Au Bimetallic Nanoparticles Research Articles

Feasibility of using bimetallic Au-Ag nanoparticles for organic light-emitting devices.

Matching the resonant wavelength of plasmonic nanoparticles (NPs) and the emission band of organic materials is critical for achieving optimal plasmon-enhanced luminescence in organic light-emitting devices (OLEDs). However, the spectral matching is often unsatisfactory because the interior architecture of OLEDs limits the dimensions of the NPs to support the desired wavelength adjustment. In this article, we proposed a design strategy via AuxAg1-x alloy NPs to enable resonance tuning while preserving the size of the NP to suit the OLED design requirements. The bimetallic NPs, especially for x < 0.6, not only add one more degree of freedom to vary the plasmon wavelength but also provide the benefits of higher scattering and more intense and outspread electric fields over a broader spectrum compared to Au monometallic NPs. These features allow smaller NPs, which are more compatible with OLED interiors, to scatter electric fields more efficiently and increase the density of molecules interacting with the NP plasmons. In the presence of a nearby dipole emitter, the bimetallic NPs can simultaneously increase radiative enhancement and suppress non-radiative losses, which are advantageous for increasing the quantum yield and luminescence efficiency of the emitter. These improvements are associated with lower intraband and interband activities resulting from the higher molar fraction of Ag in the alloy NPs. We provided composition mappings to achieve enhanced luminescence for specified wavelengths at fixed NP sizes. Finally, we theoretically demonstrated that the bimetallic NPs could improve the light-extraction efficiency of OLEDs better than Au monometallic NPs. This work provides essential guidance to enable versatile plasmon-enhanced applications with predefined nanostructural geometries and wavelengths to match the device requirements.

Effect of nanotube diameter on the photocatalytic activity of bimetallic AgAu nanoparticles grafted 1D-TiO2 nanotubes

One-dimensional (1D) titanium dioxide (TiO2) nanostructures have enormous attention for next-generation renewal energy resources. In reference to that, present work reports the effect of different voltages (40 V and 60 V) on the structural and morphological properties of 1D-TiO2 nanotubes (TONTs) and their hybrids by grafting of bimetallic nanoparticles (BiMNPs) of AgAu. The growth at different voltages affects the morphology and diameters of TONTs as imaged using field emission scanning electron microscopy (FESEM). The variation in anodization voltage from 40 to 60 V increases the diameter of TONTs that offers a larger active surface area of TONTs. It is further revealed that the crystallinity and crystallite size of TONTs is increased after increasing the anodization voltage. Furthermore, TONTs are integrated with AgAu BiMNPs to form the hybrid structures. The AgAu-TONT hybrid forms a modified interface and induces less compressive strains that improve the charge separation at the interface and hence improve the electronic structure, as investigated by X-ray photoelectron spectroscopy (XPS) and X-ray Diffraction (XRD). On further exploring the 1D-TONTs and AgAu-TONTs for photocatalytic studies, it is observed that the photocatalytic activity of AgAu-TONTs is better than TONTs-40 V and TONTs-60 V. The improved photocatalytic activity in the AgAu-TONTs is due to the large surface area, charge carrier generation, and lesser compressive strain present at the interface.

Tunable optical properties of Ni–Ag and Ni–Au nanoparticles in magneto-plasmonic nanostructures

The combined optical and magnetic properties of magneto-plasmonic nanoparticles makes them ideal candidates for various applications in biomedical fields. In the present work, the optical properties of Ni–Ag and Ni–Au bimetallic alloy nanoparticles with varying sizes 20, 30, 40, 50, and 60 nm of spherical and aspect ratio 2, 3, and 4 of non-spherical nanostructures are studied by the discrete dipole approximation method in the water surrounding medium. Moreover, optical absorption spectra are studied to see the effect of polarization and different alloy compositions. The optical spectra is observed in the range of 371–1280 nm wavelengths and merged in visible-near-infrared region on the electromagnetic spectrum. The result shows that absorption spectra of bimetallic alloy nanoparticles can be well tuned by changing the particle size, aspect ratio’s, shapes, and compositions. Furthermore, Ni–Au nanoparticles have enrich optical absorption spectra as compared to Ni–Ag bimetallic nanoparticles. Our study provides a way to analyze and broaden the applications of bimetallic alloy nanoparticles in optical imaging, biomedical field, and therapeutics.

