Hierarchical metastable γ-TaON hollow structures for efficient visible-light water splitting

Hierarchical tantalum-based oxide and (oxy)nitride with hollow urchin-like nanostructures have been synthesized for the first time by an in situ self-assembly wet-chemical route in addition with postthermal nitridation. Notably, a single-phase metastable gamma-TaON with hollow urchin-like spheres among the tantalum (oxy)nitrides was obtained during the phase transformation process from an orthorhombic Ta2O5 to a typical monoclinic beta-TaON, corresponding the order of phase formation: Ta2O5 -> gamma-TaON -> beta-TaON -> Ta3N5. The combined effect of the crystal and electronic structures and hierarchical morphology on the tunable photocatalytic and photoelectrochemical performances of the tantalum-based photocatalysts was systematically investigated. Efficient photocatalytic hydrogen production as high as 381.6 mu mol h(-1) with an apparent quantum efficiency of 9.5% under 420 nm irradiation (about 47.5 times higher than that of the conventional TaON) was achieved over this metastable gamma-TaON architecture. Furthermore, the hierarchical gamma-TaON photoanode exhibited a photocurrent density of similar to 1.4 mA cm(-2) at 0.8 V vs. SCE in Na2SO4 solution under visible light irradiation. This excellent photocatalytic activity is ascribed to the unique urchin-like nanostructure with large specific surface area, the metastable crystal structure and appropriate electronic structure as well as the efficient charge carrier separation.