Development of surface-sulfonated graft anion-exchange membranes with monovalent ion selectivity and antifouling properties for electromembrane processes

This communication describes the development of anion-exchange membrane (AEM) with a modified surface possessing monovalent ion selectivity and antifouling properties. Modified AEMs series was obtained by the formation of an oppositely-charged thin layer utilizing the surface sulfonation of the grafted AEMs. The creation of the interface layer leads to a significant increase in the Cl/SO4 selectivity and the appearance of humic acid sorption resistance. The best surface-sulfonated anion-exchange membrane (s-AEM) has a high ionic conductivity of 11.2 mS cm−1 and high Cl/SO4 selectivity up to 6.4 in electrodialysis. The sulfonated layer was characterized by IR spectroscopy and electron microscopy. The relationship between the structure and thickness of the cation-exchange surface layer and the observed changes in membrane transport properties such as diffusion permeability, ionic conductivity, potentiometric transport numbers, and current-voltage characteristics are discussed. It was shown that the Cl/SO4 selectivity of s-AEM in the desalination process depends on the current density. The obtained data were successfully interpreted using a mathematical model based on the concept of the bipolar structure of the s-AEM surface layer and diffusion control of anion transport through it.