A novel method to synthesize homogeneous and mono-dispersible CeO2 nanospheres: two-step hydrothermal process

In this study, homogeneous mono-disperse CeO2 nanosphere was successfully synthesized through two-step hydrothermal process, and the degree of sphericity was also improved comparing with the sample synthesized through one-step hydrothermal process. In the whole reaction, crystallization and ripening were regarded as two independent stages. Upper-layer transparent solution obtained through centrifugation after first-step hydrothermal process contained a large number of CeO2 crystal seeds, indicating that crystallization has taken place in this stage. Then, these seeds participated in the second hydrothermal process and ripened into homogeneous spheres finally. In addition, poly(vinylpyrrolidone) was applied as surfactant to facilitate the oriented aggregation of small CeO2 nanoparticles into nanospheres. The formation mechanism was discussed through scanning electron microscopy and transmission electron microscopy.