Au Bimetallic Nanoparticles Research Articles

Photocatalytic Ullmann coupling of aryl halides by a novel blended catalyst consisting of a TiO2 photocatalyst and an Al2O3 supported Pd–Au bimetallic catalyst

Synergy of TiO2 photocatalyst and Pd–Au bimetallic nanoparticles is essential for the efficient photocatalytic Ullmann coupling of aryl halides.

Fabrication of Ag-Au bimetallic nanoparticles by laser-induced dewetting of bilayer films

We here show that Ag-Au bimetallic nanoparticles (NPs) can be produced by dewetting an Ag/Au bilayer film coated on glass using a nanosecond-pulsed laser beam. Elemental analysis revealed that the obtained bimetallic NPs are Ag-Au alloys, with two elements well mixed over the whole volume of the particle. The composition of the produced particles was controllable by changing the relative thickness of each layer. The localized surface plasmon resonance (LSPR) peak was red-shifted with an increasing Au content and the LSPR wavelength could be tuned from 415 to 525 nm by varying the alloy composition. A film area of several square centimeters could be transformed into Ag-Au NPs by a single laser pulse of 6 ns duration. This study provides a facile and scalable route to prepare bimetallic NPs for plasmonic and other applications.

Determination of the structure and composition of Au-Ag bimetallic spherical nanoparticles using single particle ICP-MS measurements performed with normal and high temporal resolution

In this study, the information that can be obtained by combining normal and high resolution single particle ICP-MS (spICP-MS) measurements for spherical bimetallic nanoparticles (BNPs) was assessed. One commercial certified core-shell Au-Ag nanoparticle and three newly synthesized and fully characterized homogenous alloy Au-Ag nanoparticle batches of different composition were used in the experiments as BNP samples. By scrutinizing the high resolution spICP-MS signal time profiles, it was revealed that the width of the signal peak linearly correlates with the diameter of nanoparticles. It was also observed that the width of the peak for same-size nanoparticles is always significantly larger for Au than for Ag. It was also found that it can be reliably determined whether a BNP is of homogeneus alloy or core-shell structure and that, in the case of the latter, the core comprises of which element. We also assessed the performance of several ICP-MS based analytical methods in the analysis of the quantitative composition of bimetallic nanoparticles. Out of the three methods (normal resolution spICP-MS, direct NP nebulization with solution-mode ICP-MS, and solution-mode ICP-MS after the acid dissolution of the nanoparticles), the best accuracy and precision was achieved by spICP-MS. This method allows the determination of the composition with less than 10% relative inaccuracy and better than 3% precision. The analysis is fast and only requires the usual standard colloids for size calibration. Combining the results from both quantitative and structural analyses, the core diameter and shell thickness of core-shell particles can also be calculated.

4-Nitrophenol reduction catalysed by Au-Ag bimetallic nanoparticles supported on LDH: Homogeneous vs. heterogeneous catalysis

Bimetallic nanoparticles, which are composed of two metal elements in a particle, exhibit much higher catalytic activity than respective monometallic ones due to new bi-functional or synergistic effects, so-called a ligand and/or an ensemble effect. In this work, a novel homogeneous as well as heterogeneous AuAg bimetallic nanocatalyst have been synthesized and supported on layer double hydroxide (LDH) by a simple wet chemical process. The support of LDH has reduced the size as well as capped the bimetallic nanoparticles and hence prevents the agglomeration. The surface morphology and chemical composition of these bimetallic nanoparticles were examined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It was found that alloy (40–60nm) and core-shell (15–30nm) AuAg bimetallic nanoparticles were formed for heterogeneous and homogeneous composites, respectively. Moreover, the different compositions of as-synthesized AuAg bimetallic nanoparticles were utilized for the catalytic reduction of 4-nitrophenol. The highest activity was observed for the AuAg nanoparticles prepared with AuAg ratio at 1:3 and the activity became 10 to 45 times higher than that of original monometallic Au or Ag nanoparticles. The rate kinetics was studied for both homogeneous and heterogeneous system on the reduction of 4-nitrophenol and observed that the rate of reduction was greater in case of homogeneous catalysts as compared to heterogeneous catalysts. Also, the heterogeneous catalysts were effortlessly recovered and reused (up to 5cycles) after completion of the reduction reaction.

