Cardopoly(arylene ether sulfone)s membranes bearing N-cyclic cationic groups enable high performance during both diffusion dialysis and electrodialysis

To investigate the relationships between the permselectivities and physicochemical structures of AEMs during diffusive dialysis (DD) and electrodialysis (ED), a series of cardopoly(arylene ether sulfone) membranes with different N-cyclic QA cations, controllable microphase separation structures and ultrahigh H+/Fe2+ selectivity during DD were prepared, and their permselectivity during ED and DD was systematically explored. The AEMs showed universally higher H+/Mn+ selectivities than known commercial and polymer-based membranes due to their rigid and contorted structures containing both cardo groups and pendant N-cyclic QA cations, which enabled formation of unique nano ion channels. During ED, the AEMs also displayed high Cl−/SO42− permselectivities, which was associated with microphase separation. For example, the prepared membrane with the best microphase separation exhibited the highest permselectivity (PSO42−Cl−=8.54) that was 5 times higher than that of the commercial ED membrane (PSO42−Cl−=1.6). The ED performance of the prepared AEMs was influenced by the distance between the AEMs and CEMs, and a shorter distance resulted in better ED performance. In addition, AEMs with better microphase separation were preferable for desalination because of enhanced dissociation and mobility of counterions under high current densities and low feeding salt concentrations. These findings may suggest new designs for high-performance ED and DD membranes.