Au Pd Core Shell Nanoparticles Research Articles

Exploring the Biological Effect of Biosynthesized Au-Pd Core-Shell Nanoparticles through an Untargeted Metabolomics Approach.

The biosynthesis of Au-Pd core-shell nanoparticles (NPs) with wild-type Escherichia coli (Au-Pd/E. coli) is an excellent newly established, environmentally friendly synthetic method for the fabrication of nanomaterials compared to traditional chemosynthesis. However, there is insufficient detailed bioinformation on the compatibility, metabolic process, and mechanism of this approach. Metabolomics approaches have provided an excellent alternative to numerous bioinformatics approaches for shedding light on the biological response of an organism exposed to external stimuli at the molecular level. In this study, two different doses (8 and 80 μg/mL) of Au-Pd/E. coli were applied to treat human umbilical vein endothelial cells (HUVECs). Gas chromatography/mass spectrometry coupled with bioinformatics was used to analyze the changes in the HUVEC metabolome after treatment. The results indicated the occurrence of nonsignificant acute cytotoxicity based on cell proliferation and apoptosis analysis, while high concentrations (80 μg/mL) of Au-Pd/E. coli induced dramatic changes in energy metabolism, revealing a notable inhibition of the tricarboxylic acid (TCA) cycle along with the enhancement of glycolysis, the pentose phosphate pathway, fatty acid biosynthesis, and lipid accumulation, which was correlated with mitochondrial dysfunction. The metabolomics results obtained for this novel Au-Pd/E. coli-cell system could broaden our knowledge of the biological effect of Au-Pd/E. coli and possibly reveal material modifications and technological innovations.

Bimetallic Au-Pd nanoparticles supported on silica with a tunable core@shell structure: enhanced catalytic activity of Pd(core)-Au(shell) over Au(core)-Pd(shell).

A facile ligand-assisted approach of synthesizing bimetallic Au–Pd nanoparticles supported on silica with a tunable core@shell structure is presented. Maneuvering the addition sequence of metal salts, both Aucore–Pdshell (Au@Pd–SiO2) and Pdcore–Aushell (Pd@Au–SiO2) nanoparticles were synthesized. The structures and compositions of the core–shell materials were confirmed by probe-corrected HRTEM, TEM-EDX mapping, EDS line scanning, XPS, PXRD, BET, FE-SEM-EDX and ICP analysis. The synergistic potentials of the core–shell materials were evaluated for two important reactions viz. hydrogenation of nitroarenes to anilines and hydration of nitriles to amides. In fact, in both the reactions, the Au–Pd materials exhibited superior performance over monometallic Au or Pd counterparts. Notably, among the two bimetallic materials, the one with Pdcore–Aushell structure displayed superior activity over the Aucore–Pdshell structure which could be attributed to the higher stability and uniform Au–Pd bimetallic interfaces in the former compared to the latter. Apart from enhanced synergism, high chemoselectivity in hydrogenation, wide functional group tolerance, high recyclability, etc. are other advantages of our system. A kinetic study has also been performed for the nitrile hydration reaction which demonstrates first order kinetics. Evaluation of rate constants along with a brief investigation on the Hammett parameters has also been presented.

One pot in situ synthesis of nano Au–Pd core-shells embedded on reduced graphene oxide for the oxygen reduction reaction

The core–shell nanoparticles embedded on reduced graphene oxide (rGO) nanosheets usually exhibit enhanced catalytic activity because of their lattice strain effect. In this study, rGO supported core–shell Au–Pd nanoparticles (Au@Pd/rGO) were synthesized by a facile one pot sonochemical method and studied for their enhanced catalytic activity. The ultrasonic liquid processor at the frequency of 20 kHz and the power of 40 W (with an amplitude of 35%) was used to perform the synthesis. The existence of the spherical shaped Au core and size controlled Au-Pd core–shell nanoparticles incorporated into the rGO nanosheets were identified using high resolution transmission electron microscopy (HR-TEM) and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analyzes. The ordered nature and the elemental presence of Au@Pd/rGO and the mapping were studied using Raman, X-ray photoelectron (XPS) and energy dispersive X-ray (EDS) spectroscopic analyses, respectively. The electrode modified with Au@Pd/rGO deliberately showed an improved electrocatalytic activity for the oxygen reduction reaction (ORR). The kinetics involved in the ORR was intensively studied using the rotating disk electrode (RDE) and identified as the developed Au@Pd/rGO possessed a better catalytic activity compared to Au/rGO and analogous activity with the other standard ORR catalysts such as Pd20/C and Pt20/C. The number of electron exchanged for the reaction was calculated as four using Koutecky–Levich (K–L) plot.

