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NANOCERIA PREPARED BY ELECTRON BEAM EVAPORATION
Pizúrová, Naděžda ; Hlaváček, A. ; Kavčiaková, Zuzana ; Roupcová, Pavla ; Kuběna, Ivo ; Buršík, Jiří ; Sokovnin, S. Y.
Cerium oxide nanoparticles (nanoceria) are currently one of the most investigated nanomaterials because of their attractive properties used in biomedical applications, catalysis, fuel cells, and many others. These attractive properties are connected with the Ce3+ and Ce4+ valency state ratio. In the nanoparticle form, cerium oxides contain a mixture of Ce3+ and Ce4+ on the nanoparticle surfaces. Switching between these two states requires oxygen vacancies. Therefore, nanoceria's inherent ability to act as an antioxidant in an environmentally-dependent manner and a “redox switch” to confer auto-regenerating capabilities by automatically shifting between Ce4+ and Ce3+ oxidation states is significantly affected by surface morphology. Regarding this demanded behavior, we aimed to characterize synthesized nanoparticle surface quality and its influence on the cerium oxidation states. The received results were used to evaluate the synthesis method's suitability for suggested utilization. We used nanoparticles prepared by electron beam evaporation. This unique physical method includes nanoparticle creation through the fast cooling process followed by breaking radiation damaging nanoparticle surfaces to create surface off-stoichiometry. We prepared a sample containing clusters of a mixture of ultra-small nanoparticles and approximately 100 nm particles. X-ray diffraction confirmed the CeO2 phase in both components. To extract the finest component, we used centrifugal size fractionation. We received 200 nm clusters of 2-10 nm nanoparticles. Nanoparticle shapes and facet types were analyzed using transmission electron microscopy methods. We found out most nanoparticles were formed with truncated octahedrons containing {1,1,1} and {1,0,0} facet types and truncated cuboctahedrons containing {1,1,1}, {1,0,0}, and additional {1,1,0} facets. No octahedron (without truncation) containing only {1,1,1} facets was observed. Nanoparticle shapes containing {1,1,0} and {1,0,0} are suitable for redox activity. Some amount of irregular shapes, beneficial for redox activity, was also observed. Spectroscopy methods confirmed Ce3+ content.
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