Effect of Oxygen Concentration and Tantalum Addition on the Formation of High Temperature Bismuth Oxide Phase by Mechanochemical Reaction.

High-temperature face-centered cubic bismuth oxide phase is a material of great interest given its unique properties. In the present study, α-Bi2O3 and tantalum powders were used as the starting powders for the formation of high-temperature bismuth oxide phase via mechanochemical synthesis by high energy ball milling. (Bi2O3)80(Ta)20 and (Bi2O3)95(Ta)5 in weight concentrations were milled in either an oxygen-free argon-filled glove box environment or an ambient atmosphere to investigate the effects of oxygen concentration and tantalum addition. The as-milled powders were examined using X-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy, and differential scanning calorimetry to reveal the structural evolution. The experimental results showed that for (Bi2O3)95(Ta)5 powder mixtures milled within the glove box, tantalum gradually reacted with the α-Bi2O3 phase and formed a ß-Bi7.8Ta0.2O12.2 phase. For (Bi2O3)80(Ta)20 milled under the same conditions, Ta and α-Bi2O3 mechanochemically reacted to form δ-Bi3TaO7 and bismuth after 10 min of high energy ball milling, whereas milling (Bi2O3)80(Ta)20 under the ambient atmosphere with a much higher oxygen concentration accelerated the mechanochemical reaction to less than five minutes of milling and resulted in the formation of high-temperature δ-Bi3TaO7 phase.

Synthesis of Cu2O nanoparticle films at room temperature for solar water splitting.

A Cu2O nanoparticle film using ZnO nanorods as a sacrificial scaffold was fabricated near 23°C, for applications in photoelectrochemical (PEC) water splitting. Three chemical solutions were utilized to convert ZnO nanorods to a Cu2O nanoparticle film - solutions of CuCl2 and NaOH, NaBH4 and NaOH, respectively. The structural evolution from ZnO through Cu(OH)2 and metallic Cu to Cu2O phase was analyzed at each stage with X-ray diffraction and X-ray absorption spectra. The energy bandgap was deduced from IPCE; the concentration of carriers and flat-band of a Cu2O nanoparticle film were obtained from a Mott-Schottky plot. Significantly, the Cu2O nanoparticle film exhibited a useful PEC response to water oxidation. This nanostructure synthesized with no energy requirement can not only illustrate a great prospect for solar generation of hydrogen but also offer a blueprint for the future design of photocatalysts.