Microwave-induced combustion synthesis and characterization of porous nanocrystalline Ce-M-O (M=La, Pr) powders

Porous nanometer Ce-M-O (M=Pr, La) solid solutions were synthesized by a microwave-induced combustion process using cerium nitrate hexahydrate, lanthanum nitrate hexahydrate, praseodymium nitrate hexahydrate and urea as raw materials. The powders were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), laser Raman spectrum, FT-IR spectrum, transmission electron micrograph (TEM), field-emission scanning electron micrograph (FE-SEM) and so on. XRD analysis reveals that the grain size of Ce-M-O varies between 20 and 50 nm and all the samples have the structure of fluorite. XPS concludes that praseodymium has two different forms (Pr3+ and pr(4+)) in the Ce-Pr-O solid solution. Raman results show that oxygen vacancy has been produced in CeO2 crystal lattices and its concentration is increased with M3+ doping. The results of FT-IR exhibit that the absorption band of Ce-O bond rises around 1400 cm(-1) and the IR absorption band of 2346 cm(-1) disappears because of M3+ doping. The platelike structure of networked nanocrystallites was observed through the TEM images. It can be seen from SEM that the porous appearance has been obtained and the pore size distribution range is 2 to 40 nm.