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Artificial photosynthesis, which splits water into H2/O2 or reduces CO2 and N2 by visible light, catalyzed by molecular catalysts (MCs) with/without being coupled with a solar cell should serve as ...

Microspherical particles of Rh-doped SrTiO3 (SrTiO3:Rh) having size of 1–2 μm were synthesized by a spray drying (SD) method employing a water-soluble ammonium trilactatotitanate. When the calcination temperature increased up to 1200 °C, primary particles grew significantly while the microspherical morphology of the secondary particles was kept. Dynamic light scattering analysis proved well-dispersive nature of the SD sample. Photocatalytic activities of SrTiO3:Rh synthesized by the SD method, solid state reaction (SSR), and a polymerizable complex (PC) method were evaluated for H2 evolution using an electron donor such as methanol, Fe2+, or [Co(bpy)3]2+ and Z-scheme water splitting combined with BiVO4 of an O2-evolving photocatalyst and either Fe3+/2+, [Co(bpy)3]3+/2+, or reduced graphene oxide as an electron mediator. SrTiO3:Rh prepared by the SD method showed much higher activities for all Z-scheme water splitting than the samples synthesized by the SSR method. Activities of the SD sample for Z-scheme water splitting using electron shuttles, Fe3+/2+ and [Co(bpy)3]3+/2+, were slightly higher or comparable to those of the PC sample whereas the SD sample achieved higher activity in Z-scheme water splitting based on interparticle electron transfer. In addition, even when the mass of SrTiO3:Rh used for the Z-scheme system with Fe3+/2+ was decreased from 50 mg to 30 mg, the SD sample still showed high activity while the activity decreased for the SSR and PC samples. Thus, usefulness of the SD method to obtain highly active SrTiO3:Rh with well-dispersive nature has been demonstrated.

A kesterite Cu2ZnGeS4 (CZGS) thin film was prepared on an Mo-coated glass substrate by spray deposition of an aqueous solution containing constituent elements followed by heat treatment in a sulfur...

Optimizing interfacial contact between graphene and a semiconductor has often been proposed as essential for improving their charge interactions. Herein, we fabricated bismuth vanadate-reduced graphene oxide (BiVO

Various studies on functionalization of water-splitting photocatalysts have been performed toward their practical usage. Control of the cocatalyst has been investigated, and recently, in addition to particle-size control, alloying has been extensively used to achieve this goal. It is essential to investigate photocatalysts with precisely controlled cocatalysts to obtain a detailed understanding of the effect of heteroatom doping of the cocatalyst on the photocatalytic activity and thereby establish clear design guidelines for functionalization. However, previous studies have investigated photocatalysts with a variety of particle sizes and doping ratios (chemical compositions). In this study, we succeeded in loading precisely controlled Au24Pd and Au24Pt clusters on BaLa4Ti4O15, which is one of the most advanced photocatalysts, using precisely synthesized alloy clusters as the precursor. Experiments with the photocatalysts loaded with precisely controlled cocatalysts revealed the following three features o...

Formation of impurity levels by doping and control of valence bands by substitution with suitable elements into photocatalyst materials are useful strategies for sensitization of metal oxide photocatalysts with a wide band gap to visible light. In the present study, we demonstrated energy gap narrowing of a metal oxide photocatalyst by coapplication of the doping and the substitution. Rh-doped and Ag(I)-substituted Li2TiO3 (AgLi1/3Ti2/3O2:Rh, 2.2–2.3 eV) was successfully synthesized from Rh-doped Li2TiO3 (Li2TiO3:Rh, 3.0–3.2 eV) with a molten AgNO3 treatment. The AgLi1/3Ti2/3O2:Rh possessed a narrower energy gap than either Li2TiO3:Rh or Ag(I)-substituted Li2TiO3 (AgLi1/3Ti2/3O2, 2.8 eV). The AgLi1/3Ti2/3O2:Rh showed the activity for photocatalytic O2 evolution from an aqueous AgNO3 solution under irradiation of light with wavelength longer than 480 nm under which AgLi1/3Ti2/3O2 did not show the activity. The photocatalytic activity of AgLi1/3Ti2/3O2:Rh for the sacrificial O2 evolution became ∼4 times gre...

Solid solutions with of Cu3 VS4 with either Cu3 NbS4 or Cu3 TaS4 (Cu3 Nb1-x Vx S4 or Cu3 Ta1-x Vx S4 ) were prepared by a solid-state reaction and adopted a sulvanite structure. Their band gaps were 1.6-1.7 eV corresponding to the absorption of a wide range of visible light. Ru cocatalyst-loaded Cu3 MS4 (M=V, Nb, Ta), Cu3 Nb1-x Vx S4 , and Cu3 Ta1-x Vx S4 showed photocatalytic activities for sacrificial H2 evolution under visible-light irradiation. Most solid solutions showed better activities than the single-component Cu3 MS4 (M=V, Nb, Ta). Cu3 MS4 (M=V, Nb), Cu3 Nb1-x Vx S4 , and Cu3 Ta1-x Vx S4 also functioned as photoelectrodes and gave cathodic photocurrents under visible-light irradiation, indicating a p-type semiconductor character. Cu3 Nb0.9 V0.1 S4 showed the best photocatalytic and photoelectrochemical performances. When Ru-loaded Cu3 Nb0.9 V0.1 S4 was used as a photocathode with a CoOx -loaded BiVO4 photoanode, photoelectrochemical water splitting proceeded under simulated sunlight irradiation without an external bias.

