Uniformly gold nanoparticles derived from P2VP-b-PCHMA block copolymer templates with different reduction methods

The micellization of poly(2-vinylpyridine)-block-poly(cyclohexyl methacrylate) (P2VP-b-PCHMA) in THF can be induced by the complexation between the P2VP blocks and HAuCl4, forming composite polymeric micelles with PCHMA being the shell and P2VP/HAuCl4 complex being the core. In order to obtain regular arrays of gold nanoparticles (Au NPs), monolayer of HAuCl4-loaded surface micelles have been produced by spin-coating the micellar solution, and Au NPs in different size have been obtained by oxygen plasma with different reduction processes. In addition, pyrole (PY) has been used as an efficient reducing agent to fabricate dispersed Au NPs within micellar structure in a short reducing time, resulting in a raspberry-like morphology of the Au-polymer composites. With the addition of annealing processes or longer reducing time (one month), different shapes of Au NPs have been observed in the cast films. Furthermore, core-shell nanostructures of gold-polypyrole (Au-PPY) have also been observed by employing vapor phase polymerization of PY onto HAuCl4-loaded polymeric solution-cast films.     

Shape Control of Monodispersed Sub‐5 nm Pd Tetrahedrons and Laciniate Pd Nanourchins by Maneuvering the Dispersed State of Additives for Boosting ORR Performance

It is a great challenge to simultaneously control the size, morphology, and facets of monodispersed Pd nanocrystals under a sub‐5 nm regime. Meanwhile, quantitative understanding of the thermodynamic and kinetic parameters to maneuver the shape evolution of nanocrystals in a one‐pot system still deserves investigation. Herein, a systematic study of the density functional theory (DFT)‐calculated adsorption energy, thermodynamic factors, and reduction kinetics on Pd growth patterns is reported by combining theory and experiments, with a focus on the dispersed state of additives. As pure models, monodispersed Pd tetrahedrons enclosed by (111) facets with a narrow size distribution of 4.9 ± 1 nm and a high purity approaching 98% can be obtained when using 1,1′‐binaphthalene (C₂₀H₁₄) +2NH₃ as additives. Specifically, laciniate Pd nanourchins (Pd LUs) can evolve via anisotropic growth when replacing additive with dose‐consistent 1,1′‐binaphthyl‐2,2′‐diamine (C₂₀H₁₆N₂, two ? NH₂ binding in C₂₀H₁₄). Catalytic investigations show that the sub‐5 nm Pd tetrahedrons exhibit higher activity in both the oxygen reduction (E_onset = 1.025 V, E_1/2 = 0.864 V) and formic acid oxidation reaction with respect to the Pd LUs and Pd black, which represents a great step for the development of well‐defined Pd nanocrystals with size in the sub‐5 nm regime as non‐Pt electrocatalysts.     

Ni/Pd core/shell nanoparticles supported on graphene as a highly active and reusable catalyst for Suzuki-Miyaura cross-coupling reaction

Monodisperse Ni/Pd core/shell nanoparticles (NPs) have been synthesized by sequential reduction of nickel(II) acetate and palladium(II) bromide in oleylamine (OAm) and trioctylphosphine (TOP). The Ni/Pd NPs have a narrow size distribution with a mean particle size of 10 nm and a standard deviation of 5% with respect to the particle diameter. Mechanistic studies showed that the presence of TOP was essential to control the reductive decomposition of Ni-TOP and Pd-TOP, and the formation of Ni/Pd core/shell NPs. Using the current synthetic protocol, the composition of the Ni/Pd within the core/shell structure can be readily tuned by simply controlling the initial molar ratio of the Ni and Pd salts. The as-synthesized Ni/Pd core/shell NPs were supported on graphene (G) and used as catalyst in Suzuki-Miyaura cross-coupling reactions. Among three different kinds of Ni/Pd NPs tested, the Ni/Pd (Ni/Pd = 3/2) NPs were found to be the most active catalyst for the Suzuki-Miyaura cross-coupling of arylboronic acids with aryl iodides, bromides and even chlorides in a dimethylformamide/water mixture by using K₂CO₃ as a base at 110 °C. The G-Ni/Pd was also stable and reusable, providing 98% conversion after the 5^th catalytic run without showing any noticeable Ni/Pd composition change. The G-Ni/Pd structure reported in this paper combines both the efficiency of a homogeneous catalyst and the durability of a heterogeneous catalyst, and is promising catalyst candidate for various Pd-based catalytic applications.      

