Ion-selective supramolecular membrane with pH-regulated smart nanochannels for lithium extraction

Tunable gating ion-conducting membranes with high water permeability and precise ion selectivity remain urgently demanded in smart nanofiltration for efficient lithium extraction. Herein, inspired by the filtration function of protein channels, we report a smart and high-performance supramolecular membrane constructed via coordination between quaternary ammonium ligands (m-phenylenediamine/polyethyleneimine) and metal ion center (Cu2+). The pore architecture of the supramolecular membrane is dynamic and can be switched by applying pH stimulus, where coordinated interchain expands when exposed to acidic operating conditions and induces concomitantly reinforced electrostatic exclusion due to enhanced local charge density. The tunable gating regularity enables operando modulation of precise ionic separation in situ. The resulting membrane exhibits significantly enhanced water permeance (19.8 L·m-2·h-1·bar-1) and simultaneously promoted Li+/Mg2+ selectivity (RMg2+=96.4%), surpassing typical trade-off between permeability and selectivity at pH 3 condition. This study demonstrates the amazing capability of environmental-responsive regulation of membrane pore-channel structure, and provides inspiration for engineering advanced supramolecular membranes for lithium extraction and beyond.