Determination of the Stability Constant of the Intermediate Complex during the Synthesis of Au Nanoparticles Using Aurous Halide

Little is known about the chemical equilibrium formed between the micellar complex of oleylamine and aurous halide during the synthesis of Au nanoparticles employing an Au(I) precursor. In this paper, we determine for the first time the stability constant of the intermediate oleylamine/Au complex during the first stages of the reaction that produces Au nanoparticles using an amine compound as a reducing agent. We found that the intermediate complex has two stability constants that were dependent on the concentration of AuCl. These results were supported by Fourier transform infrared and mass spectroscopy analysis, which indicated that an unstable secondary amine was produced during the oxidation of oleylamine and reduction of Au(I). Our findings demonstrate that the reduction of Au(I) species promotes substeps of structural changes in the oleylamine molecule. We anticipate our assays to be a starting point for a more comprehensive understanding of the synthesis of Au nanoparticles based on a templateless approach employing amines and a Au(I) precursor.