Water adsorption on graphene influenced by silica support

A combined experimental and theoretical study of Bermudez and Robinson (US Naval Research Laboratory) has shown that, although a silica support does not influence the band structure of single-layer graphene, it does influence how water binds to the surface.

With BAND the adsorption of water on a free layer of graphene and on graphene supported on a silica surface (β-cristobalite as an amorphous silica model) was studied with dispersion-corrected DFT (revPBE-D3). Grimme’s D3 dispersion corrections were necessary to achieve a positive adsorption energy – without DFT would predict graphene not to wet.

Although an amorphous silica support did not appear to perturb the electronic structure of graphene, it did increase the binding energy of water from 207 meV on free graphene to 257 meV. On the silica-supported graphene water preferentially adsorbs in a flat geometry rather than H-atoms pointing downwards:

Water adsorbs ‘standing’ on a free, single layer of graphene (left), while it binds stronger laying down parallel to a silica-supported graphene surface (right).

The experiments further indicated that there are CH₂ defects present on the single-layer graphene which couple non-adiabatically to the electronic excitations, opening up interesting possibilities for perturbing graphene’s electronic properties.

periodic DFT with BAND, dispersion-corrected DFT (GGA-D3), adsorption, band structures

V. M. Bermudez, J. T. Robinson, Effects of Molecular Adsorption on the Electronic Structure of Single-Layer Graphene Langmuir, 27, 11026-11036 (2011).