Cationic dendrimer-directed pore architecture in polyamide membranes for tunable ion separation.

Precise ion separation is fundamentally constrained by the disordered nanochannel and heterogeneous charge. Here, we report a dendrimer-directed strategy for engineering confined nanochannels and regulated charge environments within polyamide nanofilms. Self-assembled quaternary ammonium imidazole dendrimers (QASIDs) are covalently integrated into the polymer network during interfacial polymerization, enabling the formation of narrowed transport pathways for divalent ions with reduced electrostatic attraction. The resulting membranes exhibit substantially enhanced ion sieving performance, including a 48.94% expansion of the effective Li⁺/Mg²⁺ separation regime. Under high-salinity conditions (Mg²⁺/Li⁺ = 31.2), the membrane achieves an exceptional Li⁺/Mg²⁺ selectivity of 124, nearly one order of magnitude higher than that of conventional polyamide membranes, while maintaining a high water permeance of 283.13 ± 8.89 L·m⁻²·h⁻¹·MPa⁻¹. In addition, a high Cl⁻/SO₄²⁻ separation factor of 236.81 is achieved. Molecular simulations reveal that the incorporation of QASIDs generates more uniform confined nanochannels and optimizes the coupling between size exclusion and electrostatic interactions, thereby suppressing Mg²⁺ transport while preserving rapid Li⁺ permeation. The introduced positive charges effectively reduce the net negative charge density of the membrane, thereby weakening the electrostatic attraction toward Mg²⁺ rather than relying on Donnan repulsion. This work establishes a generalizable framework for programmable nanochannel engineering in polymer membranes toward high-performance ion separations.