Microporous organic polymer-based membranes for ultrafast molecular separations

Polyamide membranes dominate the membrane industry; yet in their use they have a fundamental challenge to break through the upper bound due to an uncontrollable, excessive crosslinking degree. A novel trend is the development of microporous polymeric membranes with rigidly intrinsic pores for rapid and precise molecular separation. Advanced microporous organic polymers (MOPs), divided into crystalline (e.g., COFs) and amorphous (e.g., PIMs, PAFs, CMPs, POCs, HCPs, etc.) catalogues, have proven promising in the development of molecular sieving membranes. Different from traditional polymers with dynamic microporosity, MOPs have sturdy and well-defined pore architectures due to a significant reduction of segmental chain motion, enabled by molecular-level design of the void-forming elements. MOPs have swiftly evolved as a promising alternative to conventional materials due to their intriguing inherent attributes, including robust organic backbone, persistent porosity, and high surface area. This review commences with the introduction of the MOP categories and elucidates their critical characteristics and advantages for membrane fabrication. In addition, recent breakthroughs on ultrahigh permeability MOP-based membranes based on molecular-level design approaches are highlighted, aiming at an in-depth understanding of the structure-function correlation of MOP membranes. Furthermore, a summary of applying MOP membranes for rapid molecular separations such as gas separation, water treatment, separation in a solvent phase, pervaporation, and fuel cells is outlined. Finally, a concise conclusion, current limitations as well as future opportunities and directions on the developments and applications of MOP membranes are presented. (C) 2020 Elsevier B.V. All rights reserved.