A Simple Two-Step Template Approach for Preparing Carbon-Doped

Jul 7, 2009 - Carbon-doped TiO2 hollow microspheres with mesoporous structure were prepared by a simple two-step template method. The characterization...
0 downloads 9 Views 344KB Size
Download PDF
J. Phys. Chem. C 2009, 113, 13317–13324

13317

A Simple Two-Step Template Approach for Preparing Carbon-Doped Mesoporous TiO2 Hollow Microspheres Haiqiang Wang, Zhongbiao Wu,* and Yue Liu Department of EnVironmental Engineering, Zhejiang UniVersity, Hangzhou 310027, P. R. China ReceiVed: February 16, 2009; ReVised Manuscript ReceiVed: June 18, 2009

Carbon-doped TiO2 hollow microspheres with mesoporous structure were prepared by a simple two-step template method. The characterizations for the physicochemical properties of prepared samples under different calcination temperature were carried out by X-ray diffraction analysis, Brunauer-Emmett-Teller measurements, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectra. The carbon doping of TiO2 hollow spheres was easily achieved during the procedure for removal of carbon cores. With the doping of carbon, the absorption wavelength edge was expanded to the visible light region and the additional diffusive electronic states were observed on the valence band spectra of samples. C-doped TiO2 hollow spheres with rapid combustion at 500 °C exhibited the superior visible light photocatalytic activity for the degradation of toluene, 4.6 times greater than that of Degussa P25, due to its good crystallization, mesoporous structure composed by hollow sphere structure, and strong absorption in the visible light region. The procedure of carbon doping was discussed and the generating mechanism was proposed. Introduction Currently, TiO2 based semiconductors are one of the most widely used photocatalysts due to its high efficiency, good stability, nontoxicity, and availability.1-4 For the last 10 years, many advances have been made in the TiO2 based photocatalysts with remarkable response in the visible-light region for the purpose of using solar energy. Asahi et al. first reported N-doped TiO2 films by sputtering TiO2 target in the mixture of N2/Ar gas.5 Compared to the conventional TiO2 thin films, TiO2-xNx films showed higher visible-light activity. Since then, many efforts have been made to modify TiO2 with nonmetals elements, such as nitrogen,6-10 sulfur,11-16 and carbon17-29 to shift the optical absorption edge of TiO2 toward visible light. Those nonmetal doping approaches have displayed promising results in visible-light photodegradation. For the development of second-generation photocatalysts, the structure modification currently remains an important issue.30-32 Fabrication of titania hollow microspheres received special attention because of their unique properties, such as good surface permeability, high refractive index, and large light-harvesting efficiencies.33,34 The created sphere structure of titania will cause the stop band edge effect and the multiple scattering effect for the incident light.33,34 Generally, the synthesis methods can be divided into template methods and template-free methods.35-42 Template method is generally used because it is reproducible and facile to fabricating the hollow structure and easily adjust the hollow sphere diameter and the shell thickness. For the template methods, the classical process involves the use of structure-directing agents as templates and the later calcinations for the removal of templates. Thus the incomplete removal of template in the preparation process may lead to the contamination of product. Recently, Li et al.43-45 and Thomas et al.46 developed an amusing template method for the synthesis of metal oxide hollow spheres by using carbonaceous polysaccha* Corresponding author. E-mail: [email protected]. Phone: +86-57187952459. Fax: +86-571-87953088.

ride microspheres as a sacrificial core. While the carbonaceous polysaccharide microspheres were generated by the hydrothermal treatment of aqueous solutions of glucose and polysaccharides. Furthermore, Yu et al.47 synthesized the mesoporous TiO2 hollow spheres with high photoactivity according to this method. Evidently, the removal of template under an insufficient calcination process will lead to the carbon contamination of samples. However the carbon contamination also provides the possibility of carbon-doping during the template removal process due to the carbonaceous polysaccharide core. In the present contributions, we show a simple two-step template method to synthesize the carbon modified TiO2 hollow sphere based on the contributions of Li et al.,43-45 Tomas et al.,46 and Yu et al.47 We use the interesting core (carbonaceous polysaccharide microspheres) as the carbon dopant and achieve carbon doping in the removal process of carbon cores via a rapid combustion process. This work uses a simple and effective method to achieve the carbon doping on a TiO2 hollow sphere structure and supply a general route for the nonmetal modification via a template removal process. Experimental Section Materials and Reagents. (NH4)2TiF6 (CP, Sinopharm Chemical Reagent Co., Ltd., China) was used as a titanium source, glucose (AR, Sinopharm Chemical Reagent Co., Ltd., China) was used as a template and carbon source. Commercial TiO2 (Degussa P25, Degussa Chemical, Germany) was used for the blank experiment. All reagents were used without further purification. Distilled water was used in all experiment. Photocatalyst Preparation. Carbon-modified TiO2 hollow spheres were prepared by a hydrothermal method as illustrated in ref 47. First, 15 g (75.5 mmol) of glucose and 3.0 g (15.1 mmol) of (NH4)2TiF6 were dissolved in 80 and 40 mL of distilled water under stirring, respectively. After stirring, the above two solutions were mixed. Then the obtained solution was transferred into a Teflon-covered stainless steel autoclave

