Synthesis and crystal kinetics of cerium oxide nanocrystallites prepared by co-precipitation process

Abstract

Cerium oxide nanocrystallites were synthesized at a relatively low temperature using cerium nitrate as starting materials in a water solution by a co-precipitation process. Effect of calcination temperature on the crystallite growth of cerium oxide nano-powders was investigated by X-ray diffraction, transmission electron microscopy and electron diffraction. The crystallization temperature of the cerium oxide powders was estimated to be about 273 K by XRD analysis. When calcined from 473 to 1273 K, the crystallization of the face-centered cubic phase was observed by XRD. The crystallite size of the cerium oxide increased from 10.0 to 43.8 nm with calcining temperature increasing from 673 to 1273 K. The activation energy for growth of cerium oxide nanoparticles was found to be 16.0 kJ mol⁻¹.

Introduction

In recent years, nanocrystalline cerium oxide (CeO₂) particles have been extensively studied owing to their potential uses in many applications, such as UV absorbents and filters [1], [2], buffer layers with silicon wafer [3], gas sensors [4], catalysts in the fuel cell technology [5], [6], [7], catalytic wet oxidation [8], engine exhaust catalysts [9], NO removal [10], and photocatalytic oxidation of water [11]. However, the material performances in practical uses are strongly influenced by the properties of constituent CeO₂ particles. Numerous techniques have been proposed to synthesize nano-sized CeO₂ particles with promising control of properties, such as hydrothermal [12], [13], [14], [15], [16], reverse micelles [1], [17], sonochemical [18], pyrolysis [19] and homogeneous precipitation [2], [20], [21], [22], [23], [24]. Among them, owing to the advantages of simple process, easy scale-up and low cost, the precipitation technique has attracted the most extensive attentions. For example, Zhou et al. [20] produced CeO₂ particles of about 4 nm from cerium nitrate and ammonia. Matijević and Hsu [21] prepared sub-micron Ce₂O-(CO₃)₂·H₂O particles from cerium nitrate with urea. Chen and Chen [22] prepared CeO₂ particles from cerium nitrate with hexamethylenetetramine, whereas Li et al. [23] used ammonia carbonate and diethylamine as the precipitate agents. Yamashita et al. [2] produced CeO₂ particles from cerium chloride and sodium hydroxide with the presence of hydrogen peroxide under various pH conditions from 6 to 12. Uekawa et al. [24] obtained 7–9 nm CeO₂ particles starting from cerium nitrate in the polyethylene glycol solution. Although CeO₂ particles prepared by the precipitation technique have been extensively studied, most of the previous reports were focused on effects of cerium precursors, ligands, additives and reaction media. Less information was reported on the influences of calcined temperature on crystallite growth behavior of cerium oxide. The present investigation has used Ce(NO₃)₃·6H₂O as starting materials for the synthesis of experimental procedure cerium oxide nanocrystallite powders by the co-precipitation process. The main objective of the present study is to determine the effect of calcination temperature on the crystallite growth of cerium oxide nano-powders of green gel powders by X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron diffraction (ED).