Based on high cross-linked structure design to fabricate PEI-based nanofiltration membranes for Mg2+/Li+ separation

With the rapid development of Li-ion batteries (LiBs), the demand for lithium sharply increased. Salt lakes contribute to major extractable lithium in the world, however, the efficient separation of Mg 2+ and Li  +  remains a challenge. The PEI-based nanofiltration (NF) membrane shows great potential for Mg 2+ /Li + separation in recent studies, due to its positively charged surface and tunable pore size. In this work, ethylenediamine-terminated polyethyleneimine (EDA@PEI) was utilized as the aqueous monomer reacting with trimesoyl chloride (TMC) via interfacial polymerization (IP) to fabricate a new class of PEI-based NF membranes. This work explored critical membrane fabrication parameters and characterizations of EDA@PEI NF membranes. Additionally, this work compared EDA@PEI-TMC and PEI-TMC membranes on their physicochemical properties and NF performance. The results show that PEI containing EDA groups at ends provides the probability for connection of the backbone via TMC, thus enhancing the cross-linking degree (DNC) of EDA@PEI NF membranes. Meanwhile, the presence of EDA groups enhances the Zeta potential of membranes. The best-performing EDA@PEI-TMC membrane exhibits the highest rejection for Mg 2+ of 99.21 %, and excellent Mg 2+ /Li  +  separation that S Li/Mg reaches 69.20, 80.62 and 46.79 at Mg 2+ /Li + mass ratios of 40:1, 60:1, and 120:1, respectively. During a 48-h NF test, EDA@PEI-TFC membrane shows consistent performance and steady flux. This work demonstrates the great application potential of EDA@PEI NF membranes for Mg 2+ /Li + separation, and provides a candidate for fabricating PEI-based NF membranes.