Study of Au-Pd core-shell nanoparticles by using slow positron beam

Binary Au-Pd nanoparticles were synthesized by ultrasonic irradiation of solutions containing Au³⁺ and Pd²⁺ ions (the ion ratio from 0.3:0.7 to 0.9:0.1 mM) and cationic surfactant (SDS: sodium dodecyl sulfate). In each case the core-shell structure (Au core, Pd shell) was confirmed by scanning transmission electron microscopy (STEM). The mean diameters of them were all about 9 nm, and the thickness of the Pd shell depends on the ratio of Pd²⁺ and Au³⁺ ions in solution. In order to study the electronic states of core-shell nanoparticles and their dependence on shell thickness, Doppler broadening measurements were performed for Au-Pd core-shell nanoparticles by using slow positron beam technique. The ratio curves of Au-Pd particles did not match with those of pure Pd and pure Au, but a small difference in the low electron momentum region was observed among nanoparticles depending on Pd shell thickness.     

Synthesis and photo physical properties of Au @ Ag (core @ shell) nanoparticles disperse in poly vinyl alcohol matrix

Synthesis of core @ shell (Au @ Ag) nanoparticle with varying silver composition has been carried out in aqueous poly vinyl alcohol (PVA) matrix. Core gold nanoparticle (~15 nm) has been synthesized through seed-mediated growth process. Synthesis of silver shell with increasing thickness (~1–5 nm) has been done by reducing Ag⁺ over the gold sol in the presence of mild reducing ascorbic acid. Characterization of Au @ Ag nanoparticles has been done by UV–Vis, High resolution transmission electron microscope (HRTEM) and energy dispersive X-ray (EDX) spectroscopic study. The blue shift of surface plasmon resonance (SPR) band with increasing mole fraction of silver has been interpreted due to dampening of core, i.e. Au SPR by Ag. The dependence of nonlinear optical response of spherical core @ shell nanoparticles has been investigated as a function of relative composition of each metal. Simulation of SPR extinction spectra based on quasi-static theory is done. A comparison of our experimental and the simulated extinction spectra using quasi-static theory of nanoshell suggests that our synthesized bimetallic particles have core @ shell structure rather than bimetallic alloy particles.     

Mono and bimetallic nanoparticles of gold,silver and palladium-catalyzed NADH oxidation-coupled reduction of Eosin-Y

Abstract  

Mono metallic (Au, Ag, Pd) and bimetallic (Au–Ag, Ag–Pd, Au–Pd) with 1:1 mol stoichiometry, nanoparticles are synthesized using one-pot, temperature controlled chemical method using cetyltrimethylammonium bromide (CTAB) as the capping agent. The particle sizes (Au = 5.6, Ag = 5.0, Pd = 6.0, Au–Ag = 9.2, Ag–Pd = 9.6, Au–Pd = 9.4 nm) are characterized by UV–Vis, HRTEM, and XRD measurements, respectively. CTAB bindings onto mono and bimetallic nanoparticles are analyzed by FTIR spectra. The catalytic activities of mono and bimetallic nanoparticles are tested on the reaction between NADH oxidation and Eosin-Y reduction. The effects of base, pH, ionic strength, nature of mono and bimetallic catalysts are studied and the reaction conditions are optimized. Bimetallic nanoparticles exhibited better catalysis than the mono metallic nanoparticles, which may be due to the electronic effects of the core to shell metal atoms.     

Pick your carats: nanoparticles of gold–silver–copper alloy produced <Emphasis Type="Italic">in vivo</Emphasis>

Engineered gold nanoparticle catalysts containing a mixture of metals enable enhanced specificity and reactivity. We report the synthesis by plants of mixed metal nanoparticles suggesting the possibility of using plants to produce catalysts of specific composition, perhaps even those difficult to synthesise by traditional methods. The nanoparticles contain Au, Ag and Cu as an alloy. The structure and composition are confirmed by scanning transmission electron microscopy (STEM) and energy dispersive X-ray analysis (EDX).     