10.1021/jp9047693 CCC: $40.75  2009 American Chemical Society Published on Web 07/07/2009

13318

J. Phys. Chem. C, Vol. 113, No. 30, 2009

Wang et al.

Figure 1. SEM images of Ti4+ adsorbed carbonaceous polysaccharide microspheres by one-step hydrothermal method.

(volume: 200 mL). The autoclave was then placed in a furnace for the hydrothermal treatment (temperature: 180 °C; time: 24 h). After hydrothermal reaction, the black or puce precipitates were collected by centrifuge and then washed with distilled water and absolute alcohol five times. The washed precipitates were dried in an oven at 80 °C for 12 h (Figure 1) and directly placed in the furnace maintained at 300, 400, 500, and 600 °C for 1 h for the rapid combustion process. The prepared catalysts were named as CTHS-300, CTHS-400, CTHS-500, and CTHS-600, respectively. Characterization Techniques. X-ray diffraction analysis (XRD) of the catalysts was performed on a Rigaku diffractometer (D/max rA) at 40 kV and 150 mA (Cu KR ) 1.542 Å) at an angle of 2θ from 20° to 80°. The scan speed was 1°/min. The strongest TiO2 peaks, corresponding to anatase (101) and rutile (110), were selected to evaluate the crystal size of the samples. The mean crystal size was determined by the Scherer equation. Microstructures of the prepared samples, after being coated with gold, were observed with a scanning electron micrograph (SEM) (Phillips XL-30-ESEM, FEI Sirion200) at a voltage of 0.2-30 kV. The morphology, structure, and grain size of TiO2 particles were examined by transmission electron microscopy (TEM) and high resolution-transmission electron microscopy (HR-TEM) using a JEM-200cx instrument. The Brunauer-Emmett-Teller surface area (BET) of the powders was analyzed by a Micromeritics ASAP 2010C nitrogen adsorption apparatus (USA). Desorption isotherm was used to determine the pore distribution via the Barret-Joyner-Halender (BJH) method. The UV-vis diffuse reflectance spectra were obtained for the dry-pressed disk samples using a Scan UV-vis diffuse reflectance spectrophotometer (UV-vis DRS: TU-1901, China) equipped with an integrating sphere assembly, using BaSO4 as a reflectance sample. The spectra were recorded at room temperature in air ranged from 200 to 800 nm. X-ray photoelectron spectrum analysis (XPS) with Al KR X-rays (hν ) 1486.6 eV) radiation operated at 150 W (Thermo ESCALAB 250, USA) was used to investigate the surface properties of the samples. 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 standard. Evaluation of Photocatalytic Activity. Photocatalytic degradation of toluene is chosen as the probe reaction to evaluate the activity of the prepared samples, as toluene is a typical indoor pollutant.25,26 The experiment setup and operating conditions for photocatalytic activity tests were the same as that in our previous reports.48,49 The photocatalytic activity experiments of the as-prepared catalysts for the oxidation of toluene in gas

