Synthesis of CeO2-coated SiO2 nanoparticle and dispersion stability of its suspension

SiO2 nanoparticle prepared through sol-gel method was directly coated with CeO2 by means of chemical precipitation technique. X-ray diffraction (XRD), differential scanning calorimetry/thermogravimetry (DSC/TG), infrared (IR) spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive analysis of X-ray (EDAX) were used to characterize the CeO2-coated SiO2 nanoparticle. XRD patterns showed that the core region of the composite particles was amorphous SiO2, and the shell region was fluorite-structured CeO2. IR results indicated that the coating of the SiO2 nanoparticle with CeO2 evidently induced the presence of new bands at 960 cm-1, due to the vibration of Ce-O-Si. Isoelectric point of the CeO2-coated SiO2 nanoparticle was about 5.6, which displayed a significant shift toward pure CeO2. SEM and TEM micrographs revealed that CeO2-coated SiO2 nanoparticle showed a spherical morphology with the diameter about 300 nm and a uniform particle size. Dispersion behaviors of CeO2-coated SiO2 nanoparticle under different conditions were studied in water suspension by investigating its zeta potential and absorbance. The results indicated that zeta potential was higher when pH value was about 10, corresponding to better dispersion stability. The dispersion effect of ultrasonic wave on CeO2-coated SiO2 nanoparticle was markedly superior compared with mechanical stirring. The zeta potential grew up evidently with the increasing of sodium dodecyl benzene sulfonate (SDBS) and poly ethylene glycol (PEG) 4000 concentration. A suspension with CeO2-coated SiO2 at 0.02 wt.% was added in 0.05 g l-1 anionic surfactant SDBS, and its pH value was adjusted within the range of 10-10.5. In this condition, the stable suspension without sedimentation time was successfully obtained.