Surface coating of a side-chain type polyelectrolyte for endowing perm-selectivity between specific anions to an anion-exchange membrane with a small loss of membrane conductivity

The endowment of perm-selectivity for specific ions will further extend the applications of heterogeneous membrane. In this work, a side-chain type weak cationic polyelectrolyte, PVDF-g-PVP, was synthesized for surface hydrophobilization of heterogeneous anion-exchange membrane (AEM) in order to impart perm-selectivity between specific anions with different Gibbs hydration energy. After microstructure observation and chemical composition analyses by SEM, AFM, EA and FTIR, the perm-selectivity between specific anions, electrical resistance, transport number, limiting current density, surface homogeneity, as well as salt permeability of the modified AEMs were investigated. Series of electrodialysis experiments in SO 4 2– /Cl – system indicated that a significant perm-selectivity was indeed achieved by the attachment of PVDF-g-PVP coating. In particular, it was worth noting that only a small loss of membrane conductivity was observed after the functionalization. This should be closely related to the micro-phase separation morphology of the coating layer which was induced by the polarity difference between the main chains and side chains of PVDF-g-PVP. Besides, the chronopotentiometric analyses indicated surface homogeneity of the heterogeneous AEM was significantly enhanced and then effectively ameliorated concentration polarization behaviors at the membrane-solution interface. Meanwhile, the perm-selectivity for co-ions was also improved and suppressed back diffusion behaviors of salt driven by concentration gradient. In brief, the modifying scheme proposed in this work can effectively improve comprehensive transport properties of conventional heterogeneous AEM.