Methanol-driven structuring of Au–Pt bimetallic nanoclusters on a thin film of Al2O3/NiAl(100)

The adsorption of methanol altered structures of Au–Pt bimetallic nanoclusters on a thin film of Al₂O₃/NiAl(100). Methanol adsorbed on the Au–Pt intermixed bimetallic clusters, of which the surfaces consist of both Au and Pt, induced a segregation of Au from Pt. This segregation state was unstable, as the clusters returned to the initial Au–Pt intermixed state upon desorption or decomposition of adsorbed methanol. Ethanol and cyclohexene were adsorbed on Au–Pt bimetallic clusters for comparisons, indicating that the interaction of the hydroxyl group of methanol with the clusters accounts for the structural modifications.     

Synthesis of platinum and platinum–ruthenium-modified diamond nanoparticles

With the aim of developing dimensionally stable-supported catalysts for direct methanol fuel cell application, Pt and Pt–Ru catalyst nanoparticles were deposited onto undoped and boron-doped diamond nanoparticles (BDDNPs) through a chemical reduction route using sodium borohydride as a reducing agent. As-received commercial diamond nanoparticles (DNPs) were purified by refluxing in aqueous nitric acid solution. Prompt gamma neutron activation analysis and transmission electron microscopy (TEM) techniques were employed to characterize the as-received and purified DNPs. The purified diamond nanoparticulates, as well as the supported Pt and Pt–Ru catalyst systems, were subjected to various physicochemical characterizations, such as scanning electron microscopy, energy dispersive analysis, TEM, X-ray diffraction, inductively coupled plasma-mass spectrometry, X-ray photoelectron spectroscopy, and infrared spectroscopy. Physicochemical characterization showed that the sizes of Pt and Pt–Ru particles were only a few nanometers (2–5 nm), and they were homogeneously dispersed on the diamond surface (5–10 nm). The chemical reduction method offers a simple route to prepare the well-dispersed Pt and Pt–Ru catalyst nanoparticulates on undoped and BDDNPs for their possible employment as an advanced electrode material in direct methanol fuel cells.     

Au–Pt bimetallic nanoparticles supported on nest-like MnO2: synthesis and application in HCHO decomposition

Major research issues in oral protein delivery include the stabilization of protein in delivery devices which could increase its oral bioavailability. The study deals with development of oral insulin delivery system utilizing biodegradable poly(lactic-co-glycolic acid) (PLGA) nanoparticles and modifying its surface with Concanavalin A to increase lymphatic uptake. Surface-modified PLGA nanoparticles were characterized for conjugation efficiency of ligand, shape and surface morphology, particle size, zeta potential, polydispersity index, entrapment efficiency, and in vitro drug release. Stability of insulin in the developed formulation was confirmed by SDS-PAGE, and integrity of entrapped insulin was assessed using circular dichroism spectrum. Ex vivo study was performed on Wistar rats, which exhibited the higher intestinal uptake of Con A conjugated nanoparticles. In vivo study performed on streptozotocin-induced diabetic rats which indicate that a surface-modified nanoparticle reduces blood glucose level effectively within 4?h of its oral administration. In conclusion, the present work resulted in successful production of Con A NPs bearing insulin with sustained release profile, and better absorption and stability. The Con A NPs showed high insulin uptake, due to its relative high affinity for non-reducing carbohydrate residues i.e., fucose present on M cells and have the potential for oral insulin delivery in effective management of Type 1 diabetes condition.     

Thermoexfoliated graphite as support for production of metal–graphite nanocomposites

The method of chemical deposition of metal salts from water–salt solutions with the subsequent thermal decomposition of salt to metal or metal oxide has been developed for thermoexfoliated graphite (TEG). The type of graphite support and character of metal salt thermal decomposition was shown to influence essentially the dispersity and morphology of metal particles being formed on graphite surface. Preliminary treatment of the initial dispersed graphite by H₂SO₄ leads to the formation of oxygen-containing groups on its surface, which are the exchange centres fixing the metal cations in graphite–metal (or graphite–metal oxide) composites. Thermal exfoliation of graphite, which is accompanied by the refinement of graphite structure, occurs as a result of oxidized graphite heat treatment. High porosity, defectiveness and chemical activity of TEG surface favour the effective impregnation of TEG by aqueous salt solution. Thermal treatment of the salt-impregnated graphite leads to formation of Co particles on graphite surface. These particles are 70–150 nm in size for TEG–Co at a relatively high metal content (up to 30 wt%) and 200 nm in size for oxidized dispersed graphite–Co at Co content ∼10 wt%.     