In this paper, we report on the photoelectrochemical hydrogen evolution reaction (HER) from water using Rhodium-doped strontium titanate, surface-modified by the addition of minute amounts of platinum nanoparticles. Platinum has been used in an attempt to increase the charge transfer efficiency of the photoelectrode but also to investigate the balancing effect of surface co-catalysis on charge transfer versus recombination processes. The dynamics of the HER in pH-neutral aqueous solutions has been investigated by Photoelectrochemical Impedance Spectroscopy. Experimental impedance data has been analyzed using a model derived from considerations on heterogeneous kinetics. From the best experimental vs. calculation PEIS fits, microscopic rate parameters have been determined over an extended range of electrical potential. The charge transfer ( k t ) and recombination ( k r ) rate constants have been found to vary exponentially with the applied potential. The analysis of the potential dependence of k t led to a Butler-Volmer transfer coefficient of 0.21. The analysis of the potential dependence of the recombination rate constant k r led to the determination of a non-ideality factor β = 0.04 (β = 1 for ideal interfaces), demonstrating the strong non-ideal behavior of the interface. Such non-ideal behavior has been attributed to the presence of a high density of surface states. The space charge capacitance under inversion conditions, i.e. when a strong reversed bias is applied and when the surface of this p-semiconductor exhibits a n-type conductivity, has also been measured and analyzed.

Various types of Z-scheme systems for water splitting under visible light irradiation were successfully developed by employing Rh- and Ir-doped metal oxide powdered materials with relatively narrow energy gaps (EG): BaTa2O6:Ir,La (EG: 1.9-2.0 eV), NaTaO3:Ir,La (EG: 2.1-2.3 eV), SrTiO3:Ir (EG: 1.6-1.8 eV), NaNbO3:Rh,Ba (EG: 2.5 eV) and TiO2:Rh,Sb (EG: 2.1 eV), with conventional SrTiO3:Rh (an H2-evolving photocatalyst) or BiVO4 (an O2-evolving photocatalyst), and suitable electron mediators. The Z-scheme systems were classified into three groups depending on the combination of H2- and O2-evolving photocatalysts and electron mediator. The Z-scheme systems combining BaTa2O6:Ir,La with BiVO4, and NaTaO3:Ir,La with BiVO4 were active when a [Co(bpy)3]3+/2+ redox couple was used rather than an Fe3+/2+ one. The combination of SrTiO3:Ir with SrTiO3:Rh gave an activity when the [Co(bpy)3]3+/2+ and Fe3+/2+ redox couple ionic mediators were used. The Z-scheme systems combining NaNbO3:Rh,Ba and TiO2:Rh,Sb with SrTiO3:Rh showed activities by using the [Co(bpy)3]3+/2+ and Fe3+/2+ redox couples and also via interparticle electron transfer by just contact with/without reduced graphene oxide (RGO). These suitable combinations can be explained based on the impurity levels of doped Rh3+ and Ir3+ toward the redox potentials of the ionic mediators for the Z-scheme systems employing ionic mediators, and p-/n-type and onset potentials of the photocurrent in the photoelectrochemical properties of those photocatalyst materials for the Z-scheme systems working via interparticle electron transfer.

SrTiO3 (STO) has favorable opto-electronic properties for overall water splitting. Nevertheless, realizing a higher efficiency is impeded by its band gap which can only harvest UV light. In order to extend the spectral response towards visible light, STO is (co)doped with lanthanum (La) and rhodium (Rh). However, notwithstanding the amount of visible light absorbed, the H2 evolution rates are remarkably governed by the valence state of Rh, La doping level and ruthenium (Ru) cocatalyst loading. Hence, it is essential to unravel the underlying effect of doping on the photophysical processes to gain insight into material design. To this end, charge carrier dynamics was probed over a wide time (sub-picosecond to microsecond) and spectral (visible to IR) region using transient absorption spectroscopy. Depending on the dopant composition, an interplay between the electron trapping and the kinetics of the electron transfer to the Ru cocatalyst was rationalized. For Rh4+:STO, free electrons probed at 3435 nm decayed virtually completely by 20 ps resulting in a kinetic competition between the electron trapping and the electron transfer to Ru cocatalyst. In the case of Rh3+:STO, free electrons decayed by a factor of three by 100 ps, thus demonstrating the effect of Rh valence state on the electron lifetime. The time constant and quantum yield of electron transfer from Rh3+:STO to the Ru cocatalyst were found to be 1.6 ps and 14.7%, respectively. In addition to a longer electron lifetime, enhanced electron transfer to the Ru cocatalyst makes Rh3+:STO one of the promising photocatalysts for H2 generation. Engineering the energetic position of the dopant within the band gap to avoid undesirable carrier trapping is crucial to enhance the efficiency of photocatalytic reactions.

