Au Pd Core Shell Nanocrystals Research Articles

Self-limiting synthesis of Au–Pd core–shell nanocrystals with a near surface alloy and monolayer Pd shell structure and their superior catalytic activity on the conversion of hexavalent chromium

In eliminating environmental chromium pollution, hexavalent chromium (Cr(VI)) reduction by HCOOH on Pd-based bimetallic/multimetallic nanocatalysts is attracting an increasing attention. However, it is still a challenge by precisely controlling the surface interface structure of the nanocrystals (NCs) to obtain highly efficient nanocatalysts on Cr(VI)) conversion. Here, a simple and robust synthesis method for Au-Pd core-shell NCs with a special interface structure has been developed by a novel self-limiting strategy. This interesting structure has a near surface alloy (NSA) of AuPd layer on Au core with outer surface of monolayer (ML) of Pd shell (denoted as NSA/ML), which is achieved only by one-pot synthesis. The self-limiting strategy is developed based on the unique catalysis reduction reaction of Au core, with which the growth of Pd shell is internally regulated by the surface Au atoms until the Au–Pd NCs with NSA/ML structure i.e. Au@AuPd@PdML NCs are formed. Furthermore, the Au–Pd core–shell NCs with the shell from NSA to NSA/ML structure can be simply obtained by adjusting the added amount of Pd precursor. More importantly, the catalytic activities of Au–Pd NCs for the conversion of Cr(VI) to Cr(III) present a notable difference for the Pd in Au@AuPd and Au@AuPd@PdML structures, and the Au@AuPd@PdMLNCs exhibited the superior catalytic activity for the conversion of Cr(VI). The present study demonstrates the core@NSA@shellML is an efficient nanostructure to promote the catalytic performance of core–shell NCs for practical applications.

Synthesis of tetrahexahedral Au-Pd core–shell nanocrystals and reduction of graphene oxide for the electrochemical detection of epinephrine

An innovative epinephrine sensor was fabricated by integrating tetrahexahedral (THH) Au-Pd core–shell nanocrystals on reduced graphene oxide (rGO) nanosheets. Furthermore, the nanocomposites combined the large specific areas of rGO with the high-index facets and excellent electrocatalytic activity of the THH Au-Pd nanocrystals, and the nanocomposites were an essential adapter for detecting epinephrine. In the present work, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to identify and characterize these unique nanocomposites, and the results revealed that a unique THH Au-Pd/rGO core–shell nanostructure was synthesized successfully. To further explore the electrochemical behaviors of these nanomaterials at a GC electrode, we applied cyclic voltammetry (CV), differential pulse voltammetry (DPV) and amperometry to study the conductivity and electrocatalytic activity of the proposed sensor, and the results suggested that the sensor based on Au-Pd/rGO presented a lower limit of detection (0.0012 μM at a signal to noise ratio of 3), wide linear detection range (0.001 µM to 1000 µM), and extraordinary selectivity and reproducibility. Moreover, the data showed that the sensor possessed good stability and acceptable accuracy to detect epinephrine in human serum samples. In summary, this work is not only a potential way to manufacture various nonenzymatic sensors but also a significant contribution to further studies in catalysis, cell fuel cells and other relevant applications.

Facet-Dependent and Light-Assisted Efficient Hydrogen Evolution from Ammonia Borane Using Gold-Palladium Core-Shell Nanocatalysts.

Au-Pd core-shell nanocrystals with tetrahexahedral (THH), cubic, and octahedral shapes and comparable sizes were synthesized. Similar-sized Au and Pd cubes and octahedra were also prepared. These nanocrystals were used for the hydrogen-evolution reaction (HER) from ammonia borane. Light irradiation can enhance the reaction rate for all the catalysts. In particular, Au-Pd THH exposing {730} facets showed the highest turnover frequency for hydrogen evolution under light with 3-fold rate enhancement benefiting from lattice strain, modified surface electronic state, and a broader range of light absorption. Finite-difference time-domain (FDTD) simulations show a stronger electric field enhancement on Au-Pd core-shell THH than those on other Pd-containing nanocrystals. Light-assisted nitro reduction by ammonia borane on Au-Pd THH was also demonstrated. Au-Pd tetrahexahedra supported on activated carbon can act as a superior recyclable plasmonic photocatalyst for hydrogen evolution.

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.

Facet-Dependent Optical Properties Revealed through Investigation of Polyhedral Au-Cu₂O and Bimetallic Core-Shell Nanocrystals.

The ability to prepare Au-Cu2O core-shell nanocrystals with precise control over particle size and shape has led to the discovery of facet-dependent optical properties in cuprous oxide crystals. The use of Au cores not only allows the successful formation of Au-Cu2O core-shell nanocrystals with tunable sizes, but also enables the observation of facet-dependent optical properties in these crystals through the Au localized surface plasmon resonance (LSPR) absorption band. By tuning the Cu2O shell morphology from rhombic dodecahedral to octahedral and cubic structures, and thus the exposed facets, the Au LSPR band position can be widely tuned. Such facet-dependent optical effects are not observed in bimetallic Au-Ag and Au-Pd core-shell nanocrystals with the same precisely tuned particle sizes and shapes. It is believed that similar facet-dependent optical properties could be observed in other ionic solids and other metal-metal oxide systems. The unusually large degree of plasmonic band tuning covering from the visible to the near-infrared region in this type of nanostructure should be quite useful for a range of plasmonic applications.

