ARTICLE pubs.acs.org/Langmuir
Visible-Light-Driven Copper Acetylacetonate Decomposition by BiVO4 Shin-ichi Naya,† Masanori Tanaka,‡ Keisuke Kimura,‡ and Hiroaki Tada*,†,‡ †
Environmental Research Laboratory, and ‡Department of Applied Chemistry, School of Science and Engineering, Kinki University, 3-4-1, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan ABSTRACT: Visible-light irradiation to monoclinic scheelite BiVO4 (m-BiVO4) in a solution of copper acetylacetonate (Cu(acac)2) has led to its decomposition and Cu recovery. The photonic efficiency at λ = 440 ( 15 nm reaches 3.4%, exceeding the value for the TiO2-photocatalyzed reaction at λ = 355 ( 23 nm (2.0%). The adsorption isotherm and the light intensity-dependence of the decomposition rate indicate high adsorptivity of m-BiVO4 for Cu(acac)2 or its sufficient supply to the surface reaction sites, which mainly contributes to the high photocatalytic activity. Electrochemical measurements using cyclic voltammetry suggest that the reaction proceeds via the oxidative degradation of the ligand followed by the reduction of the resulting Cu2+ ions. Under aerobic conditions, the Cu2+ ions mediate the electron transfer from the conduction band of m-BiVO4 to O2 to complete the catalytic cycle.
I. INTRODUCTION The establishment of sunlight-driven technologies for recovering precious metals should greatly contribute to the realization of the sustainable society.1,2 BiVO4 is a promising visiblelight-active semiconductor with a fairly strong oxidation power and a small hole effective mass guaranteeing the rapid diffusion of the valence band (vb) holes from the bulk to the surface.3,4 High photocatalytic activities of BiVO4 for water oxidation to evolve O2 have been reported in the Ag+-sacrificial systems59 and the artificial photosynthetic ones.1012 Also, BiVO4 exhibits visiblelight-activities for the degradations of phenol derivatives,13,14 polycyclic aromatic hydrocarbons,15 and organic dyes.1620 However, BiVO4 has two major drawbacks: one is the low adsorptivity for organic compounds, probably due to its low isoelectric point (pH 2.32.7),2022 and another is the low-lying conduction band (cb)-edge, which makes it difficult to reduce O223 acting as the electron acceptor in the usual photocatalytic reactions. These two matters eventually result in the electron hole recombination to lower the photocatalytic activity. To enhance the adsorption and/or remove the excited electrons in the cb(BiVO4), the modification with other metal oxides2429 and metal-nanoparticles (NPs)15,3033 as well as the sacrificial agent addition21,22 has so far been devised. On the other hand, the metal recovery from aqueous solutions containing the metal complexes has been achieved by taking advantage of the TiO2 photocatalysis under UV-light irradiation.3436 Generally, precious metals are subject to reduction; however, the stabilization of the metal ions with complexation renders their reductive recovery difficult. In the semiconductor-photocatalyzed reaction, the oxidative degradation of the organic ligand can be followed by the reduction of the resulting metal ions. Also, it has been r 2011 American Chemical Society
reported that formate ions act as an interfacial anchor for the adsorption of metal ions in the TiO2 photocatalytic reduction.37 Consequently, BiVO4 is expected to exert its intrinsic visiblelight-activity for these types of reactions, if its adsorptivity for the metal complex can be large. Herein we report a copper acetylacetonate (Cu(acac)2) decomposition and the Cu recovery using BiVO4 as a visiblelight-active catalyst. Cu(acac)2, which is widely used in the Cuplating process, was selected as a model reaction substrate in this study.
