Effects of doping of metal cations into wide band gap semiconductor photocatalysts on morphology, visible light response, and photocatalytic performance were studied. Doping of lanthanide and ...alkaline earth ions improved activity of a NaTaO
3 photocatalyst for water splitting. Lanthanum was the most effective dopant. The NaTaO
3:La with a NiO cocatalyst gave 56% of a quantum yield at 270
nm. This remarkable photocatalytic activity was brought by formations of nano-crystalline particle and surface nano-step structure by the doping. On the other hand, metal cation doping into ZnS, TiO
2, and SrTiO
3 gave visible light responses for H
2 or O
2 evolution from aqueous solutions containing of sacrificial reagents. The visible light responses were due to the electronic transition from donor levels formed with dopants to conduction bands of the host photocatalysts. Codoping was effective to compensate charge unbalance brought by doping of transition metal cations, resulting in the improvement of visible light response for photocatalytic reactions. Among the transition metal-doped photocatalysts, SrTiO
3 doped with Rh (SrTiO
3:Rh) was the novel metal oxide photocatalyst that produced H
2 under visible light irradiation. The SrTiO
3:Rh photocatalyst was employed with O
2 evolution photocatalysts such as BiVO
4 and WO
3 for construction of Z-scheme systems that were active for water splitting into H
2 and O
2 under visible light irradiation.
Production of chemical fuels by direct solar energy conversion in a photoelectrochemical cell is of great practical interest for developing a sustainable energy system. Various nanoscale designs such ...as nanowires, nanotubes, heterostructures and nanocomposites have been explored to increase the energy conversion efficiency of photoelectrochemical water splitting. Here we demonstrate a self-organized nanocomposite material concept for enhancing the efficiency of photocarrier separation and electrochemical energy conversion. Mechanically robust photoelectrodes are formed by embedding self-assembled metal nanopillars in a semiconductor thin film, forming tubular Schottky junctions around each pillar. The photocarrier transport efficiency is strongly enhanced in the Schottky space charge regions while the pillars provide an efficient charge extraction path. Ir-doped SrTiO3 with embedded iridium metal nanopillars shows good operational stability in a water oxidation reaction and achieves over 80% utilization of photogenerated carriers under visible light in the 400- to 600-nm wavelength range.
In mice and humans, Nik-related protein kinase (Nrk) is an X-linked gene that encodes a serine/threonine kinase belonging to GCK group 4. Nrk knockout (Nrk KO) mice exhibit delayed delivery, possibly ...due to defective communication between the Nrk KO conceptus and its mother. However, the mechanism of delayed labor remains largely unknown. Here, we found that in pregnant mothers with the Nrk KO conceptus, the serum progesterone (P4) and placental lactogen (PL-2) concentrations in late pregnancy were higher than those in the wild type. Moreover, we demonstrated that Nrk is expressed in trophoblast giant cells (TGCs) and syncytiotrophoblast-2 (SynT-2) in the labyrinth layer of the mouse placenta. In the human placenta, NRK is also expressed in Syn-T in villi. Both human Syn-T and mouse TGCs of the labyrinth layer are present within fetal tissues that are in direct contact with the maternal blood. The labyrinth layer of the Nrk KO conceptus was gigantic, with enlarged cytoplasm and Golgi bodies in the TGCs. To investigate the function of Nrk in the labyrinth layer, a differentially expressed gene (DEG) analysis was performed. The DEG analysis revealed that labor-promoting factors, such as prostaglandins, were decreased, and pregnancy-maintaining factors, such as the prolactin family and P4 receptor, were increased. These findings suggest that the Nrk KO mice exhibit delayed delivery owing to high P4 concentrations caused by the hypersecretion of pregnancy-maintaining factors, such as PL-2, from the placenta.
(CuIn)(x)Zn2(1-x)S2 solid solutions between a ZnS photocatalyst with a wide band gap and CuInS(2) with a narrow band gap showed photocatalytic activities for H(2) evolution from aqueous solutions ...containing sacrificial reagents SO(3)(2-) and S(2-) under visible-light irradiation (lambda >/= 420 nm). Pt (0.5 wt %)-loaded (CuIn)(0.09)Zn(1.82)S(2) with a 2.3-eV band gap showed the highest activity for H(2) evolution, and the apparent quantum yield at 420 nm amounted to 12.5%. H(2) evolved at a rate of 1.5 L h(-1) m(-2) under irradiation with a solar simulator (AM 1.5). Diffuse reflection and photoluminescence spectra of the solid solutions shifted monotonically to a long wavelength side, as the ratio of CuInS(2) to ZnS increased in the solid solutions. The photocatalytic H(2) evolution depended on the composition as well as the photophysical properties. DFT calculations suggested that the visible-light response should be derived from the contribution of Cu 3d and S 3p orbitals to the valence band and that of In 5s5p and Zn 4s4p orbitals to the conduction band, respectively. The contribution of these orbitals to the energy bands affected the photophysical and photocatalytic properties.