Synthesis of Au, Ag, and Au-Ag Bimetallic Nanoparticles Using Pulicaria undulata Extract and Their Catalytic Activity for the Reduction of 4-Nitrophenol.

Plant extract of Pulicaria undulata (L.) was used as both reducing agent and stabilizing ligand for the rapid and green synthesis of gold (Au), silver (Ag), and gold–silver (Au–Ag) bimetallic (phase segregated/alloy) nanoparticles (NPs). These nanoparticles with different morphologies were prepared in two hours by stirring corresponding metal precursors in the aqueous solution of the plant extracts at ambient temperature. To infer the role of concentration of plant extract on the composition and morphology of NPs, we designed two different sets of experiments, namely (i) low concentration (LC) and (ii) high concentration (HC) of plant extract. In the case of using low concentration of the plant extract, irregular shaped Au, Ag, or phase segregated Au–Ag bimetallic NPs were obtained, whereas the use of higher concentrations of the plant extract resulted in the formation of spherical Au, Ag, and Au–Ag alloy NPs. The as-prepared Au, Ag, and Au–Ag bimetallic NPs showed morphology and composition dependent catalytic activity for the reduction of 4-nitrophenol (4-NPh) to 4-aminophenol (4-APh) in the presence of NaBH4. The bimetallic Au–Ag alloy NPs showed the highest catalytic activity compared to all other NPs.

Tuning the photocatalytic activity of nanocomposite ZnO nanorods by shape-controlling the bimetallic AuAg nanoparticles

Decorating ZnO with noble metal nanoparticles is a promising strategy for overcoming the rapid recombination of pure ZnO. In this experiment, we evaluated the effects of AuAg nanoflowers (NFl) and AuAg mesopopcorns (MPOPs) on the photocatalytic properties of ZnO (NRs) in comparison with the conventional composite ZnO/Au NPs. ZnO NRs were grown on glass substrate via the ultrasonic spray pyrolysis (USP) and the hydrothermal methods while three types of noble metal particle shapes were synthesized via wet chemical method. The highest degradation percentages of methylene blue (MB) were achieved by the composites ZnO NRs/AuAg NFl, which reached 96% under UV light and 75% under visible light for 300 min. The AuAg NFl were grown in a flower-like shape with petals consisting of AuAg NPs with diameters of 10 nm covering almost the entire surface of ZnO. The photocatalytic performance improvement may be due to bimetallic AuAg in small nanoparticles play a more effective role in O2 adsorption and have the highest interfacial area, making it easier to transfer free electrons between ZnO and AuAg NFl as well as for O2 adsorption in the MB solution.

Electrochemical Determination of Caffeine Using Bimetallic Au−Ag Nanoparticles Obtained from Low‐cost Green Synthesis

AbstractA novel caffeine sensor was constructed. The sensor is based on a platinum electrode (PtE) modified with polypyrrole (PPY) and green synthesized Ag−Au bimetallic nanoparticles. The work further describes the synthesis of silver nanoparticles (AgNPs), gold nanoparticles (AuNPs), as well as Ag−Au bimetallic nanoparticles (BMNPs) using the extract of citrus sinensis (sweet orange) peels. The nanoparticles were used to form nanocomposite material supported on polypyrrole (PPY) and, consequently used to modify PtE using drop‐cast method. Synthesized nanomaterials were characterized by FT‐IR, UV‐Vis, XRD and TEM. Electrochemical characterization of the modified electrodes was conducted using the ferrocyanide/ferricyanide redox probe prepared in PBS. PPY/Ag‐AuBMNP modified PtE exhibited faster electron transport properties as well as enhanced catalytic current response as compared to bare‐PtE, PtE/AgNPs, PtE/AuNPs, PtE/Ag‐AuBMNPs and PtE/PPY. By Square‐wave voltammetry (SWV) the PPY/Ag‐AuBMNPs modified PtE yielded a detection limit of 2.02 μM with a sensitivity of 0.75 μA/μM, in the caffeine concentration range of 0 μM to 59 μM. The proposed sensor further demonstrated good selectivity and was successfully applied for the detection of caffeine in commercial samples.

