On a role of liquid intermediates in nucleation of gold sulfide nanoparticles in aqueous media

Abstract

Previously, we found a series of fluid nanoscale intermediates preceding nucleation of gold sulfide in the reaction between aqueous HAuCl₄ and sodium sulfide. Here, the effects of temperature, addition of an inert electrolyte and some other factors on characteristics of the “dense liquid” intermediates and the formation of solid nuclei were studied using UV-vis absorption spectroscopy, DLS, zeta-potential measurements, and SAXS. It was revealed, in particular, that the negatively-charged interfaces of the dense liquid species critically impede their fusion into large enough dense droplets in which nucleation can take place. The nucleation and following coagulation of poorly crystalline gold sulfide proceed not instantly but progressively as the dense liquid droplets arise, with the process being sharply accelerated by the injection of NaCl or temperature increase.