Sonochemical Preparation of Bimetallic Nanoparticles of Gold/Palladium in Aqueous Solution

Colloidal dispersions of bimetallic nanoparticles composed of gold and palladium were prepared by a sonochemical method, in which Au(III) and Pd(II) ions in an aqueous solution of sodium tetrachloroaurate(III)dihydrate and sodium tetrachloropalladate(II) were reduced by ultrasound irradiation in the presence of sodium dodecyl sulfate (SDS). In addition to the stabilizing effect, SDS remarkably enhanced the reduction rate, probably due to the thermal decomposition that occurs at the interfacial region between cavitation bubbles and bulk solution and provides reducing radicals. Transmission electron microscopy (TEM) photographs showed spherical particles whose size had a fairly narrow distribution with a geometric mean diameter about 8 nm and a geometric standard deviation of 1.1. Analyses with UV−vis spectra indicated that Au(III) ions were first reduced and after their consumption reduction of Pd(II) ions set in. A core−shell structure of the particles, a core of gold and a shell of palladium, was confirmed by high-resolution TEM and X-ray diffraction.