In this study, we quantitatively studied the effects of the diameter and surface coating of monodisperse cerium oxide nanocrystals on their reactivity towards H2O2. These materials are formed in organic solvents by the high temperature decomposition of cerium precursors, and subsequently phase-transferred into water using amphiphilic coating agents. Quantitative analysis of the antioxidant capacity of nanoceria using GC-MS and a luminol test revealed that two moles of H2O2 reacted with every mole of cerium (III), supporting the hypothesis that the reaction proceeds via a Fenton-type mechanism. Smaller diameter cerium oxide nanocrystals have more cerium (III) and thus are more reactive towards H2O2; over a period of several weeks, the resulting cerium (IV) returns to cerium (III) and the nanocrystals can be used again to react with peroxide.  If the surface coatings were in excess of 2 nanometers thick, the samples could not undergo more than a few redox cycles before precipitating.  In contrast, nanoscale CeO2 coated with a very thin bilayer provided colloidally stable material that could undergo repeated redox cycling over 6 months and was able to reduce excess of H2O2 more than 20 times.  Finally, oleic acid-coated nanocrystalline ceria had nine times higher antioxidant capacity than Trolox in an oxygen-radical absorbance capacity (ORAC) assay.  These data suggest that appropriately derivatized nanocrystalline ceria could serve as a scavenger for radical species in biological media.

Antioxidation properties of cerium oxide nanocrystals depending on nanocrystal diameters and surface coatings

245th National Meeting (2013)

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