An investigation of crystal structure, surface area and surface chemistry of strontium niobate and their influence on photocatalytic performance

Sr_1-xNbO₃ is an unusual material that displays both metallic type conduction and photocatalytic activity, despite being an NbIV oxide, and it sustains photo-oxidation without degradation. The influence of crystal structure, surface area and surface chemistry on the photocatalytic activity of strontium niobate has been investigated. The crystal structure of strontium niobate depends on the Sr content of the A site, with cubic symmetry for Sr ≤ 0.92 and orthorhombic symmetry for 0.92 < Sr ≤ 0.97. The change of crystal structure from cubic to orthorhombic symmetry seems to have a negative effect on the photocatalytic activity, as the NbO₆ octahedra become distorted and unfavourable for d-orbital overlapping. The photocatalytic activity increased significantly by enlarging the surface area through ball milling, nevertheless, a clear trend for the surface area effect on activity is not obtained among samples with different Sr content. An enrichment of Sr on the surface of strontium niobate was observed by XPS, which seems to be a governing factor for improving stability.