phase were performed at room temperature using a 1.8 L photocatalytic reactor. The catalyst was prepared by coating an ethanol suspension of the as-prepared catalyst onto a dish with diameter of 12.5 cm. The weight of catalyst used for each test was kept at 0.20 g. The dish containing the 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 toluene concentration in the reactor was conducted with a GCFID (FULI 9790, China). The toluene vapor was allowed to reach adsorption equilibrium with the catalyst in the reactor prior to irradiation. The initial concentration of toluene after adsorption equilibrium was controlled at 250 mg/m3. A 150 W Xe lamp was placed above the reactor as the light source. For visible-light photocatalysis, a glass optical filter was inserted to cut off the short wavelength components (λ < 425 nm). The initial temperature was 25 ( 1 °C by cooling air. The initial relative humidity was controlled 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. The photocatalytic oxidation of toluene is a pseudo-first-order reaction and its kinetics may be expressed as follows: ln(C0/C) ) kt,48,49 where k is the apparent reaction rate constant, and C0 and C are the initial concentration and the reaction concentration of toluene, respectively. Results and Discussion Crystal Structure and Morphology. The XRD spectra of the TiO2 hollow spheres calcined at different heat treatments are presented in Figure 2. The crystal size of these catalysts, determining by the Scherrer equation, is listed in Table 1. As shown in Figure 2, the TiO2 hollow spheres treated at 300 °C exhibited a broad peak at about 2θ ) 25.3°, which can be attributed to the anatase structure TiO2 (JCPDS, file no. 841285) with small crystal size. At 400 °C, the (101) anatase peak became sharper and the phase transformation from anatase to rutile (JCPDS, file no. 77-442) occurred. The crystallite sizes of anatase and rutile were 12.8 and 35.4 nm and their mass percentages were 90% and 10%, respectively. By increasing the calcination temperature, the content of rutile and the crystallize size increased. The phase transformation temperature from anatase to rutile in this study was lower than the conventional temperature for TiO2 phase transformation.50 It was reported that the free carbon could act as a nucleation seed in the calcination process and promote the crystallization and phase

Carbon-Doped Mesoporous TiO2 Hollow Microspheres

Figure 2. XRD spectra of TiO2 hollow microspheres under different calcination temperature (a: CTHS-300; b: CTHS-400; c: CTHS-500; d: CTHS-600).

TABLE 1: Physicochemical Properties of TiO2 Hollow Spheres under Different Calcination Temperature catalyst items calcination temperature (°C) anatase (%) crystallite size (nm) rutile (%) crystallite size (nm) BET surface area (m2/g) BJH desorption average pore diameter (nm) pore volume (cm3/g)

CTHS-300 CTHS-400 CTHS-500 CTHS-600

300

400

500

600

100 0.8

90 12.8 10 35.4 120.32 3.96

52.8 17.6 47.2 43.2 32.61 10.1

30.2 23.6 69.8 47.6 19.32 15.3

0.0991

0.0707

0.0490

386.37 0.1930

transformation.51 Furthermore, the combustion of carbon core could provide the additional heat energy for the phase transformation. With the adequate free carbon, the lower phase transformation temperature and the better crystallization were achieved in our studies as compared to other studies. Also the color of samples was very different with the dissimilarity of calcination temperatures. CTHS-300 was black, CTHS-400 was dark gray, CTHS-500 was gray, and CTHS600 was white. The color of CTHS-400 and CTHS-500 was very similar to the reported carbon doped TiO2 in the literature. The morphology and microstructures of TiO2 hollow spheres are further investigated by SEM and TEM analysis. A typical image of TiO2 samples obtained by SEM is shown in Figure 3.

J. Phys. Chem. C, Vol. 113, No. 30, 2009 13319 The TiO2 hollow spheres after calcination (fast calcined at 500 °C for 1 h) had an average diameter of 0.5-3.0 µm (see Figure 3a) and an average shell thickness around 50-100 nm. The clear cavities which were produced by the rapid combustion process could be found on numerous TiO2 hollow spheres (see in Figure 3b). Under the fast calcination process, the burning of carbon core was rapid and the rapid emission of gas led to the production of cavities. From Figure 1, we knew that the Ti-carbon hollow spheres had a diameter range from 2 to 6 µm. Obviously, the removal of the carbon core led to a distinct shrinkage of TiO2 hollow spheres. Further morphology observations by TEM are present in Figure 4. Under the TEM images, the edges of spheres were dark and the centers of spheres were bright. Moreover, a dark round point could be clearly observed on the hollow sphere surface. It clearly proved the presence of hollow structures and cavities on the hollow spheres. This template method by using carbonaceous polysaccharide microspheres as sacrificial core is reproducible, facile, and efficient. As Li et al.43-45 and Thomas et al.46 reported, we could adjust the hollow sphere diameter by changing the hydrothermal time or temperature. Furthermore, the shell thickness of the hollow spheres also could be adjusted just by changing the concentration of the titania precursor. UV-Vis Diffuse Reflectance Spectra. Commonly, the light absorption characteristics of TiO2 will be changed after the doping of nonmetal and the UV-vis diffuse reflectance spectra (UV-vis DRS) are usually used to investigate the band structure of TiO2.52 The diffuse reflectance spectra of carbon modified TiO2 powders with different heat treatment temperature are present in Figure 5a. The CTHS-300 sample showed a broad absorption ranged from UV light to visible light (200-800 nm). It was difficult to estimate the adsorption edge of CTHS-300 from the UV-vis spectrum. Further observation of CTHS-400 showed that the absorbance in the visible region (400-800 nm) decreased with enhancement of heat treatment temperature. For CTHS-400, the adsorption intensity had an evident decrease around 475 nm, but the sample had a continuous adsorption in the full spectrum. Just as mentioned, the colors of CTHS-300 and CTHS-400 were black and dark gray, respectively. It was obviously that the remnant free carbon in those catalysts affected the light absorption characteristics of TiO2. The absorption wavelength edge for CTHS-500 and CTHS-600 were around 420 and 410 nm, and the CTHS-600 had the lowest background absorption in the full tested spectrum. From the XRD spectra, it was identified that rutile structure was the primary structure in

