Advances in photoactive g-C3N5 derived Z-and S-scheme heterojunctions for energy and environmental catalysis

Graphitic carbon nitride derivatives have received wide attention as sustainable, metal-free photoactive catalyst. Among other derivatives, N-rich-g-C 3 N 4 i.e. g-C 3 N 5 has newly emerged as a next-generation catalytic semiconductor with improved electronic and structural characteristics than g-C 3 N 4 . The higher N-content as well as exclusive motifs like: triazole, triazine, and heptazine units, give g-C 3 N 5 with a lower bandgap, extended π-conjugation, boosted charge transfer, and stronger absorption of visible-light. Numerous N-rich precursors and synthesis methods allow the formation of frameworks containing triazole linkages, triazine combinations, and azo bridges, providing flexible routes for the modifying its structure. A thorough discussion on fabrication and characterization is highlighted, focussing on their influence on optical and electronic efficacy. Special emphasis is given to Z- and S-scheme heterojunctions, which create internal electric fields and promising band bending, thereby helping directional charge migration while conserving high oxidation and reduction potential. These heterostructures enhance visible-light utilization and catalytic stability in both energy and environmental applications. Furthermore, functionalization, porosity engineering, and defect regulation have extended the reactivity of g-C 3 N 5 , representing its versatility in complex catalytic systems. This review highlights the fundamental properties, structural engineering approaches, and emerging applications of g-C 3 N 5 , while also addressing the challenges that remain for advancing its role in sustainable photocatalysis. • g-C 3 N 5 outperforms g-C 3 N 4 with higher N-content and improved properties. • Exclusive triazole, triazine, and heptazine units’ changes bandgap and absorption. • Various synthesis routes allow structure alteration and defects regulation. • g-C 3 N 5 -based Z/S-scheme heterojunctions improve charge transfer and stability. • Mechanistic insights into energy and environmental applications are widely discussed.