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.