Crown ether functionalized microporous polyimide membranes with hierarchical pore structure for enhanced Li+/Mg2+ separation

Lithium, a highly sought-after element for various industries, is primarily sourced from salt-lake brines, where its extraction faces the critical challenge of separating Li + from high concentrations of Mg 2+ . In this work, we present a crown ether functionalized polymer membrane with a hierarchical pore structure, designed for highly selective Li + /Mg 2+ separation. By grafting 12-crown-4-ether onto a microporous polyimide, ether rings matching the size of Li + are incorporated within the interconnected intrinsic micropores, facilitating Li + permeation while restricting Mg 2+ transport. The addition of PEG4000 during membrane formation creates unconnected macropores, reducing effective membrane thickness while preventing pore linkages that could lead to Mg 2+ leakage. Consequently, the Li + permeation rate significantly increases from 0.0095nmol cm −1 s −1 to 0.257 nmol cm −1 s −1 , while Mg 2+ permeation remains low at 0.0014 nmol cm −1 s −1 , achieving a remarkable Li + /Mg 2+ selectivity of up to 184. This study offers a straightforward and efficient approach for developing Li + selective membranes for efficient lithium extraction.