Enlarge the biologic coating-induced absorbance enhancement of Au-Ag bimetallic nanoshells by tuning the metal composition

Surface plasmon resonance (SPR) absorption properties of biologic layer-coated Au-Ag core-shell nanoparticle have been studied theoretically. By comparing with pure Au and Ag nanoparticles, the absorption peak intensity of Au-Ag bimetallic nanoparticle is more dependent on the dielectric coating, and the longer wavelength peak corresponding to the Au-Ag interface is more sensitive to the coating thickness. As the Au-Ag composition ratio is increased, the dielectric coating-dependent peak intensity change is always non-monotonous, and the critical Au-Ag composition ratio corresponding to the greatest peak intensity increase could be further tuned by changing the dielectric constant of the coated dielectric layer. The physical mechanism of the non-monotonous sensitivity change has been attributed to the Au-Ag composition ratio-dependent separation and overlap of the two SPR peaks from Au-Ag interface and outer Ag surface. These results indicate that the plasmonic absorption intensity of Au-Ag core-shell nanoparticle could be used in refractive index sensing and biologic detection.

Decoration of Carbon Nitride Surface with Bimetallic Nanoparticles (Ag/Pt, Ag/Pd, and Ag/Au) via Galvanic Exchange for Hydrogen Evolution Reaction

Here, we propose the synthesis of AgPt, AgPd, and AgAu bimetallic nanoparticles (NPs) on a carbon nitride (C3N4) surface via a galvanic exchange technique for the hydrogen evolution reaction (HER). Prior to the synthesis of C3N4/AgPt, AgPd, and AgAu, Ag NPs were synthesized on a C3N4 surface. For the synthesis of Ag NPs, initially Ag+ ions were adsorbed and then reduced by NaBH4 resulting in the decoration of Ag NPs. These Ag NPs were then subjected to galvanic exchange where sacrificial Ag was replaced by Pt2+, Pd2+, and Au3+ to fabricate AgPt, AgPd, and AgAu NPs. The galvanic exchange reaction occurs on a solid substrate, which favored slow exchange of Ag and resulted in the transformation of Ag into AgPt, AgPd, and AgAu alloys. The synthesized heterostructures were characterized with the help of PXRD, XPS, TEM, FESEM, and EDS techniques. All the materials were applied for hydrogen evolution using 0.5 M H2SO4 solution. C3N4/AgPt shows efficient electrocatalytic activity as it requires only −150 mV poten...

Phytochemicals mediated synthesis of multifunctional Ag-Au-TiO2 heterostructure for photocatalytic and antimicrobial applications

In this study, Ag-Au bimetallic composite type nanoparticles (∼13 nm) were prepared in aqueous media using Aegle marmelos leaf extract. Upon etching with ammonia solution, the formed ∼13 nm particles were reduced to ∼5 nm spherical alloy type Ag-Au with higher Au content (∼82.0%). In addition, with Tetrabutyl orthotitanate introduction in the same reaction media, Ag-Au-TiO2 heterostructures (∼9 nm) were obtained. The synthesized nanoparticles of various types were analyzed by UV–Vis. and photoluminescence (PL) spectroscopy, HR-TEM, and FTIR techniques. It was found that among the synthesized particles, Ag-Au-TiO2 heterostructures displayed promising PL properties, superior photocatalytic activity towards SDBS degradation, and antimicrobial activity against the studied bacterium, Escherichia coli. The multifunctionality of these particles may be useful for many industrial applications such as catalysis to waste water treatment.

Preparation of Au–Ag bimetallic nanoparticles for enhanced solar photothermal conversion

In this study, the solar photothermal conversion performance of bimetallic Au–Ag nanoparticles (NPs) was investigated experimentally. NPs were prepared using a sodium citrate thermal reduction method, using the same procedure and materials to maintain the same particle surface properties. NPs with a tunable plasmon resonance wavelength and demonstrating a high intensity in the visible region were obtained by adjusting the molar ratio of Ag to Au precursors. Experimental results show that blended Au–Ag NPs exhibit a solar photothermal conversion efficiency of 31.41%, which lies between the values of pure Au and Ag NPs under the same NP volume fraction due to the independently scatter light of the Au and Ag NPs in this composite system. Bimetallic Au–Ag NPs demonstrated the highest solar photothermal conversion efficiency of 41.37%, a 31.7% increase over that of blended Au–Ag NPs. The efficiency of the bimetallic Au–Ag NP system was also higher than that of the pure Au NPs (37.81%) with a 40% decrease in Au consumption.

