Electro-nanofiltration membranes with positively charged polyamide layer for cations separation

High performance and low-cost monovalent cation perm-selective membranes (MCPMs) are extremely desirable since the widespread demand for monovalent/multivalent cations separation. Herein, we developed a simple fabrication method for the preparation of electro-nanofiltration membranes (ENFMs), which were used as MCPMs for cations separation. The ultra-thin polyamide layer of ENFMs could offer selective channels for the transport of monovalent cations. Meanwhile, the positive charges in the polyamide layer act as useful barriers to divalent cations via electrostatic repulsion. The results show that the ENF-Q3 membrane with the highest quaternization degree owns outstanding perm-selectivity for Li+/Mg2+ system (PMg2+Li+=11.3), which is 7 times greater than that of the commercial CSO membrane, and high Li+ flux (JLi+=5.79×10-8mol·cm-2·s-1) at the current density of 10 mA cm−2. Moreover, the ENFMs exhibit high limiting current density and excellent long-term stability, indicating that the developed strategy is promising to scale up for industrial applications.