Synthesis of bimetallic silver-gold nanoparticle composites using a cellulose dope: Tunable nanostructure and its biological activity

Introducing functional metal nanoparticles (NPs) into flexible substrate is being increasingly attempted to expand their application. Here, we extend the synthesis of cellulose to its unmodified dope achieving freestanding nanocomposite decorated with bimetallic Ag-Au NPs through the one pot reaction. In the procedure, cellulose chain not only acts as a reducing agent but also a biocompatible support for NPs with a mean size of 7.9–9.7 nm. Meanwhile, changing the addition order of Ag+ and AuCl4− generated different atom arrangement in the bimetallic NPs. Moreover, the correlation of bioactivity to NP atom arrangement was studied. The result revealed that the nanocomposite containing NPs with an ultrathin Ag-rich outermost shell around an Au-rich core showed better bactericidal ability while lower cytotoxicity. In addition, the nanocomposite exhibited a sensitive SERS property for determination of R6G with a high enhancement factor of 108.

Synthesis of Bimetallic Au-Ag/CMK-3 Catalysts and Their Catalytic Activity for the Oxidation of Amino Alcohol

CMK-3 supported highly dispersed Au-Ag bimetallic nanoparticles with different Ag/Au ratios were prepared by a sequential impregnation–reduction method without the use of any polymer stabilizer. Th...

TiO2-supported Au-Ag plasmonic nanocatalysts achieved by plasma restructuring and activation

Plasmonic Au-Ag/TiO2 bimetallic nanocatalyst is regarded as a promising visible-light (VL) photocatalyst due to its wide light absorption and potentially enhanced activity. For its preparation, Au precursors usually contain Cl and co-impregnation/co-deposition suffers from AgCl precipitation, and consequently Au and Ag have to be sequentially supported. However, Au and Ag species of the sequential preparation are individually isolated and difficult to be homogeneously mixed. Here we report an Au-Ag plasmonic nanocatalyst achieved by plasma restructuring and activation from the sequential preparation. The isolated cationic Au and Ag species on the sequentially-prepared Au-Ag/TiO2 sample are restructured to be homogeneously mixed and highly activated by O2 plasma, which can be partially auto-reduced to Au-Ag bimetallic nanoparticles within the induction period of a few minutes in VL photocatalytic oxidation of CO. The Au-Ag plasmonic nanocatalyst exhibits a strongly enhanced activity in the VL photocatalytic reaction. The contribution of O2 plasma treatment and the enhancement mechanism for the Au-Ag plasmonic nanocatalyst are disclosed.

Development of Plasmonic Photocatalyst by Site‐selective Loading of Bimetallic Nanoparticles of Au and Ag on Titanium(IV) Oxide

AbstractMorphology‐controlled rutile titanium(IV) oxide (TiO2) and anatase TiO2 were prepared by a hydrothermal method and their surfaces were selectively loaded with Au, Ag and AuAg bimetallic nanoparticles (NPs) by photo‐deposition in order to obtain visible‐light responsive photocatalysts. With the help of local surface plasmon resonance (LSPR) of noble metal NPs, the photocatalytic activity of noble metal‐loaded TiO2 under visible‐light irradiation was improved compared to that of bare TiO2. The enhancement of LSPR on the photocatalytic activity of rutile TiO2 was larger than that of anatase TiO2 with optimum amount of Au or AuAg. In addition, the reusability (stability) of AuAg‐loaded TiO2 was much better than that of Ag‐loaded TiO2. Double‐beam photoacoustic results confirmed different trap energy level distribution lead to different electron transfer ways, resulting in different oxidizing capabilities and they gave one of important strategies for designing visible‐light responsive TiO2.