Sharp cubic and octahedral morphologies of poly(vinylpyrrolidone)-stabilised platinum nanoparticles by polyol method in ethylene glycol: their nucleation,growth and formation mechanisms

Pt nanoparticles (NPs) were synthesised by a modified polyol method with the addition of silver nitrate. The results showed that the specific shapes of Pt NPs were influenced by the relevant factors, which are the contents of silver nitrate, synthetic time and temperature. A small content of silver nitrate has played an important role in determining their final shapes of platinum NPs. We observed that Pt NPs in the forms of very sharp shapes such as Pt cubes, octahedrons, cuboctahedrons and tetrahedrons have been obtained. In addition, the shape growth mechanisms and formation of Pt NPs have been studied. They exist in both cubic and octahedral shapes. Importantly, Pt nanocrystals can grow into main cubic and octahedral shapes for a short time less than 15?min. Moreover, Pt nanocrystals can also grow into different shapes from cubic and octahedral into spherical ones for several hours. Especially, they exhibited interesting shapes of multiple-branched Pt nanostructures because of their overgrowth and aggregations. Clearly, large cubic and octahedral Pt NPs of 160?nm diameter were observed. The growth and formation of large cubic and octahedral Pt NPs were due to the aggregation of Pt clusters or initial Pt seeds, even small Pt nanocrystals.     

Synthesis,characterization, and enhanced formic acid electrooxidation activity of carbon supported MnOx promoted Pd nanoparticles

Formic acid (HCOOH) is one of the promising fuels for direct liquid fed fuel cells. However, CO poisoning is a major challenge for the development of effective catalytic system for formic acid electrooxidation (FAEO). Herein, a novel CO-resistive activated carbon supported Pd-MnO_x bimetallic catalyst (Pd-MnO_x/C) was presented for FAEO. Pd-MnO_x/C catalyst was prepared via simple and reproducible surfactant-free deposition-reduction technique. The characterization of this novel Pd-MnO_x/C catalyst was performed by inductively coupled plasma-optical emission spectroscopy (ICP-OES), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), bright field transmission electron microscopy (BFTEM), high resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), and scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDX). The characterization results revealed that Pd and MnO_x nanoparticles (NPs) were well dispersed and separately nucleated with a mean diameter of 2.9?nm on the surface of active carbon. FAEO studies were performed on both Pd-MnO_x/C and Pd/C catalysts to comprehend the effect of separately formed MnO_x on the electrocatalytic activity of Pd NPs. The electrochemical measurements were carried out by using Cyclic Voltammetry (CV) and Chronoamperometry (CA), CO-Strriping Voltammetry, Lineer Sweep Voltammetry (LSV), Electrochemical impedance spectroscopy (EIS) techniques. Electrochemical results revealed that FAEO was activated by the addition of MnOx. Pd_0.6-Mn_0.4 exhibited the optimum catalytic activity with 1.05?A/mg Pd current density. The sum of their results clearly points that the existence of MnO_x NPs enhances the electrocatalytic activity of Pd NPs by increasing their CO-resistivity and durability throughout the FAEO.     

Hydrothermally synthesized cubic magnesium stannate (Mg<Subscript>2</Subscript>SnO<Subscript>4</Subscript>) nanoparticles and its electrochemical performances

Cubic crystalline Mg₂SnO₄ nano particles (NPs) were prepared by the facile hydrothermal method and NaOH used as a mineralizer. The synthesized product was calcinated at different temperatures and sample calcinated at 900?°C was optimized by using XRD and TG/DT analysis. XRD result confirms that the Mg₂SnO₄ NPs has cubic phase with lattice space group of Fd3m with mean crystalline size of 26 nm. The sample calcinated at 900?°C was further characterized by FE-SEM with EDS, HR-TEM with SAED pattern, DLS and Cyclic Voltammetry. The effect of calcination temperature on the formation of Mg₂SnO₄ NPs as well as the particle size and crystalline structure were observed. The surface morphology of the sample indicates that the NPs were in irregular cubic shape and EDS analysis revealed the presence of the Mg, Sn, and O. Zeta potential depicts good stability of the sample and a specific capacitance value of 328 Fg^?1 was observed which suggests that Mg₂SnO₄ NPs could be a potential candidate for super capacitor applications.     

