Killing Two Birds with One Stone: Unveiling Hofmann-Type MOFs on Xe/Kr and Ethylene/Ethane Adsorption Separations by...

The noble gases ¹²⁹Xe and ⁸⁵Kr mainly exist in used nuclear fuel (UNF, v/v = 20/80), while C₂H₄ and C₂H₆ are present in cracked gas (v/v = 50/50). The energy-efficient adsorption separations of these two important mixtures with metal-organic frameworks (MOFs) are needed but challenging. Herein, among 150 Hofmann-type MOFs, LUFRIO01 and DUMFID exhibited the top performance on Xe/Kr and C₂H₄/C₂H₆ separation after grand canonical Monte Carlo (GCMC) simulations and adsorption experiment validations. These two frameworks possess fsc-net, where pyrazine (pyz) and [Ni(CN)₄]^2- are connected by Fe²⁺ or Co²⁺, respectively. For the Xe/Kr adsorption separation, LUFRIO01 and DUMFID facilitate the Xe uptakes over 2.69 mmol·g^-1, with Xe/Kr IAST selectivities over 160; while for the C₂H₄/C₂H₆ adsorption separation, C₂H₄ uptakes are more than 2.58 mmol·g^-1, with C₂H₄/C₂H₆ selectivity over 39.10. DFT calculations reveal that the [Ni(CN)₄]^2- bilayer can form two C-H···Ni²⁺ bonds with C₂H₄ with the optimal distance of around 7.00 Å, representing the first report of C₂H₄ agostic interaction with metal ions in MOFs. In summary, LUFRIO01 and DUMFID can overcome the "trade-off" issue between uptake and selectivity while "killing two birds with one stone". Note that the present work of "theoretical prediction, experimental validation" can accelerate material development with low cost.