The U.S. Department of Energy recently announced its first Energy Earthshot on Clean Hydrogen, with a cost target of $1/kg-H2 by 2031. Assuming future utility-scale grid electricity prices from photovoltaics ($0.02/kWh), 80% of the cost of H2 would come from performing low-temperature water electrolysis at its thermoneutral voltage, with zero additional overpotential. This fact motivates alternative, less-expensive means of using light to generate mobile charge carriers than photovoltaics, and reactor designs with exceedingly low capital costs, which we recently invented. Systems that use low capital cost reactors benefit from low-voltage operation, which represents a paradigm shift from current state-of-the-art electrolyzers that aim to operate at high current densities. Analytical models predict that solar photocatalytic water splitting inherently exhibits such low-voltage operation through use of an ensemble of optically thin photoabsorbers, which results in larger overall solar-to-hydrogen conversion efficiencies in comparison to optically thick designs. In efforts to attain these predicted higher efficiencies, we are performing detailed studies on the properties of state-of-the-art doped SrTiO3 photocatalyst particles. During my talk, I will share our recent efforts in atomic-layer deposited ultrathin oxide coatings to impart redox selectivity and materials stability, single-photocatalyst-particle current–potential behavior and mobile charge carrier properties, and atomic-level information on dopant distributions and materials interfaces obtained from electron microscopies and X-ray spectroscopies. Collectively our discoveries provide new design guidelines and additional research pathways for the development of effective composite materials to serve as active components in techno-economically viable artificial photosynthetic devices.

In the synthesis method of a BiVO4 photoanode via BiOI flakes, a BiOI film is formed by electrochemical deposition in Step 1, and a vanadium (V) source solution is placed by drop-casting on the BiOI film in Step 2. Following this, BiVO4 particles are converted from the BiOI–(V species) precursors by annealing. However, it is challenging to evenly distribute vanadium species among the BiOI flakes. As a result, the conversion reaction to form BiVO4 does not proceed simultaneously and uniformly. To address this limitation, in Step 2, we developed a new electrochemical deposition method that allowed the even distribution of V2O5 among Bi–O–I flakes to enhance the conversion reaction uniformly. Furthermore, when lactic acid was added to the electrodeposition bath solution, BiVO4 crystals with an increased (040) peak intensity of the X-ray diffractometer (XRD) pattern were obtained. The photocurrent of the BiVO4 photoanode was 2.2 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE) under solar simulated light of 100 mW/cm2 illumination. The Faradaic efficiency of oxygen evolution was close to 100%. In addition, overall water splitting was performed using a Ru/SrTiO3:Rh–BiVO4 photocatalyst sheet prepared by the BiVO4 synthesis method. The corresponding hydrogen and oxygen were produced in a 2:1 stoichiometric ratio under visible light irradiation.

Powder-based Cu3VS4 photoelectrode with 1.5–1.6 eV of a band gap that was responsive to whole range of visible light was fabricated by a particle transfer method, aiming at enhancement of the photocathodic performance. The particle-transferred Cu3VS4 photoelectrode with a Au-contacting layer (Cu3VS4/Au) showed much higher photocathodic performance for water reduction to produce H2 under simulated sunlight irradiation (AM-1.5 G) than previously reported Cu3VS4/FTO prepared by a conventional drop-casting method. This drastic enhancement is due to the good contact between photocatalyst particles and the Au-contacting layer of the substrate electrode. Loading of a Pt cocatalyst was effective for further enhancement of the photocathodic performance of the Cu3VS4/Au photoelectrode. Pt(1 nm)-loaded Cu3VS4/Au gave about 4 mA cm−2 of the cathodic photocurrent at −0.41 V vs NHE at pH7 that was four times higher than that without a Pt cocatalyst under simulated sunlight irradiation (AM-1.5 G). When Cu3VS4 particles with a small particle size were prepared by a flux method, better durability was obtained compared with a solid-state reaction. Efficient photoelectrodes based on a powdered metal sulfide utilizing whole range of visible light have successfully been developed by a particle transfer method, loading of a Pt cocatalyst, and a flux method on photoelectrochemical performance.

Na0.5Bi0.5TiO3 (BG 3.1 eV) with a valence band formed by Bi(iii) was found as a new photocatalyst for solar water splitting. The water splitting activity of highly crystalline Na0.5Bi0.5TiO3 synthesized by a flux method was much higher than that of the samples synthesized by a solid-state reaction. The optimized RhCr2Ox(0.1 mol%)/Na0.5Bi0.5TiO3/CoOOH(0.02 mol%) gave a 5.1% apparent quantum yield at 350 nm and split water even under simulated sunlight irradiation with a 0.05% solar to hydrogen energy conversion efficiency. We have successfully achieved solar water splitting using a one-step photoexcitation type photocatalyst valence-band-controlled with Bi(iii).

Linear conjugated polymers have potential as photocatalysts for hydrogen production from water but so far, most studies have involved non-scalable sacrificial reagents. Z-schemes comprising more than one semiconductor are a potential solution, but it is challenging to design these systems because multiple components must work together synergistically. Here, we show that a conjugated polymer photocatalyst for proton reduction can be coupled in a Z-scheme with an inorganic water oxidation photocatalyst to promote overall water splitting without any sacrificial reagents. First, a promising combination of an organic catalyst, an inorganic catalyst, and a redox mediator was identified by using high-throughput screening of a library of components. A Z-scheme system composed of P10 (homopolymer of dibenzo[b,d]thiophene sulfone)-Fe2+/Fe3+-BiVO4 was then constructed for overall water splitting under visible light irradiation. Transient absorption spectroscopy was used to assign timescales to the various steps in the photocatalytic process. While the overall solar-to-hydrogen efficiency of this first example is low, it provides proof of concept for other hybrid organic-inorganic Z-scheme architectures in the future.

