Efficient separation of Li+/Mg2+via positively charged TFN membrane based on the PEI interlayer

Nanofiltration (NF) technology has exceptional mono/divalent ion separation performance, providing consid-erable application potential for lithium extraction. However, polymeric NF membranes provided only restricted amounts of practical applications since of their low permeability and limited selectivity. Herein, a positively charged membrane designed for Li+/Mg2+ separation was developed, this achievement was accomplished by incorporating NH2-MIL-101(Cr) nanoparticles (NPs) into the polyamide (PA) layer situated atop the poly-ethyleneimine (PEI) interlayer. The PEI interlayer controlled the amine monomer distribution, regulated the PA nanofilm morphology, and improved the membrane positively charged properties. Meanwhile, the NH2-MIL-101 (Cr) could provide Li+ with fast transport paths to further enhance the membrane Li+/Mg2+ separation capa-bility. The improved membrane possessed MgCl2 rejection of 96.1 %, LiCl rejection of 42.3 %, and Li+/Mg2+ separation factor of 102 with outstanding permeance of 17.0 L m-2 h-1 bar-1. This research made a valuable contribution to applying NF membranes in lithium extraction processes.