Extra-thin composite nanofiltration membranes tuned by γ-cyclodextrins containing amphipathic cavities for efficient separation of magnesium/lithium ions

Although nanofiltration (NF) membrane as a new frontier technique had made significant progress in the field of lithium extraction from salt lakes, they still suffered from the conventional permeability–selectivity trade-off effect. In this study, γ-cyclodextrins(CDs) containing amphipathic cavities and polyethyleneimine (PEI) acted as the aqueous phase monomer, which was carried out interfacial polymerization with the trimesoyl chloride (TMC) as the organic phase monomer to fabricate thin film composite (TFC) NF membranes with the extra-thin active layer. The hydrophilic surface and hydrophobic cavity of γ-CDs enhanced the hydrophilicity of the membrane surface and the water flux of the nanofiltration membrane. Moreover, the cavity size of γ-CDs also effectively screened magnesium and lithium ions to a certain extent. Under the best preparation conditions, the permeation flux of the PEI/γ-CDs-TMC nanofiltration membrane was 4.86 L⋅m−2⋅h−1⋅bar−1, SLi, Mg was 10.8. It was noteworthy that we used the molecular dynamics simulation method to confirm that the participation of γ-CDs led to the diffusion rate of the water phase monomers during the interfacial polymerization reaction slowed down. Thus, the thickness of the active layer of the nanofiltration membrane formed was also significantly reduced from 110.16 nm to 52.84 nm. This PEI/γ-CDs-TMC membrane provided a new strategy for preparing nanofiltration membranes with excellent overall magnesium-lithium separation performance.