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Enhanced Photocatalytic Activity of P25 TiO [ChemPlusChem](ChemPlusChem Via Acquire Media NewsEdge) In general, an increase in O2 adsorption is highly desirable for efficient photocatalysis. Herein, commercial P25 TiO2 is modified with an F127-containing SiO2 sol, and post-treated with phosphoric acid. It is confirmed, on the basis of O2 temperature-programmed desorption measurements, that the O2 adsorption of commercial P25 TiO2 is greatly promoted through its modification with porous SiO2, especially in the phosphate-treated case. The promotion of O2 adsorption is attributed to the introduction of -Si-OH and -P-OH as surface ends, and to the slightly increased surface area. Interestingly, it is concluded that the promotion of O2 adsorption is favorable for the separation of photogenerated charge carriers, as seen from the steady-state surface photovoltage spectra, transient-state surface photovoltage responses, and measurements of the hydroxyl radicals produced. This is responsible for the clear enhancement in the photocatalytic activity of modified TiO2 for the degradation of gas-phase acetaldehyde and liquid-phase phenol as colorless pollutants. This work provides a feasible route for improving the photocatalytic activity of TiO2. Keywords : adsorption · oxygen · photocatalysis · photogenerated charge separation · Titanium dioxide Introduction In recent decades, semiconductor photocatalytic technology has been investigated extensively. Among numerous semicon- ductors, the TiO2 photocatalyst has been applied widely in het- erogeneous photocatalytic reactions for the degradation of contaminants owing to its nontoxicity, low cost, stability, high photocatalytic activity, and because it does not cause secon- dary pollution.[1-4] With these advantages, TiO2-based photoca- talysts have been used in various fields such as sterilization, self-cleaning surfaces, and the degradation of organic and inor- ganic contaminants both in aqueous systems and in the gas phase.[5-8] TiO2 is a kind of wide-bandgap semiconductor (the bandgap width values for anatase and rutile are about 3.2 and 3.0 eV, respectively), and it exhibits two main bottleneck fac- tors : low efficiency of sunlight utilization and the easy recom- bination of photogenerated charges.[9, 10] In comparison with the pure anatase and rutile phases, the phase-mixed P25 TiO2, which contains around 85 % anatase and 15 % rutile, usually displays a high photocatalytic activity.[1,11, 12] Thus, it is highly desired to improve the photocatalytic activity of P25 TiO2 by overcoming the two shortcomings mentioned above. At present, the widely accepted mechanism of TiO2 photoca- talytic oxidation is based on semiconductor band theory. The electrons in the valence band of TiO2 are excited to form elec- tron-hole pairs under UV irradiation, and the photogenerated holes react with surface hydroxyl groups and/or water mole- cules to form hydroxyl radicals (COH). Hydroxyl radicals with strong oxidation ability can oxidize pollutants to form CO2, H2O, and other inorganic substances. Alternatively, the photo- generated holes can react directly with pollutants and then induce further degradation reactions. At the same time, the photogenerated electrons can react with O2 adsorbed on the catalyst surface.[1, 13-15] It is widely accepted that the step in which the photogenerated electrons are captured by the ad- sorbed O2 is crucial for efficient photocatalysis for pollutant degradation.[16, 17] Therefore, this is a promising route for im- proving the separation of photogenerated charges so as to en- hance the photocatalytic activity of TiO2 by promoting O2 ad- sorption. To the best of our knowledge, there have been few related studies reported to date. SiO2 has been used widely to improve the photocatalytic performance of TiO2 ; the improvement is usually attributed to the decreased crystallite size, porous structure, and high ana- tase thermal stability.[18-23] Inumaru et al. reported that well- crystallized P25 TiO2 particles were incorporated directly into surfactant-templated mesoporous silica particles, and the com- posite material with a high TiO2 content (60 wt %) showed mo- lecular selectivity and an enhanced photocatalytic performance for the decomposition of 4-nonylphenol.[24] In previous work, our group also demonstrated that modification with SiO2 mark- edly enhanced the thermal stability of anatase TiO2 crystallites, and suppressed anatase crystallite growth, leading to a clearly enhanced photocatalytic activity.