Enhanced proton/iron permselectivity of sulfonated poly (ether ether ketone) membrane functionalized with basic pendant groups during electrodialysis

Abstract

High permselectivity of cation exchange membrane for H+ and divalent metallic ions is essential for waste acid recovery by electrodialysis. Basic tertiary amine and imidazole groups were introduced into sulfonated poly (ether ether ketone) (SPEEK) membrane via a facile and controllable reaction, named as TA-x and IM-x (x was the basic group content), to construct acid-base pairs and reduce the swelling degree of membranes. 1H NMR confirmed the chemical structure of the as-obtained materials and protonation of tertiary amine and imidazole groups. As expected, all TA-x and IM-x membranes showed lower Fe2+ fluxes than pristine SPEEK membrane during electrodialysis because of their lower swelling degree and the electrostatic repulsion of protonated tertiary amine and imidazole groups. Remarkably, their H+ fluxes were kept similar to that of pristine SPEEK membrane. Therefore, the H+/Fe2+ permselectivity of membrane was improved considerably. Among them, IM-30 membrane showed the highest H+/Fe2+ permselectivity of 65.4, which was over three times that of pristine SPEEK membrane (19.1). Therefore, the introduction of basic groups into cation exchange membrane could reduce the swelling degree of membrane and improve the permselectivity between H+ and divalent metallic ions.