Alkoxide structure effect on size and size distribution of Ag, Au and Ag@Au nanoparticles, prepared via alkoxide mild reduction in water

Gold and silver nanoparticles were synthesized via mild alkoxide reduction of Ag+ and AuCl4- in water, under alkaline conditions. Three non-toxic polyols (glycerin, β-cyclodextrin (βCD), and a polymer (of β-cyclodextrin)) were employed in each case as reducing and capping agent. TEM analysis revealed larger nanoparticles when glycerin was used, followed by β-cyclodextrin, and finally by the polymer. Different numbers of population maxima in nanoparticles size distribution from one alkoxide to another were observed and such variation was dependent on alkoxide’s structure complexity. In UV–Vis spectra the typical bands for gold and silver nanoparticles were detected. ζ-potential measurements showed more electrostatically stable capping layer for glycerin and βCD. For the polymer, the stability of the layer should be a result of bulk effects.On the other hand, Ag-Au bi-metallic nanoparticles with core–shell structure were obtained using glycerin and β-cyclodextrin, whereas a mixture of gold and silver nanoparticles was the result with the polymer. The latter was corroborated via TEM images, EDX, UV–Vis, ζ-potential, and DLS measurements. A systematic study was carried out to elucidate the influence of the different alkoxide molecules on the properties of the resulting nanoparticles.

Formation of Au-Ag alloy nanoparticles in amorphous silicon using sequential ion implantation

Au-Ag alloy nanoparticles were formed into amorphous silicon by sequential ion implantation of Au and Ag. Monocrystalline Si was amorphized at the initial moment of implantation with 1 × 1016 ions/cm2 gold ions, and then different silver fluences were applied in the range of 1 × 1016–1 × 1017 ions/cm2. After implantations the samples were investigated by means of Rutherford backscattering spectrometry and transmission electron microscopy. The nanoparticles were found to be formed at surface and sub-surface regions of the Si substrate, at depths corresponding to the maximum distribution of Au and Ag ions. The particles are crystalline in nature with sizes from 2 nm to 30 nm in diameter, increasing with silver ion fluence. Although the lattice constants of gold and silver are too close to be distinguished by measuring the characteristic interplanar spacings, imaging in scanning transmission mode confirms the formation of Au-Ag bimetallic nanoparticles, presenting a solid-solution alloy of gold and silver.

TD-DFT+TB: An Efficient and Fast Approach for Quantum Plasmonic Excitations

We study the quantum plasmonic features of gold and silver nanoparticles using TD-DFT+TB, a new density functional theory approach to the calculation of excited states, which combines a full DFT ground state with tight-binding approximations in the linear response calculation. In this framework, the optical properties of closed-shell Ag, Au and bimetallic Ag–Au nanoparticles with tetrahedral symmetry (with 20, 56, 120, and 165 atoms) and icosahedral structure (with 13, 55, and 147 atoms) were obtained and compared to full linear response time-dependent density functional theory (TD-DFT) as a reference and also to time-dependent density functional based tight binding (TD-DFTB) as a low-cost alternative approach. We find an excellent agreement of TD-DFT+TB calculated absorption spectra with the TD-DFT reference with errors less than 0.15 eV in peak positions, while TD-DFTB shows larger errors of about 1 eV. The computational cost for the ground state calculation is identical for TD-DFT and TD-DFT+TB, but the excited state calculation becomes about a hundred times faster when applying the TB approximation and is then almost negligible for the overall timing of the calculation. In contrast to TD-DFTB, which can only be applied to element combinations for which a suitable DFTB parametrization is available, TD-DFT+TB can be applied to any combination of elements. To assess the accuracy of TD-DFT+TB for different combinations of atoms, the plasmonic properties of bimetallic clusters with different ratios of Ag and Au atoms were obtained and the trend of energy and intensity reproduced in good agreement with TD-DFT, which is not possible using TD-DFTB with standard parameter sets.

