Evaluation of Silver Nanoparticle Size by Anodic Particle Coulometry and Optical Methods

Abstract

Silver nanoparticles (Ag NPs) with diameters in the range between 10 and 100 nm were synthesized in aqueous solution with the stepwise seed growth method. The average size and size distribution of the as-grown nanoparticles were measured in situ with Anodic Particle Coulometry (APC, also called faradaic nano-impact), an electrochemical method developed in recent years. In essence, in APC, the nanoparticles are oxidized at a constant potential for a few seconds. The oxidation and disintegration of the Ag nanoparticles on the electrode produce a series of distinctive current spikes on the curve of current versus time. The comparison of the particle sizes measured with APC and with dynamic light scattering (DLS) and UV-VIS spectroscopy shows that, under our experimental conditions, APC tends to overestimate the sizes of the smaller particles and underestimate the largest particles. The divergences can be explained in terms of the uncertainties in the charge measurements, in addition to possible lateral chemical oxidation reactions and fragmentation of the nanoparticles on the electrode.