Au Bimetallic Nanoparticles Research Articles

Synthesis of stable AuAg bimetallic nanoparticles encapsulated by diblock copolymer micelles

We present a facile method for the preparation of bimetallic AuAg nanoparticles (NPs) with controlled size and composition rendering them ideally suitable for optical and catalytic applications. In analogy to methods for the generation of monometallic Au and Ag NPs, AuAg NPs were prepared inside polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block-copolymer micelles formed in toluene, by loading the P4VP cores of the micelles first with AgNO(3) and then with HAuCl(4). In contrast to the reverse sequence of loading, homogenously bimetallic AuAg particle arrays were achieved after reduction carried out in solution with hydrazine monohydrate as the reducing agent. TEM reveals that stable and spherical NPs can be prepared well separated from one another and with a narrow size distribution with diameters of ∼3 nm. The bimetallic NP composition was confirmed by energy-dispersive X-ray spectroscopy (EDX) of single NPs. The atomic ratio of Ag and Au contained in single particles is in good agreement with the relative concentrations of both metals used in the synthesis which was confirmed by atomic absorption spectroscopy. The atomic ratio Au : Ag was systematically varied between 3 : 1 and 1 : 3. For all ratios UV-vis spectra showed a single plasmon band. Its wavelength varied from 430 for Au : Ag = 1 : 3 to 515 nm for Au : Ag = 3 : 1, showing a linear dependence on the relative amount of gold within the range of plasmon wavelengths from monometallic gold (538 nm) to silver (415 nm).

A Novel SERS-Active Tag Based on Bimetallic Flowerlike Au-Ag Nanoparticles

Bimetallic nanoparticles have received considerable attention due to their unique optical, magnetic and other properties. Their composition, architecture, shape and size can be adjusted relatively easily in order to change their properties, which provide great potential for their diverse applications. Bimetallic Au-Ag nanoparticles are very attractive because they exhibit remarkable optical properties due to their surface plasmon resonance (SPR) absorption. In this investigation, a simple synthesis process for novel, bimetallic flowerlike Au-Ag composite nanoparticles was developed. Biocompatible folic acid-conjugated chitosan with flexible molecular chains were used as the structure-directing agent in nanoparticle synthesis. The structure and properties of Au-Ag nanoparticles were studied using a variety of analytical techniques including high resolution transmission electron microscopy. These nanoparticles contained an Au core and an Ag shell and the shape and thickness of the Ag shell could be easily controlled by varying the synthesis condition. The formation and growth of flowerlike bimetallic Au-Ag composite nanoparticles was investigated and its mechanism proposed. On the basis of flowerlike Au-Ag nanoparticles which can produce surface enhanced Raman scattering (SERS), a novel SERS tag was formed, which consisted of an Au-Ag flowerlike nanoparticle, embedded Rhodamine B (RhB, a Raman reporter molecule), and a folic acid-conjugated chitosan outer layer. This new SERS tag (RhB@Au-Ag tag) exhibited greatly increased SERS intensity of RhB and hence showed great potential for tumor cell targeting and detection.

Ni–Au bi-metallic nanoparticles formed via dewetting

Solid-state dewetting in Ni/Au bi-layer films was used to fabricate Ni–Au alloy nanoparticles. Due to the limited solubility between Au and Ni, the individual particles contain both, an Au-rich phase and a Ni-rich phase. The shape of the particles can be complex and is temperature-dependent. There is a change in texture after annealing, and this is probably related to the relaxation of strain energy induced by alloying or dewetting.

