Composition Of Au Research Articles

Catalytic activity of Au–Pd/KIT-6 catalysts on the formic acid decomposition: investigation of calcination temperature and Pd:Au composition

Catalytic activity of Au–Pd/KIT-6 catalysts on the formic acid decomposition: investigation of calcination temperature and Pd:Au composition

Dual-cluster interpretation of Au–Sn binary eutectics and solders

Au–Sn alloy is an important high-temperature solder, but it has some disadvantages such as high cost and brittleness. Multicomponent alloying is often performed to improve performance and reduce their cost. However, due to the absence of an atomic structure model, there has been a lack of effective theory to guide their composition design. Since Au–Sn solders are typically eutectic-based, understanding the Au–Sn eutectic at the atomic level is of great significance for clarifying the composition origin of Au–Sn solders and the subsequent multi-component composition design. In the present work, the short-range order of Au–Sn eutectics is characterized using a dual-cluster model. In the dual-cluster formulism, the two eutectics Au69.6Sn30.3 and Sn94.6Au5.4 at. % are interpreted in terms of the hypoeutectic [SnAu12]Sn2Au3 + [Au–Au2Sn6]Au3 = Au70.0Sn30.0 and [Au–Sn8]Au1 + 2{[Sn–Sn10]Sn5} = Sn95.2Au4.8 alloys, respectively. The compositions of Au–Sn solders are then analyzed based on the interpreted dual-cluster formulas, which indicate that the number of atoms of the alloying elements that replace the atoms in the dual-cluster formulas is always an integer. The present method provides a quantitative approach toward developing a practical composition interpretation and design tool for Au–Sn-based solders.

Synthesis of AuPt Bimetal and its Catalytic Properties in Ethanol Electrooxidation Reaction

AuPt Bimetal has been successfully synthesized by electrodeposition method with potentiostat technique. By varying the concentration of Au ions in the solution they are able to control the morphology and composition of the synthesized sample. The morphology obtained from the AuPt synthesis is cauliflower. The effect of Au ion concentration in solution on the catalytic performance of AuPt, the greater the Au concentration, the greater the current density in the electrooxidation reaction. In addition, the concentration of Au ions in the solution affects the results of the deposition of Au and Pt elements. In the study of AuPt nanocatalysts with a 0.4 mM Au ion concentration in an electrolyte solution, it was shown to have good catalytic activity in the ethanol electrooxidation reaction, with the resulting current densities and If/Ib of 10.1 mA/cm2 and 43.53 mA/cm2, respectively. This is an implication of many Au compositions which are known to have the ability to absorb and oxidize CO to encourage an increase in current density and increase its catalytic activity.

ZnO-Au Hybrid Metamaterial Thin Films with Tunable Optical Properties

ZnO-Au nanocomposite thin films have been previously reported as hybrid metamaterials with unique optical properties such as plasmonic resonance properties and hyperbolic behaviors. In this study, Au composition in the ZnO-Au nanocomposites has been effectively tuned by target composition variation and thus resulted in microstructure and optical property tuning. Specifically, all the ZnO-Au nanocomposite thin films grown through the pulsed laser deposition (PLD) method show obvious vertically aligned nanocomposite (VAN) structure with the Au nanopillars embedded in the ZnO matrix. Moreover, the average diameter of Au nanopillars increases as Au concentration increases, which also leads to the redshifts in the surface plasmon resonance (SPR) wavelength and changes in the hyperbolic behaviors of the films. As a whole, this work discusses how strain-driven tuning of optical properties and microstructure resulted through a novel Au concentration variation approach which has not been previously attempted in the ZnO-Au thin film system. These highly ordered films present great promise in the areas of sensing, waveguides, and nanophotonics to name a few.

