Tunable nitrogen vacancies on g-C3N4 for efficient photocatalytic CO2 reduction and H2 production.

Vacancy defects can enhance the surface activity of photocatalyst by providing additional reactive sites, facilitating the adsorption and transformation of reactants. Therefore, by tuning the type and concentration of vacancy defects, the performance of photocatalyst can be optimized, thereby increasing their application potential in environmental remediation and energy conversion. In this work, tunable nitrogen vacancies g-C3N4 photocatalysts were prepared and treated by sodium hypophosphite (NHPO) with reducibility. Systematic characterization confirmed that the N defect sites are primarily located at the 2-coordinated N on the aromatic rings, and all the NHPO-treated g-C3N4 possess greater abundance of N defects compared to the reference g-C3N4. This improvement endowed it with superior photogenerated carrier separation and migration efficiency, resulting in significantly enhanced photocatalytic reduction performance. Specifically, under simulating solar light irradiation for 4 h, the g-C3N4 treated with the optimal concentration of NHPO achieved CO2 reduction efficiencies of 36.55 μmol g-1 and 3.36 μmol g-1 for CO and CH4, respectively, which are more than quadrupling that of the reference g-C3N4. Additionally, it demonstrated remarkable catalytic efficiency in photocatalytic hydrogen evolution (5852 μmol g-1), achieving 3.3 folds than that of the reference g-C3N4, further supporting the universality of the enhanced photocatalytic performance of NHPO-treated g-C3N4. The possible photocatalytic mechanism is elucidated to clarify the photogenerated carrier transfer path in rich N vacancies g-C3N4. This finding provides valuable guidance for introducing tunable N vacancies on g-C3N4 through environmentally friendly chemical redox methods.