Three-dimensional covalent organic frameworks for advanced membrane separations

Three-dimensional covalent organic frameworks (3D COFs) have emerged as a promising class of crystalline materials due to large surface areas, interconnected porosity, and accessible active sites. Their structural versatility, enabled by the judicious selection of organic building blocks, allows for precise tuning of pore size, architecture, and functionality. These unique attributes position 3D COFs as ideal candidates for the development of tailored membrane materials capable of high-performance separations. This review provides a comprehensive overview of the synthesis methodologies and applications of 3D COF-based membranes. The critical role of their pore size, topology, stability, hydrophilicity/hydrophobicity and surface charge on membrane structure and performance is examined. In addition, various fabrication methods for 3D COF-based membranes (e.g., blending, in situ growth, and interfacial polymerization) are presented. The usage of 3D COF-based membranes in diverse fields such as gas separation, water treatment, organic solvent nanofiltration, pervaporation, and proton exchange is also outlined. The review concludes by identifying key challenges and outlining future research directions for advancing the field of 3D COF-based membranes.