First-Principles Characterization of Bi-based Photocatalysts: Bi12TiO20, Bi2Ti2O7, and Bi4Ti3O12

The geometric, electronic, and optical properties of three Bi-based structures (Bi12TiO20, Bi2Ti2O7, and Bi4Ti3O12) with and without C and N doping as possible photocatalytic material were investigated systemically by means of the first-principles DFT calculations within the GGA scheme to explore the origin of different band gaps and high photocatalytic activity under visible light observed in experiment. Our calculated results illuminate that BTO structures show an indirect band gap characteristic and the actual band gaps of BTO structures should be wider than 3.0 eV except for Bi4Ti3O12. C and N elements can be very easily introduced into the BTO lattices during the sample preparation process according to the very small defect formation energies, and the unintentional C or N doping may be responseble for the observed different band gaps and the high photocatalytic activity under visible light. Accordingly, it can be predicted that nonmetal element doping of BTO structures may improve photocatalytic activity under visible light and can be an excellent candidate for TiO2.