Processing and Characterization of Ceria-Zirconia Containing Graphene Quantum Dots

Abstract

Zirconia-based nanoparticles have been used in various applications, such as catalyst, filters, oxygen storage, and sensors. Among many synthesis methods to produce zirconia (ZrO2) nanoparticles, aqueous sodium borohydride (NaBH4) precipitation has shown to be simple and capable of large-scale production. In this work, the NaBH4 precipitation of ZrO2 was extended to include ceria (CeO2) and graphene quantum dots (GQDs). The resulting nanocomposites were characterized by thermal, crystallographic, compositional, and electron microscopy analysis techniques. The presence of CeO2 lowered the amorphous to tetragonal phase transformation temperature by ~40 ℃. The presence of GQDs did not affect the amorphous to tetragonal transformation temperature. In addition, cerium ions were inserted into the ZrO2 lattice with an increase to the interplanar spacing, seen by a slight shift in the diffraction peaks with no new peaks. Compositional analysis showed a stoichiometry between 13-14 mol. % ceria in the ZrO2 matrix with no elevated carbon concentration consistent with GQD doping levels. Agglomerated particles of several crystallites were observed and the presence of CeO2 increased the degree of agglomeration. The presence of GQDs was not conclusive, diffraction measurements were close to the theoretical value for the GQD basal plane, however, observation of the nanoparticles were not clear. More studies are needed to conclude the presence and functional interaction of GQDs and their role in nano-particle synthesis-structure relationships.