COF-Based S-Scheme Heterojunction Photocatalyst

Semiconductor photocatalysis presents a promising route to convert solar energy into storable fuels and tackle global energy and environmental challenges. However, its efficiency is often hindered by rapid electron-hole recombination. Covalent organic frameworks (COFs)-a class of crystalline, porous organic polymers-offer exceptional potential for photocatalysis owing to their precisely tunable structures and distinctive physicochemical properties, yet their performance remains limited by intrinsic charge recombination. To overcome this limitation, the construction of S-scheme heterojunctions has been proposed as a promising strategy to enhance charge separation while maintaining strong redox capabilities. This review begins by presenting a comprehensive perspective on the development and scientific significance of S-scheme heterojunctions. It then systematically summarizes the design principles and synthetic strategies of COFs, followed by an in-depth discussion of the fabrication methods and principles of COF-based S-scheme heterojunctions. Furthermore, advanced characterization techniques that enable precise elucidation of charge migration pathways within these heterostructures are highlighted. The review also provides a comprehensive overview of recent applications of COF-based S-scheme photocatalysts, including hydrogen evolution, carbon dioxide reduction, environmental remediation, hydrogen peroxide production, and others. Finally, current challenges and future perspectives are discussed to inspire continued innovation in the development of high-performance S-scheme photocatalytic systems.