Synthesis of BaTaO2N oxynitride from Ba-rich oxide precursor for construction of visible-light-driven Z-scheme overall water splitting

Barium tantalum oxynitride (BaTaO2N) with an absorption edge of ca. 660 nm is one of the most promising photocatalysts for solar water splitting, and is usually synthesized by nitriding a mixture of Ba and Ta-containing compounds with a Ba/Ta molar ratio of unity under ammonia flow at high temperature, usually causing a high density of defect sites. Herein, we introduce a novel synthesis method for BaTaO2N (BTON) by employing Ba-rich LiBa4Ta3O12, prepared by a flux method, as a precursor of nitridation. As a comparison, BaTaOx was prepared by conventional solid state reaction and used as the precursor. The as-nitrided samples were correspondingly denoted as BTON-Flux and BTON-SSR. It was found that well-crystallized BTON oxynitride can be similarly obtained by both methods, but the BTON-Flux sample exhibits significantly decreased defect density and enhanced surface area relative to the BTON-SSR sample. As a result of their structural differences, the photocatalytic water splitting performance of the BTON-Flux sample, regardless of the H2-evolving half reaction in the presence of methanol or Z-scheme overall water splitting, is much better than that of BTON-SSR. This study may open up a novel strategy for preparing oxynitride photocatalyst with decreased defect density for the promotion of solar water splitting.