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

Abstract

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 (SLi/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 SLi/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, SLi/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.