Figure 3. SEM images of TiO2 hollow microspheres with rapid combustion at 500 °C for 1 h.

13320

J. Phys. Chem. C, Vol. 113, No. 30, 2009

Wang et al.

Figure 4. TEM images of TiO2 hollow microspheres with rapid combustion at 500 °C for 1 h.

Figure 5. UV-vis diffuse reflectance spectra of TiO2 hollow microspheres under different calcination temperatures.

CTHS-600. Furthermore, the adsorption edge of CTHS-600 was similar with the adsorption edge of rutile, so the red-shift of CTHS-600 mainly depended on the crystal structure. CTHS500 was a mixture of anatase and rutile, but it had a narrower band gap than that of CTHS-600. Thus the change of light absorption edge for CTHS-500 should be considered by the effect of carbon doping. Assuming the carbon-doped TiO2 to be an indirect semiconductor, as is TiO2, band gap energies can be estimated from the diffuse reflectance spectra. The relation between absorption coefficient (R) and incident photon energy (hν) can be written as R ) Bd(hν - Eg)1/2/hν for allowed direct transitions, where Bd is the absorption constant.49 Plots of (Rhν1/2 versus hν from the spectral data of CTHS-500 and CTHS-600 are presented in Figure 5b. Estimating from the intercept of the tangents to the plots, the direct band gap energies for CTHS-500 and CTHS600 were 2.80 and 2.90 eV, respectively. This result obviously revealed the band gap of the carbon-doped TiO2 was narrower than that of the pure TiO2. However for CTHS-300 and CTHS400, the band gap was not calculated because that the remnant free carbon in those samples would affect the light absorption characteristics. Surface Element Analysis. To investigate the chemical states of C, O, and Ti atoms of the prepared catalysts, C 1s, binding energies of CTHS-400, CTHS-500, and CTHS-600 after Ar+ 100s sputtering is measured by XPS. The high resolution XPS spectra of C1s in the surface of carbon doped TiO2 hollow spheres are shown in Figure 6a. After sputtering, four peak structures were observed at the binding

energies of 282, 284.6, 286.1, and 288.5 eV. For XPS measurements, samples for XPS measurement were coated on carbon tape attached to the sample holder. For CTHS-500 and CTHS600, the free carbon content was almost equal. Free carbon could not exist under such high calcinations temperature (600 °C for CTHS-600), so it was confirmed that the peak of carbon element (284.6 eV) in CTHS-500 and CTHS-600 came from carbon tape. But for CTHS-400, the peak (284.6 eV) could be thought to be the signal from carbon tape and free carbon in samples. The peaks for 286.4 and 288.5 eV indicated the presences of C-O and CdO bonds.53,54 The peak around 282 eV was ascribed to the existence of O-Ti-C bonds. The peak (288.6 eV) indicated the presence of C-O bonds, and the carbon might substitute for some of the lattice titanium atoms to forming a Ti-O-C structure.52,55 Obviously, the doping carbon species in CTHS500 might exist as O-Ti-C and Ti-O-C. One species was substituting the oxygen of the anatase in the as-prepared catalysts and another species was incorporating into the interstitial positions of the TiO2 lattice. Also, with the increasing calcinations temperature, the carbon doping concentration decreased. Furthermore, it was found that the N element was only detected in CTHS-400 and the F element was not detected in all samples (Figure 6b,c). For this preparation method, the Ti-N structure formed on CTHS-400 should mainly be ascribed to the adsorption of ammonium fluorotitanate on the microspheres surface. Obviously the F element was removed in the catalyst washing process, while the N ions were adsorbed on the surface of carbonaceous polysaccharide microspheres. But in the proceeding combustion process, the release of N elements took

