Metallic Copper Particles Research Articles

Nonlinear absorption and refraction in lead glasses: enhanced by the small metal particle dispersions

We investigate the nonlinear properties of several PbO–B 2O 3 glasses and their composites using 6-ns laser pulses. The nonlinear index of refraction n 2 are measured with Z-scan method at 532 nm for these samples, which are all an order larger than a CS 2 solution ( n 2=0.98×10 −11 esu) determined here; the composite materials with silver or copper metal particle dispersions exhibit larger nonlinear refractive index than the related lead glasses. These samples exhibit saturation absorption property at 532 nm under the input irradiance I 0 levels from 1.02 to 7.09 × 10 −2 GW/cm 2; the estimated saturation absorption coefficient β s (=α 0/I s ) decreases with increasing I 0. The enhancement of nonlinear absorption coefficient β at 355 nm can be attended by either increasing the lead oxide contained in glass matrix or by doping with silver or copper metal particles.

EXAFS and optical spectroscopy characterisation of reduction products of binary silver-copper ion mixture in mordenite

Ag+, Cu2+ and Ag + - Cu 2 + binary mixtures with different Ag/Cu ratios were supported on mordenite with Si/Al ratio equal to 10 and reduced in the temperature range 323-673 K. Diffuse Reflectance UV-Visible spectra reveal appearance of Ag8 clusters and small copper metal particles. Cu K-edge EXAFS show for Cu-rich non-reduced samples the presence of only oxygen shell; but for the Ag-rich sample, the presence of heavier backscatterer is also indicated producing a different EXAFS envelope. Silver EXAFS analysis suggests that, for the reduced samples, there are both Ag - O and Ag - Ag distances (Ag - Ag and Ag - O coordination numbers of approx 2 and of 1.3 respectively for the Ag/Cu = 3:1 and 1:3 samples). Importantly, for the reduced sample, the EXAFS indicates that Ag appears to promote/stabilise Cu cluster formation whereas Cu appears to impede/destabilise Ag cluster formation.

Quick, Easy, and Inexpensive Way to Detect Small Metallic Particles in Suspension Using Voltammetry of Immobilized Microparticles

Voltammetry of immobilized microparticles on the surface of a glassy carbon electrode was used to detect the presence of metallic copper particles in suspension. The solution sample containing copper particles was placed on the electrode surface and allowed to dry, then square wave voltammetry was performed. Two voltammetric peaks at −0.076 and 0.365 V vs. Ag/AgCl/KCl sat. in HCl 0.5 M were obtained, which correspond to electrooxidation of Cu particles deposited on the electrode surface.

Adsorption of hydrogen on reduced copper chromite

Temperature programmed desorption and volumetric methods in static conditions were used to study hydrogen adsorption on the surface of metallic copper particles produced by the partial reduction of copper chromite CuCr2O4 with hydrogen. In the temperature range 300-573 K and in the range of medium surface coverages by hydrogen, the main state of adsorbed hydrogen reveals the heat of adsorption q= 78 kJ/mol and activation energy of adsorption Ea = 69 kJ/mol. In the temperature range 77-300 K, an adsorption state with lower heat and activation energy was found, indicating a non-uniformity of the copper surface within ca. 8% of the total number of surface sites.

Dehydrogenation of methanol over copper-containing catalysts

The catalytic properties in methanol dehydrogenation of copper metal formed as a result of reduction by hydrogen of copper-containing oxides with different structure: copper chromite (tetragonally distorted spinel), copper hydroxysilicate (Chrysocolla), and copper-zinc hydroxysilicate (Zincsilite) have been studied. This process proceeds via successive reactions: (I) 2CH 3OH=CH 3OOCH+2H 2 and (II) CH 3OOCH=2CO+2H 2. The methyl formate selectivity for the catalysts studied was close to 1.0 at low methanol conversion, X≤0.1, where the dehydrogenation process is represented by reaction (I), occurring far from its equilibrium. At 0.2≤ X≤0.55, the selectivity decreases with increasing conversion, and the ratio of the activities in successive reactions may serve as a comparative characteristic for the catalysts. At high conversions, when reaction (I) is close to its equilibrium, selectivity is independent of the properties of studied catalysts and depends on the methanol conversion. Reaction (I) shows low sensitivity to the state of metal copper of reduced catalysts and, hence, low sensitivity to the composition and structure of oxides-precursors. The catalysts’ activity in reaction (II) greatly depends on the state of metal copper in the catalysts. It was assumed that the catalyst activity in methyl formate conversion to CO and H 2 and, hence, the selectivity of methanol dehydrogenation with respect to methyl formate in the region of moderate methanol conversion depends on the strength of interaction between metal copper particles and catalyst oxide surface, which is determined by the composition and structure of oxide-precursor.

