible route for the large-scale applications of photocatalytic materials by combination of the green synthetic approach and the facile method to enhance the activity. ’ ASSOCIATED CONTENT

bS

Supporting Information. The comparison of the reaction constant k and normalized k by SBET of undoped TiO2 and carbon-doped TiO2 under UV and UV vis irradiation is shown in Figure S1. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

(1) Hernandez-Alonso, M. D.; Fresno, F.; Suarez, S.; Coronado, J. M. Energy Environ. Sci. 2009, 2, 1231. (2) Kudo, A.; Miseki, Y. Chem. Soc. Rev. 2009, 38, 253. (3) Roy, S. C.; Varghese, O. K.; Paulose, M.; Grimes, C. A. ACS Nano 2010, 4, 1259. (4) Chen, D.; Ye, J. H. Adv. Funct. Mater. 2008, 18, 1. (5) Yin, W. Z.; Wang, W. Z.; Shang, M.; Zhou, L.; Sun, S. M.; Wang, L. Eur. J. Inorg. Chem. 2009, 4379. (6) Zhu, S. B.; Xu, T. G.; Fu, H. B.; Zhao, J. C.; Zhu, Y. F. Environ. Sci. Technol. 2007, 41, 6234. (7) Ai, Z. H.; Ho, W. K.; Lee, S. C.; Zhang, L. Z. Environ. Sci. Technol. 2009, 43, 4143. (8) Li, G. S.; Zhang, D. Q.; Yu, J. C.; Leung, M. K. H. Environ. Sci. Technol. 2010, 44, 4276. (9) Asahi, R.; Morikawa, T.; Ohwaki, T.; Aoki, K.; Taga, Y. Science 2001, 293, 269. (10) Khan, S. U. M.; Shahry, M. A.; Ingler, W. B., Jr. Science 2002, 297, 2243. (11) Chen, X. B.; Mao, S. S. Chem. Rev. 2007, 107, 2891. (12) Sakthivel, S.; Kisch, H. Angew. Chem., Int. Ed. 2003, 42, 4908. (13) Fujishima, A.; Zhang, X. T.; Tryk, D. A. Surf. Sci. Rep. 2008, 63, 515. (14) Wu, G.; Nishikawa, T.; Ohtani, B.; Chen, A. Chem. Mater. 2007, 19, 4530. (15) Cong, Y.; Zhang, J. L.; Chen, F.; Anpo, M. J. Phys. Chem. C 2007, 111, 6976. (16) Murphy, A. B. Sol. Energy Mater. Sol. Cells 2007, 91, 1326. (17) Liu, G.; Chen, Z. G.; Dong, C. L.; Zhao, Y. N.; Li, F.; Lu, G. Q.; Cheng, H. M. J. Phys. Chem. B 2006, 110, 20823. (18) Li, D. Z.; Chen, Z. X.; Chen, Y. L.; Li, W. J.; Huang, H. J.; He, Y. H.; Fu, X. Z. Environ. Sci. Technol. 2008, 42, 2130. (19) Livraghi, S.; Paganini, M. C.; Giamello, E.; Selloni, A.; Di Valentin, C.; Pacchioni, G. J. Am. Chem. Soc. 2006, 128, 15666. (20) Dong, F.; Zhao, W. R.; Wu, Z. B.; Guo, S. J. Hazard. Mater. 2008, 162, 763. (21) Li, Q.; Li, Y. W.; Wu, P. G.; Xie, R. C.; Shang, J. K. Adv. Mater. 2008, 20, 3717. (22) Yu, J. C.; Ho, W. K.; Yu, J. G.; Yip, H.; Wong, P. K.; Zhao, J. C. Environ. Sci. Technol. 2005, 39, 1175. (23) Chen, X. B.; Burda, C. J. Phys. Chem. B 2004, 108, 15446. (24) Lee, S. H.; Yamasue, E.; Okumura, H.; Ishihara, K. N. Appl. Catal., A 2009, 371, 179. (25) Ren, W. J.; Ai, Z. H.; Jia, F. L.; Zhang, L. Z.; Fan, X. X.; Zou, Z. G. Appl. Catal., B 2007, 69, 138. (26) Kang, I. C.; Zhang, Q. W.; Yin, S.; Sato, T.; Saito, F. Appl. Catal., B 2008, 80, 81. (27) Hahn, R.; Schmidt-Stein, F.; Salonen, J.; Thiemann, S.; Song, Y.; Kunze, J.; Lehto, V.; Schmuki, P. Angew. Chem., Int. Ed. 2009, 48, 7236. (28) Janus, M.; Inagaki, M.; Tryba, B.; Toyoda, M.; Morawski, A. W. Appl. Catal., B 2006, 63, 272. 13291