Carbon-Doped Mesoporous TiO2 Hollow Microspheres

J. Phys. Chem. C, Vol. 113, No. 30, 2009 13321

Figure 6. XPS spectra and valence band spectrum of TiO2 hollow microspheres under different calcination temperature. (a) C1s spectra; (b) N1s spectra; (c) F1s; (d) valence band).

place very easily under the calcination temperature, which was higher than 400 °C. Thus it could not detect the N elements in the CTHS-500, CTHS-600. Not only the information on the binding energy of a specific element can be obtained from the XPS but also the total density of states (DOS) of the valence band (VB) by using a photon energy of 1486.6 eV.56,57 The valence band XPS spectra of Degussa P25, CTHS-400, CTHS-500, and CTHS-600 after Ar+ 100s sputtering, are shown in Figure 6d. Additional diffusive electronic states were observed above the valence band edge for CTHS400, CTHS-500, and CTHS-600. However, these electronic states have not been detected on a Degussa P25. These states could be attributed to the C 2p orbitals in the carbon doped TiO2 hollow spheres. In general, carbon doping added the deepest states into the band gap compare with the nitrogen and sulfur doping.56 The direct contribution of these new states was the expanded absorption spectrum of the carbon doped TiO2. Surface Area and Pore Distribution. The BET data for the carbon doped TiO2 hollow spheres with different calcination temperature are summarized in Table 1. The BET surface areas of CTHS-300, CTHS-400, CTHS-500, and CTHS-600 were 386.37, 120.32, 32.61, and 19.32 m2/g, respectively, by calculation from the linear part of the Brunauer-Emmett-Teller (BET) plots. Obviously the BET specific surface areas and pore volumes sharply decreased with the increasing calcination temperatures due to the removal process of carbon core, but the average pore size increased with the increasing calcination temperatures due to the formation of slitlike pores. To investigate pore structure of the carbon doped TiO2 hollow spheres under different calcination temperatures, the samples

were analyzed by N2 adsorption and the BJH results are shown in Figure 7. Analyzing the adsorption isotherms in Figure 7, the hysteresis loop of CTHS-300 was not closed due to the large amount of residue carbonaceous polysaccharide microspheres. Thus the BJH result of CTHS-300 could not reflect the true pore distribution of sample. The inserted adsorption isotherms of CTHS-400, CTHS-500, and CTHS-600 showed that all of the samples presented type IV isotherms, indicating the existence of mesopores (2-50 nm).58 According to the classification of hysteresis loops in the IUPAC manual, the CTHS-400 sample had a type of H2 hysteresis loop at lower relative pressure region and CTHS-500 and CTHS-600 had a type of H3 hysteresis loop at higher relative pressure. The pore size distribution of CTHS400 was relatively narrow (2.5-4.2 nm). With the increase of calcination temperature, the hysteresis loops of CTHS-500 and CTHS-600 changed to a type of H3 at higher relative pressure. The hysteresis loop at lower relative pressure region (0.4 < P/P0 < 0.8) was attributed to a smaller mesopore, while that at the higher relative pressure (0.8 < P/P0 < 1.0) was attributed to larger mesopores.59 Thus CTHS-500 and CTHS-600 had a wide pore size distribution among the mesopores scale, as shown in Figure 7c,d. Visible-Light Photocatalytic Activity. Photodegradation of toluene in gas phase under a visible light environment is performed as a test reaction to evaluate the visible light photocatalytic activity of the carbon doped TiO2 hollow spheres. Figure 8 depicts the photocatalytic activity results of TiO2 hollow spheres under different calcination temperatures. It was clear that Degussa P25 (k ) 0.0008 min-1) exhibited little activity in the presence of visible light. CTHS-300 showed no

13322

J. Phys. Chem. C, Vol. 113, No. 30, 2009

Wang et al.

Figure 7. Pore size distribution and adsorption isotherm of TiO2 hollow microspheres under different calcination temperature (a) CTHS-300; (b) CTHS-400; (c) CTHS-500; (d) CTHS-600).