Synthesis, structural and optical characterization of nanocrystalline ZnS:Cu embedded in silica matrix

The synthesis of Cu doped ZnS nanoparticles inside the pore of an inorganic silica gel matrix is presented. The synthesized nanoparticles were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). X-ray diffraction pattern reveals the crystalline wurtzite phase of ZnS. The existence of silica gel in modeling morphologies of the nanoparticles was characterized using Fourier transform infrared (FTIR) spectrometer. Thickness of the silica shell was also calculated. UV- absorption spectrum shows the appearance of an absorption peak at 273 nm which confirms the blue shift as compared to that of bulk ZnS. The photoluminescence (PL) emission spectrum of the sample showed a broad band in the range 465-510 nm due to the transition from the conduction band edge of ZnS nanocrystals to the acceptor like t₂ state of Cu.     

An insight into the effect of composition for enhance catalytic performance of biogenic Au/Ag bimetallic nanoparticles

A comprehensive knowledge of composition‐activity property relationship of nanoparticulate materials is highly desirable for applications in various catalysis reactions. We have addressed a facile green aqueous approach for preparation of Au, Ag monometallic, Au/Ag alloy as well as core‐shell bimetallic nanoparticles. The phytochemicals present in lemon grass leaves extract were employed both as natural reducing and capping agents at room temperature. X‐ray diffraction pattern, UV‐Vis spectroscopy, and energy dispersive X‐ray studies confirmed the formation of bimetallic system. The ensuing Au core/Ag shell and Au/Ag alloy bimetallic nanoparticles were crystalline and spherical in nature with identical average diameter of ~ 18 nm as measured via transmission electron microscopy. The bimetallic systems incredibly display higher catalytic potential than their monometallic counterparts which were vividly reckoned on structural effect, lattice compression, and synergistic electronic effect.     

Preparation of functionalized platinum nanoparticles: a comparison of different methods and reagents

Au–Pd core–shell nanocubes and triangular nanoparticles were systematically synthesized from a few Pd layers up to fully grown morphologies by a modified seed-mediated growth method. The shape evolution of Au–Pd core–shell nanoparticles from single crystal and singly twinned seed to final concave nanocube and triangular plates are presented at atomic level by Cs-corrected scanning transmission electron microscopy (STEM). The growth mechanism of both morphologies was studied throughout different sizes. It was found that the concave nanocubes grew from octahedral Au seeds due to fast growth along 〈111〉 directions; while the triangular nanoparticles grew from singly twinned Au seeds, growing twice as fast in 〈110〉 directions along the twin boundary; compared to the 〈111〉 direction perpendicular to the twin boundary. Both the concave nanocubes and triangular nanoparticles presented high index facet (HIF) surfaces that will increase the catalytic activity of different reactions.     

银/二氧化钛核壳纳米颗粒对碲化镉纳米晶的荧光增强研究

利用新合成的复合纳米结构银/二氧化钛核壳纳米颗粒,研究了金属银纳米颗粒对碲化镉纳米晶层荧光的增强情况.结果表明,这种新型复合金属纳米结构能极大地增强发光纳米晶层的荧光强度.银/二氧化钛核壳纳米颗粒是以水合肼、硝酸银和四异丙氧基钛为原材料,利用胶体化学法在水溶液中合成.透射电子显微镜图片表明这种新合成的银/二氧化钛纳米材料基本上呈球形,有较为明显的核壳结构,中间黑色的核是银纳米颗粒,外层颜色较浅部分是二氧化钛壳层.另外,包裹二氧化钛壳层后,银纳米颗粒的表面等离子吸收带从409 nm红移至430 nm,也证实了这种新型核壳纳米材料的形成.将此合成方法得到的银/二氧化钛纳米颗粒和碲化镉纳米晶用旋转涂覆方法进行直接组合后,得到了银纳米颗粒对碲化镉纳米晶荧光的明显增强,并对其增强的物理过程进行了讨论.这种能够增强荧光团发光的新型复合银纳米结构将在发光器件、荧光成像、生物探测等方面具有一定的应用价值.     

