Influence of aging on the properties of cerium oxide nanoparticles - implications to quantum confinement effect

Cerium oxide (ceria) nanoparticles are widely studied for their current and potential use in catalytic, energy, environment protection and bio-medical applications. The performance of ceria in most of the applications is dependent on the ability of cerium to switch between its +3 and +4 oxidation states. We synthesized ceria nanoparticles in several aqueous media and measured their oxidation states as a function of time using UV-Visible spectroscopy. By following changes in the absorption edge, we observed that sample synthesis conditions and processing history affect the oxidation state of cerium. These time dependent, environmentally induced changes in the band edge likely contribute to inconsistencies in the literature regarding quantum-confinement effects for ceria nanoparticles.