Preparation of platinum nanoparticles by sonochemical reduction of the Pt(II) ion

Platinum nanoparticles were prepared in an aqueous system using high-intensity ultrasound (200 kHz, 6 W cm^-2). The particles formed in the presence of a surfactant (sodium dodecyl sulfate, SDS) were stable, homogeneously spherical, and relatively monodispersed with an average 2.6 nm diameter. The rate of formation of the platinum nanoparticles was 26.7 μM min^-1 in the Pt(II)-SDS system. Reducing species generated near and/or in the hot bubbles, which were sonochemically induced in the media, would react with the PtCl₄^2- complexes to form the platinum nanoparticles. Three kinds of the reducing species were proposed to be formed in the sonicated system: (a) radicals formed from the thermal decomposition of SDS at the interfacial region between the cavitation bubbles and bulk solution; (b) radicals formed via reactions of the hydroxyl radicals or hydrogen atoms with SDS; (c) hydrogen atoms. During the reduction of the Pt(II) ion, (b) and (c) ((b) > (c)) may be effective while (a) is only slightly effective, whereas in the cases of gold and palladium nanoparticles (a) was the main reductive species.