A comparative theoretical study of the catalytic activities of Au 2 - and AuAg- dimers for CO oxidation

The detailed mechanisms of catalytic CO oxidation over Au(2)(-) and AuAg(-) dimers, which represent the simplest models for monometal Au and bimetallic Au-Ag nanoparticles, have been studied by performing density functional theory calculations. It is found that both Au(2)(-) and AuAg(-) dimers catalyze the reaction according to the similar mono-center Eley-Rideal mechanism. The catalytic reaction is of the multi-channel and multi-step characteristic, which can proceed along four possible pathways via two or three elementary steps. In AuAg(-), the Au site is more active than the Ag site, and the calculated energy barrier values for the rate-determining step of the Au-site catalytic reaction are remarkably smaller than those for both the Ag-site catalytic reaction and the Au(2)(-) catalytic reaction. The better catalytic activity of bimetallic AuAg(-) dimer is attributed to the synergistic effect between Au and Ag atom. The present results provide valuable information for understanding the higher catalytic activity of Au-Ag nanoparticles and nanoalloys for low-temperature CO oxidation than either pure metallic catalyst.

Synergistic Combination of Plasma Sputtered Pd–Au Bimetallic Nanoparticles for Catalytic Methane Combustion

Pd–Au bimetallic nanoparticles supported by silicon carbide have been prepared by plasma sputtering deposition and employed as the catalyst for methane combustion. It is found that the bimetallic nanoparticles consist of tightly-coupled Pd and Au particles, which are neither Pd–Au alloyed nor core–shell structured. The catalytic activity increases with the Pd loading in the catalysts. When the temperature is higher than 520 °C, Pd catalysts have an obvious drop in the catalytic activity due to the decomposition of PdO. However, the introduction of Au can delay and weaken the drop. It is indicated that there exists a synergistic combination between Pd and Au: oxygen transfers from Pd to Au at a temperature lower than 520 °C and from Au to Pd at higher temperature. Transmission electron microscopy and X-ray photoelectron spectroscopy results further confirm the synergistic combination.

Phytosynthesis of Au, Ag and Au–Ag bimetallic nanoparticles using aqueous extract and dried leaf of Anacardium occidentale

Present study reports a green chemistry approach for the biosynthesis of Au, Ag, Au–Ag alloy and Au core–Ag shell nanoparticles using the aqueous extract and dried powder of Anacardium occidentale leaf. The effects of quantity of extract/powder, temperature and pH on the formation of nanoparticles are studied. The nanoparticles are characterized using UV–vis and FTIR spectroscopies, XRD, HRTEM and SAED analyses. XRD studies show that the particles are crystalline in the cubic phase. The formation of Au core–Ag shell nanoparticles is evidenced by the dark core and light shell images in TEM and is supported by the appearance of two SPR bands in the UV–vis spectrum. FTIR spectra of the leaf powder before and after the bioreduction of nanoparticles are used to identify possible functional groups responsible for the reduction and capping of nanoparticles. Water soluble biomolecules like polyols and proteins are expected to bring about the bio-reduction.

Effects of gas bubbling for shape, size, and composition changes in Au–Ag bimetallic nanoparticles including polygonal Au seeds under oil-bath heating at 150 °C

Effects of Ar or O2 gas bubbling for shape, size, and composition changes in Au–Ag bimetallic nanoparticles were studied under oil-bath heating at 150 °C for 10–60 min in ethylene glycol (EG). When a mixture of polygonal Au seeds, AgNO3, and polyvinylpyrrolidone (PVP) in EG solution was heated from room temperature to 150 °C and it was kept at that temperature for 10–60 min under Ar or O2 gas bubbling, different shape, size, and composition changes were observed. Under Ar gas bubbling, major products after heating for 10 min were polygonal Au core Ag-rich Ag/Au alloy shell particles, denoted as Au@Ag/Au, and spherical Ag-rich Ag/Au alloy particles. They were transformed to larger excentered Au@Ag/Au particles with an average diameter of 340 ± 106 nm after further heating for 20–50 min. Under O2 gas bubbling, major products after heating for 10 min were Au@Ag core–shell particles having a thin Ag shell, large Au-rich Au/Ag alloy particles, and many small spherical Ag particles with 4 ± 2 nm average diameter. After further heating for 20–50 min, the Au@Ag particles fuse and aggregate to form spherical Au-rich Au/Ag alloy particles with an average diameter of 259 ± 37 nm. Results show that Ag-rich or Au-rich Au–Ag bimetallic particles can be prepared easily under bubbling Ar or O2 gas, respectively. The different structure and composition changes in Au–Ag bimetallic particles under Ar or O2 bubbling are discussed in terms of fusion, aggregation, and oxidative etching of Au and Ag particles.

