Highly Li-selective fully aromatic polyamide membranes prepared via combined cosolvent addition−solvent activation

Membrane separation technologies that can effectively recover Li from natural and industrial resources under various conditions are of great interest. Although fully aromatic polyamide (PA) membranes are acid-resistant, they have not been employed in Li separation because their dense structures result in low Li⁺/Mg²⁺ selectivity ( S _Li/Mg) and water permeance ( A ). Herein, we fabricate, for the first time, a fully aromatic PA membrane with excellent Li separation performance by combining two PA-loosening strategies: cosolvent (acetonitrile [ACN]) addition and solvent (dimethyl sulfoxide [DMSO]) activation. Although ACN addition during interfacial polymerization enhances the A and S _Li/Mg of the PA membrane, it maintains a small salt (LiCl and MgCl₂) rejection difference. DMSO activation not only effectively boosts the A of the membrane but also increases its salt rejection difference. Combination of ACN addition and DMSO activation enables the formation of a PA membrane with substantially high A , S _Li/Mg, and salt rejection difference by creating a significantly loose PA structure with a reasonably narrow pore size distribution. The resultant PA membrane demonstrates considerably high Li separation performance under various feed conditions, outperforming many commercial and lab-made Li-selective nanofiltration membranes while ensuring outstanding long-term operation and acid stability. Our study proposes a practically feasible method for designing highly ion-selective membranes by effectively controlling their pore structures.