Figure 8. Photodegradation efficiency of TiO2 hollow microspheres under different calcination temperatures.

photocatalytic activity under the visible light due to the noncrystalline structure of the catalyst and the large amount of residue carbonaceous polysaccharide microspheres in the body. With the increasing of calcination temperature, the visible light photocatalytic activity of the TiO2 hollow spheres were improved and the rate constant for toluene degradation over carbon doped TiO2 hollow spheres prepared at 400, 500, and 600 °C was determined to be 0.0025, 0.0037, and 0.0014 min-1, respectively. It was obvious that C-doped TiO2 hollow sphere with rapid combustion at 500 °C exhibited the superior visible light photocatalytic activity for the degradation of toluene, 4.6

times greater than that for Degussa P25. The superior activity of CTHS-500 could be ascribed to the crystal structure and the mesporous microstructure, which is composed by hollow sphere structure. Comparing with CTHS-500, CTHS-400 had the larger surface area. However, the remnant free carbon in the CTHS400 was evident, which had an adverse effect on the photocatalytic activity. Thus the photocatalytic activity of CTHS400 was lower than that of CTHS-500, while for CTHS-600, the combustion condition was sufficient and the contents of rutile were bigger than that of anatase. The crystal size developed and the carbon doping concentration and the surface area decreased under 600 °C calcination. All these effects contributed to a decreased photocatalytic activity of CTHS-600. Discussion and the Proposed Mechanism. With the contribution of Li et al. and Tomas et al.,43-46 we proposed the generating mechanism for carbon doped TiO2 hollow sphere, as shown in Figure 9. When the mixture of (NH4)2TiF6 and glucose are treated at 180 °C under a hydrothermal condition, carbonaceous polysaccharide microspheres are formed and the Ti4+ adsorbed carbonaceous polysaccharide microspheres can be generated as follows (eq 1):

In the first stage of rapid combustion, Ti4+ on the surface of carbonaceous polysaccharide microspheres reacted with oxygen

Carbon-Doped Mesoporous TiO2 Hollow Microspheres

J. Phys. Chem. C, Vol. 113, No. 30, 2009 13323

Figure 9. Proposed generating mechanism for carbon doped TiO2 hollow microspheres.

to yield an incompact titanium dioxide shell (as shown in eq 2). The bonds between Ti4+ and carbonaceous polysaccharide microspheres are ruptured, while the structure like Ti-O-Cis maintained in part.

Obviously, the formed incompact titanium dioxide shell will hold back the oxygen to penetrating into the body of carbonaceous polysaccharide microspheres. Thus it provides a deoxidization atmosphere in the inner part of microspheres. However, the oxygen supply is sufficient in the outside of microspheres. At the deoxidization condition with a reasonable calcination temperature, Ti-O-C- can change to a Ti-O-C bond or a O-Ti-C bond (as shown in eqs 3 and 4).

All of the above results suggested that the carbon doping in TiO2 hollow sphere can be easily achieved by a rapid combustion process during the procedure for removal of carbon cores and the carbon doping is an effective way to improve the photocatalytic activity in the visible light region. Furthermore, it is easy to achieve the nonmetal doping such as nitrogen and sulfur when we use the sacrificial core containing these elements. Conclusions Carbon doped TiO2 hollow spheres with mesoporous structure could be prepared by using carbonaceous polysaccharide microspheres as a sacrificial core with a rapid combustion process. The calcination condition was the key factor for the carbon doping during the rapid combustion process. C-doped TiO2 hollow sphere with rapid combustion at 500 °C exhibited the superior visible light photocatalytic activity for the degrada-