Effect of core@shell (Au@Ag) nanostructure on surface plasmon-induced photocatalytic activity under visible light irradiation

We prepared Au-Ag nanoparticles (NPs) with two different morphologies over SrTiO3 to investigate the effect of composite nanostructure on surface plasmon-induced photocatalytic activity; core@shell (Au@Ag) NPs were synthesized by a multi-step citric reduction method, and Au-Ag bimetallic NPs were prepared by a photo-reduction method. (Au@Ag)/SrTiO3 and Au-Ag/SrTiO3 showed strong photoabsorption in the visible light response due to a localized surface plasmon resonance (LSPR) of Ag. Moreover, they could oxidize 2-propanol to acetone and CO2 under visible light irradiation (440<λ<800nm). From a comparison of action spectra for acetone evolution and the Kubelka-Munk function, it was confirmed that photocatalytic activities of (Au@Ag)/SrTiO3 and Au-Ag/SrTiO3 were induced by photoabsorption based on LSPR excitation of Ag. Interestingly, the rate of acetone evolution over (Au@Ag)/SrTiO3 was 1.5-times higher than that of over Au-Ag/SrTiO3, suggesting that the core@shell (Au@Ag) nanostructure contributes to the efficient surface plasmon-induced photocatalytic activity.

Continuous electrochemical detection of hydrogen peroxide by Au-Ag bimetallic nanoparticles in microfluidic devices

We developed electrochemical microfluidic devices containing Au-Ag bimetallic nanoparticles on single-walled carbon nanotube (SWCNT) electrodes for precise, rapid and non-enzymatic electrochemical detection of hydrogen peroxide (H2O2). A homogeneous SWCNT layer on a glass substrate was patterned by a standard photolithography method and an O2-plasma technique. The patterned SWCNT layers were used as working electrode, counter electrode, and reference electrode in a 1mm wide and 23μm deep microchannel. To enhance the electrochemical catalytic properties of the working electrode, Au covered Ag nanoparticles (NPs) were electrochemically deposited on the SWCNT working electrode with current streaming solution into a microfluidic channel. The AgNPs had catalytic activity to improve the reduction of H2O2 combined with AuNPs, which could support catalytic reaction of AgNPs. The reduction in H2O2 in fabricated devices was monitored at an optimized condition and was linear with H2O2 concentration, resulting in a sensitivity of 13.1μA·cm−2·mM−1, a correlation coefficient of r2=0.985, and limit of detection 26.8μM (S/N=3). For the analysis of real samples, diluted antiseptic solutions containing 3wt% H2O2 were used to determine the concentration of H2O2 in the pharmaceutical sample. The recovery values ranged from 97% to 107%, and relative standard deviations were below 5%. We expect that the developed microfluidic sensor is a prospective electrochemical platform for accurate, reproducible non-enzymatic detection of H2O2.

Optical spectroscopy of arrays of Ag–Au nanoparticles obtained by vacuum-thermal evaporation

The possibility of creating irregular arrays of bimetallic Ag–Au nanoparticles is investigated. The ability to manipulate their optical properties based on the simple engineering processes of thermal spraying followed by low-temperature annealing is demonstrated.

Random alloy of Au-Ag bimetallic nanoparticles at room temperature—facile synthesis and vibrational properties

The synthesis of nanometric alloys, or nanoalloys, is gaining interest in nanoscience due to their new and attractive physical properties. Furthermore, they improve the efficiency and performance of the diverse nanotechnological applications in comparison with the nanostructures composed of only one material. This study presents a novel synthesis method that facilitates the production of Au-Ag random bimetallic nanoalloys with uniform shape at room temperature, using the reducing and stabilizing properties of low-toxicity molecules, such as sucrose, ascorbic acid, and rongalite. The images taken with a transmission electron microscope (TEM) showed spherical bimetallic nanoparticles between 7 and 12 nm. The presence of Au and Ag in the nanostructures was confirmed by EDS. The optical absorption analysis showed a band centered at 480 nm, associated with surface plasmon resonance in Au-Ag nanoalloys. A Raman band was observed around 98 cm−1 after the nanoparticles were synthesized. Additionally, the behavior of the radial breathing modes (RBM) of mixed bimetallic nanoalloys of Au20-n Ag n (con n = 0–20) clusters was analyzed. The analysis was performed with the density functional theory (DFT) at Becke level, three-parameter, Lee-Yang-Parr (B3LYP) in combination with basis set Los Alamos Laboratory 2 double ζ (LANL2DZ). The predicted vibrational modes associated with RBM are located around 90–100 cm−1 approximately. This shows a good tendency and correlation with the Raman band detected experimentally at low wave numbers.

