Figure 3.

(Color online) (a) Schematic representation of the regenerative capability and oxidation state switching of ceria nanoparticles in an aqueous environment. The pictures of the bottles containing the nanoparticle suspension in DI water indicate color and oxidation state changes after different aging periods. (b) XPS Ce 3d spectra from particles removed from solution after one day and three weeks. Consistent with the optical measurements and solution color, the particles were mostly Ce⁺⁴ after one day and mostly Ce⁺³ after three weeks. When H₂O₂ was added to the aged nanoparticles in solution, they switched from Ce⁺³ back to Ce⁺⁴. Adapted with permission from Kuchibhatla et al., J. Phys. Chem. C 116, 14108 (2012). Copyright 2012, American Chemical Society.