Effect of heat treatment on local structure and photocatalytic water splitting activity of Ni-loaded LiCa2Ta3O10

The photocatalytic activity of 0.5 wt% Ni-loaded LiCa2Ta3O10 for water splitting into a stoichiometric H2/O2 mixture increased about 4-fold after heat treatment at ≥ 500°C in a flow of N2. Local structures of the photocatalysts before and after heat treatment have been studied using XRD and XAFS. Rietveld refinement of XRD patterns revealed that the heat treatment decreased the thickness of a triple-layered perovskite slab and thus increased the distortion of octahedral TaO6 units in the both side of triple-layers. The resulting increase of dipole moment is considered to be efficient for promoting a charge separation step in the photocatalytic process. The heat treatment also converted the Ni cocatalysts from NiO/Ni core-shell to fully oxidized structure, but its effect on the photocatalytic activity was negligible.