Ba2In2O5 (BG 3.0 eV) with a brownmillerite structure has arisen as a novel photocatalyst for water splitting under UV irradiation. Ba2−xLaxIn2O5+0.5x (x = 0.04) with a brownmillerite structure had ...

Intriguing photo-electrochemical characteristics of BiVO4 photoelectrodes studied in pH-neutral aqueous solutions are reported herein. Indeed, we have observed photocurrent polarity switching, as put in evidence by cyclic voltammetry under chopped illumination conditions. Such unusual behavior was analyzed in detail using Intensity Modulated Photocurrent Spectroscopy (IMPS). At potentials where positive photocurrent was observed, the expected shape of IMPS was recorded, starting in quadrant (IV) at high-frequency (HF) and reaching quadrant (I) at low-frequency (LF) with two well defined semicircles. Surprisingly, in the negative photocurrent region, IMPS started in quadrant (II) at HF and ended in quadrant (III) at LF. Such highly infrequent features were interpreted here as the rotation of the IMPS spectra around the origin of the plot, due to the sign switch of the photocurrent. A model that takes into account the existence of in-band energy states at the surface of BiVO4 has been used in order to account for the experimental results. It was found that (i) the surface state capacitance; (ii) the relaxation time constant associated to surface states; and (iii) the density of in-gap surface states, were all showing a well-marked maximum in the nearby value of the switch potential. This suggests that surface states are more influent in the nearby where photocurrent switch occurs.

A CuGaS2 thin film was formed by annealing of spray-deposited precursor films in a sulfur atmosphere. The film worked as a photocathode for photoelectrochemical CO2 reduction in a neutral aqueous s...

Electron–hole recombination always competes with desired reactions on semiconductor photocatalysts. Reducing recombination probability is essential for increasing the quantum efficiency of the reactions. Previous studies demonstrated that doping with lanthanoid or alkaline-earth metal cations reduced recombination probability in NaTaO3 photocatalysts for artificial photosynthesis. The motivation behind this study was to reveal how the guest metal cations reduced recombination probability. NaTaO3 photocatalysts were doped with Sr cations through crystallization in molten NaCl flux to produce 50–100 nm sized particles of NaTaO3–Sr(Sr1/3Ta2/3)O3 solid solution. Intraparticle distribution of Sr cations was sensitive to immersion time in the hot flux with a fixed Sr concentration of 2 mol % relative to Ta. Extended immersion for 60 h resulted in a homogeneous Sr distribution. Curtailed immersion for 1 h yielded particles capped with a 3 nm thick Sr-accumulated layer. The population of electrons bandgap-excited under Hg–Xe lamp irradiation was enhanced in the 1-h immersed photocatalyst by 160 times relative to that in a Sr-free NaTaO3 photocatalyst. In the 60-h immersed photocatalyst, population enhancement was not more than 9 times. We interpreted the large population enhancement in the 1-h immersed photocatalyst with a concentration gradient of Sr cations from the surface to bulk. The concentration gradient induced an energy gradient of conduction-band minimum. Photoexcited electrons were driven on the energy gradient to be separated from holes. The overall water splitting reaction rate was evaluated on the photocatalysts to show a 4-times enhancement on the 1-h immersed photocatalyst relative to the rate on the Sr-free photocatalyst. The reaction-rate enhancement less than the electron population enhancement was ascribed to a limited fraction of electrons overriding the energy gradient and returning back to the surface.

LaTa7O19 (BG: 4.1 eV) and CaTa4O11 (BG: 4.5 eV) with laminated structures consisting of layers of TaO6 octahedra and TaO7 decahedra were active for CO2 reduction to form CO using water as an electron donor when an Ag cocatalyst of an efficient CO2 reduction site was loaded. In contrast, the activity for the CO2 reduction of CaZrTi2O7 (BG: 3.6 eV) with an anion-defect-type fluorite structure consisting of TiO4 tetrahedra, TiO6 octahedra, and ZrO7 decahedra was negligible even when the Ag cocatalyst was introduced. Selectivity for the CO formation (CO/(H2 + CO)) over the optimized Ag/LaTa7O19 photocatalyst reached around 95% in an aqueous NaHCO3 solution. The rate of CO formation gradually decreased with a reaction time accompanied by an increase in the rate of H2 evolution. The results of scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS) revealed that aggregation of the Ag cocatalyst during the photocatalytic CO2 reduction caused the decrease in the CO formation.

