Abstract
We describe the formation of gold sulfide (Au 2 S) nanoparticle superstructures via hydrothermal synthesis approach at 175 °C using HAuCl 4 and Na 2 S reagents and cetyltrimethylammonium bromide (CTAB) surfactant. Uniform 2-4 nm Au 2 S nanoparticles were found to assemble into a densely packed lamellar phase structure, and the resulting material displays a cross-sheet-like morphology. The sheets are 125-250 nm in length and can be suspended in solution. XRD, TEM, and EDS characterization of the nanoparticle samples confirmed the composition of the nanoparticles as Au 2 S. Some isolated faceted gold nanoparticles were also observed. XPS data also support the formation of Au 2 S nanoparticles. UV-vis absorption spectra showed only absorption features from the Au 2 S nanoparticles, and an indirect band gap value of 1.77 eV was obtained. Sufficiently high concentrations of Na 2 S and CTAB in the reaction mixture were concluded to be necessary to promote the growth of Au 2 S nanoparticles, and reduce the production of gold nanocrystals. Maintenance of the superstructures after boiling in water suggests the absence of CTAB molecules on the particle surfaces. FT-IR, XPS, and NMR results indicate thermolysis of CTAB, and long alkyl chains interact with the Au 2 S nanoparticles and direct their assembly into a lamellar phase structure. © 2008 American Chemical Society.