A kinetic Monte Carlo study of Pt on Au(111) with applications to bimetalliccatalysis

Pt-decorated Au nanostructures and bimetallic PtAu nanoparticles have been shown to actas catalysts. Consequently we investigate the formation of extended Pt decorations of anAu island edge on Au(111) as possible catalysts. The investigation is by simulation usingthe kinetic Monte Carlo method. The effects of varying the rate of deposition of Pt atomsand the simulation temperature on the morphology of the resulting Pt nanostructureswere investigated. The thickness and roughness of the nanostructures are readilyinfluenced, with temperature being the more important factor. A combination of bothhigh temperature and low deposition rate was the most effective at reducing theroughness. PtAu alloying in the Au island edge was identified. This work is (tothe best of our knowledge) the first kinetic Monte Carlo simulation study of theformation of Pt nanostructures on Au. We demonstrate how the morphologyof the Pt nanostructures can be controlled. The nanostructures studied here,comprising an adjustable mix of Pt overlayers and novel 1D PtAu surface alloys, areexpected to be of considerable interest as potential bimetallic nano-catalysts.

One-pot synthesis of Ag–Au bimetallic nanoparticles with Au shell and their high catalytic activity for aerobic glucose oxidation

PVP-protected Ag core/Au shell bimetallic nanoparticles of enough small size, i.e., 1.4 nm in diameter were synthesized in one-vessel using simultaneous reduction of the corresponding ions with rapid injection of NaBH 4, and characterized by HR-TEM. The Ag core/Au shell bimetallic nanoparticles show a high and durable catalytic activity for the aerobic glucose oxidation, and the catalyst can be stably kept for more than 2 months under ambient conditions. The highest activity (16,890 mol-glucose h −1 mol-metal −1) was observed for the bimetallic nanoparticles with Ag/Au atomic ratio of 2/8, the TOF value of which is several times higher than that of Au nanoparticles with nearly the same particle size. The higher catalytic activity of the prepared bimetallic nanoparticles than the usual Au nanoparticles can be ascribed to: (1) the small average diameter, usually less than 2.0 nm, and (2) the electronic charge transfer effect from adjacent Ag atoms and protecting PVP to Au active sites. In contrast, the Ag–Au alloy nanoparticles, synthesized by dropwise addition of NaBH 4 into the starting solution and having the large mean particle size, showed a low catalytic activity.

Determination of Anthracene on Ag-Au Alloy Nanoparticles/Overoxidized-Polypyrrole Composite Modified Glassy Carbon Electrodes

A novel electrochemical sensor for the detection of anthracene was prepared by modifying a glassy carbon electrode (GCE) with over-oxidized polypyrrole (PPyox) and Ag-Au (1:3) bimetallic nanoparticles (Ag-AuNPs). The composite electrode (PPyox/Ag-AuNPs/GCE) was prepared by potentiodynamic polymerization of pyrrole on GCE followed by its overoxidation in 0.1 M NaOH. Ag-Au bimetallic nanoparticles were chemically prepared by the reduction of AgNO3 and HAuCl4 using C6H5O7Na3 as the reducing agent as well as the capping agent and then immobilized on the surface of the PPyox/GCE. The nanoparticles were characterized by UV-visible spectroscopy technique which confirmed the homogeneous formation of the bimetallic alloy nanoparticles. Transmission electron microscopy showed that the synthesized bimetallic nanoparticles were in the range of 20–50 nm. The electrochemical behaviour of anthracene at the PPyox/Ag-AuNPs/GCE with Ag: Au atomic ratio 25:75 (1:3) exhibited a higher electrocatalytic effect compared to that observed when GCE was modified with each constituent of the composite (i.e., PPyox, Ag-AuNPs) and bare GCE. A linear relationship between anodic current and anthracene concentration was attained over the range of 3.0 × 10−6 to 3.56 × 10−4 M with a detection limit of 1.69 × 10−7 M. The proposed method was simple, less time consuming and showed a high sensitivity.

