Showing papers on "Copper published in 2008"

Synthesis and photovoltaic application of copper(I) sulfide nanocrystals.

Abstract: We present the rational synthesis of colloidal copper(I) sulfide nanocrystals and demonstrate their application as an active light absorbing component in combination with CdS nanorods to make a solution-processed solar cell with 1.6% power conversion efficiency on both conventional glass substrates and flexible plastic substrates with stability over a 4 month testing period.

Rapid synthesis of silver nanowires through a CuCl- or CuCl2-mediated polyol process

Abstract: The presence of various ions has been shown to have a strong impact on the shape and size of silver nanostructures produced via the polyol reduction of AgNO3. Here we report a simple and rapid (reaction time ∼1 h) route to Ag nanowires, in which ethylene glycol serves as the solvent and a precursor to the reducing agent. The reaction could be performed in disposable glass vials, with all the reagents being delivered using pipettes. In addition to the use of poly(vinyl pyrrolidone) as a stabilizer, copper (I) or copper (II) chloride had to be added to the reaction to reduce the amount of free Ag+ during the formation of initial seeds and scavenge adsorbed oxygen from the surface of the seeds once formed. In doing so, Ag nanowires were grown preferentially.

Large-scale synthesis of copper nanoparticles by chemically controlled reduction for applications of inkjet-printed electronics.

Abstract: Copper nanoparticles are being given considerable attention as of late due to their interesting properties and potential applications in many areas of industry. One such exploitable use is as the major constituent of conductive inks and pastes used for printing various electronic components. In this study, copper nanoparticles were synthesized through a relatively large-scale (5 l), high-throughput (0.2 M) process. This facile method occurs through the chemical reduction of copper sulfate with sodium hypophosphite in ethylene glycol within the presence of a polymer surfactant (PVP), which was included to prevent aggregation and give dispersion stability to the resulting colloidal nanoparticles. Reaction yields were determined to be quantitative while particle dispersion yields were between 68 and 73%. The size of the copper nanoparticles could be controlled between 30 and 65 nm by varying the reaction time, reaction temperature, and relative ratio of copper sulfate to the surfactant. Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) images of the particles revealed a spherical shape within the reported size regime, and x-ray analysis confirmed the formation of face-centered cubic (FCC) metallic copper. Furthermore, inkjet printing nanocopper inks prepared from the polymer-stabilized copper nanoparticles onto polyimide substrates resulted in metallic copper traces with low electrical resistivities (≥3.6 µΩ cm, or ≥2.2 times the resistivity of bulk copper) after a relatively low-temperature sintering process (200 °C for up to 60 min).

Surface Interactions and Quantum Kinetic Molecular Sieving for H2 and D2 Adsorption on a Mixed Metal−Organic Framework Material

Abstract: A rational strategy has been used to immobilize open metal sites in ultramicroporosity for stronger binding of multiple H2 molecules per unsaturated metal site for H2 storage applications. The synthesis and structure of a mixed zinc/copper metal−organic framework material Zn3(BDC)3[Cu(Pyen)] ·(DMF)5(H2O)5 (H2BDC = 1,4 benzenedicarboxylic acid and PyenH2 = 5-methyl-4-oxo-1,4-dihydro-pyridine-3-carbaldehyde) is reported. Desolvation provides a bimodal porous structure Zn3(BDC)3[Cu(Pyen)] (M′MOF 1) with narrow porosity (<0.56 nm) and an array of pores in the bc crystallographic plane where the adsorbate–adsorbent interactions are maximized by both the presence of open copper centers and overlap of the potential energy fields from pore walls. The H2 and D2 adsorption isotherms for M′MOF 1 at 77.3 and 87.3 K were reversible with virtually no hysteresis. Methods for determination of the isosteric enthalpies of H2 and D2 adsorption were compared. A virial model gave the best agreement (average deviation <1 stand...

Enhanced thermal conductivity and viscosity of copper nanoparticles in ethylene glycol nanofluid

Abstract: This study investigates the thermal conductivity and viscosity of copper nanoparticles in ethylene glycol. The nanofluid was prepared by synthesizing copper nanoparticles using a chemical reduction method, with water as the solvent, and then dispersing them in ethylene glycol using a sonicator. Volume loadings of up to 2% were prepared. The measured increase in thermal conductivity was twice the value predicted by the Maxwell effective medium theory. The increase in viscosity was about four times of that predicted by the Einstein law of viscosity. Analytical calculations suggest that this nanofluid would not be beneficial as a coolant in heat exchangers without changing the tube diameter. However, increasing the tube diameter to exploit the increased thermal conductivity of the nanofluid can lead to better thermal performance.

Catalytic C-C, C-N, and C-O Ullmann-type coupling reactions: copper makes a difference.

