Synthesis and characterization of Au@Pt nanoparticles

Au_core-Pt_shell (Au@Pt) nanoparticles were synthesized at room temperature by reducing K₂PtCl₆ with hydrogen in the solution containing Au colloids and polyvinylpyrrolidone (PVP). The particles obtained were characterized with UV-Vis, TEM and XPS techniques. UV-Vis spectra show that the surface plasmon absorption feature of Au colloids is significantly reduced with increasing the amount of reduced Pt. TEM images that the metals are found always appear as spherical nanoparticles and their sizes grow apparently due to the reduction of PtCl₆^2- ions, indicating that Pt is deposited from solution onto Au particle surface and forms a Pt-layer with uniform thickness. In the XPS spectra, the signals of Au metal decrease due to the reductive deposition of Pt on the surface of the Au colloids. UV-Vis and XPS data are consistent in showing that when the amount of Pt in the AuPt colloids is increased to reach an overall atomic ratio of Pt/Au = 2, the Pt deposits form a shell covering completely the surface of Au particles, demonstrating the core-shell structure of the synthesized AuPt particles.