Bimetallic Core-shell Structure Research Articles

Ordered Ag@Pd alloy supported on Ti4O7 by ascorbic acid-assisted galvanic replacement for efficient oxygen reduction

Core-shell catalysts have been extensively researched in enhancing the activity of oxygen reduction reaction (ORR) by modifying bimetallic electrons. However, the conventional methods for synthesizing core-shell structures are not appropriate for supported catalysts. Here, we present a strategy to support ordered Ag@Pd core-shell structures on the Ti4O7 surface by ascorbic acid-assisted galvanic replacement (GR). The addition of appropriate amounts of Pd precursors during GR plays a crucial role in the morphology and activity of the ordered Ag@Pd/Ti4O7. Ordered Ag@Pd/Ti4O7 exhibits a half-wave potential of 0.895 V and mass activity of 1.22 A mgPd-1 at 0.9 V, where the latter is approximately 13.7 times higher than that of 20% Pt/C. Excitingly, the zinc-air battery with an ordered Ag@Pd/Ti4O7 catalyst as the cathode shows a maximum power density of 174 mW cm-2. The ordered characteristics of the Ag@Pd alloy and its strong electron transfer with the corrosion-resistant Ti4O7 effectively inhibit the oxidation of Ag, thus improving the catalytic activity and stability. The ingenious combination of ascorbic acid with GR provides a feasible mechanism for the synthesis of ordered bimetallic core-shell structure on oxide surfaces.

Mesoporous Bimetallic Au@Rh Core-Shell Nanowires as Efficient Electrocatalysts for pH-Universal Hydrogen Evolution.

Electrochemical water splitting is one hopeful strategy for hydrogen production, and designing efficient hydrogen evolution electrocatalysts under universal pH is one of the most critical topics. Here, we have successfully prepared mesoporous bimetallic core-shell nanostructures with Au nanowires (Au NWs) as cores and mesoporous Rh as shells (Au@mRh NWs). Due to the one-dimensional structure and mesoporous core-shell structure, Au@mRh NWs possess more active sites and provide the synergistic effect, leading to the great improvement of the electrochemical activity toward the hydrogen evolution reaction under a wide range of pH. The present work proposes a versatile strategy for preparing a bimetallic core-shell structure with a mesoporous shell, which is highly promising for more electrocatalytic applications.

MOF-derived yolk-shell Co@ZnO/Ni@NC nanocage: Structure control and electromagnetic wave absorption performance

Reasonable control of the composition and structure of porous nanomaterials is conducive to improving its electromagnetic wave absorption performance. In this paper, the bimetallic core–shell structure ZIF67@ZIF8 is used as the template, Ni(NO3)2·6H2O is used as the etchant, and the heterogeneous trimetal Co@ZnO/Ni@NC nanocage is prepared by Ni doping and vacuum carbonization. The nanocage uses Co as the core and ZnO/Ni particles coated with a nitrogen-doped carbon layer as the shell layer. When the optimal etching time is 1 h, the RLmin of Co@ZnO/Ni@NC can reach −55 dB@8.2 GHz, and the amount of filler is 27%. In addition, when the thickness of the absorber varies between 1 and 5 mm, it has an effective absorption bandwidth of 12.6 GHz (5.4–18 GHz). The research results of the absorbing performance and absorbing mechanism of the system show the synergistic effect of the three metal components, reasonable arrangement and hollow structure optimizes impedance matching, enhances the interface polarization, and thus improves the absorbing performance. This research provides a new way to prepare porous magnetic metal/carbon composites with excellent absorbing properties from heterogeneous bimetal MOFs.