Formation and microstructure of carbon encapsulated superparamagnetic Co nanoparticles

Carbon encapsulated magnetic cobalt nanoparticles have been synthesized by the modified arc-discharge method. Both high resolution transmission electron microscopy (HREM) and powder X-ray diffraction (XRD) profiles reveal the presence of 8–15 nm diameter crystallites coated with 1–3 carbon layers. In particular, HREM images indicate that the intimate and contiguous carbon fringe around those Co nanoparticles is good evidence for complete encapsulation by carbon shell layers. The encapsulated phases are identified as hcp α-Co, fcc β-Co and cobalt carbide (Co₃C) nanocrystals using X-ray diffraction (XRD), nano-area electron diffraction (SAED) and energy dispersive X-ray analysis (EDX). However, some fcc β-Co particles with a significant fraction of stacking faults are observed by HREM and confirmed by means of numerical fast Fourier transform (FFT) of HREM lattice images. The carbon encapsulation formation and growth mechanism are also reviewed.     

Pd/Au纳米结构制备和粒子组分自旋的谱学性能研究

为研究Pd/Au纳米结构制备和电催化性能、控制粒子大小组分和自旋,用油浴热分解方法制备了核/壳纳米结构Pd/Au双金属合金纳米颗粒,采用PVP和多元醇作表面活性剂和稳定剂,依据溶液浓度、颗粒大小、吸附能控制晶相获得了均匀、一致的2层和3层Pd/Au纳米样品,并采用HAADF和HRTEM测试了纳米结构尺寸形貌,用EDS测试了成分分布,试验产物用TEM/XRD进行了表征,结果表明,Pd/Au具有面心立方八面体结构,与Au/Pd核壳不同,纳米Pd/Au具有活性、耐久性、电催化性和稳定性。     

Supercritical carbon dioxide-assisted preparation of palladium nanoparticles on cyclotriphosphazene-containing polymer nanospheres

Poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) nanospheres with average diameter of 410 nm were synthesized rapidly at room temperature and then homogeneously decorated with Pd nanoparticles through an inorganic reaction in supercritical carbon dioxide-ethanol solution using PdCl₂ as a metal precursor. The resultant Pd/PZS nanocomposites were morphologically and structurally characterized by means of scanning electron microscopy, transmission electron microscope equipped with energy-dispersive X-ray spectroscopy, and X-ray diffraction techniques. Characterization results showed that the Pd nanoparticles with good dispersibility could be well anchored onto the surfaces of the PZS nanospheres and the size of Pd nanoparticles could be controlled easily by varying the ethanol-reduction time.     

Synthesis and characterisation: Zinc oxide–sulfide nanocomposites

A novel synthesis method is presented for the preparation of nanosized-semiconductor zinc oxide–sulphide (ZnO/ZnS) core–shell nanocomposites, both formed sequentially from a single-source solid precursor. ZnO nanocrystals were synthesized by a simple co-precipitation method and ZnO/ZnS core–shell nanocomposites were successfully fabricated by sulfidation of ZnO nanocrystals via a facile chemical synthesis at room temperature. The as-obtained samples were characterized by X-ray diffraction and transmission electron microscopy. The results showed that the pure ZnO nanocrystals were hexagonal wurtzite crystal structures and the ZnS nanoparticles were sphalerite structure with the size of about 10 nm grown on the surface of the ZnO nanocrystals. Optical properties measured reveal that ZnO/ZnS core–shell nanocomposites have integrated the photoluminescent effect of ZnO and ZnS. Based on the results of the experiments, a possible formation mechanism of ZnO/ZnS core–shell nanocomposites was also suggested. This treatment is suggested to improve various properties of optoelectronically valuable ZnO/ZnS nanocomposites. These nanosized semiconductor nanocomposites can form a new class of luminescent materials for various applications.     