Reversible loss of core–shell structure for Ni–Au bimetallic nanoparticles during CO2 hydrogenation

The high catalytic performance of core–shell nanoparticles is usually attributed to their distinct geometric and electronic structures. Here we reveal a dynamic mechanism that overturns this conventional understanding by a direct environmental transmission electron microscopy visualization coupled with multiple state-of-the-art in situ techniques, which include synchrotron X-ray absorption spectroscopy, infrared spectroscopy and theoretical simulations. A Ni–Au catalytic system, which exhibits a highly selective CO production in CO2 hydrogenation, features an intact ultrathin Au shell over the Ni core before and after the reaction. However, the catalytic performance could not be attributed to the Au shell surface, but rather to the formation of a transient reconstructed alloy surface, promoted by CO adsorption during the reaction. The discovery of such a reversible transformation urges us to reconsider the reaction mechanism beyond the stationary model, and may have important implications not only for core–shell nanoparticles, but also for other well-defined nanocatalysts. The structure of core–shell catalysts is often assumed to be conserved over a reaction. Now, an in situ study reveals that the shell of Ni@Au nanoparticles is reversibly converted into a Ni–Au alloy during CO2 hydrogenation, with important mechanistic implications.

Study of electrical conductivity of the coatings of bimetallic Au-Ag nanoparticles

The "metallic" temperature variation of the electrical resistivity of chemical nano gold-silver coatings with a silver content of 6.6 % at. up to 13.1 % at. determined in the temperature range 4.2-300 K. Features of low-temperature measurements of the resistance of nano-coatings were found and explained. The possibility of the appearance of superconductivity in them is discussed.

Optical Properties of Au-Ag Bimetallic Nanoparticles of Different Shapes for Making Efficient Bimetallic-Photonic Whispering Gallery Mode Hybrid Microresonators

For the first time, we propose a bimetallic-photonic whispering gallery mode (WGM) hybrid microresonator for the detection and sizing of single protein molecules in real time. To optimize the sensitivity of hybrid microresonators, theoretical simulations have been carried out to understand the optical properties of different types of Au-Ag bimetallic nanoparticles such as solid nanospheres, dielectric core-bimetallic nanoshells, nanostars, and nanoprisms using Lorenz-Mie theory, Aden-Kerker theory, and finite element method (FEM). The role of size and Au-Ag ratio on the optical properties of the nanospheres and nanoshells has been studied. In addition, the effect of the Au-Ag ratio on the optical properties of nanostars and nanoprisms has been investigated. The local electric field intensity enhancement values of bimetallic nanostructures of different shapes have been estimated using the FEM. Finally, the advantages of the bimetallic-WGM hybrid microresonator as compared to the monometallic-WGM hybrid microresonator have been explained in detail.

Functionalized Gold and Silver Bimetallic Nanoparticles Using Deinococcus radiodurans Protein Extract Mediate Degradation of Toxic Dye Malachite Green.

BackgroundBiodegradation of toxic organic dye using nanomaterial-based microbial biocatalyst is an ecofriendly and promising technique.Materials and MethodsHere, we have investigated the novel properties of functionalized Au-Ag bimetallic nanoparticles using extremophilic Deinococcus radiodurans proteins (Drp-Au-AgNPs) and their degradation efficiency on the toxic triphenylmethane dye malachite green (MG).Results and DiscussionThe prepared Drp-Au-AgNPs with an average particle size of 149.8 nm were capped by proteins through groups including hydroxyl and amide. Drp-Au-AgNPs demonstrated greater degradation ability (83.68%) of MG than D. radiodurans cells and monometallic AuNPs. The major degradation product was identified as 4-(dimethylamino) benzophenone, which is less toxic than MG. The degradation of MG was mainly attributed to the capping proteins on Drp-Au-AgNPs. The bimetallic NPs could be reused and maintained MG degradation ability (>64%) after 2 cycles.ConclusionThese results suggest that the easily prepared Drp-Au-AgNPs have potential applications as novel nanomedicine for MG detoxification, and nanomaterial for biotreatment of a toxic polyphenyl dye-containing wastewater.

