High-performance PEI-based nanofiltration membrane by MXene-regulated interfacial polymerization reaction: Design, fabrication and testing

Development of cost-effective materials and technologies for lithium extraction in salt-lake brines is of great importance to meet rising lithium demands. Nanofiltration (NF) process is a feasible solution with great separation efficiency; however, it has commonly had operational problems such as low permeability. In this study, an MXene-regulated interfacial polymerization (MRIP) method was developed for fabrication of high-performance polyethyleneimine (PEI)-based polyamide (PA) NF membrane. The MXene nanosheets tiled at the water-oil interface, by which a spatio-temporal confinement effect was achieved; such structure could nicely regulate diffusion of monomers and precisely control PA nanofilm structure. The MXene-regulated membrane (PA@M) had thinner thickness, larger pore size, and better hydrophilicity. As a result, the permeance of PA@M membrane was significantly increased by more than 300 %. Moreover, the membrane had outstanding cation selectivity with >98 % rejection for Mg2+ and <20 % rejection for Li+. Meanwhile, the selectivity factor of Li+/Mg2+ reached 31.5. Furthermore, a two-stage nanofiltration process by the membrane reduced the Mg2+/Li+ concentration ratio from 40 to 0.45, suggesting greater suitability for lithium extraction. This study offers a promising strategy and a sound method for development of high-performance PA-NF membranes for resource recovery and water purification applications.