Green synthesized Au–Ag bimetallic nanoparticles modified electrodes for the amperometric detection of hydrogen peroxide

Simple and eco-friendly electro deposition method was employed for the fabrication of Au–Ag bimetallic nanoparticles modified glassy carbon electrode. Nano Au–Ag film modified glassy carbon electrode surface morphology has been examined using atomic force microscopy. Electrodeposited Au–Ag bimetallic nanoparticles were found in the average size range of 15–50 nm. The electrochemical investigations of nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion film have been carried out using cyclic voltammetry and electrochemical impedance spectroscopy. The nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion film modified glassy carbon electrode holds the good electrochemical behavior and stability in pH 7.0 phosphate buffer solutions. The nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion modified glassy carbon electrode was successfully employed for the detection of H2O2 in the linear range of 1–250 μM in lab samples, and 1 × 10−3–2 × 10−2 M in real samples, respectively.

Biomimetic Synthesis of Gelatin Polypeptide-Assisted Noble-Metal Nanoparticles and Their Interaction Study.

Herein, the generation of gold, silver, and silver–gold (Ag–Au) bimetallic nanoparticles was carried out in collagen (gelatin) solution. It first showed that the major ingredient in gelatin polypeptide, glutamic acid, acted as reducing agent to biomimetically synthesize noble metal nanoparticles at 80°C. The size of nanoparticles can be controlled not only by the mass ratio of gelatin to gold ion but also by pH of gelatin solution. Interaction between noble-metal nanoparticles and polypeptide has been investigated by TEM, UV–visible, fluorescence spectroscopy, and HNMR. This study testified that the degradation of gelatin protein could not alter the morphology of nanoparticles, but it made nanoparticles aggregated clusters array (opposing three-dimensional α-helix folding structure) into isolated nanoparticles stabilized by gelatin residues. This is a promising merit of gelatin to apply in the synthesis of nanoparticles. Therefore, gelatin protein is an excellent template for biomimetic synthesis of noble metal/bimetallic nanoparticle growth to form nanometer-sized device.

Comparative toxicity study of Ag, Au, and Ag–Au bimetallic nanoparticles on Daphnia magna

A comparative assessment of the 48-h acute toxicity of aqueous nanoparticles synthesized using the same methodology, including Au, Ag, and Ag-Au bimetallic nanoparticles, was conducted to determine their ecological effect in freshwater environments through the use of Daphnia magna, using their mortality as a toxicological endpoint. D. magna are one of the standard organisms used for ecotoxicity studies due to their sensitivity to chemical toxicants. Particle suspensions used in toxicity testing were well-characterized through a combination of absorbance measurements, atomic force or electron microscopy, flame atomic absorption spectrometry, and dynamic light scattering to determine composition, aggregation state, and particle size. The toxicity of all nanoparticles tested was found to be dose and composition dependent. The concentration of Au nanoparticles that killed 50% of the test organisms (LC(50)) ranged from 65-75 mg/L. In addition, three different sized Ag nanoparticles (diameters = 36, 52, and 66 nm) were studied to analyze the toxicological effects of particle size on D. magna; however, it was found that toxicity was not a function of size and ranged from 3-4 μg/L for all three sets of Ag nanoparticles tested. This was possibly due to the large degree of aggregation when these nanoparticles were suspended in standard synthetic freshwater. Moreover, the LC(50) values for Ag-Au bimetallic nanoparticles were found to be between that of Ag and Au but much closer to that of Ag. The bimetallic particles containing 80% Ag and 20% Au were found to have a significantly lower toxicity to Daphnia (LC(50) of 15 μg/L) compared to Ag nanoparticles, while the toxicity of the nanoparticles containing 20% Ag and 80% Au was greater than expected at 12 μg/L. The comparison results confirm that Ag nanoparticles were much more toxic than Au nanoparticles, and that the introduction of gold into silver nanoparticles may lower their environmental impact by lowering the amount of Ag which is bioavailable.

