Preparation and Characterization of Pt/Co‐Core Au‐Shell Magnetic Nanoparticles

Pt/Co‐core Au‐shell nanoparticles were synthesized via a two‐step route using NaBH₄ as a reducing agent. The nanoparticles are characterized by UV‐vis spectroscopy, transmission electron microscopy (TEM) and powder X‐ray diffraction (XRD). The results indicate that the as‐synthesized Pt/Co‐core Au‐shell nanoparticles have a disordered face centered cubic (fcc) structure, whereas the annealed Pt/Co‐core Au‐shell nanoparticles exhibit an ordered face centered tetragonal (fct) structure. Superconducting quantum interference device (SQUID) studies reveal that the coercivity of the annealed Pt/Co‐core Au‐shell nanoparticles increases to 510 Oe after heat treatment at 500 °C for 2 h.     

Facile Synthesis of Quasi‐One‐Dimensional Au/PtAu Heterojunction Nanotubes and Their Application as Catalysts in an Oxygen‐Reduction Reaction

An intermediate‐template‐directed method has been developed for the synthesis of quasi‐one‐dimensional Au/PtAu heterojunction nanotubes by the heterogeneous nucleation and growth of Au on Te/Pt core–shell nanostructures in aqueous solution. The synthesized porous Au/PtAu bimetallic nanotubes (PABNTs) consist of porous tubular framework and attached Au nanoparticles (AuNPs). The reaction intermediates played an important role in the preparation, which fabricated the framework and provided a localized reducing agent for the reduction of the Au and Pt precursors. The Pt₇Au PABNTs showed higher electrocatalytic activity and durability in the oxygen‐reduction reaction (ORR) in 0.1 M HClO₄ than porous Pt nanotubes (PtNTs) and commercially available Pt/C. The mass activity of PABNTs was 218 % that of commercial Pt/C after an accelerated durability test. This study demonstrates the potential of PABNTs as highly efficient electrocatalysts. In addition, this method provides a facile strategy for the synthesis of desirable hetero‐nanostructures with controlled size and shape by utilizing an intermediate template.     

Au Nanoparticles Modified with Pt,Ru and SnO2 as Electrocatalysts for Ethanol Oxidation Reaction in Acids

The anodic reaction in direct ethanol fuel cells (DEFCs), ethanol oxidation reaction (EOR) faces challenges, such as incomplete electrooxidation of ethanol and high cost of the most efficient electrocatalyst, Pt in acidic media at low temperature. In this study, core‐shell electrocatalysts with an Au core and Pt‐based shell (Au@Pt) are developed. The Au core size and Pt shell thickness play an important role in the EOR activity. The Au size of 2.8 nm and one layer of Pt provide the most optimized performance, having 6 times higher peak current density in contrast to commercial Pt/C. SnO₂ as a support also enhances the EOR activity of Au@Pt by 1.73 times. Further modifying the Pt shell with Ru atoms achieve the highest EOR current density that is 15 and 2.5 times of Pt/C and Au@Pt. Our results suggest the importance of surface modification in rational design of advanced electrocatalysts.     

Modulating fcc and hcp Ruthenium on the Surface of Palladium–Copper Alloy through Tunable Lattice Mismatch

Herein, we report an epitaxial‐growth‐mediated method to grow face‐centered cubic (fcc) Ru, which is thermodynamically unfavorable in the bulk form, on the surface of Pd–Cu alloy. Induced by the galvanic replacement between Ru and Pd–Cu alloy, a shape transformation from a Pd–Cu@Ru core–shell to a yolk–shell structure was observed during the epitaxial growth. The successful coating of the unconventional crystallographic structure is critically dependent on the moderate lattice mismatch between the fcc Ru overlayer and PdCu₃ alloy substrate. Further, both fcc and hexagonal close packed (hcp) Ru can be selectively grown through varying the lattice spacing of the Pd–Cu substrate. The presented findings provide a new synthetic pathway to control the crystallographic structure of metal nanomaterials.     

