Engineering “fishnet-like” structure to boost the monovalent anion selectivity of anion exchange membranes for electrodialysis applied in organic solvent systems

Solvent-resistant anion exchange membranes (AEMs) with a microphase separation structure have demonstrated the potential for efficient separation of monovalent and multivalent ions and solvent recovery. In this work, a kind of imidazole side-chain AEM based on poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) and crosslinking agent polyethyleneimine (PEI) was synthesized to achieve efficient separation of Cl− and SO42− ions through electrodialysis (ED) in organic solvent systems. The as-prepared AEMs exhibit favorable dimensional stability in various organic solvents, such as 60 % DMSO (aq.), 60 % DMF (aq.), 60 % ethanol (aq.), and display outstanding ion separation performance for Cl−/SO42− ions during the ED process. Specifically, the swelling ratio of the AEM in the organic solvents remains < 5.5 % for the AEM with a grafting rate of 60 % of 1-butylimidazole (BIm) on BPPO benzyl bromide groups. At a current density of 2.5 mA·cm−2 during the ED process, the perm-selectivity of Cl−/SO42− ions can reach 72.1. Importantly, even in a mixed solution containing 10 % organic solvent and 0.5 M NaCl and Na2SO4 (aq.), the perm-selectivity of Cl−/SO42− ions could still remain at 29.4. This achievement can be attributed to the integration of BIm and PEI, which forms stable sub-nanometer ion channels within the AEMs, enabling selective separation of ions of different sizes in organic solvent systems.