Photocatalytic performance of graphitic carbon nitride (g-C 3 N 4 ): tuning factors, mechanisms, challenges, and opportunities

Abstract Graphitic carbon nitride (g-C3N4) has emerged as the most significant metal-free photocatalyst owing to its suitable band gap, chemical stability, and low-cost synthesis. However, its practical photocatalytic performance is limited by rapid charge recombination, low surface area, and insufficient visible-light absorption. This review provides a comprehensive and critical analysis of the key factors governing the photocatalytic activity of g-C 3 N 4 and the strategies employed to tune its performance. Fundamental properties like electronic structure and photocatalytic mechanisms are first discussed to establish a theoretical foundation. Subsequently, various tuning approaches like morphology control, heteroatom doping, heterojunction engineering, defect creation, co-catalyst loading, and synthesis optimization are systematically analyzed with mechanistic insights. A comparative evaluation highlights the advantages and limitations of each strategy. The review further explores major applications in environmental remediation, hydrogen evolution, CO 2 reduction, and pollutant degradation. Finally, critical challenges like scalability, stability, and mechanistic ambiguity are addressed followed by future research directions. This work aims to provide a clear roadmap for the rational design of high-performance g-C3N4–based photocatalysts.