Identifying the Effects of Size and Shape on the Physicochemical Properties of Cerium Oxide Nanoparticles

C.M. Sims, A.F. Myers, J.M. Gorham, I. Levin, T.J. Cho, V.A. Hackley, B.C. Nelson
National Institute of Standards and Technology,
United States

Keywords: cerium oxide nanoparticles, structure-property relationships, surface modification, nanotoxicity

Summary:

Recently, the use of cerium oxide (CeO2, ceria) nanoparticles (NPs) has grown extensively due to their current and potential applications, spanning from automotive catalysts and UV filters to agricultural treatment agents and antioxidant therapeutics. While the physicochemical characteristics (e.g. size, shape, surface chemistry) of ceria NPs are known to highly influence their performance for a given application, the impact of these characteristics on their environmental and toxicological fates is not yet fully understood. Previous research designed to understand the potential environmental and toxicological effects of ceria NPs have yielded conflicting results, with ceria NPs found to be both toxic and non-toxic to cells and organisms. The mixed results of these studies reinforce the need to better understand the physicochemical characteristics of ceria NPs and how these characteristics affect their interaction with the environment and their potential mechanisms of toxicity. Here, we utilize multiple analytical techniques, including powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electron-energy loss spectroscopy (EELS), dynamic light scattering (DLS), and ultraviolet-visible spectroscopy (UV-Vis) to thoroughly characterize a suite of ceria NPs, both as dry powders and in environmentally relevant media. Preliminary data suggest the primary particle size has a large effect on the oxidation state of the ceria NPs, with smaller particles appearing to have increased Ce3+/Ce4+ ratios compared to their larger counterparts (Figures 1 and 2), in agreement with previous research. Attempts to create stable aqueous suspensions of the studied ceria NPs were unsuccessful unless their surfaces were modified by various ligands (e.g. citrate, polyvinylpyrrolidone). Additional experiments suggest the identity and amount of surface coating on the ceria NPs highly impact their resultant dynamics in media. Imminent work will investigate the potential toxicity of ceria NPs as a function of their physicochemical characteristics and the resultant effects on uptake, distribution, and potential mechanisms of toxicity in cells and organisms.