Nanowire networks and hollow nanospheres of Ag–Au bimetallic alloys at room temperature

Due to their physicochemical properties, metallic nanoalloys have potential applications in biomedicine, electrocatalysis and electrochemical sensors, among many other fields. New alternative procedures have emerged in order to reduce production costs and the use of toxic substances. In this study we present a novel low-toxicity synthesis method for the fabrication of nanowire networks (NWNs) and Ag–Au hollow nanospheres. The synthesis process is performed at room temperature without any sophisticated equipment, such as special cameras or furnaces, etc. Transmission electron microscopy showed that the NWNs contain random alloys with a diameter of between 10–13 nm. The radius for the hollow nanospheres is approximately located between 70–130 nm. The absorption bands in the UV–vis spectrum associated with the surface plasmon in Ag–Au bimetallic nanoparticles are highlighted at 385 nm for the NWNs and 643 nm for the hollow nanospheres. The study was performed with low-toxicity substances, such as rongalite, ascorbic acid and sucrose, and showed high efficiency for the fabrication of these types of nanostructures, as well as good stability for long periods of time.

Light trapping enhancement induced by bimetallic non-alloyed nanoparticles on a disordered subwavelength flexible thin film crystalline silicon substrate using metal-assisted chemical etching.

We report the application of gold and silver (AuAg) bimetallic non-alloyed nanoparticles (BNNPs) on disordered subwavelength structures (d-SWSs). The combined advantages of the plasmonic structures and d-SWSs improved the light trapping performance of flexible thin film crystalline silicon (c-Si) solar cells. Antireflective d-SWSs were fabricated using spin-coated Ag ink and subsequent metal-assisted chemical etching, which reduced the ion-induced surface damage produced by the dry etching process. The dimensions of the d-SWSs were finely tuned by adjusting the Ag ink ratio. Au8Ag8 BNNPs were employed on optimized d-SWSs to achieve low reflectance at broadband wavelengths. The Au8Ag8 BNNPs on the d-SWSs showed 180% and 145% enhanced absorption compared to bare c-Si film and Au8Ag8 BNNPs on c-Si film, respectively, in the wavelength range of 300-1100 nm. After 200 cycles of bending the antireflection of the structures remained similar to the original level. This study introduces new approaches for light management in flexible thin film c-Si solar cells over the broadband wavelength range.

A model electrode of well-defined geometry prepared by direct laser-induced decoration of nanoporous templates with Au–Ag@C nanoparticles

We present an original type of model electrode system consisting of bimetallic Au–Ag nanoparticles embedded in an amorphous carbon matrix with an extremely well-defined geometry of parallel, straight, cylindrical macropores. The samples are prepared in one step by direct laser deposition of the metal/carbon composite onto the inner walls of a porous ‘anodic’ alumina matrix serving as a template. The coating is homogeneous from top to bottom of the pores, and the amount of material deposited can be tuned by the duration of the deposition procedure. As a test system, we demonstrate that a bimetallic Ag–Au@C system is catalytically active for the electrochemical oxidation of glucose in alkaline solution, the anodic reaction of a direct glucose fuel cell. Furthermore, the electrocatalytic current density increases with the amount of Ag–Au@C NPs deposited, up to a point at which the pores are clogged with it. This type of model system allows for the systematic study of geometric effects in fuel cell electrodes. It can be generalized to a number of different nanoparticle compositions, and thereby, to various electrocatalytic reactions.

Selective and sensitive colorimetric determination of cobalt ions using Ag–Au bimetallic nanoparticles

Selective and sensitive colorimetric detection of Co2+based on the aggregation of Ag–Au BNPs is due to the formation of positively charged (en)2CoS2O3+on the negative nanoparticle surface.

