Rotaxane Mediated Covalent Organic Framework Membranes for Efficient Desalination

Covalent organic framework (COF) membranes with adjustable and periodic channels show great potential in desalination. However, low crystallinity and inherent large pore size of COF membranes seriously hinder effective interception for salt. Herein, a rotaxane-mediated interfacial polymerization (RMIP) strategy is proposed via incorporating pseudorotaxane linkers (macrocyclic molecule and diamine host-guest complexes) into the reaction, obtaining rotaxane-based COF (RCOF) membranes with high crystallinity and sub-nanochannels. The pseudorotaxanes slow down the diffusion of diamines in the liquid phase, which regulates the Schiff base reaction rate at the oil-water interface and balances polymerization-crystallization process, facilitating crystalline, tight, and defect-free COF membrane formation. Moreover, formed rotaxanes increase interlayer steric hindrance and induce RCOF subunits with ABC stacking, narrowing pore size of membranes. During pervaporation, the optimal RCOF membrane shows permeation flux of 180.2 kg m-2 h-1 and outstanding NaCl rejection of 99.9%. Meanwhile, it exhibits stable desalination and antifouling ability in long-term operation. This study provides a new method for accurate construction of COF membranes and is of great significance for efficient separation.