Chemical Kinetics of Gold Nanorod Growth in Aqueous CTAB Solutions

The chemical kinetics of the silver-mediated growth of gold nanorods prepared by the reduction of gold precursor in aqueous cetyltrimethylammonium bromide (CTAB) solution has been systematically studied using spectroscopic monitoring and electron microscopy. The rate of monomer depletion -d[Aun+]/dt has a linear dependence on both [Aun+] and seed nuclei concentration at 30 degrees C. Particle growth is significantly retarded by hexadecyltrimethylammonium bromide (CTAB) and KBr, with the order ca. -1 for [Br-]. The rate of nanoparticle growth is dependent on the reducing ascorbate monoanion concentration and is consequently highly pH dependent around the pK(a)(1) of ascorbic acid, while AgNO3 retards the observed kinetics for both the growth of nanorods from ca. 2 nm seed nuclei and the overgrowth of Au nanorods.