XPS and reactivity study of bimetallic nanoparticles containing Ru and Pt supported on a gold disk

We report a new method of immobilization of catalytic metal/alloy nanoparticles on a gold disk for transfer from an electrochemical cell to UHV (without sample exposure to air) for XPS analyses. Using this immobilization approach, several samples were examined: a core-shell Pt-on-Ru catalyst prepared from Ru black onto which Pt was spontaneously deposited, commercial Pt/Ru 50:50 nanoparticle alloy, as well as single metal Ru and Pt nanoparticle samples. The catalysts were characterized for the Ru oxidation state and for the methanol electrooxidation activity (as Pt was always metallic). For all bimetallic samples, we found that the reduced nanoparticles were more active towards methanol oxidation than the fully or partially oxidized samples. Regardless the Ru oxidation state however, the activity was lower than that previously reported for Ru decorated Pt nanoparticle catalysts (Ru-on-Pt). Possible reasons for the reactivity differences are discussed.     

Surface plasmon resonance of Au-Cu bimetallic nanoparticles predicted by a quasi-chemical model

Au-Cu alloys are functional materials with nonlinear optical applications. However, the optical properties of such alloys are difficult to predict due to the random mixing of materials. In this paper, we present a quasi-chemical model to simulate the optical properties of Au-Cu alloy systems based on the mixing of Gibbs free energy. This model is also able to predict the position of the surface plasmon resonance peaks for Au-Cu alloy nanoparticles. The model can be applied to predict the optical properties of alloy systems in the fields of plasmonics and nanophotonics.     

An experimental and numerical study of a miniature high resolution isopotential DMA

A miniaturized version of an isopotential nano-differential mobility analyzer (DMA) [Labowsky, M., & Fernández de la Mora, J. (2006). Novel ion mobility analyzers and filters. Journal of Aerosol Science, 37, 340–362] has been tested experimentally and simulated by means of the commercial code COMSOL^® to take into account Brownian diffusion. Compared with the prototype tested by [Martínez-Lozano, P., & Fernández de la Mora, J. (2006). Resolution improvements of a nano-DMA operating transonically. Journal of Aerosol Science, 37, 500–512.] this model is half the size and weights 920 g. Resolution, defined as the inverse of the relative full width at half height (FWHH), has been improved by a 50%, attaining a maximum resolution of 75 operating at a Reynolds number (Re) of ～47,000, measuring ions of equivalent mobility diameter ～1 nm. The maximum diameter theoretically measurable by this DMA is 15 nm. The predictions of the numerical simulations are in reasonable agreement with experiments with respect to resolution and the device constant, which provides an estimation of the measurable size range. The model suggests future approaches to improve resolution and to extend the measurable size range.     

地震资料高分辨率中熵的应用

地层的反射系数由地层的结构性质决定,所以任意随机的不同性质地层组合使地层反射系数序列(r i)成为一个随机序列(r i),可以用它的各种统计量来表征。地震的反射系数具有不确定性,所以熵是研究它的有力工具。这样反射系数的频谱形状可以用反射系数频谱的熵来表征,并且验证了频带宽度对地震资料高分辨率的影响。     

A high resolution XPS study of sidewall functionalized MWCNTs by fluorination

Carbon nanotubes must be modified to magnify their application. Understanding the chemistry of carbon nanotubes is a crucial step towards their ultimate practical use. In this study, multi-walled carbon nanotubes (MWCNTs) were fluorinated at several different conditions. The change in the atomic structures of fluorinated MWCNTs was investigated using X-ray photoelectron spectroscopy (XPS). All core level spectra of MWCNTs were deconvoluted to several Pseudo-Voigt functions (sum of Gaussian–Lorentzian functions). The amount of doped fluorine increased with increasing doping fluorine partial pressure, and the fluorine atoms were covalently attached to the side-wall of the MWCNTs. However, the increasing rate of F1s component ratio became dull at 70%, as compared with ratios below 70%. This suggests that fluorine contents during the fluorination of carbon materials can be managed by controlling the fluorine mixing ratio.     

