Au Bimetallic Nanoparticles Research Articles

Hydrogen auto-transfer under aerobic oxidative conditions: Efficient synthesis of saturated ketones by aerobic C–C cross-coupling of primary and secondary alcohols catalyzed by a Au6Pd/resin catalyst

Au and Au-containing bimetallic nanoparticles are promising catalysts for the green synthesis of fine chemicals. Here, we used a Au6Pd/resin catalyst for the aerobic C–C cross-coupling of primary and secondary alcohols to produce higher ketones under mild conditions. This is of importance to the construction of a C–C bond. Various substrates were used in the reaction system, and moderate to good yields were obtained. The catalysts can be reused at least five times without decrease of yield. The control experiment and XAFS characterization results showed that hydrogen auto-transfer occurred on metallic Pd sites even under oxidative conditions. On alloying with Au, the Pd sites became resistant to oxidation and readily abstracted the β-H of the alcohols and transferred the hydride to the C=C bond in the reaction intermediate to give the saturated product.

AuCu, AgCu and AuAg Bimetallic Nanoparticles: Synthesis, Characterization and Water Remediation

ABSTRACTSelf-assembling systems of amphiphilic molecules display structures similar to those of biomineralization natural systems. This allows to somehow mimic nature to synthesize nanomaterials with low polidispersity and with diverse morphologies. In this work we describe the synthesis and characterization of gold-copper, silver-copper, and gold-silver bimetallic nanoparticles by chemical reduction in self-assembling systems of two surfactants. The nanoparticles were characterized by Transmission Electron Microscopy and UV-Vis spectroscopy. We have prepared a composite material using mesoporous silica as support of the AuAg bimetallic nanoparticles. The system was used in photocatalysis experiments for water remediation applications. Our results show that the AuAg/SBA15 composite material degrades methyl orange in water from 17 ppm to 4 ppm in 30 minutes.

Polymer Film Supported Bimetallic Au-Ag Catalysts for Electrocatalytic Oxidation of Ammonia Borane in Alkaline Media.

Ammonia borane is widely used in most areas including fuel cell applications. The present paper describes electrochemical behavior of ammonia borane in alkaline media on the poly(p-aminophenol) film modified with Au and Ag bimetallic nanoparticles. The glassy carbon electrode was firstly covered with polymeric film electrochemically and then, Au, Ag, and Au–Ag nanoparticles were deposited on the polymeric film, respectively. The surface morphology and chemical composition of these electrodes were examined by scanning electron microscopy, transmission electron microscopy, electrochemical impedance spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It was found that alloyed Au–Ag bimetallic nanoparticles are formed. Electrochemical measurements indicate that the developed electrode modified by Au–Ag bimetallic nanoparticles exhibit the highest electrocatalytic activity for ammonia borane oxidation in alkaline media. The rotating disk electrode voltammetry demonstrates that the developed electrode can catalyze almost six-electron oxidation pathway of ammonia borane. Our results may be attractive for anode materials of ammonia borane fuel cells under alkaline conditions.Graphical

Fabrication of Bimetallic Core–Shell and Alloy Ag–Au Nanoparticles on a DNA Template

DNA hydrogel was used as a template to fabricate both core–shell- and alloy-type bimetallic Au–Ag nanoparticles by either sequential or simultaneous reduction of the corresponding metal precursors,...

Eco-friendly synthesis of gelatin-capped bimetallic Au-Ag nanoparticles for chemiluminescence detection of anticancer raloxifene hydrochloride.

This study described the utility of green analytical chemistry in the synthesis of gelatin-capped silver, gold and bimetallic gold-silver nanoparticles (NPs). The preparation of nanoparticles was based on the reaction of silver nitrate or chlorauric acid with a 1.0wt% aqueous gelatin solution at 50°C. The gelatin-capped silver, gold and bimetallic NPs were characterized using transmission electron microscopy, UV-vis, X-ray diffraction and Fourier transform infrared spectroscopy, and were used to enhance a sensitive sequential injection chemiluminescence luminol-potassium ferricyanide system for determination of the anticancer drug raloxifene hydrochloride. The developed method is eco-friendly and sensitive for chemiluminescence detection of the selected drug in its bulk powder, pharmaceutical injections and biosamples. After optimizing the conditions, a linear relationship in the range of 1.0×10(-9) to 1.0×10(-1) mol/L was obtained with a limit of detection of 5.0×10(-10) mol/L and a limit of quantification of 1.0×10(-9) mol/L. Statistical treatment and method validation were performed based on ICH guidelines. Copyright © 2016 John Wiley & Sons, Ltd.

