Vacancy-modified g-C3N4 and its photocatalytic applications

As an emerging semiconductor-based catalyst, g-C3N4 has attracted significant attention for visible light-driven photocatalytic energy conversion, synthesis of chemicals, and environmental remediation. However, pristine g-C3N4 exhibits a weak response to visible light, low surface area, and rapid photogenerated carrier recombination. Thus, the introduction of structural vacancies can deeply modify the morphology and band structure of g-C3N4 to overcome these issues. This work provides a critical overview and perspective on the recent development of g-C3N4 photocatalysts modified by carbon (Cv) and nitrogen vacancies (Nv), or both, and their implementation in various photocatalytic applications. Initially, the methods for the identification of Cv and Nv in g-C3N4 and their critical role in altering the morphological and structural properties of g-C3N4 are presented. Then, the strategies for manipulating the microstructure and properties of g-C3N4 are critically discussed, including modification with Nv, Cv, and functional groups or their combination, porous architecture engineering, heteroatom doping, texture and surface area mediation, and their combinations. Based on vacancy modification and other positive structural tuning aspects, the corresponding photocatalytic performance of g-C3N4 is analyzed for the applications currently attracting significant research attention, including water splitting, CO2 reduction, N2 fixation, NO removal, pollutant degradation, selective oxidation, and H2O2 production. Finally, the current challenges and future research suggestions regarding the vacancy modification of g-C3N4 are presented.