Au–Pd core–shell nanoparticle film for optical detection of hydrogen gas

Hydrogen use, as a clean and almost infinite energy source, has an economic impact in many industries. The problem is that this gas cannot be used like any gas because of its explosiveness at 4% in the air, hence the need to know its concentration any time for security reasons. The permanent detection of hydrogen leaks is essential to monitor and to control the hydrogen concentration to prevent any possible risk. In our current research, we have developed hydrogen ultrasensitive sensors by depositing a thin film of Au–Pd core–shell nanoparticles (NPs) on a transparent glass substrate in order to detect hydrogen in its gaseous form. The colloidal Au–Pd core–shell NPs were synthesized according to a multi-reduction step method. The structural characterizations, the nature, and the density of Au–Pd core–shell NPs have been characterized by scanning electron microscopy and transmission electron microscopy. The morphology, size, and structure of Au–Pd core–shell NPs can be controlled under synthesis conditions. The size of the core–shell studied in this work is 13 nm for gold NP diameter and 0 nm–2.3 nm for palladium thicknesses. The physical properties of NPs, such as the optical absorbance response under hydrogen, strongly depend on the nature of the shell and the ratio between the core and the shell. At different hydrogen concentrations ranging from 1% to 4%, the optical response changes in the position of the surface plasmon resonance peak on the absorbance spectrum after the first loading/unloading hydrogen cycle.

Improving biosynthesis of Au[sbnd]Pd core-shell nanoparticles through Escherichia coli with the assistance of phytochelatin for catalytic enhanced chemiluminescence and benzyl alcohol oxidation

In this work, AuPd core-shell nanoparticles (NPs) biosynthesized through Arabidopsis thaliana phytochelatin synthase-modified Escherichia coli (Au-Pd/AtPCS1-E. coli) with catalytic enhanced chemiluminescence (CL) and benzyl alcohol oxidation (BAO) was investigated. Such biosynthesis of AuPd core-shell NPs was obviously enhanced due to insertion of the gene sequence of Arabidopsis thaliana phytochelatin synthase (AtPCS1) to a plasmid vector (pET-28b) of Escherichia coli (E. coli). The obtained Arabidopsis thaliana phytochelatin synthase-modified Escherichia coli (AtPCS1-E. coli) could generate phytochelatins (PCs, (γ-Glu-Cys)n-Gly, n > 1) for efficient capture and enrichment of Au3+. The component and morphology of AuPd core-shell NPs were checked through X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS). Catalytic CL (in H2O2-luminol system) and BAO (in H2O2-benzyl alcohol system) effect with different experimental conditions were examined, respectively. These results revealed that multifunctional PCs could effectively facilitate biosynthetic process of AuPd core-shell NPs with better distribution, higher yield and lower cost while stronger CL intensity and higher conversion could be obtained for further quantitative analysis and application.

Composition-dependent CO2 electrochemical reduction activity and selectivity on Au–Pd core–shell nanoparticles

Au–Pd core–shell nanoparticles can convert CO2 into CO with a high selectivity and mass activity due to the more balanced *COOH/*CO adsorption.

多层Au-Pd核壳纳米颗粒膜增敏的光纤氢气传感器

多层Au-Pd核壳纳米颗粒膜增敏的光纤氢气传感器

Atomic-Scale Structure and Stress Release Mechanism in Core-Shell Nanoparticles.

Core-shell nanoparticles find applications in catalysts, sensors, and theranostics. The full internal 3D atomic structure, however, cannot be resolved by current imaging and diffraction techniques. We analyzed the atomic positions and stress-release mechanism in a cubic Au-Pd core-shell nanoparticle in approximately 1000 times higher resolution than current experimental techniques using large-scale molecular dynamics simulation to overcome these limitations. The core-shell nanocube of 73 nm size was modeled similarly to solution synthesis by random epitaxial deposition of a 4 nm thick shell of Pd atoms onto a Au core of 65 nm side length using reliable interatomic potentials. The internal structure reveals specific deformations and stress relaxation mechanisms that are caused by the +4.8% lattice mismatch of gold relative to palladium and differential confinement of extended particle facets, edges, and corners by one, two, or three Au-Pd interfaces, respectively. The three-dimensional lattice strain causes long-range, arc-like bending of atomic rows along the faces and edges of the particle, especially near the Au-Pd interface, a bulging deformation of the Pd shell, and stacking faults in the Pd shell at the corners of the particle. The strain pattern and mechanism of stress release were further characterized by profiles of the atomic layer spacing in the principal crystallographic directions. Accordingly, strain in the Pd shell is several times larger in the extended facets than near the edges and corners of the nanoparticle, which likely affects adsorption, optical, and electrochemical properties. The findings are consistent with available experimental data, including 3D reconstructions of the same cubic nanoparticle by coherent diffractive imaging (CDI) and may be verified by more powerful experimental techniques in the future. The stress release mechanisms are representative for cubic core-shell nanoparticles with fcc structure and can be explored for different shapes by the same methods.

