排序方式: 共有12条查询结果,搜索用时 15 毫秒
1.
Carol Korzeniewski Rukma Basnayake Ganesh Vijayaraghavan Zhengrong Li Shanhong Xu Dominick J. Casadonte Jr. 《Surface science》2004,573(1):100-108
The electrochemical oxidation of CH3OH at nanometer-scale PtRu catalyst materials is reported. Comparisons are made between the properties of a Johnson Matthey (JM) PtRu black sample (50 at.% Ru (XRu ≈ 0.5)) and PtRu particles (2-6 nm, nominally XRu ≈ 0.5) prepared by sonication under anhydrous conditions. Cyclic voltammetry and in situ infrared spectroscopy measurements show the catalysts are active for the oxidation of 0.5 M CH3OH in 0.1 M HClO4 at temperatures between ambient and 70 °C. The sonochemically prepared PtRu sample displayed properties characteristic of bulk PtRu alloys with XRu ≈ 0.5. Evidence for phase separation of Pt and Ru was observed in CO stripping voltammetry from the JM catalyst adsorbed at low metal loadings (20 μg/cm2) on bulk Au electrodes. Per gram of catalyst, the JM material was more active toward CO2 formation and displayed greater resistance to poisoning by adsorbed CO than the sonochemically prepared material during ambient temperature oxidation of 0.5 M CH3OH in 0.1 M HClO4. 相似文献
2.
Some polishing experiments have been carried out on copper anodes in a hyperbolic cell designed by Gilmont and Walton, using orthophosphoric acid as the electrolyte. The results obtained have been compared to those obtained in similar experiments in a Hull cell. It has been found that very similar bands of different reflectivity and polishes are found to form in both the cells. These bands shift with time and a study of such displacements has been made. The results are briefly discussed. 相似文献
3.
Basnayake R Li Z Katar S Zhou W Rivera H Smotkin ES Casadonte DJ Korzeniewski C 《Langmuir : the ACS journal of surfaces and colloids》2006,22(25):10446-10450
Properties of PtRu nanoparticles prepared using high-intensity sonochemistry are reported. Syntheses were carried out in tetrahydrofuran (THF) containing Ru3+ and Pt4+ in a fixed mole ratio of either 1:10 or 1:1. X-ray diffraction measurements confirmed sonocation produces an alloy phase and showed that the composition of the nanometer scale metal particles is close to the mole fraction of Ru3+ and Pt4+ in solution with deviations that tend toward Ru enrichment in the alloy phase. The materials gave responses that are similar in terms of peak potential and current density, referenced to the catalyst active surface area, to those of bulk alloys in voltammetry experiments involving CO stripping and CH3OH electrochemical oxidation in 0.1 M H2SO4. The results show that sonochemical methods have the potential to produce nanometer scale bimetallic electrocatalysts that possess alloy properties. The materials have application in mechanistic studies of fuel cell reactions and as platforms for the development of CO tolerant fuel cell catalyst. 相似文献
4.
Basnayake R Peterson GR Casadonte DJ Korzeniewski C 《The journal of physical chemistry. B》2006,110(47):23938-23943
Infrared spectroscopy was applied to probe water inside pores and channels of Nafion membrane exchanged with either proton (H+) or sodium ions (Na+). Transmission measurements were performed on freestanding Nafion 112 (approximately 50 microm thickness) in a cell that enabled adjustment of the relative humidity. Experiments that employed Na+-exchanged Nafion focused on relative humidity environments at or below about 32% generated through the use of humectants. Under these conditions, narrow features in the O-H stretching spectral region near 3650-3720 cm(-1), previously attributed to interfacial water, were detected and matched to bands in vibrational sum frequency (VSF) spectra of water/air, water/organic, and salt-solution/air interfaces. The features correspond to the stretching mode of the "free" OH group of water oriented with one hydrogen atom toward other water molecules and interacting through hydrogen bonding and the other straddling the interface extending into fluorocarbon-rich regions (approximately 3668 cm(-1)) or air-filled segments (approximately 3700 cm(-1)) in the membrane. For membrane exchanged with H+, -SO3- groups were easily shifted to -SO3H as water was removed upon exposure to a few Torr of vacuum at 95 degrees C. In contrast, residual water was retained by membrane exchanged with Na+ after exposure to these conditions for up to 72 h. The permeation of methanol and acetone into Na+-exchanged Nafion 112 was also examined. The C-H and O-H stretching modes of methanol were perturbed in a manner that suggests the polymer disrupts hydrogen bonding interactions within the solvent, similar to the effect it exerts on pure water. For acetone, the C-H stretching modes were not shifted appreciably compared to those of the bulk liquid. However, the carbonyl band was affected, indicating the likely importance of dipolar interactions between solvent molecules and polar groups on the polymer. Control experiments performed with poly(hexafluoropropylene-co-tetrafluoroethylene) (FEP) membrane did not show evidence for water or methanol permeation, which demonstrates the critical role played by the ion-filled channels and pores in facilitating solvent transport within Nafion membrane. 相似文献
5.
