Tunable platinum-ruthenium nanoparticle properties using microwave synthesis

Stable polymer coated platinum-ruthenium nanoparticles were prepared. The effects of several preparation parameters have been studied in view of optimizing the particles' composition and structure characteristics. Solutions of hexachloroplatinic acid and ruthenium chloride in ethylene glycol were reduced at 173 degreesC in the presence of poly(N-vinyl-2-pyrrolidone) with rapid refluxing in a commercial microwave system. These nanoparticles form stable colloidal solutions in ethanol for several months without any precipitation. Transmission electron microscopy (TEM) analysis revealed the presence of metallic clusters with a uniform size of about 2-3 nm. Photo-correlation spectroscopy (PCS) measurements revealed an average hydrodynamic particle size of about 10 nm. X-Ray photoelectron spectroscopy (XPS) indicates that most of the Pt and Ru atoms are in reduced metallic state. X-Ray diffraction (XRD) revealed alloyed single-crystal clusters with diameters barely smaller than corresponding TEM measurements. The above TEM, PCS, XPS and XRD observations converge on a simple picture of monodisperse, uniformly alloyed Pt-Ru nanoparticles with uniform diameters in the range of 2-3 nm for the PVP-coated samples. Their compositions are comparable with the metal content of the reactants. The PVP layer is less than 7 nm thick, and probably very porous. In the absence of PVP, agglomerated, larger nanoparticles were obtained with a Pt-rich core and Ru-rich shell.