Interfacial synthesized covalent organic framework nanofiltration membranes for precisely ultrafast sieving

Covalent organic frameworks (COFs), a series of crystalline materials with ordered nanopores, are highly desirable for ultrafast and selective nanofiltration. However, COF-based membranes are typically synthesized via difficult synthetic procedures with long reaction time and show poor mechanical properties, which may hinder their widespread applications. Herein, a facile interfacial method is developed to synthesize COF membranes via the synergistic effect of interfacial diffusion and in-phase Brownian motion. Continuous free-standing COF films with a thickness of 111 nm are obtained within only 3 h under mild reaction conditions. Meanwhile, this synthesis method is suitable for the fabrication of COF membranes with a thin-film-composite (TFC) structure, enabling obtained COF membranes good mechanical properties under external forces and practical nanofiltration tests. Compared with other reported nanofiltration membranes, TFC-COFs exhibit state-of-the-art water permeance (173.94 L m2 h−1 bar−1) and superior rejections exceeding 98.50% to dyes larger than 1.3 nm. Precisely selective sieving of obtained TFC-COFs is systematically studied by separating diverse mixed dye solutions. Furthermore, monomers used in this method can be replaced, creating COF-based membranes with customizable functionality to enable a broad range of selective separations.