Characterization and catalytic activity of core-shell structured gold/palladium bimetallic nanoparticles synthesized by the sonochemical method

This is a report regarding the preparation of nanosized gold/palladium bime tallic particles utilizing a cavitation phenomenon induced by irradiation o f high-intensity ultrasound in an aqueous solution of gold(III) and palladi um(II) ions. The particles are found to be composed of gold-core and pallad ium-shell by a transmission electron microscopic and nanoarea energy-disper sive X-ray spectroscopic analyses. Sodium dodecyl sulfate added to the samp le solution is found to be a stabilizer for the nanoparticles generated as well as an important source of reducing species for noble metal ions. The t hickness of a palladium shell and the size of a gold core seem to depend on the ratio of the concentrations of noble metal ions. The morphological dif ferences in the sonochemical and radiochemical products suggest that the fo rmation of a core-shell structure can be affected by the physical effects o f ultrasound, such as effective stirring, microjet stream, or shock wave du ring the collapse of a cavitation bubble. Bimetallic nanoparticles show hig her activities for the hydrogenation of 4-pentenoic acid than for those of the mixtures of monometallic nanoparticles with a corresponding gold/pallad ium ratio. When the gold/palladium ratio is 1:4, the activity of the bimeta llic particles is about three times higher than that of palladium monometal lic nanoparticles prepared under the same conditions.