Electrodeposition Behavior of Al-Au Alloys in AlCl3-NaCl-KCl-Aucl Molten Salt

Quartz Crystal Microbalance (QCM) has been used as a highly sensitive mass sensor. This study aims to form porous gold thin films on QCM elements and apply them to highly sensitive gas sensors by attaching selective media. Physical vapor deposition and chemical etching are known methods for forming porous Au thin films. In this study, the electrochemical formation of porous gold films in AlCl3-NaCl-KCl molten salts containing AuCl was investigated. There are few reports about electrodeposition and dissolution potentials of Au in the molten salt electrolyte. As a first step in this study, voltammogram measurements and constant potential electrolysis were performed in the electrolyte, and electrodeposition potentials of Au and Al-Au alloys were discussed.An electrolyte in this study is a mixture of 61 mol% AlCl3- 26 mol% NaCl- 13 mol% KCl molten salt. The mixture salt was melted at 443 K and AuCl was added to the molten salt. A glassy carbon plate (GC) and a pure Al wire were used as the working electrode and reference electrode, respectively. The GC plate and Au mesh were used as the counter electrode for voltammogram measurement and constant potential electrolysis, respectively. Voltammogram measurements were carried out at potential range from -0.1 to 2.4 V vs. Al/Al(Ⅲ). Constant potential electrolysis was performed in the range from -0.2 to 0.3 V with an electric charge density of 40 C cm-2. The electrodeposits were observed by scanning electron microscopy (SEM) and determined the composition of Al and Au by energy dispersive X-ray spectroscopy (EDS).Au ions concentration in the electrolyte was 2.5 mmol dm-3. In voltammogram measurements, a small cathodic current was observed at about 0.8 V, then gradually increased from 0.2 V. In the potential lower than 0 V, a drastical increase of cathodic current was observed, which was attributed to Al electrodeposition. When the potential was reversed, large anodic current flowed from 0 V and a small current peak was also observed at 0.2 V. These were considered to correspond to the dissolution of Al and Al-Au alloys, respectively. Furthermore, a relatively large anodic current peak was observed at about 2 V, which was expected to be due to the dissolution of Au. From the results of constant potential electrolysis, the Au concentration in the electrodeposits at -0.1 V and -0.2 V was less than 1 at%. At 0 V, the Au concentration in the electrodeposit increased sharply to 84 at%, and at 0.3 V it increased moderately to 89 at%. From SEM observation, the morphology of the electrodeposits at -0.1 V and -0.2 V was dense, while that at potentials more than 0 V was sponge-like.AcknowledgementsThis work was supported by JST SICORP and JPMJSC2108.

Photo-induced synthesis of star poly(DL-Lactide)-templated Au and Ag nanoparticles and evaluation of their catalytic performance

In this report, photochemical synthesis of monodispersed gold (Au) and silver (Ag) nanoparticles (NPs) was reported using cholic acid functionalized star poly(DL-lactide) (CA-(PDLLA)) as a capping and reducing agent. CA-(PDLLA) was synthesized by ring-opening polymerization (ROP) of DL-lactide with a feed ratio of 1:120 (cholic acid: DL-lactide). The molecular weight of CA-(PDLLA) was measured by using the gel permeation chromatography (GPC) technique. The thermal properties of the polymer and its nanocomposite materials were studied by thermogravimetric analysis (TGA). The optical properties of Ag and Au NPs were studied by UV–visible absorption spectroscopy. Morphological studies and size of the polymer-nanocomposites were assessed by using field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) techniques. The percentage composition of Au and Ag present in the polymer-nanocomposites was calculated using energy-dispersive X-ray spectroscopic (EDX) analysis. Finally, the synthesized polymer-metal nanocomposites were used as heterogeneous catalysts for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as a model reaction and the apparent rate constant (kapp) values of CA-(PDLLA)-AuNPs and CA-(PDLLA)-AgNPs were found to be 5.76 × 10−4 s−1 and 19.7 × 10−4 s−1, respectively.

