Solvent effect in the nonaqueous synthesis of ZrO2 nanoparticles under alkaline conditions

This work deals with the synthesis of zirconium dioxide (ZrO2) nanoparticles (NPs) in different solvents and their structural characterization for better understanding the oxygen donor solvent/zirconium precursor/NPs structure relationships. By selecting solvents over their capacity to produce different crystalline states from alkalinized zirconium alkoxide, spherical nanoparticles with a size of about 1.3-3 nm and a narrow size distribution were elaborated using a nonaqueous solvothermal sol-gel route. Conventional X-ray diffraction (XRD) was used to determine the average structure and crystallite size of the nanoparticles. Well-crystallized and single-phased nanoparticles with average monoclinic and tetragonal structure were obtained with benzaldehyde and benzyl alcohol, respectively, and a much distorted structure was observed for the synthesis in anisole. The atomic pair distribution functions (PDF) of the samples were also analyzed to access the local structure of the nanoparticles. The PDF of the benzaldehyde-prepared sample is consistent with the monoclinic structure. However, the local structure of nanoparticles synthesized with benzyl alcohol does not fully conform to the tetragonal structure observed by XRD, but exhibits monoclinic-like distortions. Lastly, the anisole-prepared nanoparticles present large structural distortions at the medium range and monoclinic local structural features. The restructuring of this last sample was studied by post-treatments in different solvents and leads to the expression of the tetragonal polymorph. Moreover, it seems that the main structural features are obtained in the early stages of the nanoparticles' formation.