Modulated Interfacial Confinement for Fabrication of Covalent Organic Framework Membranes

ABSTRACT Fabricating crystalline polymer membranes through interfacial polymerization is much more complicated than that for amorphous polymer membranes, which stimulates the thinking about the correlation of interfacial confinement and membrane structure. Herein, we present an interfacial confinement engineering strategy to fabricate covalent organic framework (COF) membranes for organic solvent nanofiltration. By incorporating ionic surfactants with moderate concentration at the oil‐water interface, the generated electric double layer drives the oriented aggregation of amine monomers, as verified by sum frequency generation vibrational spectroscopy. While the thickness of the interfacial zone regulates the reversibility of the reaction, as obtained through molecular dynamics simulations. The moderate interfacial confinement degree affords suitable space for reversible polymerization and crystal growth, leading to highly crystalline and defect‐free COF membranes. The optimal COF membrane exhibits superior separation performance: methanol permeance of 240 L m − 2 h − 1 bar − 1 and Evans blue rejection rate of 99%, surpassing polyamide membranes by an order of magnitude. It also efficiently separates the high‐valued pharmaceutical molecule cannabidiol. This work elucidates the mechanism of modulated interfacial confinement by correlating the interface structure with the fabrication of crystalline polymer membranes.