Covalent Organic Frameworks

Covalent organic frameworks (COFs) are crystalline porous polymers featuring extended structures and ordered pores. They are constructed from molecular building units via covalent bonds. The diversity of building blocks with different geometric symmetry offers positional controllability and immense possibilities for the design of two- or three-dimensional COFs. By virtue of their periodically arranged porous structures, well-aligned channels, and easy-modified skeletons, COFs have shown great promise for diverse applications, such as catalysis, electrochemical energy storage and conversion, gas storage and separation, sensors, and biomedicine. Besides, the predesigned skeletons with tailored functionalities allow for the study of mechanisms and structure–function relationships. In this chapter, we describe the design concepts, the synthetic strategies of COF powders and nanosheets, characterization methods, as well as the applications of COFs. Finally, we outline key challenges and future directions of COFs.