Fe-doped CoP core–shell structure with open cages as efficient electrocatalyst for oxygen evolution

Abstract Developing a facile approach based on transition metal-based Prussian blue (PB) and its analogues (PBAs) with core–shell nanostructure is a very promising choice for constructing cost-effective electrocatalysts for oxygen evolution reaction (OER). Herein, a bimetallic core–shell structure with open cages of Fe-doped CoP (Fe-CoP cage) has been synthesized using CoFe-PBA cage-4 as precursor through a facile hydrothermal method and following phosphating process. Interestingly, there is an open hole in each face center of Fe-CoP cage, which suggests the more exposure of active sites for OER. Electrochemical measurements show that Fe-CoP cage can afford a current density of 10 mA cm−2 at a low overpotential (300 mV), which is better than that of RuO2. The excellent performance can be attributed to Fe doping composition and unique open-cage core–shell structure. The synergistic effect derived from bimetallic active for OER has been discussed. And its great catalytic stability has been evaluated via 1000 cycles of CV and chronoamperometry measurement. This work provides a potential method to design multiple transitional metal-doping electrocatalysts with complex framework derived from PBAs for water splitting.

Novel bimetallic Cu/Ni core-shell NPs and nitrogen doped GQDs composites applied in glucose in vitro detection.

In present work, a highly sensitive biosensor with high selectivity for glucose monitoring is developed based on novel nano-composites of nitrogen doped graphene quantum dots (N-GQDs) and a novel bimetallic Cu/Ni core-shell nanoparticles (CSNPs) (Cu@Ni CSNPs/N-GQDs NCs). With the tuned electronic properties, N-GQDs helped bimetallic core-shell structure nanomaterials from aggregation, and separate the charges generated at the interface. This novel nano-composites also have the good electrical conductivity of N-GQDs, catalyst property of Cu/Ni bimetallic nano composite, Cu@Ni core-shell structure and the synergistic effect of the interaction between bimetallic nano composite and N-GQDs. While modified the electrode with this novel nano-composites, the sensor’ linear range is 0.09 ~ 1 mM, and the limit of detection (LOD) is 1.5 μM (S/N = 3) with a high sensitivity of 660 μA mM-1 cm-2, and rapid response time (3 s). Its’ LOD is more than 74 times lower than the traditional Cu@Ni CSNPs modified working electrode. It also has higher sensitivity and wider linear range. This indicates the great potential of applying this kind of nano composites in electrode modification.

Fabrication of gold–silver core–shell nanoparticles for performing as ultrabright SERS-nanotags inside human ovarian cancer cells

This paper presents the fabrication and characterization of new gold–silver core–shell nanoparticles labeled with para-mercaptobenzoic acid (4MBA) molecules and demonstrates their use as surface-enhanced Raman spectroscopy (SERS)-nanotags with ultra-bright traceability inside cells and ability to convey spectrally-coded information about the intracellular pH by means of SERS. Unlike previous reported studies, our fabrication procedure includes in the first step the synthesis of chitosan-coated gold nanoparticles as a seed material with subsequent growing of a silver shell. The bimetallic core–shell structure is revealed by transmission electron microscopy, high-angle annular dark field scanning transmission electron microscopy, energy-dispersive x-ray elemental mapping and the presence of two interacting localized surface plasmon resonance modes in UV–vis extinction spectrum. The high SERS activity and sensitivity of as fabricated 4MBA-chit-Au–AgNPs nano-constructs to different pH in solution is investigated under 532 and 633 nm laser lines excitation. Next, in view of future studies in cancer diagnosis, the in vitro antiproliferative effects of SERS-nanotags against human ovarian adenocarcinoma cells (NIH:OVCAR-3) are evaluated. The capacity to operate as bright SERS nanotags with precise localization at a single cell level as well as intracellular pH indicators is clearly demonstrated by performing cell imaging under scanning confocal Raman microscopy.

Catalytically Active Au Layers Grown on Pd Nanoparticles for Direct Synthesis of H2O2: Lattice Strain and Charge-Transfer Perspective Analyses.