[18] Although many studies on SiO2-TiO2 composites have been reported, it is difficult to reveal the mechanism of SiO2 modification, because modified TiO2 often possesses different physical properties such as sur- face area, crystal composition, and crystallinity ; in addition, dif- ferent model pollutants are used, and the role of adsorbed O2 is often neglected. Therefore, it is very useful to perform a sys- tematic study on the effects of modification with porous SiO2 on the O2 adsorption and photocatalytic activity of P25 TiO2. Herein, we have improved the photocatalytic activity of P25 TiO2 for the degradation of colorless pollutants through modi- fication with porous SiO2, especially in the phosphate-treated case. It is suggested for the first time that the improved activi- ty comes from the promoted O2 adsorption, which improves the separation of photogenerated charge carriers ; the en- hanced O2 adsorption results from the introduction of ^Si^OH and ^Si^O^P^OH as surface ends, as well as the increased sur- face area. This work provides a feasible route for the enhance- ment of the photocatalytic activity of TiO2, which may be ap- plicable to other semiconductor photocatalysts. Results Structural characterization and surface composition In this work, commercial P25 TiO2 was modified with SiO2 sol and F127-containing SiO2 sol to obtain the XS-T and YF-XS-T samples, respectively (Supporting Information, Figure S1). The XRD patterns of the different TiO2 samples are shown in Fig- ure 1A and Figure S2 A. The peaks at the values of 25.38 and 27.48 correspond to the (101) face of anatase and (110) face of rutile TiO2, respectively.[26] According to the strengths of the specific diffractive peaks, it is calculated that P25 TiO2 has a mixed phase with 85 % anatase and 15 % rutile. The TEM images (Figure 1 B) show that TiO2 consists of spherical nano- particles of about 20 nm in diameter. On the basis of the XRD patterns, TEM images, and diffuse reflectance spectra (Fig- ure S2 B), it is confirmed that the crystal phase composition, crystallinity, nanoparticle size and morphology, and optical ab- sorption of TiO2 are unchanged after modification with a certain amount of SiO2. In the FTIR spectra (Figure 2 A, and Figure S2 C), the broad absorption at low frequency (below 1000 cm^1) is attributed to the vibration of the Ti^O^Ti bonds in TiO2.[27] The surface-ad- sorbed water molecules give rise to a broad envelope around 3400 cm^1, and the peak at 1630 cm^1 is attributed to the sur- face hydroxyl groups.[28] In particular, we have focused on the Ti^O^Si stretching absorption bands in the 930-970 cm^1 region and the stretching absorption band at around 1050 cm^1, which is attributed to Si^O^Si.[18, 29] Beyond that, one can easily find that the intensities of the Si^O^Si bands become much stronger with increasing amounts of modified SiO2. As shown in Figure 2B and Figure S3, the Ti 2p spectra show binding energies of 464.1 and 458.5 eV, attributed to Ti 2p1/2 and Ti 2p3/2 in TiO2, respectively.[30] The O 1s XPS spectra exhibit peaks at about 529.5 and 531.5 eV, resulting from the crystal lattice oxygen and hydroxyl oxygen, respectively.[27,31] The Si 2p XPS peak is centered at about 102.2 eV, indicating that the va- lence of Si is + 4.[5,18,32] Note that the amounts of hydroxyl oxygen and Si increase as the amount of modified SiO2 increas- es. According to the TG curves (Figure S4), it is confirmed that the introduced F127 surfactant could be removed after calcina- tion at 300 8C. Interestingly, it is seen from Table S1 that the surface area of TiO2 increases slightly (by about 2 m2 g^) upon modification with SiO2, and increases much more clearly (by about 4 m2 g^) upon modification with F127-treated SiO2.The increase in surface area is ascribed to the introduction of SiO2 with a porous structure, especially for the F127-containing SiO2. On the basis of the above analyses, it is concluded that the TiO2 surface is modified successfully with SiO2. Photogenerated charge properties We used steady-state surface photovoltage spectroscopy (SS- SPS) and transient-state surface photovoltage (TS-SPV) spec- troscopy to investigate the properties of the photogenerated charges of the resulting TiO2, as shown in Figure 3 and Fig- ure S5. Similarly to un-modified TiO2, it is demonstrated by means of the SPS responses in atmospheres with different O2 contents as an inset of Figure 3 A that the presence of O2 is necessary for SPS of modified TiO2, and the higher the O2 con- tent, the stronger the SPS response. Hence, it is concluded that the SPS signal originates mainly from the photogenerated charge separation through the diffusion process in the pres- ence of O2 capturing photogenerated electrons.