II. EXPERIMENTAL SECTION BiVO4 Preparation and Characterization. BiVO4 was synthesized from aqueous solutions of Bi(NO3)3 and NH4VO3 according to the method reported by Kohtani et al.13 The particle size and morphologies were examined by scanning electron microscopy (SEM, Hitachi S-800) at an acceleration voltage of 15 kV. The specific surface area was determined by nitrogen adsorptiondesorption isotherms at 77 K with a Micromeritics Automatic Surface Area and Porosimetry Analyzer (TriStar 3000, Shimadzu). Prior to N2-sorption, the sample was degassed at 423 K for 1 h under vacuum. X-ray diffraction (XRD) measurements were performed on a Rigaku Mini Flex X-ray diffractometer operating at 40 kV and 80 mA. The scans were collected in the range from 5 to 105° (2θ) by the use of Cu KR radiation (λ = 1.545 Å). Diffuse reflectance UVvisNIR spectra of the resulting samples were recorded on a Hitachi U-4000 spectrometer mounted with an integrating sphere at room temperature. The reflectance (R∞) was recorded Received: May 6, 2011 Revised: July 4, 2011 Published: July 07, 2011 10334
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with respect to a reference of BaSO4, and the KubelkaMunk function [F(R∞)] expressing the relative absorption coefficient was calculated by the equation F(R∞) = (1 R∞)2/2R∞.
BiVO4-Photocatalyzed Cu(acac)2 Decomposition and Cu Recovery. Cu(acac)2 was unstable under acidic conditions, and then the reactions were carried out at pH >7.3. After the suspension of BiVO4 (200 mg) in a Cu(acac)2 solution (40 μM, H2O: tetrahydrofuran (THF) = 99: 1 v/v or 30400 μM, H2O: THF = 9: 1 v/v, 200 mL) with or without pH adjusting to 10.4 by NaOH had been stirred at 298 K in the dark, irradiation was started using a 300 W Xe lamp (HX-500, Wacom) with a cut off filter Y-45 (AGC TECHNO GLASS) in a double jacket type reaction cell (81 mm in diameter and 77 mm in length). THF was added to completely dissolve Cu(acac)2. The reaction temperature was kept at 298 K by circulating thermostatted water through the outer jacket around the cell. The light intensity integrated from 420 to 485 nm (I420485) was measured to be 3.6 mW cm2. The Cu(acac)2 concentration was determined by UVvis spectroscopy (UV-1800, Shimadzu). Cu(acac)2 and Cu2+ ions adsorbed on m-BiVO4 were confirmed to be easily removed from the surface by washing with THF and H2O. After the m-BiVO4 particles recovered after irradiation had been sufficiently washed, the Cu in the deposits was completely dissolved into a HNO3 solution, and then the Cu amount was quantified by inductively coupled plasma spectroscopy (ICPS-7500, Shimadzu). X-ray photoelectron spectroscopic (XPS) measurements were performed using a Kratos Axis Nova X-ray photoelectron spectrometer with a monochromated Al KR X-ray source operated at 15 kV and 10 mA using C1s as the energy reference (284.6 eV). Transmission electron microscopic (TEM) observation was carried out using a JEOL JEM-3000F and Gatan Imaging Filter at an applied voltage of 300 kV. The samples were stored in dark and in vacuo until the XPS measurements and TEM observation. Adsorption Measurement. Adsorption isotherm of Cu(acac)2 was obtained by exposing BiVO4 (200 mg) to solutions with different concentrations of Cu(acac)2 (50 mL) at 298 K for 18 h in the dark. The adsorbing amount of Cu(acac)2 on the recovered BiVO4 was quantified by inductively coupled plasma spectroscopy (ICPS-7500, Shimadzu). Cyclic Voltammetry. Cyclic voltammograms were measured in a MeCN solution containing 0.5 mM Cu(acac)2 and 0.1 M Bu4N 3 ClO4 supporting electrolyte under deaerated conditions using glassy carbons as working and counter electrodes, and Ag/AgCl as a reference electrode. Cyclic voltammograms were also measured in a H2O solution containing 0.05 mM CuSO4 and 0.1 M Na2SO4 supporting electrolyte (pH 7.0) under deaerated and aerated conditions using the same electrodes.
