Au Alloy Research Articles

Atomic Ordering Kinetics in a Cu–56 at % Au Alloy at a Temperature of 250°C

Atomic Ordering Kinetics in a Cu–56 at % Au Alloy at a Temperature of 250°C

Two-Step Synthesis of Large Gold–Silver Alloy Nanoparticles via the Combination of Seeded Growth and Citrate Co-reduction

We report a novel two-step method for the synthesis of uniform quasi-spherical and monodisperse gold–silver alloy nanoparticles with diameters of approximately 80 nm. In step one, gold–silver alloy seeds (G0) with diameters of approximately 30 nm are synthesized by citrate co-reduction of gold acetate and silver nitrate. In step two, the seeds grow into large alloy nanoparticles with diameters of approximately 80 nm by the combination of seeded growth and citrate co-reduction of gold and silver precursors. Our method makes use of gold acetate (rather than chloroauric acid) as a gold precursor to avoid the formation of silver chloride precipitates during synthesis. To our knowledge, we are the first to prepare gold–silver alloy nanoparticles with diameters of above 70 nm using gold acetate as a gold precursor. The alloy seeds and seed-grown nanoparticles show good control of size and composition, which enables tuning of the plasmonic band of these gold–silver alloy nanoparticles. Gold and silver are distributed uniformly within the cores of all Au-Ag alloy nanoparticles, while the surface is enriched in silver. This silver-enriched surface layer is thicker and more prominent for 25% Au alloy nanoparticles than for 50% and 75% Au alloy nanoparticles.

Composition‐Controlled Laser‐Induced Alloying of Colloidal Au–Cu Hetero Nanoparticles

AbstractDue to their optical properties (localized surface plasmon resonance, LSPR), colloidally dispersed metal nanoparticles are well suited for selective heating by high‐energy laser radiation above their melting point without being limited by the boiling point of the solvent, which represents an excellent complement to wet‐chemical nanoparticle synthesis. By combining wet‐chemical synthesis and postsynthesis laser treatment, the advantages of both methods can be used to specifically control the properties of nanoparticles. Especially in the colloidal synthesis of nanoalloys consisting of two or more metals with different redox potentials, wet‐chemical synthesis quickly reaches its limits in terms of composition control and homogeneity. For this reason, the direct synthesis path is divided into two parts to take the strengths of both methods. After preparing Au–Cu hetero nanoparticles by wet‐chemical synthesis, nanoalloys with previous adjusted composition can be formed by postsynthesis laser treatment. The formation of these nanoalloys can be followed by different characterization methods, such as transmission electron microscopy (TEM), where the fusion of both metal domains and the formation of spherical and homogeneous Au–Cu nanoparticles can be observed. Moreover, the alloy formation can be followed by different shifts of X‐ray diffraction (XRD) reflections and LSPR maxima depending on the composition.

Flexible Surface-enhanced Raman Scattering Strips Using Colloidal Ink of Gold-silver Alloyed Nanoparticles

Surface-enhanced Raman scattering (SERS) has been used for trace detection at the single-molecule level. The low-cost preparation of high-performance test strips has enabled the development of SERS techniques. In this study, oil-dispersible metal or alloy nanoparticles prepared by the Brust-Schiffrin method were used as "inks" in a ballpoint pen to handwrite SERS test strips on polytetrafluoroethylene (PTFE) membranes. Because of the good PTFE lipophilicity, the flexible substrates had good uniformity. The large laser damage threshold of the PTFE membrane also enabled increased laser powers for SERS testing. The Au and Ag alloy nanoparticle inks exhibited increased performance with larger proportions of Ag. The Au1Ag8 nanoparticles had the best properties, and those strips could detect 10-11-M Rhodamine 6G dyes in a 10-µL volume with an enhancement factor of 5.4×108. The SERS strips were used to demonstrate detection of malachite green, the use of which is prohibited in aquaculture and fish tanks.