AuAg bimetallic nanoparticles film fabricated based on H 2O 2-mediated silver reduction and its application

A method to fabricate AuAg bimetallic nanoparticles film by H 2O 2-mediated reduction of silver was reported. Gold nanoparticles (Au NPs) were first adsorbed onto the surface of a self-assembled 2-aminoethanethiol monolayer-modified gold film or 3-aminopropyltriethoxysilane (APTES) monolayer-modified quartz slide. Upon further treatment of this modified film with the solution containing silver nitrate (AgNO 3) and H 2O 2, silver was deposited on the surface of Au NPs. The size of the AuAg bimetallic particles could be readily tuned by manipulating the concentration of H 2O 2. Surface plasmon resonance (SPR) was used to investigate the process, the deposition of silver on Au NPs modified gold film resulted in an obvious decrease of depth in the SPR reflectance intensity and minimum angle curves (SPR R-θ curves), which may be utilized for the quantitative SPR detection of the analyte, H 2O 2. Combination of the biocatalytic reaction that could yield H 2O 2 by using the enzyme, glucose oxidase, with the deposition of silver may enable the design of a glucose biosensor by SPR technique. Furthermore, we evaluated the AuAg bimetallic nanoparticles film for their ability to be an effective substrate for surface-enhanced Raman scattering (SERS).

Monodispersity control in the synthesis of monometallic and bimetallic quasi-spherical gold and silver nanoparticles

In order for the nanoparticles of Au and Ag to be useful for a wide range of applications, the tailorability of the nanoparticle properties through controlled changes of composition, size, shape, and crystal structure is absolutely essential. Furthermore, these nanoparticle attributes must be delivered in high monodispersity to assure a consistent application performance. High monodispersity is also a requirement for the assembly of nanoparticles into extended nanostructures or mesoscale devices which may be needed for some applications. This article describes a variety of colloidal synthesis methods in use today for the preparation of monodisperse Au, Ag, and bimetallic Au-Ag nanoparticles. The emphasis is on the analysis of the efficacy of each method for tailoring the nanoparticle size and crystal structure. The scope of work surveyed is confined to quasi-spherical nanoparticles in the size range from sub-nanometre to several tens of nanometres.

Synthesis and optical properties of Au@Ag bimetallic nanoparticles

Synthesis of Au, Ag monometallic, and Au-Ag bimetallic nanoparticles have been synthesised by successive reduction of metal salts with ascorbic acid on prefabricated seeds in the presence of cetyltrimethylammonium bromide (C16H33)N(CH3)3Br (CTAB), as a cationic surfactant, is presented in this paper. This coverage method for the prefabricated seeds is uniform, although in some cases deviations from a spherical shape are observed with the formation of nanorods or nanoprisms. Results using high-resolution STEM-XEDS elemental mapping suggest that the actual distribution of the two metals within the multilayer spheres may involve partial alloying of the metals.

A Facile and Controllable Strategy to Synthesize Au−Ag Alloy Nanoparticles within Polyelectrolyte Multilayer Nanoreactors upon Thermal Reduction

A new synthesis strategy has been developed for the preparation of bimetallic gold-silver (Au-Ag) alloy nanoparticles by the virtue of polyelectrolyte multilayer (PEM) nanoreactors. By controlling the assembly conditions, gold and silver ions can be effectively loaded onto the PEM composed of polyethylenimine (PEI) and poly(acrylic acid) (PAA) simultaneously. Upon further thermal treatment, Au-Ag alloy nanoparticles with sizes of ca. 3.8 nm formed in the PEM, which were characterized in detail by UV-vis absorption spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) analysis. Appearance of a single plasmon band in the visible region and lack of apparent core-shell structures in the TEM images confirm the formation of homogeneous Au-Ag alloy nanoparticles. In addition, the surface plasmon absorption band of the Au-Ag alloy nanoparticles shows linear blue-shift with increasing Ag content, which also supported the formation of alloy nanoparticles. Several key parameters of the present strategy have been investigated, which showed that pH of both the assembly solution and gold salt solution and the choice of polymers for constructing PEM, as well as the reduction approach, all played an important role in successfully synthesizing bimetallic Au-Ag nanoparticles. The formation mechanism of alloy nanoparticles has also been discussed based on the spectral evolution during the thermal reduction.

