Facile synthesis of bimetallic Cu–Ag nanoparticles under microwave irradiation and their oxidation resistance

Air-stable bimetallic Cu–Ag nanoparticles in the range of 12–30 nm have been synthesized at gram scale by a facile alcohol reduction in the absence of surfactants with the assistance of microwave irradiation. The synthesized nanoparticles were analyzed by x-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning TEM, ultraviolet–visible spectroscopy, x-ray photoelectron spectroscopy and thermogravimetry (TG). The stability of the bimetallic nanoparticles against oxidation was examined by TG and in situ temperature-programmed XRD analyses in the atmosphere. No oxidation of copper was confirmed by XRD after storing for longer than 6 months in the atmosphere at room temperature. No oxidation took place below 118 ° C and the Cu(200) diffraction peak decreased by only 7% after heating at 100 ° C for 30 min. The oxidation resistance has been ascribed to a Cu core–Ag shell structure, probably owing to the suppressive effect of Ag on the surface through the electronic interaction with Cu and a physical barrier of oxygen. (paper)