Synthesis of Pt/Ag bimetallic nanoparticles in water-in-oil microemulsions

The synthesis of Pt/Ag bimetallic nanoparticles at various molar ratios by simultaneous reduction of H2PtCl6 and AgNO3 with hydrazine in the microemulsions of water/AOT/isooctane at 25 °C was investigated. TEM photographs show that the Pt/Ag bimetallic nanoparticles essentially are monodispersed and have a negative deviation in the mean diameters. Both the UV–vis absorption spectra and XRD patterns suggest the formation of bimetallic nanoparticles. The EDX analysis on the individual particle confirms the presence of two metals in a particle. Also, the composition for each particle is roughly consistent with that of feeding solution. According to the EDX and XPS measurements, the bimetallic nanoparticle structure should be homogeneous alloy. All the analyses suggest that the reduction of PtC l 6 − 2 and Ag+ ions is almost finished before the formation of nuclei, the size of the bimetallic nanoparticles is determined by the number of the nuclei formed at the early state of reaction, and the nuclei for the bimetallic system might be composed of Pt and Ag.