Copper Oxygen Research Articles

DC-Current-Limiting Characteristics of YBCO Tapes for DC Currents of 50 A to 10 kA

The amplitude and rise time of fault currents can be reduced by installing a resistive-type superconducting fault current limiter (SFCL) in a voltage-source converter high-voltage DC (VSC-HVDC) system. Such an SFCL can provide sufficient time for a mechanical-type dc circuit breaker to interrupt a fault current. The objective of this paper is to elucidate the dc-current-limiting characteristics of Yttrium Barium Copper Oxygen (YBCO)-coated conductor tapes for a wide range of prospective currents (ranging from 50 to 10 kA). The factors investigated include critical currents (I c ) of the tape of 102 and 225 A, circuit time constants of 1 and 3 ms, and rated dc voltages of 250 and 500 V. The experimental results show that the limited current remains nearly constant with prospective current when the prospective current is higher than ten times I c . The circuit time constant affects only the peak value and rise rate of the limited current. A single tape (I c = 102 A) can limit a 10-kA prospective current to a peak value of 555 A. The limited current for a rated voltage of 500 V is always higher than that for a rated voltage of 250 V.

Aspergillus fumigatus Copper Export Machinery and Reactive Oxygen Intermediate Defense Counter Host Copper-Mediated Oxidative Antimicrobial Offense

The Fenton-chemistry-generating properties of copper ions are considered a potent phagolysosome defense against pathogenic microbes, yet our understanding of underlying host/microbe dynamics remains unclear. We address this issue in invasive aspergillosis and demonstrate that host and fungal responses inextricably connect copper and reactive oxygen intermediate (ROI) mechanisms. Loss of the copper-binding transcription factor AceA yields an Aspergillus fumigatus strain displaying increased sensitivity to copper and ROI invitro, increased intracellular copper concentrations, decreased survival inchallenge with murine alveolar macrophages (AMΦs), and reduced virulence in a non-neutropenic murine model. ΔaceA survival is remediated by dampening of host ROI (chemically or genetically) or enhancement of copper-exporting activity (CrpA) in A.fumigatus. Our study exposes a complex host/microbe multifactorial interplay that highlights the importance of host immune status and reveals key targetable A.fumigatus counter-defenses.

CO2 reduction over Cu-ZnGaMO (M = Al, Zr) catalysts prepared by a sol-gel method: Unique performance for the RWGS reaction

Cu-ZnGaMO (M=Al, Zr) catalysts prepared by a surfactant-free sol-gel method were characterized and tested in the reverse water-gas shift (RWGS) reaction. Their catalytic behavior was analyzed under 0.1–3MPa at 250–325°C and using a reactant mixture of CO2/H2=1/3. The catalytic results are analyzed in the light of the characteristics of the catalysts. The Cu-ZnGaZrO catalysts were highly selective for the RWGS reaction; a major role of surface copper and interface oxygen vacancies is proposed. CO2 conversion and CO selectivity increased on increasing the reaction temperature. CO2 conversion reaches 16.8% with 99.7% selectivity for CO under 0.1MPa at 325°C over the Cu-ZnGaZrO1 catalyst. It is suggested that CO and methanol production proceed via independent reaction pathways.

A reduced fidelity model for the rotary chemical looping combustion reactor

The rotary chemical looping combustion reactor has great potential for efficient integration with CO2 capture-enabled energy conversion systems. In earlier studies, we described a one-dimensional rotary reactor model, and used it to demonstrate the feasibility of continuous reactor operation. Though this detailed model provides a high resolution representation of the rotary reactor performance, it is too computationally expensive for studies that require multiple model evaluations. Specifically, it is not ideal for system-level studies where the reactor is a single component in an energy conversion system. In this study, we present a reduced fidelity model (RFM) of the rotary reactor that reduces computational cost and determines an optimal combination of variables that satisfy reactor design requirements. Simulation results for copper, nickel and iron-based oxygen carriers show a four-order of magnitude reduction in simulation time, and reasonable prediction accuracy. Deviations from the detailed reference model predictions range from 3% to 20%, depending on oxygen carrier type and operating conditions. This study also demonstrates how the reduced model can be modified to deal with both optimization and design oriented problems. A parametric study using the reduced model is then applied to analyze the sensitivity of the optimal reactor design to changes in selected operating and kinetic parameters. These studies show that temperature and activation energy have a greater impact on optimal geometry than parameters like pressure or feed fuel fraction for the selected oxygen carrier materials.