Carbons of high surface area. A study by adsorption and high resolution electron microscopy

Five carbons of high surface area, ~ 2000–3000 m²g^?1 are studied by adsorption of carbon dioxide at 195 and 273 K. Effective surface areas are calculated using Langmuir and Dubinin- Radushkevich equations. Structure in these carbons is assessed by phase contrast high resolution transmission electron microscopy. The lamellae or constituent layers of these carbons are resolved as fringe images. Careful examination of thin sections of these carbons shows significant differences in separation distances of lamellae which indicate differences in the size and shape of the supermicroporosity which exists as the space between the lamellae. These differences correlate closely with the effective surface areas. The supermicroporosity consists of cage-like voids 1–5 nm dia., the cages being separated by walls of 1–3 carbonaceous layers in thickness. The filling of such supermicroporosity by a mechanism of increasing adsorption potential or cooperative adsorption adequately accounts for high internal volumes of up to 1.7cm³g^?1 and of effective surface areas of about 3000 m²g^?1. The size and shape of supermicroporosity can be deduced from micrographs.     

High resolution mapping of surface reduction in ceria nanoparticles

Surface reduction of ceria nano octahedra with predominant {111} and {100} type surfaces is studied using a combination of aberration-corrected Transmission Electron Microscopy (TEM) and spatially resolved electron energy-loss spectroscopy (EELS) at high energy resolution and atomic spatial resolution. The valency of cerium ions at the surface of the nanoparticles is mapped using the fine structure of the Ce M(4,5) edge as a fingerprint. The valency of the surface cerium ions is found to change from 4+ to 3+ owing to oxygen deficiency (vacancies) close to the surface. The thickness of this Ce(3+) shell is measured using atomic-resolution Scanning Transmission Electron Microscopy (STEM)-EELS mapping over a {111} surface (the predominant facet for this ceria morphology), {111} type surface island steps and {100} terminating planes. For the {111} facets and for {111} surface islands, the reduction shell is found to extend over a single fully reduced surface plane and 1-2 underlying mixed valency planes. For the {100} facets the reduction shell extends over a larger area of 5-6 oxygen vacancy-rich planes. This finding provides a plausible explanation for the higher catalytic activity of the {100} surface facets in ceria.     

Pt/Pd alloy nanoparticles composed of bimetallic nanobowls: Synthesis, characterization and electrocatalytic activities

Bowl-like nanostructures of Pt/Pd bimetallic nanocrystals are prepared by employing Ag nanoparticles as a template and completely removing the residual Ag after the displacement. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations display that the thin walls of Pt/Pd nanobowls are composed of nanoparticles. X-ray diffraction (XRD) pattern demonstrates that Pt and Pd form the alloy in the nanobowls. The crystal structures of the nanobowls consist of [1 1 1], [2 0 0], [2 2 0] surfaces as revealed by both high-resolution TEM (HRTEM) and XRD results. The Pt/Pd nanobowls exhibit significant high electrocatalytic activities toward the methanol oxidation and oxygen reduction compared with the Pt/Pd nanospheres and Pt nanobowls.     

Sol derived gold–palladium bimetallic nanoparticles on TiO2: structure and catalytic activity in CO oxidation

Bimetallic AuPd catalysts were prepared by deposition of bimetallic aqueous sols formed in different ways: (i) co-reduction of the precursor Au and Pd ions by Na-citrate/tannic acid mixture, (ii) reduction of Au(III) ions onto preformed Pd sol, and (iii) reduction of Pd(II) ions onto a preformed Au sol. The Au/TiO₂ and Pd/TiO₂ samples as references were prepared from their respective sols. The structure of the samples was characterized by XRF, XRD, XPS, TEM and CO chemisorption both in the as-prepared state and after calcination and reduction. The catalytic activities of the calcined/reduced catalysts in the CO oxidation were compared. The presence of bimetallic crystalline phases was evidenced in all three samples both in the as prepared and calcined/reduced states, however, various extents of Pd surface enrichment were determined. The catalytic activity of the bimetallic samples regardless of the preparation method, is about the same as that of the mixture of the monometallic samples. No significant synergism is suggested in the present bimetallic samples.     

