Van der Waals density functional study of hydrocarbon adsorption and separation in metal–organic frameworks without open metal sites

Abstract

Abstract Metal–organic frameworks (MOFs) have received significant attention thanks to their promising features in the storage and separation of guest molecules. MOFs without open metal sites are emerging as they are often less susceptible to poisoning compared to those with open metal sites. However, a complete understanding of the binding and gas separation mechanisms in such materials is still missing. In this work, we perform a comparative study of two classes of vanadium-based MOFs without open metal sites: MFM-300-V$$^\text{(III)}$$ (III) and MFM-300-V$$^\text{(IV)}$$ (IV) , as well as MIL-47-V$$^\text{(III)}$$ (III) and MIL-47-V$$^\text{(IV)}$$ (IV) . We employ first-principles van der Waals density functional theory to find the optimal binding conformations and binding energies of a series of small hydrocarbons within the pores of the aforementioned MOFs. Our study provides insight into the host–guest interactions in such MOFs without open metal sites, especially the role played by the bridging hydroxyl group ($$\mu _2$$ μ 2 –OH). We conclude that the bridging –OH group acts as a pseudo open metal site in these MOFs. Graphic abstract