Wafer-scale hysteresis-free plasmonic hydrogen sensors based on Pd–Au alloy nanoarrays

The prospective market of hydrogen energy has dramatically boosted the demand for accurate and stable detection of ambient hydrogen. In this work, we fabricated wafer-scale plasmonic hydrogen sensors consisting of periodically distributed Pd–Au alloy nanodiscs by holographic lithography and other semiconductor-compatible techniques, thus obtaining reliable and low-cost sensing devices. Light transmittance measurements at specific light wavelength close to the plasmonic absorption peak position are conducted to investigate the hydrogen sensing performance on account that optical signals afford spark-free operation and high tolerance. Upon alloying Pd with appropriate content of Au, the hysteresis between hydrogen absorption and desorption curves is completely suppressed which greatly improves the sensing accuracy throughout the hydrogen pressure range of 102–105 Pa. Moreover, the precisely defined Pd–Au alloy nanodiscs provide satisfactory stability and device-to-device reproducibility. This work demonstrates an attractive route into practical applications of hydrogen detection for the facile fabrication method and satisfactory performance.

Effect of Ternary Element Addition on Properties of TiNi-Based Shape Memory Alloys for Engineering and Medical Applications

Shape memory alloys (SMAs) are a type of smart material and have excellent engineering and medical applications. TiNi binary alloys possess remarkable shape recovery, mechanical properties, corrosion resistance, and excellent biocompatibility. By ternary elements addition just like Au, Pt, Pd, Hf, and Zr, increases transformation temperatures, leading to high-temperature shape memory alloys (more than 100°C) but other elements (Fe, Cu, Co, and Mo) form low-temperature shape memory alloys, (lower than 100°C). In the present work, it is reported that the effect of ternary element addition on microstructural properties, shape memory properties, mechanical properties, corrosion resistance, and biocompatibility of ternary shape memory alloys. Ag, Au, and Cu-based TiNi ternary alloys have excellent biocompatibility. The addition of ternary elements such as Ag and Nb increases corrosion resistance, Fe rises the hysteresis loop, Hf enhances thermal stability, and Mo raises workability.

Achieving Ultralow-Density, High-Purity Au Foam Hohlraum with Hierarchical Porous Structure

High Z (atomic number) metallic foams with a low density and high purity are urgent demands in high energy-density physical experiments. They suppress plasma expansion and convert the laser pulses to X-rays more uniformly and efficiently. Thus, we synthesized an ultralow-density and high-purity Au foam hohlraum with a hierarchical porous structure via a template-dealloying method in this paper. Silica (SiO2) beads were introduced as the sacrificial templates due to their high stability at an elevated temperature. The Au and Ag nanoparticles were successively deposited onto the SiO2 templates via an electroless deposition process to form an Ag@Au@SiO2 core-shell structure. Cylindrical Ag@Au@SiO2 hohlraum was achieved using a filter-casting technique with a patented mold. Afterward, an Au-Ag alloy was generated during 36 h of calcination at 400 °C. Self-supported Au foam hohlraum with the hierarchical porous structure was gained after the SiO2 templates were removed, followed by the dealloying of the Ag from the Au-Ag alloy. A self-supporting Au foam hohlraum with a density as low as 0.2 g/cm3 and a purity of 99.37% was achieved, and the density decreased by about 44.5% when compared with our previous Au foam (density: 0.36 g/cm3, purity: less than 96%) using microspherical polystyrene as the sacrificial template. Thus, the ultralow-density, high-purity Au foam hohlraum may exhibit profound application in high-energy physical experiments in the near future.

A paleoplacer component to the gold hosted in meta-conglomeratic units of the Neoarchaean moto greenstone belt, DRC

