Unlocking sunlight driven photocatalysis: synthesis, diversity, and applications of COF-based S-scheme heterojunctions

Covalent organic frameworks (COFs) are highly porous and crystalline organic polymers with remarkable thermal and chemical stability. Their tunable structures and properties have enabled their applications in diverse fields. However, COFs suffer from significant drawbacks, including poor processability, strong self-stacking tendencies, limited electrical conductivity, restricted ion transport owing to pore blockage, and quick recombination of photogenerated electron–hole pairs. To address these limitations, construction of heterojunctions between COFs and other semiconductors has emerged as an effective approach. In particular, the S-scheme heterojunction design has recently attracted increasing interest owing to its ability to suppress charge carrier recombination while preserving strong redox capability, thereby enhancing photocatalytic efficiency. Despite these advantages, there is a scarcity of comprehensive reviews focusing on COF-based S-scheme heterojunctions. This review provides a detailed overview of the structural and functional properties of these materials in photocatalysis. It further discusses various synthesis strategies and charge-transfer mechanisms involved in constructing S-scheme heterojunctions by integrating COFs with different semiconductor materials. Additionally, recent advancements in COF-based S-scheme heterojunction photocatalysts are summarized, highlighting their various applications. Finally, the persistent challenges and potential future research directions in this domain are critically examined.