Formation of gold nanoparticles during the reduction of HAuBr4 in reverse micelles of oxyethylated surfactant: Influence of gold precursor on the growth kinetics and properties of the particles

The growth kinetics of gold nanoparticles (NPs) during the reduction of HAuBr4 by hydrazine in the reverse micelles of oxyethylated surfactant Tergitol NP 4 was studied in situ by UV-vis spectroscopy. Kinetic mechanism includes the steps of slow, continuous nucleation and fast, autocatalytic surface growth. Both steps are under kinetic control of the precursor reduction. The rate of nucleation is limited by reaction in the droplets of the aqueous phase forming the cores of reverse micelles, and growth rate is limited by the reaction on the surface of gold NPs growing inside the micelles. The chemical mechanism of reduction of halogenated forms of gold AuX4(-) by hydrazine is the same in the case of X = Cl, Br and includes the equilibria of formation and redox decomposition of the intermediate complexes Au-III(N2H4)X-3 and Au-I(N2H4)X. The initial form of AuX4- (X = Cl, Br) does not affect the size of the final NPs synthesized in micellar solution of oxyethylated surfactant.