Synthesis of -Al2O3/CeO2 Coated Nanoparticles and Dispersion Stability of Their Suspension

-Al2O3 nanoparticles prepared through a chemical precipitation method were directly coated with CeO2 by means of a precipitation technique. X-ray diffraction (XRD), infrared (IR) spectra, transmission electron microscopy (TEM) and energy dispersive analysis of X-ray (EDAX) were used to characterize the -Al2O3/CeO2 coated nanoparticles. XRD patterns show that the composite nanoparticles are the cubic crystal -Al2O3 and the fluorite-structured CeO2. IR results indicate that the coating of the -Al2O3 nanoparticles with CeO2 evidently gives rise to the bands at 720 and 600cm(-1) whose vibration intensity becomes strong shift to lower wavenumbers. The IEP of the -Al2O3/CeO2 coated nanoparticles is about 7.2, which displays a significant shift toward pure CeO2. TEM micrographs reveal that -Al2O3/CeO2 coated nanoparticles show a spherical morphology with the diameter about 15nm. Dispersion behaviors of -Al2O3/CeO2 coated nanoparticles under different conditions were studied in water suspension by investigating the zeta potential and absorbance. The results indicate that the surfaces of -Al2O3/CeO2 suspension are charged with positive charge under acid condition and with negative charge under alkaline condition, respectively. Zeta potential is higher when pH value is about 4, corresponding to dispersion stability is better. The dispersion effect of ultrasonic wave on -Al2O3/CeO2 nanoparticles is markedly superior to mechanical stirring. Only nonionic surfactant can improve the dispersion stability. A suspension with -Al2O3/CeO2 at 0.02wt% is added in 0.05 g/L nonionic surfactant PEG4000, and its pH value is adjusted to within the range of 3.5-4. In this condition, the stable suspension without sedimentation for a long time is successfully obtained.