H-D exchange on graphite–potassium intercalation compounds

Potassium graphite intercalation compounds are able to activate C–H bonds of hydrocarbons at room temperature. In this paper, the hydrogen–deuterium exchange of CHD₃ in the presence of C₈K, C₂₄K and C₃₆K is described.     

Synthesis,characterization, and electrochemical performance of nitrogen-modified Pt–Fe alloy nanoparticles supported on ordered mesoporous carbons

A method has been demonstrated to synthesize nitrogen-modified Pt–Fe alloyed nanoparticles (9.2–11.3 nm) supported on ordered mesoporous carbon (Pt _x Fe_100?x N/OMC), which is fabricated by a conventional wet chemical synthesis of Pt–Fe alloyed nanoparticles and followed by carbonization of the nanoparticles with tetraethylenepentamine as nitrogen chelating agent. Among these electrocatalysts, the Pt₃₀Fe₇₀N/OMC has highly catalytic activity for the oxygen reduction reaction (ORR) with significantly enhanced methanol tolerance as well. Combining the results from X-ray diffraction and X-ray absorption spectroscopy, it can be observed that Pt metal in the Pt₃₀Fe₇₀N/OMC is present in the outer shell of Pt–Fe alloys with face-centered cubic crystalline structure. By X-ray photoelectron spectroscopy, the nitrogen-modified Pt surface of Pt₃₀Fe₇₀N/OMC exhibits significant selectivity toward the ORR in the presence of methanol. This enhancement of methanol tolerance could be attributed to the inhibition of methanol adsorption resulting from the modification of the Pt surface with nitrogen.     

Effects of La–Zn substitution on microstructure and magnetic properties of strontium ferrite nanofibers

Sr_1−x La _x Zn _x Fe_12−x O₁₉/poly(vinylpyrrolidone) (PVP) (0.0≤x≤0.5) precursor nanofibers were prepared by the sol–gel assisted electrospinning method from starting reagents of metal salts and PVP. Subsequently, the Sr_1−x La _x Zn _x Fe_12−x O₁₉ nanofibers with diameters of around 100 nm were obtained by calcination of the precursor at 800 to 1000°C for 2 h. The precursor and resultant Sr_1−x La _x Zn _x Fe_12−x O₁₉ nanofibers were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometer and vibrating sample magnetometer. The grain sizes of Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers are in a nanoscale from 40 to 48 nm corresponding to the calcination temperature from 800 to 1000°C. With La–Zn substitution content increase from 0 to 0.5, the grain size and lattice constants for the Sr_1−x La _x Zn _x Fe_12−x O₁₉ nanofibers obtained at 900°C show a steady reduction trend. With variations of the ferrite particle size arising from the La–Zn substitution, the nanofiber morphology changes from the necklace-like structure linking by single elongated plate-like particles to the structure building of multi-particles on the nanofiber cross-section. The specific saturation magnetization of Sr_1−x La _x Zn _x Fe_12−x O₁₉ nanofibers initially increases with the La–Zn content, reaching a maximum value 72 A m² kg⁻¹ at x=0.2, and then decreases with a further La–Zn content increase up to x=0.5, while the coercivity exhibits a continuous reduction from 413 (x=0) to 219 kA m⁻¹ (x=0.5). The mechanism for the La–Zn substitution and the nanofiber magnetic property are analyzed.     

Formation of ring-patterned nanoclusters by laser–plume interaction

Journal of Nanoparticle Research - Nanocrystalline SnS powder has been prepared using tin chloride (SnCl2) as a tin ion source and sodium sulfide (Na2S) as a sulfur ion source with the help of...     