Microstructural characterization of gold nanoparticles synthesized by solution plasma processing

Microstructural characteristics of gold nanoparticles (Au NPs) fabricated by solution plasma processing (SPP) in reverse micelle solutions have been studied by high-resolution transmission electron microscopy (HRTEM). The synthesized Au NPs, with an average size of 6.3 ± 1.4?nm, have different crystal characteristics; fcc single-crystalline particles, multiply twinned particles (MTPs), and incomplete MTPs (single-nanotwinned fcc configuration). The crystal structure characteristics of the Au NPs synthesized by the SPP method were analyzed and compared with similar-size Au NPs obtained by the conventional chemical reduction synthesis (CRS) method. The TEM analysis results show that the Au NPs synthesized by the CRS method have shapes and crystal structures similar to those nanoparticles obtained by the SPP method. However, from the detailed HRTEM analysis, the relative number of the Au MTPs and incomplete MTPs to the total number of the Au NPs synthesized by the SPP method was observed to be around 94%, whereas the relative number of these kinds of crystal structures fabricated by the CRS method was about 63%. It is most likely that the enhanced formation of the Au MTPs is due to the fact that the SPP method generates highly reaction-activated species under low environmental temperature conditions.     

Surfactant-induced postsynthetic modulation of Pd nanoparticle crystallinity

Modulation of Pd nanoparticle (NP) crystallinity is achieved by switching the surfactants of different binding strengths. Pd NPs synthesized in the presence of weak binding surfactants such as oleylamine possess polyhedral shapes and a polycrystalline nature. When oleylamine is substituted by trioctylphosphine, a much stronger binding surfactant, the particles become spherical and their crystallinity decreases significantly. Moreover, the Pd NPs reconvert their polycrystalline structure when the surfactant is switched back to oleylamine. Through control experiments and molecular dynamics simulation, we propose that this unusual nanocrystallinity transition induced by surfactant exchange was resulted from a counterbalance between the surfactant binding energy and the nanocrystal adhesive energy. The findings represent a novel postsynthetic approach to tailoring the structure and corresponding functional performance of nanomaterials.     

A facile method to prepare size-tunable silver nanoparticles and its antibacterial mechanism

The antibacterial effect of silver nanoparticles (denoted as Ag NPs) is closely related to size. This could partly explain why size controllable synthesis of Ag NPs for bactericidal application is drawing much attention. Thus, we establish a facile and mild route to prepare size-tunable Ag NPs with highly uniform morphologies and narrow size distributions. The as-prepared Ag NPs with averaged sizes of 2, 12 and 32?nm were characterized by transmission electron microscopy (TEM), ultraviolet–visible absorption spectroscopy (UV–vis), X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The antimicrobial effect of the as-prepared Ag NPs with different particles size was assessed by broth dilution and disk diffusion as well as measurement of optical density (OD₆₀₀). Moreover, their antibacterial mechanism was discussed in relation to morphology observation of microorganism by scanning electron microscopy (SEM) and to concentration detection of Ag⁺ by stripping voltammetry. It was found that the parameters such as reactant molar ratio, reaction time, dropping speed, and most of all, pH of the reactant solutions, have significant influences on size-regulation of Ag NPs. The as-prepared Ag NPs exhibit excellent antibacterial properties, and their antimicrobial activities increase with decreasing particles size. Besides, two kinds of mechanisms, i.e., contact action and release of Ag⁺, are responsible for the antimicrobial effect of Ag NPs.     

Morphology control and texture of Fe3O4 nanoparticle-coated polystyrene microspheres by ethylene glycol in forced hydrolysis reaction

The effects of ethylene glycol (EG) on morphology and texture of the magnetite shell/core polystyrene microspheres produced from a forced hydrolysis reaction of FeCl₂ solution were investigated. The morphology of magnetite-shell of synthetic composite spheres was dependent on EG concentration. They changed from large sphere with the shell-thickness of ca. 35 nm to corrugated films with increasing EG concentration in the coating solution accompanying a reduction of their shell-particles size to 10 nm. The magnetite coating on latex is formed by a phase transformation from β-FeOOH to magnetite due to the oxidation from Fe²⁺ to Fe³⁺ and adsorption of a lot of Fe²⁺ ions. The shell magnetite formed with EG was hydro-magnetite with a crystal lattice distortion, and they exhibited a polycrystalline nature. The nanoporous magnetite shell was produced in the presence of EG acting as a templating agent. This paper indicates that good superparamagnetic magnetite particles in shell have been synthesized at 5% EG concentration.     

