Hydrothermal Synthesis of Free-Floating Au₂S Nanoparticle Superstructures

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.

Self‐Assembled Monolayer Stabilized Gold‐Vanadate Nanoflute for Water Splitting Reactions

“…The high shifting of the band approximately to 780 nm suggested for aurophillic (Au−Au) interaction observed in such type of gold‐thiol clusters . The band gap was calculated using Tauc's formula (αυh) 2 =A (hυ‐E g ) and was estimated to be 2.67 eV (see the inset, Figure S1d) . Thus from the above analyses of the compound it was established that the TGA coordinated to both Au and V through sulphur and carboxylate unit, respectively.…”

“…The presence of lattice vibrational bands in the FIR (318 and 354 cm −1 for VO 4 bending and 205 and 182 cm −1 for Au 2 S lattice vibration) and also in Raman spectrums (324 and 366 cm −1 for VO 4 and 234 and 182 cm −1 for Au 2 S)— strongly suggested for the stabilization of Au NPs via the TGA bound to vanadium (V) (Figure S1b and S1c). Furthermore, the presence of intense ‐CH 2 vibrational bands in the region of 2853 to 2955 cm −1 (see the inset, Figure S1a) also confirmed for the coordination of TGA with the two metal centres …”

“…The peaks at 2θ values in degrees 38.1, 44.2, 64.5 and 77.5 were the characteristic of gold nanoparticles (Au NPs) . The formation of Au 2 S was also confirmed with the appearance of peaks at 31.4, 35.1, 51.3, 60.8 and 62.1(Figure d, red line) . In addition to Au/Au 2 S, the peaks for VOx units were also observed at 2θ values 24.1, 27.1, 29.2, 32.5, 36.3, 40.8, 49.5, 58.5 and 68.1 (Figure d) .…”

Trichloroacetic acid assisted synthesis of gold nanoparticles and its application in detection and estimation of pesticide

“…The XRD pattern of the GNP shown in Figure 5(A) indicates the face centered cubic (fcc) structure of the bulk gold having peaks at 38.175o, 44.525o, 64.675o, 77.675o and 81.825o corresponding to (111), (200), (220), (311) and (222) planes, respectively. In literature we find Au2S shows peaks near 31o, 35.5o, 51.5o, 61.5o and 65o in XRD (Kuo & Huang 2008). The XRD spectrum of the GNP after reaction with methyl parathion are shown in Figure 5(B) and it is visible that the spectrum has all peaks due to Au as well as some additional peaks at 50.5 o, 60.06o and 64.5 o which may be attributed to the Au-S co-ordination bond.…”

Contrasting Surficial Composition of Native Gold from Two Different Types of Gold Ore Deposits

“…Even thermodynamically-unstable gold (I) sulfide is known to form in hydrothermal conditions at 175 • C [26]. The existence of gold and silver sulfides, which are thermodynamically stable at relatively low temperatures [12,27] at epithermal deposits of different genesis does not, therefore, seem surprising.…”