Liquid‐Phase Epitaxial Growth of Two‐Dimensional Semiconductor Hetero‐nanostructures

Although many two‐dimensional (2D) hybrid nanostructures are being prepared, the engineering of epitaxial 2D semiconductor hetero‐nanostructures in the liquid phase still remains a challenge. The preparation of 2D semiconductor hetero‐nanostructures by epitaxial growth of metal sulfide nanocrystals, including CuS, ZnS and Ni₃S₂, is achieved on ultrathin TiS₂ nanosheets by a simple electrochemical approach by using the TiS₂ crystal and metal foils. Ultrathin CuS nanoplates that are 50–120 nm in size and have a triangular/hexagonal shape are epitaxially grown on TiS₂ nanosheets with perfect epitaxial alignment. ZnS and Ni₃S₂ nanoplates can be also epitaxially grown on TiS₂ nanosheets. As a proof‐of‐concept application, the obtained 2D CuS–TiS₂ composite is used as the anode in a lithium ion battery, which exhibits a high capacity and excellent cycling stability.     

Quasi‐Dual‐Packed‐Kerneled Au49(2,4‐DMBT)27 Nanoclusters and the Influence of Kernel Packing on the Electrochemical Gap

Although face‐centered cubic (fcc), body‐centered cubic (bcc), hexagonal close‐packed (hcp), and other structured gold nanoclusters have been reported, it was unclear whether gold nanoclusters with mix‐packed (fcc and non‐fcc) kernels exist, and the correlation between kernel packing and the properties of gold nanoclusters is unknown. A Au₄₉(2,4‐DMBT)₂₇ nanocluster with a shell electron count of 22 has now been been synthesized and structurally resolved by single‐crystal X‐ray crystallography, which revealed that Au₄₉(2,4‐DMBT)₂₇ contains a unique Au₃₄ kernel consisting of one quasi‐fcc‐structured Au₂₁ and one non‐fcc‐structured Au₁₃ unit (where 2,4‐DMBTH=2,4‐dimethylbenzenethiol). Further experiments revealed that the kernel packing greatly influences the electrochemical gap (EG) and the fcc structure has a larger EG than the investigated non‐fcc structure.     

Well-controlled synthesis of Au@Pt nanostructures by gold-nanorod-seeded growth

Pt nanodots were formed on Au nanorods (NRs) by using a simple seed-mediated growth. Their density and distribution on the Au NR can be finely tuned by varying the reaction parameters. At lower Pt/Au ratios, the Pt nanodots mainly appear at endcaps and side edges of the Au rod. At higher Pt/Au ratios, they distribute homogeneously over the whole Au rod. The obtained Pt nanostructure is a single crystal owing to the epitaxial growth of Pt on the Au rod. Due to the unique surface plasmon resonance (SPR) features of the Au NRs, the Au core/Pt shell (Au@Pt) nanostructures also exhibit well-defined and red-shifted longitudinal SPR bands in the visible and near-infrared region. The position and intensity can be regulated by the thickness and amount of the Pt shell. At a thinner Pt thickness, the Au@Pt NRs show higher dielectric sensitivity than the corresponding Au NRs. It thus opens up the potential of Pt nanostructures for SPR-based sensing.     

Thermoregulated Phase‐Transition Synthesis of Two‐Dimensional Carbon Nanoplates Rich in sp2 Carbon and Unimodal Ultramicropores for Kinetic Gas Separation

The development of highly selective, chemically stable and moisture‐resistant adsorbents is a key milestone for gas separation. Porous carbons featured with random orientation and cross‐linking of turbostratic nanodomains usually have a wide distribution of micropores. Here we have developed a thermoregulated phase‐transition‐assisted synthesis of carbon nanoplates with more than 80 % sp² carbon, unimodal ultramicropore and a controllable thickness. The thin structure allows oriented growth of carbon crystallites, and stacking of crystallites in nearly parallel orientation are responsible for the single size of the micropores. When used for gas separation from CH₄, carbon nanoplates exhibit high uptakes (5.2, 5.3 and 5.1 mmol g^?1) and selectivities (7, 71 and 386) for CO₂, C₂H₆ and C₃H₈ under ambient conditions. The dynamic adsorption capacities are close to equilibrium uptakes of single components, further demonstrating superiority of carbon nanoplates in terms of selectivity and sorption kinetics.     

hcp‐Co Nanowires Grown on Metallic Foams as Catalysts for Fischer–Tropsch Synthesis

The Fischer–Tropsch synthesis (FTS) is a structure‐sensitive exothermic reaction that enables catalytic transformation of syngas to high quality liquid fuels. Now, monolithic cobalt‐based heterogeneous catalysts were elaborated through a wet chemistry approach that allows control over nanocrystal shape and crystallographic phase, while at the same time enables heat management. Copper and nickel foams have been employed as supports for the epitaxial growth of hcp‐Co nanowires directly from a solution containing a coordination compound of cobalt and stabilizing ligands. The Co/Cu_foam catalyst was tested for Fischer–Tropsch synthesis in a fixed‐bed reactor, showing stability and significantly superior activity and selectivity towards C5+ compared to a Co/SiO₂‐Al₂O₃ reference catalyst under the same conditions.     

