Precise and ultra-wide molecular sieving capability with size-dependent COF layers for fast organic solvent nanofiltration

Four covalent organic framework (COF) layers with different alkyl side chains are used to create thin film composite (TFC) membranes via the improved unidirectional diffusion synthetic (UDS) technique. The synthesized membranes consist of polyacrylonitrile (PAN) substrates and TAPB-TPOCx COF (x = 1, 4, 6, and 8) layers, whose pore size and pore environment are tuned by direct integration of variable-length of TPOCx monomers. For organic solvent nanofiltration (OSN), we apply these COF membranes with variable thickness and pore size to test for the sieving ability of various organic pollutant surrogates. With the COF layers' bi-variable thickness and substituent length, the range cut-off molecular weight (330–970 g mol−1) for TAPB-TPOCx COF membranes involves the vast majority of OSN molecular sieving ranges. The COF membranes demonstrate precise molecular sieving capability with higher permeance of polar and nonpolar organic solvents than the state-of-the-art polymeric membranes.