| AVS 54th International Symposium | |
| Nanometer-scale Science and Technology | Thursday Sessions |
| Session NS-ThP |
| Session: | Nanometer-Scale Science & Techology Poster Session II |
| Presenter: | S.V.N.T. Kuchibhatla, University of Central Florida |
| Authors: | S.V.N.T. Kuchibhatla, University of Central Florida A.S. Karakoti, University of Central Florida S. Seal, University of Central Florida M.H. Engelhard, Pacific Northwest National Laboratory D.R. Baer, Pacific Northwest National Laboratory S. Thevuthasan, Pacific Northwest National Laboratory |
| Correspondent: | Click to Email |
Quantum confinement is a frequently observed and potentially useful property of nano-sized particles. An increase in band gap with the decrease in particle size is the phenomena of quantum confinement, typically valid when the particle size is approximately the exciton radius. However, because small particles are highly dependent on their surface, sample history and the local environments may also alter their properties and produce effects that may be interpreted as quantum confinement. We show that cerium oxide (Ceria, CeO2) is impacted by such effects. Nanoceria is a potential material for a spectrum of applications including solid oxide fuel cells, catalysis, oxygen sensors, biomedical use, and chemical mechanical planarization. The major characteristic of ceria crucial for these applications is its oxygen storage capability (OSC). The OSC is rendered to ceria by the ability to effectively switch between the 3+ and 4+ oxidation states based on ambient conditions. In the nanoscale regime, there are a number of reports that analyzed the ceria particles synthesized under different conditions. Many authors have computed the band gap and particle size by comparing the experimental UV Vis absorbance data to the effective mass approximation (EMA) theory. While some of the researchers have hypothesized that counter acting phenomena like dielectric confinement will nullify the confinement effects in ceria, others have strongly supported the quantum confinement effect. We attribute the reason for such a discrepancy in the open literature to the differences in synthesis and characterization environments along with the agglomeration of nanoparticles. We have synthesized ceria nanoparticles in different aqueous media (DI water, poly (ethylene glycol), dextran, and glucose). The optical absorbance spectra were collected as a function of time. A careful analysis of these data has clearly indicated that the ceria nanoparticles change their oxidation state in solution with time and the rate is dependent on environment. This change in chemistry denies the possibility to use the EMA theory for the particle size interpretation from the absorbance data and also raises questions about reported band gap values. Transmission electron microscopy and X-ray photo electron spectroscopy have been used to compliment the results from UV Vis analysis.