Au Pd Bimetallic Nanoparticles Research Articles

Facile synthesis of AuPd/g-C3N4 nanocomposite: An effective strategy to enhance photocatalytic hydrogen evolution activity

AuPd bimetallic nanoparticle (NP) modified ultra-thin graphitic carbon nitride nanosheet photocatalysts were synthesized via photochemical deposition-precipitation followed by hydrogen reduction. The crystal structure, chemical properties, and charge carrier behavior of these photocatalysts were characterized by X-ray diffraction (XRD), surface photovoltage spectroscopy (SPS), transient photovoltage spectroscopy (TPV), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and UV-Vis diffuse-reflectance spectroscopy (DRS). Photocatalytic H2 evolution experiments indicate that the hydrogen treated AuPd nanoparticles can effectively promote the separation efficiency of electron-hole pairs photo-excited in the g-C3N4 photocatalyst, which consequently promotes photocatalytic H2 evolution. The 1.0 wt% AuPd/g-C3N4 (H2) composite photocatalyst showed the best performance with a corresponding photocatalytic H2 evolution rate of 107 μmol h−1. The photocatalyst can maintain most of its photocatalytic activity after four photocatalytic experiment cycles. These results demonstrate that the synergistic effect of light reduction and hydrogen reduction of AuPd and g-C3N4 help to greatly improve the photocatalytic activity of the composite photocatalyst.

Deactivation studies of bimetallic AuPd nanoparticles supported on MgO during selective aerobic oxidation of alcohols

Here we report the synthesis and characterisation of high surface area MgO prepared via the thermal decomposition of various magnesium precursors (MgCO3, Mg(OH)2 and MgC2O4). Bimetallic gold-palladium nanoalloy particles were supported on these MgO materials and were tested as catalysts for the solvent-free selective aerobic oxidation of benzyl alcohol to benzaldehyde. All these catalysts were found to be active and very selective (>97%) to the desired product (benzaldehyde). However, MgO prepared via the thermal decomposition of magnesium oxalate displayed the highest activity among all the magnesium oxide supports tested. Attempts were made to unravel the reasons for the deactivation of these catalysts using different characterisation techniques namely in situ XRD, XPS, ICP-MS, TEM, and TGA-MS. From the data obtained, it is clear that MgO undergoes phase changes from MgO to Mg(OH)2 and MgCO3 during catalyst preparation as well as during the catalytic reaction. Besides phase changes, strong adsorption of reactants and products on the catalyst surface, during the reaction, were also observed and washing the catalyst with organic solvents did not completely remove them. The phase change and catalyst poisoning were reversed through high temperature heat treatments. However, these processes led to the sintering of the metal nanoparticles. Moreover, substantial leaching of the support material (MgO) was also observed during the reaction. These latter two processes led to the irreversible deactivation of AuPd nanoparticles supported on MgO catalyst during the solvent-free selective aerobic oxidation of alcohols. Among the three different MgO supports studied in this article, an inverse correlation between the catalytic activity and Mg leaching has been observed. This article reports a deeper understanding of the mode of deactivation observed in metal nanoparticles supported on MgO during liquid phase reactions.

Structural optimization of Au–Pd bimetallic nanoparticles with improved particle swarm optimization method**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474234 and 61403318) and the Fundamental Research Funds for the Central Universities of China (Grant No. 20720160085).

Due to the dependence of the chemical and physical properties of the bimetallic nanoparticles (NPs) on their structures, a fundamental understanding of their structural characteristics is crucial for their syntheses and wide applications. In this article, a systematical atomic-level investigation of Au–Pd bimetallic NPs is conducted by using the improved particle swarm optimization (IPSO) with quantum correction Sutton–Chen potentials (Q-SC) at different Au/Pd ratios and different sizes. In the IPSO, the simulated annealing is introduced into the classical particle swarm optimization (PSO) to improve the effectiveness and reliability. In addition, the influences of initial structure, particle size and composition on structural stability and structural features are also studied. The simulation results reveal that the initial structures have little effects on the stable structures, but influence the converging rate greatly, and the convergence rate of the mixing initial structure is clearly faster than those of the core-shell and phase structures. We find that the Au–Pd NPs prefer the structures with Au-rich in the outer layers while Pd-rich in the inner ones. Especially, when the Au/Pd ratio is 6:4, the structure of the nanoparticle (NP) presents a standardized PdcoreAushell structure.

