Water Solvation of Charged and Neutral Gold Nanoparticles

TL;DR

This study investigates how water interacts with charged and neutral gold nanoparticles using spectroscopy, revealing that positive charge affects water's hydrogen bonding and vibrational properties at the nanoparticle interface.

Contribution

It provides the first direct spectroscopic comparison of water solvation around charged and neutral gold nanoparticles, highlighting charge-dependent differences in water structure.

Findings

Hydration water around gold-loaded micelles has weaker hydrogen bonds than bulk water.

Positive charge on nanoparticles causes a larger blue shift in OH stretch.

Water at positively charged nanoparticle interfaces exhibits a stiffer potential energy surface.

Abstract

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 indications that the hydration water around the gold-loaded micelles is characterized by weaker hydrogen bonds than bulk water. A positive nanoparticle charge is observed to result in a larger blue shift of the OH stretch, quenches the intensity of the 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 thermodynamic properties.