Hybrid photocatalysts composed of metal sulfide semiconductors combined with various Ru-complex catalysts were synthesized for use during visible light-driven CO2 reduction with powder suspension systems. A variety of Zn-based sulfides, including Ni-doped ZnS, (CuGa)0.8Zn0.4S2 and (AgIn)0.22Zn1.56S2, were adopted by conducting the CO2 reduction reaction in acetonitrile containing an electron donor. The photocatalytic activities were found to be largely dependent on the basic characteristics of the Ru-complex and the metal sulfide. The results demonstrate that several of these sulfide semiconductors improve the CO2 reduction selectivity when employed in the semiconductor/metal-complex system, and that (AgIn)0.22Zn1.56S2 or Ni (0.2 mol%)-doped ZnS combined with a neutral Ru-complex incorporating a phosphonate ligand [Ru(4,4′-diphosphonate-2,2′-bipyridine)(CO)2Cl2] exhibit the highest CO2 photoconversion activity when synthesizing formic acid, with a turnover number above 100, which catalysts were stable for 16 h irradiation. These results suggest that metal sulfides are potential candidates for use in powdered semiconductor/metal-complex systems for selective CO2 photoreduction.

Nitrogen/fluorine-codoped rutile TiO2 (R-TiO2:N,F) was newly synthesized, and its photocatalytic activity for water oxidation was evaluated. R-TiO2:N,F could be prepared by nitridation of the rutile TiO2 (R-TiO2) and (NH4)2TiF6 mixture at 773 K. The prepared samples produced O2 from aqueous AgNO3 solution under visible light irradiation, while R-TiO2 nitrided at the same temperature without any fluorine source showed negligible activity. The highest activity was obtained with the sample prepared at the (NH4)2TiF6/R-TiO2 ratio of 15/85, exhibiting water oxidation activity even in the presence of a reversible electron acceptor such as IO3− or Fe3+ with the aid of a RuO2 cocatalyst. Stoichiometric water splitting into H2 and O2 was achieved using a mixture of Ru/SrTiO3:Rh and RuO2/TiO2:N,F in the presence of [Co(bpy)3]3+/2+ (bpy = 2,2′-bipyridine) as a shuttle redox mediator without noticeable degradation of activity under visible light and even under AM1.5G simulated sunlight. Transient absorption spectroscopy revealed that appropriate nitrogen/fluorine codoping reduces the density of mid-gap states working as deep traps of photogenerated electrons, and increases the number of free electrons compared to only nitrogen-doped R-TiO2. Experimental results highlighted that the photocatalytic activity of R-TiO2:N,F could be enhanced by improving visible-light absorption capability through N/F codoping while suppressing the density of deep trap sites.

We report here a new class of co-catalysts for hydrogen evolution on TiO2 particles upon photo-irradiation. TiO2 particles prepared by sol/gel method was allowed to graft metal ion by a simple treatment with metal salts (Pt (IV), Rh (III), Cu (II), Fe(III), Al (III) ions) in water. The metal ion surface-grafted particles of TiO2(sol/gel) exhibit excellent photochemical hydrogen evolution compared to Pt (0) cluster loaded particles of TiO2(sol/gel) under the UV light irradiation of λ > 290 nm. XPS analysis shows that the valence states of the metal ions grafted on the TiO2 particles are the same with the parent metal ion salts and no metal (0) clusters were detected. DFT calculation of the simple model of metal ion/TiO2 indicated that an injected electron mostly localized on the metal ion sites, but not on Ti sites, which rationalizes the metal ion serve as the hydrogen evolution sites. Earth abundant metal ions, Cu (II), Fe (III), and Al (III) thus can provide new class of hydrogen evolution sites for artificial photosynthetic systems. To explore the possibility of utilizing semiconductor as an electron relay in the future system of molecular-catalyst-sensitized water splitting into hydrogen and hydrogen peroxide, the stability of hydrogen peroxide on various TiO2 surfaces was examined. Hydrogen peroxide was found to be pretty stable on Rh (III), Fe (III), and Al (III) ions surface-grafted TiO2, while Pt (IV) and Cu (II) ion grafted one similarly caused decomposition of hydrogen peroxide as Pt (0) cluster loaded TiO2 (Pt(0)/TiO2).

We report herein remarkable improvement of activity and stability of an Au25-loaded BaLa4Ti4O15 water-splitting photocatalyst. We first examined the influence of refining the gold cocatalyst on the individual reactions over the BaLa4Ti4O15 photocatalyst in this water-splitting system. The results revealed that refining the gold cocatalyst accelerates not only the hydrogen generation reaction, but also oxygen photoreduction reaction, which suppresses the H2 generation via photoreduction of protons. This finding suggests that photocatalytic activity will be enhanced if the O2 photoreduction reaction can be selectively suppressed by covering Au25 with a Cr2O3 shell which is impermeable to O2 but permeable to H+. Then, we developed new method for the formation of the Cr2O3 shell onto Au25. Our method utilizes the strong metal–support interaction between them. Water-splitting photoactivity of Au25–BaLa4Ti4O15 was improved by 19 times under an optimized coverage of the Cr2O3 shell. The Cr2O3 shell also elongate...

Mo- and W-doped BiVO4 fine particles with a diameter of 50–200 nm were prepared from Bi2O3 and, Mo- and W-doped V2O5 by an aqueous route using an aqueous acetic acid solution. The Mo- and W-doped BiVO4 calcined at 673 K was elongate polyhedral particles grown along with the b-axis, while the non-doped BiVO4 prepared by the same method was featureless particles. X-ray absorption near edge structure (XANES) and electron spin resonance (ESR) measurements revealed that the Mo6+ and W6+ ions were doped at V sites, resulting in the formation of V4+ in BiVO4. The Mo- and W-doped BiVO4 powders showed lower activity for photocatalytic O2 evolution than the non-doped BiVO4. In contrast, the Mo- and W-doped BiVO4 photoelectrodes fabricated by an electrophoresis method using these fine particles gave higher photoelectrochemical performance due to a positive effect of the increase in the n-type character by Mo- and W-doping.