Methanol synthesis from carbon monoxide and hydrogen over ceria-supported copper catalyst prepared by a coprecipitation method

High catalytic activity in the synthesis of methanol from carbon monoxide and hydrogen can be produced with ceria-supported copper catalysts prepared by a coprecipitation method. The activity at 468 K is comparable with that produced with commercial copper-zinc catalysts at 503-523 K, while it is still unstable. Although the reaction atmosphere is reductive, metallic copper particles on cerium oxide are oxidized during the reaction and the catalyst is activated. Hence, formation of the copper oxide species is indispensable for the appearance of the high catalytic activity.

Preparation and Characterization of Copper/Yttria Titania Zirconia Cermets for Use as Possible Solid Oxide Fuel Cell Anodes

The potential of a new anode cermet based on Cu and titania doped yttria stabilized zirconia (YZT) for high temperature fuel cells was examined. Cermets were prepared by a standard solid-state reaction using Y0.2Ti0.18Zr0.62O1.9 and CuO as starting materials. Green pellets were sintered at 1000 °C for 10 hours resulting in sound pellets. These were successfully reduced in 5 % H2 in Argon again yielding sound pellets with a porosity of 50 %. These were characterized by SEM, XRD and TGA methods and their conductivity measured by ac impedance and the 4 point DC method as a function of both temperature and oxygen partial pressure. On sintering there was evidence of a small amount of reaction between CuO and YZT. This resulted in a slight tetragonal distortion of YZT; however, most of the copper oxide was not incorporated into the zirconia. The cermet was successfully redox cycled and percolation was achieved when the copper composition exceeded 33 % of the volume. Conductivity remains high under a wide range of oxygen partial pressures from the most reducing conditions up to 10–4 atm O2. Electrochemical testing performed using three-electrode geometry showed good performance for hydrogen oxidation for temperatures up to 800 °C. At higher temperatures up to 1000 °C copper was observed to be very mobile with considerable agglomeration of metallic copper particles. Indeed in some instances there was a total segregation of copper from YZT resulting in a copper layer forming at the electrolyte interface with the outer layer of the electrode being essentially YZT. This agglomeration and migration of Cu led to a significant degradation in electrochemical performance with large increases in the series resistance and polarization resistance, especially under anodic bias. Due to these segregation problems copper based cermets produced in this manner are not thought to be good candidates for fuel cell electrodes operating at 1000 °C.

Copper thin coating deposition on natural pollen particles

We have deposited thin copper coatings on micro-sized natural pollen particles by electroless plating, using palladium as the catalyst, copper sulfate as the source of deposited metal, and formaldehyde as the reducing agent. A two-step pretreatment process is used to activate the pollen surface with stannous chloride and palladium chloride. The results of XRD, SEM, AES, and cross-section metallography show that the pollen particles are completely coated by a pure and porous FCC-structured crystalline copper film about 1 μm thick. The film is composed of spherical and some needle-shaped metallic copper particles. The latter are attributed to the strong aggregation tendency among neighboring nano-sized copper particles grown with rapid hydrogen release. We find that lightweighted pollen particles are good candidates for fabricating metallic composite microspheres with core-shell structures.

Synthesis of Silver and Copper Nanoparticles in a Water-in-Supercritical-Carbon Dioxide Microemulsion

Nanometer-sized silver and copper metal particles can be synthesized by chemical reduction of Ag+ and Cu2+ ions dissolved in the water core of a water in supercritical fluid carbon dioxide microemulsion. Sodium cyanoborohydride and N,N,N‘,N‘-tetramethyl-p-phenylenediamine are effective reducing agents for synthesizing these metal nanoparticles in the microemulsion. Formation of the metal nanoparticles was monitored spectroscopically using a high-pressure fiber-optic reactor equipped with a CCD array UV−vis spectrometer. Silver and copper nanoparticles synthesized in the microemulsion showed characteristic surface plasmon resonance absorption bands centered at 400 and 557 nm, respectively. Diffusion and distribution of the oxidized form of the reducing agent between the micellar core and supercritical CO2 appeared to be the rate-determining step for the formation of the silver nanoparticles in this system.

