Ultrathin heterostructured covalent organic framework membranes with interfacial molecular sieving capacity for fast water-selective permeation

Abstract

Covalent organic frameworks (COFs) with designable architectures and superior stability have afforded intriguing opportunities to develop advanced separation membranes. Currently, COF membranes are rarely used in molecular separations due to their relatively large pore sizes. Herein, we report a vapor–liquid interfacial synthesis approach to in situ generate an azine-linked COF layer onto a pre-assembled carboxyl-functionalized COF layer at room temperature, acquiring an ultrathin heterostructured COF membrane with narrowly distributed interfacial sub-nanopores. Attributed to the covalent linkages between the two COF layers, the narrowly distributed interfacial sub-nanopores of ∼0.39 nm within the heterostructured COF membranes were formed, which endow the membranes with distinct interfacial molecular sieving capacity. The resulting COF membrane with a thickness of 28 nm exhibits a superior separation factor of 4464 and a high permeation flux of 14.35 kg m⁻² h⁻¹ for water/n-butanol separations. The design of ultrathin heterostructured COF membranes with interfacial molecular sieving capacity may facilitate the development of framework nanomaterial based membranes.