Gold Bulletin最新文献

This work presents a new and simple procedure for the shape selective purification of gold nanorods from a mixture of rods and spheres. Previously reported methods were time-consuming and revealed several drawbacks such as low yields and difficulty to recover the purified nanoparticles. Additionally, they were mostly applied to high aspect ratio (AR) nanorods. Our process is based on only simple and short centrifugation steps in order to precipitate specifically gold nanospheres. Samples containing low AR nanorods (AR?<?6) were selected to perform the purification process. The supernatant content was followed by UV-Visible absorption spectroscopy after each centrifugation step. Then, transmission electron microscopy (TEM) allowed extract the purification efficiency thanks to shape analyses performed on more than 1000 nanoparticles. These results showed that our centrifugation process was applied successfully to three sizes of nanorods (2.4, 3.7, and 5.3). High purification yields of 72 and 78% were attained for AR?=?3.7 and AR?=?5.3 nanorods, respectively.

Gold ball bonding wires of 2N purity were bonded to Si devices with aluminium alloy bond pad metallisation. Specimens were subjected to isothermal annealing at 175?°C in a fan-circulated oven in an air environment for various times t. Samples of ball bonds from each specimen were cross-sectioned, and the total intermetallic thickness x at the centre of the ball bonds was measured. The kinetics of x versus t were modelled using a power law expression ( x(t)={x}_0+{theta}_1{t}^{theta_2} ) with growth parameter θ ₁ and constrained parameter 0?<?θ ₂?≤?1. The parameter θ ₂ is supposedly capable of differentiating between diffusion controlled intermetallic growth (grain boundary and/or volume diffusion) and interfacial reaction controlled growth with the presence/absence of grain growth solely based on its numerical value. The parameters θ ₁?and θ ₂ and the regression function were obtained by log-transformation of both the response variable x and the explanatory variable t and data fitting using simple linear regression (SLR), taking care to perform diagnostic checks to confirm that transformed data satisfied the requirements of SLR. Simulated intermetallic thickness data obtained by sampling from lognormal distributions was observed to closely approximate the experimental observations. Values of the exponent θ ₂ were observed in the range 0.2–0.4, which was interpreted as indicative of grain boundary dominated interdiffusion with grain growth.

Perovskites (ABO₃ structures), which can be manipulated by partial substitution, are reported to be active supports for CO oxidation, but only at high temperatures, with no activity being shown for temperatures below 200?°C. In this study, these perovskites were investigated at low temperatures (below 100?°C) with improved activity found upon gold deposition. The presence of gold nanoparticles therefore significantly enhanced the catalytic activity, while the support itself was suspected to be involved in the reaction mechanism. A series of perovskites of the type ABO₃ (LaMnO₃, LaFeO₃, LaCoO₃, and LaCuO₃) were prepared using the citrate method, while the gold was deposited on them using the deposition-precipitation method. The supports were calcined at different temperatures for optimization. With the support calcined at 800?°C, the best catalyst was 1?wt% Au supported on LaFeO₃. Calcium-doping of this system showed decreased surface area, poorer crystallinity, and a drop in catalytic activity relative to the Au-LaFeO₃. In addition, Au-LaFeO₃ showed online stability over 21?h. Calcining the support improved the incorporation of gold nanoparticles into the perovskite lattice, resulting in superior catalytic activity. Nevertheless, at higher calcination temperatures, the catalytic activity of Au-CaTiO₃ was depressed while that of Au-LaFeO3 was enhanced. XPS revealed that in the active catalysts, both cationic and metallic gold coexisted, while in the inactive catalysts, the gold existed predominantly either as cationic or metallic gold.

We present a novel one-pot synthesis of stable water dispersible multi-branched anisotropic gold nanoparticles using hydrazine as the principal reducing agent and chitosan as the secondary reducing agent, growth directing agent and stabilizer. They are colour tuneable in the purple to blue range due to the presence of both transverse and longitudinal overlapping localized surface plasmon resonance (LSPR) absorptions arising from the multi-branched nanoparticle morphology. The longitudinal LSPR absorbance tails into the near IR range. This provides a simple alternative approach to producing anisotropic gold nanoparticles.

