Visible light responsive La and Fe co-doped NaTaO3 photocatalysts: Local structure around dopants

NaTaO3 doubly doped with La and transition metal cations has been of interest for photocatalytic water splitting under visible light. However, there is not yet convincing evidence to propose a plausible structure for the dopant pair incorporated in the NaTaO3 host. In this study, efforts were made to reveal the local structure of La and Fe cations doped in NaTaO3. For this purpose, we employed X-ray absorption spectroscopy, including extended X-ray absorption fine structure and X-ray absorption near-edge structure. It was revealed that upon double doping, La cations occupied the Na-sites, whereas Fe cations occupied the Ta-sites. A LaFeO3-NaTaO3 solid solution was formed accordingly, together with a trace amount of iron oxide impurities. The solid solution was able to absorb visible light to produce electrons. A volcano-shaped pattern of the electron population with respect to the dopant concentration was present, in which 2 + 2 mol% gave the highest electron population.