Fabrication of poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) nanotubes decorated with Ag–Au bimetallic nanoparticles with enhanced catalytic activity for the reduction of 4-nitrophenol

Poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) nanotubes are facilely prepared and employed as a support to deposit Ag–Au bimetallic nanoparticles directly, which show superior catalytic performance.

Hollow Au–Ag bimetallic nanoparticles with high photothermal stability

We report the synthesis of hollow Au–Ag bimetallic nanoparticles with high photothermal stability under NIR irradiation.

AuAg bimetallic nonalloyed nanoparticles on a periodically nanostructured GaAs substrate for enhancing light trapping.

We present a light trapping structure consisting of AuAg bimetallic nonalloyed nanoparticles (BNNPs) on cone-shaped GaAs subwavelength structures (SWSs), combining the advantages of plasmonic structures and SWSs for GaAs-based solar cell applications. To obtain efficient light trapping in solar cells, the optical properties' dependence on the size and composition of the Ag and Au metal nanoparticles was systematically investigated. Cone-shaped GaAs SWSs with AuAg BNNPs formed from an Au film of 12 nm and an Ag film of 10 nm exhibited the extremely low average reflectance (R(avg)) of 2.43% and the solar-weighted reflectance (SWR) of 2.38%, compared to that of a bare GaAs substrate (R(avg), 37.50%; SWR, 36.72%) in the wavelength range of 300 to 870 nm.

Studies on plasmon characteristics and the local density of states of Au and Ag based nanoparticles

Knowledge about the conductive properties and the local density of states of chemically pure Au, Ag, Ag@Au core–shell and Au–Ag bimetallic nanoparticles is technologically important. Herein, the I–V characteristics and the density of states derived from scanning tunneling microscopy measurements made under atmospheric conditions is reported. The nanoparticles in thin film form used in this study were prepared by laser ablation in water followed by drop and evaporation. The morphology of the surface of the nanostructures was observed from optimizing tunneling current in each case. The monometallic Au and Ag particles shows almost similar current characteristics as well as discrete energy states but the slope of I–V characteristics was different for bimetallic structures. An attempt has also been made to compare the current measurements done in the nanoscale with the surface plasmon characteristics.

Electrochemical fabrication of polyproline modified graphite electrode decorated with Pd–Au bimetallic nanoparticles: Application for determination of carminic acid

A novel modified electrode has been developed, by electrodeposition of Pd–Au bimetallic nanoparticles (Pd–AuNps) on a polypyroline coated (Poly(Pr)) graphite electrode (GE). The structure and morphologies of Pd–AuNps/Poly(Pr)/GE were characterized by cyclic voltammetry (CV), square wave voltammetry (SWV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray photon spectroscopy (XPS) techniques. The electrocatalytic activities and morphologies of the new electrode were compared with individual monometallic AuNps/Poly(Pr)/GE and PdNps/Poly(Pr)/GE. This new bimetallic nanoparticle modified electrode (Pd–AuNps/Poly(Pr)/GE) was evaluated for determination of carminic acid. The oxidation peak (0.750 V) of carminic acid was found to be linearly related to carminic acid concentration in the range of 1.0 × 10− 8 to 1.0 × 10− 6 M with a detection limit of 5.90 × 10− 9 M. The proposed method was simple, less time consuming and showed a high sensitivity.

Biosynthesis of Au and Ag–Au Bimetallic Nanoparticles by Pedicellamide for Catalytic Reduction of 4-Nitrophenol

Biosynthesis of Au and Ag–Au Bimetallic Nanoparticles by Pedicellamide for Catalytic Reduction of 4-Nitrophenol

Biosynthesis Of Bimetallic Au-Ag Nanoparticles Using Ocimum Basilicum (L.) With Antidiabetic And Antimicrobial Properties

This study was aimed at developing a simple, eco-friendly and cost effective green chemistry method for the synthesis of bimetallic Au-Ag nanoparticles using Ocimum basilicum aqueous leaf and flower extracts, respectively as the natural reducing agents. The successive reduction of chloroauric acid and silver nitrate led to the formation of Au-Ag nanoparticles within 10 min at room temperature, suggesting a higher reaction rate than chemical methods involved in the synthesis. Stable, spherical nanoparticles with well-defined dimensions of average size of 3-25 nm was confirmed by UV-Visible spectroscopy, TEM, SEM-EDX, DLS, and zeta potential, whilst, FTIR in combination with GC-MS analyzed the functional groups adhered to the surface of the nanoparticles. The colloidal suspension displayed enhanced antihyperglycemic activity at 69.97 ± 3.42% (leaf) against α-amylase (from porcine) and at 85.77 ± 5.82% (flower) against Bacillus stearothermophilus α-glucosidase than that of acarbose and their respective crude extracts. Furthermore, revealed good antibacterial activity against bacterial species Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa. Copyright © 2015 VBRI Press.