Synthesis of Trimetallic Au/Pd/Ag Hollow Dendrite for Enhancing Electrochemical Sensing Ability Toward Nitrofurans

This study demonstrated a galvanic replacement reaction that synthesized trimetallic Au/Pd/Ag hollow dendrites in a choline chloride deep eutectic solvent. The dendrites' compositions of Au:Pd: Ag ratio can be well controlled by changing the displacement time and the precursor concentration. Their morphologies, chemical compositions, and electronic properties were carefully characterized by TEM, SEM, and XPS techniques. The synthesized dendrites were also employed as modified electrodes for the reduction of nitrofurans. The results show that the trimetallic Au/Pd/Ag hollow dendrites provided better sensing ability than those obtained from bimetallic Pd/Ag and Au/Ag electrodes and monometallic counterparts. This study demonstrated that both the atomic ratio of constituent metal and hollow interior structure strongly affect the catalytic activities of the synthesized Au/Pd/Ag hollow dendrites.

Modulating incident light for improved CO2 photoreduction in freestanding silver bismuth iodide/nanocellulose films with exotic gold nanoparticles

In response to the severe climate change caused by significant carbon dioxide emissions, researchers have been exploring the conversion of CO2 into carbon-based fuels through photocatalytic reactions inspired by photosynthesis. Particulate photocatalysts are known for their easy fabrication and diverse material configuration, with immobilization onto composite polymers enhancing reusability and practicality. In this study, we fabricated a novel freestanding photocatalyst composite film by immobilizing Ag3BiI6 (SBI) onto a nanocellulose (CNF) transparent film using a sequential process involving noble metal nanoparticle solutions and thermal evaporation of BiI3. The effect of the sequence and composition of Au and SBI/CNF on the morphology, optical property, and CO2 photoreduction performance was also investigated. The resulting SBI-Au/CNF film exhibited the highest photocatalytic activity for CO2 reduction, achieving a CO yield of 31.96 μmol/g⋅h with high stability for long-term photocatalytic reactions lasting 72 h. This study demonstrates the potential of photocatalytic materials to mitigate climate change by converting CO2 emissions into useful fuels.

Synthesis, optimization, and characterization of silver/gold allied bimetallic from Hippeastrum hybridum (L.) and their ex vivo anti‐acetylcholinesterase activity in rat brain

Nanotechnology, a modern technique, is apprehensive for small‐size nanoparticle (NP) generation via superficial, straightforward, and pharmaceutically modes. The main aim of the current research was to project the development of a green justifiable method to synthesize Ag/Au bimetallic NPs (BNPs) via Hippeastrum hybridum (HH) extract and then to use these BNPs as rat brain anti‐acetylcholinesterase (anti‐AChE) in ex vivo mode. According to the current results, BNPs exhibited a sharp peak of 542 nm when characterized by ultravioet (UV)–visible spectroscopy; Fourier transform infrared (FT‐IR) analysis exhibited peaks, which confirmed the existence of various phytochemicals in HH plant extract; X‐ray diffraction (XRD) analysis confirmed the crystal BNPs 8.34 nm mean size; scanning electron microscopy (SEM) showed that BNPs had a square shape with 20‐nm nanomeasures calculated sizes; and energy dispersive X‐ray (EDX) analysis confirmed Ag and Au composition, which was reported to be 12% and 38.26%, respectively. Moreover, the anti‐AChE potential of BNPs was also tested to cure Alzheimer's disease (AD). An excellent anti‐AChE activity was exhibited by BNPs in which AChE exhibited 31 ± 0.22% activity at 150‐μg concentration of BNPs with 103 ± 0.42 μg IC50. Statistical analysis exhibited that BNPs inhibit AChE noncompetitively, Km remain constant, whereas Vmax decreased from 7.24 to 6.1 (18.23% to 31.11%). Ag/Au BNPs do not affect KIapp, while increasing Vmaxiapp from 11.07 to 16 (17.39% to 67.4%). The Km, Ki, and KI were described to be 0.024 mM, 169 μg, and 91 μg, respectively. So, it is concluded that small‐size, stable, potent Ag/Au BNPs were synthesized from HH extract, and consequently, these BNPs significantly inhibit AChE activity in rat brain homogenate and thus prove to be a significant remedy in the treatment of AD.

