Preparation of platinum nanoparticles by sonochemical reduction of the Pt(IV) ions: role of surfactants

Sonochemical reduction processes of Pt(TV) ions in water have been investig ated in the presence of various kinds of surfactants such as sodium dodecyl sulfate (SDS) and sodium dodecylbenzenesulfonate (DBS) as anionic surfactan ts, and polyethylene glycol monostearate (PEG-MS) as non-ionic, dodecyltrim ethylammonium chloride (DTAC) and bromide (DTAB) as cationic surfactants. A n improved colorimetric determination reveals that Pt(IV) ion is reduced to zero valent metal in two steps: step (1) - Pt(IV) ion to Pt(II) ion, and s tep (2) - Pt(II) ion to Pt(0), and after the completion of step (1), step ( 2) sets in. It appears that rapid scrambling reactions among platinum ions and/or atoms, that is, Pt(I) + Pt(IV) --> Pt(II) + Pt(III), etc. take place . In the sonolysis of aqueous solutions of SDS, DBS or PEG-MS, two kinds of organic reducing radicals, R-ab and R-py are proposed to contribute to the reduction. Radical R-ab is formed from the reaction of the surfactants wit h primary radicals such as hydroxyl radicals and hydrogen atoms originated from the sonolysis of water, and radical R-py is formed from the direct the rmal decomposition of surfactants in the interfacial region between the col lapsing cavities and the bulk water. R-ab is effective for both the reducti on steps, whereas R-py is involved only in the reduction step (1). This fac t coincides with the previous reported sonochemical reduction of Pt(II) ion s. Hydrogen atoms themselves scarcely participate in the reduction. The ave rage diameter (1.0 nm) of platinum particles prepared from the system of PE G-MS is smaller than those from the aqueous solution of anionic surfactant SDS (3.0 nm) and DBS (3.0 nm). (C) 2001 Elsevier Science B.V. All rights re served.