In this paper, we report for the first time finite size effects on Néel temperature (T
N) of magnetoelectric BiFeO3 system. Novel wet chemical route has been developed to produce fine particles of BiFeO3 with controlled size and size distribution. Unlike other oxide systems, lattice volume contraction has been observed with
decrease in particle size. The decrease in T
N is co-related to unit cell volume contraction occurring with reduction in particle size. 相似文献
6.
Loo L Guenther RH Basnayake VR Lommel SA Franzen S 《Journal of the American Chemical Society》2006,128(14):4502-4503
Icosahedral virus capsids demonstrate a high degree of selectivity in packaging cognate nucleic acid components during assembly. This packaging specificity, when integrated as part of a nanotechnological protocol, has the potential to encapsidate a wide array of foreign materials for delivery of therapeutics or biosensors into target cells. Red clover necrotic mosaic virus (RCNMV) exclusively packages two genomic ssRNAs initiated by a specific protein:RNA interaction between the RCNMV coat protein (CP) and the viral RNA origin of assembly (OAS) element. In the present work, an oligonucleotide mimic of the RCNMV OAS sequences is attached to Au nanoparticles as a recognition signal to initiate the virion-like assembly by RCNMV CP. Covalent linkage of the OAS to Au functions as a trigger for specific encapsidation and demonstrates that foreign cargo can be packaged into RCNMV virions. 相似文献
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8.
Journal of Nonlinear Science - In section 5.1 entitled “The shortest NEP from a bounded domain in prviously. 相似文献
9.
What are the paths associated with the fastest Brownian particles that reach a narrow window located on the boundary of a microdomain? Although the distribution of the fastest arrival times has been well studied in dimension 1, much less is known in higher dimensions. Based on the Wiener path-integral, we suggest that the paths of the fastest particle are concentrated near the shortest paths that minimize the energy-action. Stochastic simulations confirm the present result when an obstacle is positioned between the source point and a narrow window. To conclude paths associated with the fastest arrival times differ significantly from the ones of mean properties of Brownian motions, associated to mean first passage times of a single particle. These extreme properties should be considered instead of the classical Smoluchowski's rate of chemical reactions, because the statistics of the extreme for many copies of the same molecule changes the time scales of activation in cellular domain. 相似文献
10.
Optical flow is one of the classical problems in computer vision, but it has recently also been adapted to applications from other fields, such as fluid mechanics and dynamical systems. If the goal is to analyze the dynamics of system whose evolution is governed by a flow field that is the gradient of a potential function – which describes many flows in fluid dynamics – it is natural to approach the optical flow problem by reconstructing the potential function, also called the stream function, rather than reconstructing the components of the flow directly. This alternate approach allows one to impose scientific priors, via regularization, directly on the flow itself rather than on its components independently. We demonstrate the stream function formulation of optical flow and its application to reconstructing an oceanic fluid flow driven by satellite measurements. It is also shown how these flow fields can be used to analyze mixing and mass transport in the fluid system being imaged. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献