III. RESULTS AND DISCUSSION Bright yellow powders were obtained by the synthetic method.13 Scanning electron microscopic (SEM) image showed that the solid consists of several micrometer-sized particles, and the specific surface area was determined to be 2.1 m2 g1 by the BrunauerEmmettTeller (BET) method. Figure 1A(a) shows the X-ray diffraction pattern of the synthesized solids, indicating that the particles crystallize with the monoclinic scheelite structure (m-BiVO4). BiVO4 possesses three crystalline phases, i. e. monoclinic scheelite, tetragonal scheelite, and tetragonal zircon, among which monoclinic scheelite exhibits the highest photocatalytic activity.38 Figure 1B(a) shows the diffuse reflectance UVvis absorption spectrum of m-BiVO4: F(R∞) denotes the KubelkaMunk function. The m-BiVO4 has intense absorption due to the interband transition at λ < 520 nm. Recent density functional theory calculations have shown that the strong absorption can result from the direct gap transition.3,4 From the absorption edge, the band gap was determined to be 2.4 eV that is in agreement with the literature value.6
Figure 1. (A) XRD patterns of the synthesized sample (a) and the sample recovered after repeating the photoreaction three times (b). (B) Diffuse reflectance UVvis absorption spectra of m-BiVO4 (a), m-BiVO4 recovered after the photoreaction (b), and after repeating the photoreaction three times (c) under deaerated conditions.
Under deaerated conditions, visible-light irradiation (λ > 420 nm) to m-BiVO4 in a Cu(acac)2 solution at pH 10.4 led to the rapid Cu(acac)2 degradation. The reaction was completed at irradiation time (tp) ∼0.5 h, while the pH of the solution decreased to 9.2. The Cu in the initial solution was deposited on the m-BiVO4 surface in 89% yield. The deposited amount (35.6 μmol g1) was much greater than the adsorption amount of Cu(acac)2 (1.4 μmol g1, vide infra). As shown in Figure 1B(b), the solid sample recovered after the photoreaction exhibits broad absorption in the vis-NIR. However, no particle was observed on the m-BiVO4 surface by transmission electron microscopy (TEM). In order to grow the deposits, the initial concentration of Cu(acac)2 was increased to 400 μM, and the photoreaction was repeated three times. Figure 2A shows the TEM images of the resulting sample (a), and Cu(acac)2adsorbed m-BiVO4 (b) for comparison. Many particles ranging from 1 to 3 nm are formed on the m-BiVO4 surface in sample (a), while no particle was observed in sample (b). Generally, such a small Cu particle is highly reactive, and it has recently been reported that Cu NPs (average 8.4 nm) are readily oxidized to yield Cu2O or Cu(core)-Cu2O(shell) particles under ambient conditions.39 By using XPS, one can distinguish Cu2+ (CuO) from the other forms of Cu, whereas Cu0 and Cu+ (Cu2O) have virtually the same peak shape and binding energy (EB).40 Figure 2B shows the Cu2p-XPS spectra of samples (a) and (b). In the spectrum for sample (a), the signals are present at 932.0 and 951.7 eV, which are assignable to the emissions from the Cu2p3/2 and Cu2p1/2 levels, respectively.41 This result implies that the Cu in the deposits has the oxidation state of Cu0 and/or Cu+. However, the binding energies (EB(Cu2p3/2) = 932.4 and EB(Cu2p1/2) = 952.2 eV) for sample (b) are close to those for sample (a) in spite that the Cu oxidation state in sample (b) is Cu2+.42 The samples possibly undergo reduction by the electron beam for the correction of charging, and therefore the Cu oxidation sate can not be determined by the XPS measurements. Figure 1B(c) also shows the UVvisNIR absorption spectrum of the sample obtained after repeating the photoreaction three times. A broad absorption resulting from the localized surface plasmon resonance of Cu NPs is observed around 670 nm in addition to the absorption of the Cu2O interband transition at λ < 610 nm (band gap ∼2 eV). In the XRD pattern for the same sample (Figure 1 A(b)), a clear diffraction peak from the Cu2O(111) plane is observed, whereas the diffractions of Cu are veiled by the intense diffractions from m-BiVO4. The cbelectrons(BiVO4) has a sufficient potential to reduce Cu2+ ions 10335
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Figure 2. (A) TEM images and (B) XPS spectra of the solid sample obtained after repeating the photoreaction three times under deaerated conditions (a) and the Cu(acac)2-adsorbed BiVO4 (b).