DNA Damage by Heavy Metals in Animals and Human Beings: An Overview

Cancer causing materials are found in air, water and in some other consumer products in the form of heavy metals. Biomedical research has shown that exposure to heavy metals is an important source of DNA damage in human beings and in animals. Heavy metals like iron, copper, chromium, lead, zinc, mercury, nickel etc. and reactive oxygen species enhance peroxidation of lipids and DNA damage. Elements like arsenic, nickel and cadmium are the ambassadors of mutagenic changes in cell. In mammalian cells it was found that DNA single strand breaks chromosomal aberrations occurred and sister chromatids exchange due to various nickel salts. It is now a wellestablished fact that cadmium causes cancer in tissues of animals. Exposure to cadmium develops cancer in prostate gland, kidney, liver and stomach. Through base pair mutation cancer causing metals damage DNA. However, some heavy metals directly damage the DNA thus generating negative results. The synthesis of nucleic acids and proteins is affected by cadmium. However, cadmium does not have a strong mutagenic nature when compared to other heavy metals. The present review aims to prospect the exposure (of human beings and animals) to heavy metals, cause of different diseases in both and mutagenic effect of heavy metals on double strand repair.

Vacancy relaxation in cuprous oxide (Cu2−xO1−y)

Phonons are produced when an excited vacancy in cuprous oxide (Cu2O) relaxes. Time resolved luminescence was used to find the excited copper vacancy (acceptor) and oxygen vacancy (donor) trap levels and lifetimes. It was also used to determine the typical energy and number of phonons in the phonon pulses emitted by vacancies. The vacancy properties of cuprous oxide are controlled by several synthesis parameters and by the temperature. We directly demonstrate the absorption of light by oxygen vacancies with transient absorption. Copper and oxygen vacancies behave differently, in part because the two kinds of traps capture carriers from different states. For example, the copper vacancy luminescence lifetime is around 25 times greater at low temperature. However, both kinds of vacancy luminescence are consistent with a Poissonian multiple phonon emission model.

CuCo Hybrid Oxides as Bifunctional Electrocatalyst for Efficient Water Splitting

Solar‐driven water splitting is a promising approach for renewable energy, where the development of efficient and stable bifunctional electrocatalysts for simultaneously producing hydrogen and oxygen is still challenging. Herein, combined with the hydrogen evolution reaction (HER) activity of a copper(I) complex and oxygen evolution reaction (OER) activity of cobalt‐based oxides, a type of 1D copper‐cobalt hybrid oxide nanowires (CuCoO‐NWs) is developed via a facile two‐step growth‐conversion process toward a bifunctional water splitting catalyst. The CuCoO‐NWs exhibit excellent catalytic performances for both HER and OER in the same basic electrolyte, with optimized low onset overpotentials and high current densities. The efficient HER activity is ascribed to the formation of Cu2O, while the activity for OER is primarily enabled by Co‐based oxides and abundant oxygen vacancies. The CuCoO‐NWs allow for the assembly of a water electrolyzer with strong alkaline media, with a current density of 10 mA cm−2 at 1.61 V. Further combination with a commercial silicon photovoltaic allows the direct use of solar energy for spontaneous water splitting with excellent stability for over 72 h, suggesting the potential as a promising bifunctional electrocatalyst for efficient solar‐driven water splitting.