STEM-EDX tomography of bimetallic nanoparticles: A methodological investigation

This paper presents an investigation of the limitations and optimisation of energy dispersive X-ray (EDX) tomography within the scanning transmission electron microscope, focussing on application of the technique to characterising the 3D elemental distribution of bimetallic AgAu nanoparticles. The detector collection efficiency when using a standard tomography holder is characterised using a tomographic data set from a single nanoparticle and compared to a standard low background double tilt holder. Optical depth profiling is used to investigate the angles and origin of detector shadowing as a function of specimen field of view. A novel time-varied acquisition scheme is described to compensate for variations in the intensity of spectrum images at each sample tilt. Finally, the ability of EDX spectrum images to satisfy the projection requirement for nanoparticle samples is discussed, with consideration of the effect of absorption and shadowing variations.

Effect of composition and distribution on structural and surface electronic properties of palladium–gold bimetallic nanoparticles: a density functional theory investigation

The effects of atomic composition and distribution on structural and surface electronic properties of a series of Pd–Au bimetallic nanoparticles are systematically investigated by density functional theory. We employed the 55-atom icosahedral model structure in this work. It is found that the structure with more Pd–Au bonds number presents more stability. For the Pd–Au bimetallic NPs, the electrons redistribution of the surface atoms, especially for the Au atoms, is strongly influenced by the atomic distribution. The valance d-band vacancy number of the surface Pd and Au atoms decreases due to the mixing of the two metals. In contrast to the Au atoms, the d-band center of the surface Pd changes almost linearly with the Pd composition increasing. In addition, the d-band center of the vertex atoms is closer to the Fermi level compared with that of the edge atoms in Pd n Au55−n bimetallic NPs. The investigations may be helpful in designing catalysis of Pd–Au bimetallic NPs since d-band center could be used as a general measure of local surface reactivity.

Effect of the synthesis method on the properties and catalytic activities of Au/Pd nanoparticles supported on organophilic clay

Au and Pd mono and bimetallic nanoparticles supported on organoclay were prepared using two different approaches. In the first method (POST), the intercalated surfactant molecules were used as capturing and stabilizing agents of metal cations to prepare metal nanoparticles. In the second method (PRE), pre-made surfactant-stabilized metal nanoparticles were directly incorporated in the cationic clay. The structure and composition of the materials were probed by XRD, ICP-AES, XPS, CHN, TGA, and UV–Vis spectroscopy, while morphology was characterized by SEM. It was revealed that by the POST method, the particles remained majoritarily on the outer surface of the clay, while by the PRE method, the particles were intercalated. The materials were tested on the oxidation of benzyl alcohol, and the results showed that monometallic catalysts synthesized by the PRE method were more active. For the bimetallic materials, the activity was higher for the POST material, which was composed of AuPd alloy nanoparticles, while the PRE material was composed of isolated Au and Pd nanoparticles.

Rapid and green synthesis of bimetallic Au–Ag nanoparticles using an otherwise worthless weed Antigonon leptopus

We demonstrate a simple, straightforward, clean-green, single pot approach for the synthesis of bimetallic Ag/Au nanoparticles (BNPs) by using a highly invasive terrestrial weed coral vine (Antigonon leptopus). Aqueous extracts of the weed were found to reduce the metal ions to form nanosised aggregates and then stabilise them by preventing further aggregation. The efficacy of the extracts of all its parts was explored by varying the stoichiometry of reactants, temperature, pH and reaction time. The electron micrographs of the synthesised BNPs indicated the presence of particles of predominantly spherical shapes in sizes ranging from 10 to 60 nm. The presence of gold and silver atoms was confirmed from the energy dispersive X-ray, X-ray photoelectron and X-ray diffraction studies. The Fourier transform infra-red spectroscopic spectral study indicated that the phenolics (including flavonoids) and proteins contained in the plant extract could have been responsible for the formation and stabilisation of the BNPs.