[33] Notably, it is found from Figure S5 that modification with an appropriate amount of SiO2 could enhance the SPS response of TiO2 great- ly. Among the modified TiO2 samples, 3S-T displays the stron- gest SPS response. However, the SPS response would begin to decrease if excess SiO2 were modified. Interestingly, the 2.1F- 3S-T sample exhibits a much stronger SPS response than the 3S-T sample (Figure 3 A). This is further supported by the TS- SPV responses (Figure 3 B). It is seen that the SiO2-modified TiO2 exhibits a very strong TS-TPV response with a prolonged carrier lifetime, especially for 2.1F-3S-T, compared with the unmodified sample. On the basis of the SPV principle, it is widely accepted that the strong SPV response in the presence of O2 corresponds to the high photogenerated charge separation. Hence, it is assumed from the above SPV analyses that the photocatalytic activity of P25 TiO2 would be improved upon modification with an appropri- ate amount of SiO2. Photocatalytic activities As shown in Figure S6, the photocatalytic activity of TiO2 for the degradation of gas-phase acetaldehyde was improved by modification with an appropriate amount of SiO2, and the 3S-T sample exhibits the highest activity. The 5S-T sample possesses a lower activity than the unmodified TiO2. Interestingly, the 2.1F-3S-T sample displays a much higher activity for the degra- dation of acetaldehyde and phenol than 3S-T (Figure 4). Clear- ly, the rate constant for acetaldehyde degradation is greatly enhanced from 0.007 (T) to 0.011 (2.1F-3S-T). As expected, the photocatalytic activity of the resulting TiO2 is in good agreement with the corresponding SPS response in the presence of O2. Hence, it is clearly demonstrated that the strong SPS (SPV) response of TiO2 comes from the high photo- generated charge separation, leading to high photocatalytic activities for pollutant degradation. On the basis of the SPS (SPV) results mentioned above, it is accepted that the presence of O2 is necessary for SPS of TiO2. This is similar to the impor- tant role of O2 in the photocatalytic degradation of pollutants. Thus, it is understandable that a strong SPS response corre- sponds to a high photocatalytic activity. In addition, it is found that the photocatalytic activity of porous-SiO2-modified TiO2 begins to decline if excess F127 is introduced, as shown in Fig- ure S7. This may be because the excess F127 used is unfavora- ble for the porous structure of SiO2. Discussion On the basis of the above analyses, it is concluded that modifi- cation with an appropriate amount of SiO2 can enhance the separation of photogenerated charges of TiO2, especially with the porous SiO2, leading to an improved photocatalytic activity. This is further proved by the amounts of hydroxyl radicals pro- duced on the different TiO2 samples after irradiation for 0.5 h (Figure 5 A and Figure S8). Generally speaking, the larger the amount of produced COH, the higher the separation of photo- generated charges. A highly sensitive and widely used tech- nique to detect the amount of COH is the coumarin fluorescent method, in which the fluorescent 7-hydroxycoumarin is formed through the facile reactions between coumarin molecules and COH groups.[34] The amount of COH produced on the modified TiO2 is consistent with its corresponding SPS intensity. As ex- pected, the amount of COH produced for the porous SiO2- modified TiO2 (2.1F-3S-T) is the largest of the modified TiO2 samples, and modification with excess SiO2 is unfavorable for ·COH production. It is understandable that excess SiO2 would in- hibit the transportation and separation of photogenerated charges of TiO2. What causes the enhanced separation of photogenerated charges of TiO2 after modification with SiO2 ? From the above XRD patterns, TEM images, and DRS spectra, it is suggested that the crystal phase composition, crystallinity, nanoparticle size and morphology, and optical absorption of TiO2 are not changed after modification with SiO2. Hence, it is anticipated, according to the SPS attribute of TiO2, that the enhanced sepa- ration of photogenerated charges is related to the increased O2 adsorption. To prove this idea, we recorded the O2 tempera- ture-programmed desorption (O2-TPD) curves on different TiO2 samples (Figure 5 B). It is clear that the amount of adsorbed O2 on TiO2 is increased upon modification with 3 % SiO2, especially for the porous SiO2-modified