The giant Karagba-Chauffeur-Durba (KCD) gold deposit and its peripheral gold satellite deposits are located within the Kibali gold district in the Neoarchaean Moto Greenstone Belt in the northeast of the Congo Craton, Democratic Republic of Congo. The gold mineralisation within the KCD area occurs within altered chemical sedimentary rocks such as banded iron formation (BIF) and chert, as well as in meta-carbonaceous argillite, meta-sandstones and poorly-sorted pebble meta-conglomerates. To elucidate and characterise the controls on gold mineralisation in the siliciclastic rocks of this sedimentary sequence dating from approximately 2630 to 2625 Ma, the present study critically considers an extensive data set comprising borehole logs, petrographic observations, gold assay data, and mineral chemistry. Detailed high magnification petrographic analyses of polished sections enabled evaluation of 3824 gold grains from meta-conglomerate and siliciclastic sedimentary host rock specimens. These were compared to an additional 985 gold grains from deformed quartz-carbonate (ACSA) altered rocks and BIF host rock types, representing end-members for a purely hydrothermal style of gold mineralisation. These analyses revealed that most of the gold grains in the meta-conglomerates occur within the gangue mineral assemblage in the form of free gold generally distal to any sulphide minerals, with a second population associated with the sulphides, mainly pyrite, followed by arsenopyrite and lesser pyrrhotite. The gold grains in the meta-conglomerates show larger average sizes (433 µm2) than in the grains in the ACSA (311 µm2) and BIF (180 µm2) host rock types. A large dataset of assayed gold results of 9,632,470 data from 3953 drill holes highlights that the ACSA-altered rocks and the chemical sedimentary rocks (chert and BIF) are the main hosts for gold, showing average grades of 3.9, 2.5 and 2.4 g/t when a 0.5 g/t cut-off is applied, respectively. Conversely, meta-conglomerates have a relatively low Au content (1.84 g/t), yet this dataset has an extensive set of outlying values, with 86 data points reflecting grades over 100 g/t. Scanning Electron Microscope (SEM-EDS/WDS) performed on 397 gold grains from meta-conglomerates and deformed quartz-carbonate (ACSA) altered rocks shows mainly Au-Ag alloys, dominated by native gold with averages of 85.46 wt% of Au and 9.76 wt% of Ag in the meta-conglomerates and 86.56 wt% of Au and 12.84 wt% of Ag within the ACSA. Minor amounts of Au-Ag alloys electrum and Au-Hg-Ag alloys amalgams are present predominantly at Gorumbwa and KCD deposits. Our analysis of textural features, mineral chemistry, morphology, assay results, and mineral associations suggests that there are significant differences between the purely hydrothermal mineralisation and the mineralisation hosted by the meta-conglomeratic units. We suggest that the pre-enrichment of these meta-conglomerates by placer processes has played a role in enhancing the fertility for gold mineralisation in the KCD area. This has far-reaching implications for the existing ore-genesis models and exploration paradigms employed in the KCD area. This work presents new opportunities for exploration by highlighting the significance of understanding the stratigraphy and identifying sub-basins that may have undergone early placer enrichments. To achieve this, the early sedimentary environment should be thoroughly investigated.

A fast‐integrated x‐ray emission spectrometer dedicated to the investigation of Pt presence in gold Celtic coins (3rd–1st century BCE)

AbstractWith this study, we present the development of a transportable x‐ray emission spectrometer (XES) that was realized in a net time of 20 h, in order to verify the presence of Platinum (Pt) in gold Celtic coins belonging to 3rd–1st century BCE. Prior to the XES study, measurements using Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM‐EDS) revealed that the coins were made of highly concentrated gold (Au) alloy with trace amounts of bismuth (Bi) and, in one case, osmium (Os) and iridium (Ir). Os and Ir together with Pt and other components belong to the Platinum Group Elements (PGE). They form inclusions in ancient gold alloys and their presence is significant in provenance studies since they indicate the use of alluvial gold. Detection of platinum trace elements in a golden matrix is not possible using energy dispersive x‐ray emission techniques (SEM‐EDS, ED‐XRF, or PIXE) because of the limited energy resolution of the Si detectors. A way to overcome this problem is by using a high‐resolution wavelength dispersive x‐ray emission technique. For this purpose, we built a crystal spectrometer in Von‐Hamos geometry. In the framework of this study three samples/coins have been measured, and the presence of Pt was verified in one of them. The limitations of our spectrometer are critically evaluated and ways to optimize the performance of the spectrometer are discussed.