Highly Facet‐Dependent Photocatalytic Properties of Cu2O Crystals Established through the Formation of Au‐Decorated Cu2O Heterostructures

This work confirms the presence of a large facet‐dependent photocatalytic activity of Cu₂O crystals through sparse deposition of gold particles on Cu₂O cubes, octahedra, and rhombic dodecahedra. Au‐decorated Cu₂O rhombic dodecahedra and octahedra showed greatly enhanced photodegradation rates of methyl orange resulting from a better separation of the photogenerated electrons and holes, with the rhombic dodecahedra giving the best efficiency. Au–Cu₂O core–shell rhombic dodecahedra also displayed a better photocatalytic activity than pristine rhombic dodecahedra. However, Au‐deposited Cu₂O cubes, pristine cubes, and Au‐deposited small nanocubes bound by entirely {100} facets are all photocatalytically inactive. X‐ray photoelectron spectra (XPS) showed identical copper peak positions for these Au‐decorated crystals. Remarkably, electron paramagnetic resonance (EPR) measurements indicated a higher production of hydroxyl radicals for the photoirradiated Cu₂O rhombic dodecahedra than for the octahedra, but no radicals were produced from photoirradiated Cu₂O cubes. The Cu₂O {100} face may present a high energy barrier through its large band edge bending and/or electrostatic repulsion, preventing charge carriers from reaching to this surface. The conventional photocatalysis model fails in this case. The facet‐dependent photocatalytic differences should be observable in other semiconductor systems whenever a photoinduced charge‐transfer process occurs across an interface.     

Platinum‐Decorated Au Porous Nanotubes as Highly Efficient Catalysts for Formic Acid Electro‐Oxidation

Au porous nanotubes (PNTs) were synthesized by a templating technique that involves the chemical synthesis of Ag nanowire precursors, electroless surface modification with Au, and selective etching. A subsequent galvanic replacement reaction between [PtCl₆]^2? and residual Ag generates Pt‐decorated Au porous nanotubes (Pt/Au PNTs), which represents a new type of self‐sustained high surface area electrocatalysts with ultra‐low Pt loading. Structural characterizations with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray powder diffraction (XRD) reveal a novel nanoarchitecture with multimodal open porosity and excellent structural continuity and integrity. Cyclic voltammetry (CV) demonstrates that these Pt/Au PNTs possess very high electrocatalytic activity toward formic acid oxidation with enhanced tolerance to CO poisoning.     

The Structure–Property Correlations in the Isomerism of Au21(SR)15 Nanoclusters by Density Functional Theory Study

Isomerism of atomically precise noble metal nanoclusters provides an excellent platform to investigate the structure–property correlations of metal nanomaterials. In this study, we performed density functional theory (DFT) and time‐dependent (TD‐DFT) calculations on two Au₂₁(SR)₁₅ nanoclusters, one with a hexagonal closed packed core (denoted as Au₂₁ ^hcp ), and the other one with a face‐centered cubic core (denoted as Au₂₁ ^fcc ). The structural and electronic analysis on the typical Au–Au and Au–S bond distances, bond orders, composition of the frontier orbitals and the origin of optical absorptions shed light on the inherent correlations between these two clusters.     

Adsorption of CO on various M@Pt core–shell nanoparticles: Surface-enhanced infrared absorption and DFT studies

