Gold-induced crystallization of SiO2 and TiO2 powders

Gold nanoparticles with an average size of similar to 5 nm have been deposited with the aid of power ultrasound on the surface of silica submicrospheres and on the surface of mesoporous titania. The sonochemical reduction of the gold ions is carried out by ultrasonic irradiation under argon-hydrogen atmosphere. A unique crystallization process of the silica and titania particles has been observed and characterized by X-ray powder diffraction, transmission electron microscopy, differential scanning calorimetry, and BET measurements. The crystallization process of the substrates (silica or titania) is assisted by the gold nanoparticles yielding the cristobalite phase of silica at a relatively low temperature and the anatase phase of titania at the temperature of the sonication bath (80 degrees C).