Time-Resolved Ex Situ Kinetics of Au Nanoparticles by Alternating Voltage-Induced Electrochemical Synthesis

The kinetic and formation mechanism of gold nanoparticles obtained by an electrochemical method of alternating voltage and ascorbic acid as a supporting reductant is described. The reaction was monitored ex situ through UV-vis spectroscopy and high-resolution electronic microscopy. The UV-vis spectroscopy revealed an increase in the localized surface plasmon resonance at 540 nm, accompanied by a progressive decrease in the characteristic peak of ascorbic acid. Kinetic analyses derived from absorbance at 540 nm, concentration, and reaction rate indicated first-order kinetics. Additionally, morphological and size distribution monitoring by HR-TEM showed an increase in nanoparticle size from 5 to 35 nm as a function of reaction time, as well as the appearance of unusual anisotropies in nanoparticle morphology such as icosahedrons, octahedrons, cubes, and triangles with cubic crystallinity. The results provide critical information on kinetic and mechanistic aspects, highlighting the ability to control the size and diversity of anisotropic morphologies without the need for surfactants or multiple synthesis steps. This accentuates the potential of this method, often overshadowed by more conventional approaches, for the controlled synthesis of gold nanoparticles.