Template-free solvothermal synthesis of ZnO nanoparticles with controllable size and their size-dependent optical properties

ZnO nanoparticles (NPs) have been synthesized via a facile and template-free solvothermal method. The size of ZnO NPs could be tailored by adjusting the ratio of ethanol to ethylene glycol (EG). Their structure and morphology have been investigated. The as-prepared samples are monodispersed ZnO NPs with controllable sizes of about 24.2, 18.9 and 14.7 nm. The cathodoluminescence (CL) spectra of the samples show that the relative intensity ratio of the visible emission peak at 500-650 nm to the band-edge UV emission peak at 380 nm increases as the particle size decreases. Sample with smaller crystallites would have larger surface area and more oxygen vacancy defects, thus it exhibits higher visible emission peak. The UV-vis absorption spectrum indicates the band gap variation of the ZnO NPs with their size. Moreover, the size-dependent blue shifts of both the CL emission and the UV-vis absorption spectra reveal the effect of quantum confinement.     

Structural,electrical, and rheological properties of palladium/silver bimetallic nanoparticles prepared by conventional and ultrasonic-assisted reduction methods

Polyvinylpyrrolidone stabilized Pd/Ag bimetallic nanoparticles (NPs) with average particle sizes of 9 and 6 nm were synthesized by simultaneous reduction in the presence and absence of ultrasound waves, respectively. The prepared NPs were characterized by six methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution-TEM (HRTEM), UV–vis spectroscopy, scanning tunneling microscopy (STM), and energy dispersive X-ray (EDX) analysis. The rheological properties of Pd/Ag NPs in ethylene glycol as a base fluid with various mass fractions of NPs from 2% to 5% at different temperatures were studied experimentally and theoretically. The experimental results showed that viscosity of Pd/Ag NPs in ethylene glycol increases with increasing particle mass fraction and decreases with increasing temperature. A maximum of 31.58% increase in viscosity of ethylene glycol at 20 °C was observed when 5% Pd/Ag NPs was added. Measurement of the electrical conductivity of nanofluids of Pd/Ag bimetallic NPs in distilled water at different mass fractions and temperatures was performed. A 3841% increase in electrical conductivity of distilled water at 25 °C was observed when 1% Pd/Ag NPs was added. Both the rheological and electrical properties of Pd/Ag bimetallic NPs were measured in ethylene glycol and distilled water, respectively for the first time.     

Low temperature and cost-effective growth of vertically aligned carbon nanofibers using spin-coated polymer-stabilized palladium nanocatalysts

Abstract

We describe a fast and cost-effective process for the growth of carbon nanofibers (CNFs) at a temperature compatible with complementary metal oxide semiconductor technology, using highly stable polymer–Pd nanohybrid colloidal solutions of palladium catalyst nanoparticles (NPs). Two polymer–Pd nanohybrids, namely poly(lauryl methacrylate)-block-poly((2-acetoacetoxy)ethyl methacrylate)/Pd (LauMA_x-b-AEMA_y/Pd) and polyvinylpyrrolidone/Pd were prepared in organic solvents and spin-coated onto silicon substrates. Subsequently, vertically aligned CNFs were grown on these NPs by plasma enhanced chemical vapor deposition at different temperatures. The electrical properties of the grown CNFs were evaluated using an electrochemical method, commonly used for the characterization of supercapacitors. The results show that the polymer–Pd nanohybrid solutions offer the optimum size range of palladium catalyst NPs enabling the growth of CNFs at temperatures as low as 350 °C. Furthermore, the CNFs grown at such a low temperature are vertically aligned similar to the CNFs grown at 550 °C. Finally the capacitive behavior of these CNFs was similar to that of the CNFs grown at high temperature assuring the same electrical properties thus enabling their usage in different applications such as on-chip capacitors, interconnects, thermal heat sink and energy storage solutions.     

