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-C₃N₄ 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-C₃N₄ 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.