High-permeance Mg2+/Li+ separation nanofiltration membranes intensified by quadruple imidazolium salts

Nanofiltration represents an efficient technology for mono/divalent ions separation, such as Mg2+/Li + mixtures which are crucial for lithium extraction from salt lakes. This work shows that charge intensification of loose structure nanofiltration membranes is an effective way to reconcile high flux with Mg2+/Li+ selectivity. A new electrolyte monomer (QTHIM) containing quadruple imidazolium and hydroxyl groups was synthesized to react with residual acyl chloride groups on the nascent polyethyleneimine-based polyamide membranes (PEI-TMC), leading to the formation of a high-permeance nanofiltration membrane (PEI-TMC-QTHIM). The modified membrane highlights loose structures combined with enhanced positive charge, exhibiting high water permeance (-33 L m-2 h-1 bar- 1), good MgCl2 rejection (-92%) and high flux to 100 Mg2+/Li+ ratio mixture (-170 L m- 2 h-1). Notably, flux of the modified membrane is ca. 6 times as high as that of the nascent membrane.