Electronic structure of bimetallic Ni–Rh nanowires

The electronic structure of a bare Rh(553) surface and of a Ni-decorated Rh(553) surface has been investigated by angle-resolved UV photoelectron spectroscopy and density functional theory calculations. The self-assembly of Ni adatoms leads to the decoration of the steps of the Rh(553) surface with monoatomic Ni rows under suitable kinetic conditions, thus forming a regular array of pseudomorphic bimetallic Ni–Rh nanowires. The electronic structure of the clean Rh(553) surface has been compared to the one of the flat Rh(111) surface, and additional surface states localized at the step edges due to the lower coordination of the step atoms have been detected. The Ni wires are weakly hybridized with the Rh substrate states and are characterized by only weakly dispersing states. This leads to a strong narrowing of the d-band, which is argued to be the origin of the observed high chemical reactivity of the Ni–Rh nanowires.     

Low-loss optical magnetic metamaterials on Ag–Au bimetallic fishnets

We have designed a low-loss magnetic metamaterial with double-fishnet structures of silver and gold operating at near-infrared wavelength. A Particle swarm optimization algorithm was employed to optimize the geometry dimensions of Ag–dielectric–Au unit cell. The Ag–Au bimetallic fishnet produces a maximum figure of merit value of 21, transmission as high as 62%, moderate negative permeability Re(μ) of −0.5, and Re(n) of −1 at 1463 nm. The negative permeability Re(μ) reaches minimum value of −5 at 1573 nm, where the antisymmetric charge distribution in fishnet metamaterials was observed. The antisymmetric plasmonic resonance at 1573 nm is a mixed mode of asymmetric magnetic dipole and symmetric electrical quadrupole in Ag–MgF₂–Au fishnet structures.     

Optimization of a magneto–optic trap using nanofibers

We experimentally demonstrate a reliable method based on a nanofiber to optimize the number of cold atoms in a magneto–optical trap(MOT) and to monitor the MOT in real time.The atomic fluorescence is collected by a nanofiber with subwavelength diameter of about 400 nm.The MOT parameters are experimentally adjusted in order to match the maximum number of cold atoms provided by the fluorescence collected by the nanofiber.The maximum number of cold atoms is obtained when the intensities of the cooling and re-pumping beams are about 23.5 mW/cm~2 and 7.1 mW/cm~2,respectively; the detuning of the cooling beam is-13.0 MHz, and the axial magnetic gradient is about 9.7 Gauss/cm.We observe a maximum photon counting rate of nearly(4.5 ± 0.1) × 10~5 counts/s.The nanofiber–atom system can provide a powerful and flexible tool for sensitive atom detection and for monitoring atom–matter coupling.It can be widely used from quantum optics to quantum precision measurement.     

Gold nanoparticle growth on self-assembled monolayers of ferrocenyl-substituted terpyridine on graphite

In this contribution we demonstrate that densely packed gold nanoparticles can be grown by Volmer–Weber mode on ferrocenyl functionalized terpyridine (FcTerp) on graphite. FcTerp forms highly ordered and dense self-assembled monolayers (SAMs) on graphite which significantly reduces the diffusion length of gold atoms and increases the sticking coefficient compared to bare graphite. Both effects lead to an increased nucleation and thus, to the growth of densely packed gold nanoparticles with diameters in the nanometer range. The optical properties of the nanoparticles as well as their morphology and the structure of the SAMs were characterized by optical extinction spectroscopy and scanning tunneling microscopy.     

