Dependence of Photoexcited Electron Behavior on Octahedral Distortion in Barium-Doped NaTaO3 Photocatalysts

This study aims to investigate the behavior of photoexcited electrons in intentionally distorted Ba-doped NaTaO3 photocatalysts with time-resolved microwave conductivity and steady-state IR absorption induced by UV light. As probed by X-ray absorption fine structure and Raman spectroscopies, doping NaTaO3 with Ba2+ produces structural nonperiodicity and distorts the octahedral sublattice, proposedly resulting in the formation of electron traps. A higher density of shallow electron traps is suggested to be responsible for the longer electron lifetime and larger electron population, because shallowly trapped electrons are less likely to recombine with holes. The half-lifetime of photoexcited electrons is considerably long, even longer than 0.8 ms in the Ba-doped NaTaO3 sample with moderate distortion. The population of photoexcited electrons under Hg–Xe lamp irradiation increases by 32 times in this sample compared to that in undoped NaTaO3, generating H2/O2 mixtures with the rates of 385 μmol h–1 (H2) and 180 μmol h–1 (O2) when irradiated with a Hg lamp in the absence of cocatalyst and sacrificial compound. Moderate distortion seems favorable to produce shallow electron traps in comparison to large and small distortions, leading to the highest water splitting rate. The orders of photocatalysts based on their electron lifetime, electron population, and water splitting rate are identical, indicating that the photoexcited electrons worked in the water splitting reactions.