sample (2.1F-3S-T). This is in good agreement with the corresponding SPS intensity (Figure 3). Notably, the amount of desorbed O2 at high temper- atures (>350 8C), corresponding to the chemically adsorbed O2,[35] is greater, which is favorable for capturing photogenerat- ed electrons. From the results of FTIR, XPS, and BET measure- ments, it is suggested that the increase in the adsorbed O2 of TiO2 after SiO2 modification can be attributed to two factors. First, the surfaces of TiO2 are changed by the introduction of ^ Si^OH groups as new ends. Compared with ^Ti^OH, ^Si^OH may be more favorable for O2 adsorption. The second factor is the slightly increased surface area, which leads to the presence of more surface hydroxyl groups. On the basis of our previous works, it is confirmed that phosphate modification could be favorable for O2 adsorption through the ^P^OH surface ends.[17, 25] For further support of the above point related to O2 adsorption, we further treated the optimized porous-SiO2-modified TiO2 with phosphoric acid, as shown in Figure S1. It is noted that the phosphate modifica- tion does not influence the physical properties of 2.1F-3S-T, such as its crystallite size, phase composition, crystallization, and optical absorption, according to the XRD patterns and DRS spectra (Figure S9 A,B). Furthermore, new FTIR bands appear in the range 1010-1250 cm^1 (Figure S9 C), indicating that the phosphate groups, [PO4]3^,[36] are fixed on the surfaces of the porous-SiO2-modified TiO2. This is further proved by the P 2p XPS spectra (Figure S9 D), in which the banding energy of P2p in the [PO4]3^ group is 133.6 eV.[25,36,37] Figure 6 A shows that, as expected, treatment with an appro- priate amount of phosphoric acid can increase the amount of produced COH of 2.1F-3S-T, corresponding to high photogener- ated charge separation. This is responsible for its enhanced photocatalytic activity for the degradation of acetaldehyde (Figure 6 B). If excess phosphoric acid is used, this is unfavora- ble for photogenerated charge separation, and hence, for pho- tocatalytic reactions. In addition, it is found that the H3PO3- treated sample has good stability in aqueous solution, as its photocatalytic activity remains almost unchanged after five cycles of photocatalytic degradation of liquid-phase phenol (Figure S9 E). From the O2-TPD measurements (Figure S9F), it is deduced that the phosphate treatment may increase the amount of adsorbed O2, and thus, promote photogenerated charge separation. Therefore, it is suggested that the increase in adsorbed O2 is a feasible route to improving the activity of the photocatalyst. Conclusion We have improved the photocatalytic activity of P25 TiO2 for the degradation of gas-phase acetaldehyde and liquid-phase phenol (as colorless model pollutants) through its modification with an appropriate amount of porous SiO2, and in particular, with an appropriate amount of phosphate-treated porous SiO2. On the basis of the steady-state surface photovoltage spectra, transient-state surface photovoltage responses, and hydroxyl radical measurements, along with the O2 temperature-pro- grammed desorption curves, it is clearly demonstrated that the O2 adsorption of TiO2 is greatly increased after modification with porous SiO2 (especially with phosphate-treated SiO2), en- hancing the separation of photogenerated charge carriers of TiO2. This is responsible for the improved photocatalytic activi- ty of the resulting modified TiO2. It is suggested for the first time that the introduction of ^Si^OH and ^P^OH as surface ends is favorable for O2 adsorption, and hence, for efficient photocatalysis for pollutant degradation. This work provides a feasible route for improving the photocatalytic activity of TiO2 for the degradation of colorless pollutants, which may also be applicable to other photocatalysts. In addition, this work implies that the ^Si^OH and ^P^OH groups can trans- port charge effectively, which is meaningful for their use as electronic bridges for heterojunction nanocomposite photoca- talysts. Experimental Section All chemicals were obtained from commercial sources and used without further purification. Distilled water was used in the experi- ments. Synthesis of materials P25 TiO2 modified with SiO2 In this process, distilled water (15 mL) was placed in a glass con- tainer and the temperature was maintained at 60 8C. P25 TiO2 powder (0.3 g) purchased from Degussa Company was added to the heated distilled water under stirring for 10 min. Then, tetrae- thoxysilane-containing alcohol solution of