MOF-based homogeneous ion exchange membranes 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 key challenges of permeability and perm-selectivity. Herein, we have constructed a functional sieving layer for monovalent-ion-selective 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 have shown that the membranes 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 P_{Na⁺/Mg²⁺} = 26.2 and P_{Li⁺/Mg²⁺} = 32.2, which markedly outperform commercial membranes 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.

Keywords: Electrodialysis-based monovalent/multivalent ion sieving; Metal-organic framework; Interfacial polymerization; High Li⁺ permeation flux; High perm-selectivity.