Figure 3. (A) Change in electronic absorption of a Cu(acac)2 solution with vis-irradiation (λ > 420 nm) in the presence of m-BiVO4 under aerobic conditions. (B) Plots of [Cu(acac)2] under vis-irradiation (λ > 420 or 570 nm) in the presence or absence of m-BiVO4 and in the dark with m-BiVO4.
Figure 4. (A) Change in electronic absorption of a Cu(acac)2 solution with room light-irradiation in the presence of m-BiVO4 under aerobic conditions. (B) Plots of [Cu(acac)2] under room light-irradiation in the presence or absence of m-BiVO4.
to Cu0 (vide post). Consequently, a conclusion can be drawn that the photoreaction yields Cu NPs, of which surface is oxidized to Cu2O by the exposure to air during the sample recovery and characterization. When the photoreaction was repeated, the reaction rate was almost invariant in spite of the decrease in the surface area of m-BiVO4 with the Cu deposition. This result would be explained in terms of the charge separation enhancement due to the interfacial electron transfer from the cb(mBiVO4) to Cu with a large work function.43 Under aerobic conditions, the visible-light-induced Cu(acac)2 degradation proceeds without pH adjustment (pH 8.9). Figure 3A shows the UVvis absorption spectral change of the reaction solution with irradiation time (tp). At tp = 2 h, the absorption of Cu(acac)2 at λ > 240 nm almost disappears, whereas under deaerated conditions, a weak absorption of acetylacetone appears around 272 nm. Figure 3B shows time courses for the Cu(acac)2 decomposition under various conditions. On irradiation with m-BiVO4, the decomposition was completed at tp ≈ 2 h, while the pH of the solution hardly changed (pH 8.7). Both m-BiVO4 and illumination at λ < 570 nm were necessary for the decomposition to take place. In contrast to the deaerated reaction system, no Cu was deposited on the m-BiVO4 surface. The reaction is accelerated with an increase in the initial pH from 8.9 to 10.4. After 1 h irradiation at pH 10.4 under aerobic conditions, the reaction solution was successively irradiated with Ar bubbling for additional 1 h. As a result, the Cu in the solution was deposited on m-BiVO4 in 85% yield. Further, the photonic efficiency (ϕ, molecules decomposed/incident
photons) for the Cu(acac)2 decomposition was measured by using optical band-pass filters. For comparison, the ϕ value of anatase TiO2 (A-100, Ishihara Sangyo) for Cu(acac)2 decomposition was also evaluated. The ϕ value for m-BiVO4 at λ = 440 ( 15 nm was 3.4%, exceeding that for the anatase TiO2 at λ = 355 ( 23 nm (2.0%). The m-BiVO4-photoinduced decomposition of Cu(acac)2 proceeds under room light. Figure 4A shows the UVvis absorption spectral change of the reaction solution with illumination by fluorescent light (I420485 ≈ 10 μW cm2). As tp increases, the absorption of Cu(acac)2 at λ > 240 nm monotonically weakens without appearance of new absorption. Figure 4B shows the change in the Cu(acac)2 concentration under illumination by fluorescent light in the presence and absence of m-BiVO4. Even under such a low light intensity, the m-BiVO4-photocatalyzed reaction is almost completed at tp ≈ 8 h. This fact allows us to expect that the reaction can proceed under the sunlight in cloudy or rainy day. To clarify the origin for this efficient reaction, the light intensity-dependence of the photocatalytic activity was studied. Figure 5 shows plots of the initial decomposition rate (v0) vs the light intensity from 420 to 485 nm (I420485). Clearly, the v0 value is proportional to the light intensity. Previous reports showed that the reaction rate constant (k) can be related to the light intensity (I) as k = AIn, where A is constant, and n can range between 0.5 and 1.44,45 The linear correlation (n = 1) means that the rate of this reaction is controlled by the light intensity; that is, Cu(acac)2 is sufficiently supplied to the reaction 10336
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Figure 5. Plots of v0 vs light intensity.
