Adsorption of Ethanol, Water, and Ethanol–Water Dimers on Open-Ended Graphene Capillaries Studied by Ab Initio Methods: Unraveling the Ethanol and Water Attachment at the Edges

Abstract

This ab initio study evaluated the interaction of ethanol, water, and ethanol–water dimers with an open-ended graphene capillary (GC). The results for a 10 Å GC showed that the ethanol stability on the surface depends on the molecule orientation within the structure and its position along the GC cross-section. The vertically oriented adsorbed ethanol finds the most stable site at the GC edges. However, when the ethanol lies on the surface, it is more stable at the GC center. In contrast, the water molecules are more stable at the GC edge. The analysis shows that the vertically aligned molecule presents a stronger ethanol–GC bond at the edge, with enhanced covalent characteristics. This holds for GCs with different widths but is modified as a function of the interlayer separation (d). For d larger than ∼12 Å the ethanol laying on the GC center becomes favorable, as well as the vertically oriented molecule laying on the surface at ∼7 Å. As single molecules, ethanol and water receive charges, but upon dimer formation, ethanol donates and water gains. Interestingly, the ethanol–GC covalent bond enhances while it decreases for water–GC in the dimer, compared to the single molecule adsorption. These results clarify the ethanol–water/GC interaction.