AuPd/3DOM-TiO2 catalysts for photocatalytic reduction of CO2: High efficient separation of photogenerated charge carriers

The photocatalytic conversion of CO2 and H2O into value-added chemicals using sunlight is significant to solve energy crisis and environmental problems. In this work, a series of novel bifunctional catalysts of core-shell structured AuPd nanoparticles decorated 3DOM TiO2 (AuPd/3DOM-TiO2) w were successfully fabricated via a facile one-pot method of gas bubbling-assisted membrane reduction (GBMR). AuPd/3DOM-TiO2 catalysts show uniform 3D ordered macroporous structure, and the slow photon effect of 3DOM-TiO2 as a photonic crystal can enhance light-harvesting efficiency. AuPd nanoparticles are highly dispersed on the surface of 3DOM-TiO2 carrier. Since bimetallic AuPd nanoparticles with the relatively low Fermi level have good capacity of trapping electron, they can efficiently promote the separation of photogenerated electron-hole pairs in TiO2. The AuPd/3DOM-TiO2 catalysts exhibit excellent photocatalytic activity for CO2 reduction with H2O to CH4 under light irradiation. Among the studied catalysts, Au3Pd1/3DOM-TiO2 catalyst exhibits the highest photocatalytic activity and selectivity for CO2 reduction, e.g., its formation rate of CH4 is 18.5μmolg−1h−1 and its selectivity to CH4 production by CO2 reduction is 93.9%. The possible mechanism of AuPd/3DOM-TiO2 catalysts for photocatalytic CO2 reduction is also proposed, and it would guide further design and synthesis of high efficient photocatalysts for CO2 reduction with H2O.

Facile synthesis of amine-functionalized SBA-15-supported bimetallic Au–Pd nanoparticles as an efficient catalyst for hydrogen generation from formic acid

Superior catalytic activity arises from synergy between Au–Pd and SBA-15-Amine.

PdAu bimetallic nanoparticles anchored on amine-modified mesoporous ZrSBA-15 for dehydrogenation of formic acid under ambient conditions

Highly active catalysts for the dehydrogenation of formic acid were screened by using different amine-modified ZrSBA-15 as supports.

Fabrication of Lab-on-Paper Using Porous Au-Paper Electrode: Application to Tumor Marker Electrochemical Immunoassays.

A simple, low-cost, and sensitive electrochemical lab-on-paper assay is developed based on a novel gold nanoparticle modified porous paper working electrode for use in point-of-care testing (POCT). Electrochemical methods are introduced for lab-on-paper based on screen-printed paper electrodes. To further improve specificity, performance, and sensitivity for point-of-care testing, a novel porous Au-paper working electrode (Au-PWE) is designed for lab-on-paper using growth of an interconnected Au nanoparticle (NP) layer on the surface of cellulose fibers in order to enhance the conductivity of the paper sample zone and immobilize the primary antibodies (Ab1). With a sandwich-type immunoassay format, Pd-Au bimetallic nanoparticles possessing peroxidase-like activity are used as a matrix to immobilize secondary antibodies (Ab2) for rapid detection of targets. This lab-on-paper based immunodevice is applied to the diagnosis of a cancer biomarker in clinical serum samples.

Nanosized Pd-Au bimetallic phases on carbon nanotubes for selective phenylacetylene hydrogenation.

Palladium (Pd)-catalyzed selective hydrogenation of alkynes has been one of the most studied hydrogenation reactions in the last century. However, kinetic studies conducted to reveal the catalyst's active centers have been hindered because of dynamic surface changes on Pd during the reaction. In the present study, bimetallic Pd-Au nanoparticles supported on carbon nanotubes have been synthesized at room temperature as catalysts for selective hydrogenation of phenylacetylene, which show effectively enhanced selectivity compared to their monometallic counterparts. Structural and surface analyses of fresh and reacted catalysts reveal that selective hydrogenation of phenylacetylene is favored over nanosized Pd-Au bimetallic phases due to modifications in the Pd surface in terms of neighboring site isolation and electron density reduction.

DNA-Mediated Morphological Control of Pd-Au Bimetallic Nanoparticles.

