Enhanced Mg2+/Li+ separation by amino crown ether composite nanofiltration membrane with Mg2+ transport barrier

Selective separation property enhancement is quite important for membranes separations, especially for high mass ratio Mg 2+ /Li + separations. Low selectivity and unclear separation mechanism are the challenges for current membranes. In this study, we designed 4-aminophenyl-15-crown-5 incorporated polyamide nanofiltration membranes through interfacial polymerization for Li + enrichment. The electrochemical tests and energy barrier calculations using transition state theory confirmed that the crown ether in nanofiltration membrane is responsible for governing Mg 2+ transportation, resulting in a substantial energy barrier impeding its transport. Furthermore, a two-stage nanofiltration process was employed to enhance Li + enrichment in simulated brine and achieved 35-fold increase in Li + enrichment using as-fabricated membranes. These results demonstrate the substantial potential for Li  +  extraction from brine with a high Mg 2+ /Li + mass ratio using the crown ether incorporated membrane. Meanwhile, the proposed strategy incorporating transport barriers presents a novel approach for designing ion-selective channels within membranes.