Addition of some other metals to platinum causes significant increase of its catalytic activity towards ethanol electrochemical oxidation. This may be caused by different adsorption of CO molecules on the surface of the catalyst, and hence different resistance of the M@Pt nanostructures to poisoning by CO. In this work we attempt to verify this hypothesis analyzing vibrational spectra of CO adsorbed on various metal nanoparticles. Au@Pt nanoparticles revealing significantly higher catalytic activity towards ethanol oxidation than one-element Pt nanoparticles have been synthesized. Surface-enhanced infrared absorption (SEIRA) spectra of CO adsorbed on Au@Pt and Pt nanoparticles have been measured. Obtained spectra were very similar, which suggests that the higher catalytic activity of Au@Pt nanoparticles is rather not caused by different adsorption of CO molecules on Pt and Au@Pt nanoparticles. We suppose that better performance of core–shell M@Pt nanoparticles than one elements Pt nanoparticles towards ethanol electrochemical oxidation can be explained as follows: core–shell nanoparticles are probably much more defected than one-element nanoparticles, hence the M@Pt nanoparticles posses greater number of active sites (kinks, adatoms, and so on) for ethanol electrochemical oxidation. Analysis of the catalytic activity and CO adsorption have been also carried out for other nanoparticles including: Sn@Pt, Pb@Pt, Pd, Au@Pd, Sn@Pd and Pb@Pd. Density functional theory (DFT) calculations of CO modes for CO adsorbed on tetrahedral Pt₁₀ or Pd₁₀ clusters with different metal–metal distance have been also performed.     

A Computational Study of 3‐D Helium Clusters

Physical and thermodynamic properties have been calculated and analyzed for the best and optimized geometries of the 3‐D clusters with N = 3 to N = 10 atoms and unit cells of three types of crystalline systems using ab initio RHF/6–31G^** method. Dependence of the lattice binding energy on the cluster parameter, R, has been studied. Similar behavior observed for the binding energies for all clusters shows that probabilities of their existence in the condensed phase are more or less the same. In the next step, thermodynamic properties have been calculated and analyzed for He₂₇ 3‐D helium clusters with simple cubic, body centered cubic (bcc), trigonal and hexagonal (hcp) configurations. The results show that the hexagonal cluster is more favored over other clusters. It is found that these clusters are electronically stable over a limited range of the values for the lattice parameter. Δ_fH is constant in this stability region and thus the Δ_fG exactly follows the variations of TΔ_fS. Surface effects have been investigated by comparing the square and hexagonal He₉ 2‐D lattices with the cubic and hexagonal He₂₇ 3‐D lattices, respectively. The lattice parameters, densities and molar volumes calculated for the clusters with hcp and bcc configurations have satisfactory agreement with the available experimental values. Properties of the He₁₃, He₃₄ and He₁₀₄ hcp clusters have also been calculated and analyzed.     

Screw‐Dislocation‐Driven Bidirectional Spiral Growth of Bi2Se3 Nanoplates

Bi₂Se₃ attracts intensive attention as a typical thermoelectric material and a promising topological insulator material. However, previously reported Bi₂Se₃ nanostructures are limited to nanoribbons and smooth nanoplates. Herein, we report the synthesis of spiral Bi₂Se₃ nanoplates and their screw‐dislocation‐driven (SDD) bidirectional growth process. Typical products showed a bipyramid‐like shape with two sets of centrosymmetric helical fringes on the top and bottom faces. Other evidence for the unique structure and growth mode include herringbone contours, spiral arms, and hollow cores. Through the manipulation of kinetic factors, including the precursor concentration, the pH value, and the amount of reductant, we were able to tune the supersaturation in the regime of SDD to layer‐by‐layer growth. Nanoplates with preliminary dislocations were discovered in samples with an appropriate supersaturation value and employed for investigation of the SDD growth process.     

Preparation of disk‐like Pt/CeO2‐p‐TiO2 catalyst derived from MIL‐125(Ti) for excellent catalytic performance

A feasible strategy is reported for the synthesis of a disk‐like Pt/CeO₂‐p‐TiO₂ catalyst derived from the titanium‐based metal–organic framework (MOF) MIL‐125(Ti) through a few valid steps. To verify the successful synthesis and structural features of the Pt/CeO₂‐p‐TiO₂ catalyst, as‐prepared samples were characterized using several techniques. The characterizations demonstrated that MOF‐derived porous TiO₂ was appropriate for application as a support owing to its moderate surface area (101 m² g^?1) and suitable pore size (6 nm). Moreover, to study the effect of calcination temperature on the catalytic performance, the obtained catalyst was calcined at various temperatures. It was found that Pt/CeO₂‐p‐TiO₂ calcined at 550 °C exhibited the highest catalytic performance, evaluated by means of the reduction of 4‐nitrophenol monitored by UV–visible spectra. Furthermore, this catalyst showed good reusability with a conversion of 94% even after six cycles. Finally, a possible reaction mechanism was proposed to explain the reduction of 4‐nitrophenol to 4‐aminophenol over the Pt/CeO₂‐p‐TiO₂ catalyst.     

