Synthesis of gold nanoparticles in a Winsor II type microemulsion and their characterization

Dodecanethiol-capped nanospherical gold metal particles have been synthesized using a biphasic Winsor II type microemulsion of diethyl ether/aerosol-OT/water. The reduction of gold(III) chloride in the presence of dodecanethiol results in the formation of stable, organically soluble nanoparticles of 4+/-0.6 nm average diameter. The UV-vis plasmon absorption band and transmission electron microscopic (TEM) analysis confirmed the formation and size of the particles. TEM morphology shows a two-dimensional array of these particles with an average spacing between gold cores of about 1.8 nm onto hydrophobic carbon surfaces. Elemental analysis results and the similarity of the Fourier transform infrared (FT-IR) spectrum of free dodecanethiol to that of composite material reveal the encapsulation of gold particles by dodecanethiol. The detailed analysis of FT-IR spectra of our composite material and its comparison with literature reports disclose that a Winsor 11 type system is superior for the synthesis of nanoparticles bounded by, a three-dimensional self-assembled monolayer of alkanethiol with a close-packed all trans zigzag conformation. H-1 NMR spectroscopic observations suggest the absence of free thiols. X-ray photoelectron spectroscopic analysis supports that the oxidation state of gold is zero (Audegrees). Thermogravimetric and differential thermal analysis indicates an interaction between thiol group and gold surfaces and thiol molecule per nearly three gold atoms in the composite particles. (C) 2002 Elsevier Science (USA).