Post-oxidation treated graphene quantum dots as a fluorescent probe for sensitive detection of copper ions

Graphene quantum dots (GQDs) have been an ideal probe for copper ions detection due to its excellent optical properties, low toxicity and biocompatibility. However, most of GQDs prepared by present methods have low oxidation degree, which could hinder the complexation between copper ions and oxygen functional groups on the surface of GQDs. Therefore, we proposed a universal, mild and in situ post-treated approach for modifying GQDs obtained by any methods, which will increase the oxidation degree of GQDs without any other affect and its influence on the responsivity of copper ions.

Improved Low-Temperature Activity of CuO–CeO2–ZrO2 Catalysts for Preferential Oxidation of CO in H2-Rich Streams

In this work, CuO–CeO2–ZrO2 catalysts for CO preferential oxidation have been prepared by ultrasound assisted reverse coprecipitation and slow coprecipitation, and characterized via BET, XRD, XPS and H2-TPR techniques, respectively. It is found that the catalyst prepared with ultrasound assisted reverse coprecipitation preserves large specific surface area, fine crystalline grain and high dispersion of active copper species. Meanwhile, the reducibility is improved significantly and more active copper species and oxygen vacancies are formed in the copper–ceria boundaries. The ultrasound assisted reverse coprecipitation prepared CuO–CeO2–ZrO2 catalyst exhibits superior low-temperature activity and CO2 selectivity, over which the temperature responding to 50 % CO conversion is as low as 67 °C, and the temperature window of full CO conversion is significantly widen from 100 to 160 °C. The ultrasound assisted reverse coprecipitation prepared CuO–CeO2–ZrO2 catalyst exhibits superior low-temperature activity for CO preferential oxidation and wide temperature window of full CO conversion comparing with the catalyst prepared with slow coprecipitation.

Paramagnetism of copper–oxygen chains in high-temperature YBa2Cu3O6 + δ superconductors

Experimental evidence for the existence of chain paramagnetic Curie-type contributions to the temperature dependence of static magnetic susceptibility χ(T) in the normal (nonsuperconducting) state is obtained for a series of pure YBa2Cu3O6 + δ high temperature superconductors with different oxygen contents (0.6 < δ ≤ 1). It is shown that the chain contribution is obvious on χ(T) curves only in the T < 150K range of temperatures, grows along with the number of oxygen vacancies in Cu1–O4 chains, and depends on the ordering of these vacancies.

Leaching of silver contained in mining tailings, using sodium thiosulfate: A kinetic study

Several years of mining in the Pachuca y Real del Monte mining district have led to the production of a great amount of mining tailings which is currently a great environmental problem. However, these residues contain metals of value and interest that cannot be recovered using harmful and aggressive reagents such as cyanide. Thiosulfate solutions represent a good alternative because of the advances made during the last few years of research on this subject. The kinetic study carried out indicates that the process involved in the leaching treatment of mining tailings for silver was only slightly affected by the stirring rate in the range studied; the reaction orders were 1 (oxygen partial pressure 0.2–1atm), 0.074 (thiosulfate concentration 100–500mol·m−3), 0.455 (pH4–12) and 0.26 (Copper concentration 50–300mol·m−3). The apparent activation energy of the process was 1.912kJ·mol−1 in the temperature range from 288 to 318K. A change of control seemed to occur above 318K, possibly due to the destabilization of oxygen in the inner portion of the solution at higher temperatures. According to the results, kinetic is controlled by a mass transfer of oxygen at the solid–liquid interface. In the presence of copper ions and oxygen, the reaction rate increases, so the process was carried out using a stoichiometric excess of oxygen. The process was applied to a mining tailing, containing both metallic and silver sulfides, having a similar behavior to that observed by previous authors using silver powder and silver plate.

