Study of the preparation and properties of CeO2 single/multiwall hollow microspheres

Novel slight yellow CeO2 single/multiwall hollow microspheres were synthesized by the hydrothermal method without any surfactant and characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM), and x-ray photoelectron spectra (XPS). The results showed that the products were CeO2 single/multiwall hollow microspheres, the shells of which were composed of CeO2 nanoparticles with a mean size of 70 nm. The effect of the preparation conditions, the reaction temperature, the reaction time, and the molar ratios of urea to Ce(NO3)(3)center dot 6H(2)O on the morphology of the products, was investigated. The optimal preparation conditions are determined as follows: the reaction temperature of 230 degrees C, the reaction time of 6 to 10 h, and the molar ratios of urea to Ce(NO3)(3)center dot 6H(2)O of 3:1 to 6:1. The formation mechanism of CeO2 single/multiwall hollow microspheres was proposed. The ultraviolet-visible (UV-VIS) diffuse reflectance spectra of the samples were measured. The results showed that the absorption edges of the samples were red-shifted compared with that of bulk CeO2, and that the red-shift of the absorption edges and the yellow of the samples enhanced with increasing the yield of CeO2 single/multiwall hollow microspheres. The catalytic activity and the recycling performance of the sample on CO oxidation were tested and the T-100% (the temperature at which CO 100% conversion) was 230 degrees C in the first run and decreased by 270 and 205 degrees C compared with that of bulk CeO2 and CeO2 nanocrystal, respectively.