Confinement-Directed Adsorption of Noble Gases (Xe/Kr) in MFM-300(M)-Based Metal–Organic Framework Materials

Abstract

Entrapment of radioactive inert gases, Xe and Kr, generated from the spent nuclear fuel reprocessing or nuclear accidents is one of the challenging issues in successful implementation of nuclear energy as an alternative and sustainable energy. Metal–organic frameworks (MOFs) gained immense research interest for adsorption and separation of various important gases because of their fine tunable pore chemistry and topology. Here, we investigated a series of MOFs, MFM-300(M) (M = Al, In, Ga, Sc, V, Cr, and Fe), for selective entrapment of Xe over Kr using both density functional theory (DFT) and grand canonical Monte Carlo (GCMC) simulation techniques. The calculated structural parameters of all of the considered MOFs are consistent with the reported experimental results. Different textural properties such as pore-limiting diameter, largest cavity diameter, surface area, void fraction, etc., are measured. From the binding energies calculated through DFT calculations at different loading capacities, adsorption of Xe is found to be stronger as compared to adsorption of Kr, and the binding energy is found to increase with loading. GCMC simulations indicate that the considered MOFs have significantly higher uptake capacities and are selective for Xe over Kr. Energy decomposition analysis indicates a strong adsorbate–adsorbate interaction at higher loading, which is more significant for Xe as compared to Kr. The strong adsorbate–adsorbate interactions are driven by the confinement effects of the one-dimensional cylindrical channels present in MFM-300(M). Among the series of MOFs considered, MFM-300(In) is shown to have the best selectivity for Xe over Kr. Our computational studies can provide valuable inputs for exploring MFM-300(M) MOFs for selective separation and storage of noble gases.