Oxygen reduction catalyzed by nanocomposites based on graphene quantum dots-supported copper nanoparticles

Nanocomposites based on graphene quantum dots (GQDs)-supported copper nanoparticles were prepared by thermal refluxing of copper salts in 1,2-propanediol at 140 °C in the presence of GQDs. Transmission electron microscopic measurements showed that the resulting Cu/GQD nanoparticles increased from 5 to 15 nm in average diameter with increasing metal loadings. Raman spectroscopic measurements showed that all nanocomposites exhibited well-defined D and G vibrational bands. X-ray photoelectron spectroscopic studies indicated the formation of Cu2O and CuO in the nanocomposite particles, along with various defect concentrations within the GQD graphitic skeletons. Electrochemical studies showed that the nanocomposites exhibited apparent electrocatalytic activity in oxygen reduction in alkaline media, and the sample with a Cu/C atomic ratio of 2.88% exhibited the best ORR activity among the series, within the context of onset potential, number of electron transfer and kinetic current density. The performance was further improved by deliberate hydrothermal treatments of the sample, and 160 °C was identified as the optimal temperature, which was ascribed to manipulation of the electronic interactions between copper nanoparticles and oxygen intermediates by the GQD structural defects.

Removal of elemental mercury from flue gas by recyclable CuCl2 modified magnetospheres catalyst from fly ash. Part 2. Identification of involved reaction mechanism

The Hg0 adsorption and oxidation sites on the CuCl2-MF catalyst as well as the role of atomic Cu and Cl in Hg0 removal were identified by a temperature programmed desorption (TPD) experiment. The reaction mechanism with the participation of O2 and HCl was investigated. The changes in surface chemistry of fresh, spent and in situ pretreated catalyst with O2 and/or HCl were investigated by EPR and XPS to better understand the intermediate reaction products and steps. The results suggested that different mercury adsorption sites are existed on the catalyst: Cl adsorption sites and Cu adsorption sites. The binding energy of mercury on the Cu adsorption sites is higher than that on the Cl adsorption sites. O2 and HCl significantly affected the state of Cu and Cl on the spent catalyst. The interaction between Hg0 and CuCl2 with the participation of O2 and/or HCl follows three steps mechanism: (1) the reduction of CuCl2 to CuCl for the interaction with Hg0, (2) the reoxidation of CuCl for the interaction with O2 forming an intermediate copper oxygen chloride species, (3) the rechlorination of oxychloride species resulting in the restoration of CuCl2. This demonstrated that the interaction between Hg0 and CuCl2 is a cycle when O2 and HCl are contained in the reaction system.

Redox property and kinetics of copper oxygen carrier under different oxygen concentrations

Chemical looping with oxygen uncoupling and chemical looping air separation technologies all depend on the redox property of oxygen carrier. The present work investigated the redox properties of Cu/Zr oxygen carrier under different oxygen concentrations by TG technique. The durability and stability of oxygen carrier is also investigated under 1065°C reduction and 800°C oxidation temperatures. For reduction, the starting and ending temperatures and the peaks of DTG curves shift to high values with oxygen concentration increasing. The effect of oxygen concentration on oxidation is little and the regeneration of Cu/Zr oxygen carrier can be achieved in thin oxygen environment. For reduction and oxidation, times for complete conversion decrease with heating rates increasing. Kinetic models were proposed based on the nucleation and nuclei growth model. The reduction mechanism function is: and the oxidation mechanism function is: . For reduction, the values of E and A all increase as oxygen concentrations increase and heating rates decrease. For oxidation, the values of E and A are almost the same. The Cu/Zr oxygen carrier has high stability and it is a good candidate for chemical looping technologies at high temperatures. © 2015 American Institute of Chemical Engineers Environ Prog, 35: 531–539, 2016

Insights into unknown foreign ligand in copper nitrite reductase

Bifunctional copper nitrite reductase (CuNIR) catalyzes nitrite reduction to nitric oxide and dioxygen reduction to hydrogen peroxide. In contrast to the well-researched nitrite reduction mechanism, the oxygen reduction mechanism in CuNIR has been totally unknown, because mononuclear copper–oxygen complexes decompose so readily that their visualization has been challenging. Here, we provide spectroscopic evidence that a foreign ligand binds to the catalytic copper (T2Cu) site of CuNIR, and determine CuNIR structures displaying a diatomic molecule on T2Cu. This unknown ligand can be interpreted as dioxygen and may provide insights into the oxygen reduction mechanism of CuNIR.