Nanostructures of gold coated iron core-shell nanoparticles and the nanobands assembled under magnetic field

Pure metal iron nanoparticles are unstable in the air. By a coating iron on nanoparticle surface with a stable noble metal, these air-stable nanoparticles are protected from the oxidation and retain most of the favorable magnetic properties, which possess the potential application in high density memory device by forming self-assembling nanoarrays. Gold-coated iron core-shell structure nanoparticles (Fe/Au) synthesized using reverse micelles were characterized by transmission electron microscopy (TEM). The average nanoparticle size of the core-shell structure is about 8 nm, with about 6 nm diameter core and 1∼2 nm shell. Since the gold shell is not epitaxial growth related to the iron core, the morié pattern can be seen from the overlapping of iron core and gold shell. However, the gold shell lattice can be seen by changing the defocus of TEM. An energy dispersive X-ray spectrum (EDS) also shows the nanoparticles are air-stable. The magnetic measurement of the nanoparticles also proved successful synthesis of gold coated iron core-shell structure. The nanoparticles were then assembled under 0.5 T magnetic field and formed parallel nanobands with about 10 μm long. Assembling two dimensional ordered nanoarrays are still under going. Received 29 November 2000     

Chemical synthesis and structural characterization of small AuZn nanoparticles

In this paper, we report the aqueous synthesis of bimetallic Au-Zn nanoparticles of different compositions by the simultaneous reduction technique. The stability and atomic configuration of the particles are studied through high-resolution transmission electron microscopy (HRTEM) and UV-Vis optical absorption techniques. Depending on the composition, small bimetallic nanoparticles of 1–15 nm in size were obtained. The average size and size distribution of the bimetallic nanoparticles are seen to be critically dependent on the atomic ratio of the constituting elements Au and Zn. While a 1:1 atomic proportion of Au and Zn produced most stable nanoparticles of smallest average size, nanoparticles produced with higher content of either of the component elements are unstable, inducing agglomeration and coalescence to form elongated structures with uneven morphologies. Au₃Zn₁ nanoparticles followed a directional growth pattern, producing bimetallic nanorods with multiple crystalline domains. Interestingly, in these rod-like nanostructures, the domains are in well array of solid solution-like bimetallic and pure mono-metallic regions alternatively. Such nanostructures with uneven morphology and compositions might show distinct catalytic selectivity in chemical reactions. PACS 61.46.-w; 87.64.Ee; 74.62.Bf     

Metal Nanoparticle Coating of Oxide Nanospheres for Core‐Shell Structures

A low‐temperature route for coating oxide nanospheres with metal nanoparticles to achieve core‐shell structures is introduced. First results indicating a dense coverage of silica nanospheres of about 300 nm size with regularly arranged Ag and Au nanoparticles deposited by a modified incipient wetness impregnation procedure are presented. This synthesis works completely without external reducing agents or media, adhesive aids or functionalizing agents. Metal particles of only a few nanometers in size may serve as seeds for continuous metal coating of the oxide spheres by complementary processes. Structural characterization of the materials by transmission electron microscopy reveals a nearly spherical shape of the metal particles, the structure of which ranges from single crystalline to single twinned and multiply twinned configurations.     

Polyol mediated hexadecylamine capped silver allied nanobimetallic particles and their fluxional properties

The syntheses of hexadecylamine seed mediated Ag/M (M=Co, Ni, Pd and Pt) allied nanobimetallic particles were successfully carried out by the successive reduction of ligand capped metal ions with polyols, resulting in concomitant precipitation of some high index faceted hybrid Ag/M bimetal nanoparticles. The optical measurements revealed the existence of surface plasmon band and peak broadening that causes diffusion processes of the metal sols to decrease making it possible to monitor the changes spectrophotometrically. The bimetallic nanoparticles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and electron microscopy techniques which confirm the formation of alloyed clusters.     

