Methyl-functionalized microporous metal-organic framework for efficient SF₆/N₂ separation

The capture and separation of sulfur hexafluoride (SF₆) from nitrogen (N₂) has the potential to reduce greenhouse gas emissions and provide economic benefits to the semiconductor industry. Herein, a series of metal–organic frameworks (MOFs) with different pore environments (Ni(pba)₂ (pba = 4-(4-pyridyl)benzoate), Ni(3-mpba)₂ (3-mpba = 3-methyl-4-(4-pyridyl)benzoate), and Co(3-mpba)₂) were designed and synthesized for SF₆/N₂ separation. The most promising candidate is Ni(3-mpba)₂, which exhibits excellent SF₆ uptake capacity (63.4 cm³ g⁻¹ at 298 K and 100 kPa) and the highest SF₆/N₂ selectivity (221 at 298 K and 100 kPa). X-ray diffraction analysis and theoretical calculations indicate that introducing the methyl group into Ni(3-mpba)₂ alters the microchemical environment of the pores. Ni(3-mpba)₂ has a smaller pore structure and more binding sites than Ni(pba)₂; its structure and binding sites enhance the affinity between sulfur hexafluoride and the adsorbent. Dynamic breakthrough experiments further verify the remarkable separation performance of Ni(3-mpba)₂ under simulated actual working conditions. In combination with its excellent regeneration ability and cycling performance, this porous coordination network shows great promise for SF₆/N₂ separation.