AuCu Nanoparticles Research Articles

Bimetallic AuCu nanoparticles coupled with multi-walled carbon nanotubes as ion-to-electron transducers in solid-contact potentiometric sensors

This work reports the first implementation of potentiometric solid-contact ion-selective electrodes (SC-ISEs) using the nanocomposite of ordered bimetallic AuCu nanoparticles coupled with multi-walled carbon nanotubes (oAuCuNPs-MWCNTs) as transducers. The unexplored nanocomposite oAuCuNPs-MWCNTs is deposited by solvent casting on gold sputtered copper electrodes as an intermediate layer and then covered with ion-selective membranes to form potentiometric sensors. The performance of the sensors is evaluated by determining Ca2+ and SO42− as an example of cation and anion, respectively. The obtained electrodes show response slopes of 29.0 mV/decade for Ca2+-selective SC-ISEs from 10−6 to 10−1 M, and −27.0 mV/decade for SO42--selective SC-ISEs from 10−5 to 10−1 M. Moreover, they exhibit high double layer capacitance (54 μF for Ca2+-selective SC-ISEs and 105 μF for SO42--selective SC-ISEs), fast charge transfer (resistance of 2.22 MΩ for Ca2+-selective SC-ISEs and 0.46 MΩ for SO42--selective SC-ISEs) and low potential drift (15 ± 3 μV/h for Ca2+-selective SC-ISEs and 118 ± 16 μV/h for SO42--selective SC-ISEs over 12 h). Additionally, none of the redox reactions, light interference and water films is observed. These results indicate that the combination of bimetallic nanoparticles and carbon nanomaterials offers great promise for the development of more robust and useful electrochemical sensors.

Combinatorial Synthesis of Binary Nanoparticles in Ionic Liquids by Cosputtering and Mixing of Elemental Nanoparticles.

Binary alloy nanoparticles were fabricated by two combinatorial methods: (I) cosputtering from elemental targets into the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [Bmim][(Tf)2N] and (II) by mixing elemental nanoparticles after sputtering them separately into [Bmim][(Tf)2N]. Both methods lead to the formation of Au-Cu nanoparticles (2.3 nm for cosputtered, 3.6 nm for mixed), however with different resulting compositions: cosputtered nanoparticles show a composition range of Au80-90Cu20-10; mixing of Au- and Cu-loaded ionic liquids leads to the formation of Au75Cu25 nanoparticles. Annealing the binary nanoparticles at 100 °C shows that the mixed nanoparticles grow to sizes of 4.1 nm, whereas the cosputterednanoparticles grow only to 3 nm.

Confined clustering of AuCu nanoparticles under ambient conditions

Abstract The study of bimetallic clusters has been increasing in recent years due to the wide range of novel applications, when compared with monometallic nanoparticles This paper presents a simple method of low toxicity to obtain bimetallic nanoparticle clusters of AuCu. The localized surface plasmon resonance (LSPR) of the nanoalloy was located in a value in between those reported for AuNP and CuNP. Raman bands of nanoparticle clusters of AuCu were observed in the range 130-300 cm−1. The structural and optical analysis of the synthesized nanoparticles confirmed the presence of the bond Au-Cu, with a particle size ranging from 1 to 2 nm. The geometries and vibrational modes were predicted for small metallic clusters of Au, Cu and bimetallic AuCu. The AgCu nanoparticles have been recently implemented in glasses to study optical properties, as well as antibacterial applications.

Disorder-to-Order Transition Mediated by Size Refocusing: A Route toward Monodisperse Intermetallic Nanoparticles.

Intermetallic nanoparticles are remarkable due to their often enhanced catalytic, magnetic, and optical properties, which arise from their ordered crystal structures and high structural stability. Typical syntheses of intermetallic nanoparticles include thermal annealing of the disordered counterpart in atmosphere (or vacuum) or colloidal syntheses, where the phase transformation is achieved in solution. Although both methods can produce intermetallic nanoparticles, there is difficulty in achieving monodisperse nanoparticles, which is critical to exploiting their properties for various applications. Here, we show that overgrowth on random alloy AuCu nanoparticles mediated by size refocusing yields monodisperse intermetallic AuCu nanoparticles. Size refocusing has been used in syntheses of semiconductor and upconverting nanocrystals to achieve monodisperse samples, but now we demonstrate size refocusing as a mechanism to achieve the disorder-to-order phase transformation in multimetallic nanoparticles. The phase transformation was monitored by time evolution experiments, where analysis of reaction aliquots with transmission electron microscopy and powder X-ray diffraction revealed the generation and dissolution of small nanoparticles coupled with an increase in the average size of the nanoparticles and conversion to the ordered phase. This demonstration advances the understanding of intermetallic nanoparticle formation in colloidal syntheses, which can expedite the development of electrocatalysts and magnetic storage materials.

