Simultaneous Boost of SF6 Adsorption Capacity and Kinetics Through Isoreticular Functionalization of Zinc(II)-Pyrazolate Frameworks.

The capture of sulfur hexafluoride (SF6), the most potent greenhouse gas, is of critical importance. Enhancement of dynamic SF6 capture capacity presents significant challenges due to its chemical inertness and low concentration in industrial effluent streams. Herein, we demonstrate that the isoreticular functionalization of zinc-pyrazolate metal-organic frameworks (MOFs) enables simultaneous enhancement of both SF6 adsorption capacity and uptake kinetics. Through replacement of benzene with pyridine in the ligand, BUT-125 (BUT: Beijing University of Technology) achieves a record-high SF6 adsorption capacity of 3.57 mmol cm-3 at 0.1 bar and 298 K, representing a 27% improvement over its structural analogue Zn-DPB (DPB: 1,3-di(pyrazolate-4-yl)benzene). Density functional theory (DFT) calculations reveal that pyridine functionalization increases the positive charge density on hydrogen atoms within molecular trap sites, strengthening C─H···F interactions with SF6 molecules. Remarkably, BUT-125 also exhibits outstanding adsorption kinetics, that combined with high equilibrium uptake, leads to an exceptional dynamic SF6 capture capacity of 3.42 mmol cm-3 from the SF6/N2 (10/90) mixture, surpassing reported porous sorbents.