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(LII) an d Pd(II) ions in an aqueous solution of sodium tetrachloroaurate(III)d ihydrate and sodium tetrachloropalladate(II) were reduced by ultrasoun d irradiation in the presence of sodium dodecyl sulfate (SDS). In addi tion to the stabilizing effect, SDS remarkably enhanced the reduction rate, probably due to the thermal decomposition that occurs at the int erfacial region between cavitation bubbles and bulk solution and provi des reducing radicals. Transmission electron microscopy (TEM) photogra phs showed spherical particles whose size had a fairly narrow distribu tion with a geometric mean diameter about 8 nm and a geometric standar d 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 go ld and a shell of palladium, was confirmed by high-resolution TEM and X-ray diffraction.