Revealing the structure-property relationships of amorphous carbon tribofilms on platinum-gold surfaces

Nanocrystalline metal alloys have shown great promise as electrical contact materials, given their mechanical and tribological properties. In particular, platinum-gold (Pt–Au) nanocrystalline alloys have demonstrated coefficients of friction as low as 0.01 and specific wear rates on the order of 10−9 mm3 N−1 m−1, largely due to the formation of carbon-based tribofilms at the sliding interfaces. In this study, we advance our understanding of the Pt–Au tribofilm structure-property relations and growth mechanisms via high-throughput and high-resolution measurements as a function of Pt–Au composition. As the solute content increased from 0 at. % to 10 at. % Au, cross-sectional and plan-view transmission electron microscopy demonstrated a decrease in average grain size d and an accompanied increase in grain boundary (GB) segregation. The decrease in d and increase in GB solute segregation translated to a decrease in modulus Er and an increase in hardness H as determined via nanoindentation; the Er trend was mainly described using a rule-of-mixtures approximation, whereas the H trend was ascribed to solid solution strengthening and GB stabilization. The steady state-friction μ and wear rate decreased with the addition of Au; low Au-content films showed substrate wear, while high Au-content films showed stable tribofilm growth in both macroscale and nanoscale friction tests. The carbon bonding configuration of the tribofilms was investigated by near-edge X-ray absorption fine structure spectroscopic analyses and found to be similar to that of hydrogenated amorphous carbon films. Altogether, the study provided insight into the mechanistic origins of the tribofilms, thus opening the door to tunable properties ranging from mitigation for electrical contacts to the creation of self-healing films for solid lubricants.

Synthesis and Characterization of Magnetoplasmonic Air-Stable Au@FeCo

The synthesis of FeCo alloys as highly magnetic nanoparticles has been valuable, as far as applications for magnetic nanoparticles are concerned. However, recently, a field of magnetoplasmonics in which magnetic nanoparticles such as the FeCo alloys doped with plasmonic materials such as Au and Ag to create a hybrid nanostructure with both properties has emerged. These magnetoplasmonic metamaterials have greatly enhanced the limit of detection of analytes in spectroscopic methods, as well as providing a more widely applicable nanoparticle to broaden the use of FeCo alloys even further. Herein, we discuss the synthesis of high-yield and fairly monodisperse spherical FeCo and Au-doped FeCo (Au@FeCo) with varying compositions of Au synthesized via the thermal decomposition of iron pentacarbonyl (Fe(CO)5) and dicobalt octacarbonyl (Co2(CO)8), followed by the addition of Au atoms using triphenylphosphine gold(I) chloride ((Ph3P)AuCl) via both coprecipitation and by delayed addition methods. The products were separated using a hand-held magnet, and then characterized via ultraviolet-visible light (UV-vis), scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDX), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), flame atomic absorption spectrometry (F-AAS), and magnetization measurements. Optical studies revealed a plasmonic peak at 550 nm in the Au@FeCo nanoparticles that had a gold content (%Au) of >2% (by weight), determined using F-AAS. Colocation of the Fe, Co, and Au were demonstrated through EDX analysis. Location of the Au atoms in the core were seen through high-resolution bright-field imaging. To understand the use of these nanoparticles for potential application in therapeutics and/or electronics, resistance measurements were performed to assess power loss as a function of frequency. We also achieved magnetization values as high as 150 emu/g and as low as 50 emu/g for gold-loaded samples based on %Au by weight. This paves the way to continue to develop magneto-plasmonic structures chemically using these synthesis strategies.

