Diazonium-induced anchoring process: an application to improve the monovalent selectivity of cation exchange membranes

An efficient and one-step chemical process (diazonium-induced anchoring process) to graft covalently a thin polyaniline-like layer on the surface of the Selemion CMV commercial cation exchange membrane is reported. SEM, IR and XPS techniques were used to characterize the obtained polymer film. The ability of such a surface modification layer to improve the membrane selectivity for hydrogen ions was confirmed by means of electrodialysis test. In contact with a mixed solution of sulfuric acid and metallic divalent salts, the protonation reaction of the polyaniline-like layer creates positive charges, thus leading to an electrical repulsion barrier which may reduce the penetration of divalent cations with respect to hydrogen ions. The ion exchange capacity, the membrane conductivity as well as the competitive transport of nickel and proton ions inside the modified membrane are discussed in detail in comparison with those of the bare membrane.