Applied Catalysis A, General (v.521, #C)

Contents (iii-xi).

Preface: Photocatalysis by Takashi Hisatomi; Kentaro Teramura; Tsunehiro Tanaka; Kazunari Domen (1).

Layering MoS2 on soft hollow g-C3N4 nanostructures for photocatalytic hydrogen evolution by Dandan Zheng; Guigang Zhang; Yidong Hou; Xinchen Wang (2-8).
Efficient hydrogen evolution catalysis has been achieved over polymeric hollow nanospheres modified with MoS2 under visible light. The hybrid nanocomposites enhances the light-harvesting ability, promotes fast charge separation and creates active sites to support hydrogen photosynthesis, giving an impetus to the rational design of hybrid nanocomposites based on earth-abundant elements for photocatalysis.Display OmittedHollow MoS2/g-C3N4 hybrids were obtained through a combination route of hard-templating technique and impregnation-sulfidation method. The physicochemical, optical/electric and electrocatalytic properties of the obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy, photoluminescence (PL) spectroscopy and electrochemical measurement. Their photocatalytic activities were evaluated by H2 production from lactic acid aqueous solution with visible-light irradiation. The results showed that MoS2/HCNS nanojunctions exhibited enhanced photocatalytic H2 production, which could be attributed to the thin layered junctions formed between MoS2 and HCNS for efficient charge separation and the active sites provided by MoS2 for H2 production at lower over potentials.
Keywords: Conjugated polymer; Photocatalysis; MoS2; Hollow nanospheres; Cocatalyst;

Enhancement of the Cr(VI) adsorption and photocatalytic reduction activity of g-C3N4 by hydrothermal treatment in HNO3 aqueous solution by Hongtao Wei; Qian Zhang; Yongcai Zhang; Zhanjun Yang; Aiping Zhu; Dionysios D. Dionysiou (9-18).
Display OmittedAn effective and environmental-friendly method was adopted to enhance the Cr(VI) adsorption and photocatalytic reduction activity of g-C3N4, which was prepared by thermal condensation of melamine. The enhancement was realized by hydrothermal treatment of g-C3N4 in 1.9–7.6 mol/L HNO3 aqueous solutions at 80–120 °C for 3–12 h. The compositions, structures and physiochemical properties of the hydrothermally treated g-C3N4 were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption isotherms, Zeta potential analysis, UV–vis diffuse reflectance spectroscopy and photocurrent measurement, and their dark adsorption and visible-light (wavelength >420 nm)-driven photocatalytic reduction of Cr(VI) in aqueous solution were tested. It was found that the hydrothermally treated g-C3N4 exhibited significantly enhanced Cr(VI) adsorption and photocatalytic reduction activity than g-C3N4. Moreover, larger concentration of HNO3 aqueous solution, higher hydrothermal temperature or longer treatment time resulted in higher Cr(VI) adsorption and photocatalytic reduction activity of the hydrothermally treated g-C3N4. The reasons accounting for the enhanced Cr(VI) adsorption and photocatalytic reduction activity of the hydrothermally treated g-C3N4 were discussed, and the different mechanisms for the photocatalytic reduction of Cr(VI) over g-C3N4 and the hydrothermally treated g-C3N4 were also proposed.
Keywords: Graphitic carbon nitride; Hydrothermal treatment; Adsorption; Photocatalytic reduction; Hexavalent chromium;

Synergetic effect of TiO2 as co-catalyst for enhanced visible light photocatalytic reduction of Cr(VI) on MoSe2 by Haipeng Chu; Wenyan Lei; Xinjuan Liu; Jinliang Li; Wei Zheng; Guang Zhu; Can Li; Likun Pan; Changqing Sun (19-25).
Display OmittedMoSe2-TiO2 composites were successfully synthesized via a facile solvothermal method. Their morphology, structure and photocatalytic activity in the reduction of Cr(VI) were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy and electrochemical impedance spectra, respectively. The results show that the introduction of TiO2 into MoSe2 boosts the light harvesting efficiency and charge separation and transfer due to their synergistic effect, thus enhancing the visible light photocatalytic activity of MoSe2 with a maximum Cr(VI) reduction rate of 91% at 120 min compared with pure MoSe2 (61%) and TiO2 (5%).
Keywords: Transition metal dichalcogenides; MoSe2; TiO2; Cr(VI); Photocatalysis;

Application of LaMg1/3Ta2/3O2N as a hydrogen evolution photocatalyst of a photocatalyst sheet for Z-scheme water splitting by Zhenhua Pan; Takashi Hisatomi; Qian Wang; Mamiko Nakabayashi; Naoya Shibata; Chengsi Pan; Tsuyoshi Takata; Kazunari Domen (26-33).
Display OmittedZ-scheme water splitting systems are suited for photocatalysts with long absorption edge wavelengths because H2 and O2 evolution reactions occur on different photocatalysts via two-step excitation. In this study, the applicability of LaMg 1/3 Ta 2/3 O 2 N, a 600-nm-class photocatalyst, as a H2 evolution photocatalyst (HEP) in Z-scheme systems was investigated. The redox-mediator-free Z-scheme system composed of RhCrO x /LaMg1/3Ta2/3O2N as a HEP and rutile as an O2 evolution photocatalyst (OEP) showed higher activity than one-step excitation systems of RhCrO x /LaMg1/3Ta2/3O2N or rutile alone under irradiation (λ  ≥ 300 nm). Moreover, a photocatalyst sheet, which consisted of RhCrO x /LaMg1/3Ta2/3O2N and rutile embedded in a Au layer by the particle transfer method, exhibited a photocatalytic activity one order of magnitude higher than the Z-scheme powder suspension system, although LaMg1/3Ta2/3O2N suffered from self-oxidation. Coating the photocatalyst sheet with an amorphous titanium oxide (a-TiO2) protective layer suppressed the self-oxidation of LaMg1/3Ta2/3O2N effectively while maintaining a high photocatalytic activity. This is because the overlying a-TiO2 layer stabilized LaMg1/3Ta2/3O2N while the underlying Au layer transferred charges between RhCrO x /LaMg1/3Ta2/3O2N and rutile effectively. The present study demonstrates the feasibility of the use of LaMg1/3Ta2/3O2N in Z-scheme systems as a HEP with a long absorption edge wavelength and provides a facile approach to stabilizing oxynitrides in photocatalyst sheet systems.
Keywords: Z-scheme; Water splitting; Photocatalyst sheet; Protective layer; Oxynitride;

