Recent advances in g-C₃N₅-based S-scheme heterojunction photocatalysts: From design to application

Graphitic carbon nitride g-C₃N₅ is a subject of significant research interest as an advanced photocatalyst, largely attributed to its distinctive electronic structure and nitrogen-rich, extended π-conjugated framework. Compared to traditional g-C₃N₄, it offers a narrower bandgap, enhanced charge carrier mobility, and stronger redox potential, making it highly suitable for solar-driven applications such as green energy production, effluent remediation and synthesis of commercially viable chemicals. However, its performance is limited by rapid e^-/h⁺ pair recombination. To overcome this, the construction of S-scheme heterojunctions has emerged as a promising strategy, as it enables efficient charge separation while retaining strong redox capabilities and advantages that conventional Type-I and Type-II heterojunctions lack. The built-in electric field and band bending are inherent to S-scheme heterojunctions, that further enhances charge migration and utilization of absorbed solar energy. Despite these benefits, detailed studies on g-C₃N₅-based S-scheme systems remain sparse. Therefore, this review critically examines the charge transfer mechanisms in g-C₃N₅ S-scheme systems and highlights their enhanced performance relative to conventional heterostructures. Furthermore, the review provides an in-depth discussion on various synthesis strategies via dimensional assembled S-scheme for g-C₃N₅-based heterojunctions and evaluates advanced characterization techniques used to probe charge migration behavior. Finally, the study explores the photocatalytic mechanisms of these heterojunctions for green hydrogen evolution, pollutant degradation, CO₂ reduction, and H₂O₂ synthesis. Collectively, this review offers a comprehensive analysis of g-C₃N₅-based S-scheme heterojunction photocatalysts and outlines key directions for advancing their development to meet future sustainability challenges.