Solid-state, reagent-free and one-step laser-induced synthesis of graphene-supported metal nanocomposites from metal leaves and application to glucose sensing

The laser-induced method to prepare three-dimensional (3D) porous graphene has been widely used in many fields owing to its low-cost, easy operation, maskless patterning and ease of mass production. Metal nanoparticles are further introduced on the surface of 3D graphene to enhance its property. The existing methods, however, such as laser irradiation and electrodeposition of metal precursor solution, suffer from many shortcomings, including complicated procedure of metal precursor solution preparation, strict experimental control, and poor adhesion of metal nanoparticles. Herein, a solid-state, reagent-free, and one-step laser-induced strategy has been developed for the fabrication of metal nanoparticle modified-3D porous graphene nanocomposites. Commercial transfer metal leaves were covered on a polyimide film followed by direct laser irradiation to produce 3D graphene nanocomposites modified with metal nanoparticles. The proposed method is versatile and applicable to incorporate various metal nanoparticles including gold silver, platinum, palladium, and copper. Furthermore, the 3D graphene nanocomposites modified with AuAg alloy nanoparticles were successfully synthesized in both 21 Karat (K) and 18K gold leaves. Its electrochemical characterization demonstrated that the synthesized 3D graphene-AuAg alloy nanocomposites exhibited excellent electrocatalytic properties. Finally, we fabricated LIG-AuAg alloy nanocomposites as enzyme-free flexible sensors for glucose detection. The LIG-18K electrodes exhibited the superior glucose sensitivity of 1194 μA mM−1 cm−2 and low detection limits of 0.21 μM. The LIG-21K nanocomposite sensors showed two linear ranges from 1 μM to 1 mM and 2 mM–20 mM with good sensitivity. Furthermore, the flexible glucose sensor showed good stability, sensitivity, and ability to sense in blood plasma samples. The proposed one-step fabrication of reagent-free and metal alloy nanoparticles on LIG with excellent electrochemical performance opens up possibilities for diversifying potential applications of sensing, water treatment and electrocatalysis.

Inversion of the Complex Refractive Index of Au-Ag Alloy Nanospheres Based on the Contour Intersection Method.

The contour intersection method is a new method used to invert the complex refractive index of small particles. Research has yet to be reported on using this method to invert the complex refractive index of nanoparticles. This paper reports the feasibility and reliability of the contour intersection method in the inversion of the complex refractive index of nanoparticles using Au-Ag alloy nanospheres. The Mie theory and the size-dependent dielectric function are used to calculate the light scattering and absorption efficiency of Au-Ag alloy nanospheres corresponding to the complex refractive index. The complex refractive index of the particles is obtained by inversion with the contour intersection method. The backscattering efficiency constraint method is used to determine the unique solution when multiple valid solutions from the contour intersection method appear. The effects of the Au component percentage, particle size, and measurement errors on the inversion results are quantitatively analyzed. Finally, the inversion accuracy is compared and analyzed with the traditional iterative method. The results show that as long as the light scattering efficiency, light absorption efficiency, and backscattering efficiency of Au nanospheres can be measured, the accurate complex refractive index can also be calculated by inversion using the contour intersection method. The accuracy of the inversion results can be ensured when the measurement error is less than 5%. The results of inversion using the contour intersection method are better than those of the iterative methods under the same conditions. This study provides a simple and reliable inversion method for measuring the complex refractive index of Au-Ag alloy nanospheres.

Atomically Dispersed Cu–Au Alloy for Efficient Electrocatalytic Reduction of Carbon Monoxide to Acetate

Electrocatalytic carbon monoxide reduction reaction (CORR) is a promising strategy to convert carbon monoxide into high-value multi-carbon products such as acetate. Nonetheless, the activity and selectivity for CO-to-multi-carbon product conversion remains low due to the lack of efficient catalysts. Herein, we report a Cu–Au alloy catalyst with abundant atomic Cu–Au interfaces to drive efficient CORR for acetate production. The unique geometric and electronic structure of atomic Cu–Au interfaces affords improved acetate activity and selectivity, surpassing metallic Cu nanoparticles and CuAu bulk alloys. A Faradaic efficiency of 39% was achieved with a large partial current density of 217 mA cm–2 for acetate production in an alkaline flow cell. Density functional theory calculation reveals that the introduction of Au atoms into the Cu support promotes C–C coupling and improves acetate formation by weakening the binding strength of *CO +*CO on the catalyst surface.