Controlled growth of CuO/Cu2O hollow microsphere composites as efficient visible-light-active photocatalysts by Xiaolu Liu; Jiangyao Chen; Porun Liu; Haimin Zhang; Guiying Li; Taicheng An; Huijun Zhao (34-41).
Display OmittedCopper oxide composites with tunable composition and morphology were hydrothermally synthesized and used as highly efficient photocatalysts towards the degradation of dye pollutants under visible light irradiation. Effects of key synthesis reaction parameters, i.e., soft template (P123), pH of precursor solution, hydrothermal reaction temperature, the durations on the resultant copper oxide structures have been systematically investigated and a tentative mechanism was proposed for the formation of the copper oxide composites with different synthesis reaction parameters. Furthermore, the photocatalytic activities of resultant copper oxide materials towards the degradation of dye (methyl orange) demonstrated strong dependence on the compositional and morphological properties of the photocatalysts. CuO/Cu2O hollow microsphere composites exhibited the highest visible light photocatalytic activity that can be attributed to their unique hollow structure and CuO/Cu2O heterostructure. The demonstrated controlled growth of metal oxide composite hollow structure provides enlightenments in fabrication of highly efficient heterostructured photocatalysts for environmental remediation.
Keywords: Copper oxide composite; Hollow structure; Visible light; Photocatalysis; Dye pollutant;

A shuriken-shaped m-BiVO4/{0 0 1}–TiO2 heterojunction: Synthesis, structure and enhanced visible light photocatalytic activity by Xiaodi Zhu; Fan Zhang; Mengjiao Wang; Xiang Gao; Ying Luo; Jiawei Xue; Yi Zhang; Jianjun Ding; Song Sun; Jun Bao; Chen Gao (42-49).
Display OmittedShuriken-shaped BiVO4/TiO2 composite with heterojunction structure was synthesized by a facile hydrothermal reaction. The photocatalyst was characterized by X-ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, UV–vis diffuse reflectance spectra, N2 adsorption/desorption, X-ray photoelectron spectroscopy techniques, photoluminescence spectra and photoelectrochemical measurements. The photocatalytic activities were evaluated by the degradation of methyl blue (MB) under visible light irradiation. The results indicated that the synthesized monoclinic BiVO4 had a shuriken shape. The TiO2 nanosheets (NSs) with dominant {0 0 1} facets adhered uniformly on the surface of BiVO4, forming the heterojunction structure. The obtained BiVO4/TiO2 showed about 1.4 times and 8.9 times higher photocatalytic activity than that of the bare BiVO4 and physical mixture BiVO2–TiO2 sample, respectively, which can be attributed to the synergistic effect of BiVO4/TiO2 heterojunction and TiO2 NSs. The incorporation of TiO2 not only did not affect the visible light absorption ability of BiVO4, but also improved the specific surface area as well as pore diameter, which suggesting a better adsorption ability for pollutants. More importantly, the formed heterojunction between m-BiVO4 and TiO2 significantly improved the separation efficiency of the photogenerated electron–hole pairs. These factors contribute to the enhancement of photocatalytic activity. A possible mechanism was also proposed to understand the origin of enhanced performance in the heterojunction system.
Keywords: BiVO4/TiO2; Heterojunction; Photocatalytic degradation; Visible light;

Display OmittedControllable synthesis of one-dimensional (1D)/three-dimensional (3D) nanocomposites with promising photocatalytic performances has been attracting ever-increasing research attention in recent years. Here, we report the self-assembly of TiO2 nanobelts/CdS nanospheres (TNBs/CdS NSPs) photocatalyst via the electrostatic interaction of positively charged CdS nanospheres (CdS NSPs) with negatively charged TiO2 nanobelts in aqueous phase. The as-formed TNBs/CdS NSPs nanocomposite exhibited significantly enhanced visible-light-driven photocatalytic activities in comparison with the single counterpart (TNBs and CdS NSPs) owing to the formation of well-defined heterojunction between TNBs and CdS NSPs, thus leading to much enhanced light absorption and prolonged lifetime of photogenerated charge carriers. It is anticipated that our work could provide an efficient synthetic approach to design a large variety of 1D/3D photocatalysts for diverse photocatalytic applications.
Keywords: TiO2 nanobelts; CdS nanospheres; Self-assembly; Photocatalysis;

A proof of the direct hole transfer in photocatalysis: The case of melamine by Valter Maurino; Marco Minella; Fabrizio Sordello; Claudio Minero (57-67).
Display OmittedThe photoinduced transformation of 2,4,6-triamino-1,3,5-triazine (melamine) was studied by using different advanced oxidation technologies under a variety of experimental conditions. The systems involving homogeneous hydroxyl radicals, as generated by H2O2/hν, Fenton reagent, and sonocatalysis are ineffective. However, melamine is degraded under photocatalytic conditions or by SO4 (S2O8 2−/hν). The time evolution of long-living intermediates, such as 2,4-diamino-6-hydroxy-1,3,5-triazine (ammeline) and 2-amino-4,6-dihydroxy-1,3,5-triazine (ammelide), has been followed, being 2,4,6-trihydroxy-1,3,5-triazine (cyanuric acid) the final stable product. During both photocatalytic and S2O8 2−/hν experiments, in the early steps, a fairly stable intermediate evolving to ammelide is observed in a large extent. This intermediate was identified as 2,4-diamino-6-nitro-1,3,5-triazine. This indicates that the primary photocatalytic event is the oxidation of the amino-group to nitro-group through several consecutive fast oxidation steps, and that a hydrolytic step leads to the release of nitrite in solution. To elucidate the nature of the oxidant species hole scavengers such as methanol and bromide ions were added to the irradiated TiO2. They completely stop the degradation, whereas chloride and fluoride ions decrease the degradation rate.The study of the photocatalytic degradation rate of melamine at increasing concentrations using two different commercial titanium dioxides, such as P25 and Merck TiO2, showed an intriguing behavior. A drastic abatement of the melamine transformation rate was observed when coagulation of the P25 slurry occurs due both to the pH change and melamine concentration effect that increase melamine adsorption. In the presence of TiO2 (Merck) the melamine initial degradation rates are significantly lower than those observed in the presence of P25 but are not depressed at larger concentrations. The experimental evidences (e.g., absence of melamine adsorption onto TiO2 surface at low concentrations or at acidic pH or due to the catalyst surface texture, and the lack of reactivity toward •OH free and bound) suggest that the effective photocatalytic mechanism is based on an outer sphere direct hole transfer to the melamine. Its formal potential lies in the range 1.9–2.3 V vs NHE. Then, the photodegradation of melamine is an efficient tool to evaluate the direct hole transfer ability of a photocatalyst.
Keywords: Photocatalysis; Melamine; Hydroxyl radicals; TiO2; Advanced Oxidation Technologies; Fluorinated titania;

