Dual defect sites at g-C3N4 synergistically induce the electron localization effect for boosting photocatalytic H2O2 production†

Defect engineering (such as doping of non-metallic elements or vacancies) is a universally effective modification to improve the electronic structure and physical properties of g-C₃N₄, which has been widely applied in various photocatalytic systems. However, the key mechanism between the defect sites is not clear. In this work, elemental sulfur and N vacancies are sequentially introduced into g-C₃N₄ by two consecutive thermal calcination for photocatalytic green synthesis of H₂O₂. The experimental and characterization results reveal the important roles of the dual defect sites in the photocatalytic H₂O₂ reaction mechanism: sulfur doping can effectively broaden the visible-light response range of g-C₃N₄, and nitrogen vacancies can significantly enhance the adsorption of O₂ molecules. More importantly, dual defect sites induce the change of the charge distribution at g-C₃N₃, which results to the electron localization effect, enhancing the ability of the carriers to separate and transfer. After one hour of visible light irradiation, the H₂O₂ generation rate of the dual defect modified photocatalysts is as high as 1593.34 μmol g⁻¹, which is 14.31-fold higher compared to that of pristine g-C₃N₄. This work provides a viable strategy for understanding and rationalizing the design of photocatalysts with desirable defect structures.