Electrochemical and Optical Analysis of Various Compositions of Au and Ag Layers for Blood Cancer Prognosis

The fabrication of silver (Ag) and gold (Au) thin film electrodes was successfully carried out using the DC sputtering deposition method. These thin film electrodes were able to detect the increase in serum albumin concentration that was used as a prognostic factor for leukemia. The simulation and the optical experimental analysis show that an increase in BSA concentration can increase the absorbance peak observed at a wavelength of 435 nm on hypoalbumin medium and 470 nm on normal concentration of serum albumin medium. The performance of the electrodes was electrochemically tested, in which it was shown that a decrease in oxidation and reduction peaks occurred with respect to an increase in BSA concentration. An oxidation peak was observed at a voltage of 0.5 V for the Ag thin film. For the Au, Au/Ag, and Ag/Au thin films, an oxidation peak was observed at a voltage of 1.0 V. The limits of detection (LODs) of the Ag, Ag/Au, Au, and Au/Ag thin films were 0.56, 0.24, 0.64, and 0.36 g/dL, respectively. Therefore, based on both the electrochemical and optical analysis, the Ag/Au thin film possessed the highest potential for prognosis monitoring of leukemia compared with the other Ag and Au thin films.

Size- and Shape-Dependent Photoexcitation Electron Transfer in Metal Nanoclusters

There are some unresolved fundamental issues for metal nanoclusters; for instance, the close-packed structure transformation from face-centered cubic (fcc) to hexagonal close-packed (hcp) has not yet been reported, and photoexcitation electron transfer is not well understood. Herein, we realized for the first time the fcc-to-hcp structure transformation and revealed the size- and shape-dependent photoexcitation electron transfer for metal nanoclusters. Specifically, a thermally induced ligand exchange method was developed, and a rod-shaped hcp Au42(SCH2Ph)32 (HSCH2Ph: benzyl mercaptan) with the largest aspect ratio was synthesized from fcc Au28(SPh-tBu)20 (HSPh-tBu: p-tert-butylphenol) and structurally resolved, which shows a sharp absorption at 815 nm and dual emission that is well interpreted by time-dependent density functional theory (TD-DFT) calculations. The structure transformation pathway was proposed, and a novel, rod-shaped hcp Au58(SR)40 with larger aspect ratio was predicted. Interestingly, it is found that the kernel-based middle-to-both ends sp ← sp photoexcitation electron transfer can be extended to other rod-like (one-dimensional) gold nanoclusters, and the major photoexcitation turns to the kernel-based sp ← sp transition from the staple-to-kernel sp ← d transition when the spherical gold nanocluster size is increased to Au42 and the Au(6sp) composition increases with increasing size for structure-similar nanoclusters. These findings deepen our understanding of metal nanocluster photoexcitation electron transfer and provide guidance for future nanocluster property tuning aimed at practical applications.

Electrochemical and Optical Analysis of Various Compositions of Au and Ag Layers for Blood Cancer Prognosis

Electrochemical and Optical Analysis of Various Compositions of Au and Ag Layers for Blood Cancer Prognosis

Leaching Behavior of the Main Metals from Copper Anode Slime during the Pretreatment Stage of the Kaldor Furnace Smelting Process

The Kaldor furnace smelting process is currently the mainstream process for treating copper anode slime, but the existence of copper, tellurium and other impurities has adverse effects on the recovery of gold and silver during the Kaldor furnace smelting stage. Therefore, it is necessary to pretreat the copper anode slime to remove these impurities before Kaldor furnace reduction smelting. However, the current pretreatment process of copper anode slime generally has the problem of low removal efficiency of copper and tellurium, and little research on the occurrence state of main metals in copper anode slime. Therefore, this study quantitatively determined the phase composition of Cu, Te, Pb, Bi, As, Sb, Se, Ag and Au, and hydrogen peroxide was introduced to enhance the leaching of impurities. The leaching behavior of each metal in copper anode slime was investigated in detail. The results demonstrate that Cu and Te in the copper anode slime mainly exist in the form of CuO and CuSO4 and Te and AuTe2, respectively. More than 99% of the Cu and 97% of the Te were leached out using 250 g/L H2SO4 and 28.8 g/L H2O2 with a leaching pressure of 0.8 MPa at 150 °C for 2 h, while the leaching of Au and Ag was both < 0.03%. The removal of Cu and Te and the enrichment of precious metals were achieved. This study provides a rich theoretical reference for the optimization of the Kaldor furnace process.

