Photophysical and photocatalytic properties of Ag₂M ₂O₇ (M=Mo, W)

Ag-based oxides, Ag₂M₂O₇ (M=Mo, W) with a triclinic structure, were prepared using a conventional solid-state reaction method, and their band structures and photocatalytic properties were investigated. From the electronic band structure calculations, Ag ₂Mo₂O₇ had an indirect band gap of 2.65 eV, whereas Ag₂W₂O₇ had a direct band gap of 3.18 eV. Moreover, the calculated electron affinities were 4.75 eV for Ag ₂Mo₂O₇ and 4.62 eV for Ag₂W ₂O₇. The smaller band gap and higher electron affinity of Ag₂Mo₂O₇ than those of Ag₂W ₂O₇ originated from the contribution of the unoccupied Mo 4d orbital to the conduction band, which was positioned at a lower energy level than the W 5d orbital. The effects of the different band structure characteristics in Ag₂M₂O₇ (M=Mo, W) on the photocatalytic activity were investigated by the degradation of a Rhodamine B dye solution under visible light irradiation. The results showed that the photocatalytic activity of Ag₂Mo₂O₇ was much higher than that of Ag₂W₂O₇ and comparable with a well-known WO₃ powder. The higher photocatalytic property of Ag₂Mo₂O₇ was attributed to its higher optical absorption ability and lower charge recombination rate.