A Novel Series of the New Visible-Light-Driven Photocatalysts MCo1/3Nb2/3O3 (M = Ca, Sr, and Ba) with Special Electronic Structures

A new series of ABO 3 -type perovskite photocatalysts MCo 1/3 Nb 2/3 O 3 (M = Ca, Sr, and Ba) were synthesized by a solid-state reaction method, in which the B site is occupied by Co 2+ and Nb 5+ randomly in a charge-balanced manner. They were characterized by powder X-ray diffraction, UV−vis diffuse reflectance spectroscopy and photocatalytic activity measurements with Pt and NiO x cocatalyst under visible-light irradiation (λ > 420 nm), respectively. It is determined from the reflectance spectra that the optical transitions for these compounds, corresponding to visible-light absorption, are directly forbidden, and the band structures are suggested to be composed of the Co 2+ 3d states and the Nb 5+ 4d states. The feature of the electronic structure for BaCo 1/3 Nb 2/3 O 3 calculated by the full potential-linearized augmented plane wave (F-LAPW) method shows that the O 2p states are strongly hybridized with the Co 2+ 3d states, and little hybridized with the Nb 5+ 4d states. The difference in their photocatalytic activity is ascribed to their special crystal and electronic structures.