High proton selectivity membrane based on the keto-linked cationic covalent organic framework for acid recovery

The cationic covalent organic frameworks (COFs) with editable pore environment and pore size are promising candidates for constructing the ion channel of anion exchange membranes (AEMs) with excellent separation properties, but the high reversible linking bond (e.g. imine) makes these membranes unstable in the industrial applications. In this work, the keto-linked COF (TpTGCl) with high acid-stability was fabricated on the surface of carboxyl-modified polyacrylonitrile (CPAN) ultrafiltration membrane. The COF active layer with positively charged property in pore channels afforded high separation factor of H+/Fe2+ up to 450 under batch dialysis process. Owing to the electrostatic repulsion, the cationic nanopore demonstrated a screening feature that transmitted H+ and rejected Fe2+. Moreover, the membranes (TpTGCl/CPAN) exhibited outstanding acid-stability, which could maintain high separation performance after 10 cycle under strong-acid conditions. The result suggested that COF with chemical stability and functional embellishment offered opportunities to synthesis high performance ion exchange membrane, and it could further be leveraged to tackle other challenges in membrane separation field.