Progress of Covalent Organic Framework Photocatalysts: From Crystallinity–Stability Dilemma to Photocatalytic Performance Improvement

Covalent organic frameworks (COFs) are a category of organic crystalline porous materials, which have been identified as an appealing and promising photocatalyst owing to attractive characteristics such as molecular structure designability, extended π-conjugation, rich porosity, and high surface area. In the past decade, research on COFs has been blossoming and currently represents one of the most prospective forefronts in heterogeneous photocatalysis. This review summarizes the latest advances in the synthesis, characterization, and properties of COF-based photocatalysts, with emphasis on the state-of-the-art strategies to tackle the crystallinity–stability dichotomy of COFs, in particular, by means of the conversion of the linkages and the control of the interlayer interactions. In addition, an arsenal of approaches for enhancing the photocatalytic performance of COFs are discussed in detail, such as boosting exciton dissociation, improving crystallinity, regulating molecular structure, doping, loading cocatalyst, coupling sensitizer, constructing heterojunction, and modulating morphology. Finally, this review concludes with opportunities, challenges, and perspectives for the further cutting-edge development of COF-based photocatalysts.