Novel Two-Step Approach for the Synthesis of Cadmium Selenide/Zinc Sulfide Core/Shell Nanocomposites with Precursor Injection Technique

This work describes the synthesis of cadmium selenide/zinc sulfide core/shell nanoparticles from the cadmium oxide precursor through a convenient, two-step approach. This modified novel synthesis procedure for cadmium selenide/zinc sulfide nanoparticles in trioctylphosphine oxide and trioctyl phosphine provides better control over growth dynamics. The outer zinc sulfide shell provides efficient confinement of electron and hole wave functions inside the nanocrystals as well as high photochemical stability. The materials have been characterized using a range of optical and structural techniques. The high resolution transmission electron microscope micrographs of the cadmium selenide/zinc sulfide core/shell nanoparticles show well-defined spherical particles with an increase in diameter as compared to the parent cadmium selenide material. Thus, the present simulation and its extension can give insight to the understanding of the formation of core/shell or other heterostructures in different kinds of self-assembled aggregates.     

Synthesis of Nanoscale Bimetallic Particles in Polyelectrolyte Membrane Matrix for Reductive Transformation of Halogenated Organic Compounds

Nanosized Fe/Ni and Fe/Pd particles were synthesized in the polyacrylic acid (PAA)/polyether sulfone (PES) composite membrane matrix for reductive transformation of halogenated organic compounds (HOCs). The advantages of using membrane to immobilize nanoparticles are the reduction of particles loss, prevention of particles agglomeration, and potential application of convective flow. Cross-linked PAA/PES composite membranes containing metal ions as particles precursor were prepared by heat treatment with ethylene glycol (EG) as a cross-linking agent. Nanoscale metal particles were formed and immobilized inside the membrane matrix after reduction with sodium borohydride. Membrane morphology and structure were observed by scanning electron microscopy (SEM). Particle size and distribution were characterized by SEM and transmission electron microscopy (TEM). Energy dispersive X-ray spectroscopy (EDS) was used to obtain the qualitative and quantitative element information of particles. A specimen-drift-free EDS line profile and EDS mapping system was performed in a scanning transmission electron microscopy (STEM) to determine the two-dimensional element distribution of iron and nickel in the nano domain. In the dechlorination study with trichloroethylene (TCE) as a representative HOCs, rapid and complete destruction of TCE was achieved by using nanosized bimetallic Fe/Ni or Fe/Pd in PAA/PES composite membranes. Typically more than 95% of 10 mg/l TCE was reduced within 1 h. Ethane was found in the headspace as the main product.     

Elaboration and characterization of bimetallic nanoparticles obtained by laser ablation of Ni75Pd25 and Au75Ag25 targets in water

A YAG laser operating at the second harmonic wavelength (532 nm, 10 Hz, 8 ns and 40 mJ) was used to elaborate bimetallic nanoparticles by laser ablation of Ni₇₅Pd₂₅ and Au₇₅Ag₂₅ targets in water. TEM–EDX, UV–Vis spectroscopy and PIXE measurements were performed to obtain information on their mean sizes, size distributions and chemical composition as a function of the time of laser ablation. The surface of the laser impacted regions of the targets were characterized by RBS in order to check their composition after the laser ablation. The so-obtained bimetallic nanoparticles always show a homogeneous composition. However, while the composition of Au–Ag nanoparticles was found to be very similar to the one of the alloy target, the composition of the Ni–Pd nanoparticles can be different from the nominal composition of the alloy target. Segregation phenomena can be invoked to explain the difference between the Ni–Pd nanoparticles and the Au–Ag nanoparticles compositions obtained in the same conditions. However, an influence of chemical reactions occurring in the high pressure plasma created locally at liquid–solid interface (called ‘reactive quenching’) cannot be completely ruled out.