Bimetallic AuCu nanoparticles supported on CeO2 as selective catalysts for glycerol conversion to lactic acid in aqueous basic medium

Gold-based catalysts, monometallic Au/CeO2 or bimetallic AuCu/CeO2, evaluated on the glycerol conversion to lactic acid, demonstrated to be active and selective at a reaction temperature of 220 °C in aqueous basic medium at low base concentration. The concentration of NaOH slightly modified the activity of AuCu/CeO2 for converting glycerol, while selectivity toward lactic acid increased on AuCu/CeO2 catalyst but had no influence on Au/CeO2 catalytic performance. Recyclability tests demonstrated that AuCu/CeO2 kept high conversion for up to the fourth catalytic cycle and selectivity remained stable, while conversion on Au/CeO2 significantly decreased in the second cycle. For instance, copper stabilized gold on AuCu/CeO2 catalysts for converting glycerol to lactic acid in aqueous medium at relatively high temperature of 220 °C. Characterization of AuCu/CeO2 catalyst using H2-TPR showed that the presence of Au modified the reduction events of Cu species, while HRTEM analysis of nanoparticles showed particles of an average size of 6.3 nm and lattice fringes for metallic Au and Cu. These results suggest that Au and Cu might be in close proximity.

Synthesis of rod-shaped Au-Cu intermetallic nanoparticles and SERS detection

Intermetallic phases in Au-Cu nanoparticles has been synthesized chemically in liquid phase. The heat-treatment of these nanoparticles at 180 °C for 1 h in solution phase led to the formation of Au-Cu alloy nanoparticles with nearly spherical shapes and monodispersed size of ∼10 nm. Subsequent heat-treatment at 300 °C for 30 min of these Au-Cu alloy nanoparticles not only revealed structural transformation to intermetallic phases (tetragonal AuCu (tP4) and cubic Cu3Au (cP4)) but also shape change occurs from spherical to rods having average aspect ratio ∼3.0. The structural determination at the particle has been carried out through nano-beam electron diffraction coupled with simulation of electron diffraction patterns and high resolution phase contrast images. These Au–Cu intermetallic nanoparticles exhibit an excellent surface enhanced Raman spectroscopic activity with methylene blue compared to that of Au-Cu alloy nanoparticles.

Investigation of Graphene Supported Au-Cu Nanoparticles As Electrocatalyst for CO2 Electro-Reduction

Carbon dioxide (CO2) is the most common greenhouse gas in our planet. Reduction of CO2 production and conversion of CO2 into useful materials at the same time is necessary. CO2 conversion using electro-catalysis can be controlled by electrode potentials and the reaction temperature. Also the electrochemical reaction systems are compact, modular and easy for scale-up applications. Cu-based composites with different compositions can seriously influence its electrocatalytic performance toward CO2 reduction reaction. In the present study, a rapid microwave heating method was used to prepare the graphene or carbon supported Au-Cu nanoparticles as electrocatalysts for the electrochemical reduction of CO2. The morphology and composition of the fabricated catalysts were examined using Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The activity of the fabricated catalysts for CO2 electro-reduction was examined using cyclic voltammetry and linear sweep voltammetry in acidic (pH=1.7), neutral (pH=6.3) and alkaline (pH=10.3) media. It was found that the graphene or carbon supported Au-Cu catalysts show a similar electrocatalytic activity for the electro-reduction of CO2 in the acidic media, whereas the graphene supported Au-Cu catalyst shows a higher activity in the neutral and alkaline media as compared with that of carbon supported Au-Cu catalyst.

Au and AuCu Nanoparticles Supported on SBA-15 Ordered Mesoporous Titania-Silica as Catalysts for Methylene Blue Photodegradation.

The photocatalytic degradation of methylene blue (MB) dye has been performed under UV irradiation in aqueous suspension, employing photocatalysts based on Au (1.5 wt %) and AuCu (Au/Cu = 1, 2.0 wt %), and supported on SBA-15-ordered mesoporous silica, with and without titania (Si/Ti = 3), in order to evaluate the versatility of this mesoporous support in this type of reaction of great impact from the environmental point of view. Samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption-desorption at −196 °C, and X-ray photoelectron spectroscopy (XPS), so as to study their structural, optical, and chemical properties. All the prepared catalysts were found to be active in the test reaction. The bimetallic AuCu-based catalysts attained very high MB degradation values, in particular AuCu/SBA-15 titania-silica sample reached 100% of dye oxidation after the monitored reaction period (120 min).