Display OmittedPhotoreductive transformation of mono- and di-fluoromethyl acetophenone (AP) derivatives on the P25 titanium dioxide (TiO2) has been studied in deaerated ethanol solution under UV irradiation. 2-Monofluoromethyl AP (MFAP) was stable in the dark and existed as keto form in ethanol, whereas 64% of 2,2-difluoromethyl AP (DFAP) transformed into hemiketal form (photocatalytically inactive form) under the same condition. Under the UV irradiation with the TiO2 particles, the reduction of MFAP afforded only the defluorinated ketone, while the reduction of DFAP provided not only defluorinated ketones but also a hydrogenated alcohol. The reduction of carbonyl group and defluorination of DFAP concurrently occurred on TiO2, in which the formation of MFAP was observed as an intermediate of the sequential defluorinations. These two parallel reactions were initiated by electron transfer from the surface defect sites (Tisd) to DFAP adsorbed on the TiO2 surface. A possible reaction mechanism for DFAP is proposed and discussed on the basis of thermodynamic data upon the C―F bond cleavage of anion radical species generated during the photocatalysis.
Keywords: Titanium dioxide; Photocatalytic reduction; Hydrogenation; Defluorination; Acetophenone derivatives;

Display OmittedTiO2 films with exposed {0 0 1} facets and uniform Pt nanoparticles on the crystal facets were fabricated on a Ti substrate using a simple low temperature electrostatic self-assembly method. Proper Pt colloidal pH value was selected by determining ξ potential of Pt NPs and TiO2 film with exposed {0 0 1} facets. Ultra high-resolution FESEM observation shows that Pt NPs with diameter of 2–4 nm were physically separated and dispersed on TiO2 facets. The Pt NPs were found to be apt to deposit on the {1 0 1} facet with more positive surface potential of TiO2 film and the mean size and the number density of Pt NPs on different facet could be rationally tailored by controlling immersion time of TiO2 film with exposed {0 0 1} facets. The Pt-TiO2 film with exposed {0 0 1} facets prepared at immersion time of 5 min shows considerably higher UV photocatalytic activity than TiO2 film with exposed {0 0 1} facets and single UV irradiation for all the experimented initial ethenzamide concentrations, and also no deactivation was observed during 3 recyling runs. The UV photocatalysis employing Pt-TiO2 film with exposed {0 0 1} facets as photocatalyst shows significant potential for application in degradation of pharmaceutical and personal care products (PPCPs) with amide bonds.
Keywords: Pt-TiO2 films; {0 0 1} Facets; Photocatalytic degradation; PPCPs; Ethenzamide;

Polyoxometalate immobilized in MIL-101(Cr) as an efficient catalyst for water oxidation by Jianyu Han; Danping Wang; YongHua Du; Shibo Xi; Zhong Chen; Shengming Yin; Tianhua Zhou; Rong Xu (83-89).
Display OmittedWater oxidation is an essential reaction in artificial photosynthesis. Finding efficient and stable catalysts for this reaction is still a challenging task. Recently, a series of polyoxometalates (POMs) comprised of earth abundant materials are reported to be efficient water oxidation catalysts (WOCs). In this study, we investigated the effect of a support material to the catalytic performance of [Co(H2O)2(PW9O34)2]10− (CoPOM) by immobilizing this molecular POM-based catalyst on MIL-101(Cr), a highly porous and robust metal-organic framework (MOF). The successful encapsulation of CoPOM in MIL-101 achieved by a facile ion exchange method was evidenced by combined XRD, FTIR, XPS, XANES, TEM and elemental mapping analyses. Both the photocatalytic and electrochemical studies have indicated that the CoPOM loaded on MIL-101 displays enhanced activity and improved stability due to the its electrostatic interaction with MIL-101. In addition, the heterogenization of the homogeneous CoPOM also makes it easier to be recycled.
Keywords: Polyoxometalates; MIL-101; Water oxidation; Photocatalysis; Electrocatalysis;

Design of visible light responsive photocatalysts for selective reduction of chlorinated organic compounds in water by Junfeng Niu; Lifeng Yin; Yunrong Dai; Yueping Bao; John C. Crittenden (90-95).
Display OmittedPeriodic density functional theory (DFT) calculations were performed for β-Bi2O3 photocatalyst that was modified with 32 elements. Our focus was to design visible light responsive photocatalysts for selective reduction of chlorinated organic compounds (COCs) in water. The wanted photocatalysts should have (1) a moderate adsorption potential for COCs; (2) a wide adsorption spectrum for harvesting visible light; and (3) a reduction potential enough to destroy COCs. Based on these assumptions, a combined grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation study was used to investigate the adsorption and diffusion behaviors of COCs in 32 modified β-Bi2O3; a Becke-three-parameter-Lee-Yand-Par (B3LYP) DFT method was used to calculate the energy band structures and redox potentials of different modified β-Bi2O3. Sequentially, these modified β-Bi2O3 were synthesized by solvothermal method, and the photo-reactivity of them were quantified in terms of the conduction band (CB) electron reduction using pentachlorophenol (PCP), trichloroethylene (TCE), and γ-hexachlorocyclohexane (HCH) as model COCs. The results demonstrated that the adsorption, photoabsorption, and photo-reactivity of modified β-Bi2O3 appear to be a complex function of the periodicity of 32 doped elements, which can be explained by the structural changes on the crystalline form and energy band structure. Based on this principle, a series of competent photocatalysts were believed to be efficient on the reduction of COCs. We designed and synthesized: (1) Ti-β-Bi2O3 photocatalyst that performed best on reduction of PCP (37.2 μmol L−1) with apparent quantum yield (Φ PCP) of 1.20%; (2) Sr-β-Bi2O3 photocatalyst for TCE (76.2 μmol L−1) reduction (Φ TCE 1.03%); and, (3) Zr-β-Bi2O3 photocatalyst for HCH (27.5 μmol L−1) reduction (Φ HCH 0.67%).
Keywords: First principle theory; Density functional theory; Photocatalyst; Photocatalytic reduction; Chlorinated organic pollutants;