Phase relations in the pseudo ternary systems In2O3-TiO2-ZnO, In2O3-TiO2-CoO and In2O3-TiO2-NiO at 1200 °C in air were determined by means of a classic quenching method. In6Ti6BO22 (B: Zn, Co and Ni) which has the monoclinic In(Fe1/4Ti3/4)O27/8-type of structure with a 4-dimensional super space group exists in a stable form. There exist homologous phases In1+x(Ti1/2Zn1/2)1−xO3(ZnO)m (m: natural number, 0 3 ¯ m (No. 166) for m = odd or P63/mmc (No. 194) for m = even in space group. Lattice constants for each of the homologous compounds as a hexagonal setting and In6Ti6BO22 as the monoclinic system were determined by means of the powder X-ray diffraction method at room temperature. The temperature dependence of resistivity for In1+x(Ti1/2Zn1/2)1−x(ZnO)4 (0.15 ≤ x ≤ 1) showed semiconducting-like behavior for all samples examined at T(K) = 2–300. The resistivity increased systematically with decreasing x (0.7 ≤ x ≤ 1), and it was found that samples where x ≤ 0.7 became insulators. The optical band gap Eg (eV) of In1+x(Ti1/2Zn1/2)1−x(ZnO)4 has been estimated from the diffuse reflection spectra for the whole range of x (0.15 ≤ x ≤ 1). A minimum value of 2.0717 eV for x = 1 and a maximum one of 3.066 eV for x = 0.15 were observed. Dependence of the crystal structures of the InAO3(BO), In(Ti1/2B1/2)O3(B′O) and stability of In6Ti6BO22 upon the constituent cations in the pseudo quaternary system In2O3-TiO2-A2O3-BO (A: Fe, Ga and Cr; B, B′: Mg, Zn, Co, Ni, Ca and Sr) were discussed in terms of their ionic radii and site preference effects.

Ir cocatalyst-loaded SrTiO3:Ir has arisen as a promising photocatalyst for H2 evolution with a response to the whole range of visible light up to 800 nm. The key factor for the high activity lies in H2-reduction after loading of an Ir cocatalyst to obtain metallic and adhesive Ir-cocatalysts.

Photoelectrochemical water splitting has attracted much attention in recent years as an alternative energy source. However, there have been several significant issues such as low efficiency, high cost and less scalability for its practical application. Here, we show that (CuGa1−yIny)1−xZn2xS2 (CGIZS)-based photocathodes fabricated with a particle transfer method exhibited a photocurrent of 4.5 mA cm−2 at 0.6 V vs. RHE along with a largely positive onset potential of 1.0 V vs. RHE under simulated sunlight (AM 1.5G) and an initial solar-to-hydrogen energy conversion efficiency of 1.1% was obtained with photoelectrochemical water splitting using a two-electrode cell composed of the CGIZS-based photocathode and a BiVO4-based photoanode. CGIZS used for the particle transfer method was obtained in a powder state with high crystallinity by a flux method using a molten-salt of LiCl–KCl, and also formed solid solutions with a chalcopyrite single phase structure in a wide range of Ga/In ratios and Zn contents, in which the absorption edges of photocatalysts were tunable up to 880 nm.

Visible-light-driven Z-schematic CO2 reduction using H2O as an electron donor was achieved using a simple mixture of a metal-sulfide/molecular hybrid photocatalyst for CO2 reduction, a water oxidation photocatalyst and a redox-shuttle electron mediator. This is the first demonstration of a highly selective particulate CO2 reduction system accompanying O2 generation utilizing a semiconductor/molecular hybrid photocatalyst.

A visible-light-responsive Rh–Sb co-doped SrTiO3 photocatalyst (STO:Rh,Sb) via a solid-state reaction was successfully developed, following pulverization by using ball-milling. The prepared STO:Rh,Sb exhibited a large surface area and showed efficient photocatalytic degradation of acetaldehyde. The photocatalytic activity of STO:Rh,Sb ground for 60 min exceeded that of STO:Rh ground for 60 min (photocatalyst doped without antimony), indicating that doped antimony plays an important role in suppressing the Rh4+, which works as a recombination center, in STO:Rh,Sb. Furthermore, the photocatalytic performance of STO:Rh,Sb ground for 60 min was sustained over 3 cycles, confirming the chemical stability of the photocatalyst. Therefore, ground STO:Rh,Sb has the potential to be applied to environmental remediation under visible light irradiation.