Despite its effectiveness in improving the properties of materials, strain engineering has not yet been employed to endow catalytic characteristics to apparently nonactive metals. This limitation can be overcome by controlling simultaneously lattice strains and charge transfer originated from the epitaxially prepared bimetallic core-shell structure. Here, we report the experimental results of the direct H2O2 synthesis enabled by a strained Au layer grown on Pd nanoparticles. This system can benefit the individual catalytic properties of each involved material, and the heterostructured catalyst displays an improved productivity for the direct synthesis of H2O2 by ∼100% relative to existing Pd catalysts. This is explained here by exploring the individual effects of lattice strain and charge transfer on the alteration of the electronic structure of ultrathin Au layers grown on Pd nanoparticles. The approach used in this study can be viewed as a means of designing catalysts with multiple catalytic functions.

Core-shell structure Ag@Pd nanoparticles supported on layered MnO2 substrate as toluene oxidation catalyst

The silver palladium bimetallic core-shell structure nanoparticles (Ag@Pd NPs) were synthesized by a thin Pd shell slowly generating on the outmost of Ag nanoparticle according to galvanic replacement mechanism. Then, the 2D layered structure manganese dioxide (MnO2) substrate was used to support the as-synthesize Ag@Pd NPs to prepare Ag@Pd/MnO2 catalyst for toluene purification in oxidation reaction. Physicochemical properties of the samples were characterized by a number of different analytical techniques. It is found that the Ag@Pd NPs are homogeneously spherical shape with an average particle diameter size of 7.1 nm. And the MnO2 substrate can not only uniformly disperse Ag@Pd active component on its surface for its high specific surface area and mesopore volume, but also provide the reactive lattice oxygen by its mixed oxidation states of Mn3+/Mn4+. Moreover, the core-shell configuration of Ag@Pd NPs can improve the state phase transformation from Pd0 to PdO2 with the aid of lattice oxygen of MnO2 substrate, because of the lattice oxygen migration controlled strong metal-support interaction (SMSI) effect between palladium active component and MnO2 substrate. So, there would be more exposed PdO2 active sites on the Ag@Pd/MnO2 catalyst relative to monometallic Pd/MnO2 catalyst. Hence, the as-prepared bimetallic core-shell Ag@Pd/MnO2 catalyst exhibits greatly higher toluene oxidation activity at lower reaction temperature than monometallic Pd/MnO2 catalyst, indicating it is a promising catalyst for use in volatile organic compounds (VOCs) purification.

Silver palladium bimetallic core-shell structure catalyst supported on TiO2 for toluene oxidation

We show that silver palladium bimetallic core-shell structure catalysts supported on TiO2 substrate (Ag@Pd/TiO2) are highly active with a low palladium loading for toluene purification in oxidation reaction. The Ag@Pd catalysts were synthesized by galvanic replacement of Pd coating on Ag nanoparticles. Transmission electron microscopy (TEM), high-resolution TEM, and scanning TEM with energy dispersive spectrometer confirmed that the catalysts have a core-shell configuration, and are spherical in shape with an average diameter size of about 9.0 nm. The UV–vis absorption spectroscopy and selected area electron diffraction further proved that the intimate contact and different electronegativity of Ag and Pd in core-shell structure result in electrons transferring from Ag core to Pd shell, which increases local electron density around Pd atom. In addition, X-ray photoelectron spectroscopy reveals that such an increase of electron density on Pd active site in Ag@Pd/TiO2 catalyst can substantially strengthen the chemisorption with reactant of O2, further promote the phase transformation from Pd0 metal to PdO oxidation state, and finally maintain the normal operation of Pd0-PdO synergic mechanism during toluene oxidation reaction. Hence, compared to monometallic Pd/TiO2 catalyst, the as-prepared bimetallic core-shell Ag@Pd/TiO2 catalyst exhibits greatly higher toluene oxidation activity as a whole although its palladium loading value is just one third of Pd/TiO2. The high catalytic oxidation activity with a low Pd loading makes the Ag@Pd/TiO2 a promising catalyst for use in VOCs purification.

Silver-gold bimetallic nanoparticles and their applications as optical materials.