Nanohybrid materials of titania nanosheets and plasmonic gold nanoparticles for effective hydrogen evolution by Zheng Xing; Xu Zong; Teera Butburee; Jian Pan; Yang Bai; Lianzhou Wang (96-103).
Display OmittedA new type of nanocomposites containing titania and gold were prepared via the coupling between exfoliated Ti0.91O2 nanosheets and surfactant-capped Au nanoparticles, followed by flocculation and calcination. After hybridization with Ti0.91O2 nanosheets, octahedral Au nanoparticles were embedded intimately into the matrix of titania, leading to a broad absorption peak assigned to surface plasmon resonance (SPR) effect in the visible region. The obtained nanocomposite exhibited remarkably improved photocatalytic hydrogen evolution performance compared to naked titania and conventional titania with photodeposited Au co-catalyst, due to the special SPR effect of the relatively large octahedral Au nanoparticles. Through control experiments, we demonstrated that the octahedral Au nanoparticles mainly functioned as local light intensifier and photon scattering agent.
Keywords: Nanocomposite; Gold nanoparticles; Titania nanosheets; Surface plasmon resonance effect; Photocatalysis; Hydrogen;

Efficiently visible-light-responsive mesoporous structured carbon/bismuth oxide photocatalyst were successfully fabricated through a facile and green process in CO2 mediated medium.Display OmittedMesoporous structured carbon/bismuth oxide (mCBiO) composites were successfully fabricated through a facile and green process through CO2 mediated approach, which provided a unique medium without the need of any precipitant and mesoscaled organic template. For the photodegradation of RhB and phenol, the photocatalyst synthesized by CO2 mediated approach exhibited excellent recycling stability and enhanced photodegradation rate compared with the pure Bi2O3 and the reference sample synthesized in pure ethanol. Additionally, the possible mechanism of visible-light activity over mCBiO composites was proposed. This work developed a simple, green and economic route for the fabrication of mesoporous structured C-based metal oxide composites without the necessary of mesoporous template and precipitant.
Keywords: Carbon; Bismuth oxide; Mesoporous structure; CO2 mediated approach; Visible-light photocatalysis;

Enhanced photocatalytic hydrogen evolution over graphitic carbon nitride modified with Ti-activated mesoporous silica by Shaohua Shen; Daming Zhao; Jie Chen; Liejin Guo; Samuel S. Mao (111-117).
Display OmittedIn this study, it was demonstrated that the visible light photocatalytic hydrogen evolution performance of g-C3N4 could be enhanced when g-C3N4 was loaded onto the MCM-41 mesoporous silica, and the photocatalytic activity of obtained MCM-41/g-C3N4 was 1.2 times as high as that of pure g-C3N4. This is mainly because the high dispersion of g-C3N4 on MCM-41 leads to the improved separation efficiency of electrons and holes photoexcited in g-C3N4. By introducing Ti into the MCM-41 framework structure to create [Ti4+-O2−] active centers, the visible light driven photocatalytic activity of the obtained Ti-MCM-41/g-C3N4 was further increased, with hydrogen production rate reaching 80.76 μmol h−1  g−1, which was 1.6 times as high as that of pure g-C3N4. In the Ti-MCM-41/g-C3N4 composite photocatalysts, the photo-generated electrons in the conduction band of g-C3N4 can be easily transferred to the [Ti4+-O2−] active centers in Ti-MCM-41 framework, hence, the separation efficiency of the photo-generated charge carriers was further improved, achieving higher photocatalytic activity of Ti-MCM-41/g-C3N4 than MCM-41/g-C3N4 as well as pure g-C3N4.
Keywords: Photocatalytic hydrogen production; g-C3N4; Ti-MCM-41; Active centers;

Display OmittedThis study proposes incorporating nitrogen-doped graphene oxide dots (NGODs) with graphene oxide (GO) sheets to form a stable and effective NGOD:GO composite for photocatalytic H2 production through water splitting under visible light illumination. Although Pt-deposited NGOD catalysts were active in the photocatalytic H2 production reaction, they were only moderately stable. Introducing GO sheets in light-absorbing NGODs effectively mediated the transfer of photogenerated electrons from the NGODs to the GO sheets. This vectorial electron transfer, confirmed by a photoluminescence spectroscopy analysis, led to the relocation of the reaction sites from the NGODs to the GO sheets, protecting the NGODs from attack by reaction intermediates. Moreover, the GO sheets acted as an electron sink, facilitating charge separation in the NGODs. When 3 wt% Pt was deposited on the developed NGOD:GO catalyst, the catalyst steadily catalyzed H2 production from a 10 vol% aqueous solution of triethanolamine under visible light illumination for 96 h, unlike a NGOD catalyst that exhibited an activity decay of 50% within 96 h. The apparent quantum yield of H2 under 420-nm light irradiation was 16.0%, demonstrating the high activity of the NGOD:GO catalyst.
Keywords: Water splitting; Graphene oxide; Hydrogen production; Electron transfer; Photocatalysis;

Display OmittedLanthanum-doped sodium tantalate samples (NaTaO3:La) were prepared by a flux method using a sodium chloride flux with various parameters, such as presence or absence of the flux, solute concentration, hold temperature, and amount of lanthanum doping. SEM images showed cubic and rectangular shapes for the samples prepared by the flux method, somewhat rounded shape for the sample prepared in the absence of the flux, and large particles for the sample without lanthanum doping. Among the parameters, the lanthanum doping and solute concentration much influenced the crystallites size of the NaTaO3:La samples. Most of these NaTaO3:La samples loaded with platinum cocatalyst exhibited the photocatalytic activity in the photocatalytic steam reforming of methane around room temperature. Among them, the highest activity was obtained by the Pt/NaTaO3:La sample prepared by the flux method with moderate solute concentration, enough high hold temperature, and moderate amount of platinum and lanthanum doping. A positive correlation was found between the crystallite size and the photocatalytic activity. When we compared the catalysts having the same crystallite size, the sample prepared by the flux method showed higher photocatalytic activity than the catalyst prepared without the flux. It is suggested that the difference in the shape of particle would be important factor for the photocatalytic activity.
Keywords: Photocatalytic steam reforming of methane; Hydrogen production; Sodium tantalite; Flux method; Molten salt method;

