Phase-transfer identification of core-shell structures in bimetallic nanoparticles

On the basis of a combination of previously published experimental procedures, ultraviolet-visible spectroscopy, transmission electron microscopy, and energy-dispersive X-ray measurements, a systematic investigation was carried out on the phase-transfer characteristics of different bimetallic nanoparticles (Ag- Au, Ag-Pt, Ag-Ru, Au-Pt, Au-Ru, and Pt-Ru) formed by the seed-mediated growth reactions. The different phase-transfer characteristics of the monometallic nanoparticles of Au, Ag, Pt, and Ru were used to form the basis of differentiation between various possible structures existing in the bimetallic systems (core-shell particles or a physical mixture of nanoparticles). The experimental results indicate clearly the formation of core-shell nanoparticles of Ag- Au, Ag-Pt, Ru-Ag, Pt-Au, Au-Ru, and Pt-Ru when the nanoparticles of the first metal were used as the seeds in the seed-mediated growth reactions. However, when the order of the synthesis was reversed using the nanoparticles of the second metal as the seeds, only a physical mixture of the two metal nanoparticles was obtained instead.