Gold nanoparticles with an average size of ∼5 nm were deposited on the surface of preformed silica submicrospheres with the aid of power ultrasound. The sonochemical reduction was carried out by ultrasonic irradiation in an argon atmosphere at room temperature. Ultrasonic irradiation of a slurry of silica submicrospheres, chloroauric acid (HAuCl4), and ammonia in an aqueous medium for 45 min yielded a gold−silica nanocomposite. By controlling reaction conditions, we could achieve the deposition of metallic gold on the surface of the silica spheres. A unique crystallization process of the silica particles is observed. The crystallization process is assisted by the gold nanoparticles yielding the cristobalite phase of silica at a relatively low temperature. The resulting gold-deposited silica submicrosphere samples were characterized with XRD, EDAX, TEM, TGA, DSC, HR-SEM, and FT-IR, photoacoustic, and UV−visible spectroscopy.

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