Water is a promising source of clean hydrogen. Besides water electrolysis, the direct photoelectrochemical dissociation of water that combines light absorption and electrochemical water splitting into a single device is actively investigated by the scientific community. We report results on the p-type rhodium-doped strontium titanate (Rh:SrTiO 3 ) surface-modified by adsorption of a 3d -transition metal complex which is known to be a good catalyst of the hydrogen evolution reaction (HER) from water. The tris-dioximate cobalt hexachloroclathrochelate with an encapsulated cobalt(II) ion was selected as a surface HER co-catalyst for this study. Samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The kinetics of the photoelectrochemical water dissociation was studied using the open circuit photovoltage decay (OCPD) and photoelectrochemical impedance spectroscopy (PEIS) methods. Under open circuit conditions, the cobalt cage complex did not substantially affect the HER kinetics compared to the bare doped Rh:SrTiO 3 semiconductor. But when a reverse bias was applied, a significant difference caused by presence of the clathrochelate was observed. The rate constants of the charge transfer and the recombination processes were both affected, leading to the conclusion that the macrobicyclic cobalt-encapsulated species not only increased the rate of charge transfer, but also played a role as recombination centers for photoexcited minority carriers. The space charge capacitance was determined under the inversion conditions. Only under strong reverse bias it was found that, whereas bulk Rh:SrTiO 3 has a p- type conductivity, the surface of both bare Rh:SrTiO 3 and the cobalt clathrochelate-covered Rh:SrTiO 3 show the properties of a n -type semiconductor.

Heterogeneous photocatalytic water splitting under the irradiation of sunlight is an attractive method for generating hydrogen from water. While the photocatalytic mechanism has been extensively studied, most of experimental studies have been performed with an ensemble of photocatalyst particles with various sizes, morphologies, and secondary structures. To gain a deeper understanding of the mechanism of photocatalysis, it is indispensable to clarify how the geometric structure of photocatalyst affects the kinetics of photogenerated carriers and redox reactions. In this study, the hole decay characteristics and photocatalytic activity of BiVO4, a promising photocatalyst for oxygen evolution with visible light, have been investigated with single-particle transient absorption microscopy. Upon the irradiation with 527 nm light, well-faceted non-aggregated crystallites show fast hole decay and little reactivity for Fe3+ reduction. In contrast, aggregated particles with grain boundaries between small primary c...

Bacteriophage (denoted as phage) infection in the bacterial fermentation industry is a major problem, leading to the loss of fermented products such as alcohol and lactic acid. Currently, the prevention of phage infection is limited to biological approaches, which are difficult to apply in an industrial setting. Herein, we report an alternative chemical approach using ground Rh-doped SrTiO3 (denoted as g-STO:Rh) as a visible-light-driven photocatalyst. The g-STO:Rh showed selective inactivation of phage without bactericidal activity when irradiated with visible light (λ > 440 nm). After inactivation, the color of g-STO:Rh changed from gray to purple, suggesting that the Rh valence state partially changed from 3+ to 4+ induced by photocatalysis, as confirmed by diffuse reflectance spectroscopy. To study the effect of the Rh4+ ion on phage inactivation under visible-light irradiation, the survival rate of phage for g-STO:Rh was compared to that for ground Rh,Sb-codoped SrTiO3 (denoted as g-STO:Rh,Sb), where...

An efficient Mo-doped BiVO4 photoelectrode for water oxidation was easily prepared from a Bi-, V-, and Mo-containing aqueous precursor solution. The thickness of BiVO4 films was controllable by changing the volume of the precursor solution, giving a transparent BiVO4 film with a thickness of 130–260 nm. The Mo-doped BiVO4 photoelectrodes showed higher photocurrents than a non-doped BiVO4 photoelectrode prepared by the same procedure. An incident photon-to-current efficacy (IPCE) of the Mo-doped BiVO4 electrode with CoOx surface modification reached 33% at 1.23 V vs. RHE at 420 nm.

We have developed metal sulfide photocatalysts with various crystal structures and constituent metal cations with d0, d5, and d10 electron configurations. Cu3VS4, Cu3NbS4, and Cu3TaS4 with a sulvanite structure, ZnGaxIn2−xS4 (x = 0–0.6), and MnGaInS4 with layered structures, BaLaCuS3 with a one-dimensionally anisotropic structure along the b-axis, and a (ZnS)0.9-(CuCl)0.1 solid solution with a zinc blende structure have arisen as new photocatalysts for H2 evolution in the presence of sacrificial electron donors under visible light irradiation.

CuGaS2, (AgInS2)x–(ZnS)2−2x, Ag2ZnGeS4, Ni- or Pb-doped ZnS, (ZnS)0.9–(CuCl)0.1, and ZnGa0.5In1.5S4 showed activities for CO2 reduction to form CO and/or HCOOH in an aqueous solution containing K2SO3 and Na2S as electron donors under visible light irradiation. Among them, CuGaS2 and Ni-doped ZnS photocatalysts showed relatively high activities for CO and HCOOH formation, respectively. CuGaS2 was applied in a powdered Z-scheme system combining with reduced graphene oxide (RGO)-incorporated TiO2 as an O2-evolving photocatalyst. The powdered Z-scheme system produced CO from CO2 in addition to H2 and O2 due to water splitting. Oxygen evolution with an almost stoichiometric amount indicates that water was consumed as an electron donor in the Z-schematic CO2 reduction. Thus, we successfully demonstrated CO2 reduction of artificial photosynthesis using a simple Z-scheme system in which two kinds of photocatalyst powders (CuGaS2 and an RGO–TiO2 composite) were only dispersed in water under 1 atm of CO2.

