Green and facile synthesis of Pd-Pt alloy nanoparticles by laser irradiation of aqueous solution

Solid-solution palladium-platinum (Pd-Pt) alloy nanoparticles (NPs) with fully tunable compositions were directly fabricated through high-intensity laser irradiation of an aqueous solution of palladium and platinum ions without using any reducing agents or thermal processes. Transmission electron microscopy (TEM) observations showed that nanometer-sized particles were fabricated by laser irradiation of mixed aqueous solutions of palladium and platinum ions with different feeding ratios. The crystalline nature of the NPs was precisely characterized by X-ray diffraction (XRD). Despite the fact that, for the bulk systems, a pair of XRD peak was detected between the palladium and platinum peaks because of the large miscibility gap in the Pd-Pt binary phase diagram, only a single XRD peak was seen for the Pd-Pt NPs fabricated in the present study. Moreover, the peak position shifted from that of pure palladium towards platinum with increasing fraction of platinum ions in solution. Consequently, the interplanar spacings of the alloy NPs agreed well with the estimated values obtained from Vegard's law. These observations strongly indicate the formation of solid-solution Pd-Pt alloy NPs with fully tunable compositions. This technique is not only a "green" (environmentally-friendly) and facile process, but is also widely applicable to other binary and ternary systems.