Structure and magnetism of Co:CoO core–shell nanoclusters

Transmission electron microscopy (TEM) and electron diffraction (ED) are used to investigate the nanostructures of two ensembles of Co:CoO core–shell particles. TEM images show that particles of size about 12 nm are almost fully oxidized, while particles with size about 18 nm have a core–shell structure where a Co core is surrounded by a shell of CoO. ED simulation confirms that the larger particles have an fcc-structured Co core and a rock-salt CoO shell structure, while the smaller particles mostly have the rock-salt CoO structure. The core–shell structure is responsible for the unusual magnetic properties of the Co:CoO nanoclusters, especially the occurrence of inverted hysteresis loops (proteresis), but previous research has been indirect, largely based on magnetic measurements and on a cross-comparison with granular materials. Our measurements show that the structures have ferromagnetic fcc Co cores of varying sizes down to 1 nm which are surrounded by antiferromagnetic rock-salt CoO shells. The core radii obtained from the TEM pictures are used to estimate the exchange interactions responsible for proteresis and to pinpoint the core-size window in which proteresis occurs.     

Investigation on nanobubbles on graphite substrate produced by the water–NaCl solution replacement

How to produce nanobubbles repeatedly on a certain surface with sufficient amount is a key issue in nanobubbles research. It is well known that nanobubbles can be produced by exchanging water with organic solutions like alcohol which contains higher concentration of dissolved gas than that in water. However, it is not clear if this mechanism would work when exchanging water with the relatively low concentrations of dissolved gas such as salt solutions. In this paper, we employed NaCl solutions with different concentrations to replace water on graphite surface. We found that nanobubbles could indeed be generated and showed similar properties with those produced by other methods. Nanobubbles could be apparently observed when the NaCl concentration was as low as 0.15 M and their densities increased with the salt concentrations. When the concentration of NaCl was higher than 2.00 M, the number of nanobubbles increased slowly and nearly kept a constant. We also showed that the dissolved gas played an important role in the formation process of nanobubbles.     

Morphology and structural stability of Pt–Pd bimetallic nanoparticles

The morphologies and structures of Pt–Pd bimetallic nanoparticles determine their chemical and physical properties.Therefore, a fundamental understanding of their morphologies and structural stabilities is of crucial importance to their applications. In this article, we have performed Monte Carlo simulations to systematically explore the structural stability and structural features of Pt–Pd alloy nanoparticles. Different Pt/Pd ratios, and particle sizes and shapes were considered.The simulated results reveal that the truncated octahedron, which has the remarkably lowest energy among all the considered shapes, exhibits the best structural stability while the tetrahedron has the worst invariably. Furthermore, all the structures of Pt–Pd alloy nanoparticles present Pd-rich in the outmost layer but Pt-rich in the sub-outmost layer. Especially, atomic distribution and chemical short-range order parameter were applied to further characterize the structural features of Pt–Pd alloy nanoparticles. This study provides a significant insight not only into the structural stability of Pt–Pd alloy nanoparticles with different compositions, and particle sizes and shapes but also to the design of bimetallic nanoparticles.     

Experimental investigation of the effect of nozzle numbers on Ranque–Hilsch vortex tube performance

The present study investigates the effects of the orifice nozzle number and the inlet pressure experimentally on the cooling performance of the counter flow-type vortex tube. The energy generation has been conducted using a stream-tek generator (model GNMD-KIT) with different numbers of nozzles (2, 3, and 6), an aspect ratio of 1:6, and an inner diameter of 7.5 mm. In the experiments, for each of the orifices, inlet pressures have been adjusted from 200–600 kPa. The energy separation investigated here focuses on the cold temperature difference and coefficient of performance for cooling. The experimental results concluded in this article prove that the greatest effect of nozzle number is for three nozzles, and hence, that nozzle number could affect the energy separation efficiently. A comparison of the present experiments with other published works has been conducted. An analytical study of the characteristics equation has been carried out to evaluate the best correlation of the ratio of cold temperature difference to the inlet temperature as a function of pressure, cold mass fraction, and nozzle number.     