Size-controlled TiO2 nanoparticles on porous hosts for enhanced photocatalytic hydrogen production by Chaoran Jiang; Ki Yip Lee; Christopher M.A. Parlett; Mustafa K. Bayazit; Chi Ching Lau; Qiushi Ruan; Savio J.A. Moniz; Adam F. Lee; Junwang Tang (133-139).
Display OmittedNanocystalline TiO2 particles were successfully synthesized on porous hosts (SBA-15 and ZSM15) via a sol–gel impregnation method. Resulting nanocomposites were characterized by XRD, TEM, BET surface analysis, Raman and UV–vis diffuse reflectance spectroscopy, and their photocatalytic activity for H2 production evaluated. XRD evidences the formation of anatase nanoparticles over both ZSM-5 and SBA-15 porous supports, with TEM highlighting a strong particle size dependence on titania precursor concentration. Photocatalytic activities of TiO2/ZSM-5 and TiO2/SBA-15 composites were significantly enhanced compared to pure TiO2, owing to the smaller TiO2 particle size and higher surface area of the former. TiO2 loadings over the porous supports and concomitant photocatalytic hydrogen production were optimized with respect to light absorption, available surface reaction sites and particle size. 10%TiO2/ZSM-5 and 20%TiO2/SBA-15 proved the most active photocatalysts, exhibiting extraordinary hydrogen evolution rates of 10,000 and 8800 μmol gTiO2 −1  h−1 under full arc, associated with high external quantum efficiencies of 12.6% and 5.4% respectively under 365 nm irradiation.
Keywords: TiO2; ZSM-5; SBA-15; Porous supports; Photocatalysis; Hydrogen evolution;

Photocatalytic degradation of gallic acid over CuO–TiO2 composites under UV/Vis LEDs irradiation by Ana L. Luna; Miguel A. Valenzuela; Christophe Colbeau-Justin; Patricia Vázquez; Julia L. Rodriguez; Juan R. Avendaño; Salvador Alfaro; Salvador Tirado; Adrián Garduño; José M. De la Rosa (140-148).
A proposed scheme showing the photoredox processes during degradation of gallic acid (GA) in presence of Cu2O–CuO–TiO2 photocatalysts, air and visible light (LEDs).Display OmittedCoupling TiO2 with narrow band gap semiconductors has been a strategy to obtain visible light active photocatalysts. In this work we present, the characterization and photocatalytic results of high-loaded CuO–TiO2 composites prepared by impregnation of TiO2 powder (Evonik, P25) with copper acetate followed by calcination. The resulting composite materials were characterized by X-ray diffraction, nitrogen adsorption/desorption, UV–vis diffuse reflectance, scanning electron microscopy, X-ray photoelectron spectroscopy and time-resolved microwave conductivity. The photocatalysts were used to degrade gallic acid by using low power ultraviolet and visible light emitting diodes (UV-LED and Vis-LED) as light sources. According to the results, the photocatalytic degradation of the pollutant was efficiently converted to several intermediate products and partially mineralized to CO2 by using visible light. These results were explained in terms of an enhancement of the optical and electronic properties of TiO2 by the presence of Cu2O and CuO phases.
Keywords: Photocatalysis; Semiconductor composites; CuO–Cu2O–TiO2; Gallic acid; LEDs;

Display OmittedAu-based catalysts were widely applied in photocatalytic areas owing to Au local surface plasmon resonance (LSPR), especially in the reactions of secondary alcohol dehydrogenation. However, there were rare cases reporting Au catalysts to dehydrogenate secondary alcohols under dark condition at room temperature. In this work, basic semiconductor birnessite, with easily extractable lattice oxygen in its lattice structure, was employed as support of Au catalyst and it was found that the Au/birnessite catalyst could dehydrogenate iso-propanol (IPA) to acetone under dark condition (3.7 μmol acetone was produced within 5 h). With the utilization of lattice oxygen in the reaction under dark condition, oxygen vacancies were instantaneously formed which enhanced the light absorbing properties of Au/birnessite and further improved its photocatalytic activity (13.6 μmol acetone production within 5 h). The synergistic effects between lattice oxygen and oxygen vacancies enhanced the performance of Au-based catalyst in IPA dehydrogenation and this work provides a synthesis tactic for effective catalysts in the dehydrogenation of various secondary alcohols.
Keywords: Lattice oxygen; Oxygen vacancy; Secondary alcohol dehydrogenation; Visible light; Local surface plasmon resonance;

Sub-2 nm cobalt oxide cluster catalyst supported on alumina for efficient water oxidation by Zheng Chen; Shu Miao; Jingqi Guan; Fuxiang Zhang; Can Li (154-159).
Display OmittedEarth-abundant cobalt oxides as active water oxidation catalysts have attracted extensive attention, but the controlled synthesis of small cobalt oxide clusters still remains challenging. Herein we introduce a novel approach to deposit small cobalt oxide clusters on alumina which involves mild oxidation of molecularly dispersed Co4(CO)12 precursor. Scanning transmission electron microscope (STEM) shows that the size of prepared CoO x clusters is smaller than 2 nm. Turnover frequency (TOF) value of water oxidation on the synthesized cobalt oxide clusters can reach as high as 0.067 s−1 in photochemical Ru(bpy)3 2+-Na2S2O8 system, which is at least an order of magnitude higher than bulk cobalt oxide nanoparticles. The remarkably enhanced activity of cobalt oxide cluster is attributed to its more surface-exposed cobalt atoms and higher intrinsic activity.
Keywords: Water oxidation; Cobalt oxide; Cluster;

