Effect of SDS concentration on colloidal suspensions of Ag and Au nanoparticles

We present a kinetic study of the effects of sodium dodecyl sulfate (SDS) concentration on reduction and aggregation of Ag(+) and Au(3+) ions in aqueous solutions. There are distinct differences between the surface plasmon absorption bands of Ag nanoparticles at different concentrations of SDS. The results reveal the existence of two competing SDS-induced processes: stabilization of the Ag nanoparticles due to adsorption and aggregation of the Ag nanoparticles due to increase in ionic strength. However, SDS induced aggregation of Au nanoparticles is negligible because of less surface passivity as evident from eaq(-) reaction with AuCl4(-). Nevertheless, the average size of the Ag and Au nanoparticles remains almost similar at all SDS concentrations. UV-Vis spectrophotometry and transmission electron microscopy are used to characterize the nanoparticles. Moreover, it is shown that these SDS-capped Ag, Au and Au/Ag bimetallic nanoparticles could function as catalysts for the reduction of o-nitro aniline in the presence of NaBH4.