Structural properties of CuAu nanoparticles with different type. Molecular dynamic simulations

The paper is devoted to the thermal stability of a CuAu nanoparticles structure (D=5 nm) of various type (binary alloy, core-shell, "Janus" type) and of various percentage of copper atoms. The simulation was carried out with molecular dynamics, using the embedded atom potential. The authors defined the most preferable structural options from the standpoint of thermodynamics, as well as studied in detail the influence of different temperatures on the structural stability of CuAu nanoparticles.

Stimulation of secondary metabolites by copper and gold nanoparticles in submerge adventitious root cultures of Stevia rebaudiana (Bert.).

Nanotechnology is one of the advance technologies that almost found implications in every field of science. The importance is due to the unique properties of nanoparticles. In this study, bimetallic alloys of copper (Cu) and gold (Au) were tested in submerge root cultures of Stevia rebaudiana for production of biomass and secondary metabolites. A known amount of inoculum roots were submerged in liquid Murashige and Skoog medium containing combination of naphthalene acetic acid (NAA; 0.5 mg l-1) and different ratios of nanoparticles (NPs). NAA augmented medium was used as control. The addition of nanoparticles (30 µg l-1) stimulated biomass accumulation (1.447 g/flask) on 27th day of log phases. The maximum total phenolics content (TPC; 16.17 mg/g-DW) and total flavonoids content (TFC; 4.20 mg/g-DW) were displayed using AuCu-NPs (1:3) and NAA. The same combinations enhanced total phenolic production (TPP; 116 mg/L) and total flavonoid production (TFP; 29.5 mg/L) in submerged cultures. A strong correlation was observed between phenolics, flavonoids and dry biomass. Moreover, maximum 1, 1-diphenyl-2-picrylhydrazyl (DPPH) activity of 79% was displayed by addition of AuCu (1:3) nanoparticles. In conclusion, nanoparticles application has shown a positive effect in enhancing biomass and secondary metabolites production in adventitious root cultures of Stevia rebaudiana.

Electrochemical reduction of CO2 at CuAu nanoparticles: size and alloy effects

Reduction of CO2 at Cu or Au electrodes typically yields methane or CO, respectively. Cu and Au nanoparticles and their alloys offer unique advantages over foil electrodes in terms of reduced overpotentials and product selectivities. In this work, we explore the electrochemical reduction of CO2 in aqueous electrolytes using alloys of Cu and Au including 2 and 6 nm nanoparticles along with polycrystalline foils. These results show the CuAu alloys primarily produce CO; however, yields are dramatically increased relative to Au. CuAu electrodes in the form of planar foils produce up to 3.4 times more CO yields relative to Au foil. Most remarkably, nanoparticle electrodes provide up to 12.5-fold CO yield increases relative to polycrystalline alloy foils and 175-fold CO yield increases relative to bulk Au foils. Voltammetry shows that onset potentials for CO2 reduction are shifted anodically with smaller nanoparticle sizes and with greater Au content. The dramatic increase in CO yields with nanoparticle alloys is attributed to the improved CO2 deoxygenation associated with Cu interfaces and the relatively facile desorption of CO from low-coordination Au sites.

Gold-copper bimetallic nanoparticles supported on nano P zeolite modified carbon paste electrode as an efficient electrocatalyst and sensitive sensor for determination of hydrazine

In this report, a facile, efficient and low cost electrochemical sensor based on bimetallic Au-Cu nanoparticles supported on P nanozeolite modified carbon paste electrode (Au-Cu/NPZ/CPE) was constructed and its efficiency for determination of hydrazine in trace level was studied. For this purpose, agro waste material, stem sweep ash (SSA) was employed as the starting material (silica source) for the synthesis of nano P zeolite (NPZ). After characterization of the synthesized NPZ by analytical instruments (scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy), construction of Au-Cu/NPZ/CPE was performed by three steps procedure involving preparation of nano P zeolite modified carbon paste electrode (NPZ/CPE), introducing Cu+2 ions into nano zeolite structure by ion exchange and electrochemical reduction of Cu+2 ions upon applying constant potential. This procedure is followed by partial replacement of Cu by Au due to galvanic replacement reaction (GRR). The electrochemical properties of hydrazine at the surface of Au-Cu/NPZ/CPE was evaluated using cyclic voltammetry (CV), amperometry, and chronoamperometry methods in 0.1 M phosphate buffer solution (PBS). It was found that the prepared sensor has higher electrocatalytic activity at a relatively lower potential compared to other modified electrodes including Au/NPZ/CPE, Cu/NPZ/CPE, Au-Cu/CPE and etc. Moreover, the proposed electrochemical sensor presented the favorable analytical properties for determination of hydrazine such as low detection limit (0.04 µM), rapid response time (3 s), wide linear range (0.01–150 mM), and high sensitivity (99.53 µA mM−1) that are related to the synergic effect of bimetallic of Au-Cu, porous structure and enough surface area of NPZ. In addition, capability of Au-Cu/NPZ/CPE sensor was successfully tested in real samples with good accuracy and precision.