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Figure 7. (A) Cyclic voltammograms in a deaerated 0.5 mM Cu(acac)2 solution. (B) Cyclic voltammograms in a deaerated 0.5 mM Cu(acac)2 solution (a), and in a deaerated (b), and a aerated (c) 0.05 mM CuSO4 solutions.
Scheme 1. Schematic Presentation of the Visible LightInduced Decomposition of Cu(acac)2 and Cu-Recovery
Figure 6. (A) Adsorption isotherms of Cu(acac)2 on m-BiVO4. (B) Langmuir plots for Cu(acac)2 adsorption.
sites on the m-BiVO4 surface under the present conditions. On the other hand, in the diffusion-controlled limit, n reduces to 0.5. Further, the adsorption property of m-BiVO4 for Cu(acac)2 was examined in detail. Figure 6A shows the adsorption isotherm at 298 K: Y denotes the equilibrium adsorption amount of Cu(acac)2 per unit mass of m-BiVO4. Apparently, m-BiVO4 exhibits a good adsorptivity for Cu(acac)2. As shown in Figure 6B, the Langmuir plot shows a straight line, of which slope and intercept provide the saturated adsorption amount of 3.71 μmol g1 and the adsorption equilibrium constant of 1.60 104 M1. Also, no acetylacetone was generated during the adsorption. These results indicate that Cu(acac)2 is chemisorbed on the m-BiVO4 surface without ligand exchange. This feature is similar to the adsorption of Cu(acac)2 on the surfaces of SiO2 and anatase TiO2,46 whereas Fe(acac)3 is adsorbed on anatase TiO2 by the ligand exchange between the acac-ligand and the surface OH group.47 From the saturated adsorption amount and the BET surface area, the area occupied by one Cu(acac)2 complex was estimated to be 0.94 nm2 complex1, which is comparable to the molecular cross-sectional area (0.97 nm2 complex1).48,49 This high level of adsorptivity should contribute to the high photocatalytic activity of m-BiVO4 in the present reaction, whereas the reaction rate is severely limited by the supply of reaction substrates in the usual BiVO4-photocatalyzed reactions.15 To gain information about the reaction mechanism, cyclic voltammograms (CV) were measured in the solutions of Cu(acac)2 and CuSO4. Figure 7A shows the CV curve of a glassy carbon electrode in a deaerated MeCN solution of Cu(acac)2 in the potential range from 0.1 to +2.2 V vs standard hydrogen electrode (SHE). Two anodic current peaks due to the acacligand oxidations are observed at +1.7 and +1.9 V. The irreversible nature suggests that the Cu(acac)2 decomposition is caused
by the ligand oxidation. Also, Figure 7B compares the CV curves of the glassy carbon electrode in a deaerated Cu(acac)2 solution (a) in the potential range from 1.3 to +0.4 V, and in a deaerated (b) and an aerated (c) solutions of CuSO4 in the potential range from 0.6 to +1.0 V. The comparison of curve (a) with curve (b) indicates that the peak of the cathodic current due to the reduction of [Cu(H2O)6]2+ (abbreviated as Cu2+) is shifted from 0.8 to 0.1 V as a result of the complexation with acetylacetone. Also, in curve (b), a Cu2+/Cu0 redox pair is present at a half-wave potential of +0.16 V. On the other hand, in curve (c), the anodic current peak corresponding to the cathodic current peak at 0.1 V is absent. Evidently, the Cu2+ ions generated by the acac-ligand oxidation can be more easily reduced than Cu(acac)2, and the resulting Cu0 is suggested to undergo the reoxidation by O2. On the basis of these results, the essential mechanism on the m-BiVO4-photocatalyzed reaction can be summarized in the following way (Scheme 1). Cu(acac)2 is chemisorbed on the m-BiVO4 surface in the dark (S1). Visible-light-irradiation to m-BiVO4 initiates the interband transition to generate electron hole pairs (S2). In the anodic process, the vb-holes(m-BiVO4) escaping the recombination (S3) with a potential of +2.0 V (pH 8.9)23 oxidize the acac-ligands of Cu(acac)2 to yield Cu2+ ions (S4). In the cathodic process, the cb-electrons(BiVO4) with a potential of 0.4 V (pH 8.9)23 reduce the Cu2+ ions to Cu0 in the deoxygenated solution (S5), whereas the direct reduction of 10337
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efficiency defined as kox/(kox + krec) was estimated to be ca. 0.3. In addition to the higher photonic efficiency exceeding that in the TiO2-photocatalyzed reaction, these results show that this is an efficient visible-light-driven reaction system induced solely by BiVO4.