Abstract: Copper-catalyzed arylations of nucleophiles (Ullmann, Ullmann-Goldberg and UllmannHurtley condensations) have been well known for more than a century for being one the most useful and practical methods in the formation of C(aryl)-N, C(aryl)-C and C(aryl)-O bonds.[1] These reactions are thus involved in numerous industrial applications such as the synthesis of intermediates as well as synthetic targets throughout the life science and polymer industries. However until 2000, Ullmann condensations have not been employed to their full potential. They indeed suffered from reduced synthetic scope as a result of the harsh reaction conditions often required, a limited substrate scope and the moderate yields obtained. Condensations were traditionally conducted at temperatures as high as 210 °C, often in the presence of stoichiometric amounts of copper reagents and preferentially with activated aryl halides.[1]. Early studies revealed rate enhancement when arylation were conducted in the presence of copper additive.[2] The additive compounds were thought to increase catalyst solubility and stability, but their exact role was not well established. Finally in 2001, important breakthroughs [3] were achieved by two groups with the discoveries of versatile and very efficiency new copper/ligand systems (C-C, C-N or C-O coupling) allowing the use of catalytic amount of metal under very mild conditions (90-110°C). Since 2001, these works and the potentially attractiveness of copper has led to a spectacular resurgence of interest in catalyzed Ullmann-type reactions. Many groups have thus been developing so far new Cu/Ligand systems to improve the variety and efficiency of the coupling reactions. We present here recent major developments in Cu-catalyzed C-C, C-O and C-N bond formation. The two selected contributions are of highly impact for cross coupling reaction, and deal with enantioselective and chemoselectivitive copper catalytic systems.

Utilization of copper slag in cement and concrete

Abstract: Copper slag is a by-product obtained during matte smelting and refining of copper. The common management options for copper slag are recycling, recovering of metal, production of value added products such as abrasive tools, roofing granules, cutting tools, abrasive, tiles, glass, road-base construction, railroad ballast, asphalt pavements. Despite increasing rate of reusing copper slag, the huge amount of its annual production is disposed in dumps or stockpiles to date. One of the greatest potential applications for reusing copper slag is in cement and concrete production. Many researchers have investigated the use of copper slag in the production of cement, mortar and concrete as raw materials for clinker, cement replacement, coarse and fine aggregates. The use of copper slag in cement and concrete provides potential environmental as well as economic benefits for all related industries, particularly in areas where a considerable amount of copper slag is produced. This paper reviews the characteristics of copper slag and its effects on the engineering properties of cement, mortars and concrete.

Interfacial design of Cu-based composites prepared by powder metallurgy for heat sink applications

Abstract: Thermal aspects are becoming increasingly important for the reliability of the electronic components due to the continuous progress of the electronic industries. Therefore, the effective thermal management is a key issue for packaging of high performance semiconductors. The ideal material working as heat sink and heat spreader should have a CTE of (4–8) × 10−6 K−1 and a high thermal conductivity. Metal matrix composites offer the possibility to tailor the properties of a metal by adding an appropriate reinforcement phase and to meet the demands in thermal management. Copper/SiC and copper/diamond composites have been produced by powder metallurgy. The major challenge in development of Cu/SiC is the control of the interfacial interactions. Silicon carbide is not stable in copper at the temperature needed for the fabrication of Cu/SiC. It is known that the bonding between diamond and copper is very weak in the Cu/diamond composite. Improvements in bonding strength and thermo-physical properties of the composites have been achieved by • a vapour deposited molybdenum coating on SiC powders to control interface reactions, • using atomized Cu(X) alloys with minor additions of carbide formers, e.g. X = Cr, B, to improve the interfacial bonding in Cu-diamond composites.

Highly Dispersed Silica-Supported Copper Nanoparticles Prepared by Precipitation−Gel Method: A Simple but Efficient and Stable Catalyst for Glycerol Hydrogenolysis

Abstract: Highly dispersed copper nanoparticles supported on silica were successfully prepared by a simple and convenient precipitation−gel technique, and their physicochemical properties and activity were compared to those of a catalyst prepared by the conventional impregnation method. As a consequence of the preparation method, the texture (BET), dispersion (dissociative N2O adsorption), morphology (TEM), reduction behavior (TPR, XRD), state of copper species (XPS), and catalytic performance (glycerol hydrogenolysis) differ between samples. Both samples showed high selectivity (>98%) toward 1,2-propanediol in glycerol reaction. Because of a much smaller particle size, a higher dispersion of copper species with a strong metal−support interaction, and more resistance to sintering, the CuO/SiO2 catalyst prepared by precipitation–gel method presented a much higher activity and remarkably better long-term stability in glycerol reaction than did the catalyst prepared by impregnation method. The catalytic behavior of ca...

