3D Covalent Organic Network Membranes With Regionally Ordered Nanochannels for Efficient Molecular Sieving

Polymeric composite membranes hold significant promise for molecular sieving in organic solvents, yet struggle with the precise fractionation of small molecules, a critical need in the chemical and pharmaceutical industries. Here an innovative covalent organic network (CON) membrane featuring 3D interpenetrated ultra-microporous channels for effective fractionation of small-molecule solutes is presented. Rational utilization of unique tetrahedral amine (TAM) as aqueous-phase building blocks to crosslink with acyl chlorides yields CON polyamide thin films with finely tuned ordered porosity. Importantly, three-node acyl chloride (TMC) with high reactivity facilitates sharpening the membrane pore size distribution due to the partially ordered and elevated crosslinked structure. Molecular dynamics simulations reveal that these TAM-TMC membranes possess a high fractional free volume, contributing to superior permeability-selectivity performance. Further post-activation with polar solvents effectively modulates the inherent pore polarity and width, resulting in an exceptional methanol permeability of 7.5 L m^-2 h^-1 bar^-1 and a molecular weight cut-off of 248 Da. This ultrafine 3D hierarchical pore architecture enables excellent fractionation of dye mixtures with similar molecular weights and efficient antibiotic concentration. This work rationalizes the design of chemically stable covalent organic network membranes with 3D partially ordered sub-microporosity, extending their application to precision molecular separations.