Controlled Synthesis and Characterization of Rucore-Ptshell Bimetallic Nanoparticles

A combined polyol and redox-transmetalation strategy has been proposed to synthesize Ru-core-Pt-shell bimetallic nanoparticles. By following the in situ X-ray absorption spectroscopy (XAS) at the Pt L-III and Ru K edges, the reduction mechanism of Ru nanoparticles (NPs) in tetraethylene glycol (TEG) solutions and the corresponding reaction of Ru NPs with the added Pt2+ ions in ethylene glycol (EG) solutions to form Ru-core-Pt-shell bimetallic nanoparticles was examined. The Pt L-III-edge XAS indicates that when the pH of H2PtCl6 in EG solution is adjusted to 12 and heated at 80 degrees C for 5 min, the platinum compound is found to be reduced to a Pt(II) form corresponding to [PtCl4](2-) anionic species. At further reaction time of 10 min, the ligand environment around Pt(II) is changed from Cl- to OH- forming the [Pt(OH)(4)](2-) species. Analysis of the Ru K-edge XAS results confirms that Ru-3(CO)(12) in TEG undergoes a partial decarbonylation when it is heated at 300 degrees C for 30 min and forms Ru-3(CO)(9) species. At further reaction time of 60 min, Ru-3(CO)(9) species are subjected to a complete decarbonylation to form Ru clusters in TEG solutions. When the EG solution containing [Pt(OH)(4)](2-) ionic species is mixed with preformed Ru clusters, Pt2+ ions are reduced to Pt-0 on preformed Ru clusters at the expense of Ru via a redox-transmetalation process. The XAS structural parameters suggested that the resulting nanoparticles were of Ru-core-Pt-shell type structure with a higher extent of atomic distribution of Pt in the cluster when compared with Ru. The unique application of XAS as a fundamental characterization tool to realize the core-shell structure demonstrated here on the Ru-Pt bimetallic system can easily be extended to construct many other types of bimetallic systems for interesting applications.