Solvent Effects on Copper Nanoparticle Growth Behavior in AOT Reverse Micelle Systems

In this paper, we present the results of variations in the bulk solvent type and the addition of cosolvents on the growth rate of metallic copper nanoparticles produced through a reduction reaction within AOT reverse micelles. The metallic copper particles were characterized using both UV−vis spectroscopy and TEM microscopy. Growth rates are discussed in terms of an absorbance ratio, which provides a correlation between UV−vis absorption spectra and particle size. Time-resolved measurements showed that the intermicellar exchange rate and subsequent particle growth rate is a function of water content, bulk solvent, and the addition of cosolvents and cosurfactants. The copper particle growth rate was found to increase with increasing water content, but essentially the same particle size was eventually approached at all water contents. Copper particle growth was faster in isooctane than in cyclohexane because of the structure of the bulk solvent and the resulting degree of solvation into the micellar tail region. The cosolvent 1-octanol was found to decrease the copper particle growth rate when added in small amounts (up to 3 mol %) at two different water contents, but larger amounts of the cosolvent destabilized the micelle, increasing the growth rate and decreasing the terminal particle size. The cosolvent benzyl alcohol had the opposite effect, increasing the copper particle growth rate and decreasing the terminal particle size at all of the concentrations studied.

Enhanced response properties of a chromophore physisorbed on a metal particle

We present a theoretical methodology to study the electronic response properties of a chromophore physisorbed on a metal particle. In particular the chromophore is treated at ab initio level whereas the metal particle is described through its dielectric properties. The use of a boundary elements method for the resolution of the electrostatic problem allows the study of particles with complex shapes. The theoretical procedure is applied to the study of different quantities such as the chromophore effective polarizability, the UV-VIS absorption of the chromophore coated metal particle, and the surface enhanced Raman scattering (SERS) of the physisorbed molecule for two reliable chromophores (merocyanine dyes) physisorbed on copper and silver metal particles of various sizes and shapes.

Metallic Copper Nanoparticle Synthesis in AOT Reverse Micelles in Compressed Propane and Supercritical Ethane Solutions

In this articles, we present the formation of nanosized metallic copper particles synthesized in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles in compressed propane and supercritical fluid (SCF) ethane solutions. Specifically, copper particles (<20 nm) were produced by the reduction of copper ions from copper bis(2-ethylhexyl) sulfosuccinate, Cu(AOT)2, incorporated within AOT reverse micelles dispersed in compressed propane and SCF ethane solvent along with small amounts of isooctane cosolvent. The effects of the compressed solvents on the particle characteristics and particle growth rate are discussed and comparisons are made with growth rates in normal liquid solvents. The metallic nanoparticles were characterized using both in situ UV−vis spectroscopy and transmission electron microscopy. The UV−vis spectrum of these nanosized copper particles is sensitive to particle size, and hence time-resolved spectral measurements were used to monitor the particle growth process. The particle growth rate in AOT reverse micelles in SCF ethane is faster than in either of the two normal liquid solvents partly because of intermediate physical and transport properties of the SCF solvent (e.g. increased mass transfer, decreased viscosity and density, lower dielectric constant), which results in increased collision frequencies and exchange rates between micelles.

Metal Particle Size in Silica-Supported Copper Catalysts. Influence of the Conditions of Preparation and of Thermal Pretreatments

The size of metal copper particles supported on silica was studied as a function of the following parameters: the preparation route, the nature of the metallic precursor, the copper content, and the thermal pretreatments before reduction. Two modes of preparation were investigated: (i) incipient wetness impregnation with copper nitrate; (ii) cationic exchange with copper tetraammine and copper bis-ethanediamine complexes. The key step for the obtention of small metal particles after reduction to 700 °C is the drying step at room temperature for the Cu/SiO2 samples prepared by impregnation and the presence of chemical bonds between Cu2+ and the support for the samples prepared by cationic exchange. The chemical bonding is established during drying or calcination, depending on the metal complex. The characterization studies clearly showed that different Cu(II) species (copper nitrate hydroxide, CuO, copper phyllosilicate, or isolated−grafted Cu2+ ions) can exist depending on the preparation method and the...

