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 nanopartides is very meaningful for the measurement of their corresponding chemical and physical properties and the establishment of their structure-catalytic property relationship.