Structural characterization of bimetallic Ag-Au nanoparticles in glass

Metal nanoparticles embedded in glass have been thoroughly studied because of their specific optical properties. The present work is directed to the fabrication of bimetallic Ag/Au nanoparticles by double ion implantation and their structural investigation. Ion-implanted samples were measured at the Ag K- and Au L3-edge at HASYLAB/Hamburg and ESRF/Grenoble, respectively, in fluorescence mode (at 10 and 20 K). The Fourier transformed spectra show Ag-Ag and Ag-O bonds for small ion doses. For high ion doses two different correlations (Ag-Ag and Ag-Au) can be found between 2 and 3 Å. At the Au L3-edge, the high-dose implantation creates an additional Au-Ag correlation visible in the Fourier transformed spectra. These results indicate the formation of Ag-Au alloy nanoparticles for high-dose sequential implantation of Ag and Au ions (4×1016 ions/cm2 in each case) whereas for lower doses mainly the ionic state of implanted ions should exist. Transmission electron microscopy characterization revealed the formation of smaller homogeneous particles of ≈5 nm mean size and larger ones of ≈15 nm that exhibit an internal void, i.e. hollow core-shell particles. EXAFS data prove bimetallic structures for all nanoparticles.

Ionic liquid assisted one step green synthesis of Au–Ag bimetallic nanoparticles

Au–Ag bimetallic nanoparticles have been fabricated by one-step simple electrochemical deposition method using ionic liquid as green electrolyte (1-butyl-3-methylimidazolium tetrafluoro borate). Fabricated Au–Ag bimetallic nanoparticles have been characterized using cyclic voltammetry (CV), FE-SEM, UV–vis spectroscopy, and X-ray diffraction (XRD) studies. The electrodeposited Au–Ag bimetallic nanoparticles were found in the size range of 16–30 nm, respectively. This type of Au–Ag bimetallic nanoparticles could be directly applied for the optoelectronic and biosensing applications.

Synthesis of bi-metallic Au–Ag nanoparticles loaded on functionalized MCM-41 for immobilization of alkaline protease and study of its biocatalytic activity

In this work, Au–Ag nanoparticles (Au–Ag-bi-MNPs) have been prepared on amine functionalized Si-MCM-41 (NH 2–Si-MCM-41) particles through a reduction of AgNO 3 and HAuCl 4 by NaBH 4 at ambient conditions. Au–Ag-bi-MNPs loaded on the NH2–Si-MCM-41, provide a good biocompatible surface for immobilization of the enzyme alkaline protease. This immobilization, presumably due to bonding between core shell nanoparticles and OH in serine 183 in alkaline protease seems to be of an ionic exchange nature. We found that the alkaline protease immobilized on the Au–Ag-bi-MNPs/Si-MCM-41 is an active biocatalyst, stable at different pH and temperature. The bio catalytic activity of free alkaline protease in solution was 64 U/mg (Units per milligram), whereas that of the alkaline protease immobilized on Au–Ag-bi-MNPs/Si-MCM-41 was 75 U/mg. This improvement of the biocatalytic activity may be due to a really increased activity per molecule of immobilized enzyme or to a purification of the enzyme. The alkaline protease molecules immobilized on the (Au–Ag)/ NH 2-MCM-41 surface retained as much as 80% of the catalytic activity recorded at pH=8, and showed significant catalytic activity of alkaline protease in the bioconjugate material. The biocatalytic materials were easily separated from the reaction medium by mild centrifugation and exhibits excellent reuse and stability characteristics over four successive cycles. The optimum temperature ranged from 35 ∘C–55 ∘C and pH=8 for bioactivity of the alkaline protease in the assembly system was observed to be higher than that of the free enzyme in solution. The enzyme biocatalytic activity was monitored by UV-visible spectroscopy. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and dispersive analysis of X-RAY (EDAX) were used to characterize the size and morphology of the prepared materials.