Defect-engineered and gel-state UiO-66-NH2 embedded polyamide membranes for electric-field enhanced Li+/Mg2+ separation

The selective recovery of lithium from salt-lake brines using functionalized polyamide nanofiltration (NF) membranes offers a promising strategy to alleviate the global lithium resource shortage. However, the structural controllability of functional fillers and their interfacial compatibility remain critical challenges in constructing high-performance NF membranes. In this study, a polyamide NF membrane was modified with defect-engineered and gel-state UiO-66-NH 2 nanoparticles, combined with an external electric field, to achieve efficient Li + /Mg 2+ separation. By tuning the HCl/HAc ratio, the nucleation and growth of UiO-66-NH 2 were regulated, yielding gel-state nanoparticles with abundant defects (defect coordination number ~ 0.73), excellent dispersibility, and high protonation, facilitating interfacial integration with the polyamide matrix. In situ characterization revealed that defect-engineered and gel-state UiO-66-NH 2 enhanced the membrane's positive surface charge and formed a “spinal-like” microstructure. Under the optimal acid ratio, the nanoparticles promoted higher polyamide cross-linking, reducing the average effective pore size from 0.54 to 0.46 nm, enabling synergistic control of both physical and chemical membrane properties. With an applied electric field, monovalent ion dehydration and migration were accelerated, enhancing ion decoupling and achieving a separation factor of 83.87 for Li + /Mg 2+ at an applied current of 6 mA. This work demonstrates a triple synergistic mechanism involving interface regulation, structural optimization, and electric-field coupling, highlighting the pivotal role of gel-state defect-engineered MOFs in tuning membrane microstructure and surface charge. This finding provides new theoretical guidance and design strategies for efficient lithium recovery using electric-field assisted functional nanofiber membranes.