A synergistic strategy for efficient Li+/Mg2+ separation based on γ-CD cavity regulation and histidine electrostatic repulsion

Highly selective Mg 2+ /Li + separation membranes hold significant application prospects in extraction of lithium. However, the high Mg 2+ /Li + concentration ratio commonly found in brines and the very close hydrated ionic radii of the two ions limit the separation efficiency of conventional membranes. This study proposes a dual-phase supramolecular synergistic sieving nanofiltration membrane design strategy. Leveraging the unique molecular recognition unit and hydrophilic external interface characteristics of γ -cyclodextrin ( γ -CD), combined with the multifunctional positively charged groups of histidine, the strategy achieves the directional construction of highly efficient Mg 2+ /Li + sieving channels within the membrane. The strategy is accomplished through the synergistic action of γ -CD’s selective capture of high-valent Mg 2 + and histidine’s electrostatic repulsion effect. During the Mg 2 + /Li + separation process, the fabricated γ -CD-histidine composite membrane (HCF membrane) demonstrates outstanding comprehensive performance. It achieves a remarkably high Li + /Mg 2+ separation factor of 28.98 and maintains excellent separation performance across a wide Mg 2+ /Li + ratio range (1:1–100:1). The enhanced hydrophilicity of the HCF membrane significantly boosts permeate flux, while also exhibiting long-term operational stability and biofouling resistance during continuous operation under high Mg 2+ /Li + ratios. This research enables the high-selectivity separation of Mg 2+ and Li + with concurrent Li + enrichment, demonstrating significant potential for lithium extraction from salt-lake.