First-principles study of S-doped point defects with different charge states in monolayer g-C3N4

Abstract

Non-metal-doped graphitic carbonitride (g-C3N4) can improve the redox capacity and photocatalytic activity, as a photocatalyst for the degradation of organic pollutants. In the present study, the theoretical defect models of S-doping with different doping sites and valence states were built in g-C3N4. The stability of charged defects was systematically investigated by the first-principles calculations based on the density functional theory. The effects of S-doping on the electronic structures and optical properties of g-C3N4 were revealed. According to the results, the g-C3N4 doped with positive divalent S is the most favorable defect form in energy. A new electron transfer pathway between adjacent heptazine rings on S-doped g-C3N4 was proposed. It is found that the special electronic states and the enhanced local charge density of S-doped g-C3N4 could effectively optimize the electron transport dynamic, leading to the increased reduction ability of photo-generated holes. As a result, the S-doped g-C3N4 shows better ability to separate photo-generated electron/hole pairs and improve photocatalytic efficiency with respect to the pristine g-C3N4.