tion of toluene, 4.6 times greater than that of Degussa P25. XPS results showed that the doping carbon species in CTHS-500 existed as O-Ti-C and Ti-O-C. During the rapid combustion process, the removal of carbon core led to a distinct shrinkage of hollow spheres diameter and induced a mesoporous structure with a wide pore size distribution. The concept in our catalyst preparation provides a possible way for the nonmetal doping for TiO2 generated from a template method while the sacrificial core contains nonmetal elements such as carbon, nitrogen, and sulfur. Acknowledgment. The project was financially supported by the National Natural Science Foundation of China (NSFC50808156) and the Hangzhou Science & Technology Development Program (20061133B27). Special thanks are given to Dr. X. B. Chen for his helpful discussion. References and Notes (1) Yang, H. G.; Sun, C. H.; Qiao, S. Z.; Zou, J.; Liu, G.; Smith, S. C.; Cheng, H. M.; Lu, G. Q. Nature 2008, 453, 638. (2) Burda, C.; Chen, X. B.; Narayanan, R.; El-Sayed, M. A. Chem. ReV. 2005, 105, 1025. (3) Yu, H. T.; Quan, X.; Chen, S.; Zhao, H. M. J. Phys. Chem. C 2007, 111, 12987. (4) Ao, C. H.; Lee, S. C.; Yu, J. Z.; Xu, J. H. Appl. Catal., B 2004, 54, 41. (5) Asahi, R.; Morikawa, T.; Ohwaki, T.; Aoki, K.; Taga, Y. Science 2001, 293, 269. (6) Valentin, C. D.; Pacchioni, G.; Selloni, A.; Livraghi, S.; Giamello, E. J. Phys. Chem. B 2005, 109, 11414. (7) Sakthivel, S.; Janczarek, M.; Kisch, H. J. Phys. Chem. B 2004, 108, 19384. (8) Chen, X. B.; Lou, Y. B.; Samia, A. C. S.; Burda, C.; Gole, J. L. AdV. Funct. Mater. 2005, 15, 41. (9) Livraghi, S.; Paganini, M. C.; Giamello, E.; Selloni, A.; Di Valentin, C.; Pacchioni, G. J. Am. Chem. Soc. 2006, 128, 15666. (10) Mitoraj, D.; Kisch, H. Angew. Chem., Int. Ed. 2008, 47, 9975. (11) Ohno, T.; Akiyoshi, M.; Umebayashi, T.; Asai, K.; Mitsui, T.; Matsumura, M. Appl. Catal., A 2004, 265, 115. (12) Yu, J. C.; Ho, W. K.; Yu, J. G.; Yip, H.; Wong, P. K.; Zhao, J. C. EnViron. Sci. Technol. 2005, 39, 1175. (13) Ho, W. K.; Yu, J. C.; Lee, S. C. J. Solid State Chem. 2006, 179, 1171. (14) Katoh, M.; Aihara, H.; Horikawa, T.; Tomida, T. J. Colloid Interface Sci. 2006, 298, 805. (15) Hamal, D. B.; Klabunde, K. J. J. Colloid Interface Sci. 2007, 311, 514. (16) Yoshinaga, M.; Yamamoto, K.; Sato, N.; Aoki, K.; Morikawa, T.; Muramatsu, A. Appl. Catal., B 2009, 87, 239. (17) Khan, S. U. M.; Al-Shahry, M.; Ingler, W. B., Jr. Science 2002, 297, 2243.

13324

J. Phys. Chem. C, Vol. 113, No. 30, 2009

(18) Choi, Y.; Umebayashi, T.; Yamamoto, S.; Tanaka, S. J. Mater. Sci. Lett. 2003, 22, 1209. (19) Sakthivel, S.; Kisch, H. Angew. Chem., Int. Ed. 2003, 42, 4908. (20) Martyanov, I. N.; Uma, S.; Rodrigues, S.; Klabunde, K. J. Chem. Commun. 2004, 2476. (21) Park, J. H.; Kim, S.; Bard, A. J. Nano Lett. 2006, 6, 24. (22) Shen, M.; Wu, Z. Y.; Huang, H.; Du, Y. K.; Zou, Z. G.; Yang, P. Mater. Lett. 2006, 60, 693. (23) Xu, C.; Killmeyer, R.; Gray, M. L.; Khan, S. U. M. Appl. Catal., B 2006, 64, 312. (24) Wu, G.; Nishikawa, T.; Ohtani, B.; Chen, A. Chem. Mater. 2007, 19, 4530. (25) Kuo, C. S.; Tseng, Y. H.; Huang, C. H.; Li, Y. Y. J. Mol. Catal. A: Chem. 2007, 270, 93. (26) Liu, H.; Imanishi, A.; Nakato, Y. J. Phys. Chem. C 2007, 111, 8603. (27) Yang, X.; Cao, C.; Hohn, Erickson, K. L.; Maghirang, R.; Hamal, D.; Klabunde, K. J. Catal. 2007, 252, 296. (28) Huang, Y.; Ho, W. K.; Lee, S. C.; Zhang, L. Z.; Li, G. S.; Yu, J. C. Langmuir 2008, 24, 3510. (29) Xiao, Q.; Zhang, J.; Xiao, C.; Si, Z. C.; Tan, X. K. Sol. Energy 2008, 82, 706. (30) 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. (31) Martı´nez-Ferrero, E.; Sakatani, Y.; Boissie`re, C.; Grosso, D.; Fuertes, A.; Fraxedas, J.; Sanchez, C. AdV. Funct. Mater. 2007, 17, 3348. (32) Liu, G.; Zhao, Y. N.; Sun, C. H.; Li, F.; Lu, G. Q.; Cheng, H. M. Angew. Chem., Int. Ed. 2008, 47, 4516. (33) Li, Y. Z.; Kunitake, T.; Fujikawa, S. J. Phys. Chem. B 2006, 110, 13000. (34) Ao, Y. H.; Xu, J. J.; Fu, D. G.; Yuan, C. W. Microporous Mesoporous Mater. 2009, 118, 382. (35) Li, H. X.; Bian, Z. F.; Zhu, J.; Zhang, D. Q.; Li, G. S.; Huo, Y. N.; Li, H.; Lu, Y. F. J. Am. Chem. Soc. 2007, 129, 8406. (36) Ho, W. K.; Yu, J. C.; Lee, S. C. Chem. Commun. 2006, 10, 1115. (37) Yu, J. G.; Liu, S. W.; Yu, H. G. J. Catal. 2007, 249, 59. (38) Syoufian, A.; Satriya, O. H.; Nakashima, K. Catal. Commun. 2007, 8, 755.

