Preparation of nanoparticles by reducing intermediate radicals formed in sonolytical pyrolysis of surfactants

Metal nanoparticles with a narrow size distribution could be prepared by sonolysis of aqueous solutions of metal cations in the presence of surfactants such as sodium dodecyl sulfate, polyethylene glycol monostearate, etc. The role of the surfactans is not only to stabilize formed particles, but also to produce reductive radicals in pyrolysis or hydrogen abstraction of OH radicals from surfactants. Particles with a smaller size could be obtained in a faster reduction rate with dilute metal cations concentration. Pt(IV) is consecutively reduced in two steps to Pt(0) via Pt(II). By comparing the sonolytical reduction with γ-ray radiolysis, two kinds of organic reducing radicals are proposed to contribute to the reduction. One (R_ab) is an intermediate radical which is produced by hydrogen abstraction of OH radical from surfactant and effective only on the reduction of Pt(II) to Pt(0). The other (R _py) is also an intermediate radical which is produced by thermal decomposition of surfactant at the interface between the cavity and bulk solution and effective on the reduction of Pt(IV) to Pt(II).