Can Adsorption on Graphene be Used for Isotopic Enrichment? A DFT Perspective.

We have explored the theoretical applicability of adsorption on graphene for the isotopic enrichment of aromatic compounds. Our results indicate that for nonpolar molecules, like benzene, the model compound used in these studies shows a reasonable isotopic fractionation that is obtained only for the deuterated species. For heavier elements, isotopic enrichment might be possible with more polar compounds, e.g., nitro- or chloro-substituted aromatics. For benzene, it is also not possible to use isotopic fractionation to differentiate between different orientations of the adsorbed molecule over the graphene surface. Our results also allowed for the identification of theory levels and computational procedures that can be used for the reliable prediction of the isotope effects on adsorption on graphene. In particular, the use of partial Hessian is an attractive approach that yields acceptable values at an enormous increase of speed.