Homogeneous Polymerization of Self-standing Covalent Organic Framework Films with High Performance in Molecular Separation.

Covalent organic frameworks (COFs) are typically isolated as microcrystalline powders. It remains fundamentally challenging to fabricate COFs into high-quality self-standing films to take full advantage of their ordered pore channels for molecular separation. Here, we report a new strategy for fabricating self-standing imine-linked COF films via homogeneous polymerization where films emerge from clear solutions without forming amorphous precipitates. The abundant basic nitrogen atoms of the monomers acted as a reaction controller to realize the homogeneous polymerization and also promoted the tight self-aggregation of COF crystallites to form compact films via H-bonding. The chemically supported self-standing COF films on nylon membranes were also developed via an in situ growth method. The resulting films showed an unprecedentedly ultrafast permeance of 2822 L m-2 h-1 MPa-1 with a high rejection rate (99.8%) in the filtration of a congo red (CR) solution, demonstrating the advantage of this new strategy in fabricating high-quality self-standing COF films.