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

Abstract

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.

Isotopic Consequences of Host–Guest Interactions; Noncovalent Chlorine Isotope Effects

“…Therefore, the reported experimental structural results provided us with a unique opportunity to evaluate the quality of different theoretical models used in quantum-chemical calculations of isotope effects associated with changes in weak interactions. We have resorted to the theory level, which proved successful in our recent studies on carbon vapor pressure isotope effects of ethanol, 42 carbon isotope effects on adsorption on graphene, 43 and isotope effects of oxygen and sulfur in phosphates. 44 This level has also been used recently for studies of over 12 000 chemical reactions 45 and thus provides an excellent reference level for future studies.…”

Quantum approach to the mechanism of monothiopyrophosphate isomerization

“…Our failures in finding the transition state for the dissociative pathway at the B3LYP/6-31+G(d) and ωB97xD/def2-SVPP levels of theory are in line with the observation that the basis set of the triple-zeta quality is necessary for reactions that involve reactions at the phosphorus center. We have, therefore, decided to employ ωB97xD functional, which we found performing very well for other systems [43]. The decision on the basis set has been made on the basis of charge distribution in phosphathioate anion that we have studied experimentally.…”

Density Functional Theory Predictions of Noncovalent Hydrogen Isotope Effects during Octane Sorption to a Kaolinite Surface

“…However, these results are not strictly comparable to fractionation during sorption, as the model represented 2 H/ 1 H exchange, which does not occur during sorption. In a subsequent modeling study, benzene sorbed to a graphite surface was slightly enriched in 2 H. 34 This finding is not supported by the experimental results, which have consistently reported an inverse H isotope effect (i.e., 2 H-depletion in the sorbed phase).…”