Covalent organic framework-based S-scheme photocatalysts: mechanistic insights and emerging applications in energy and environment

Photocatalysis represents a promising strategy to address pressing global energy and environmental challenges. Among emerging photocatalysts, covalent organic frameworks (COFs) have garnered significant attention owing to their broad visible-light absorption, tunable band structures, intrinsic porosity, efficient intramolecular charge separation, and rapid mass transport. However, the practical applications of COFs are often hindered by the rapid recombination of photogenerated charge carriers, which limits their overall photocatalytic efficiency. To mitigate these drawbacks, S-scheme heterojunctions based on COFs, constructed by coupling COFs with materials such as metal sulfides, metal oxides, carbon-based materials, metal-organic frameworks, other COFs, perovskites, and MXenes, have recently emerged as a powerful design strategy. These hybrid systems not only promote efficient charge carrier separation while preserving strong redox potentials but also exhibit remarkable performance across diverse photocatalytic applications, including environmental remediation, energy conversion, and energy storage. Despite the growing interest, comprehensive reviews focusing specifically on constructing S-scheme heterojunctions based on COFs remain scarce. This article aims to fill this gap by systematically summarizing the basic design principles, material construction strategies, photocatalytic performance, catalytic charge transfer mechanisms, and basic principles of S-scheme heterojunction strategies for COF-based photocatalyst materials. Furthermore, we discuss advanced characterization techniques used to investigate charge carrier separation and evaluate photocatalytic efficiency. Finally, contemporary challenges and prospective opportunities for the development of COF-derived S-scheme heterojunctions are outlined to guide further research in this promising field. • COF with tunable band structures is emerging as versatile visible-light photocatalysts. • Modification strategies such as ISIXPS confirm the S-scheme charge transfer mechanism. • Various applications of COF in photocatalytic H 2 production, CO 2 reduction and so on.