Synergistic Pore Microenvironment Engineering in Zinc Metal-Organic Frameworks for High SF₆/N₂ Selectivity and...

Sulfur hexafluoride (SF₆) is a potent greenhouse gas widely used in electrical insulation. Although the size difference between SF₆ and N₂ enables separation in principle, achieving high SF₆ selectivity at trace concentrations, large adsorption capacity, and long-term stability remains a formidable challenge. Herein, we report a family of new zinc-based metal-organic frameworks (Zn-tcpb, Zn-tcpb-bim, Zn-tppb-bim) with systematically tunable pore sizes and electrostatic microenvironments. By integrating a mixed-ligand strategy (tetracarboxylic acids plus 2,2'-biimidazole) with pore functionalization, we achieve synergistic control over adsorption and separation properties. Among them, Zn-tppb-bim-featuring electron-withdrawing pyrazine rings-exhibits a remarkable low-pressure SF₆ uptake of 3.06 mmol/g at 0.1 bar, and an excellent SF₆/N₂ IAST selectivity of 606 (1:9, 1 bar), achieving a balance between uptake and selectivity. Theoretical calculations reveal that the N-heterocyclic units in Zn-tppb-bim generate a stronger positive framework charge, enhancing C─H···F interactions with SF₆. Dynamic breakthrough experiments confirm complete separation of SF₆/N₂ mixtures. Remarkably, the materials retain full separation performance even at 80% relative humidity. This work demonstrates a viable and generalizable design strategy that synergistically optimizes adsorption capacity, selectivity, and humidity resistance, providing a rare example of metal-organic framework that are both highly efficient and stable under practical conditions.