Surfactant-Directed Fabrication of Supercrystals from the Assembly of Polyhedral Au–Pd Core–Shell Nanocrystals and Their Electrical and Optical Properties

Au-Pd core-shell nanocrystals with cubic, truncated cubic, cuboctahedral, truncated octahedral, and octahedral structures have been employed to form micrometer-sized polyhedral supercrystals by both the droplet evaporation method and novel surfactant diffusion methods. Observation of cross-sectional samples indicates shape preservation of interior nanocrystals within a supercrystal. Low-angle X-ray diffraction techniques and electron microscopy have been used to confirm the presence of surfactant between contacting nanocrystals. By diluting the nanocrystal concentration or increasing the solution temperature, supercrystal size can be tuned gradually to well below 1 μm using the surfactant diffusion method. Rectangular supercrystal microbars were obtained by increasing the amounts of cubic nanocrystals and surfactant used. Au-Ag core-shell cubes and PbS cubes with sizes of 30-40 nm have also been fabricated into supercrystals, showing the generality of the surfactant diffusion approach to form supercrystals with diverse composition. Electrical conductivity measurements on single Au-Pd supercrystals reveal loss of metallic conductivity due to the presence of insulating surfactant. Cubic Au-Pd supercrystals show infrared absorption at 3.2 μm due to extensive plasmon coupling. Mie-type resonances centered at 9.8 μm for the Au-Pd supercrystals disappear once the Pd shells are converted into PdH after hydrogen absorption.

Facile synthesis of Au-Pd core-shell nanocrystals with systematic shape evolution and tunable size for plasmonic property examination.

A facile synthetic method has been developed for the formation of Au-Pd core-shell nanocrystals in aqueous solution in just 0.5-2 h at 50 °C with systematic shape evolution from cubic to truncated cubic, cuboctahedral, truncated octahedral, and octahedral structures using octahedral gold cores. By adjusting the amounts of H2PdCl4, ascorbic acid, and sometimes surfactants and gold cores added, the particle morphology can be finely tuned, and Pd shells with ultrathin thicknesses have been achieved. Gold cores of three different sizes (35, 45, and 74 nm in opposite corner distance) were used to obtain a full range of particle sizes and shapes for a most complete examination of their plasmonic properties. Visual observations made during particle synthesis reveal that Au-Pd cubes are formed at a faster rate than that for the growth of octahedra. For the smaller cubes, cuboctahedra, and truncated octahedra prepared using 35 and 45 nm gold cores, the surface plasmon resonance (SPR) absorption band from the gold cores can be seen only when the Pd shell thickness is just 1 nm at the thinnest points of the particles. For small-sized Au-Pd octahedra, this band is observable at a Pd shell thickness of around 5 nm. For larger Au-Pd nanocrystals synthesized from 74 nm gold cores, the Au SPR band is more recognizable for all particle shapes, although octahedra still exhibit the most obvious band. The band shifts slightly to the red going from cubes to octahedra. Simulation spectra have been performed, and they roughly match with the experimental spectra. Au-Pd octahedra with two different core sizes and shell thicknesses have been used for hydrogen sensing by comparing their UV-vis spectra before and after hydrogen incorporation forming PdH. The results show that the shell thickness is more important in producing a larger spectral red-shift after hydrogen absorption.

Polyhedral Au–Pd Core–Shell Nanocrystals as Highly Spectrally Responsive and Reusable Hydrogen Sensors in Aqueous Solution

Absorption zeigt Absorption an: Die Oberflächenplasmonenresonanzbande von tetrahexaedrischen, oktaedrischen und kubischen Au/Pd-Kern/Schale-Nanokristallen wird bei Absorption von Wasserstoff in die Pd-Schale stark rotverschoben. Diese reversible Spektralverschiebung könnte für die Entwicklung von Sensoren für Wasserstoffgas genutzt werden. Bei den Kern-Schale-Oktaedern lässt sich die Wasserstoffabsorption sogar mit dem bloßen Auge erkennen (siehe Bild).

Polyhedral Au–Pd Core–Shell Nanocrystals as Highly Spectrally Responsive and Reusable Hydrogen Sensors in Aqueous Solution

Polyhedral Au–Pd Core–Shell Nanocrystals as Highly Spectrally Responsive and Reusable Hydrogen Sensors in Aqueous Solution

Gold–Palladium Core–Shell Nanocrystals with Size and Shape Control Optimized for Catalytic Performance

Right to the core: The design of nanocatalysts with maximized catalytic performance relies on control of the size, shape, and composition. The shell thickness of nanocrystals with core–shell structures can be controlled, thus enabling control over the nanocrystal electronic structure and catalytic properties. Monodisperse faceted icosahedral Au–Pd core–shell nanocrystals (see picture) were synthesized, and optimized for the oxidation of benzyl alcohol to benzaldehyde.

Rod-Shaped Au–Pd Core–Shell Nanostructures

A series of anisotropic Au–Pd core–shell nanocrystals (NCs) have been synthesized by controlled overgrowth of Pd on preintroduced Au nanorods serving as seeds. Iodide ions can selectively adsorb on the {110} facets of Pd and change the final morphology of core–shell nanostructures. The overall morphology can be manipulated by changing the structure directing core or the amount H2PdCl4 introduced. These anisotropic nanostructures with adjustable exposure facets and sizes enrich the types of Au–Pd core–shell structures, while the mechanism discussing the formation process will provide useful information for the further investigation.