Thermal annealing-boosted photoinduced electron transfer efficiency of g-C3N4/Au NPs hybrids for promoting SERS detection of uric acids

As for the ultrasensitive diagnosis of biomolecules via surface-enhanced Raman scattering spectroscopy (SERS), the primary requirement is to effectively enhance the activity of nano-substrates. Herein, we report an interesting strategy for further boosting SERS activity by thermal annealing treatment of as-prepared hybrid substrates. Initially, highly dense and monodisperse plasmonic Au nanoparticles (NPs) were loaded on two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheets. By adopting uric acids (UAs) as probe biomolecules, the g-C3N4/Au NPs with appropriate ~2.1% Au compositions exhibit much higher Raman signals than that of the hybrids with other Au contents. Besides the enhancement by routinely controlling hybrid components, the further maximizing SERS activity with a ~2.6-fold improvement than the original one can be obtained by thermal annealing of g-C3N4/Au NPs at 350 ℃ condition. It enables the thermal modified g-C3N4/Au NPs to be applied for highly sensitive monitoring of UAs in artificial urine. The corresponding detection limit is achieved at the ultralow level of 10−11 M, which is nearly two orders of magnitude better than that of the unannealed sample. It should be attributed to the stronger synergistic coupling effect by thermal annealing treatment that gives rise to the higher-efficiency photoinduced electron transfer (PIET) between g-C3N4 supports and plasmonic Au NPs. The present work provides a new opportunity for further promoting the SERS activity of prefabricating nano-substrates, holding great potential for practical monitoring of ultra-trace biomolecules in the near future.

Theoretical research on vacuum separation of Au−Ag alloy

To provide an accurate prediction of the product component dependence of temperature and pressure in vacuum distillation and give convenient and efficient guidance for the designing of the process parameters of industrial production, according to the molecular interaction volume model (MIVM), the separation coefficient (β) and vapor−liquid equilibrium composition of Au−Ag alloy at different temperatures are calculated. Combined with the vapor−liquid equilibrium (VLE) theory, the VLE phase diagrams, including the temperature−composition (T−x) and pressure−composition (p−x) diagrams of Au−Ag alloy in vacuum distillation are plotted. The triple points and condensation temperatures of gold and silver vapors are calculated as well. The results show that the β decreases and the contents of gold in vapor phase increase with the distillation temperature increasing. Low pressures have positive effect on the separation of Ag and Au. The difference between the condensation temperatures of gold and silver is about 450 K in the pressure range of 1−10 Pa.

Tuning Catalytic Activity in Ultrathin Bimetallic Nanowires Via Surface Segregation: Application in Electrochemical Methanol Oxidation

