Electronic structure and photocatalytic properties of ABi2Ta2O9 (A=Ca, Sr, Ba)

A new series of layered perovskite photocatalysts, ABi2Ta2O9 (A=Ca, Sr, Ba), were synthesized by the conventional solid-state reaction method and the crystal structures were characterized by powder X-ray diffraction. The results showed that the structure of ABi2Ta2O9 (A=Ca, Sr) is orthorhombic, while that of BaBi2Ta2O9 is tetragonal. First-principles calculations of the electronic band structures and density of states (DOS) revealed that the conduction bands of these photocatalysts are mainly attributable to the Ta 5d+Bi 6p+O 2p orbitals, while their valence bands are composed of hybridization with O 2p+Ta 5d+Bi 6s orbitals. Photocatalytic activities for water splitting were investigated under UV light irradiation and indicated that these photocatalysts are highly active even without co-catalysts. The formation rate of H2 evolution from an aqueous methanol solution is about 2.26 mmol h-1 for the photocatalyst SrBi2Ta2O9, which is much higher than that of CaBi2Ta2O9 and BaBi2Ta2O9. The photocatalytic properties are discussed in close connection with the crystal structure and the electronic structure in details. - Graphical abstract: The valence band of the photocatalysts is consisted of O 2p, Ta 5d and Bi 6s orbitals and the conduction band is from Bi 6p, Ta 5d and O 2p orbitals. Photocatalytic properties of the photocatalyst for H2 evolution without using other co-catalysts from CH3OH/H2O solution and O2 evolution from AgNO3/H2O solution were observed under Hg lamp irradiation