Synthesis and characterization of three-dimensionally ordered macroporous rare earth oxides

Three-dimensionally ordered macroporous (3DOM) CeO2 and La2O3 have been successfully fabricated by using polystyrene (PS) beads with diameters of about 600 and 676 ran as templates, rare metal nitrate as raw materials, and citric acid as chelator. Scanning electron microscope (SEM) observation shows that the macropores are highly ordered in fcc structure and connect with each other by small windows. Compared with the polystyrene beads used, the macropore size has shrunk during the process of the calcinations, but the long-range ordered structure of the samples was not destroyed and the pore size of samples is mainly determined by the diameter of template beads. The 3DOM structure of samples is completely maintained after calcined at 800 degreesC for 5 h, showing a high thermostability. The study demonstrates that it is hard to obtain 3DOM structure by using nitrates as precursors only, however, adding citrate acid is in favor of forming the 3DOM structure. XRD determination indicates that CeO2 was obtained after calcined at 400 degreesC for 5 h, and La2O3 was produced after calcined at 800 degreesC for 5 h. (C) 2004 Elsevier B.V. All rights reserved.