Preparation of Agcore/Aushell bimetallic nanoparticles from physical mixtures of Au clusters and Ag ions under dark conditions and their catalytic activity for aerobic glucose oxidation

AgAu bimetallic nanoparticles (BNPs), one of the most extensively studied bimetallic systems in the literatures, could have various structures and compositions depending on their preparation conditions. In the present work, catalytically highly active PVP-protected Ag-core/Au-shell BNPs of about 2.5 nm in diameter were fabricated from physical mixtures of aqueous dispersions of Au nanoparticles and Ag+ ions under dark conditions without using any reducing agents. The prepared Ag-core/Au-shell BNP colloidal catalysts, which possessed a high activity for aerobic glucose oxidation, were characterized by Ultraviolet-visible spectrophotometry (UV-Vis), Inductive coupled plasma emission spectrometer (ICP), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Energy disperse spectroscopy (EDS) in High-resolution scanning transmission electron microscopy (HR-STEM). The highest activity (11,360 mol-glucose h (1) mol-metal (1)) was observed for the BNPs with the Ag/Au atomic ratio of 1/9, the TOF value of which is about two times higher than that of Au nanoparticles with the particle size of 1.3 nm. The enhanced catalytic activity of the prepared Ag-core/Au-shell BNPs compared to Au NPs can be ascribed to the presence of negatively charged Au atoms resulted from electron donations from neighboring Ag atoms and PVP due to electronic charge transfer effects. XPS measurements as well as electronic structure calculation based on the density functional theory have revealed that the Au atoms are indeed negatively charged. (C) 2013 Elsevier B. V. All rights reserved.