Ultrathin nanofiltration membrane based on <scp>MXene</scp> interlayer for efficient Li ⁺ /Mg ²⁺ separation

Abstract Nanofiltration (NF) membranes with sub‐nano structure are promising for the extraction of lithium from brine resources, yet often face a trade‐off between separation efficiency and permeation rate. Here, the ultrathin nanocomposite membranes (TFN AM ) with high Li + /Mg 2+ selectivity and permeability are prepared by introducing the positive aminated‐MXene interlayer in the process of interfacial polymerization (IP). This interlayer modulates the diffusion behavior of amine monomers and reduces the thickness of the polyamide (PA) layer by six times; meantime, it provides excellent positive charge on the membrane surface. The aminated‐MXene interlayer endows the high positive charge density of TFN AM enhancing the Donnan exclusion effect on the improvement of Li + /Mg 2+ selectivity. As a result, the TFN AM exhibits a high permeability of 12.5 L m −2 h −1 bar −1 and a Li + /Mg 2+ selectivity of 17.5, while maintaining performance over 100 h. This work proposes a facile and effective strategy to address the challenge of NF membrane limitations and advance lithium recovery technologies from brines.