Recent reports have shown that different DNA sequences can mediate the control of shapes and surface properties of nanoparticles. However, all previous studies have involved only monometallic particles, most of which were gold nanoparticles. Controlling the shape of bimetallic nanoparticles is more challenging, and there is little research into the use of DNA-based ligands for their morphological control. We report the DNA-templated synthesis of Pd-Au bimetallic nanoparticles starting from palladium nanocube seeds. The presence of different homo-oligomer DNA sequences containing 10 deoxy-ribonucleotides of thymine, adenine, cytosine, or guanine results in the growth of four distinct morphologies. Through detailed kinetic studies by absorption spectroscopy, scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM), we have determined the role of DNA in controlling Pd-Au nanoparticle growth morphologies. One major function of DNA is affecting various properties of the incoming metal atoms, including their diffusion and deposition on the Pd nanocube seed. Interestingly, nanoparticle growth in the presence of A10 follows an aggregative growth mechanism that is unique when compared to the other base oligomers. These findings demonstrate that DNA can allow for programmable control of bimetallic nanoparticle morphologies, resulting in more complex hybrid materials with different plasmonic properties. The capability to finely tune multimetallic nanoparticle morphology stems from the versatile structure that is unique to DNA in comparison to conventionally used capping agents in colloidal nanomaterial synthesis.

Visible-light-driven catalytic activity enhancement of Pd in AuPd nanoparticles for hydrogen evolution from formic acid at room temperature

A series of bimetallic AuPd nanoparticles (NPs) supported by graphene oxide (GO) were synthesized using a facile impregnation-reduction method, which were used as catalysts for the hydrogen evolution reaction (HER) from formic acid (HCOOH) under visible light irradiation at 298K. The results showed that the bimetallic catalysts strongly absorbed visible light, and in comparison with the activities of all the catalsyts with various molar ratios of Au/Pd in the dark, their activities were remarkably enhanced under visible light irradiation. Especially, Au1Pd2/GO exhibited the highest activity featuring initial turnover frequency (TOF) value of 954.2h−1 at 298K, which was among the highest values for the reported heterogeneous catalysts. The enhanced photocatalytic activities of bimetallic catalysts could be mainly attributed to the efficient electron transfer from inactive Au species with localized surface plasmon resonance (LSPR) effect to active Pd sites. Support GO in the catalysts could be regarded as the electron collector and transporter and then also contributed to the enhanced catalytic activity. Furthermore, the catalytic activity of Au1Pd2/GO strongly depended on the intensity and wavelength of incident light, indicating that the visible light irradiation indeed played a key role in the enhanced catalytic activity.

Novel AuPd bimetallic alloy decorated 2D BiVO4 nanosheets with enhanced photocatalytic performance under visible light irradiation

Novel AuPd bimetallic alloy nanoparticles (NPs) decorated two-dimensional (2D) BiVO4 nanosheet photocatalysts were successfully synthesized via mild wet-chemical process and facile deposition procedure. The composite photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electronic microscope (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflection spectroscopy (DRS), electron spin resonance (ESR) and surface photovoltage spectroscopy (SPV). The 1.0wt% AuPd/BiVO4 nanosheets showed highest photocatalytic activity for the degradation of Rhodamine B (RhB) under visible light (300W Xe lamp coupled with a UV-cutoff filter (λ≥400nm)), and the photocatalytic efficiency was improved for about 21.9 and 6.1 times as compared to that of pure BiVO4 and 1.0wt% Au/BiVO4, respectively. The novel AuPd/BiVO4 composites may make a way to synthesize 2D semiconductor composites with potential applications for solar energy conversion and environmental purifications.

Core-shell Au-Pd nanoparticles as cathode catalysts for microbial fuel cell applications.

Bimetallic nanoparticles with core-shell structures usually display enhanced catalytic properties due to the lattice strain created between the core and shell regions. In this study, we demonstrate the application of bimetallic Au-Pd nanoparticles with an Au core and a thin Pd shell as cathode catalysts in microbial fuel cells, which represent a promising technology for wastewater treatment, while directly generating electrical energy. In specific, in comparison with the hollow structured Pt nanoparticles, a benchmark for the electrocatalysis, the bimetallic core-shell Au-Pd nanoparticles are found to have superior activity and stability for oxygen reduction reaction in a neutral condition due to the strong electronic interaction and lattice strain effect between the Au core and the Pd shell domains. The maximum power density generated in a membraneless single-chamber microbial fuel cell running on wastewater with core-shell Au-Pd as cathode catalysts is ca. 16.0 W m−3 and remains stable over 150 days, clearly illustrating the potential of core-shell nanostructures in the applications of microbial fuel cells.

