The improvement of comprehensive transport properties to heterogeneous cation exchange membrane by the covalent immobilization of polyethyleneimine

In this work, a three-step modification scheme was devised to covalently immobilize the polyethyleneimine (PEI) multilayers for improving the comprehensive transport properties of a heterogeneous cation exchange membrane (CEM), including the grafting of carboxyl groups, the PEI immobilization by amidation reaction and glutaraldehyde-induced PEI multilayers deposition. Firstly, the changes in surface chemical composition and morphology after modification were investigated by attenuated total reflection-Fourier transform infrared spectroscopy and scanning probe microscope. Then, the membrane properties corresponding to different modification steps were comprehensively evaluated by the measurements of ion exchange capacity, water content, salt permeability coefficient, membrane electrical resistance, limiting current density and so on. Especially, in order to simulate the possible applications in the reclamation of the industrial effluents from the hydrometallurgy processes and the comprehensive utilization of seawater, respectively, some electrodialysis experiments for H+/Zn2+ system and Na+/Mg2+ system were performed to estimate and compare the monovalent selectivity of the membrane samples. Furthermore, the alteration of surface heterogeneity after modification was explored by current-voltage curves and chronopotentiometric curves. The experimental results showed that the modification scheme proposed in this work can make significant contributions to a heterogeneous CEM, such as the endowment of monovalent cation permselectivity, the improvement of surface homogeneity for ameliorating concentration polarization, the ability to impeding salt diffusion and even the possibility of extending membrane life-span.