Centrifugal Deposited Au-Pd Core-Shell Nanoparticle Film for Room-Temperature Optical Detection of Hydrogen Gas.

In the present work, centrifugal deposited Au-Pd core-shell nanoparticle (NP) film was proposed for the room-temperature optical detection of hydrogen gas. The size dimension of 44, 48, 54, and 62 nm Au-Pd core-shell nanocubes with 40 nm Au core were synthesized following a solution-based seed-mediated growth method. Compared to a pure Pd NP, this core-shell structure with an inert Au core could decrease the H diffusion length in the Pd shell. Through a modified centrifugal deposition process, continues film samples with different core-shell NPs were deposited on 10 mm diameter quartz substrates. Under various hydrogen concentration conditions, the optical response properties of these samples were characterized by an intensity-based optical fiber bundle sensor. Experimental results show that the continues film that was composed of 62 nm Au-Pd core-shell NPs has achieved a stable and repeatable reflectance response with low zero drift in the range of 4 to 0.1% hydrogen after a stress relaxation mechanism at first few loading/unloading cycles. Because of the short H diffusion length due to the thinner Pd shell, the film sample composed of 44 nm Au-Pd NPs has achieved a dramatically decreased response/recovery time to 4 s/30 s. The experiments present the promising prospect of this simple method to fabricate optical hydrogen sensors with controllable high sensitivity and response rate at low cost.

Carbon black supported Au–Pd core-shell nanoparticles within a dihexadecylphosphate film for the development of hydrazine electrochemical sensor

An amperometric method for the determination of hydrazine (HDZ) using a glassy carbon (GC) electrode modified with carbon black supported Au–Pd core–shell structured nanoparticles (Au@Pd/CB) within dihexadecylphosphate (DHP) film (Au@Pd/CB-DHP/GCE) is proposed. Au@Pd nanoparticles were synthesized by chemical reduction of AuCl3 and PdCl2 using ethylene glycol as a reducing agent, and the nanoparticles supported on CB were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The proposed Au@Pd/CB-DHP/GCE and CB-DHP/GCE (without Au@Pd) electrodes were used to investigate the electrochemical behavior of HDZ using cyclic voltammetry. When the Au@Pd/CB-DHP/GCE was used, an electrocatalytic effect was observed, the analytical signal was substantially increased (87%) and the oxidation potential decreased, i.e. in 728mV. Additionally, the apparently heterogeneous electron-transfer rate constant (k0) obtained for the Au@Pd/CB-DHP/GCE (0.15cms−1) was about two orders of magnitude greater than that obtained using the CB-DHP/GCE (0.068cms−1). Under the optimized conditions for the amperometric technique, a linear analytical curve for HDZ was obtained in the range of 2.50–88.0μmolL−1, with a limit of detection of 0.23μmolL−1 (0.0074ppm). The proposed method was satisfactorily applied to determine the concentration of HDZ in natural lake and tap water samples.

Stability of Au–Pd Core–Shell Nanoparticles

The stability of Au–Pd alloys with sizes close to 3 nm and icosahedral, decahedral, and truncated octahedral geometries with AucorePdshell and PdcoreAushell elemental distributions have been studied using canonical molecular dynamics simulations. The analysis of excess energy show that the PdcoreAushell ordering is more stable than the AucorePdshell for particles of this size, while the analysis of the order parameter Q6 revealed that some of the particles with AucorePdshell ordering exhibited geometric and structural changes previous to melting of the particles. Analysis of the local density of the species revealed that these changes are due to diffusion of Pd atoms into the inner core of the particles. The geometry and structure of all of the particles with PdcoreAushell were preserved until just before the solid–liquid transition, as well as showing a lower melting temperature than the AucorePdshell particles.

