Composition engineering in covalent organic frameworks for tailored photocatalysis

The harmful effects of the energy crisis and environmental degradation are becoming increasingly severe, which urgently demands the advancement of eco-friendly and sustainable production techniques. Direct conversion of abundant solar energy into chemical energy represents a promising green and efficient technological solution. In this process, photocatalysts play a pivotal role. Covalent organic frameworks (COFs), a class of porous materials interconnected by covalent bonds, exhibit exceptional potential for photocatalysis due to their high surface area, excellent crystallinity, and tunable structures. This review discusses the roles of compositional regulation in enhancing the photocatalytic performance of COFs, including modulating light absorption, increasing active sites, promoting exciton dissociation, and improving carrier separation. Furthermore, computational and mechanistic characterization methods are also discussed. More importantly, the key strategies in compositional regulation, such as heteroatom engineering, metal single-atom engineering, ion engineering, functional group engineering, Donor-Acceptor (D-A) molecular engineering, side chain engineering, multi-component engineering, isomerism engineering, conjugate bridge engineering, single-molecule junction engineering, and interlayer engineering, are carefully summarized. Moreover, their diversified modification strategies and applications in photocatalytic hydrogen (H₂) evolution, hydrogen peroxide (H₂O₂) production, and carbon dioxide (CO₂) reduction are also addressed. Finally, the current challenges and future opportunities for COF-based photocatalysis are outlined.