(Invited) Cyclic Voltammetry of Gold Nanoparticles: Comparative Analysis of Redox, Electronic and Optical Properties

Abstract

It has been reported that cyclic voltammetry (CV) can be a useful tool for the electrosynthesis of gold nanoparticles (AuNPs) from AuCl4 - solutions in the presence of different protective (surfactant) agents. However, the use of this electrochemical analytical tools for the characterization of electroactive nanomaterials has been scarcely explored. In this work, cyclic voltammetry has been used to characterize the redox properties of AuNPs with controlled sizes and almost monodisperse, previously synthesized by chemical reduction of AuCl4 -in aqueous solutions, in the presence of two different surface protective agents (citric acid and tartaric acid). For the CV characterization, the as prepared AuNPs colloidal solution were used without addition of any supporting electrolyte. A typical three electrode system was used, with a glassy carbon electrode as a working electrode, a platinum wire as the counter electrode and a Ag/AgCl (KCl sat) electrode as reference. The potential window was scanned from +0.4 V to +0.95 V and ended at 0.25 V, at a scan rate of 1.0 Vs-1. Nanoparticles size distribution and zeta potential (ζ) were previously characterized by dynamic light scattering (DLS) in aqueous suspensions, while precise size and morphology analyses were performed using high-resolution scanning electron microscopy (HR-SEM) in a MAIA Tescan FESEM. The UV-VIS surface plasmon resonance spectrum of the AuNPs was obtained by UV-Vis spectroscopy in water. The nanoparticles chosen for this electrochemical analysis, which were nearly monodispersed, had average sizes of 15 and 40 nm and an almost spherical morphology. Their electrochemical behavior showed an irreversible oxidation peak at +0.7 V and it was observed that the generated current and potential was dependent of nanoparticle size: the 40 nm AuNPs showed a higher oxidation potential than those AuNPs with an average diameter of 15 nm. The current evolved during cycling the AuNPs solution. A comparative analysis of redox properties and other physical properties (plasmon energy, size distribution) will be discussed in this work.