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

Graphitic carbon nitride g-CN 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-CN, 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-CN-based S-scheme systems remain sparse. Therefore, this review critically examines the charge transfer mechanisms in g-CN 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-CN-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, CO reduction, and HO synthesis. Collectively, this review offers a comprehensive analysis of g-CN-based S-scheme heterojunction photocatalysts and outlines key directions for advancing their development to meet future sustainability challenges.