Real-time SAXS and ultraviolet-visible spectral studies on size and shape evolution of gold nanoparticles in aqueous solution

Gold nanoparticles were synthesized with seed mediated wet growth method. A coexistent system with gold nanorods and nanospheres was prepared. In-situ real-time small angle X-ray scattering (SAXS) and ultraviolet-visible (UV-vis) absorption were used to monitor the growth process of Au nanoparticles in the aqueous solution. Combining SAXS measurement and UV-vis spectra, the contribution of gold nanorods was separated from that of gold nanospheres. The growth behavior of the gold nanorods and the gold nanospheres was studied. The size and shape evolution of both gold nanoparticles as well as their volume fractions were obtained. After adding the seed-solution into the growth solution to form a particle suspension, within the first 18 min, a mutual competitive growth occurred between the gold nanorods and nanospheres. And their average particle sizes always increased with growth time. 18-min later, the evolution of size and shape of gold nanoparticles was almost stopped. The results demonstrate that the aspect ratio of gold nanorods in the particle suspension follows an exponential decay change after the initial 5-min growth. The evolution process of size and shape of gold nanoparticles in the particle suspension has been discussed. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010