Polycrystalline covalent organic frameworks

Covalent organic frameworks (COFs) are a promising class of crystalline porous polymers formed by reticulating organic units into two-dimensional (2D) or three-dimensional (3D) networks via covalent bonds. COFs have gained significant interest because of their great potential applications in separation, sensing, catalysis, optoelectronics, biomedicine, etc. However, the development of COF materials has been mainly limited to polycrystalline powders, which result in poor processability and low mechanical strength that are unsuitable for nanofiltration membranes and optoelectronic devices. Thus, it is highly desirable to develop simple and effective synthetic approaches to afford high-quality COFs for various emerging applications. This review highlights the recent achievements on the synthesis of polycrystalline COFs from the perspective of energy input and provides outlooks on future directions for bridging the gap between fundamental research and industrial applications.