Highly crystalline ionic covalent organic framework membrane for nanofiltration and charge-controlled organic pollutants removal

Organic pollutants are biological toxicity and should be removed from the environment. Membrane separation offers several advantages in organic pollutants removal such as high pollutants selectivity and high solvent permeability. Covalent organic framework membrane is regarded as an emerging porous membrane for nanofiltration owing to their permanent porosity and well-defined pore structure in various organic media. Herein, a self-standing 2D sulfonate anionic COF membrane with nanometer pore size and -SO₃Na groups has been successfully prepared. The surface charge combines with nanopore sieving property endow the COF membrane high nanofiltration separation performances and charge-controlled organic molecular separation. The anionic membrane can effectively intercept > 99% of cationic organic pollutants, while maintaining excellent solvent permeability due to its rigid porous structure and high porosity. The density functional theory (DFT) calculation provides further understanding on the charge-controlled separation in ionic nanoporous membranes. Our work may open up a new avenue for developing charged COF membrane for nanofiltration and organic pollutants separation applications.