Photocatalytic conversion of CO2 in water using fluorinated layered double hydroxides as photocatalysts by Shoji Iguchi; Kentaro Teramura; Saburo Hosokawa; Tsunehiro Tanaka (160-167).
Display OmittedThe photocatalytic conversion of CO2, which can convert CO2 into useful chemicals, such as CH4, CH3OH, HCOOH, HCHO, and CO, is attractive process for creating an artificial carbon cycling system. It was found that the synthetic Ni–Al layered double hydroxide (Ni–Al LDH) can reduce CO2 into CO in an aqueous solution of NaCl under UV light irradiation, and chloride ions (Cl) in the reaction solution scavenge the photogenerated holes. In this study, we prepared fluorinated Mg–Al LDH and Ni–Al LDH for altering the chemical and/or physical properties of the LDH as a solid base, and investigated the effect of fluorination on the photocatalytic activity for the conversion of CO2 in an aqueous solution. We found that the fluorination of LDH by incorporation of hexafluoroaluminate (AlF6 3−) units in the hydroxide sheets clearly improved the amount of CO evolved as a reduction product of CO2.
Keywords: CO2 reduction; Photocatalyst; Layered double hydroxide; Fluorination;

Photochemistry of hematite photoanodes under zero applied bias by Timothy L. Shelton; Nicholas Harvey; Jiarui Wang; Frank E. Osterloh (168-173).
Display OmittedSurface photovoltage spectroscopy (SPS) was used to observe photochemical charge separation and oxidation reactions on Fe2O3 nanorod arrays under zero applied bias. Nanorod films were grown from FeCl3 under hydrothermal conditions followed by calcination at 550 °C. A negative photovoltage of up −130 mV is observed under 2.0–4.5 eV (0.1 mW cm−2) illumination, confirming 2.0 eV as the effective bandgap of the material, and electrons as majority carriers. SPS in the presence of air, nitrogen, water, oxygen, and under vacuum suggest that the photovoltage is associated with the oxidation of surface water and with reversible surface hole trapping on the 1 min time scale and de-trapping on the 1 h time scale. O2 promotes water oxidation by increasing the concentration of surface holes. Sacrificial donors KI, H2O2 or potassium hydroxide increase the voltage to −240 and −400 mV, due to improved hole transfer. Cobalt oxide and Co-Pi cocatalysts quench the voltage, which is tentatively attributed to the removal of surface states and enhanced e/h recombination. An energy diagram is used to relate the experimental photovoltage to the built-in potentials at the respective interfaces.
Keywords: Photocatalysis; Water splitting; Surface photovoltage spectroscopy; Hole trap; Built-in voltage;

Anodic TiO2 nanotube layer directly formed on the inner surface of Ti pipe for a tubular photocatalytic reactor by Hyoung-il Kim; Doohun Kim; Wooyul Kim; Yoon-Cheol Ha; Seong-Ju Sim; Sujeong Kim; Wonyong Choi (174-181).
A tubular photocatalytic reactor made of Ti pipes with vertically well-aligned TiO2 nanotube (TNT) layer was successfully fabricated and evaluated for water purification activity. The TNT layers directly formed on Ti pipes have strong adhesiveness and high surface area with showing high activity and stability.Display OmittedWe demonstrated the successful water treatment performance of a continuous-flow tubular TiO2 nanotube reactor made of Ti pipe where a TiO2 nanotube (TNT) layer was directly formed on the inner wall by an electrochemical anodization process. A cylindrical UV lamp was inserted into the pipe to irradiate the inner TNT surface as a light source. To optimize the thickness of TNT layer on Ti pipe, TNT layers with 1, 5 and 10 μm thickness were prepared and their photocatalytic activities were tested for the degradation of various organic substrates (acid orange 7 (AO7), dichloroacetate (DCA), and 4-chlorophenol (4-CP)) under UV illumination. The TNT layer with 10 μm thickness showed the highest photocatalytic activity, with first-order removal rate constants (k:min−1) of 0.019, 0.039, and 0.025 for AO7, 4-CP, and DCA, respectively. The directly formed TNTs (10 μm thickness) on Ti pipes in the continuous-flow tubular TNT reactor, having a strong adhesiveness and a high surface area, enabled the successful degradation of organic compounds and to have kept the activity without decrease during the repeated cycles and long-term experiments. The photocatalytic performance of the tubular TNT reactor was tested with a higher concentration, smaller volume ([4-CP]0  = 100 μM, solution vol. = 15 mL) and a lower concentration, larger volume ([4-CP]0  = 20 μM, solution vol. = 100 mL) in the circulation-flow mode (20 mL min−1). A good performance was achieved under the low intensity UV illumination (≈2 mW cm−2) with a half-life of ca. 50 min and ca. 11 h with 80% and 79% removal of TOC for the above two test conditions, respectively. The proposed tubular TNT reactor can be an effective option in the design of continuous flow-type photocatalytic reactors for practical water purification.
Keywords: TiO2 nanotube; Photocatalytic oxidation; Photocatalytic water treatment; Organic pollutant degradation; Continuous photocatalytic reactor;

Intrinsic kinetics of plasmon-enhanced reverse water gas shift on Au and Au–Mo interfacial sites supported on silica by Insoo Ro; Ronald Carrasquillo-Flores; James A. Dumesic; George W. Huber (182-189).
Display OmittedWell characterized AuMox catalysts were synthesized by controlled surface reactions (CSR) and studied in reverse water gas shift (RWGS) reaction with and without visible light addition. The numbers of Au and Au–Mo interfacial sites on these catalysts were quantified using low temperature (173 K) CO adsorption with Fourier transform infrared spectroscopy (FT-IR) and electron microscopy. Due to the localized surface plasmon resonance (LSPR) effect, visible light irradiation of the catalyst caused a decrease in the apparent activation energy from 80.2 ± 3.9 kJ/mol to 55.5 ± 3.1 kJ/mol and 67.5 ± 1.3 kJ/mol to 38.7 ± 1.9 kJ/mol with visible light irradiation over Au/SiO2 and Au1Mo0.1/SiO2, respectively. The catalytic activity went through a maximum upon addition of Mo, with Au1Mo0.1/SiO2 being the most active catalyst. The Au1Mo0.1 catalyst with LSPR was 30 times more active than the reference Au catalyst under dark conditions. Visible light irradiation increased the reaction rate 4.7–4.8 times at 573 K for all catalysts. The turnover rates (CO mole produced per mole of Au or AuMox site per min) on the Au and AuMox interfacial sites were measured to be 0.98 min−1 and 14 min−1 in the dark conditions and 4.4 min−1 and 63 min−1 under the light conditions at 573 K. The rate per AuMox interfacial site is 14 times greater than the rate per Au site under both dark and light conditions. These results indicate that the LSPR has the same enhancement effect on both Au and AuMox catalytic sites.
Keywords: Gold; Molybdenum; Active site; Bimetallic catalyst; Interfacial sites; Reverse water gas shift reaction;

