Van der Waals density functional study of binding and separation of hydrocarbons in metal organic frameworks without open metal sites

Metal organic frameworks (MOFs) have received significant attention over the past years thanks to their promising features for binding, 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 separation mechanisms in such materials is still missing. In this work, we compare two classes of vanadium-based MOFs without open metal sites: MFM-300(V^III) and its oxidized iso-structural counterpart MFM-300(V^IV), as well as MIL-47(V^III) and its oxidized counterpart MIL-47(V^IV). We employ first-principles van der Waals density functional theory to compute the binding energies of a series of short-chain hydrocarbons, to understand their separation in these MOFs. Our study provides insight into the host-guest binding interactions, in particular the role played by the bridging -OH group in such materials. Our results successfully explain existing experiments and provide guidance for future experiments.