Interconnected 3D Framework of CeO₂ with High Oxygen Storage Capacity: High-Resolution Scanning Electron Microscopic Observation

CeO2 nanocasting in a mesoporous hard template provides a three-dimensionally (3D) interconnected skeleton framework consisting of CeO2 nanoparticles with particles smaller than 7 nm. Low-voltage high-resolution scanning electron microscopy with Ar-ion-beam cross-sectional polishing revealed numerous CeO2 (∼250 nm) clusters distributed in the SBA-15 mesochannels. Each CeO2 framework consists of CeO2 primary nanocrystals that are mutually and coherently connected. The mesochannel walls of the mesoporous silica might confine the growth of the CeO2 nanocrystals, resulting in a high oxygen storage capacity of the material. A series of cross-sectional images obtained by using damage-free Ar-ion-beam polishing revealed the mechanism of pore filling and CeO2 structuring process: that from the nucleation and growth of the CeO2 in the mesopores to the self-organization of nanocrystals that form multiple nanowires along the mesochannels. Furthermore, self-organized nanowires were arranged periodically and were mutually connected finally to form a negative replica of the ordered mesoporous SBA-15 silica.