Morphology-controllable synthesis of mesoporous CeO₂ nano- and microstructures

Spherical cerium oxide nanoparticles and microsized rod-shaped and spindle-like CeO₂ structures have been synthesized using a polyol method. When the duration of reaction and the concentration of cerium precursor are controlled, CeO₂ products of different morphologies can be selectively produced. Results from XRD, XPS, SEM, and FT-IR measurements suggest that the CeO₂ nanospheres are formed from the decomposition of the cerium precursor. Further reactions between the as-prepared CeO₂ and ethylene glycol yield the rods/spindle-like cerium formate particles. These morphologies are preserved even after calcination. The order of band gap energy of these samples was found to be rod-shaped > spherical > spindle-like samples, as determined by the UV-Vis spectroscopic method. Compared to a nonoriented polycrystalline CeO₂, these samples show an increase in band gap energy due to the quantum size effect. The higher catalytic activity on CO conversion in a spindle-like sample can be explained from the extent of Ce(IV) reduction and the oxygen vacancy.