The study of hydrogenations of olefins catalyzed by polymer-supported palladium-lanthanoid bimetallic catalysts

Palladium-lanthanoid bimetallic complex catalysts supported on chloromethylated polystyrene beads derivatized with anthranilic acid have been synthesized. Their characterization and catalytic activity have been studied. Under mild conditions, the polymer-bound Pd-La complex catalyzed the hydrogenation of olefins. The hydrogenation rate was correlated with the solubility parameter, δ, of the solvents and substrates. The rates of hydrogenation of octene were studied and the dependence of factors such as catalyst concentration, octene concentration, hydrogen pressure and temperature has been determined. The rate equation for the hydrogenation of octene in ethyl acetate solvent was found to be R = kP_H2C_Cat. The activation energy of this reaction was 3.0 kcal/mol. It was also found that the promotion effect by anchored Ln ions varied with the atomic number of the Ln series. When the f electron number was 0, 7 or 14, the polymer-bound Pd-Ln catalyst possessed the highest activity in hydrogenation.     

Instability of horizontal fluid interface in a perpendicular electric field: Observational study

In order to obtain some insight into the potential applicability of electrohydrodynamic augmentation to the direct-contact heat or mass exchange between stratified fluids, observations were made of the phenomena related to the field-induced instabilities at stationary interfaces between air and slightly-conducting oil, slightly-conducting oil and conducting aqueous solution, and two slightly-conducting oils. Established theories assuming the interface conducting or charge-free failed to predict the onset of instability under d.c. or a.c. fields in the last fluid system of the three. The geometries and fluid motions at disturbed interfaces are described laying stress on those, found in the last fluid system, which are very peculiar and have not been reported so far.     

Interaction between Pd and Cu nanoparticles in bimetallic CuPdx nanoparticles and its impact on oxidation of 1,2-propanediol to aliphatic acids

Bimetallic CuPd_x nanoparticles synthesized by the wet chemical reduction method were used as the catalysts in the catalytic oxidation of 1,2-propanediol with gaseous oxygen to aliphatic acids. The palladium and copper nanoparticles in the bimetallic CuP dxnanoparticles had an alloying trend. The catalytic activity of the palladium nanoparticles in the bimetallic CuP dxnanoparticles was enhanced by the interaction between the palladium and copper nanoparticles. When the bimetallic CuPd_7 nanoparticles catalyzed the oxidation of 1,2-propanediol in an alkaline aqueous solution at 100℃ for 3h, lactic, formic, and acetic acids were dominantly produced with the total selectivity of above 99% at the 1,2-propanediol conversion of 85.9%. The simulation of the reaction kinetic equation on the CuPd_7 catalyst showed that the reaction activation energy was 29.4kJ·mol~(-1), indicating that the bimetallic CuPd_7 nanoparticles had a high catalytic activity in the oxidation reaction between 1,2-propanediol and gaseous oxygen.     

The use of a high resolution NMR spectrometer controlled by a dedicated computer for quantitative analytical chemistry

Operational complexity of high resolution NMR spectrometers has severely limited their use in quantitative analysis in spite of the many inherent advantages of the NMR technique. In order to demonstrate the feasibility of routine analyses in a rapid and accurate fashion with no special demands on the skill of the operator, the authors have programmed a small general purpose computer to control an NMR spectrometer, maintain adjustment of critical operating parameters, acquire data, numerically integrate appropriate spectral regions, calculate results and errors, and print out a teletype record of results. The unsaturation in natural edible oils, expressed as the iodine number and a polyunsaturation factor, has been chosen to illustrate in a specific case the application of this general approach to the analysis of multicomponent mixtures. It is shown in this paper that iodine numbers obtained by NMR agree with those obtained by the classical titration method within two or three iodine numbers over a wide range of values. The effect of varying NMR instrumental parameter settings over a wide range has also been investigated and reported. In view of the results obtained in the present work, it appears that computers aided quantitative analysis using sophisticated analytical instrumentation such as NMR spectrometers, and should now be given serious consideration by many high volume, multicomponent analyses in the food, drug and chemical industries. Presented at the Pittsburgh Conference on Applied Spectroscopy, Cleveland, Ohio, April 1969.     

