Electronic structures of efficient MBiO₃ (M = Li, Na, K, Ag) photocatalyst

In order to deepen the understanding of the relationship between fundamental properties (including: microstructure and composition) and photocatalytic performance, four bismuthate compounds, including: LiBiO₃, NaBiO₃, KBiO₃, and AgBiO₃, are regarded as research examples in the present work, because they have particular crystal structures and similar compositions. Using density functional theory calculations, their structural, electronic, and optical properties are investigated and compared systematically. First of all, the calculated results of crystal structures and optical properties are in agreement with available published experimental data. Based on the calculated results, it is found that the tunneled or layered micro-structural properties lead to the stronger interaction between bismuth and oxygen, and the weaker interaction between alkaline-earth metal and [BiO₆] octahedron, resulting in the feature of multi-band gaps in the cases of LiBiO₃, NaBiO₃, and KBiO₃. This conclusion is supported by the case of AgBiO₃, in which the feature of multi-band gaps disappears, due to the stronger interaction between the noble metal and [BiO₆] octahedron. These properties have significant advantages in the photocatalytic performance: absorbing low energy photons, rapidly transferring energy carriers. Furthermore, the features of electronic structures of bismuthate compounds are well reflected by the absorption spectra, which could be confirmed by experimental measurements in practice. Combined with the calculated results, it could be considered that the crystal structures and compositions of the photocatalyst determine the electronic structures and optical properties, and subsequently determine the corresponding photocatalytic performance. Thus, a novel Bi-based photocatalyst driven by visible-light could be designed by utilizing specific compositions to form favorable electronic structures or specific micro-structures to form a beneficial channel for energy carriers. (paper)