Interactions of Water and Ions with Graphene and Graphene Oxide Surfaces*

Graphene and its derivative, graphene oxide (GO), have garnered significant attention for their potential in energy storage, catalysis, and separation processes. The nanoscale behavior of ions and water molecules near graphene and GO surfaces is pivotal to both the fundamental understanding and practical application of these materials. We examined various systems, including alkali metal salts, rare earth elements, and uranyl ions in aqueous environments, using sum frequency generation (SFG) spectroscopy combined with surface-specific synchrotron X-ray scattering and spectroscopy techniques. The findings highlight the intricate relationship between ion adsorption, interfacial water arrangement, and factors such as surface hydrophobicity/hydrophilicity, functional groups present, and solution conditions like concentration and pH.