(700d) Enhanced Selectivity of Trace SF6 over N2 Via Functionalization of Ni-Based Metal-Organic Framework

Sulfur hexafluoride (SF₆) is a heavy, inert gas which has garnered significant attention in the last few decades due to its increasing atmospheric concentration and industrial applications. SF₆ is predominantly used in industrial processes such as microchip manufacturing or in high-voltage power equipment. To reduce demand, SF₆ is commonly diluted with nitrogen gas (N₂) to ratios of 1:9 or 1:99 SF₆:N₂. The recovery of SF₆ at trace concentrations (ppm_v) from leaks, exhaust, accidental release, or end-of-life equipment is a concern from both an economic and safety perspective. Due to its inertness, SF₆ is difficult and costly to produce with the standard separation method relying on cryogenic distillation. From a safety perspective, SF₆ can pose an asphyxiation hazard in settings where it can accumulate, and the depletion of SF₆ from high-voltage power equipment increases the risk of part failure. An alternative to liquification-based separation is physisorption-based separation via porous materials. Metal-organic frameworks (MOFs) are a class of porous solids composed of inorganic nodes coordinated by organic linkers. MOFs have high internal surface areas and, given the variety of linker and node combinations, encompass a vast chemical space. Due to their highly tunable structure and surface properties, MOFs have shown great promise in applications such as dilute gas separations. In this work, we demonstrate enhanced SF₆/N₂ selectivity at dilute concentrations in MOFs via linker functionalization of Ni(ina)₂. First, using Grand Canonical Monte Carlo simulations, evaluate several SF₆ molecular models to determine which accurately recover experimental adsorption trends. We then performed high-throughput computational screening of the ARCMOF database and several MOFs from the literature. Of the top performing MOFs, we chose Ni(ina)₂ to pursue for further investigation. We then simulated the impact of various functional groups on SF₆ adsorption. The most promising material, Ni(ina-NH₂)₂, has been synthesized via a novel synthetic method and validated with experimental adsorption isotherms. Finally, we use density functional theory (DFT) to investigate the mechanism driving the enhanced selectivity.

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