Synthesis and self-organization of Au nanoparticles

Abstract

Monodisperse (diameter 10 nm) Au nanoparticles have been synthesized by the reduction ofAuCl3 at high temperatures, in commercial oleyl amine, in the presence of tri-octyl phosphineoxide (TOPO). The oleyl amine molecule has multiple roles, acting as high-boiling-pointsolvent, capping agent and reducing agent. The Au nanocrystalline particles have beenstudied by powder x-ray diffraction (XRD) and transmission electron microscopy (TEM).The nanoparticles can disperse well in non-polar solvents such as hexane, toluene andchloroform. The as-received Au nanoparticles, capped with the alkylamine-TOPOmolecules, form two-dimensional superlattices via solvent evaporation. Moreover, they canbe converted into a water-soluble derivative via a simple procedure based on the formationof a physisorbed layer of an ionic (cationic or anionic) surfactant around the cappedsurface. The charged particles can assemble in aqueous solution into three-dimensionalstructures via electrostatic interactions.