Effect of alloying on the stabilities and catalytic properties of Pt–Au bimetallic subnanoclusters: a theoretical investigation

Density functional theory (DFT) has been applied to study the geometrical and electronic structures and the catalytic properties for NO oxidation of pure Pt and PtAu clusters. The calculated results suggest that Pt₁₀ clusters shows the most stable structure among the pure Pt _n (n = 2–13) clusters with the local maximum Δ₂ E value. The doping of Au atoms reduces the stability of the clusters, and Pt₆Au₄ cluster has the most stable structure among Pt_10?n Au _n (n = 1–7) clusters, due to the closest band centers between Pt and Au atoms (0.83 eV) and the obvious s–p resonance peaks near the Fermi level. Pt₆Au₄ cluster displays the strongest activation of O₂ molecules among Pt_10?n Au _n (n = 0–7) clusters, owing to the clear overlap between O 2p and Pt 6 s and Au 6 s near the Fermi level, and the more positive d band center than the others. The interaction between NO and metals changes slightly in NO/Pt_10-nAu_n (n = 2–7) systems, which is weaker than that in NO/Pt₉Au system, as a result of the decreasing resonance peaks of sp hybridization near the Fermi level. Compared to pure Pt₁₀ cluster, the lower energy barriers and larger reaction energies on Pt₆Au₄ cluster suggest a higher catalytic activity of PtAu cluster for the O₂ dissociation and NO oxidation reactions. Our study provides atomic-scale insights into the nature of the interfacial effect that determines NO oxidation on PtAu cluster catalysts.     

Effects of annealing holding time on capacitance performance of RuO2–IrO2–graphene/Ti electrodes

The thermal decomposition method was used to prepare composite electrodes of the Ruthenium oxide–Iridium oxide–Graphene (RuO₂–IrO₂–G). Scanning Electron Microscopy (SEM), X–ray diffraction analysis (XRD), and electrochemical tests were used to study the influence of different annealing holding time on the surface morphology, phase composition, and capacitive performance of the coatings. The results showed that more and more RuO₂, IrO₂ nanoparticles were observed on the surface and cracks of the coating as the annealing holding time increasing. The RuO₂–IrO₂–G/Ti electrode was obtained by annealing for 5 h. The coating of the electrode consists of a certain amount of amorphous phase and nano–crystalline phase, and it had good electronic conductivity and ionic conductivity. At the same time, the electrode was prepared at 5 h had the largest specific capacitance of 778.46 F/g, which increased by 430.89 F/g than the electrode was prepared at 1 h. In addition, the electrode also had superior capacitance performance, capacitance retention and power characteristics.     

Fabrication and characterization of bismuth oxide–holmia nanofibers and nanoceramics

In this article, a novel and simple method to produce both boron doped and undoped holmia stabilized bismuth oxide nanoceramic materials has been put forward. Boron doped and undoped poly (vinyl alcohol)/bismuth–holmia acetate nanofibers were produced using the electrospinning technique and were calcined at 850 °C afterward in order to obtain nanopowder. The characteristics of the nanofibers were investigated with FT-IR, XRD, and SEM. XRD analyses showed that boron undoped holmia stabilized bismuth oxide nanopowders have the face-centered cubic structure (δ-phase), and that the incorporation of boron atoms into the composite prevents the nucleus formation and turns the structure into a more amorphous glassy form. The SEM micrographs of the fibers showed that the addition of boron results in the formation of cross-linked bright-surfaced fibers. The average fiber diameters for electrospun boron doped and undoped PVA/Bi–Ho acetate nanofibers were calculated using the ImageJ software as 102 nm and 171 nm, respectively.     

Structural and electronic properties of small bimetallic Ag–Cu clusters

The structural and electronic properties of small gas-phase Ag_mCu_n clusters with m+n=2–5 atoms are investigated using spin-polarized density functional theory. The LANL2DZ effective core potential and the corresponding basis set are employed while the performance of several exchange-correlation functionals is assessed. For a given cluster size all possible compositions are subject to optimization using a variety of initial structures. The geometry, binding energy, relative stability, ionization potential, electron affinity and HOMO-LUMO gap are reported for the lowest energy structure of every cluster size and composition. The results show that planar structures are favored, triangular for trimers, rhombic for tetramers and trapezoidal for pentamers. Moreover, for tetramers and pentamers we found that silver atoms demonstrate a clear tendency to occupy edge positions. The calculation of electronic properties indicates that although all exchange-correlation functionals predict the same trends, the choice of method is crucial concerning the final quantitative results.