Figure 8. (A) Plots of v0 as a function of [Cu(acac)2]0. (B) Plots of (v0)1 vs [Cu(acac)2]01.
Cu(acac)2 is difficult. In the presence of O2, the Cu0 formed on the m-BiVO4 surface is reoxidized to Cu2+ ions (S6); that is, the Cu2+/Cu0 couple acts as an electron mediator from the cb(m-BiVO4) to O2. In this case, the pH of the solution is almost maintained since the H+ generated in S4 is consumed in S6. Consequently, the Cu(acac)2 degradation rapidly proceeds without pH adjustment in the presence of O2. The increase in the pH of the solution rises the cb(m-BiVO4), which favors the reduction of the Cu2+ ions to Cu0 to increase the decomposition rate. No H2O2 was detected by iodometric titration of the irradiated solutions, since H2O2 could undergo fast reductive decomposition by the cb-electrons(BiVO4).21 K
BiVO4 þ CuðacacÞ2 T CuðacacÞ2 ad 3 3 3 BiVO4 Iη
ðS1Þ
BiVO4 þ hv f ecb 3 3 3 hvb þ
ðS2Þ
krec
ðS3Þ
ecb 3 3 3 hvb þ f heat kox
CuðacacÞ2 ad þ 2hvb þ f Cu2þ þ decomposed products þ Hþ kred
Cu2þ þ 2ecb f Cu0 kreox
Cu0 þ O2 þ 2Hþ f Cu2þ þ H2 O2
ðS4Þ ðS5Þ ðS6Þ
In this scheme, the application of the steady-state approximation for [ecb] and [hvb+] yields eq 1 for the initial stage of the reaction50 v0 1 ¼ ð1=IηÞf1 þ ðkrec =Kkox Þ½CuðacacÞ2 0 1 g
ð1Þ
where [Cu(acac)2]0 expresses the initial concentration of Cu(acac)2. The reactions were carried out by varying [Cu(acac)2]0 from 30 to 400 μM with the light intensity maintained constant (I420485 = 3.6 mW cm2). Figure 8A shows plots of v0 vs [Cu(acac)2]0. Increasing [Cu(acac)2]0 causes a significant increase in v0, and the profile of this curve resembles that of the adsorption isotherm (Figure 6). This result confirms again the importance of the substrate supply to the BiVO4 surface in this reaction. Figure 8B shows plots of v01 vs [Cu(acac)2]01. As expected from eq 1, the plots provide a straight line, and from the slope and intercept, the krec/Kkox value was calculated to be 1.36 104 M. From the values of krec/Kkox and K, the reaction
IV. CONCLUSIONS We have found that m-BiVO4-visible light photocatalyzed Cu(acac)2 decomposition proceeds with a photonic efficiency of 3.4% (at λ = 440 ( 15 nm), and the Cu in the solution has been recovered in 89% yield under deaerated conditions. This study has shown the importance of the simultaneous enhancement of the adsorptivity for substrates and the electron transfer from the conduction band to acceptors to achieve efficient m-BiVO4-photocatalyzed reaction systems. ’ AUTHOR INFORMATION Corresponding Author
*Tel: +81 6 6721 2332. Fax: +81 6 6721 2500. E-mail: h-tada@ apch.kindai.ac.jp.
