Convenient confinement: Examining ion and water behavior near graphene and graphene oxide thin films*

Understanding ion distributions and water orientation near graphene and graphene oxide surfaces is relevant to a range of applications, including capacitive deionization, heavy metal separations, and improved membrane performance. In each of these applications, ions and water interact with a graphene or graphene oxide surface in the small region forming between the solid and bulk liquid. Properties in this confined region greatly differ from typical bulk attributes, but experimentally probing interfaces is challenging, as most techniques are dominated by bulk signal. We experimentally characterize ion and water organization near both graphene and graphene oxide interfaces with molecular-scale resolution using a combination of surface-sensitive x-ray scattering and spectroscopy techniques. From these methods, we can fully describe the interface, including the structure of the graphene and graphene oxide films themselves, ion adsorption, and water orientation. These studies reveal the fundamental science underpinning downstream separation success.