DFT Studies of the Interactions of a Graphene Layer with Small Water Aggregates

Abstract

We have investigated the structure, adsorption, electronic states, and charge transfer of small water aggregates on the surface of a graphene layer using density functional theory. Our calculations were focused on water adsorbates containing up to five water molecules interacting with one and both sides of a perfect freestanding sheet. Different orientations of the aggregates with respect to the graphene sites were considered. The results show that the adsorption energy of one water molecule is primarily determined by its orientation, although it is also strongly dependent on the implemented functional scheme. Despite its intrinsic difficulties with dispersion interactions, the Perdew and Wang's exchange-correlation functional may be a viable alternative to investigate the adsorption of large molecular aggregates on a graphene surface. Although water physisorption is expected to occur in the regime of droplets, we found no induced impurity states close to the Fermi level of graphene interacting with small water clusters. In order to investigate the donor/acceptor tendency of the water clusters on graphene, we have performed a Bader charge analysis. Considering the charge transfer mechanism, we have noticed that it should preferentially occur from water to graphene only when the oxygen atom is pointing toward the surface. Otherwise, and in the case of larger adsorbed clusters, charge transfers systematically occur from graphene to water.

Exploring Adsorption of Water and Ions on Carbon Surfaces Using a Polarizable Force Field

“…18–27 The most favorable orientation of a water molecule normally has the oxygen above the ring centroid and the two hydrogen atoms facing the surface, as in Figures 1 and 2. However, for the complex with benzene, the most favorable water orientation has one of the hydrogen atoms pointing toward the center of the ring (Figure 1).…”

Polymorphism of Water in Two Dimensions

“…4,9,10 Hence, the recent high-resolution electron microscopy observation of square ice confined between two graphene sheets 11 was rather surprising, as the water−graphene interaction possesses only a weak dependence on the position and orientation of the water molecule. 12,13 There is an ongoing discussion about whether or not the transmission electron microscopy images 11 should be attributed to a film of square water or to accumulated salt sandwiched between graphene sheets. 14,15 Still, this experimental study has raised interest in the fundamental question of whether under ambient conditions two-dimensional water layers can realize geometries that are not feasible for bulk ice.…”

A Molecular View of Adsorption on Nanostructured Carbon Materials

“…The structure, adsorption, electronic states, and charge transfer of small water aggregates (5H 2 O) on the surface of a graphene layer was investigated by DFT. 148 The results show that the adsorption energy of one water molecule is primarily determined by its orientation. Although water physisorption was expected to occur in the regime of droplets, no induced impurity states close to the Fermi level of graphene interacting with small water clusters were found.…”