Dual structural transition in small nanoparticles of Cu-Au alloy

Cu-Au alloy nanoparticles are known to be widely used in the catalysis of various chemical reactions as it was experimentally defined that in many cases the partial substitution of copper with gold increases catalytic activity. However, providing the reaction capacity of alloy nanoparticles the surface electronic structure strongly depends on their atomic ordering. Therefore, to theoretically determine catalytic properties, one needs to use a most real structural model complying with Cu-Au nanoparticles under various external influences. So, thermal stability limits were studied for the initial L12 phase in Cu3Au nanoalloy clusters up to 8.0 nm and Cu-Au clusters up to 3.0 nm at various degrees of Au atom concentration, with molecular dynamics method using a modified tight-binding TB-SMA potential. Dual structural transition L12 → FCC and further FCC → Ih is shown to be possible under the thermal factor in Cu3Au and Cu-Au clusters with the diameter up to 3.0 nm. The temperature of the structural transition FCC → Ih is established to decrease for small particles of Cu-Au alloy under the increase of Au atom concentration. For clusters with this structural transition, the melting point is found to be a linear increasing function of concentration, and for clusters without FCC → Ih structural transition, the melting point is a linear decreasing function of Au content. Thus, the article shows that doping Cu nanoclusters with Au atoms allows to control the forming structure as well as the melting point.

Sinter-Resistant and Highly Active Sub-5 nm Bimetallic Au-Cu Nanoparticle Catalysts Encapsulated in Silica for High-Temperature Carbon Monoxide Oxidation.

A novel gold-copper-based silica-encapsulated mixed metal oxide (MMO) core-shell catalyst-with sub-5 nm MMO particles-was successfully synthesized via a reverse micelle process. The SiO2-encapsulated MMO catalyst was reduced under hydrogen flow to produce an Au-Cu@SiO2 catalyst. X-ray diffraction and X-ray photoelectron spectroscopy characterization confirmed the presence of Au-Cu nanocomposites in the catalyst, while transmission electron microscopy characterization revealed the core-shell structure of the catalyst with the presence of sub-5 nm Au-Cu nanoparticle cores inside SiO2 shells. Brunauer-Emmett-Teller surface characterization identified that the catalyst is porous and bimodal in nature. The effects of promoter metal ion, catalyst pretreatment (calcination), and the presence of CO2 in the feed stream on carbon monoxide (CO) oxidation over the Au-Cu@SiO2 catalyst were examined in the temperature range of 50-400 °C. A catalyst stability test was performed at 300 °C by conducting a CO oxidation reaction for 116 h on stream. The catalyst exhibited excellent efficacy for CO oxidation, with ∼100% conversion to CO2 achieved at 400 °C. While the presence of Cu enhanced the CO conversion at low to intermediate temperatures (50-300 °C), silica encapsulation of the Au-Cu nanocomposites facilitated remarkable stability of the catalyst. The activity of the Au-Cu@SiO2 catalyst is suitable for its application in automotive after-treatment devices, especially in low-temperature combustion engine exhausts.

The Crucial Role of the Support in the Transformations of Bimetallic Nanoparticles and Catalytic Performance

The combination of two or more metals, forming alloys, core–shells, or other complex heterometallic nanostructures, has substantially spanned the available options to finely tune electronic and structural properties, opening a myriad of opportunities that has yet to be fully explored in different fields. In catalysis, the rational exploitation and design of bimetallic and trimetallic catalysts has just started. Several major aspects such as stability, phase segregation, and alloy–dealloy mechanisms have yet to be deeply understood and correlated with intrinsic factors such as nanoparticle size, composition, and structure and with extrinsic factors, or external agents, such as temperature, reaction gases, and support. Here, by combining model catalysts based on AuCu nanoparticles supported on silica or alumina with in situ characterization techniques under redox pretreatments and CO oxidation reaction, we demonstrate the crucial role of the support with regard to determining the stable active phase of bime...