Bimetallic Ag‐Au Nanoparticles Inside Mesoporous Titania Thin Films: Synthesis by Photoreduction and Galvanic Replacement, and Catalytic Activity

In this work, the synthesis and catalytic activity of bimetallic Ag–Au nanoparticles (NPs) supported in TiO2 mesoporous thin films (MTFs) are presented. The composite materials were obtained through a two‐step procedure, performed at room conditions. In the first step, Ag NPs were grown inside the MTFs by photoreduction. Then, a galvanic replacement reaction with Au was carried out, yielding the bimetallic NPs. The composites were characterized by UV/Vis spectroscopy, transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS) and X‐ray reflectometry (XRR), which show that the alloyed Ag–Au NPs are present inside the mesopores. Moreover, Ag and Au composition relationship can be controlled by adjusting the reaction times of the photoreduction and galvanic replacement reactions, respectively. Pores remain accessible after NPs synthesis, a feature that ensures their possible applications in any device that requires the contact between the NPs and the medium. Catalytic activity of the composites towards 4‐nitrophenol reduction by sodium borohydride was evaluated. Although all the bimetallic systems exhibit improved catalytic properties in comparison with the monometallic Ag composite, the sample with lower Au/Ag relationship is the most effective. For the first time, to the best of our knowledge, bimetallic Au–Ag NPs are encapsulated inside mesoporous TiO2 films, paving the way towards a wide variety of applications.

Bimetallic Ag–Au nanoparticles as pH dependent dual sensing probe for Mn(II) ion and ciprofloxacin

A facile and eco-friendly method for the synthesis of bimetallic nanoparticles of two coinage metals such as silver and gold ((Ag–Au)mixNP) are detailed in this paper. β-cyclodextrin mediated microwave method was used for the synthesis of bimetallic nanoparticles in aqueous medium. Under the optimal conditions, the addition of Mn(II) ion and ciprofloxacin (CIP) changed the colour and surface plasmon resonance of the (Ag–Au)mixNP. The pH dependent changes associated with the introduction of CIP and Mn(II) ion in (Ag–Au)mixNP were studied using various characterization techniques such as UV–vis., FT-IR, XRD, zeta potential, dynamic light scattering, transmission electron microscopy, EDAX and electrochemical techniques. The host-guest interaction and the corresponding morphological changes of bimetallic nanoparticles induced the aggregation of nanoparticles resulting in a visual colour change of the brick red colour of (Ag–Au)mixNP. The electrochemical behaviour of the (Ag–Au)mixNP/AuE electrode in presence of Mn(II) ion and CIP is a highly sensitive detection method. The detection limits of Mn (II) ion by optical and electrochemical methods were 18.40 and 8.42 nM, respectively. In the case of CIP, these limits were found to be 10.26 and 7.24 nM, respectively. The successful monitoring of Mn(II) ion and CIP were possible in real samples with optical and electrochemical methods.

A novel modification method via in-situ reduction of AuAg bimetallic nanoparticles by polydopamine on carbon fiber microelectrode for H2O2 detection

In this work, a facile in-situ reduction method was developed for the modification of carbon fiber microelectrode (CFME) to build novel electrochemical sensors for the detection of H2O2. The polydopamine (PDA) was employed as the surface modification material for one-step decoration of AuAg bimetallic nanoparticles through in-situ reduction on the surface of PDA/CFME. Compared to Au-PDA/CFME and Ag-PDA/CFME, 2Au1Ag-PDA/CFME (immersed PDA/CFME in AgNO3 for 1 h, HAuCl4•4H2O for 2 h in order) exhibited higher electrocatalytic activity toward H2O2 sensing due to bimetal synergism. Under the optimal condition, the 2Au1Ag-PDA/CFME appeared a wide linear range of 0 μM - 55 μM (R2 = 0.990), 55 μM – 2775 μM (R2 = 0.991) with high sensitivity (12966 μA mM−1cm−2, 0–55 μM; 2534 μA mM−1 cm−2, 55–2775 μM), and low detection limit (0.12 μM). Furthermore, good selectivity and repeatability of 2Au1Ag-PDA/CFME favored its applications in biological samples, especially in cellular level. The detection of H2O2 released from HepG2 living cells was realized by applying 2Au1Ag-PDA/CFME, indicating a potential usage of the fabricated electrode for H2O2 detection in cancer cells. In addition, the above simple in-situ reduction method based on PDA's adhesion and reducibility offered a universal strategy to decorate noble metals onto microelectrode for different application in the future.