Recently, nanoscale metallic particles have been studied extensively due to their tunable and strong optical properties that are well beyond those of organic chromophores. As monometallic nanoparticles have shown strong but narrow absorption bands within the ultraviolet and visible wavelengths, the preparation of bimetallic core-shell structures can give rise to strong, wide, and tunable absorption bands across the visible to near infrared areas. The silver-gold bimetallic nanoparticles with core-shell structures can offer unique physical and optical properties inaccessible to monometallic systems. These nanoparticles have been utilized in many areas of research including chemical catalysis, surface-enhanced Raman spectroscopy, and photothermal therapy. This review article is a comprehensive overview of bimetallic nanoparticle systems consisting of gold and silver; it is based on the recent advances in wet-chemical synthetic methodologies, the characterization of size and shape-dependent optical properties, and various optically driven applications including catalysis, signal-enhancing devices, and biomedical purposes.

Structural, electronic and magnetic properties of 22-, 35- and 55-atom core–shell Au–Cu nanoclusters

Compared to monometallic clusters, bimetallic nanoclusters combine the distinctive properties of varied materials and thus exhibit a broader range of the degrees of freedom due to the presence of two different metals. This affords greater opportunity to control their properties by modifying composition as well as size. In this work, we investigated magnetic and electronic properties for Au–Cu bimetallic core-shell structures using the first-principle calculations based on the density functional theory. Our work indicated that the Au–Cu core–shell can have a half-metal property through chemical composition modification. Half-metallic ferromagnets attract increasing research interest as potential materials for spintronic device applications. Au20Cu2 and Au32Cu6 clusters are half-metallic ferromagnets with large half-metallic gaps.

Hollow Ag@Pd core–shell nanotubes as highly active catalysts for the electro-oxidation of formic acid

Ag nanowires are prepared as templates by a polyol reduction process. Then Ag nanotubes coated with a thin layer of Pd are synthesized through sequential reduction accompanied with the galvanic displacement reaction. The products show a hollow core–shell nanotubular structure, as demonstrated by detailed characterizations. The Ag@Pd can significantly improve the electrocatalytic activity towards the electro-oxidation of formic acid and enhance the stability of the Pd component. It is proposed that the enhanced electrochemically active surface area and modulated electron structure of Pd by Ag are responsible for the improvement of electrocatalytic activity and durability. The results obtained in this work are different from those previous reports, in which alloy walls with hollow interiors are usually formed. This work provides a new and simple method for synthesizing novel bimetallic core–shell structure with a hollow interior, which can be applied as high-performance catalysts for the electro-oxidation of formic acid.

Structural Characterization of Nanoparticles Obtained by a Polyol Synthesis in the Bimetallic System Pt-Pd

ABSTRACTA modified polyol synthesis has been utilized to study the different structures obtained in the bimetallic system of platinum (Pt) and palladium (Pd). Some results are shown in this work. Thermal methods under refluxing, carrying on the reaction up to 285 ºC, have been assayed to reduce metallic salts using ethylene glycol (EG) as reducer and polyvinylpyrrolidone (PVP) as protective reagent of the formed bimetallic nanoparticles. The special core-shell structure has been observed in these bimetallic nanoparticles, whose synthesis was assisted by Ag, showing polyhedral shapes. The average diameter size of the core has been estimated at 10 nm, and the diameter size of the shell in 13 nm, consequently the thickness of the shell is around 1.5 nm. Nanoparticles were structurally characterized with transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) equipped with detector to generate high angle annular dark field (HAADF) images. This kind of structures have been studied and utilized to increase successfully the catalytic properties of monometallic nanoparticles of Pt or Pd according to other works. Here, the synthesis procedure is described; as the main results, several images are presented showing the obtained bimetallic core-shell structures and their fast Fourier transform (FFT), and also the size and the elemental analysis of the nanoparticles are reported, concluding that this synthesis method is very efficient for preparing bimetallic core shell structures.