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•Ag/LaTa7O19 and Ag/CaTa4O11 have arisen as new photocatalysts for CO2 reduction.•CO was obtained as the reduction product of a CO2 molecule.•Water was consumed as the electron source ...for the CO2 reduction.•The relationship between the band structures and the activities has been clarified.•Aggregation of the Ag cocatalyst caused the deterioration of CO formation.
LaTa7O19 (BG: 4.1eV) and CaTa4O11 (BG: 4.5eV) 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: 3.6eV) 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.
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 (BiVO4/rGO) composites with tailored interfacial contact extents and revealed their disparate behavior in photoelectrochemical (PEC) and powder suspension (PS) water oxidation systems. BiVO4/rGO with a high rGO coverage on the BiVO4 surface (BiVO4/rGO HC) exhibited an 8-fold enhancement in the PEC photocurrent density with respect to neat BiVO4 at 0 V versus Ag/AgCl, while BiVO4/rGO with a low rGO coverage (BiVO4/rGO LC) gave a lesser 3-fold enhancement. In contrast, BiVO4/rGO HC delivered a detrimental effect, while BiVO4/rGO LC exhibited an enhanced performance for oxygen evolution in the PS system. The phenomenon is attributed to changes in the hydrophobicity of the BiVO4/rGO composite in conjunction with the interfacial contact configuration. A better BiVO4/rGO interfacial contact was found to improve the charge separation efficiency and charge transfer ability of the composite material, explaining the superior PEC performance of BiVO4/rGO HC. Additionally, optimization of the interfacial contact extent was revealed to further improve the energetics of the composite material, as evidenced by a Fermi level shift to a more negative potential. However, the high hydrophobicity of BiVO4/rGO HC arising from the higher rGO reduction extent triggered poor water miscibility, reducing the surface wettability and therefore hampering the photocatalytic O2 evolution activity of the sample. The study underlines water miscibility as a governing issue in the PS system.
Tantalum nitride (Ta3N5) modified with various O2‐evolution cocatalysts was employed as a photocatalyst for water oxidation under visible light (λ>420 nm) in an attempt to construct a ...redox‐mediator‐free Z‐scheme water‐splitting system. Ta3N5 was prepared by nitriding Ta2O5 powder under a flow of NH3 at 1023–1223 K. The activity of Ta3N5 for water oxidation from an aqueous AgNO3 solution as an electron acceptor without cocatalyst was dependent on the generation of a well‐crystallized Ta3N5 phase with a low density of anionic defects. Modification of Ta3N5 with nanoparticulate metal oxides as cocatalysts for O2 evolution improved water‐oxidation activity. Of the cocatalysts examined, cobalt oxide (CoOx) was found to be the most effective, improving the water‐oxidation efficiency of Ta3N5 by six to seven times. Further modification of CoOx/Ta3N5 with metallic Ir as an electron sink allowed one to achieve Z‐scheme water splitting under simulated sunlight through interparticle electron transfer without the need for a shuttle redox mediator in combination with Ru‐loaded SrTiO3 doped with Rh as a H2‐evolution photocatalyst.
Split me! A redox‐mediator‐free Z‐scheme water‐splitting system capable of working under simulated sunlight was achieved by using Ir/CoOx/Ta3N5 in combination with Ru/SrTiO3:Rh as a H2‐evolution photocatalyst.
Water splitting to produce H2 using sunlight is a form of artificial photosynthesis in that light energy is converted to chemical energy. As such, water splitting using powdered photocatalysts has ...attracted attention in the framework of energy and environmental issues. This article reviews z-scheme photocatalyst systems for water splitting under visible light irradiation, especially focused on the systems consisting of SrTiO3:Rh of a H2-evolving photocatalyst, and O2-evolving photocatalysts with and without electron mediators. These photocatalyst systems showed activities for water splitting into H2 and O2 in a stoichiometric amount under visible light irradiation and even under sunlight irradiation. The photocatalytic activity was sensitive to pH. The optimum pH was 2.4 when iron ions were used as electron mediators. Co-catalysts also affected the activity. The photodeposited Ru co-catalyst gave an excellent performance. The best performance achieved by the pH adjustment and the selection of a co-catalyst was obtained mainly by suppression of back reactions to form H2O from evolved H2 and O2.
Nanoparticles of ZnS−AgInS2 solid solution (ZAIS) were synthesized by the thermal decomposition of (AgIn) x Zn2(1- x )(S2CN(C2H5)2)4 precursors in a hot oleylamine solution. X-ray powder diffraction ...analyses revealed that the resulting nanoparticle powders were not a mixture of ZnS and AgInS2 but a ZnS−AgInS2 solid solution in which the fraction of ZnS was enlarged with a decrease in the value of x, that is, an increase in the content of Zn2+ in the precursors used. The energy gap of ZAIS nanoparticles could be controlled by the composition of solid solution. Intense emission was observed at room temperature, regardless of the kind of the particles, the peak wavelength of PL being blue-shifted from 720 to 540 nm with a decrease in the value of x. The highest quantum yield of ca. 24% was obtained for nanoparticles prepared with x = 0.86, which was much higher than the quantum yields reported for I−III−VI2-based semiconductor nanoparticles, such as CuInS2 and ZnS−CuInS2 solid solution.
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