Tuning Electrocatalytic Activity of Ultrathin Pd Shells: CO2 to Fuels

It is well established that thin metal layers on a foreign support can exhibit very distinctive electrocatalytic activity with respect to bulk electrodes. In the case of d­-metals, changes in reactivity can be rationalised in terms of the so-called ligand or strain (also known as geometric) effects. Although is commoly argued that ligand effects are rather short range (sub-monolayer to few atomic layers), it is notoriusly difficult to experimentally differentiate the contributions from these two phenomena. In this contribution, we shall explore ligand and strain effects on the electrocatalytic properties of Au-Pd core-shell nanoparticles towards CO2 reduction to fuels. The electrochemical properties and product generation are probed by off-line 1H NMR, differential electrochemical mass spectrometry (DEMS), on-line Mass spectrometry (OLEMS) and in-situ FTIR. Thin Pd shells were grown onto 20 nm Au nanoparticles employing a colloidal synthesis method at low temperatures, generating continuous shells with tuneable mean thickness between 1.3±0.1 (CS1) and 9.9±1.1 nm (CS10). Selected area electron diffraction patterns revealed that the effective Pd strain decreases from 3.5 to less than 1% in this thickness range, which is consistent with strain relaxtion mechanisms at Au {111} surfaces. DEMS was used to calculate the faradaic efficiency associated with the CO2 reduction vs hydrogen evolution at the core-shell nanostructures supported on a porous carbon layer. The data show that over 90% of the faradaic charge in the range between 0.0 to -0.5 V vs RHE is consumed in CO2 conversion at CS1 nanoparticles, as opposed to approximately 40% in the case of CS10. The analysis of the electrolyte solution employing 1H NMR revealed the formation of HCOO- only in the case of CS10 over a narrow potential range centred at -0.4 V, with faradaic efficiencies close to 30%. Furthermore, CH4 and C2H6 were also detected using OLEMS at potentials as negative as -0.7 V at the CS10 nanoparticles. No products in solution were detected In the case of CS1, indicating that CO is the main product generated over the entire potential range. The contrast in reaction pathway and electrocatalytic performance are rationalised in terms of the CO affinity to the Pd nanoshells. To probe this, in-situ FTIR studies were performed revealing that the potential dependence of the adsorbed C-O stretching band (stark slope) is significantly weaker on CS1 in comparison to CS10. Furthermore, the effective CO coverage increases with increasing Pd thickness, reaching values reported for polycrystalline bulk Pd electrodes in the case of CS10. These results show that CO has a significantly weaker binding to strain Pd shells (CS1). Finally DFT calculations are used to estimate the contributions of the so-called ligand and strain effects on the local density of states of the Pd d-band. The calculations strongly suggest that the key parameters contributing to the change in mechanism is the effective lattice strain.

Strain Effects on the Oxidation of CO and HCOOH on Au–Pd Core–Shell Nanoparticles

The mechanism of CO and HCOOH electrooxidation in an acidic solution on carbon-supported Au–Pd core–shell nanoparticles was investigated by differential electrochemical mass spectrometry and in situ Fourier transform infrared (FTIR) spectroscopy. Analysis performed in nanostructures with 1.3 ± 0.1 nm (CS1) and 9.9 ± 1.1 nm (CS10) Pd shells provides compelling evidence that the mechanism of adsorbed CO (COads) oxidation is affected by structural and electronic effects introduced by the Au cores. In the case of CS10, a band associated with adsorbed OH species (OHads) is observed in the potential range of CO oxidation. This feature is not detected in the case of CS1, suggesting that the reaction follows an alternative mechanism involving COOHads species. The faradaic charge associated with COads oxidation as well as the Stark slope measured from FTIR indicates that the overall affinity and orbital coupling of CO to Pd are weaker for CS1 shells. FTIR spectroscopy also revealed the presence of HCOOads intermed...

Direct Observation of the Growth of Au-Pd Core-Shell Nanoparticles Using Low-Dose STEM with the Liquid Cell in situ

Journal Article Direct Observation of the Growth of Au-Pd Core-Shell Nanoparticles Using Low-Dose STEM with the Liquid Cell in situ Get access Nabraj Bhattarai, Nabraj Bhattarai Emergent Atomic and Magnetic Structures, Division of Materials Sciences and Engineering, Ames Laboratory, Ames, IA 50011, USA Search for other works by this author on: Oxford Academic Google Scholar Tanya Prozorov Tanya Prozorov Emergent Atomic and Magnetic Structures, Division of Materials Sciences and Engineering, Ames Laboratory, Ames, IA 50011, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 22, Issue S3, 1 July 2016, Pages 744–745, https://doi.org/10.1017/S1431927616004578 Published: 25 July 2016

Carbon supported Au–Pd core–shell nanoparticles for hydrogen production by alcohol electroreforming

Monodisperse faceted icosahedral Au–Pd core–shell nanocrystals of small size (<12 nm) supported on Vulcan XC-72 (Au–Pd/C) are employed in electroreforming for the cogeneration of hydrogen and valuable chemicals.