a certain concentration (15 mL) was dropped into the former mixture, which was stirred for a further 20 min. Subsequently, the suspension was heated to 80 8C, and this temperature was maintained under vigorous stirring to evaporate the solvent. After calcination at the desired tempera- ture in air for 1 h, SiO2-modified TiO2 was obtained, which is denot- ed as XS-T (X is the percentage ratio of Si/Ti in atomic number). P25 TiO2 modified with porous SiO2 Different amounts of F127 (EO106PO70EO106) as a surfactant template were added to the distilled water (15 mL), and the mixture was kept at 60 8C for 20 min under continuous stirring. The subsequent series of processes were the same as for the previous experiments for SiO2-modified TiO2. For the removal of F127, the dried precursor was washed through a reflux process in a round-bottomed flask with 50 mL solvent (80 % ethanol/water solution) under stirring at 70 8C for 1.5 h. Then, the resulting suspension was centrifuged and washed twice with distilled water. Subsequently, the material was dried at 80 8C and calcined at 300 8C for 1 h, after which porous- SiO2-modified TiO2 was obtained, which is denoted as YF-XS-T (Y is the percentage ratio of F127/Si by mass). Phosphoric-acid-treated porous-SiO2-modified TiO2 A certain amount of the resulting porous-SiO2-modified TiO2 was added to the planned concentration of phosphoric acid solution in a glass container under stirring. Subsequently, the mixture was heated to 808C to evaporate the solvent. After drying at 80 8C and calcination at 300 8C for 1 h, the desired TiO2 was obtained, denot- ed as ZP-YF-XS-T (Z is the molar percentage ratio of P/Ti). Characterization of materials Powder X-ray diffraction (XRD) patterns were recorded on a Rigaku D/MAX-rA diffractometer using a CuKa (0.15418 nm) radiation source. Transmission electron microscopy (TEM) images were ob- tained with a JEOL JEM-2010 instrument with an accelerating volt- age of 200 kV. The Fourier-transform infrared (FTIR) spectra of the samples were collected with a Bruker Equinox 55 Spectrometer, using KBr as diluents. X-ray photoelectron spectroscopy (XPS) measurements were performed on a Kratos-AXIS ULTRA DLD appa- ratus with an Al (Mono) X-ray excitation source. The likely charging of samples was corrected by setting the binding energy of the ad- ventitious carbon (C 1s) to 284.6 eV. The UV/Vis diffuse reflectance spectra (UV/Vis DRS) of the samples were measured with a Model Shimadzu UV2550 spectrophotometer. Thermal gravimetric (TG) analysis was performed with an SDTQ 600 instrument in a constant flow of air with a flow rate of 60 mL min^1; the temperature was raised from room temperature to 1173 K at a ramp rate of 10 K min^1. Nitrogen adsorption/desorption isotherms were mea- sured at 77 K with a Micromeritics Tristar II, and the specific surface areas of the materials were calculated by using the Brunauer- Emmett-Teller (BET) method. The steady-state surface photovoltage spectroscopy (SS-SPS) in- strument was a home-built apparatus equipped with a lock-in am- plifier (SR830) synchronized with a light chopper (SR540). The powder sample was sandwiched between two ITO glass electrodes, and the sandwiched electrodes were arranged in an atmosphere- controlled container with a quartz window. The monochromatic light was obtained by passing light from a 500 W xenon lamp (CHF XQ500W, Global xenon lamp power) through a double prism mon- ochromator (SBP300).[25] Transient-state surface photovoltage (TS- SPV) measurements were performed with a self-assembled device in air at room temperature, in which the sample chamber was con- nected to an ITO glass as the top electrode and to a steel substrate as the bottom electrode, and a mica spacer (10 mm thickness) was placed between the ITO glass and the sample to decrease the space charge region at the ITO/sample interface. The samples were excited by radiation from a 355 nm laser with a pulse width of 10 ns from a second harmonic Nd :YAG laser (Lab-130-10H, New- port, Co.). The laser intensity was modulated with an optical neu- tral filter and measured with a high-energy pyroelectric sensor (PE50BF-DIF-C, Ophir Photonics Group). Temperature-programmed desorption (TPD) of oxygen was mea- sured with a home-built facility. The sample powder (30 mg) was pretreated in a Pyrex tube (i.d. 6 mm) at 450 8C for 30 min with an ultra-high-purity He flow, and then cooled to room temperature (25 8C). For O2 adsorption saturation, the sample was blown contin- uously with ultra-high-purity O2 for 90 min at 25 8C. After O2 ad- sorption, the