’ ACKNOWLEDGMENT This work was supported by a Grant-in-Aid for Scientific Research (B) No. 20350097 from the Ministry of Education, Science, Sport, and Culture, Japan, by the Nippon Sheet Glass Foundation for Materials Science and Engineering, and by the Sumitomo Foundation. ’ REFERENCES (1) Rajeshwar, K.; de Tacconi, N. R. Chem. Soc. Rev. 2009, 38, 1984. (2) Anpo, M. Bull. Chem. Soc. Jpn. 2004, 77, 1427. (3) Walsh, A.; Yan, Y.; Huda, M. N.; Al-Jassim, M. M.; Wei, S.-H. Chem. Mater. 2009, 21, 547. (4) Zhao, Z.; Li, Z.; Zou, Z. Phys. Chem. Chem. Phys. 2011, 13, 4746. (5) Kudo, A.; Ueda, K.; Kato, H.; Mikami, I. Catal. Lett. 1998, 53, 229. (6) Kudo, A.; Omori, K.; Kato, H. J. Am. Chem. Soc. 1999, 121, 11459. (7) Yu, J.; Kudo, A. Adv. Funct. Mater. 2006, 16, 2163. (8) Ke, D.; Peng, T.; Ma, L.; Cai, P.; Jiang, P. Appl. Catal., A 2008, 350, 111. (9) Xi, G.; Ye, J. Chem. Commun. 2010, 46, 1893. (10) Kato, H.; Hori, M.; Konta, R.; Shimodaira, Y.; Kudo, A. Chem. Lett. 2004, 1348. (11) Kato, H.; Sasaki, Y.; Iwase, A.; Kudo, A. Bull. Chem. Soc. Jpn. 2007, 80, 2457. (12) Sasaki, Y.; Nemoto, H.; Saito, K.; Kudo, A. J. Phys. Chem. C 2009, 113, 17536. (13) Kohtani, S.; Makino, S.; Kudo, A.; Tokumura, K.; Ishigaki, Y.; Matsunaga, T.; Nikaido, O.; Hayakawa, K.; Nakagaki, R. Chem. Lett. 2002, 660. (14) Kohtani, S.; Koshiko, M.; Kudo, A.; Tokumura, K.; Ishigaki, Y.; Toriba, A.; Hayakawa, K.; Nakagaki, R. Appl. Catal., B 2003, 46, 573. (15) Kohtani, S.; Tomohiro, M.; Tokumura, K.; Nakagaki, R. Appl. Catal., B 2005, 58, 265. (16) Li, G.; Zhang, D.; Yu, J. C. Chem. Mater. 2008, 20, 3983. (17) Li, H.; Liu, G.; Duan, X. Mater. Chem. Phys. 2009, 115, 9. (18) Zhang, L.; Chen., D.; Jiao, X. J. Phys. Chem. B 2006, 110, 2668. (19) Zhou, Y.; Vuille, K.; Heel, A.; Probst, B.; Kontic, R.; Patzke, G. R. Appl. Catal., A 2010, 375, 140. (20) Castillo, N. C.; Heel, A.; Graule, T.; Pulgarin, C. Appl. Catal., B 2010, 95, 335. 10338
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(21) Castillo, N. C.; Ding, L.; Heel, A.; Graule, T.; Pulgarin, C. J. Photochem. Photobiol., A 2010, 216, 221. (22) Xie, B.; Zhang, H.; Cai, P.; Qiu, R.; Xiong, Y. Chemosphere 2006, 63, 956. (23) Long, M.; Cai, W.; Kisch, H. J. Phys. Chem. C 2008, 112, 548. (24) Long, M.; Cai, W.; Cai, J.; Zhou, B.; Cai, X.; Wu, Y. J. Phys. Chem. B 2006, 110, 20211. (25) Xu, H.; Li, H.; Wu, C.; Chu, J.; Yan, Y.; Shu, H. Mater. Sci. Eng., B 2008, 147, 52. (26) Xu, H.; Li, H.; Wu, C.; Chu, J.; Yan, Y.; Shu, H.; Gu, Z. J. Hazardous Mater. 