Surfactant-assisted interfacial polymerization towards high-crystallinity COF membranes for organic solvent nanofiltration

Preparing high-crystallinity covalent organic framework (COF) membranes by interfacial polymerization remains a grand challenge. Herein, a monomer pre-assembly process is proposed to prepare high-crystallinity COF membranes by surfactant-assisted interfacial polymerization (SAIP) strategy. The self-assembled chains of amphiphilic surfactants across interface can gather and pre-assemble monomers and improve their interphase transport for complete topological growth. Apart from the reduction in polymerization time from over 72 h–48 h, the crystallinity and pore uniformity of COF membranes are highly enhanced. This strategy is universal and four kinds of amine monomers are utilized to tune COF pore size. The 1.8 nm-sized COF membrane shows highly enhanced rejection from 65.5% to 95.7% for reactive black with a size of 2.0 nm, when compared to that without surfactants. Importantly, the orderly stacked pores permit fast molecule transport with a 76% increase in acetonitrile permeance (366.9 L m−2 h−1 bar−1). Meanwhile, the robust crystal properties endow this COF membrane with excellent solvent resistance, compressive strength, and hence operational stability for over 100 h. The amphiphilic molecule-assisted interface engineering may represent a technology for scalable fabrication of high-crystallinity framework materials for molecule separation.