Co-reduced Ag/Pd Bimetallic Nanoparticles: Surface Enrichment of Pd Revealed by Raman Spectroscopy

Abstract

In the hope of developing metal nanoparticles that are expected to possess simultaneously higher surface-enhanced Raman scattering (SERS) activity and also catalytic activity, we have prepared Ag/Pd alloy nanoparticles by coreduction of Ag and Pd ions using citrate and then examined their characteristics in terms of their composition. Ag/Pd(2% in atomic percent) particles, about 53 nm in diameter, are alloy-like, with their surfaces being composed of Ag and Pd atoms. Ag/Pd(5%) particles, about 29 nm in diameter, are also alloy-like, but their surfaces appear to be covered fully with Pd atoms of ∼2 nm thickness. The surface enrichment of Pd atoms were clearly identified by the SERS spectra of 2,6-dimethylphenylisocyanide, 4-nitrobenzenethiol, and 4-aminobenzenethiol, as well as by high-angle annular dark-field scanning transmission electron microscopy analysis, even though the presence of Pd atoms was hardly detectable by X-ray diffraction. Owing to the borrowing effect from Ag, the SERS activity of Ag/Pd(...