Compositional Effect in AuPd Bimetallic Nanoparticles Towards Product Selectivity during Aerobic Oxidation of α-Hydroxy Esters and Phosphonates

Aerobic oxidation of α-hydroxy esters and phosphonates for direct formation of α-keto esters and α-keto phosphonates was explored using Au nanoparticle based catalytic systems. Alloying Au with Pd resulted in high activity and selectivity for the aerobic oxidation reaction under base and solvent free conditions. The formation of desired α-keto esters and α-keto phosphonates as sole products were highly dependent on the composition of the alloy nanocatalyst. Addition of a secondary oxidizer such as tert-butylhydroperoxide (TBHP) significantly enhanced the yield of the products at shorter reaction time under mild reaction conditions.

Peptide-Directed PdAu Nanoscale Surface Segregation: Toward Controlled Bimetallic Architecture for Catalytic Materials.

Bimetallic nanoparticles are of immense scientific and technological interest given the synergistic properties observed when two different metallic species are mixed at the nanoscale. This is particularly prevalent in catalysis, where bimetallic nanoparticles often exhibit improved catalytic activity and durability over their monometallic counterparts. Yet despite intense research efforts, little is understood regarding how to optimize bimetallic surface composition and structure synthetically using rational design principles. Recently, it has been demonstrated that peptide-enabled routes for nanoparticle synthesis result in materials with sequence-dependent catalytic properties, providing an opportunity for rational design through sequence manipulation. In this study, bimetallic PdAu nanoparticles are synthesized with a small set of peptides containing known Pd and Au binding motifs. The resulting nanoparticles were extensively characterized using high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy, and high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Structural information obtained from synchrotron radiation methods was then used to generate model nanoparticle configurations using reverse Monte Carlo simulations, which illustrate sequence dependence in both surface structure and surface composition. Replica exchange with solute tempering molecular dynamics simulations were also used to predict the modes of peptide binding on monometallic surfaces, indicating that different sequences bind to the metal interfaces via different mechanisms. As a testbed reaction, electrocatalytic methanol oxidation experiments were performed, wherein differences in catalytic activity are clearly observed in materials with identical bimetallic composition. Taken together, this study indicates that peptides could be used to arrive at bimetallic surfaces with enhanced catalytic properties, which could be leveraged for rational bimetallic nanoparticle design using peptide-enabled approaches.

Molybdenum disulfide nanosheets supported Au-Pd bimetallic nanoparticles for non-enzymatic electrochemical sensing of hydrogen peroxide and glucose

The molybdenum disulfide (MoS2) nanosheets supported Au-Pd bimetallic nanoparticles were synthesized using a facile thermal co-reduction method. The Au-Pd/MoS2 nanocomposites showed good electrocatalytic activities toward the reduction of hydrogen peroxide (H2O2) in neutral solution and the oxidation of glucose in alkaline solution, attributed to the synergistic effects of the Au-Pd bimetallic nanoparticles and MoS2 nanosheets. The fabricated non-enzymatic electrochemical sensors exhibited the linear responses of H2O2 and glucose in the concentration ranges of 0.8μM–10mM and 0.5–20mM with the detection limits of 0.16μM and 0.40mM (S/N=3), respectively, together with good stability and reproducibility. The Au-Pd/MoS2 nanocomposites provide new potential materials for the development of other non-enzymatic sensors.

Supported bimetallic AuPd clusters using activated Au25 clusters

Bimetallic AuPd nanoparticles on alumina supports were prepared using Au25(SR)18 precursors activated by mild calcination or LiBH4 treatment, followed by selective deposition of Pd via ascorbic acid reduction. Comparison of their catalytic activity for the oxidation of crotyl alcohol showed that bimetallic structure had significantly improved catalysis compared to Pd/Al2O3. In particular, AuPd samples grown from LiBH4-activated Au25 clusters exhibit the highest catalytic activity as well as high selectivity towards crotonaldehyde formation, likely due to their smaller particle sizes as compared to AuPd samples grown from calcined Au25 clusters. X-ray absorption spectroscopy (XAS) at the Au L3-edge, Pd L3-edge and Pd K-edges showed that the resulting bimetallic AuPd nanoparticles had Au-Pd core-shell structures with a 4d-electron poor Pd surface.

