| Nanoceria is widely being investigated for applications as support materials for fuel cell catalysts, free radical scavengers, and as chemical and mechanical abrasives due to its high antioxidant capacity and its oxygen buffering capacity. This antioxidant or oxygen buffering capacity has been reported to be highly size dependent and related to its redox properties. However, the quantification of this antioxidant capacity has not been well defined or understood and has been often been carried out using colorimetric assays which do not directly correlate to ceria nanoparticle properties. Fabrication rules for developing materials with optimal antioxidant/oxygen buffering capacities are not yet defined and one of the limitations has been the challenge of obtaining quantitative measurements of the antioxidant properties. In this work, we create our own library of ceria nanoparticles of various size distributions by two synthesis methods: sol-gel peroxo and thermal decomposition/calcination and annealing in open atmosphere at three different temperatures. The synthesis methods and conditions produce characteristic sizes and morphologies of ceria nanoparticles. Qualitative and quantitative approaches are used for characterization and to predict reactivity. Qualitative approaches include Brunauer-Emmett-Teller (BET) surface area measurements and Raman analysis while quantitative approaches include a combination of powder X-ray diffraction (XRD) Rietveld analysis, Transmission Electron Microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) to measure crystallite sizes, lattice parameters, oxygen site occupancies, and the relative abundance of Ce(III) ions in a nanoceria sample. These methods are discussed in detail in addition to their limitations and challenges. These methods are used to predict nanocrystalline or bulk-like behavior of ceria nanoparticles. The investigation of the material properties is also extended to test the redox properties of ceria nanocrystals in aqueous environments via redox titrations and measurement of ceria suspension potentials and additional electrochemical behavior is tested by cyclic voltammetry using a three-electrode system. This work shows that ceria nanoparticles do not undergo complete dissolution in high concentrations of acids and therefore activity is predicted to be more surface based interactions. The findings from this work will contribute to measuring and understanding ceria nanocrystal activity in various applications as well as the impact to the environment. |
