Fluorinated Covalent Organic Framework Antifouling Nanofiltration Membranes Through Defect Engineering

Covalent organic framework (COF) membrane holds great promise in water treat-ment. Improving the antifouling property of COF membrane is critical for practical application while rare investigations have been reported. Grafting fluorinated chains on the COF membrane surface is expected an effective strategy but quite challenging due to the lack of grafting sites. In this work, the defect engineering strategy is adopted to generate free amino groups as grafting sites through the Schiff-base reaction between amine monomer and mixed aldehyde monomers, then perfluoroalkyl chains are grafted on the COF membrane surface through the reaction between the free amino groups and the perfluorooctanoyl chloride. The content of perfluoroalkyl chains can be regulated and optimized by controlling the amount of free amino groups. The fluorinated COF membrane shows superior antifouling performance with a significantly increased flux recovery ratio and reduced flux decline ratio against oil/water emulsions and humic acid (FRR ≈ 98%, DRt = 10%). Furthermore, the fluorinated COF membrane exhibits high water permeance up to ≈115 L m^-2 h^-1 bar^-1 while acquiring a high salt/dye selective factor. This work affords an effective approach to the development of antifouling, high-separation-performance COF membranes, and other kinds of organic molecular sieve membranes.