Electronic structure and photocatalytic properties of ABi ₂Ta₂O₉ (A = Ca, Sr, Ba)

A new series of layered perovskite photocatalysts, ABi₂Ta ₂O₉ (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 ABi ₂Ta₂O₉ (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 SrBi₂Ta ₂O₉, which is much higher than that of CaBi ₂Ta₂O₉ and BaBi₂Ta₂O ₉, The photocatalytic properties are discussed in close connection with the crystal structure and the electronic structure in details.