Covalent organic frameworks: Design, synthesis, and performance for photocatalytic applications

To resolve the issues of environmental pollution and seek for sustainable clean fuels, many photocatalytic systems based on metal compounds and amorphous polymers have been studied over the past few years. However, applications of these photocatalytic systems were limited due to intrinsic drawbacks of the structures, which make the exploitation of new class of materials necessary. Recently, covalent organic frameworks (COFs) comprised of light elements, have attracted tremendous attention due to their excellent physiochemical properties. Specially, high crystallinity, good stability, intrinsic porosity and unique covalent linkages make COFs suitable for the application under harsh photocatalytic conditions. Predesigned structure of COFs provides a good platform for constructing diverse photocatalytic systems. Up to now, though the research on COFs and COFs-based photocatalysts is still in its infancy, great progress has been made especially in the H2 or O2 evolution, CO2 reduction, photocatalytic organic transformations, and elimination of organic pollutants. In this review, we focus on the developments in COFs-based photocatalytic materials and analyze the relationship between the predesigned COFs structures and their photocatalytic properties. Moreover, we elaborate the strategies for enhancing catalytic activities of COFs-based photocatalysts. Finally, the perspectives on new opportunities and challenges in the field are discussed.