Direct Relationship Between Shape and Size of Template and Synthesis of Copper Metal Particles

Well-defined surfactant self-assembled microstructures are needed to take full advantage of the templating strategy for the generation of nanoparticles with controlled size and anisometry, as demonstrated here. For example, at a high concentration of Cu(AOT)2 (AOT = bis(ethylhexyl)sulfosuccinate) in isooctane–water the micellar supra-aggregate depicted in the Figure forms, and spherical copper metal particles are produced.

Direct Relationship Between Shape and Size of Template and Synthesis of Copper Metal Particles

Direct Relationship Between Shape and Size of Template and Synthesis of Copper Metal Particles

Direct Relationship Between Shape and Size of Template and Synthesis of Copper Metal Particles

Direct Relationship Between Shape and Size of Template and Synthesis of Copper Metal Particles

Origin of the Red Color of Satsuma Copper‐Ruby Glass as Determined by EXAFS and Optical Absorption Spectroscopy

The origin of the ruby color of Satsuma glass, a famous copper‐ruby glass produced in Japan in the mid‐19th century, has been examined by electron microprobe analysis (EPMA), X‐ray absorption fine structure (XAFS), and optical absorption spectroscopy analyses. CuK XAFS analysis reveals that the major component of copper in the ruby glass consists of Cu(I) ions in the glass structure. This species is distinct from Cu2O (cuprite), which we conclude is not responsible for the ruby color. Optical absorption spectra measured at 300 and 77 K clearly distinguishes the absorptions due to the colloidal particles of metallic copper and Cu2O. It is concluded that the trace amount of copper in the ruby glass, which is below the detection limit of the EPMA and XAFS techniques, exists as metallic copper particles of nanometer size and is responsible for the ruby‐red appearance of the Satsuma glass.

Spectroscopic Study of a Cu/CeO2Catalyst Subjected to Redox Treatments in Carbon Monoxide and Oxygen

Redox processes induced by interaction of a calcined Cu/CeO2catalyst with CO and reoxidation with O2have been investigated by CO-TPR, EPR, FTIR of adsorbed CO, and XPS. The initial calcined sample shows the presence of dispersed Cu2+species, which give rise in the EPR spectrum to signals due to isolated entities, a somewhat more aggregated Cu2+-containing phase, and copper ionic pairs, in coexistence with an EPR-silent CuO-type phase, revealed by XPS. A significant reduction of copper is produced already by contact with CO at room temperature, EPR results suggesting that reducibility of Cu2+species decreases with their aggregation degree. Simultaneously, the ceria surface is also reduced by this interaction, copper acting as a strong promoter of this process. A singular consequence of the synergistic reduction of both components is observed by subjecting the catalyst to CO atTr≥ 473 K, at which the CO adsorption capability of copper is apparently suppressed, in view of the absence of copper carbonyls in the FTIR spectrum. This is attributed to the establishment of electronic interactions between reduced ceria and small metallic copper particles generated by the reduction process. Contact of the CO-reduced sample with O2at room or higher temperature produces an important reoxidation of both copper and ceria, revealed by FTIR and EPR. The synergetic effects between copper and ceria in the reduction process and the easy reoxidation of deeply reduced ceria are thought to be crucial to explaining the high catalytic activity shown by this system for CO oxidation.

Formation and Properties of Sol-Gel Films and Glasses with Ultrafine Metal and Semiconductor Particles

A novel method of fabrication of silica-based sol-gel films and glasses containing small semiconductor particles was developed. A series of films and glasses with nanoparticles of copper chalcogenides (CuS, Cu2Se, CuInS2) and metal particles (Cu) were fabricated through the chemical transformation of precursors incorporated into a sol-gel derived matrix. The properties of the nanoparticles studied by means of XRD, XPS, TEM and optical spectroscopy are provided both by size effects and the chemical nature of surface states and can be controlled at different steps of chemical treatment.

Copper nanoparticles in zeolite Y

A. Seidel, J. Loos and B. Boddenberg, J. Mater. Chem., 1999, 9, 2495 DOI: 10.1039/A902806D