Engineering Ion Affinity of Zr-MOF Hybrid PDMS Membranes for the Selective Separation of Na⁺/Ca²

Ion-selective separation, especially Na⁺/Ca²⁺ separation, is of significant importance in the realms of biomimetic research and the fabrication of biomimetic devices, underscoring the pivotal role that sodium and calcium ions play in cellular metabolism. However, the analogous ionic radii and charge densities shared by sodium and calcium ions significantly impede their effective discrimination, presenting formidable challenges for the precise engineering of ion separation materials, such as separation membranes. In this study, a polydimethylsiloxane (PDMS) separation membrane hybridized with zirconium-based metal-organic frameworks (UiO-66, UiO-66-NO₂ and UiO-66-NH₂) was constructed. Through the meticulous design of the MOF functional groups, the material's affinity for specific ions was modulated, thereby achieving efficient Na⁺/Ca²⁺ separation. Notably, the PDMS integrated with amino-modified Zr-MOF exhibited an efficacious selective separation of Na⁺ and Ca²⁺ ions. The interaction between the amino group of UiO-66-NH₂ and Ca²⁺ gave rise to the observed superior selectivity toward Ca²⁺ cations and enhanced separation efficiencies of up to 64% compared to pristine PDMS for UiO-66-NH₂-embedded membranes.