RESUMO
Sunlight-driven photocatalytic water splitting shows promise for green H2 production. In an attempt to achieve seawater splitting, we constructed a new stoichiometric brine splitting system that produces H2 along with Cl2 instead of O2. Cl2-a more potent high-value-added oxidant than O2-was obtained with 100% selectivity over 10 h by adjusting the solution pH to acidic using a UV-light-driven Pt-loaded TiO2 photocatalyst. Our new photosynthesis system can permit economically feasible solar chemical production.
RESUMO
Ferroelectric thin films are important because of their great potential for use in various electric devices such as ferroelectric random-access memory. It was expected that Bi2SiO5, a Si-containing ferroelectric material, would show improved ferroelectricity by targeting a film with the (001)-orientation (polar-axis) on the substrate. Although there was a narrow process window for the deposition of the (010)/(001)-oriented Bi2SiO5 thin film, it was successfully prepared on a (101)-oriented TiO2 single substrate using the pulsed layer deposition technique. The optimum film deposition conditions and film thickness were found, and in this material, the volume fraction of the (001)-oriented domain reached about 70%. By controlling film orientation to the polar axis, the remanent polarization value of this film was 4.8 µC cm-2, which is the highest value among reported Bi2SiO5.
RESUMO
Photocatalytic/photoelectrochemical water splitting using metal oxide semiconductors is a promising technology for direct and simple solar-energy conversion. The addition of carbonate salts to an aqueous reaction solution has been known to promote stoichiometric O2 evolution and H2O2 production via H2O oxidation. To elucidate the effect of carbonates, density functional theory calculations are performed to study the photoinduced H2O and H2CO3 oxidation mechanisms on TiO2 and BiVO4. The oxidation reactions proceeded via peroxide intermediates, such as H2O2 for H2O, H2C2O6 for H2CO3, and H2CO4 for the coexistence of H2O and H2CO3 molecules. Regardless of the reactant and metal oxide, the free energy changes in the four proton-coupled electron-transfer (PCET) steps of the oxidation mechanism indicate that the first PCET requires the highest energy input and is the rate-limiting step. All PCET steps of the H2O oxidation, except the second one, are more endergonic than those of the H2CO3 oxidation. The H2O reactant requires a larger energy barrier at the highest energy profile, as well as at the final state, than the H2CO3 reactant. The computational results verify that the adsorbed H2CO3 molecule is easily photo-oxidized compared with the adsorbed H2O molecule, facilitating the formation of the peroxide intermediate and improving O2 evolution and H2O2 production.
RESUMO
The processes involved in the nitridation of Sr2Nb2O7 and SrNbO3 to SrNbO2N were assessed by varying the nitridation time, and the related effects on the physical and photoelectrochemical properties of the nitrided products were investigated. In the case of the layered perovskite-type oxide Sr2Nb2O7, the introduction of nitrogen and the extraction of oxygen took place concurrently, leading to lattice shrinkage and a porous structure. In contrast, during nitridation of the perovskite-type oxide SrNbO3, nitrogen was initially introduced without any loss of oxygen, which caused phase separation as a result of a lattice expansion and a charge compensation. The photoelectrochemical properties of obtained SrNbO2N under simulated sunlight were found to vary with the oxide precursor used and with the nitridation process.
