New pathway for the synthesis of ultrafine silver nanoparticles from bulk silver substrates in aqueous solutions by sonoelectrochemical methods

Abstract

Ultrafine silver nanoparticles with diameters less than 2 nm were first prepared in 0.1 M HCl aqueous solutions without addition of any stabilizer by sonoelectrochemical methods from silver substrates. First, an Ag substrate was cycled in a deoxygenated aqueous solution containing 0.1 M HCl from −0.30 to +0.30 V vs Ag/AgCl at 5 mV/s with 30 scans. After that Ag- and Cl-containing complexes were found existing in this aqueous solution. Then the Ag working electrode was immediately replaced by a Pt electrode and a cathodic overpotential of 0.2 V was applied under sonication to synthesize Ag nanoparticles. The resulting Ag nanoparticles are too small to exhibit any surface plasmon absorption, as illustrated in the UV–Vis absorption spectrum. An interesting phenomenon was also found from X-ray photoelectron spectroscopy (XPS) analyses that the binding energy of the prepared Ag nanoparticles shifts towards a higher value by ca. 0.2 eV, as compared with that of the employed Ag substrates. Furthermore, the particle sizes of the prepared Ag nanoparticles can be increased from less than 2 to 20 nm by increasing the cathodic overpotential applied from 0.2 to 0.8 V.