Surfactant Induced Non-Hydrolytic Synthesis of Phase-Pure ZrO2 Nanoparticles using Metal-Organic and Oxocluster Precursors

Nonhydrolytic/non-sol–gel pyrolytic synthesis technique, as a convenient method, was applied to synthesize zirconium oxide nanoparticles (ZrO2 NPs). Pyrolysis of either the mononuclear keto ester/alkoxide complex zirconium bis(isopropoxide)bis(tert-butylacetoacetate) [Zr(OiPr)2(tbaoac)2] (I) or the oligonuclear oxocluster compound [Zr6(OH)4O4(OMc)12] (II, Mc = methacrylate) generated ZrO2 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 ZrO2 nanoparticles, which yield the high-temperature tetragonal phase at moderate conditions of 335 °C. Those as-synthesized samples that contained both monoclinic and tetragonal ZrO2 phases (depending on the choice of the surfactant) were transformed into pure tetragonal phase at 1000 °C. An unambiguous phase determination of ZrO2 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 ZrO2 nanoparticles upon annealing were followed via Raman spectroscopy.

Nonhydrolytic/non-sol−gel pyrolytic synthesis technique, as a convenient method, was applied to synthesize zirconium oxide nanoparticles (ZrO2 NPs). Pyrolysis of either the 12 mononuclear keto ester/alkoxide complex zirconium bis(isopropoxide)bis(tert-butylacetoacetate) 13 [Zr(OiPr)2(tbaoac)2] (I) or the oligonuclear oxocluster compound [Zr6(OH)4O4(OMc)12] (II, 14 Mc = methacrylate) generated ZrO2 NPs at moderate conditions of 300−400 °C. Trioctylamine, 15 stearic acid, and/or oleic acid, which act as both solvents and stabilizing agents, were used. Under 16 the adopted process conditions, the stabilizing agent oleic acid plays a vital role in determining the 17 phase of as-synthesized colloidal ZrO2 nanoparticles, which yield the high-temperature tetragonal 18 phase at moderate conditions of 335 °C. Those as-synthesized samples that contained both 19 monoclinic and tetragonal ZrO2 phases (depending on the choice of the surfactant) were 20 transformed into pure tetragonal phase at 1000 °C. An unambiguous phase determination of ZrO2 21 nanoparticles was carried out by the combination of powder X-ray diffraction (XRD) and Raman 22 spectroscopy. Furthermore, the samples were analyzed by transmission electron microscopy 23 (TEM), ultraviolet−visible (UV−vis) and photoluminescence (PL) spectroscopy, dynamic light scattering (DLS), and Fourier 24 transform infrared (FT-IR) spectroscopy to elucidate the structure, chemical composition, and morphology of the obtained 25 nanoparticles. Also, the phase transformations of the as-synthesized ZrO2 nanoparticles upon annealing were followed via Raman spectroscopy.