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

Abstract

Selective separation property enhancement is quite important for membranes separations, especially for high mass ratio Mg2+/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 Mg2+ 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 Mg2+/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.