Simultaneous removal of trihalomethanes by bimetallic Ag/Zn: kinetics study

In the present work, bimetallic silver/zinc was applied into the degradation of trihalomethanes, THMs: CHCl₃, CHBrCl₂, CHBr₂Cl, and CHBr₃. The kinetics reaction rates and removal efficiencies of the THM compound mixtures, in the aqueous solutions, were investigated. Batch experiments were conducted under mild conditions, ambient temperature, and pressure. The primary degradation reaction followed a pseudo-first-order kinetic law. The first-order rate constants and the degradation efficiencies followed the decreasing order of CHBr₃>CHBr₂Cl>CHBrCl₂>CHCl₃. The bond dissociation energy and hydrophilic/hydrophobic characteristics of the THM compounds may become the most important parameters affecting the degradation kinetics and efficiency by bimetallic Ag/Zn.     

Functionalized gold nanoparticles: a detailed in vivo multimodal microscopic brain distribution study

In the present study, the in vivo distribution of polyelectrolyte multilayer coated gold nanoparticles is shown, starting from the living animal down to cellular level. The coating was designed with functional moieties to serve as a potential nano drug for prion disease. With near infrared time-domain imaging we followed the biodistribution in mice up to 7 days after intravenous injection of the nanoparticles. The peak concentration in the head of mice was detected between 19 and 24 h. The precise particle distribution in the brain was studied ex vivo by X-ray microtomography, confocal laser and fluorescence microscopy. We found that the particles mainly accumulate in the hippocampus, thalamus, hypothalamus, and the cerebral cortex.     

Simultaneous removal of trihalomethanes by bimetallic Ag/Zn: kinetics study

In the present work, bimetallic silver/zinc was applied into the degradation of trihalomethanes, THMs: CHCl₃, CHBrCl₂, CHBr₂Cl, and CHBr₃. The kinetics reaction rates and removal efficiencies of the THM compound mixtures, in the aqueous solutions, were investigated. Batch experiments were conducted under mild conditions, ambient temperature, and pressure. The primary degradation reaction followed a pseudo-first-order kinetic law. The first-order rate constants and the degradation efficiencies followed the decreasing order of CHBr₃>CHBr₂Cl>CHBrCl₂>CHCl₃. The bond dissociation energy and hydrophilic/hydrophobic characteristics of the THM compounds may become the most important parameters affecting the degradation kinetics and efficiency by bimetallic Ag/Zn.     

A high performance bimetallic catalyst for photo-Fenton oxidation of Orange II over a wide pH range

A bimetallic catalyst supported on MCM-41 was synthesized by chemical vapour deposition and evaluated in the photo-Fenton degradation of Orange II. An in situ oxidation method recently developed in our group was applied to stabilize the metal catalyst supported on MCM-41, achieving an extremely low metal leaching level. This FeCu/MCM-41 shows TOC removals of 93%, 83%, and 78% at pHs of 3, 5.5, and 7, respectively, and maintains its high catalytic activity after 10 consecutive runs. This catalyst successfully overcomes the two problems faced by the heterogeneous photo-Fenton process – metal leaching and narrow working pH range.     

Synthesis of graphene-supported bimetallic nanoparticles for the sunlight photodegradation of Basic Green 5 dye in aqueous medium

Graphene nanosheets-supported Sn-Pt bimetallic nanoparticles (GNs/Sn-Pt) were prepared by precipitation method. The obtained GNs/Sn-Pt was used as a photocatalyst for photodegradation of Basic Green 5 (BG5) in aqueous solution under sunlight. The morphology and photodegradation study was performed by SEM and UV–VIS spectrophotometry, respectively. The SEM image showed the presence of Sn and Pt on GNs, being confirmed by energy dispersive X-ray (EDX) analysis. The photodegradation study of BG5 showed that the dye degradation increases as a function of irradiation time. The degradation of BG5 was found to be pH dependent and maximum degradation was found at higher pH.     

Numerical study of flow at a liquid-porous medium interface

The problem of the two-dimensional creeping flow of a viscous incompressible liquid in a flat channel partially filled with a model fibrous porous medium that is represented by a regular system of square cylinders (prisms) located across the flow is solved. Two types of flows are considered: a shear flow due to the motion of the upper wall of the channel and a gradient flow due to the presence of a pressure drop along the channel. The hydrodynamic microscopic fields of velocity are numerically found. The macroparameters such as the rate of filtration, the permeability of a system of cylinders, the flow rate of the liquid through the channel, tangential stresses on the upper wall of the channel and the porous boundary, and a slip coefficient, the use of which in the Saffman slip boundary condition makes it possible to considerably simplify the solution of the original problem, are obtained as a result of averaging.