Three-Dimensional Structure of CeO₂ Nanocrystals

Visualization of three-dimensional (3D) structures of materials at the nanometer scale can shed important information on the performance of their applications and provide insight into the growth mechanism of shape-controlled nanomaterials. In this paper, the 3D structures and growth pathway of CeO₂ nanocrystals prepared by the hydrothermal method were investigated by electron tomography and high-resolution transmission electron microscopy (HRTEM). Two typical shapes (regular truncated octahedrons and irregular compressed truncated octahedron with {111} and {001} as the major facets) were identified in samples synthesized under different conditions. The homogeneous growth environment in solution with polyvinylpyrrolidone (PVP) molecules led to the formation of regular octahedral CeO₂ nanocrystals with small {001} facet truncations. When the PVP surfactant was removed, the aggregation of regular truncated octahedral CeO₂ particles through a lattice matched interface generated irregular compressed truncated octahedral CeO₂ nanoparticles. The formation of this irregular shape is attributed to the lower surface diffusion and slow incorporation of atoms on surfaces by step attachment of the fused particles. From a thermodynamic point of view, the exposure of {001} planes can be suppressed by the formation of this irregular metastable shape compared with a regular octahedron with large {001} facets. The confirmation of the shape and morphology of the CeO₂ nanoparticles is very meaningful for the measurement of their corresponding chemical and physical properties and the establishment of their structure−catalytic property relationship.