Ir and La-codoped BaTa2O6 was developed as a novel photocatalyst for H2 evolution utilizing visible light up to 640 nm. The Ir and La-codoped BaTa2O6 with a Ru cocatalyst functioned as an H2-evolving photocatalyst for Z-schematic water splitting under visible light irradiation upon combination with a BiVO4 O2-evolving photocatalyst and a [Co(bpy)3]3+/2+ electron mediator.

SnNb2O6 has arisen as a candidate for photoanodes for solar water splitting. CoOx cocatalyst-loaded SnNb2O6 showed a stable, high anodic photocurrent with an incident photon-to-current conversion efficiency (IPCE) of 18% at 0.6 VRHE and a half-cell solar-to-hydrogen (HC-STH) efficiency of 0.39% at 0.6 VRHE.

Ultrafast excitation of photocatalytically active BiVO4 was characterized by femto- and picosecond transient X-ray absorption fine structure spectroscopy. An initial photoexcited state (≪500 fs) changed to a metastable state accompanied by a structural change with a time constant of ∼14 ps. The structural change might stabilize holes on oxygen atoms since the interaction between Bi and O increases.

We have successfully demonstrated solar water splitting using a newly fabricated photoelectrochemical system with a Pt-loaded SiC photocathode, a CoOx -loaded BiVO4 photoanode, and a perovskite solar cell. Detection of the evolved H2 and O2 with a 100 % Faradaic efficiency indicates that the observed photocurrent was used for water splitting. The solar-to-hydrogen (STH) efficiency was 0.55 % under no additional bias conditions.

Water splitting using semiconductor photocatalysts has been attracting growing interest as a means of solar energy based conversion of water to hydrogen, a clean and renewable fuel. Z-scheme photocatalytic water splitting based on the two-step excitation of an oxygen evolution photocatalyst (OEP) and a hydrogen evolution photocatalyst (HEP) is a promising approach toward the utilisation of visible light. In particular, a photocatalyst sheet system consisting of HEP and OEP particles embedded in a conductive layer has been recently proposed as a new means of obtaining efficient and scalable redox mediator-free Z-scheme solar water splitting. In this paper, we discuss the advantages and disadvantages of the photocatalyst sheet approach compared to conventional photocatalyst powder suspension and photoelectrochemical systems through an examination of the water splitting activity of Z-scheme systems based on SrTiO3:La,Rh as the HEP and BiVO4:Mo as the OEP. This photocatalyst sheet was found to split pure water much more efficiently than the powder suspension and photoelectrochemical systems, because the underlying metal layer efficiently transfers electrons from the OEP to the HEP. The photocatalyst sheet also outperformed a photoelectrochemical parallel cell during pure water splitting. The effects of H+/OH− concentration overpotentials and of the IR drop are reduced in the case of the photocatalyst sheet compared to photoelectrochemical systems, because the HEP and OEP are situated in close proximity to one another. Therefore, the photocatalyst sheet design is well-suited to efficient large-scale applications. Nevertheless, it is also noted that the photocatalytic activity of these sheets drops markedly with increasing background pressure because of reverse reactions involving molecular oxygen under illumination as well as delays in gas bubble desorption. It is shown that appropriate surface modifications allow the photocatalyst sheet to maintain its water splitting activity at elevated pressure. Accordingly, we conclude that the photocatalyst sheet system is a viable option for the realisation of efficient solar fuel production.

Metal sulfides are an excellent material group for highly efficient water reduction to H2. We demonstrate the uphill reaction using a single-particulate metal sulfide photocatalyst. A Ru cocatalyst-loaded ZnS photocatalyst showed an activity for the decomposition of an aqueous solution into H2 and N2 under simulated sunlight irradiation.

The function of actin is regulated by various posttranslational modifications. We have previously shown that in the kidneys of nonobese type 2 diabetes model Goto-Kakizaki rats, increased O-GlcNAcylation of β-actin protein is observed. It has also been reported that both O-GlcNAcylation and phosphorylation occur on Ser199of β-actin. However, their roles are not known. To elucidate their roles in diabetic nephropathy, we examined the rat kidney for changes in O-GlcNAcylation of Ser199(gS199)-actin and in the phosphorylation of Ser199(pS199)-actin. Both gS199- and pS199-actin molecules had an apparent molecular weight of 40 kDa and were localized as nonfilamentous actin in both the cytoplasm and nucleus. Compared with the normal kidney, the immunostaining intensity of gS199-actin increased in podocytes of the glomeruli and in proximal tubules of the diabetic kidney, whereas that of pS199-actin did not change in podocytes but decreased in proximal tubules. We confirmed that the same results could be observed in the glomeruli of the human diabetic kidney. In podocytes of glomeruli cultured in the presence of the O-GlcNAcase inhibitor Thiamet G, increased O-GlcNAcylation was accompanied by a concomitant decrease in the amount of filamentous actin and in morphological changes. Our present results demonstrate that dysregulation of O-GlcNAcylation and phosphorylation of Ser199occurred in diabetes, which may contribute partially to the causes of the morphological changes in the glomeruli and tubules. gS199- and pS199-actin will thus be useful for the pathological evaluation of diabetic nephropathy.