From cerium oxycarbonate to nanostructured ceria: Relations between synthesis, thermal process and morphologies

Nanostructured cerium dioxide rods and powders were synthesized via two sol–gel routes, respectively at 200 °C, and in room conditions without any thermal treatment. The initial solution involved nitrates, urea and polyvinyl-pyrrolidine in aqueous medium. In a first step, we synthesized cerium oxycarbonate by heating the solution at 80 °C: crystalline grains of (Ce3+)2O(CO3)2, H2O phase were obtained in the form of elongated crystalline spindles (5–10 μm long). Thermal decomposition of these spindle-like crystals gave rise to smaller elongated rods of nanostructured ceria. A second sol–gel route allowed obtaining nanosized ceria, after NH4OH addition and without any heating process. X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses allowed characterizing the oxycarbonate polycrystalline samples and the two types of nanocrystalline ceria phases.