In situ SR SAXS study of liquid intermediates arising during nucleation of gold sulfide nanoparticles in aqueous media
Recently, using DLS, AFM (both, in situ and ex situ), STM and SAXS techniques, we found a series of fluid nanoscale intermediates preceding nucleation of gold sulfide in the reaction between aqueous HAuCl4 and sodium sulfide. In present contribution SR SAXS technique was applied to monitor the size evolution of scatterers which are presented initially by “liquid clusters”. The “liquid clusters” were found to have a small negative charge and coalescence into larger species exhibiting negative zeta-potential of about 30-40 mV and associating to submicrometer aggregates. The nucleation and following aggregation of gold sulfide nanoparticles proceed progressively rather than instantly. The processes were accelerated critically by the addition of 0.05M NaCl solution or at elevated temperatures. On the onset of reaction single fraction sticky spheres model fits the experimental SAXS data satisfactorily. However, starting from some instance, the second (smaller in size) fraction needs to be taken into account to successfully describe the SAXS data, which means that SAXS can be used to get insights into the prenucleation and nucleation processes.Similiar results were taken for the process of hexachloroplatinic acid reduction by sodium sulfide.