Ni2P-Graphite Nanoplatelets Supported Au–Pd Core–Shell Nanoparticles with Superior Electrochemical Properties

Nanoparticles of Au–Pd with core–shell structure were synthesized through the coreduction of HAuCl4 and Na2PdCl4 in aqueous media by using cetyltrimethylammonium chloride as a reducing agent. The morphology and structure of the core–shell NPs were confirmed by transmission electron microscopy, X-ray diffraction, and UV–vis spectroscopy. We further demonstrate that the core–shell structure is formed as a synergistic result of low interfacial energy and small lattice mismatch between Au and Pd, different redox potentials of PdCl42–/Pd and AuCl4–/Au, and low reduction rates of HAuCl4 and Na2PdCl4. The catalyst of Au–Pd core–shell nanoparticles supported on Ni2P–graphite nanoplatelets (Au@Pd/Ni2P-GNPs) exhibits a noticeably higher activity than Pd and Pt catalysts in electrochemical ethanol oxidation. Moreover, we show that the activity and stability of Au–Pd core–shell for ethanol oxidation can be significantly enhanced using Ni2P nanoparticles as a cocatalyst. The prepared Au@Pd/Ni2P-GNPs catalyst exhibits ...

One step preparation of ‘ready to use’ Au@Pd nanoparticle modified surface using deep eutectic solvents and a study of its electrocatalytic properties in methanol oxidation reaction

A facile one pot synthesis andin situelectrodeposition of Au–Pd core–shell nanoparticles (Au@Pd NPs) could be achieved in a deep eutectic solvent. The fabricated Au@Pd NPs modified graphite showed superior electrocatalytic properties for methanol oxidation at low activation energies.

Atomic Structure Characterization of Au–Pd Bimetallic Nanoparticles by Aberration-Corrected Scanning Transmission Electron Microscopy

Au–Pd core–shell nanoparticles were structurally characterized using spherical aberration (Cs) corrected scanning transmission electron microscopy (STEM). The microscope is equipped with a detector of high-angle annular dark field (HAADF)-STEM, in addition with an energy-dispersive X-ray spectrometer (EDS). The high-resolution elemental line-scan was carried out using the combination of STEM-EDS which allowed us to obtain an elemental analysis at atomic level. The effect of the Pd in the formation of Au–Pd core–shell has been studied by HAADF-STEM images and molecular dynamics studies. The obtained results predict that the growth of Pd on the Au core is through the formation of islands, suggesting a preferential growth of the Volmer–Weber type model.

Electrochemical Properties of Gold-Palladium Core-Shell Nanostructures for Ethanol Oxidation

Gold-palladium nanoparticles (NPs) have been used as catalysts due to their catalytic activity, selectivity and stability for a variety of reactions, such as the small organic molecule oxidations (i.e. ethanol). In the present contribution, the catalytic activity of Pd and Au-Pd core-shell (CS) NPs is investigated towards the ethanol oxidation (Figures 1A and 1B). The Au-Pd CS NPs were synthesised by a seed-mediated growth method, where PdCl4 2- is reduced at the surface of Au NPs in the presence of ascorbic acid. This method allows adjusting the average Pd shell thickness between 1 (CS1) and 10 (CS10) nm, by varying the amount of palladium chloride. Electrochemical studies in potassium hydroxide (KOH) containing electrolyte solutions with ethanol show that the current density of ethanol oxidation decreases as the shell thickness decreases. Correlation between catalytic activity and shell thickness will be discussed in terms of the structural parameters.

Volcano-like behavior of Au-Pd core-shell nanoparticles in the selective oxidation of alcohols.

Gold-palladium (AuPd) nanoparticles have shown significantly enhanced activity relative to monometallic Au and Pd catalysts. Knowledge of composition and metal domain distributions is crucial to understanding activity and selectivity, but these parameters are difficult to ascertain in catalytic experiments that have primarily been devoted to equimolar nanoparticles. Here, we report AuPd nanoparticles of varying Au:Pd molar ratios that were prepared by a seed growth method. The selective oxidation of benzyl alcohol was used as a model reaction to study catalytic activity and selectivity changes that occurred after varying the composition of Pd in bimetallic catalysts. We observed a remarkable increase in catalytic conversion when using a 10:1 Au:Pd molar ratio. This composition corresponds to the amount of Pd necessary to cover the existing Au cores with a monolayer of Pd as a full-shell cluster. The key to increased catalytic activity derives from the balance between the number of active sites and the ease of product desorption. According to density functional theory calculations, both parameters are extremely sensitive to the Pd content resulting in the volcano-like activity observed.