Surface Modification of Anion Exchange Membrane by Covalent Grafting for Imparting Permselectivity between Specific Anions

Abstract

An anion exchange membrane (AEM) embracing stable permselectivity for the specific anions is badly needed in the relevant electrodialysis process. Accordingly, a covalent modification scheme for a conventional AEM was put forward in this work, including the introduction of carboxyl groups by chemical reduction of aryl diazonium salts, the PEI immobilization by amidation reaction and then glutaraldehyde-induced PEI multilayers deposition. Firstly, the changes in the surface morphology and its chemical composition after membrane modification were investigated by scanning probe microscope and attenuated total reflection-Fourier transform infrared spectroscopy. Then, the ion exchange capacity, water content, membrane conductivity, limiting current density as well as salt permeability coefficient corresponding to different modified stages were discussed in detail. Especially, in order to simulate the possible applications in the comprehensive seawater utilization and water purification, series of electrodialysis experiments for SO42−/Cl− system were conducted for evaluating the selective separation property of the membranes after modification in terms of the permselectivity coefficient of sulfate ion against chlorine ion and the leakage rate of sulfate ion. In addition, the surface homogeneity after modification was also explored by chronopotentiometric curves and current–voltage curves. The experiment results indicated that the covalent modification scheme proposed in this study can effectively adjust the surface hydrophilicity of heterogeneous AEMs for imparting the permselectivity between the specific anions with different hydration energy and improve its surface homogeneity for ameliorating concentration polarization at the same time.