Hybrid Density Functional Theory Study of Native Defects and Nonmetal (C, N, S, and P) Doping in a Bi₂WO₆Photocatalyst

Abstract

Native defects and nonmetal doping have been shown to be an effective way to optimize the photocatalytic properties of Bi₂WO₆. However, a detailed understanding of defect physics in Bi₂WO₆ has been lacking. Here, using the Heyd-Scuseria-Ernzerhof hybrid functional defect calculations, we study the formation energies, electronic structures, and optical properties of native defects and nonmetal element (C, N, S, and P) doping into Bi₂WO₆. We find that the Bi vacancy (Bi_vac), O vacancy (O_vac), S doping on the O site (S_O), and N doping on the O site (N_O) defects in the Bi₂WO₆ can be stable depending on the Fermi level and chemical potentials. By contrast, the substitution of an O atom by a C or P atom (C_O, P_O) has high formation energy and is unlikely to form. The calculated electronic structures of the Bi_vac, O_vac, S_O, and N_O defects indicate that the band-gap reduction of O_vac ²⁺, Bi_vac ^3-, and S_O defects is mainly due to forming shallow impurity levels within the band gap. The calculated absorption coefficients of O_vac ²⁺, Bi_vac ^3-, and S_O show strong absorption in the visible light region, which is in good agreement with the experimental results. Hence, O_vac ²⁺, Bi_vac ^3-, and S_O defects can improve the adsorption capacity of Bi₂WO₆, which helps enhance its photocatalytic performance. Our results provide insights into how to enhance the photocatalytic activity of Bi₂WO₆ for energy and environmental applications through the rational design of defect-controlled synthesis conditions.