sample was flushed in an ultra-high-purity He flow to remove the physically adsorbed O2 in the system. The O2-TPD pro- file of the sample was recorded by increasing the temperature from 25 to 650 8C at a heating rate of 10 8C min^1 under a flow of ultra-high-purity He (20 mL min^1). The desorbed O2 was analyzed by a gas chromatograph (GC-2014, SHIMADZU) with a TCD detec- tor. The COH amount under light irradiation was detected by using the coumarin photoluminescence probing technique. The experiments were performed in a 50*70 mm weighing bottle, and a 150 W spherical xenon lamp, the emitting spectrum of which was similar to sunlight, was used as the light source. The distance between the light source and the reactor was 10 cm. In a typical process, the photocatalyst (20 mg) and coumarin solution (50 mL, 1 ^ 10^3 mol L^1) were mixed through magnetic stirring for 30 min in the absence of light, to keep the reactive system uniform. The mixed solutions after irradiation for 0.5 h were measured by fluo- rescence detection with an LS55 spectrofluorometer after centrifu- gation. The excitation and emission wavelengths were 332 and 456 nm, respectively. Photocatalytic activity evaluation The photocatalytic performances of different samples were evalu- ated with gas-phase acetaldehyde and liquid-phase phenol. For the photocatalytic degradation of acetaldehyde, the powder (0.1 g) was placed in a quadrate porcelain boat, which was then put in a Pyrex glass cylindrical reactor with a diameter of 7.0 cm and ef- fective volume of 640 mL. The reactor was placed horizontally and irradiated from the top by using a 9 W ultraviolet lamp (lmax = 365 nm). A mixed gas containing O2 (20 %), N2 (80 %), and acetalde- hyde (810 ppm), was introduced to pass through the reactor for 30 min to ensure the mixed gas reached adsorption-desorption equilibrium, and the initial concentration of acetaldehyde was 810 ppm. The acetaldehyde concentration was measured at inter- vals of 20 min with a gas chromatograph (GC-2014, SHIMADZU) equipped with a flame ionization detector. The liquid-phase photocatalytic experiment was performed in a similar way to the test for the amount of produced C OH described above. The powder (0.10 g) and phenol solution (100 mL, 15 mg L^1) were mixed in a 150 mL photochemical glass reactor under magnetic stirring at room temperature and atmospheric pressure. The light source was positioned 15 cm from the reactor. Prior to irradiation, the reactive system was stirred magnetically in the dark for 30 min to allow adsorption-desorption equilibrium to be attained. After centrifugation, the phenol concentration after the photocatalytic reaction for 1.0 h was measured with a Shimadzu UV-2550 spectrophotometer through the 4-aminoantipyrine spec- trophotometric method at the characteristic optical absorption (510 nm) of phenol. Acknowledgements We are grateful for financial support from the NSFC (21071048), the Program for Innovative Research Team in Chinese Universities (IRT1237), the Project of Chinese Ministry of Education (213011A), the Specialized Research Fund for the Doctoral Program of Higher Education (20122301110002), the Chang Jiang Scholar Candidates Program for Heilongjiang Universities (2012CJHB003), the National Scientific Fund for Distinguished Young Scholars (51125033), Funds for Creative Research Group of China (51121062), and State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology (grant no. 2013DX08). [1] M. R. Hoffmann, S. T. Martin, W. Y. Choi, D. W. Bahnemann, Chem. Rev. 1995, 95, 69. [2] O. Legrini, E. Oliveros, A. M. Braun, Chem. Rev. 1993 , 93, 671. [3] S. G. Kumar, L. G. Devi, J. Phys. Chem. A 2011, 115, 13211. [4] W. Zhou, F. F. Sun, K. Pan, G. H. Tian, B. J. Jiang, Z. Y. Ren, C. G. Tian, H. G. Fu, Adv. Funct. Mater. 2011, 21, 1922. [5] H. R. 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Received : March 13, 2014 Published online on June 11, 2014 Yunbo Luan,[a] Yujie Feng,*[a] Haiqin Cui,[b] Yue Cao,[b] and Liqiang Jing*[b] [a] Dr. Y. Luan, Prof. Y. Feng National Engineer Research Center of Urban Water Resources State Key Laboratory of Urban Water Resource and Environment Harbin Institute of Technology Harbin 150090 (P. R. China) E-mail : [email protected] [b] Dr. H. Cui, Y. Cao, Prof. L. Jing Key Lab of Functional Inorganic Materials Chemistry Heilongjiang University Ministry of Education School of Chemistry and Materials Science Harbin 150080 (P. R. China) E-mail : [email protected] Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cplu.201402063. (c) 2014 Blackwell Publishing Ltd. |