Preparation of BaZrO_3-BaTaO_2N solid solutions and the photocatalytic activities for water reduction and oxidation under visible light

摘要

Particulate solid solutions between BaTaO_2N and BaZrO_3, having a single-phase perovskite structure, were examined over the Zr/Ta range from 0 to 0.5 as photocatalysts for water splitting under visible light. With increasing BaZrO_3 content (that is, Zr/Ta ratio), the band edge of BaTaO_2N shifted from 660 to 620 nm, due primarily to the contribution from the larger band gap of BaZrO_3 compared to BaTaO_2N. These materials, with modification by the cocatalysts Pt and IrO_2, were capable of reducing and oxidizing water into H_2 and O_2, respectively, under visible light (λ > 420 nm) in the presence of methanol and silver nitrate as an electron donor and acceptor, respectively. When a small amount of BaZrO_3 was introduced into BaTaO_2N (Zr/Ta 6 0.05) using a suitably prepared oxide precursor, the highest activity was obtained for both water reduction and oxidation. On the other hand, when added in excess, BaZrO_3 lowered the crystallinity of the solid solution, contributing directly to a decrease in photocatalytic activities, especially for water oxidation. The results of photoelectrochemical measurements indicated that the conduction band minimum and the valence band maximum of BaZrO_3-BaTaO_2N solid solution straddle the water-splitting potential.