Surfactant-Induced Nonhydrolytic Synthesis of Phase-Pure ZrO₂ Nanoparticles from Metal–Organic and Oxocluster Precursors

Nonhydrolytic/non-sol–gel pyrolytic synthesis technique, as a convenient method, was applied to synthesize zirconium oxide nanoparticles (ZrO 2 NPs). Pyrolysis of either the mononuclear keto ester/alkoxide complex zirconium bis(isopropoxide)bis( tert -butylacetoacetate) [Zr(O i Pr) 2 (tbaoac) 2 ] ( I ) or the oligonuclear oxocluster compound [Zr 6 (OH) 4 O 4 (OMc) 12 ] ( II, Mc = methacrylate) generated ZrO 2 NPs at moderate conditions of 300–400 °C. Trioctylamine, stearic acid, and/or oleic acid, which act as both solvents and stabilizing agents, were used. Under the adopted process conditions, the stabilizing agent oleic acid plays a vital role in determining the phase of as-synthesized colloidal ZrO 2 nanoparticles, which yield the high-temperature tetragonal phase at moderate conditions of 335 °C. Those as-synthesized samples that contained both monoclinic and tetragonal ZrO 2 phases (depending on the choice of the surfactant) were transformed into pure tetragonal phase at 1000 °C. An unambiguous phase determination of ZrO 2 nanoparticles was carried out by the combination of powder X-ray diffraction (XRD) and Raman spectroscopy. Furthermore, the samples were analyzed by transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) and photoluminescence (PL) spectroscopy, dynamic light scattering (DLS), and Fourier transform infrared (FT-IR) spectroscopy to elucidate the structure, chemical composition, and morphology of the obtained nanoparticles. Also, the phase transformations of the as-synthesized ZrO 2 nanoparticles upon annealing were followed via Raman spectroscopy.