Investigating graphene oxide-aqueous interfaces*

Graphene oxides (GO) are nanosheets of graphene with oxygen bearing defects. The GO sheet is highly heterogeneous with the sp³carbons, connected to oxygen bearing functional groups, interspersed between the usual sp²carbons of graphene resulting in competition between aromatic regions and highly hydrophilic domains (from the oxygen containing functional groups, typically -OH and epoxy groups) at the GO-aqueous interface. GO materials are increasingly gaining traction for ion and molecule separations. The interfacial region between the GO material and aqueous solutions plays a key role in these applications. Our efforts are focused on gaining molecular level insight into the interfacial ordering using molecular simulations. Classical and Born-Oppenheimer molecular dynamics were performed to study the interfacial water structure, including hydrogen bonding environments, using different order parameters. The simulations were used to gain insight into the results from recent vibrational sum frequency generation experiments. The reactivity of the graphene oxide-neat water interface as well as in the presence of an acidic excess proton were also investigated. The results of this study will be presented and discussed.