The growing demand for sustainable energy and environmental remediation has intensified the search for efficient, metal-free catalysts. Among these, graphitic carbon nitride (g-C₃N₅) has garnered significant attention due to its nitrogen-rich structure, extended π-conjugation, and tunable bandgap. Its abundant raw materials, non-toxic nature, and exceptional physicochemical properties make it a promising candidate for energy and environmental applications. This review comprehensively analyzes advancements in g-C₃N₅-based photocatalysts for energy and environmental applications. The g-C₃N₅ structures, highlighting their physicochemical characteristics and bandgap variations, and a detailed overview of synthesis methods are presented. Furthermore, we explore advanced engineering strategies such as doping, defect engineering, heterojunction formation, and co-doping to enhance catalytic efficiency. The applications of g-C₃N₅ in water treatment, H2 production, nitrogen fixation, CO₂ reduction, and H₂O₂ synthesis are examined, addressing key challenges like stability, efficiency, and recyclability. Unlike previous reviews, this study offers a unified and holistic overview encompassing all energy and environmental applications of g-C₃N₅, while also identifying critical bottlenecks and future research opportunities for practical implementation. The strengths, limitations, and outlook of g-C₃N₅-based systems are systematically discussed, with emphasis on innovative strategies to overcome current barriers and accelerate real-world deployment.
