Band structure and photocatalytic activities for H₂ production of ABi₂Nb₂O₉ (A = Ca, Sr, Ba)

A new series of layered perovskite photocatalysts, ABi₂Nb₂O₉ (A = Ca, Sr, Ba), were synthesized by the conventional solid-state reaction method and characterized by X-ray diffraction (XRD) and UV-visible spectrometer. The results showed that the structure of ABi₂Nb₂O₉ (A = Ca, Sr) is orthorhombic, while that of BaBi₂Nb₂O₉ is tetragonal. The band gaps of CaBi₂Nb₂O₉, SrBi₂Nb₂O₉, and BaBi₂Nb₂O₉ were estimated to be 3.46, 3.43, and 3.30 eV, respectively. It was found from the electronic band structure study, using the density functional theory (DFT) with planewave basis, that the conduction bands of these photocatalysts mainly consist of Nb 4d + Bi 6p + O 2p orbitals and the valence bands are composed of hybridization with O 2p + Nb 4d + Bi 6s orbitals. The photocatalytic activities for water splitting were investigated under UV-light irradiation and indicated that these photocatalysts showed photocatalytic activity for H₂ and O₂ evolution from aqueous solutions containing sacrificial reagents (methanol and Ag⁺).