Comparison of Y[formula omitted]O[formula omitted] nanoparticles synthesized by precipitation, hydrothermal and microwave-assisted hydrothermal methods using urea

Abstract

Three wet chemistry methods (precipitation, hydrothermal and microwave-assisted hydrothermal synthesis) were compared for the production of yttrium oxide (Y2O3) nanoparticles from yttrium nitrate using urea. For the precipitation method, the annealing temperature and the molar ratio of urea/Y3+ were varied. For a urea/Y3+ ratio of 3, the optimal temperature for producing the smallest crystalline Y2O3 nanoparticles was 700 °C. Scanning electron microscopy (SEM) images of these samples showed that the particles were spherical with some agglomeration and that the particle size was (146 ± 21) nm, approximately an order of magnitude larger than the crystallite size of 17 nm as determined from X-ray diffraction. Varying the ratio of urea/Y3+ over a wide range from 5 to 80 did not have a strong influence on the crystallite size or micro-strain of the Y2O3 nanoparticles produced. For the hydrothermal method, the variation of the reaction temperature between 100 and 180 °C and the reaction time between 2 and 12 h had little influence on the crystallite size of the particles, which was in the range of 20 to 24 nm. Although the SEM images showed that the particle sizes of the Y2O3 nanoparticles produced by hydrothermal synthesis at 130 °C for 2 h were significantly smaller than those produced by the precipitation method, the particles were strongly agglomerated into clusters. Even with the microwave-assisted hydrothermal method, annealing was still required to convert the almost amorphous precipitate into crystalline Y2O3. However, this synthesis technique produced samples of a similar size to those produced by the standard hydrothermal synthesis, but with less agglomeration and in a shorter time. The particle size was (65 ± 6) nm for a reaction temperature of 160 °C. Therefore microwave-assisted hydrothermal synthesis had significant advantages over the precipitation method and standard hydrothermal synthesis for preparing Y2O3 samples, producing the least agglomerated nanoparticles in a shorter time.