Kinetics and mechanism of gold nanoparticle growth studied via optical extinction spectroscopy and computational modeling

The successful design of nanoparticle synthesis protocols requires insight from mechanistic models, whose development relies on the availability of experimental data. For this purpose, optical extinction spectroscopy (OES) is rarely used in spite of being significantly less expensive and widely available when compared to frequently used synchrotron-based techniques. In this study, we developed protocols for the application of in situ OES to study the kinetics of gold nanoparticle (GNP) growth, serving as a model system. Spectra collected under six different experimental conditions were regressed using a physical model, built on extensive previous observations, calculating extinction by ensembles of GNPs. We considered the average size and shape of particles, and the possible electromagnetic interactions between them using a retarded effective medium theory. We identified the role of nucleation accompanying particle enlargement, the latter occurring via both molecular growth and aggregation. We further discovered instances of peptization consistent with previous experimental evidence.