Reactive Hydrogel Patch for SERS Detection of Environmental Formaldehyde

The tobacco epidemic is a public health threat that has taken a heavy toll of lives around the globe each year. As one of the poison species from smoking, formaldehyde (FA) affects both the smokers and nearby persons who are exposed to second-hand smoke. Therefore, on-site tracking of FA exposure could evaluate the public environmental safety and mitigate the potential hazards. Herein, we first prepare SiO2-shelled AuAg alloy nanoparticles (AuAg@SiO2) and then embed AuAg@SiO2 within agarose hydrogel to construct the three-dimensional (3D) surface-enhanced Raman scattering (SERS) substrate. A reagent of 3-methyl-2-benzothiazolinone hydrazine (MBTH) with reaction activity toward FA is loaded in the 3D substrate to obtain the selective SERS patch (designated as M-hydrogel patch). Based on a marker Raman peak at 1273 cm-1 from the reaction product of MBTH-FA, the M-hydrogel patch is used to realize SERS detection of FA in smoke. A good linear relationship from 5 × 10-4 to 5 mg/m3 and a limit of detection (LOD) of 2.92 × 10-5 mg/m3 could be reached. While for detection of FA in aqueous, a linear range of 1 × 10-7-1 × 10-3 mg/mL with an LOD of 1.46 × 10-8 mg/mL could be achieved. As the real application, the proposed M-hydrogel patch could be placed anywhere indoor to SERS evaluate the spatial distribution of FA in tobacco smoke, which is in connection with the second-hand smoke effect on children and adults. Such M-hydrogel patch-based SERS assay is exerted for on-field detection of FA in water and furniture panels by using a portable Raman system, showing satisfactory selectivity and reproducibility.

Bimetallic Ag-Cu Alloy SERS Substrates as Label-Free Biomedical Sensors: Femtomolar Detection of Anticancer Drug Mitoxantrone with Multiplexing.

Surface-enhanced Raman spectroscopy (SERS) has been recognized as a promising label-free technology for clinical monitoring due to its high sensitivity and multiplexing ability, which should accelerate the screening of important drugs in the blood and plasma of cancer patients in a simpler, faster, and less-expensive manner. In this work, bimetallic Ag-Au and Ag-Cu alloy microflowers (MFs) with tunable surface compositions were fabricated on a glass cover slip by simple thermolysis of a metal alkyl ammonium halide precursor and used as SERS substrates for the sensitive detection of anticancer drug mitoxantrone (MTO). Two different laser excitation sources, 532 and 632.8 nm, were used to explore the possibility of surface-enhanced resonance Raman scattering. The Ag-Cu substrate showed superior detection capability over Ag-Au, whereby the sensor recorded a noteworthy "limit of detection" value of 1 fM for MTO. Theoretical electromagnetic field maps were simulated on appropriately chosen plasmonic systems to compare the electromagnetic field enhancements with the experimental SERS efficiencies of the substrates. Further, using a 10% Ag-Cu substrate, efficient multiplexing detection of MTO was demonstrated with another anticancer drug doxorubicin (DOX) in water and mouse blood plasma.

Mixing properties of liquid Al-Au alloys

The thermodynamic and structural properties of liquid Al-Au alloy have been studied in frame-work of R-K polynomial using temperature-dependent energy interaction parameters at different temperatures. Thermodynamic properties, excess free energy of mixing and activity, and in structural properties, concentration fluctuation in long wave-length limit have been computed at temperatures 1338 K, 1500 K and 1600 K. The properties, such as surface tension and surface concentration of the system have been computed at above mentioned temperatures using Butler model. The system shows transformation from segregating to ordering in nature with increase in concentration of Au.

The Fabrication and SERS Performance of Multi-layer Hollow Au-Ag Alloy Nano Urchins Structure-based SERS Fiber Probe

The Fabrication and SERS Performance of Multi-layer Hollow Au-Ag Alloy Nano Urchins Structure-based SERS Fiber Probe

Synergetic effect of the interface electric field and the plasmon electromagnetic field in Au-Ag alloy mediated Z-type heterostructure for photocatalytic hydrogen production and CO2 reduction

