Preparation of Pd/Pt bimetallic nanoparticles in water/AOT/isooctane microemulsions

Bimetallic nanoparticles of I'd and Pt at various molar ratios have been pr epared by the coreduction of H2PdCl4 and H2PtCl6 with hydrazine in water/AO T/isooctane microemulsions at 25 degreesC. The size, structure, and composi tion of the resultant nanoparticles were characterized by TEM, XRD, EDX, an d XPS. It was shown that the bimetallic nanoparticles obtained at feeding c ompositions of [H2PdCl4]/[H2PtCl6] = 9/1 similar to 1/9 were essentially mo nodispersed and that their mean diameters with a positive deviation were in the range of 7 similar to 11 mn. The bimetallic nanoparticles had a homoge neous alloy structure except when the molar ratio of Pd/Pt was above 9/1. A lso, the composition for each particle was roughly consistent with that of the feeding solution. Furthermore, the characterization and formation kinet ics of the particles suggested that the reduction of PtCl6- and PdCl4-2 ion s was finished before the formation of nuclei , the nucleation rate of Pd w as much faster than that of Pt, the size of bimetallic nanoparticles was de termined by the number of the nuclei formed at the beginning of reaction, a nd the nuclei for a bimetallic system might be composed of I'd and Pt. Acco rding to these, a formation process for Pd/Pt bimetallic nanoparticles was suggested. (C) 2001 Academic Press.