Imidazole-functionalized siloxane cross-linked poly(aryl ether sulfone) anion exchange membranes for monovalent anion separation via electrodialysis

A siloxane cross-linked, amino-long-chain modified poly(aryl ether sulfone) (PPH-Im_SiO-NH₂-X) anion exchange membrane (AEM) has been synthesized. The results demonstrated that the perm-selectivity ($P_{S{O}_4^{2-}}^{C{l}^{-}}$) of the PPH-Im_SiO-NH₂-X AEMs gradually increased with the increasing content of the amino chains and reached its maximum value of 30.17 in the PPH-Im_SiO-NH₂-50 AEM. The mechanism underlying the enhanced selectivity was systematically analyzed by combining SAXS characterization with physico-chemical property evaluations. Specifically: (i) The siloxane cross-linked network effectively suppressed membrane swelling (water uptake ≤8.81 ​%, swelling ratio ≤3.03 ​%), thereby ensuring the stability of the ion transport channels; (ii) The amino long-chain interacted physically with the cross-linked network to form entanglements, reducing the size of ion clusters to 0.332 ​nm and further narrowing the ion channels, which selectively inhibited the migration of SO₄²⁻ via a size-sieving effect. This study not only broadened the application scope of siloxane cross-linking agents in the field of ion exchange membranes (IEMs) but also provided a novel material design strategy for developing anion exchange membranes with high selectivity and excellent stability.