(101c) Hydrothermal Synthesis of Cerium-Based Mixed Oxide Nanocrystals

Hydrothermal Synthesis
of Cerium-Based Mixed Oxide Nanocrystals

Ruigang Wang, Samuel I. Mutinda, Varun Sama

Department of Chemistry and Materials
Science and Engineering Program,

Youngstown State University, Youngstown,
OH 44555

We
report a facile hydrothermal synthesis in base solution for
shape/size-controlled ceria (CeO₂) nanocrystals and Ce-M-O oxide solid
solutions (M= Zr, Ti, Pr, Tb etc.). By controlling the crystallization process
inspired from the formation of Ce(OH)₃nanocrystal
seeds, the morphology of CeO₂ could be tuned into different regular
shapes such as nanorods, nanocuboids, and nanocubes with reactive {110} and
{200} faces, shown in Figure 1. We found that hydrothermal reaction temperature is
a critical parameter to control the shape and size of CeO₂
nanocrystals. Above 130^oC, high resolution transmission electron
microscopy studies revealed that the CeO₂ nanocubes/nanocuboids
expose predominant {200} crystal planes. The
compositionally homogeneous Ce-M-O oxide solid solution nanopowders can
also readily prepared. Microscopic investigation and catalytic characterization show that the
synthesized mixed oxide solid solutions using this method have high
crystallinity, and compositional homogeneity, and improved low-temperature
reducibility. Reduction treatment of Ce_0.5Zr_0.5O₂
causes a phase transformation, instead of phase separation, from fluoride to
pyrochlore structure, suggesting nanoscale
compositionally homogeneity of CeO₂-ZrO₂ nanocrystals. We
envision that the synthesis process presented here can be extended to
synthesize other cerium-based mixed oxides for use in low-temperature redox
active materials in automobile catalytic converter, as well as for catalysis
and sensor applications.

Figure 1. Some typical morphologies
of CeO₂ nanoparticles prepared by a facile hydrothermal method at
different temperatures: (a): 70°C; (b): 90°C;
(c): 110°C;
(d): 130°C.