Site-selective formation of nitrogen vacancy in g-C3N4 for enhanced photocatalytic performance

Vacancy engineering in photocatalysts is a common strategy to enhance performance, but stochastic vacancy formation typically introduces multiple defect types with conflicting effects. Here, we selectively introduce N 2C –coordinated vacancies in g-C 3 N 4 via a two-step polymerization route and explore their role in enhancing photocatalytic behavior. Structural characterization shows that N 2C vacancies were selectively created and the crystallinity of g-C 3 N 4 was also significantly improved via this approach. The resulting catalyst degrades 95% of tetracycline in 80 min under visible light irradiation and achieves an apparent rate constant of 0.0382 min −1 , which is 6.6 times that of catalyst with randomly generated vacancies (0.0058 min −1 ). Combined experimental analyses and DFT calculations indicate that N 2C vacancies introduce shallow defect states that act as electron traps to promote charge separation, whereas N 3C vacancies create deep states that serve as nonradiative recombination centers. Site-selective vacancy formation thus decouples the roles of individual defect types and provides guidance for the rational design of high-performance photocatalysts. • Site-selective formation of N vacancies is successfully realized. • N 2C vacancies facilitate the formation of shallow defect states. • N 2C vacancies enriched g-C 3 N 4 exhibits excellent photocatalytic activity. • A controllable route of surface modification in designing photocatalysts.