Study on the sonochemical preparation and phase stability of binary alloy nanoparticles from aqueous solution

Binary alloy nanoparticles of Au/Pd and Au/Pt were prepared by a sonochemical method. Three kinds of noble metal complexes (NaAuCl4, PdCl2 and H2PtCl6) and surfactants were simultaneously reduced in argon-saturated aqueous solution by ultrasound irradiation. The obtained colloidal dispersions were stable for more than several months in the presence of surfactant. Nanoparticles synthesized under various conditions were characterized and their phase stability was examined by electron microscope observations. The particle size was on the order of ten nanometers or lower. It was found that the fine particle structure of Au/Pd nanoparticles depends on surfactants. Electron diffraction patterns of in situ annealed Au/Pd nanoparticles exhibited that the order-disorder transition took place at a temperature lower than that expected from the phase diagram.