Green-Chemical Synthesis of Monodisperse Au, Pd and Bimetallic (Core–Shell) Au–Pd, Pd–Au Nanoparticles

Abstract

Gold and palladium nanoparticles as well as bimetallic AucorePdshell and PdcoreAushell nanoparticles were synthesized at 25 � C from aqueous solutions of Au(III) and Pd(II) species using ascorbic acid as reducing agent. The optical properties of these nanoparticles were assessed by UV-Vis absorption spectroscopy. Gold nanoparticles in aqueous solution exhibit a well defined absorption band whose maximum and position depends on the initial concentration of ascorbic acid. UV-Visible spectra of bimetallic Au–Pd nanoparticles suggest a core–shell structure. A surface plasmon band around 520 nm indicates the formation of a gold layer on the surface of pre-formed palladium nanoparticles, while the absence of this band when Au(III) and Pd(II) species are coreduced indicates the formation of a palladium layer on a core of gold. Particle shape and size distribution were assessed from transmission electron micrographs, whereas the average particle size was calculated from image analysis of these micrographs. For a fixed concentration of Au(III) species, the size distribution and average size of gold nanoparticles depends on the ascorbic acid concentration. The synthesized Pd nanoparticles exhibit flower-like shape.