Photophysical and photocatalytic properties of novel M2BiNbO7 (M = In and Ga)

M2BiNbO7 ( M = In and Ga) were synthesized by solid- state reaction method and their structural and photocatalytic properties were investigated. The results indicated that these compounds crystallize in the pyrochlore-type structure, cubic system with space group Fd-3m. In addition, the band gaps of In2BiNbO7 and Ga2BiNbO7 were estimated to be about 2.52( 5) and 2.57( 8) eV, respectively. For the photocatalytic water splitting reaction, H-2 or O-2 evolution was observed from pure water respectively with M2BiNbO7 ( M = In and Ga) as the photocatalysts under ultraviolet light irradiation. Photocatalytic degradation of aqueous methylene blue ( MB) dye over these compounds was further investigated under visible light irradiation. M2BiNbO7 ( M = In and Ga) showed markedly higher catalytic activity compared to P-25 for MB photocatalytic degradation under visible light irradiation. Complete removal of aqueous MB was observed after visible light irradiation for 160 min with the Ga2BiNbO7 as the photocatalyst and for 180 min with the In2BiNbO7 as the photocatalyst. The decrease of the total organic carbon ( TOC) and the formation of inorganic products, SO42- and NO3-, demonstrated the continuous mineralization of aqueous MB during the photocatalytic process.