Preparation of monovalent cation selective membranes through annealing treatment

Different from enhancing permselectivity of cation exchange membrane (CEM) by the common surface modification, this study reports an annealing treatment strategy to enhance the density of PVA-based CEM by tuning crystallinity, which can improve pore-size sieving effect for ions. X-ray diffraction (XRD) suggests that these membranes possess controllable crystallinity ranging from 11.8% to 43.9%. AFM analysis implies that after annealing treatment crystalline regions increase remarkably and distribute uniformly in membrane. When they are applied to electrodialysis (ED) for acid recovery from H+/Zn2+ solution, it is experimentally evidenced that the permselectivity (PH+Zn2+) and Zn2+ leakage are dependent on crystallinity. The optimal membrane with a crystallinity of 43.9% exhibits a favorable permselectivity of 0.007 between Zn2+ and H+ and only 0.01% of Zn2+ leakage, which are better than that of monovalent cation exchange membrane modified by surface modification.