A review on 2D porous organic polymers for membrane-based separations: Processing and engineering of transport channels

The expansion of separation demands at molecular and ionic levels has triggered extensive research to explore new materials as promising practical membranes for separations. Owing to their dimension-related properties of two-dimensional (2D) porous organic polymers (POPs), promising research on the construction of 2D POPs into membranes has emerged and progressed rapidly, offering membranes with highly tunable pores/channels, robust frameworks/networks, intrinsic flexibility, and light weight for multiple separation purposes. In this review, up-to-date strategies for processing of 2D POPs into diverse continuous membranes and engineering of their nanochannels are highlighted. The 2D POPs materials discussed include the examples of 2D covalent organic frameworks (COFs), 2D covalent triazine frameworks (CTFs) and 2D conjugated microporous polymers (CMPs). Case studies on these materials for potential membrane applications including gas separation, water treatment, organic solvent nanofiltration (OSN), pervaporation are summarized. Finally, the critical challenges and futuristic upgrades of research directions and opportunities of 2D POPs based advanced membranes are outlined.