Fabricating compact covalent organic framework membranes with superior performance in dye separation

Covalent organic frameworks (COFs) based membranes have exhibited great potentials in molecular separation due to their tunable porosity. Most of studies focused on developing approaches for fabricating the COF membranes. Herein, we investigated the effect of the chemical composition of COFs on the formation of COF membranes and the separation performance. We aimed to synthesize a high-performance and compact COF film by introducing H-bonding between COF crystallites. In this exploration, 2,5-dihydroxyterephthaldeyde (DHTP) with -OH groups and 2,5-dimethoxyterephthaldehyde (DMTP) with –OCH3 groups were selected to condense with 1,3,5-Tris (4-aminophenyl) benzene (TAPB) separately to construct supported COF films. The prepared COF-TBDH/nylon and COF-TBDM/nylon membranes were characterized, evaluated and compared to understand the effect of the functional groups (-OH and –OCH3) on the formation of COF films and the separation performance. The prepared COF-TBDH/nylon membrane with –OH groups in the COFs was compact and exhibited unprecedented performance with permeation flux of 4394 L m-2 h−1 MPa−1 and 100 % rejection in the filtration of Congo red solution, demonstrating the important role of the –OH groups. This work provides a significant concept and strategy to the preparation of high-performance COF membranes.