Dependence of Crystal Growth of Gold Nanoparticles on the Capping Behavior of Surfactant at Ambient Conditions

A seed-mediated approach was applied to synthesize gold (Au) nanoparticles (NP) by using twin tail alkylammonium cationic surfactants such as 12-6-12 and 12-0-12 as capping agents in aqueous phase at ambient conditions. The growth of Au NP was monitored by changing the amount of seed. Spherical NP (10–50nm) and nanorods (aspect ratio ) 2–3) were obtained in the presence of 12-6-12 as capping agent; their shape and size systematically deformed because of anisotropic growth with a decrease in the amount of seed. In contrast, when 12-0-12 was used as a capping agent, no anisotropic growth was observed. An effective liquid/solid interfacial adsorption of 12-0-12 prevented anisotropic growth which led to precise morphologies. This was not observed in the case of 12-6-12 because of the presence of a spacer which restricted an effective interfacial adsorption because of the steric factors. XPS and FTIR studies clearly indicated the presence of a surfactant film on the surface of Au NP, while XRD analysis demonstrated a difference in the preferential adsorption of 12-6-12 and 12-0-12 at different crystal planes of fcc geometry which resulted in a difference in their capping behaviors.