Multigram Scale Synthesis and Characterization of Monodisperse Tetragonal Zirconia Nanocrystals

Abstract

A new and simple method has been developed to synthesize large quantities of highly monodisperse tetragonal zirconia nanocrystals. In this synthesis, a nonhydrolytic sol−gel reaction between zirconium(IV) isopropoxide and zirconium(IV) chloride at 340 °C generated 4 nm sized zirconia nanoparticles. A high-resolution transmission electron microscopic (HRTEM) image showed that the particles have a uniform particle size distribution and that they are highly crystalline. These monodisperse nanoparticles were synthesized without any size selection process. X-ray diffraction studies combined with Rietveld refinement revealed that the ZrO₂ nanocrystals are the high-temperature tetragonal phase, and very close to a cubic phase. When zirconium(IV) bromide is used as a precursor instead of zirconium chloride, zirconia nanoparticles with an average size of 2.9 nm were obtained. The UV−visible absorption spectrum of 4 nm sized zirconia nanoparticles exhibited a strong absorption starting at around 270 nm. A fluorescence spectrum with excitation at 300 nm showed a broad fluorescence band centered around 370 nm. FTIR spectra showed indication of TOPO binding on the ZrO₂ nanoparticle surface. These optical studies also suggest that the nanoparticles are of high quality in terms of narrow particle size distribution and relatively low density of surface trap states.