The reaction kinetics and efficiency in any catalytic process is controlled by the adsorption and desorption of reactant and intermediates on the surface of catalyst. As a consequence, the surface properties, composition and geometry of the catalyst dictates the mechanism of reactions. The surface electronic structure is modulated by variations in surface and subsurface atomic configurations, e.g., ordering and surface segregation, which in turn can vividly affects catalytic properties.1,2 A great deal of efforts are being devoted to develop efficient heterogenous catalyst by critically controlling the surface structure and chemistry. Here, I would like to present results on two different strategies for controlling the surface composition in ultrathin bimetallic AuPd nanowires. Au nanowire template-based method was used to grow AuPd wires by gradually increasing the amount of Pd.3 Percentage of composition of Au and Pd in AuPd nanowires gave either alloy nanowires with Au-rich compositions or core-shell structure at higher Pd compositions with Au-rich core and Pd-rich shell. Surface morphology of alloyed nanowires were induced through segregation of Pd to the surface by annealing under controlled CO atmosphere. High resolution microscopic imaging was possible due to the fact of substantial difference in the atomic number between Au and Pd. Electrocatalytic methanol oxidation reaction (MOR) in alkaline medium is important for energy conversion and was selected to study the catalytic activity of AuPd nanowires. A nearly monotonic increase of MOR potential was observed with increase in Pd content. Interestingly, a typical volcano type behavior of the specific activity was observed with different composition and with 40 and 50% Pd samples showed the optimum values in terms of current, potential and If/Ib values. Owing to a higher Pd content of CO-annealed nanowires, a lowering of potential was observed though the specific activity was maintained. These findings provide clear strategies to independently control the reaction potential and the activities of nanocatalysts with smaller amounts of the expensive active metal. The compositional effects on the electronic structure of the AuPd nanowires (catalyst surface) as well as binding energy of intermediates involved in the MOR was investigated using DFT calculations. d-band center analysis was employed to check interaction of CO* which a major intermediate of MOR with the catalyst surface. The theoretical investigation align well with the experimental results where it was found that the MOR potential increases with increasing amount of Pd and for the Au rich case the reaction does not reach up to CO2 but yields HCHO as a product at lower potentials. From our experimental finding it was evident that it is possible to lower the MOR potential to attain comparable or better activity through enrichment with the precious metal on the surface while essentially dropping the real quantity used.

Au composition dependent order-disorder transitions of Fe−Pt intermetallic compounds: Experiments and thermodynamic analysis

The Fe−Pt intermetallic nanocrystals exhibit good chemical stability, unique magnetic and catalytic properties, but suffer from the ordering difficulty. It has been found that the addition of Au can promote the disorder-order transitions, but the mechanism is far from being well understood. In this work, the phase equilibria and phase transformations of the Fe−Pt−Au alloys have been experimentally investigated and thermodynamically analyzed. The results show that the driving forces for both the L10_FePt and L12_FePt3 ordering are so weak that the homogeneous nucleation in the disordered fcc matrix is difficult, while a heterogeneous nucleation mechanism on the pre-existed phase boundary is preferred. On the other hand, there exists a metastable ternary miscibility gap between αAu and fcc-FePt or fcc-FePt3, and accordingly, when Au content is properly designed in the spinodal region, the enrichment of Au can take place spontaneously throughout a fcc Fe−Pt−Au structure during annealing. The segregation of αAu in the Fe−Pt−Au alloys can further accelerate the diffusion of Pt and Fe atoms, facilitate the nucleation of the ordered L10_FePt and L12_FePt3 phases, and stimulate the ordering process. These results correlate the Au addition with the ordering of Fe−Pt intermetallics and further the magnetic and catalytic properties, and it is thus expected to provide guidance for a rational alloy design of Fe–Pt–Au materials.

Surface-wrinkled SnO2 hollow microspheres decorated with AuAg bimetallic nanoparticles for triethylamine detection

Surface modification of metal oxides with bimetallic nanoparticles is regarded as an appealing way to improve the gas sensing properties. Herein, SnO2 hollow microspheres with wrinkle surface were synthesized, and were then decorated with Au, Ag, and bimetallic AuAg nanoparticles by immersing SnO2 into the solutions containing these as-prepared metal particles. Gas test results showed that the SnO2-AuAg displayed a higher response (61.3 to 100 ppm triethylamine at 240 °C), and shorter response/recovery time (4/24 s) than SnO2-Au (36.4, 5/26 s), SnO2-Ag (27.1, 5/32 s), and pure SnO2 (12.5, 6/37 s). Moreover, it showed excellent long-term stability. The surface chemical state of SnO2-AuAg were studied based on the experimental results. The mechanism of enhanced gas sensing performance was also proposed by the analysis of the morphological and structural composition, electronic and chemical sensitizations of Au and Ag, and the synergistic catalysis effect of AuAg bimetallic nanoparticles.