(Invited) Electrochemical Reduction of CO2 on Ligand-Protected Metal Nanoclusters

In this presentation, we report on the utilization of first-principles based computational technique to study electrochemical CO2 reduction mechanism on ligand protected metal nanoparticles. These materials are being pursued by the National Energy Technology Laboratory’s CO2 Utilization Technologies program in the quest to develop more active and selective catalyst for CO2 conversion into higher value products. We previously discovered an excellent CO2 conversion catalyst based on negatively charged, ligand-protected Au25(SC2H4Ph)18 - nanoclusters. A significant finding from our modeling is that ligand-protected nanocatalysts must be activated through the creation of surface defects. The exposed metals site is then free to function as critical reaction center for the conversion of CO2 into more valuable products. We have used this concept in our ongoing effort to understand the reduction process on ligand protected bimetallic Au-Cu nanoparticles. The reduction properties of such materials were experimentally found to be sensitive to the variation in the Cu content. Lastly, we present our ongoing investigation to predict trends in the activity of Ag, Au, Cu, Ir, Ni, Pd, Pt and Rh nanoparticles for CO2 reduction. We specifically looked at different particle sizes to investigate its influence on the activity.

Core-shell Cu@Au nanoparticles as an optical probe for ultrasensitive detection of chromium(VI) via an etching effect

Under normal circumstances, chromate ions cannot oxidize core-shell Cu-Au nanoparticles (NPs) because the standard redox potential of the Cr(VI)/Cr(III) system is lower than that of Au(I)/Au. However, in the presence of a certain concentration of hydrogen bromide, the Nernst potential becomes higher than that of Au(I)/Au and Cu(II)/Cu (as calculated by the Nernst equation). Based on this finding, a colorimetric method was developed that is based on oxidative etching of Cu@Au NPs by chromate. The Cu-Au NPs have a light red color in the presence of 5 mM HBr. On addition of Cr(VI), the gold shell is rapidly etched from the surface of the Cu-Au NPs, and this is accompanied by a color change to blue. The color changes were characterized by UV-vis spectroscopy. The absorbance at 526 nm changes in the 0.4 nM to 1 μM chromate concentration range, and the detection limit is 0.21 nM.

Structural Transformations of Au and Au-Cu Nanoparticles during Liquid-Phase Synthesis and Redox Reactions in Gaseous Environment

Structural Transformations of Au and Au-Cu Nanoparticles during Liquid-Phase Synthesis and Redox Reactions in Gaseous Environment

Electrochemical Activation of CO2 through Atomic Ordering Transformations of AuCu Nanoparticles.

Precise control of elemental configurations within multimetallic nanoparticles (NPs) could enable access to functional nanomaterials with significant performance benefits. This can be achieved down to the atomic level by the disorder-to-order transformation of individual NPs. Here, by systematically controlling the ordering degree, we show that the atomic ordering transformation, applied to AuCu NPs, activates them to perform as selective electrocatalysts for CO2 reduction. In contrast to the disordered alloy NP, which is catalytically active for hydrogen evolution, ordered AuCu NPs selectively converted CO2 to CO at faradaic efficiency reaching 80%. CO formation could be achieved with a reduction in overpotential of ∼200 mV, and catalytic turnover was enhanced by 3.2-fold. In comparison to those obtained with a pure gold catalyst, mass activities could be improved as well. Atomic-level structural investigations revealed three atomic gold layers over the intermetallic core to be sufficient for enhanced catalytic behavior, which is further supported by DFT analysis.

Electrochemical Reduction of CO2 Using Cu-Au Nanoparticles: Effects of Size and Composition

The electrochemical reduction of CO2 to light hydrocarbons allows renewable energy storage without increasing net atmospheric CO2. Alloys and nanoscale catalysts have emerged as potential electrocatalysts with high efficiencies and selectivities to valuable products. Here, we describe CuAu alloy nanoclusters with diameters of 2 nm and 5 nm for use as CO2 electroreduction catalysts. The Cu:Au ratio was controlled to yield nanoparticles with a range of alloy compositions ranging from Cu25Au75 to Cu72Au28. The yields and onset potentials were measured and compared to Cu, Au and CuAu bulk foils, where the nanoparticles showed a 50 fold increase in CO yield compared to Au foil, and greater than a 100 mV anodic shift in CO2 reduction onset potentials. As seen in Figure 1, the alloys showed greater improvements in yield as Au content increased. These improvements are attributed to low coordination active sites and to the bimetallic nature of these active sites. Figure 1