(6,7‐Dimethyl‐2,3‐di‐2‐pyridyl­quinoxaline)bis­(3‐methyl­pyridine)­platinum(II) bis­(hexa­fluoro­phosphate) acetone solvate 0.5‐hydrate

The crystal structure of the title compound, [Pt(C₆H₇N)₂(C₂₀H₁₆N₄)](PF₆)₂·C₃H₆O·0.5H₂O, is composed of a bivalent square‐planar platinum(II) complex, two PF₆⁻ counter‐ions and solvent mol­ecules. The di‐2‐pyridylquinoxaline ligands are known to confer an `L shape' on square‐planar platinum(II) complexes, which also display inter­calating properties. The structural characterization reported here is a contribution to a wide‐ranging study focused on structural and dynamical analyses of these substrates, which may provide better insight into their biological mechanisms and activities. The expected `L‐shaped' skeleton of the metallic complex combined with the antiparallel orientation of substituted pyridines (anti conformation) generates chiral objects, found in the solid state as a racemic mixture.     

Nanoelectrocatalyst Based on High‐Density Au/Pt Hybrid Nanoparticles Supported on a Silica Nanosphere

A high‐efficiency nanoelectrocatalyst based on high‐density Au/Pt hybrid nanoparticles supported on a silica nanosphere (Au‐Pt/SiO₂) has been prepared by a facile wet chemical method. Scanning electron microscopy, transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, and X‐ray photoelectron spectroscopy are employed to characterize the obtained Au‐Pt/SiO₂. It was found that each hybrid nanosphere is composed of high‐density small Au/Pt hybrid nanoparticles with rough surfaces. These small Au/Pt hybrid nanoparticles interconnect and form a porous nanostructure, which provides highly accessible activity sites, as required for high electrocatalytic activity. We suggest that the particular morphology of the Au‐Pt/SiO₂ may be the reason for the high catalytic activity. Thus, this hybrid nanomaterial may find a potential application in fuel cells.     

Theoretical study of the electronic spectra of bi‐ and tri‐heteronuclear platinum complexes

The electronic structure and the spectroscopic properties of [Pt(NH₃)₄][Au(CN)₂]₂, [Pt(NH₃)₄][Ag(CN)₂]₂, [Pt(CNCH₃)₄][Pt(CN)₄], and [Pt(CNCH₃)₄][Pd(CN)₄] were studied at the HF, MP2, B3LYP, and PBE levels. In all the complexes, it was found that the nature of the intermetal interactions is consistent with the presence of a high‐ionic contribution (90%) and a dispersion‐type interaction (10%). The absorption spectra of these complexes were calculated by the single‐excitation time‐dependent (TD) method at the HF, B3LYP, and PBE levels. The [Pt(NH₃)₄][M(CN)₂]₂ (M ? Au, Ag) complexes showed a ¹(dσ* → pσ) transition associated with a metal–metal charge transfer. On the other hand, the [Pt(CNCH₃)₄][M(CN)₄] (M ? Pt, Pd) complexes showed a ¹(dσ* → π*) transition associated with a metal‐to‐metal and ligand charge transfer. The values obtained theoretically are in agreement with the experimental range. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

(Di‐tert‐butylmethylphosphane)(η2‐di‐tert‐butylphosphanylphosphinidene)(triphenylphosphane)platinum(0)

The crystal structure of the title compound, [Pt(C₈H₁₈P₂)(C₉H₂₁P)(C₁₈H₁₅P)] or [(Ph₃P)(^tBu₂PMe)Pt(η²‐^tBu₂PP)], contains four molecules in the asymmetric unit with slightly different conformations. The P—P distances in the ^tBu₂PP ligands are similar for all four molecules [2.0661 (13)–2.0678 (13) Å] and indicate a multiple character of the P—P bond in the ^tBu₂PP ligand. Molecules of the asymmetric unit can be assembled into a tetrahedron that fulfils the requirements for a rhombic disphenoid. The coordination of the Pt atom in all four molecules is square planar, with r.m.s. deviations from the PtP₄ planes in the range 0.03–0.05 Å. All planes of the PtP₄ groups are approximately parallel to the ab plane of the unit cell. The structure represents an unusual unsymmetrical platinum phosphinidene derivative.