The challenge of synergistically optimizing different mechanisms limits the further improvement of plasmon-mediated photocatalytic activities. In this work, the CdS/Au-Ag/B-TiO2 photocatalyst, combining a heterojunction structure with localized surface plasmon resonance (LSPR), is prepared by a high-temperature hydrogen reduction and hot solvent method. The novel synergistic interaction at the interface between the electric field and the plasmon electromagnetic field drives effective charge separation with improved photocatalytic efficiency. The Cd3Ti2 catalyst exhibits the highest photocatalytic activity, and the H2 generation efficiency under the full solar spectrum is 15.97 mmol⋅h−1⋅g−1 with good stability as high as 81.3% in 24 h cycles. The CH4 and CO precipitation performances are achieved at 14.2 μmol⋅h−1⋅g−1 and 113.9 μmol⋅h−1⋅g−1, respectively, in the CO2RR process. The design of the synergistic mechanism of the dual electric field offers an important development in the field of plasma-mediated photoredox catalysis.

A comparative study of Cu-Au, Ag-Au and Ag-Cu alloys: A pseudopotential approach

Using the pseudopotential approach, we have calculated the mechanical characteristics of the alloys Cu-Au, Ag-Au, and Ag-Cu. We have employed pseudopotentials due to Pandya et al. (Physica B, 2001;307:138–149) and Bhatia et al. (Philos. Mag., 2021;101(13): 1602–1618) to calculate PDC (Phonon dispersion curves), P-DoS (Phonon density of states), WT (Debye-Waller factor), u¯2 (mean square displacement), heat capacity (CP), elastic constants (C11, C12 and C44), bulk modulus (B) and anisotropic factor (A). In the absence of experimental research, theoretical findings of PDC for alloys AgAu3 and AgCu3 (excluding CuAu3) are provided for the first time, which may be used to estimate the comprehensive physical characteristics. Our elastic constants findings agree with existing experimental results. These pseudopotentials have been found successfully for the study of solid as well as liquid metal properties.

Ultra-trace detection of diverse analyte molecules using femtosecond laser structured Ag–Au alloy substrates and SERRS

Choosing a wavelength close to the electronic excitation of the analyte molecules is known to enhance the Surface Enhanced Raman Spectroscopy signal further. This technique is often referred to as Surface Enhanced Resonance Raman Spectroscopy (SERRS). Here we use SERRS for sensing different classes of molecules and demonstrate how it can be used for ultra-trace detection. Diverse SERS substrates were fabricated by femtosecond laser ablation of Ag–Au alloy (1:1) in the air by changing the angle of incidence. Further, we have examined the SERRS performance of each substrate. Often in laser ablation in air, the surface debris is considered undesirable. Here we have shown that this debris of nanoparticles can be used as an advantage for ultra-trace detection of different molecules. Further, with the advantage of having randomly stacked nanoparticles in debris and periodic substrates without debris from a single experiment, we have examined the much-debated relationship between enhancement and reproducibility in SERS and found that they are inversely correlated. The sensitivity of the substrate for rhodamine 6G, crystal violet, picric acid, and cysteine was found to be 10 fM, 100 fM, 100 nM, and 100 nM, respectively, with good reproducibility.

Electrochemical Dealloying Preparation and Morphology Evolution of Nanoporous Au with Enhanced SERS Activity

Nanoporous Au (NPG) prepared by dealloying is one of the most used substrates for surface-enhanced Raman scattering (SERS). The morphology tailoring of the NPG to obtain both ultrafine pores and suitable Au/Ag ratio is of great importance for the acquiring of enhanced SERS performance. Compared with the chemical dealloying, the electrochemical dealloying can tailor the NPG to be more flexible by the additional adjustment of dealloying voltage and current. Thus, further understanding on the morphology evolution of NPG during the electrochemical dealloying to obtain enhanced SERS performance is of great importance. In the presented work, the morphology and composition evolution of the NPG film during the electrochemical dealloying was investigated. NPG films with a stable pore diameter of approximately 11 nm as well as diverse compositions were obtained by electrochemical dealloying an Au-Ag alloy film. The prepared NPG film exhibits an enhanced SERS activity with an enhancement factor (EF) of 7.3 × 106 and an excellent detection limit of 10−9 M. This work provides insights into the morphology and composition evolution of the NPG during the electrochemical dealloying process to obtain enhanced SERS performance.