Hydration of Charged and Neutral Gold Nanoparticles

Gold nanoparticles are unique electrocatalysts for oxygen reduction, carbon dioxide reduction, and alcohol oxidation. Electrocatalytic processes are influenced by the interaction with the solvent, yet the direct investigation of the solvation of nanoparticles is scarce. Here we select gold nanoparticles as 10 nm sized solutes of which we can control the charge. We perform mid-infrared and terahertz spectroscopy to compare the behavior of the water in solution with micelles loaded with neutral and positive gold nanoparticles. We find indication that the hydration of the gold-loaded micelles is characterized by weak hydrogen bonds which do not form a full 3D network. A positive nanoparticle charge results in a larger blue-shift of the OH stretch, quenches the intensity of collective translational mode, and increases the absorption by librating water molecules. Water at the interface of a positive gold nanoparticle could experience a stiffer potential energy surface which, in turn, might unveil local thermo...