Exploring Cu oxidation state on TiO2 and its transformation during photocatalytic hydrogen evolution by Minsu Jung; Judy N. Hart; Jason Scott; Yun Hau Ng; Yijiao Jiang; Rose Amal (190-201).
Display OmittedIn-depth characteristic studies with H2 activity and theoretical calculations were used to reveal the copper oxidation states most effective for photocatalytic hydrogen production when loaded on TiO2. When the copper was originally present as CuO, photogenerated electrons initially reduced the Cu2+ to Cu+ in preference to proton reduction. The resulting Cu2O then behaved as a secondary photocatalyst on the TiO2 surface acting to improve the hydrogen production rate (1.4 times greater than neat TiO2). When the copper was originally present as Cu0, an improved hydrogen generation rate was also evident (2.4 times greater than Cu2O/TiO2) and the metallic state was retained over the course of the reaction. In this case, the Cu0 deposits function as a co-catalyst for proton reduction. The findings reconcile past disagreements associated with this system, demonstrating both Cu+ (following reduction from Cu2+) and Cu0 are able to photocatalytically generate hydrogen, albeit by distinctly different mechanisms.
Keywords: Metallic copper; Cuprous oxide; Cupric oxide; Titanium dioxide; Glycerol; Photocatalytic hydrogen production; Density functional theory;

Metal ion-modified TiO2 photocatalysts having controllable oxidative performance under irradiation of visible light by Sho Kitano; Atsuhiro Tanaka; Keiji Hashimoto; Hiroshi Kominami (202-207).
Display OmittedMetal ion-modified TiO2 photocatalysts designated by combinations of various metal ions and TiO2 powders that respond to visible light and exhibit controllable photocatalytic oxidative performances were examined. The photocatalytic oxidative performances were evaluated by selective oxidation of benzyl alcohol in water in the presence of O2 under irradiation of visible light. The TiO2 samples modified with Ru3+, Pd2+ and Rh3+ (Ru3+/TiO2, Pd2+/TiO2 and Rh3+/TiO2) exhibited high levels of photocatalytic activity. The effects of metal ions and the kind of TiO2 on photocatalytic performances of Rh3+/TiO2 and Ru3+/TiO2 were investigated in detail.
Keywords: Photocatalyst; Visible light; Oxidation; Metal ion;

Visible light responsive Zeolite/WO3–Pt hybrid photocatalysts for degradation of pollutants in air by I. Jansson; K. Yoshiiri; H. Hori; F.J. García-García; S. Rojas; B. Sánchez; B. Ohtani; S. Suárez (208-219).
Display OmittedAdsorbent–photocatalyst hybrids based on WO3 and Pt as cocatalyst immobilized on different type of zeolites were prepared. Their performance for the degradation of pollutants under UV and Vis light was analyzed. Two types of zeolites (ZSM-5 and Zeolite Y) with Si/Al ratios ranging between 5 and 280 were selected as hierarchical microporous materials acting as adsorbents. The incorporation of platinum on tungsten oxide was done by means of the photodeposition method. Pt-loaded WO3 was dispersed on the zeolites and subjected to a lyophilization process. Their photocatalytic properties towards the abatement of representative pollutants e.g., acetic acid, acetaldehyde and trichloroethylene, were analyzed under different operating conditions in batch and continuous flow photoreactors. Raw materials and hybrid photocatalysts were characterized by N2 adsorption–desorption, XRD, UV–vis spectroscopy, XPS and TEM microscopy. The adsorption ability of the photocatalysts towards the selected pollutants was studied under dynamic conditions. The textural properties of the photocatalysts were not the main factor controlling their adsorption ability. The incorporation of WO3–Pt on the zeolite results in Vis light responsive materials. Monoclinic WO3 crystal phase was identify in all zeolitic materials. Large WO3–Pt aggregates were detected on Zeolite Y (ca. 300 nm) with low Si/Al content in contrast with highly disperse phase for ZSM-5 (SiO2/Al2O3  = 280) (ca. 100 nm). All WO3–Pt hybridized zeolites showed photoactivity for the degradation of the studied pollutants under Vis light, improving the performance of bare WO3–Pt. The results shown in this work reveal the influence of the hydrophobicity of the siliceous material for the adsorption of reaction intermediates or byproducts and as a consequence for the determination of the rates of CO2 formation under static conditions. A F(Static) function, dependent of the Si/Al ratio and the BET area, to correlate the difference trend of the amount of CO2 released produced by the hybrid composites, under static and dynamic conditions is proposed.
Keywords: Visible Light; WO3–Pt; Zeolites; Adsorbent–photocatalyst hybrids; Air treatment; VOC;

Photocatalytic activity of one step flame-made fluorine doped TiO2 by Maria Vittoria Dozzi; Alessio Zuliani; Ivan Grigioni; Gian Luca Chiarello; Laura Meda; Elena Selli (220-226).
Display OmittedThe photocatalytic performance of a series of fluorinated TiO2 samples (F for O molar substitution ranging from 0 to 1.5 at.%) synthesized by flame spray pyrolysis (FSP) in single step is examined in relation to the results of several complementary characterization techniques, including BET, XRD, XPS and UV–vis analyses. While the rate of photocatalytic hydroxyl radicals production increased when the photocatalyst contained small amounts of fluorine, the rate of formic acid mineralization was maximum with flame-made pure TiO2, showing an activity even better than that of P25 TiO2 in experiments performed in the presence of the same photocatalyst amount. However, the reaction rate decreased with increasing the nominal fluorine content of the materials, as expected for reactions occurring by direct interaction of the substrate with photoproduced holes. On the other hand, incident photon to current efficiency measurements evidenced that the presence of fluorine in the photocatalyst is beneficial, 0.29 at.% effective F for O substitution in TiO2 leading to the best performing photocatalyst powder, in line with previous results obtained in photocatalytic hydrogen production from methanol steam reforming with similarly FSP-prepared TiO2-based materials also containing platinum nanoparticles.
Keywords: Photocatalysis; Flame spray pyrolysis; Fluorinated TiO2; Oxidation reactions; Photocurrent measurements; Incident photons to current efficiency;

