Bimetallic clusters by underpotential deposition on layered an nanoparticle films

Abstract

In this paper, we describe the well-defined underpotential deposition systems consisting of Cu, Ag, Pb, and Tl on layered gold nanoparticle (AuNP) thin films linked with bifunctional 1,6-hexanedithiol (HDT). Scanning electron microscopy informs the morphological Structures of layered AuNPs accumulated by stepwise immersion in citrate-stabilized AuNP and HDT solutions. Although cyclic voltammograms for typical Au oxide formation show that colloidal AuNP frameworks are polycrystalline, (I 11) reflection is the major character in X-ray diffraction measurements. As the AuNP layers are piled up on indium tin oxide, faradaic currents for the underpotential deposition adsorption increase linearly, indicating that entire AuNPs are electrochemically accessible; as a result, the mass transport and the electron transfer are plausible in AuNP frameworks. Voltammetric profiles of Ag on AuNP and Cu on AuNP exhibit similar features with those on the bulk metal film. On the other hand, heavy metal systems of Pb/AuNP and Tl/AuNP reveal more enhanced adsorption currents and particularly irreversible cyclic voltammograms which explicate their strong binding properties to AuNPs by the small size of the hydrated metal ions. This electrochemical approach gives an alternative route to the construction of bimetallic clusters. The potential cycling, X-ray photoelectron spectroscopy and scanning electron microscopy demonstrate that the bimetallic cluster of Ag or Cu on AuNPs is a core-shelled shape, while the bimetallic cluster of Pb or Tl on AuNPs forms an alloyed structure.