Low temperature and cost-effective growth of vertically aligned carbon nanofibers using spin-coated polymer-stabilized palladium nanocatalysts

We describe a fast and cost-effective process for the growth of carbon nanofibers (CNFs) at a temperature compatible with complementary metal oxide semiconductor technology, using highly stable polymer–Pd nanohybrid colloidal solutions of palladium catalyst nanoparticles (NPs). Two polymer–Pd nanohybrids, namely poly(lauryl methacrylate)-block-poly((2-acetoacetoxy)ethyl methacrylate)/Pd (LauMA_x-b-AEMA_y/Pd) and polyvinylpyrrolidone/Pd were prepared in organic solvents and spin-coated onto silicon substrates. Subsequently, vertically aligned CNFs were grown on these NPs by plasma enhanced chemical vapor deposition at different temperatures. The electrical properties of the grown CNFs were evaluated using an electrochemical method, commonly used for the characterization of supercapacitors. The results show that the polymer–Pd nanohybrid solutions offer the optimum size range of palladium catalyst NPs enabling the growth of CNFs at temperatures as low as 350 °C. Furthermore, the CNFs grown at such a low temperature are vertically aligned similar to the CNFs grown at 550 °C. Finally the capacitive behavior of these CNFs was similar to that of the CNFs grown at high temperature assuring the same electrical properties thus enabling their usage in different applications such as on-chip capacitors, interconnects, thermal heat sink and energy storage solutions.     

Electrochemical preparation of ionic liquid-stabilized palladium nanoparticles

We have successfully synthesized ionic liquid (IL)-stabilized palladium (Pd) nanoparticles (NPs) by electrochemical reduction. The particle size was controlled by adjusting the current density. Transmission electron microscopic (TEM) images showed that the average diameters of the Pd NPs were 2.4, 3.2, and 3.5 nm, depending on the synthetic conditions. Particle size increased as the current density and the length of the alkyl chain in the cation decreased. X-ray diffraction of the resulting NPs indicated that the particles had a crystalline structure. Overall, the results show that NPs can be finely tuned according to the kinds of ILs employed, as well as by electrochemical reduction.     

Effects of temperature and dispersants on the phases and morphology of Ag–Cu nanoparticles

Ultrafine Ag–Cu nanoparticles (NPs) have been synthesized by a rapid one-step reduction within only 10 min. Effects of temperature and dispersants on the phases and morphology of Ag–Cu NPs were investigated. Results showed that citric acid exhibited an advantageous nature to avoid the formation of Cu₂O and form uniform morphology over PVP. The average particle size of the Ag–Cu NPs synthesized simply in ice-cubes bath could be controlled in 8.6 nm about a quarter of that synthesized at room temperature. The synthesized Ag–Cu NPs presented alloy states near the eutectic composition of 72:28. Due to the lower Ostwald ripening rate and citric acid protection, smaller Ag–Cu NPs were achieved in ice-cube bath. Results also showed that the ultrafine Ag–Cu NPs could be expected to sinter at about 330 °C which was much lower than the eutectic temperature (779 °C) of bulk Ag–Cu alloy. The ultrafine Ag–Cu NPs could be applied as potential die attach materials for SiC power devices.     

Pt-Pd alloy nanoparticle-decorated carbon nanotubes: a durable and methanol tolerant oxygen reduction electrocatalyst

We describe the decoration of multiwalled carbon nanotubes (MCNTs) with Pt-Pd alloy nanoelectrocatalysts of three different compositions and their electrocatalytic performance toward the oxygen reduction reaction (ORR). The decoration of the MCNTs involves polymer-assisted impregnation of metal precursors [Formula: see text] and [Formula: see text] and the subsequent reduction of the impregnated precursors by a modified polyol route. The composition of the catalyst was controlled by tuning the molar ratio of the precursors during their impregnation. Electron probe microscopic analysis shows that the catalysts have compositions of Pt(46)Pd(54,) Pt(64)Pd(36) and Pt(28)Pd(72). The Pt(46)Pd(54) and Pt(64)Pd(36) catalysts have truncated octahedral and icosahedral shapes with a size ranging from 8 to 10?nm. On the other hand, the catalyst of Pt(28)Pd(72) composition has a spherical/quasispherical shape with a size distribution of 1-2?nm. The XPS measurement confirms the signature of metallic Pt and Pd. The Pt(46)Pd(54) catalyst has a pronounced electrocatalytic activity toward the ORR with a specific and mass activity of 378 [Formula: see text] and [Formula: see text], respectively at 0.8?V. Moreover, the Pt(46)Pd(54) nanoelectrocatalyst is highly durable and it retains its initial catalytic activity even after 1000 extensive cycles. Interestingly, this catalyst has a very high tolerance toward methanol and it does not favor the oxidation of methanol in the potential window of 0.1-1.4?V. The electrocatalytic activity of the alloy electrocatalyst is compared with commercially available Pt black and MCNT-supported spherical Pt nanoparticles. The catalytic activity of the Pt(46)Pd(54) nanoelectrocatalyst is higher than the other catalysts. The Pt(46)Pd(54) catalyst outperforms the electrocatalytic activity of all other catalysts.     

