An anion exchange membrane modified by alternate electro-deposition layers with enhanced monovalent selectivity

A novel anion exchange membrane (AEM) is developed through poly (sodium 4-styrene sulfonate) (PSS) and hydroxypropyltrimethyl ammonium chloride chitosan (HACC) alternate electro-deposition to enhance the monovalent selectivity. Compared to the commercial original AEM, coating of the (PSS/HACC)N alternate electro-deposition multilayer on the membrane surface dramatically enhance the selectivity of anions. In addition, the permselectivity for monovalent anions of the membranes was investigated by electrodialysis experiments. For comparison, the corresponding Cl−/SO42− were chosen and the average values of permselectivity and separation efficiency of commercial AEM are 0.66 and −0.19 respectively. As result of alternate electro-deposition of PSS/HACC layers, the permselectivity raised up to 2.90 and the separation efficiency also increased up to 0.28 for nine PSS/HACC bilayers needed. Under the optimal fabricating conditions, the area resistance of membrane arrived at 4.52 Ω cm2 with nine PSS/HACC bilayers. Meanwhile, the polarization current-voltage curves and ζ-potential of membranes were also tested to characterize the electrochemical behavior of the modified membrane. The high selectivities of these membranes may enable electrodialysis applications in separation of monovalent and divalent anions.