Gold-Induced Crystallization of SiO₂ and TiO₂ Powders

Abstract

Gold nanoparticles with an average size of ∼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 °C).

Effect of seed particles on crystallization and crystallite size of anatase TiO2 nanocrystals by solvothermal treatment

“…In comparison, phase transformation from the amorphous TiO 2 to the crystalline or partially crystalline, anatase nano-framework in solutions has received less attention [11][12][13], despite a clear importance of preparing phase-pure anatase nanocrystals at a favorably reduced temperature together with a tailored pore/grain morphology from both technological and environmental viewpoints [14,15]. Use of crystalline seed to facilitate the crystallization of anatase TiO 2 from the amorphous phase in particular has been carried out when nanoparticles [16][17][18][19][20][21], nanotapes/ nanowires [22,23], and thin films [24][25][26] are of interest. Effect of the TiO 2 seeding to the crystallization temperature varies yet considerably, resulting primarily from the interplay between the crystallization and grain growth of the anatase phase in the presence of liquid solution or air atmosphere.…”

Sonochemical Insertion of Silver Nanoparticles into Two-Dimensional Mesoporous Alumina

“…The decrease in the surface area upon the insertion of nanoparticles inside the pores of the matrix has already been studied by our group. 31 Hence, it can be inferred that the Ag nanoparticles strongly influence the mesoporous structure of γ-Al 2 O 3 . This is a novel finding in this research work.…”

Synthesis and Physicochemical Properties of Gold‐based Catalysts

“…Sonication induces chemical changes such as reduction, due to cavitation phenomena caused by the formation, growth and implosive collapse of bubbles in a liquid; 148 this induces homolytic dissociation of water into H and OH radicals, the former being able to reduce Au(III) species in a solution. This method has been largely developed by Gedanken et al for the formation of gold nanoparticles on silica submicrospheres, 149 on powders of silica and titania, 150 and on mesoporous supports of TiO 2 , Fe 2 O 3 and Fe 2 O 3 -TiO 2 . 151 After immersion of the support in an aqueous solution of HAuCl 4 followed by addition of ethylene glycol basified with ammonia, the suspension was sonicated under Ar, 149 or Ar and H 2 (5%).…”

“…151 After immersion of the support in an aqueous solution of HAuCl 4 followed by addition of ethylene glycol basified with ammonia, the suspension was sonicated under Ar, 149 or Ar and H 2 (5%). 150 After washing, drying and calcination, gold particles with an average size of B4-5 nm were, for instance, obtained on silica submicrospheres, and all the gold was deposited onto these supports (5 to 7 wt%).…”