Size-controlled synthesis of gold nanoparticles from bulk gold substrates by sonoelectrochemical methods

Size-controlled gold nanoparticles, ranging from 2 to 15 nm in diameter, were first prepared from gold substrates in 0.1 N HCl aqueous solutions without the addition of any stabilizers by sonoelectrochemical methods. First, an Au substrate was cycled in a deoxygenated aqueous solution containing 0.1 N HCl from -0.28 to + 1.22 V vs Ag/AgCl at 500 mV/s with 100 scans. The durations at the cathodic and anodic vertexes are 10 and 5 s, respectively. After this process, Au- and Cl-containing complexes were left in the solution. The Au working electrode was then immediately replaced by a Pt electrode, and cathodic over-potentials of 0.2, 0.4, and 0.6 V from the open circuit potential (OCP) of ca. 0.82 V vs Ag/AgCl were applied under sonification to synthesize Au nanoparticles. The prepared nanoparticles increase in size from 2 to 15 nm with the increase of the cathodic overpotential applied from 0.2 to 0.6 V. Furthermore, the ratio of Au nanoparticles to Aucontaining nanocomplexes in solutions can be controlled by adjusting the sonoelectrochemical reduction time.