MOF-based homogeneous ion exchange membrane for high-efficiency magnesium-lithium separation

Abstract

The rapidly increasing demand for lithium resources has driven significant advances in membrane-based separation technologies for extracting lithium from salt lake brines. However, conventional polymer membranes often suffer from a key challenge of permeability and selectivity. Herein, we have constructed a functional sieving layer for monovalent-ionselective membranes through interfacial polymerization by incorporating UiO-66-NH₂ with poly(diallyldimethylammonium chloride) (PDADMAc) polyelectrolyte, which has been successfully applied in electrodialysis processes for efficient Li⁺/Mg²⁺ separation. The fabricated membranes have facilitated Li⁺ transport while blocking Mg²⁺ effectively, owing to the synergistic effect between stable electrostatic repulsion and sufficient functional transport channels. Experimental results haven shown that the membrane have exhibited extremely high permeation fluxes of monovalent ions (Li⁺/Na⁺): the permeation flux of Li⁺ reaches 1.59 × 10⁻⁸ mol•cm⁻²•s⁻¹, the permeation flux of Na⁺ reaches 1.48 × 10⁻⁸ mol•cm⁻²•s⁻¹, whereas the corresponding Mg²⁺ flux is only 0.40 × 10⁻⁸ mol•cm⁻²•s⁻¹. These results correspond to high separation selectivities of PNa + /Mg 2+ =26.2 and PLi + /Mg 2+ =32.2, which are markedly outperform commercial membrane and those reported in published studies.It also provides a novel electrodialysis strategy for Li⁺/Mg²⁺ separation by leveraging MOF-based membranes, offering valuable insights for the efficient recovery of monovalent ion resources.