Fabrication a new modified electrochemical sensor based on Au–Pd bimetallic nanoparticle decorated graphene for citalopram determination

This paper proposes a simple approach for sensing of citalopram (CTL) using gold–palladium bimetallic nanoparticles (Au–PdNPs) decorated graphene modified gold electrode. Au–PdNPs were deposited at the surface of a graphene modified gold electrode with simple electrodeposition method. The morphology and the electrochemical properties of the modified electrode were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), energy dispersion spectroscopy (EDS), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and square wave voltammetry (SWV). The novel sensor exhibited an excellent catalytic activity towards the oxidation of CTL. The oxidation peak current of CTL, was linear in the range of 0.5–50μM with a detection limit 0.049μM with respect to concentration of citalopram. The proposed sensor was successfully applied for determination of CTL tablet and human plasma samples with satisfactory results.

AuPd bimetallic nanoparticles decorated Cd0.5Zn0.5S photocatalysts with enhanced visible-light photocatalytic H2 production activity

In this study, novel AuPd bimetallic co-catalyst decorated Cd0.5Zn0.5S photocatalyst was successfully synthesized via an in-situ chemical deposition method. The physical as well as the photophysical properties of the as-obtained AuPd/Cd0.5Zn0.5S samples were characterized by X-ray diffractometry (XRD), Transmission electron microscope (TEM), UV–vis diffuse reflection spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and surface photovoltage spectroscopy (SPV). The AuPd bimetallic co-catalysts showed dramatic photo-generated charge separation efficiency in Cd0.5Zn0.5S sample, and thus significantly enhance the H2 production activity under visible light irradiation. The AuPd/Cd0.5Zn0.5S sample with 0.5 wt% content had the highest catalytic activity, and the corresponding H2 evolution rate is 3.65 mmol g−1 h−1, which was about 12 times as that of pure Cd0.5Zn0.5S sample under visible light irradiation. The photocatalytic activity of the photocatalyst was stable even after 9 cycling photocatalytic experiments. A possible mechanism on the photocatalytic enhancement of AuPd NPs was systematically investigated, which can provide a novel concept for the synthesis of other desirable photocatalytic materials.

Selective Hydrogenation of Unsaturated Carbon–Carbon Bonds in Aromatic-Containing Platform Molecules

The combination of chemical and biological catalysis enables the production from biomass of coumarin and dihydrocoumarin (DHC), opening new routes to the formation of fine chemicals and pharmaceutical building blocks. Each of these products requires the hydrogenation of 4-hydroxycoumarin (4HC) to 4-hydroxydihydrocoumarin (4HDHC), which, in turn, requires the reduction of an unsaturated C–C bond in the presence of an aromatic ring. Using in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, we show that reaction at 348 K over monometallic Pd catalysts leads to the partial reduction of the aromatic ring in 4HC, obtaining 93% selectivity for C═C bond hydrogenation at 82% 4HC conversion and with a low turnover frequency (TOF). Decreasing the Pd dispersion from 70% to 6% not only leads to an increase in the rate of 4HC hydrogenation, but it also leads to an increase in the rate of overhydrogenation. However, the formation of bimetallic PdAu nanoparticles inhibits the overhydrogenation reaction while also doubling the TOF to a value of 6 ks–1 for 4HDHC production. A bimetallic PdAu catalyst supported on SiO2 leads to 97% selectivity for C═C bond hydrogenation at 86% 4HC conversion, while an acidic support such as amorphous silica–alumina can be used to produce DHC directly from 4HC.

Au-Pd Bimetallic Nanoparticle Electrodes for Direct Electroreduction of Hexavalent Chromium Complexes

This paper reports a simple, low-cost, and effective electrochemical technique for sensing and reducing CrVI based on a Au-Pd bimetallic nanoparticle (BNP)-decorated indium tin oxide (ITO) conducting glass electrode. It was observed that the Au-Pd BNP-decorated ITO electrode could significantly boost the electrochemical reduction of CrVI when compared with either Au nanoparticle- or Pd nanoparticle-decorated ITO electrodes. These BNP-decorated electrodes exhibited a wide linear concentration range of 0.001–100 μM, a very low detection limit (signal-to-noise ratio = 3) of 0.3 nM, and a high sensitivity of 1.701 μA μM–1. From electrochemical impedance spectroscopy, it was revealed that this significant improvement was mainly due to the reduction in the charge-transfer resistance, which leads to faster free exchange of the reaction intermediates. The proposed Au-Pd BNP electrode also demonstrated excellent stability, selectivity, repeatability, and reproducibility.