Effect of Electric Current Passing Through the Interface on the Wetting of ZrO2 Ceramics with Silver–Copper–Oxygen Melt in Air

The wetting of ZrO2 ceramics with Ag–Cu–O melts in air when electric current passes through th interface has been studied. Special samples were fabricated for experiments: parallel ZrO2 ceramic plates, with drops of copper–silver alloy being located between them. Direct current was induced on the plates after melting of the drops. It is found that the anode plate is wetted better at certain amperage. Microstructural analysis shows that much more copper oxide adsorbs on the anode plate than on the cathode. It is assumed that oxidized copper is reduced on the cathode and thus migrates to the anode, worsening the wetting of the cathode.

ChemInform Abstract: Copper‐Catalyzed Oxidative N—S Bond Formation for the Synthesis of N‐Sulfenylimines.

Despite the remarkable success of the copper-catalyzed oxidative coupling reaction, direct cross-coupling of amines and thiols for the synthesis of N-sulfenylimines has not been previously reported. Using commercially available copper catalysts (CuI) and oxygen as an environmentally benign oxidant, synthetically useful N-sulfenylimines were prepared from amines and thiols in good yields without overoxidation of sulfur atoms.

Single-site trinuclear copper oxygen clusters in mordenite for selective conversion of methane to methanol.

Copper-exchanged zeolites with mordenite structure mimic the nuclearity and reactivity of active sites in particulate methane monooxygenase, which are enzymes able to selectively oxidize methane to methanol. Here we show that the mordenite micropores provide a perfect confined environment for the highly selective stabilization of trinuclear copper-oxo clusters that exhibit a high reactivity towards activation of carbon–hydrogen bonds in methane and its subsequent transformation to methanol. The similarity with the enzymatic systems is also implied from the similarity of the reversible rearrangements of the trinuclear clusters occurring during the selective transformations of methane along the reaction path towards methanol, in both the enzyme system and copper-exchanged mordenite.

Kinetics of metallic silver leaching in the O2–thiosulfate system

In recent years, many researchers have studied processes for extracting gold and silver from ores using alternatives that are less harmful and aggressive to the environment than cyanides. Thiosulfate solutions represent one such alternative. Metallic silver can be dissolved in O2–thiosulfate in different experimental conditions. Silver dissolution was obtained without the formation of passivation layers on the surface of the silver plate used. The kinetic study conducted indicated that the process is affected by a stirring speed of between 8.3 and 15s−1 (the reaction rate increased threefold), and the reaction orders were 1 (oxygen partial pressure 0.2–1atm), 0.41 (thiosulfate concentration 25–200molm−3), 0 (thiosulfate concentration 200–600molm−3), 0.35 (hydronium concentration 1·10−8–1·10−7molm−3) and 0 (hydronium concentration 1·10−6–1·10−2molm−3). The apparent activation energy of the process was 4.5kJmol−1. Kinetics is controlled by a mass transfer of oxygen in the solid–liquid interface. In the presence of copper ions and oxygen, the reaction rate increased by 30% with respect to the process without copper. However, the thiosulfate partially decomposed and a layer of silver sulfide formed on the surface of the silver. The process was applied to a metallic silver powder, which showed a similar behavior to the silver plate.

D-wave pairing of spin-polaron quasiparticles in the spin–fermion model of the electronic structure of the CuO2 plane

It is shown that the strong coupling between spin moments of copper ions and oxygen holes resulting from the hybridization processes in the Emery model determines the formation of spin-polaron quasiparticles and ensures their effective attraction. This induces Cooper instability with d-wave pairing of spinpolaron quasiparticles. The obtained phase diagram agrees with the available experimental data.