Foot-and-mouth disease is an acute, highly contagious infection of domestic and wild cloven-hoofed animals, which can be transmitted to humans. In many cases, the existing vaccines are not quite effective. The purpose of this study was to test the possibility of using gold nanoparticles as an antigen carrier and an adjuvant. The immunogenic properties of gold nanoparticles were assessed by conjugating the particles to a synthetic peptide of the VP₁ capsid protein of the foot-and-mouth disease virus. The resulting conjugate (with or without the use of complete Freund’s adjuvant), a commercial vaccine, and the native peptide served to immunize guinea pigs. The titer and sensitivity of the raised antibodies were maximal for the combination comprising the nanoparticle–peptide conjugate and complete Freund’s adjuvant. Antibody biosynthesis was accompanied by increased production of proinflammatory cytokines (especially IFN-γ) and by stimulation of the respiratory activity of peritoneal macrophages. The use of gold nanoparticles as a hapten carrier enhanced the immune response even when complete Freund’s adjuvant was not used.

A new way to elaborate coloured carat gold materials has been developed. Instead of using traditional metallurgy route, we built a new 18-K bulk material using nanostructured gold particles. The resulting colour is the consequence of a well-known property of gold nanoparticles: the surface plasmon resonance effect. Depending on the chemical environment around the nanoparticles, their shape and size, it is possible to tune the colour of gold. Thanks to this property, it is possible to obtain a large panel of colours not achievable via conventional alloying route. Here, we focus on one hybrid nanostructured material: Au-SiO₂. The development of a new synthesis route enables us to obtain nanostructured micrometric powders that can then be pressed to obtain a bulk material. The resulting nanocomposites are characterized by means of energy-dispersive X-ray spectroscopy (EDX), fire assay, TEM and spectrophotocolorimetry. All these characterizations have shown that our composites exhibit a gold content superior to 75?% by weight and have a much more vivid colour than classical coloured gold. The new composites are therefore deeply coloured 18-K materials.

Hierarchically organized γ-Al₂O₃ hollow microspheres were prepared via a hydrothermal method using potassium aluminum sulfate and urea as reactants. The corresponding Au/Al₂O₃ catalysts were obtained using a deposition-precipitation (DP) method. The effect of the pretreatment under different atmospheres (N₂, air, and H₂) on the activity and stability of the Au/Al₂O₃ catalysts in CO oxidation was investigated. The results showed that the pretreatment under H₂ atmosphere improved the low-temperature CO oxidation activity. Furthermore, a 50?h long-term test at 30?°C showed no significant deactivation for the H₂-pretreated catalyst. Moreover, the catalytic activity was promoted by H₂O vapor in all cases, and the H₂-pretreated catalyst exhibited a good tolerance in the co-presence of CO₂ and H₂O. Finally, oxygen temperature-programmed desorption (O₂-TPD) and in situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) revealed that the reductive atmosphere pretreatment greatly improved the CO adsorption capacity and facilitated the oxygen activation.

The hardening effect of the pre- and post-firing heat treatments and their dual treatment was examined for a firing-simulated Au-Pd-In metal-ceramic alloy to determine if an additional post-firing heat treatment is effective in the hardening of an Au-Pd-In metal-ceramic alloy as well as to compare the hardening effects of pre- and post-firing heat treatments for a firing-simulated Au-Pd-In metal-ceramic alloy. The post-firing heat treatment was much more effective than the pre-firing heat treatment or dual treatments. The hardening effect of the pre- and post-firing heat treatments was caused by the induction of fine grain interior precipitation. In the pre-firing heat-treated specimen after casting, the apparent hardening was achieved during simulated porcelain firing, but an additional post-firing heat treatment did not introduce severe grain interior precipitation, resulting in very weak hardening. In the as-cast specimen without the pre-firing heat treatment, apparent hardening by grain interior precipitation was achieved only by post-firing heat treatment and not by simulated porcelain firing.