AVS 59th Annual International Symposium and Exhibition
    Applied Surface Science Tuesday Sessions
       Session AS+BI-TuA

Paper AS+BI-TuA12
Characterization Challenges of Ceria Nanoparticles: When is a Nanoparticle Not a Nanoparticle?

Tuesday, October 30, 2012, 5:40 pm, Room 20

Session: Surface Analysis of Materials Using Vibrational Techniques (2:00-3:20 pm)/ Multi-Technique Analysis (4:00-6:00 pm)
Presenter: D.R. Baer, EMSL, Pacific Northwest National Laboratory
Authors: D.R. Baer, EMSL, Pacific Northwest National Laboratory
P. Munusamy, EMSL, Pacific Northwest National Laboratory
A.S. Karakoti, EMSL, Pacific Northwest National Laboratory
S.V.N.T. Kuchibhatla, Battelle Science and Technology India
S.S. Seal, University of Central Florida
S. Thevuthasan, EMSL, Pacific Northwest National Laboratory
C.F. Windisch, Jr., EMSL, Pacific Northwest National Laboratory
Correspondent: Click to Email
Cerium oxide (ceria) nanoparticles are widely studied for their current and potential use in catalytic, energy, environmental protection and bio-medical applications. The performance of ceria in many of these applications depends on the ability of cerium to switch between +3 and +4 oxidation states. Unfortunately the physical and chemical properties of ceria nanoparticles reported in the literature are often in consistent and at times contradictory. Our research involves examination of the properties of ceria nanoparticles as they apply to materials science research and impact biological systems. We have found that it is possible a obtain what appears to be a self-consistent understanding of these particles by integrating dynamic light scattering, surface potential and UV-Vis adsorption measurements made in solution with ex situ x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and transmission electron microscopy (TEM) observations. These measurements have demonstrated that a simple understanding of the chemical state of ceria nanoparticles as dependent on size is not adequate and has led to some of the inconsistent results in the literature. However, Raman and microXRD of wet ceria nanoparticles (pseudo in situ) show that the nature of the particles in solution is even more complex than indicated the above measurements. Raman and microXRD measurements indicate that both the chemical state and structure of the smallest nanoparticles can change depending on the nature of the solution. In solutions with low oxygen activity these particles have a ceria structure with cerium in +3 oxidation state while in highly oxidizing conditions the chemical state switches to +4 but the structure can be highly defected (XRD) and appears to be some type of cerium oxy-hydroxide (Raman). The extent of the transformation depends on the size of the particles and appears complete for the smallest particles and partial or possibly not present for larger particles. These measurements demonstrate that the environment, size and time can impact the nature of these particles and that a variety of analysis methods – in situ as well as ex situ – are required for comprehensive understanding of ceria nanoparticle behaviors. Acknowledgement - Aspects of the work have been supported by the National Institute of Environmental Health Sciences under grant NIH U19 ES019544. Portions of this work were conducted in the Environmental Molecular Sciences Laboratory, a DOE user facility operated by Pacific Northwest National Laboratory for the Office of Biological and Environmental Research of the DOE.