Characterization of Copper Adsorption onto an Alginate Encapsulated Magnetic Sorbent by a Combined FT-IR, XPS, and Mathematical Modeling Study

Abstract: Copper adsorption onto calcium alginate encapsulated magnetic sorbent is studied in this paper. The objective of this study was to qualitatively and quantitatively elucidate the copper binding onto the sorbent. The adsorption increases from around 0 to almost 100% as the initial pH is increased from 2 to 5. A maximum adsorption capacity of 0.99 mmol g−1 is achieved. The FT-IR and XPS studies show that the C—O in carboxyl group of alginate directly attaches to the copper ion that leads to most of the adsorption. A mathematical model is developed, and it includes ion exchange between the calcium and the copper, coordination reaction between the functional group and the copper, as well as surface complex formation between the iron oxide and the copper. The model is capable of describing and predicting effects of various key operational parameters on the adsorption process, such as initial pH, metal concentration, and dosage of sorbent.

Contribution of copper ion resistance to survival of Escherichia coli on metallic copper surfaces

Abstract: Bacterial contamination of touch surfaces poses a serious threat for public health. The use of bactericidal surface materials, such as copper and its alloys, might constitute a way to aid the use of antibiotics and disinfectants, thus minimizing the risk of emergence and spread of multiresistant germs. The survival of Escherichia coli on metallic copper surfaces has been studied previously; however, the mechanisms underlying bacterial inactivation on copper surfaces have not been elucidated. Data presented in this study suggest that bacteria are killed rapidly on dry copper surfaces. Several factors, such as copper ion toxicity, copper chelators, cold, osmotic stress, and reactive oxygen species, but not anaerobiosis, influenced killing rates. Strains deleted in copper detoxification systems were slightly more sensitive than was the wild type. Preadaptation to copper enhanced survival rates upon copper surface exposure. This study constitutes a first step toward understanding the reasons for metallic copper surface-mediated killing of bacteria.

Graphene-stabilized copper nanoparticles as an air-stable substitute for silver and gold in low-cost ink-jet printable electronics

Abstract: Metallic copper nanoparticles were synthesized by a bottom-up approach, and in situ coated with protective shells of graphene in order to get a metal nanopowder of high air stability and chemical inertness. Using an amphiphilic surfactant, a water-based copper nanocolloid could be prepared and successfully printed onto a polymer substrate by conventional ink-jet printing using household printers. The dried printed patterns exhibited strong metallic gloss and an electrical conductivity of >1 S cm−1 without the need for a sintering or densification step. This conductivity currently limits use in electronics to low current application or shielding and decorative effects. The high stability of graphene-coated copper nanoparticles makes them economically a most attractive alternative to silver or gold nanocolloids, and will strongly facilitate the industrial use of metal nanocolloids in consumer goods.

Nanostructured Cu and Cu@Cu2O core shell catalysts for hydrogen generation from ammonia–borane

Abstract: Copper nanoparticles have been prepared by the solvated metal atom dispersion (SMAD) method. Oxidation of the SMAD prepared copper colloids resulted in Cu@Cu2O core shell structures (7.7 ± 1.8 nm) or Cu2O nanoparticles depending on the reaction conditions. The nano Cu, Cu@Cu2O core shell, and Cu2O particles were found to be catalytically active for the generation of hydrogen from ammonia–borane either viahydrolysis or methanolysis reaction.

Copper cha zeolite catalysts

Abstract: Zeolite catalysts and systems and methods for preparing and using zeolite catalysts having the CHA crystal structure are disclosed. The catalysts can be used to remove nitrogen oxides from a gaseous medium across a broad temperature range and exhibit hydrothermal stable at high reaction temperatures. The zeolite catalysts include a zeolite carrier having a silica to alumina ratio from about 15:1 to about 256:1 and a copper to alumina ratio from about 0.25:1 to about 1:1.

Copper sulphide (CuxS) as an ammonia gas sensor working at room temperature

Abstract: A solution growth technique (SGT) has been used to deposit Cu x S ( x = 1, 1.4, and 2) thin films on glass substrates at room temperature (300 K). These as-deposited thin films are characterized for their structural, optical and electrical properties by X-ray diffraction (XRD), energy dispersive analysis of X-rays (EDAX), scanning electron microscopy (SEM) and atomic force microscopy (AFM), optical absorption and current–voltage ( I – V ) measurements. XRD shows that the Cu x S layer grew with hexagonal and monoclinic phases for x = 1 and 2, respectively. SEM and AFM show the nano-particles ( x = 1 and 1.4) and nano-discs ( x = 2) formation. The optical band gaps ( E g ) of thin films are 1.26 eV (CuS), 1.96 eV (Cu 1.4 S), and 2.31 eV (Cu 2 S). In addition, surface wettability is studied by using double-distilled water drops for contact angle measurements. It is observed that the contact angle for Cu 1.4 S is larger than those for CuS and Cu 2 S films. It suggests that the x = 1.4 films have high-surface energy. Ammonia gas sensors are fabricated by using these copper sulphide thin films with silver metal contacts. Based on the time-dependent experimental results nanostructured Cu x S serve as sensor material for the detection of NH 3 molecules at room temperature.

