Porosity, structural and fractal study of sol-gel TiO2-CeO2 mixed oxides

Sol-gel TiO2-CeO2 materials were synthesized at pH = 3 employing HNO3 as hydrolysis agent. Gels were thermally treated at 473, 673, 873. and 1073 K, respectively. Morphologies of the final substrates were studied via N-2 sorption, XRD and TEM. N-2 isotherms indicated a steady porosity in TiO2-CeO2 samples treated up to 873 K. Adsorption-desorption isotherms and TEM micrographs were used to perform fractal analyses of annealed samples. A dominant anatase phase was detected by XRD between 473 and 873 K while a rutile phase was evident at 1073 K. The presence of cerium conferred an increased thermal stability to the TiO2 materials against particle sintering and pore collapse. The structure of cerium-doped anatase lattice was visualized through crystal simulation to investigate the possible substitution of Ti4+ by Ce+4 ions. This effect and the progressive segregation of CeO2 crystals with temperature on the surface of TiO2 grains lead to substrates of assorted morphologies. (C) 2004 Elsevier Inc. All rights reserved.