ARTICLE

(29) Xiao, Q.; Ouyang, L. L. Chem. Eng. J. 2009, 148, 248. (30) Li, Q.; Li, Y. W.; Wu, P. G.; Xie, R. C.; Shang, J. K. Adv. Mater. 2008, 20, 3717. (31) Cong, Y.; Zhang, J. L.; Chen, F.; Anpo, M.; He, D. N. J. Phys. Chem. C 2007, 111, 10618. (32) Wu, Z. B.; Dong, F.; Liu, Y.; Wang, H. Q. Catal. Commun. 2009, 11, 82. (33) Ohno, T.; Miyamoto, Z.; Nishijima, K.; Kanemitsu, H.; Feng, X. Y. Appl. Catal., A 2006, 302, 62. (34) Ozaki, H.; Iwamoto, S.; Inoue., M. J. Phys. Chem. C 2007, 111, 17061. (35) Dong, F.; Wang, H. Q.; Wu, Z. B.; Qiu., J. F. J. Colloid Interface Sci. 2010, 343, 200. (36) Martyanov, I. N.; Uma, S.; Rodrigues, S.; Klabunde, K. J. Chem. Commun. 2004, 2476. (37) Shen, M.; Wu, Z. Y.; Huang, H.; Du, Y. K.; Zou, Z. G.; Yang, P. Mater. Lett. 2006, 60, 693. (38) Wu, G.; Nishikawa, T.; Ohtani, B.; Chen, A. Chem. Mater. 2007, 19, 4530. (39) Kuo, C. S.; Tseng, Y. H.; Huang, C. H.; Li, Y. Y. J. Mol. Catal. A 2007, 270, 93. (40) Park, Y.; Kim, W.; Park, H.; Tachikawa, T.; Majima, T.; Choi, W. Appl. Catal., B 2009, 91, 355. (41) Huang, Y.; Ho, W. K.; Lee, S. C.; Zhang, L. Z.; Li, G. S.; Yu, J. C. Langmuir 2008, 24, 3510. (42) Dong, F.; Wang, H. Q.; Wu., Z. B. J. Phys. Chem. C 2009, 113, 16717. (43) Ao, C. H.; Lee, S. C.; Mak, C. L.; Chan, L. Y. Appl. Catal., B 2003, 42, 119. (44) Mo, J. H.; Zhang, Y. P.; Xu, Q. J.; Zhu, Y. F.; Lamson, J. J.; Zhao, R. Y. Appl. Catal., B 2009, 89, 570. (45) Yu, J. G.; Liu, S. W.; Yu, H. G. J. Catal. 2007, 249, 59. (46) Yu, J. G.; Wang, G. H.; Cheng, B.; Zhou, M. H. Appl. Catal., B 2007, 69, 171. (47) Wang, H.; Quan, X.; Yu, H. T.; Chen, S. Carbon 2008, 46, 1126. (48) Su, Y. R.; Yu, J. G.; Lin, J. J. Solid State Chem. 2007, 180, 2080. (49) Chen, X. F.; Wang, X. C.; Hou, Y. D.; Huang, J. H.; Wu, L.; Fu, X. Z. J. Catal. 2008, 255, 59. (50) Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.; Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T. Pure Appl. Chem. 1985, 57, 603. (51) Wu, Z. B.; Dong, F.; Zhao, W. R.; Guo, S. J. Hazard. Mater. 2008, 157, 57. (52) Barraud, E.; Bosc, F.; Edwards, D.; Keller, N.; Keller, V. J. Catal. 2005, 235, 318. (53) Gu, D. E.; Lu, Y.; Yang, B. C.; Hu, Y. D. Chem. Commun. 2008, 2453. (54) Chen, X. B.; Burda, C. J. Am. Chem. Soc. 2008, 130, 5018. (55) Chen, X. B.; Glans, P. A.; Qiu, X.; Dayal, S.; Jennings, W. D.; Smith, K. E.; Burda, C.; Guo, J. J. Electron Spectrosc. Relat. Phenom. 2008, 162, 67. (56) Yu, J. G.; Zhou, M. H.; Cheng, B.; Zhao, X. J. J. Mol. Catal. A 2006, 246, 176. (57) Zhang, D.; Downing, J. A.; Knorr, F. J.; McHale., J. L. J. Phys. Chem. C 2006, 110, 21890. (58) Wang, X. C.; Maeda, K.; Lee, Y.; Domen, K. Chem. Phys. Lett. 2008, 457, 134.

13292


Enhancement of the Visible Light Photocatalytic Activity of C-Doped

Recommend Documents