Active BaTaO2N photocatalysts prepared from an amorphous Ta2O5 precursor for overall water splitting under visible light

Barium tantalum oxynitride (BaTaO2N), a photocatalyst active during one-step-excitation overall water splitting under visible light, was synthesized by NH3-based nitridation of a mixture of BaCO3 and amorphous Ta2O5 center dot 3H(2)O. H-2 and O-2 were generated from water in stoichiometric amounts and in a stable manner using this material modified with Rh (or Ru), Cr2O3 and IrO2 cocatalysts. This photocatalyst was responsive to visible light up to a wavelength of 540 nm for the water splitting reaction. Trials using nitridation temperatures from 1023 to 1273 K and durations from 0.5 to 20 h indicated that mild nitridation conditions such as 1123 K and 5 h provided high-performance specimens, whereas prolonged nitridation (15-20 h) dramatically decreased the photocatalytic activity. Transient absorption spectroscopy showed that BaTaO2N generated abundant photoexcited free electrons with long lifetimes due to a low concentration of defects such as oxygen vacancies, but was deactivated after prolonged nitridation. X-ray photoelectron spectra indicated that overly long nitridation generated recombination sites such as Ta3+. The mechanism by which active BaTaO2N was formed was examined, and the high reactivity of the amorphous Ta2O5 center dot 3H(2)O nanoparticles was determined to be important. The use of highly reactive nanoparticles under mild nitridation conditions could allow the future development of high-performance oxynitride photocatalysts for overall water splitting.