Synthesis of Core-Shell (Pd-Au) Bimetallic Nanoparticles in Microemulsions

Abstract

Palladium-gold core-shell nanoparticles were synthesized in the aqueous domains of water in oil microemulsions by the sequential reduction of H₂PdCl₄ and HAuCl₄. The nanoparticles were characterized by ultraviolet-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM). The UV-vis spectra confirm the presence of palladium nanoparticles after reducing H₂PdCl₄. These particles have been used as seeds for the core-shell particles. UV-vis spectra show that, after reducing HAuCl₄, the surface plasmon absorption of the nanoparticles is dominated by gold, revealing the encapsulation of the palladium seeds. These results agree with crystallographic analysis performed with high-resolution TEM pictures, as well as with selected area electron diffraction. The TEM pictures show the core-shell nanoparticles with an average diameter of 9.1 nm, as compared with 5 nm for the palladium seeds, in good agreement with the used Pd:Au molar ratio.

Keywords:

• Core-shell
• microemulsions
• nanoparticles
• palladium-gold

Acknowledgments

E. R.-L. acknowledges a fellowship from Conacyt (Mexico). The TEM experiments were performed in the Laboratorio de Microscopía Electrónica of Universidad de Sonora.