Trace-Level Detection of Secondary Explosives Using Hybrid Silver–Gold Nanoparticles and Nanostructures Achieved with Femtosecond Laser Ablation

Hybrid silver–gold targets were achieved by effortless mixing of pure silver (Ag) and gold (Au) metals at different ratios (Ag0.65Au0.35, Ag0.5Au0.5, and Ag0.35Au0.65) and embracing a manual melting process. The obtained targets were ablated by ultrafast (∼40 fs) laser pulses in acetone ensuing the fabrication of Ag–Au bimetallic nanoparticles (NPs) and nanostructures (NSs) in a single experiment. UV–visible extinction spectra of Ag–Au colloids demonstrated the tuning of localized surface plasmon resonance (LSPR) in the spectral range of 406–524 nm. The morphologies of NSs were investigated by the field emission scanning electron microscopy (FESEM) technique. Ag–Au NPs and NSs were utilized as surface enhanced Raman scattering (SERS) platforms to detect secondary explosive molecules such as 1,1-diamino-2,2-dinitroethene (FOX-7, 5 μM concentration) and 1-nitro pyrazole (1NPZ, 20 nM concentration). Our experimental observations clearly demonstrated that the increment in gold percentage reduced the surface a...

Annealing effect: Controlled modification of the structure, composition and plasmon resonance of hybrid Au–Ag/C nanostructures

Here we present a novel approach to the synthesis of hybrid Au–Ag/C nanoparticles (NPs) which were found to be carbon nanospheres containing dispersed Au–Ag bimetallic nanoparticles (1–5nm). The Au–Ag/C NPs were obtained by laser-induced liquid phase deposition from solutions of supramolecular complex. It was revealed that subsequent annealing procedure of Au–Ag/C NPs at various temperatures over the range 100–600°C allows variation and directed control of NPs’ morphology and composition (relative contents of principal components). For nanoscale carbon material the critical evaporation temperature was found to be about 300°C, while for Ag and Au components – 500°C and 600°C accordingly. The morphology and composition variation makes possible tuning of the surface plasmon resonance characteristics that opens an efficient way of the NPs’ functional properties control, like for example Surface-Enhanced Raman Scattering (SERS). It was found that the obtained hybrid Au–Ag/C NPs display pronounced SERS activity with the enhancement factor (EF) ca. 105.

Toxicity of silver and gold nanoparticles on marine microalgae

The increased use of nanomaterials in several novel industrial applications during the last decade has led to a rise in concerns about the potential toxic effects of released engineered nanoparticles (NPs) into the environment, as their potential toxicity to aquatic organisms is just beginning to be recognised. Toxicity of metallic nanoparticles to aquatic organisms, including microalgae, seems to be related to their physical and chemical properties, as well as their behaviour in the aquatic media where processes of dissolution, aggregation and agglomeration can occur. Although the production of these particles has increased considerably in recent years, data on their toxicity on microalgae, especially those belonging to marine or estuarine environments remain scarce and scattered. The literature shows a wide variation of results on toxicity, mainly due to the different methodology used in bioassays involving microalgae. These can range for up to EC50 data, in the case of AgNPs, representing five orders of magnitude. The importance of initial cellular density is also addressed in the text, as well as the need for keeping test conditions as close as possible to environmental conditions, in order to increase their environmental relevance. This review focuses on the fate and toxicity of silver, gold, and gold–silver alloy nanoparticles on microalgae, as key organisms in aquatic ecosystems. It is prompted by their increased production and use, and taking into account that oceans and estuaries are the final sink for those NPs. The design of bioassays and further research in the field of microalgae nanoecotoxicology is discussed, with a brief survey on newly developed technology of green (algae mediated) production of Ag, Au and Ag–Au bimetallic NPs, as well as some final considerations about future research on this field.

Synthesis and characterization of Ni–Au bimetallic nanoparticles

Bimetallic structure of nanoparticles is of great interest due to their extraordinary properties, especially in combining the specialty of the core and its shell. This work reports the effect of pH on the synthesis of Ni – Au (nickel–gold) bimetallic nanoparticles. The synthesis involves a two-step process where Ni nanoparticles were first synthesized using polyol method with hydrazine as the reducing agent. This was followed by the process of reducing [Formula: see text] to Au in the solution containing pre-prepared Ni to form Ni – Au bimetallic nanoparticles using sodium citrate as the reducing agent. The results obtained from Transmission Electron Microscopy (TEM) show that the process can possibly produce either core-shell structure, or mixture of Ni and Au nanoparticles. Magnetic property of core-shell structure investigated using Vibrating Sample Magnetometer (VSM) demonstrated typical characteristic of ferromagnetic with an increased magnetization as compared to Ni nanoparticles. The saturation magnetization (Ms) and coercivity (Hc) were obtained as 19.1 emu/g and 222.3 Oe, respectively.