Photocatalysts For Solar Water Splitting Research Articles

Application of content optimized ZnS-ZnO-CuS-CdS heterostructured photocatalyst for solar water splitting and organic dye decomposition

Heterostructured ZnS-ZnO-CuS-CdS photocatalyst was synthesized via a sequential fabrication approach (ZnS→thermal treatment (ZnS-ZnO)→CuS formation (ZnS-ZnO-CuS)→CdS addition (ZnS-ZnO-CuS-CdS)). Each component in this heterostructure has its own role for photocatalytic reaction. The oxide content controlled by thermal processing condition is a crucial factor for improving photocatalytic activity, and the CuS and CdS contents are controlled by their feedstocks. The effects of heterostructure composition on the solar water splitting and organic dye decomposition were investigated under 1 sun irradiation (100 mW/cm2, AM 1.5G filter). The content optimized ZnS-ZnO-CuS-CdS photocatalyst produces 2452.7 μmol g−1 h−1 hydrogen, and it decomposes methyl blue much faster than the other cases. Thus, heterostructured photocatalysts can benefit the use of electrons and holes for improved photocatalytic activity.

Computational prediction and characterization of single-layer CrS2

Using first-principles calculations, we predict a previously unreported bulk CrS2 phase that is stable against competing phases and a low energy dynamically stable single-layer CrS2 phase. We characterize the electronic, optical, and piezoelectric properties of this single-layer material. Like single-layer MoS2, CrS2 has a direct bandgap and valley polarization. The optical bandgap of CrS2 is 1.3 eV, close to the ideal bandgap of 1.4 eV for photovoltaic applications. Applying compressive strain increases the bandgap and optical absorbance, transforming it into a promising photocatalyst for solar water splitting. Finally, we show that single-layer CrS2 possesses superior piezoelectric properties to single-layer MoS2.

BiVO4–Ru/SrTiO3:Rh composite Z-scheme photocatalyst for solar water splitting

BiVO4–SrTiO3:Rh composites in which the Rh-doped SrTiO3 particles of a H2-evolving photocatalyst attached on the BiVO4 particles of an O2-evolving photocatalyst were prepared by an impregnation method and a liquid–solid state reaction. The composites showed photocatalytic activity for Z-schematic water splitting under visible light or simulated sunlight irradiation without an electron mediator. The optimum pH for the water splitting was neutral. Water splitting over the composite proceeded via an interparticle electron transfer from BiVO4 to Ru/SrTiO3:Rh particles at the large interfacial area obtained by those preparation methods. The photocatalytic water splitting activity of the composite depended on the crystallinity and morphology of BiVO4. The composite prepared by the liquid–solid state reaction showed the highest photocatalytic activity. This was due to the formation of well-crystallized BiVO4 single-crystal-like particles. The BiVO4–Ru/SrTiO3:Rh composite photocatalyst gave a quantum yield of 1.6% at 420 nm and a stable activity. Thus, we have developed the simplest system requiring no additives, except for photocatalyst powder and water, for photocatalytic solar water splitting.

Enhanced Water Oxidation on Ta3N5 Photocatalysts by Modification with Alkaline Metal Salts

Tantalum nitride (Ta(3)N(5)) is a promising nitride semiconductor photocatalyst for solar water splitting because it has band edge potentials capable of producing hydrogen and oxygen from water under visible light (λ < 590 nm). However, the photocatalytic performance of Ta(3)N(5) has been far below expectations because insufficient crystallization upon thermal nitridation of the oxide precursors enhances undesirable charge recombination limiting the quantum efficiency of the photocatalytic reaction. This problem was successfully rectified in this study by modifying the surface of the starting Ta(2)O(5) with a small amount of alkaline metal (AM) salts. Compared with conventional Ta(3)N(5), Ta(3)N(5) nitrided from AM salt-modified Ta(2)O(5) had better crystallinity and smaller particles with smoother surfaces and, most importantly, demonstrated a 6-fold improvement in photocatalytic activity for O(2) evolution under visible light. AM salt modification was compatible with the loading of an O(2) evolution cocatalyst, such as CoO(x), yielding an apparent quantum efficiency of 5.2% at 500-600 nm. This indicates that the effects of AM modification were attributable to the changes in the crystallinity and the morphology of Ta(3)N(5) rather than to catalytic effects. Detailed characterization of the Na(2)CO(3)-modified Ta(3)N(5) suggested partial dissolution of Ta(2)O(5) and nucleation of NaTaO(3) in the early stages of nitridation, which gave rise to the characteristic particle morphologies and improved the crystallinity of the nitridation products. This study demonstrates that a facile pretreatment of a starting material can improve the physical and photocatalytic properties of photocatalysts drastically, enabling the development of advanced photocatalysts for solar water splitting.