Dual Heterogeneous Catalyst Pd–Au@Mn(II)-MOF for One-Pot Tandem Synthesis of Imines from Alcohols and Amines

A new Mn(II) metal-organic framework (MOF) 1 was synthesized by the combination of 4,4,4-trifluoro-1-(4-(pyridin-4-yl)phenyl)butane-1,3-dione (L) and Mn(OAc)2 in solution. 1 features a threefold-interpenetrating NbO net containing honeycomb-like channels, in which the opposite Mn(II)···Mn(II) distance is 23.5075(10) Å. Furthermore, 1 can be an ideal platform to support Pd-Au bimetallic alloy nanoparticles to generate a composite catalytic system of Pd-Au@Mn(II)-MOF (2). 2 can be a highly active bifunctional heterogeneous catalyst for the one-pot tandem synthesis of imines from benzyl alcohols and anilines and from benzyl alcohols and benzylamines.

Studies on l-histidine capped Ag and Au nanoparticles for dopamine detection

This work demonstrates the effective surface functionalization of Ag, Au and bimetallic Ag-Au nanoparticles using l-histidine for colorimetric detection of dopamine (DA) which plays majorly in recognizing the neurological disorder. l-Histidine (l-His) capped Ag, Au, and bimetallic Ag-Au nanoparticles are characterized using physico-chemical techniques. The optical behaviour of nanoparticles has been analysed at various time intervals using UV–Vis absorption spectroscopy. FT-IR results provide the evidence of chemical bonding between l-histidine and metal nanoparticles. Its structure with the capping of l-His was clearly shown in HR-TEM images. The average size of nanoparticles has calculated from TEM image fringes are 11nm, 5nm and 6.5nm respectively, matches with crystals size calculated from X-ray diffraction pattern. Enhanced optical nature of nanoparticles provides the best platform to develop a colorimetric-based biosensor for DA detection. After addition of DA, a rapid colour change has been noted in colloids of nanoparticles. The substantial changes in absorbance and λmax in metal nanoparticles respect to DA concentration have been observed and formulated. This is one of the successive methods for trace level determination of DA and will be going to a significant material for designing biosensor to determine DA in real extracellular body fluids.

Understanding Segregation Behavior in AuPt, NiPt, and AgAu Bimetallic Nanoparticles Using Distribution Coefficients

Bimetallic nanoparticles (BNPs) often possess peculiar segregation behavior as the particle size, composition, shape, and temperature are varied. However, a thermodynamic model for this phenomenon has been lacking thus far. We show for the first time that the distribution of metal species within a nanoparticle can be adequately captured in terms of distribution coefficients calculated for the facets, facet edges, and bulk regions. Thermodynamic relations for the distribution coefficients are derived. Only m distribution coefficients from the m(m – 1) distribution coefficients are independent, where m denotes the number of regions. The theory is applied to AuPt, NiPt, and AuAg BNPs. Distribution coefficients are calculated at 400 and 600 K using Monte Carlo (MC) simulations of varying BNP sizes and compositions. A wide range of mixing behavior from alloying to partial or full segregation and core–shell to onion-like structures can be observed. A key finding is that the distribution coefficients are indepen...

Yolk@Shell Nanoarchitectures with Bimetallic Nanocores-Synthesis and Electrocatalytic Applications.

In the present paper, we demonstrate a versatile approach for the one-pot synthesis of metal oxide yolk@shell nanostructures filled with bimetallic nanocores. This novel approach is based on the principles of hydrophobic nanoreactor soft-templating and is exemplified for the synthesis of various AgAuNP@tin-rich ITO (AgAu@ITOTR) yolk@shell nanomaterials. Hydrophobic nanoreactor soft-templating thereby takes advantage of polystyrene-block-poly(4-vinylpiridine) inverse micelles as two-compartment nanoreactor template, in which the core and the shell of the micelles serve as metal and metal oxide precursor reservoir, respectively. The composition, size and number of AuAg bimetallic nanoparticles incorporated within the ITOTR yolk@shell can easily be tuned. The conductivity of the ITOTR shell and the bimetallic composition of the AuAg nanoparticles, the as-synthesized AuAgNP@ITOTR yolk@shell materials could be used as efficient electrocatalysts for electrochemical glucose oxidation with improved onset potential when compared to their gold counterpart.