Photocatalytic property of metal ion added SrTiO3 to Overall H2O splitting by Yoshihisa Sakata; Yoshiko Miyoshi; Tatsuya Maeda; Kohki Ishikiriyama; Yuki Yamazaki; Hayao Imamura; Yeilin Ham; Takashi Hisatomi; Jun Kubota; Akira Yamakata; Kazunari Domen (227-232).
Display OmittedThe effects of the metal ion addition to SrTiO3 to the overall H2O splitting were investigated to improve the photocatalytic activity. The addition of metal ions was carried out by impregnation method. The preparation condition of metal ion added SrTiO3 was examined with applying Na+ ion as additive and SrTiO3 prepared by polymerizable complex method. The photocatalytic activity was markedly improved by the addition of Na+ ion and calcined above 1173 K. The preferable state of the photocatalyst was Na ion (2 atm%) added SrTiO3 obtained by calcination at 1273 K and the photocatalytic activity with a Rh0.3Cr1.7O3 (Rh:0.3 wt%) co-catalyst was 16 mmol/h for H2 and 8 mmol/h for O2 production. The apparent quantum yield (AQY) was 16% under the irradiation of 360 nm. The photocatalytic performance of Na+ ion added various SrTiO3 and the effects of various metal ion addition to SrTiO3 to the photocatalytic activity of the overall H2O splitting were investigated to discuss the influence of the added metal ions to the photocatalytic activity.
Keywords: SrTiO3; Photocatalyst; Overall H2O splitting; Metal ion addition;

Facile surfactant driven fabrication of transparent WO3 photoanodes for improved photoelectrochemical properties by Jin Hyun Kim; Byeong Jun Lee; Ping Wang; Min Hye Son; Jae Sung Lee (233-239).
Display OmittedA facile polymer-assisted direct deposition method is reported for fabrication of transparent WO3 films for photoelectrochemical water oxidation. Addition of Triton X 114 as a polymer additive brings a significant impact on morphology, optical property and crystallinity of WO3 film that leads to improved photoelectrochemical activity. An optimum amount of Triton X 114 added during the WO3 synthesis makes a photoanode with near glass-like transparency with activity improvement. Moreover, bulk charge separation efficiency as high as 80% at 1.23 VRHE is obtained by Triton X 114 addition by forming preferentially (200) oriented WO3 crystals of better bulk charge transfer property.
Keywords: Photoelectrochemical water oxidation; WO3 photoanodes; Preferential orientation; Charge separation efficiency;

Display OmittedThe reduction of CO2 to fuels is an active research topic with much interest in using solar radiation and photocatalysts to transform CO2 into higher value chemicals. However, to date there are no photocatalysts known that can use solar radiation to efficiently reduce CO2. One particularly difficult problem is activating CO2 due to its high stability. In this paper we use density functional theory simulations to study novel surface modified TiO2 composites, based on modifying rutile and anatase TiO2 with molecular-sized metal oxide nanoclusters of SnO, ZrO2 and CeO2 and the interaction between CO2 and nanocluster-modified TiO2. We show that reduction of the supported nanocluster is favourable which then provides reduced cations and sites for CO2 adsorption. The atomic structures and energies of different adsorption configurations of CO2 on the reduced modified TiO2 composites are studied. Generally on reduced SnO and CeO2 nanoclusters, the interaction of CO2 is weak producing adsorbed carbonates. On reduced ZrO2, we find a stronger interaction with CO2 and carbonate formation. The role of the energies of oxygen vacancy formation in CO2 adsorption is important because if reduction is too favourable, the interaction with CO2 is not so favourable. We do find an adsorption configuration of CO2 at reduced CeO2 where a C―O bond breaks, releasing CO and filling the oxygen vacancy site in the supported ceria nanocluster. These initial results for the interaction of CO2 at surface modified TiO2 provide important insights for future work on CO2 reduction using novel materials.
Keywords: Photocatalysis; TiO2; Surface modification; Density functional theory; Oxygen vacancy; CO2; Adsorption;

Display OmittedGallium-zinc oxynitride (GaZnON) solid solution is a photocatalyst capable of effective overall water splitting under visible light. In order to address the inefficiencies of the synthesis of GaZnON solid solution (e.g., 10+ h at 850 °C under 250 ml min−1 NH3 flow), a facile technique is proposed. The technique utilizes crystalline Ga3+ and Zn2+ layered double hydroxides (LDHs) material as an atomic-level uniform precursor, and urea as the nanotemplated source of nitrogen. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis confirm the formation of wurtzite GaZnON in a 12 min process through distribution of the uniform Ga3+ and Zn2+ LDHs precursor within the nanotemplate formed through urea pyrolysis. The structural, optical, and electrochemical properties of the prepared samples were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, and photoluminescence (PL) analysis. The newly synthesized photocatalyst consists of nanopores distributed uniformly through the surface and bulk of the solid solution particles; the presence of these nanopores improves the active surface area of the photocatalyst up to seven times, as compared to the one for traditionally prepared solid solution photocatalyst. The proposed technique is capable of controlling the composition of the final photocatalyst in a wide range of ZnO content ([Zn]/[Zn + Ga] up to 0.66). Apparent quantum yield (AQY) up to 2.5% at 420–440 was achieved by the photocatalyst with bulk [Zn]/[Zn + Ga] = 0.32, loaded with 1 wt% Rh nanoparticles. The effect of crystal defects and Zn content of the solid solution on the PL emission of the samples revealed that the GaZnON samples prepared with the LDHs precursor contain fewer crystal imperfections, which aids their water-splitting performance. The performance of the newly synthesized photocatalyst is among the highest reported in the open literature for photocatalysts loaded with a single co-catalyst. This photocatalyst has potential for future improvement through enhancement of the crystalline structure and improvement of the charge separation.
Keywords: GaZnON solid solution; Synthesis; Nanoporosity; Water splitting; Solar hydrogen;