Effects of distortion of metal-oxygen octahedra on photocatalytic water-splitting performance of RuO2-loaded niobium and tantalum phosphate bronzes.

Sodium, niobium, and tantalum phosphate bronzes Na(4)M(8)P(4)O(32) (M=Nb, Ta) are employed as photocatalysts for water splitting to reveal the effects of the distortion of metal-oxygen octahedra on the photocatalytic performance. Addition of RuO(2) as a co-catalyst leads to high, stable activity in the stoichiometric production of H(2) and O(2) under UV irradiation. The combination of highly crystallized phosphates and a high dispersion of RuO(2) particles result in high photocatalytic activity. The sodium niobium phosphate bronze Na(2)Nb(8)P(4)O(32), consisting of a framework built up from slabs of corner-sharing NbO(6) octahedra connected through isolated PO(4) tetrahedra, provide heavily distorted NbO(6) octahedra with large internal dipole moments. The results support the existing view that the activity correlates with the magnitude of the dipole moment. The heavy distortion of NbO(6) octahedra is shown to play a significant role in photocatalytic water splitting.