E. Méndez, S. Botasini
Universidad de la Republica Uruguay,
Keywords: gold nanoparticles, synthesis, DLS, mechanism
Summary:In the past few decades, much effort was made to understand the mechanism of the synthesis of gold nanoparticles. Several models emerge, with LaMer's theory being the most accepted. Despite that, some other authors challenge this model. For instance, several authors reported that large aggregates of gold nanoparticles were observed at the initial of the synthesis of gold nanoparticles which in contradict the idea of the formation of small seed as proposed in the nucleation theory. This finding was also verified by other authors as well, and supported by TEM microscopy and UV-Vis experiments. However, other authors attribute these observations to artefacts during the TEM preparation. It is also relevant to note that USAXS / XANES experiments do not reveal large particles at the beginning of the syntheses. In the present work, we present a new explanation for both previous findings, showing a new insight towards the understanding of the synthesis mechanism supported by UV-Vis and DLS in real-time. We found that effectively ultra-small particles appeared in the initial step, attributed to the seeds, but they tend to form clusters of larger size without losing its identity. This clusters appeared to be large particles and could explain the observation seen by DLS, UV-Vis and TEM. These large aggregates seen at the initial step of the synthesis is progressively divided into the final product. The large aggregates affect plasmon resonance as well as light scattering, but there are not observed by XANES since the small particles are rather aggregated than coalesced. In addition, our model provides a new vision on how to control the synthesis parameters to form narrow size nanoparticles.