Unraveling the dual defect sites in graphite carbon nitride for ultra-high photocatalytic H2O2 evolution

Defect engineering modified graphite carbon nitride (g-C3N4) has been widely used in various photocatalytic systems due to the enhanced catalytic activity of multiple defect sites (such as vacancies or functional groups). However, the key mechanism of action in each defect site in the corresponding photocatalytic surface reactions is still unclear. Here, the -C N groups and N vacancies were sequentially introduced into g-C3N4 (Nv-C N-CN) for photocatalytic production of high-value and multifunctional H2O2, and the effect of dual defect sites on the overall photocatalytic conversion process was systematically analyzed. The modification of the dual defect sites forms an electron-rich structure and leads to a more localized charge density distribution, which not only enhances the light absorption and carrier separation capabilities, but also significantly improves the selectivity and activity of H2O2 generation. Importantly, detailed experimental characterizations and theoretical calculations clearly revealed the key role of each defect site in the photocataLytic H2O2 surface reaction mechanism: the N vacancies can effectively adsorb and activate O-2, and the -C N groups facilitate the adsorption of H+, which synergistically promote H2O2 generation. The Nv-C N-CN reached a H2O2 generation rate of 3093 mu moL g(-1)h(-1) and achieved an apparent quantum efficiency of 36.2% at 400 nm, significantly surpassing the previously reported g-C3N4-based photocatalysts. Meanwhile, a solar-to-chemical conversion efficiency of 0.23% was achieved in pure water. Constructing defects and understanding their crucial role provides significant insights into the rational use of defect engineering to design and synthesize highly active catalytic materials for energy conversion and environmental remediation.