Effect of water of crystallization on synthesis of nanocrystalline ceria by non-hydrolytic method (original) (raw)
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Cerium oxide (CeO2) or ceria has been shown to be an interesting support material for noble metals in catalysts designed for emission control, mainly due to its oxygen storage capacity. Ceria nanoparticles were prepared by precipitation method. The precursor materials used in this research were cerium nitrate hexahydrate (as a basic material), potassium carbonate and potassium hydroxide (as precipitants). The morphological properties were characterized by high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and UV-Vis spectrophotometer. XRD results showed face centered cubic CeO2 nanoparticles for annealed nanoparticles at 1000°C. SEM measurement showed that by increasing the calcinations temperature from 200 to 600°C, the crystallite size decreased from 90 to 28 nm. The SEM results showed that the size of the CeO2 nanoparticles decreased with increasing temperature. T...
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Given the scientific and technological interest in cerium oxide (ceria), in this paper nanoparticles of ceria (ceria-NPs) were synthesized using a modified polymer complex process (modified Pechini), while varying the pH of the system. This methodology made it possible to obtain, in a reproducible and controlled way, nanoparticles of ceria (<100nm) of a high chemical purity at low temperatures. The precalcined cerium solid obtained at 350°C was characterized using differential thermal analysis (DTA), thermogravimetric analysis (TG) and IR spectroscopy. Very little organic phase was found in the respective spectra, indicating that the inorganic phase, cerium oxide, is predominant. Carbonaceous residues still present in the solids were removed by heating at temperatures above 500°C and the samples obtained were characterized using X-ray diffraction (XRD), IR, UV-visible absorption and diffuse reflectance spectroscopies, and Transmission Electron Microscopy (TEM). The diffractograms of the samples showed that the only crystalline phase present was CeO2. From the results of UV-vis absorption and diffuse reflectance spectroscopy, two important energy values were obtained, 3.8 eV and 3.4 eV. These could be attributed to the energy gap value (3.8 eV) and to a possible "mid-gap" (3.4 eV). Furthermore, on increasing the synthesis pH, a reduction in particle size results, the particle being between 10 and 20 nm, with a spheroidal shape. By looking at the different stages of the synthesis process, a mechanism is proposed to explain how nanoparticles of ceria are formed.
International Journal of the Physical Sciences, 2012
In the present work, the cerium nitrate hexa-hydrate and ammonium hydroxide, used as the starting materials and the weakly agglomerated cerium oxide nanoparticles was synthesized by simple and cost effective reverse co-precipitation method. The effect of aging time and calcination temperature on structural properties of synthesized nanopowder was investigated by X-ray diffractometry (XRD), simultaneous thermal analysis (STA), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM) and transmission electron spectroscopy (TEM) analytical methods. The investigation showed that aging of the precipitated precursors has pronounced effect on the decreasing of the agglomeration, increase in the crystallinity and the crystallite size of the final product obtained after calcination. Also, increase in the calcination temperature led to the appreciable increase in the crystallite size as well as the crystallinity.
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Materials Research Bulletin - MATER RES BULL, 2006
Nanocrystalline ceria powders (CeO2) have been prepared by adding NaOH to a cerium ammonium nitrate aqueous solution under microwave–hydrothermal conditions. In particular the effect of the synthesis conditions (time, pressure and concentration of both the precursor and the precipitant agent solutions) on the physical properties of the crystals have been evaluated. Microwave–hydrothermal treatment of 5min at 13.4atm allows to obtain almost crystallized powders (amorphous phase 4%) as underlined by Rietveld-reference intensity ratio (RIR) results.