Mitochondrial copper metabolism and delivery to cytochrome c oxidase.

Abstract: Metals are essential elements of all living organisms. Among them, copper is required for a multiplicity of functions including mitochondrial oxidative phosphorylation and protection against oxidative stress. Here we will focus on describing the pathways involved in the delivery of copper to cytochrome c oxidase (COX), a mitochondrial metalloenzyme acting as the terminal enzyme of the mitochondrial respiratory chain. The catalytic core of COX is formed by three mitochondrially-encoded subunits and contains three copper atoms. Two copper atoms bound to subunit 2 constitute the Cu(A) site, the primary acceptor of electrons from ferrocytochrome c. The third copper, Cu(B), is associated with the high-spin heme a(3) group of subunit 1. Recent studies, mostly performed in the yeast Saccharomyces cerevisiae, have provided new clues about 1) the source of the copper used for COX metallation; 2) the roles of Sco1p and Cox11p, the proteins involved in the direct delivery of copper to the Cu(A) and Cu(B) sites, respectively; 3) the action mechanism of Cox17p, a copper chaperone that provides copper to Sco1p and Cox11p; 4) the existence of at least four Cox17p homologues carrying a similar twin CX(9)C domain suggestive of metal binding, Cox19p, Cox23p, Pet191p and Cmc1p, that could be part of the same pathway; and 5) the presence of a disulfide relay system in the intermembrane space of mitochondria that mediates import of proteins with conserved cysteines motifs such as the CX(9)C characteristic of Cox17p and its homologues. The different pathways are reviewed and discussed in the context of both mitochondrial COX assembly and copper homeostasis.

Formation of metallic copper nanoparticles at the soil-root interface.

Abstract: Copper is an essential element in the cellular electron-transport chain, but as a free ion it can catalyze production of damaging radicals. Thus, all life forms attempt to prevent copper toxicity. Plants diminish excess copper in two structural regions: rare hyperaccumulators bind cationic copper to organic ligands in subaerial tissues, whereas widespread metal-tolerant plants segregate copper dominantly in roots by mechanisms thought to be analogous. Here we show using synchrotron microanalyses that common wetlands plants Phragmites australis and Iris pseudoacorus can transform copper into metallic nanoparticles in and near roots with evidence of assistance by endomycorrhizal fungi when grown in contaminated soil in the natural environment. Biomolecular responses to oxidative stress, similar to reactions used to abiotically synthesize Cu0 nanostructures of controlled size and shape, likely cause the transformation. This newly identified mode of copper biomineralization by plant roots under copper stress ...

On the role of redox properties of CuO/CeO2 catalysts in the preferential oxidation of CO in H2-rich gases

Abstract: CuO/CeO 2 catalysts with CuO content ranging from 0.5 wt.% to 8 wt.%, prepared by wet impregnation of commercial ceria, have been tested for the preferential oxidation of CO (CO-PROX) under H 2 -rich conditions at 70–210 °C. Catalytic activity increases up to 4 wt.% CuO content, with less concentrated catalysts showing higher intrinsic activity. Catalysts have been characterized by means of XRD, BET analysis and UV spectroscopy. Formation of segregated CuO clusters has been detected for Cu richest CuO/CeO 2 sample. Redox properties have been deeply investigated using TP analysis (H 2 TPR, CO TPR, TPO) of fresh or pre-treated samples. Participation of surface ceria, induced by the strong interaction with copper, to reduction/oxidation reactions in the temperature range explored (up to 430 °C) has been demonstrated. Different copper species and their reactivity towards H 2 and CO have been individuated by comparing TPR of fully oxidized catalysts with those of partially oxidized catalysts. Active species have been identified as copper-ceria sites able to oxidize CO even at room temperature and to be re-oxidized by O 2 at the same temperature. Transient experiments have been carried out at different temperature using a diluted mixture starting from oxidized or reduced catalysts and followed by a H 2 TPR of the used samples. The results of these tests have showed that active centres for CO oxidation contain copper in the +2 oxidation state. At T > 100 °C some reduced copper sites are stabilized which promote H 2 oxidation thus lowering the selectivity of the CO-PROX process.