Hybrid Density Functional Theory Study of Native Defects and Nonmetal (C, N, S, and P) Doping in a Bi2WO6 Photocatalyst

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, 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.