Cerium oxide (CeO2) is a wide-bandgap metal oxide of great importance for solid oxide fuel cells, catalysis, and even oxidative protection within cells. Oxygen vacancies, which form when Ce4+ ions are reduced to Ce3+, are key to many of the desirable properties of CeO2, but their effects on physical and chemical properties are poorly understood, especially at the solid-liquid interface. We discovered that several nm diameter CeO2 nanoparticles, which are very stable in acidic (pH &lt; 3), aqueous solution in the dark, steadily release Ce3+ ions into the solvent when exposed to UV irradiation. The quantum yield for photoreductive dissolution is 3% at 300 nm. The yield increases by as much as an order of magnitude with the addition of 1 M ethylene glycol or glycerol, but added ethanol has no effect. Shifts in the absorption onset of CeO2 to longer wavelengths suggest that ethylene glycol and glycerol chemisorb to the metal oxide surface. The resulting ligand-to-metal charge transfer absorption may foster Ce4+ reduction. Additionally, the chemisorbed species may react with surface-bound holes, preventing the oxidation of Ce3+ ions and enabling their escape into the solvent. Femtosecond transient absorption experiments are providing insights into the effects of interfacial charge transfer vs. sub-surface electron-hole pair generation on the photocorrosion of CeO2.

Photoreductive dissolution of cerium oxide nanoparticles upon UV irradiation

255th National Meeting (2018)

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