Wang et al. (39) Song, X. F.; Gao, L. J. Phys. Chem. C 2007, 111, 8180. (40) Shchukin, D. G.; Caruso, R. A. Chem. Mater. 2004, 16, 2287. (41) Wang, D. B.; Song, C. X.; Lin, Y. S.; Hu, Z. S. Mater. Lett. 2006, 60, 77. (42) Gu, D. E.; Lu, Y.; Yang, B. C.; Hu, Y. D. Chem. Commun. 2008, 21, 2453. (43) Sun, X. M.; Liu, J. F.; Li, Y. D. Chem.sEur. J. 2006, 12, 2039. (44) Li, X. L.; Lou, T. J.; Sun, X. M.; Li, Y. D. Inorg. Chem. 2004, 43, 5442. (45) Sun, X. M.; Li, Y. D. Angew. Chem. 2004, 116, 3915. (46) Titirici, M.-M.; Antonietti, M.; Thomas, A. Chem. Mater. 2006, 18, 3808. (47) Yu, J. G.; Wang, G. H. J. Phys. Chem. Solids 2008, 69, 1147. (48) Wu, Z. B.; Dong, F.; Zhao, W. R.; Guo, S. J. Hazard. Mater. 2008, 157, 57. (49) Dong, F.; Zhao, W. R.; Wu, Z. B. Nanotechnology 2008, 19, 365607. (50) Zhang, J.; Xu, Q.; Feng, Z. C.; Li, M. J.; Li, C. Angew. Chem., Int. Ed. 2008, 47, 1766. (51) Li, Q.; Xie, R.; Li, Y. W.; Mintz, E. A.; Shang, J. EnViron. Sci. Technol. 2007, 41, 5050. (52) Ren, W. J.; Ai, Z. H.; Jia, F. L.; Zhang, L. Z.; Fan, X. X.; Zou, Z. G. Appl. Catal., B 2007, 69, 138. (53) Sun, H. Q.; Bai, Y.; Cheng, Y. P.; Jin, W. Q.; Xu, N. P. Ind. Eng. Chem. Res. 2006, 45, 4971. (54) Chen, D. M.; Jiang, Z. Y.; Geng, J. Q.; Wang, Q.; Yang, D. Ind. Eng. Chem. Res. 2007, 46, 2741. (55) Li, Y. Z.; Hwang, D. S.; Lee, N. H.; Kim, S. J. Chem. Phys. Lett. 2005, 404, 25. (56) Chen, X. B.; Burda, C. J. Am. Chem. Soc. 2008, 130, 5018. (57) Chen, X. B.; Glans, P. A.; Qiu, X. F.; Dayal, S.; Jennings, W. D.; Smith, K. E.; Burda, C.; Guo, J. H. J. Electron Spectrosc. Relat. Phenom. 2008, 162, 67. (58) Gregg, S. J.; Sing, K. S. W. Adsorption Surface Area and Porosity, 2nd ed.; Academic Press Inc.: London, 1982. (59) Chen, Y.; Dionysiou, D. D. Appl. Catal., B 2008, 80, 147.

JP9047693