2008, 153, 877. (27) Jiang, H. Q.; Endo, H.; Natori, H.; Nagai, M.; Kobayashi, J. Mater. Res. Bull. 2009, 44, 700. (28) Yao, W.; Iwai, H.; Ye, J. Dalton Trans. 2008, 1426. (29) Chatchai, P.; Murakami, Y.; Kishioka, S.; Nosaka, A. Y.; Nosaka, Y. Electrochim. Acta 2009, 54, 1147. (30) Kohtani, S.; Hiro, J.; Yamamoto, N.; Kudo, A.; Toukmura, K.; Nakagaki, R. Catal. Commun. 2005, 6, 185. (31) Ge., L. Mater. Lett. 2008, 62, 926. (32) Shan, Z.; Wu, J.; Xu, F.; Huang, F.-Q.; Ding, H. J. Phys. Chem. C 2008, 112, 15423. (33) Zhanga, X.; Zhanga, Y.; Quana, X.; Chena, S. J. Hazardous Mater. 2009, 167, 911. (34) Kagaya, S.; Bitoh, Y.; Hasegawa, K. Chem. Lett. 1997, 155. (35) Rhoads, K. R.; Davis, A. P. J. Environ. Eng. 2004, 130, 425. (36) Park, E. H.; Jung, J.; Chung, H.H. Chemosphere 2006, 64, 432. (37) Chenthamarakshan, C. R.; Rajeshwar, K. Electrochem. Commun. 2000, 2, 527. (38) Tokunaga, S.; Kato, H.; Kudo, A. Chem. Mater. 2001, 13, 4624. (39) Hung, L-I; Tsung, C-K; Huang, W.; Yang, P. Adv. Mater. 2010, 22, 1910. (40) Wu, C.-K.; Yin, M.; O’Brien, S.; Koberstein, J. T. Chem. Mater. 2006, 18, 6054. (41) Abdulla-Al-Mamun, M.; Kusumoto, Y. Chem. Lett. 2009, 38, 826. (42) Okada, K.; Kawai, J.; Kotani, A. Phys. Rev. B 1993, 48, 10733. (43) Tada, H.; Kiyonaga, T.; Naya, S. Chem. Soc. Rev. 2009, 38, 1849. (44) Hoffmann, M. R.; Martin, S. T.; Choi, W.; Bahnemann, D. W. Chem. Rev. 1995, 95, 69. (45) Park, H.; Lee, J.; Choi, W. Catal. Today 2006, 111, 259. (46) Mitchell, M. B.; Chakravarthy, V. R.; White, M. G. Langmuir 1994, 10, 4523. (47) Tada, H.; Jin, Q.; Nishijima, H.; Yamamoto, H.; Fujishima, M.; Okuoka, S.; Hattori, T.; Sumida, Y.; Kobayashi, H. Angew. Chem., Int. Ed. 2011, 50, 3501. (48) Lebrun, P. C.; Lyon, W. D.; Kuska, H. A. J. Cryst. Spectrosc. Res. 1986, 16, 889. (49) de Almeida, K. J.; Cesar, A.; Rinkevicius, Z.; Vahtras, O.; Ågren, H. Chem. Phys. Lett. 2010, 492, 14. (50) Fujii, M.; Nagasuna, K.; Fujishima, M.; Akita, T.; Tada, H. J. Phys. Chem. C 2009, 113, 16711.
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dx.doi.org/10.1021/la2016935 |Langmuir 2011, 27, 10334–10339
