Solvent-induced interfacial polymerization enables highly crystalline covalent organic framework membranes

Covalent organic frameworks (COFs) are porous crystalline polymers with uniform pore channels and excellent stability, holding great promise in the field of membrane. The liquid-liquid interfacial polymerization is designed as an effective and convenient approach to preparing COF membranes, but the crystallinity of membranes synthesized by this method tends to be poor and thus superiorities of COF crystalline channels can hardly be utilized. In this work, a solvent-induced interfacial polymerization strategy was proposed to prepare COF membranes with high crystallinity. Due to the interaction between the acetonitrile solvent inducer and COF network, the reaction and self-assembly in film formation process were effectively manipulated. The optimized COF membrane exhibited much higher crystallinity and porosity, whose surface area was about an order of magnitude higher than the membrane prepared in the traditional system. The highly crystalline COF membrane showed significantly improved separation performance in desalination. This work provides a powerful strategy to prepare COF membranes with high crystallinity. ∙ A solvent-induced interfacial polymerization strategy was designed to prepare COF membranes with high crystallinity. ∙The interaction between COF networks and solvent was regulated by acetonitrile to promote crystallization. ∙Well-defined channels of COF membranes promised rapid molecular transport and high selectivity. ∙The outstanding salt rejection performance was a breakthrough for COF membranes with large apertures.