Precision Construction Of Nanofiltration Membrane Based On γ-cyclodextrin And Efficient Separation Of Magnesium And Lithiu

Nanofiltration（NF）membrane as a new frontier technique had made significant progress in the field of lithium extraction from salt lakes,but they still suffered from the conventional permeability–selectivity trade-off effect.In this study,γ-cyclodextrins（CD）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 ofγ-CD enhanced the hydrophilicity of the membrane surface and the water flux of the nanofiltration membrane.Moreover,the cavity size ofγ-CD also effectively screened magnesium and lithium ions to a certain extent.Under the best preparation conditions,the permeation flux of the PEI/γ-CD-TMC nanofiltration membrane was 4.86 L?m^-2?h^-1?bar^-1,S_Li,Mg was 10.8.We also used the molecular dynamics simulation method to confirm that the participation ofγ-CD 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 110.16nm to 52.84 nm.This PEI/γ-CD-TMC membrane provided a new strategy for preparing nanofiltration membranes with excellent magnesium-lithium separation performance.In addition,in order to improve the selectivity and long-term stability of the nanofiltration membrane,γ-CD are grafted onto the surface of the active layer.The thickness of the active layer of the nanofiltration membrane obtained by this method is smaller,and the membrane surface is more hydrophilic.Furthermore,a large number of hydroxyl groups on the surface ofγ-CD react chemically with acid chloride groups and carboxyl groups to enhance the degree of cross-linking of the active layer and form a denser film surface.The experimental results show that when the concentration of intercalatedγ-CD is 0.3 wt%（TFC-2）,the magnesium-lithium separation factor of the nanofiltration membrane is increased to 23.61,and the flux is only reduced by 0.2 L?m^-2?h^-1?bar^-1.In the long-term nanofiltration operation experiment,TFC-2 membrane showed stable selectivity.This work provides a new method for the subsequent cyclodextrin modification of nanofiltration membranes.