Preparation,characterization and catalytic behavior of copper oxide nanoparticles on thermal decomposition of ammonium perchlorate particles

In this study, copper oxide nanoparticles (CuO NPs) with mean particle size of 43–32?nm were prepared by wet grinding of commercial micronized CuO powders in a high-energy wet ball-milling apparatus during 20 and 30?h, respectively. X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) analyses were used to characterize the structure, mean particle size and morphology of the resulting CuO NPs. The results confirmed that the CuO NPs obtained at different milling times consist of nanostructures with nearly spherical morphology and by increasing the milling time, smaller particle size was obtained. The catalytic activities of the synthesized CuO NPs on the thermal decomposition of ammonium perchlorate (AP) particles were examined through differential scanning calorimetry and thermogravimetry (DSC/TG) analyses. Evaluation of the experimental results illustrated that the surfaces of CuO NPs were effectively coated with AP particles and by adding 5%CuO NPs with 32?nm, the thermal decomposition temperature of the treated particles reduced by 83.0°C and the heat of decomposition reached 1553.7?Jg^?1. Moreover, the kinetic and thermodynamic parameters of the thermal decomposition of pure and AP?+?5%CW30 nanocomposites have been investigated by using the Kissinger, Boswell and Ozawa methods.     

Synthesis and characterization of Fe–B nanoparticles for potential magnetic applications

The crystallization and structure of Fe–B nanoparticles (NPs) of different sizes formed in a single process by gas aggregation from Fe₈₀B₂₀ targets were analyzed by transmission electron microscopy. It is concluded that all NPs are covered by an amorphous Fe–B shell while the crystal structure of the NPs core depends on their size. Large NPs with diameters ≥30 nm are monocrystalline tetragonal Fe₃B, small diameter NPs (≤20 nm) are completely amorphous whereas in middle size NPs, with diameters between 20 and 30 nm, difference Fe–B phases (tetragonal Fe₃B and orthorhombic FeB) together with defaulted areas are observed. This work opens new possibilities to produce Fe–B NPs tailoring their magnetic properties by controlling their size and composition.     

Microbial synthesis of core/shell gold/palladium nanoparticles for applications in green chemistry

We report a novel biochemical method based on the sacrificial hydrogen strategy to synthesize bimetallic gold (Au)–palladium (Pd) nanoparticles (NPs) with a core/shell configuration. The ability of Escherichia coli cells supplied with H₂ as electron donor to rapidly precipitate Pd(II) ions from solution is used to promote the reduction of soluble Au(III). Pre-coating cells with Pd(0) (bioPd) dramatically accelerated Au(III) reduction, with the Au(III) reduction rate being dependent upon the initial Pd loading by mass on the cells. Following Au(III) addition, the bioPd–Au(III) mixture rapidly turned purple, indicating the formation of colloidal gold. Mapping of bio-NPs by energy dispersive X-ray microanalysis suggested Au-dense core regions and peripheral Pd but only Au was detected by X-ray diffraction (XRD) analysis. However, surface analysis of cleaned NPs by cyclic voltammetry revealed large Pd surface sites, suggesting, since XRD shows no crystalline Pd component, that layers of Pd atoms surround Au NPs. Characterization of the bimetallic particles using X-ray absorption spectroscopy confirmed the existence of Au-rich core and Pd-rich shell type bimetallic biogenic NPs. These showed comparable catalytic activity to chemical counterparts with respect to the oxidation of benzyl alcohol, in air, and at a low temperature (90°C).