Cu2O System Research Articles

Facile One‐Pot Synthesis of Uniquely Designed Au−Cu2O Nanocomposites for Effective Catalytic Degradation of Azo Dyes

AbstractIn the study of metal–semiconductor nanocomposites, the Au−Cu2O system is of significant interest because it can give rise to a variety of hybrid designs with pronounced activity for catalytic applications. In this work, a facile one‐pot synthetic strategy was developed to prepare Au−Cu2O nanocomposites with a unique core–shell nanoflower configuration, where a cluster of tiny Au nanoparticles constitutes the core, while larger cube‐like Cu2O nanoparticles surround this core in a petal‐like arrangement. Unlike previously published procedures that rely on two‐pot synthesis routes to generate the Au−Cu2O hybrid, the one‐pot synthesis protocol presented in this work is a more straightforward and less laborious approach that does not require a separate pre‐synthesis step. Furthermore, the synthesis can be conveniently performed at ambient conditions using nontoxic reagents. When tested as catalysts, the uniquely designed Au@Cu2O nanoflowers were found to effectively catalyze the borohydride‐mediated degradation of synthetic azo dyes (methyl orange and congo red). The hybrid exhibited superior catalytic activity relative to pristine Cu2O, underscoring the significance of creating a nanocomposite.

Calcination Strategy for Scalable Synthesis of Pithecellobium-Type Hierarchical Dual-Phase Nanostructured Cu x O to Columnar Self-Assembled CuO and Its Electrochemical Performances.

The search for low-cost environmentally benign promising electrode materials for high-performance electrochemical application is an urgent need for an applaudable solution for the energy crisis. For this, the present attempt has been made to develop a scalable synthetic strategy for the preparation of pure and dual-phase copper oxide self-hybrid/self-assembled materials from a copper oxalate precursor using the calcination route. The obtained samples were characterized by means of various physicochemical analytical techniques. Notably, we found that the BET surface area and pore volume of copper oxides measured by N2 adsorption–desorption decrease with the elevation of calcination temperature. From the XRD analysis, we observed the formation of a Cu2O cubic phase at low temperatures and a CuO monoclinic phase at high temperatures (i.e., 450 and 550 °C). FTIR and RAMAN spectroscopy were employed for bonding and vibrational structure analysis. The self-assembled dual-phase copper oxide particle as a pithecellobium-type hierarchical structure was observed through SEM of the sample prepared at 350 °C. The surface morphological structure for the samples obtained at 450 and 550 °C was a bundle-like structure developed though columnar self-assembling of the particles. All the above techniques confirmed the successful formation of Cu2O/CuO nanoparticles. Afterward, the electrochemical properties of the as-synthesized copper oxides reinforced by introducing carbon black (10% wt) were explored via cyclic voltammetry, electrochemical impedance spectroscopy, and galvanometric charge–discharge analysis. The Cu2O system exhibits the maximum specific capacitance performance value of 1355 F/g, whereas in the CuO system (at 450 and 550 °C), it possesses values of 903 and 724 F/g at a scan rate of 2 mV/s. This study reveals that the electrochemical properties of Cu2O are better than those of the CuO nanoparticles, which could be ascribed to the high surface area and morphology. The present assessment of the electrochemical properties of the developed material could pave the way to a low-cost electrode material for developing other high-performance hybrid electrodes for supercapacitor or battery applications.

Photoelectrochemical reduction of CO2: Stabilization and enhancement of activity of copper(I) oxide semiconductor by over-coating with tungsten carbide and carbide-derived carbons

Hybrid photocathode materials, which are composed of hierarchically deposited (onto the transparent fluorine-doped conducting glass electrode) copper(I) oxide (inner layer) and robust carbon structures, such as carbide derived carbons (CDC) or mixture of CDC with 70% (weight) tungsten carbide (WC-CDC), have been fabricated and examined using electrochemical methods, X-ray diffraction and various spectroscopic approaches including Raman technique. The resulting systems have been characterized by good stability and have exhibited high photoelectrochemical activity toward reduction of CO2 upon illumination with sunlight in the Na2SO4 neutral medium. While the semiconducting properties of Cu2O are not largely affected by the interfacial modification with CDC and WC-CDC, the photostability of the hybrid photocathode is significantly improved. The stabilization effect should reflect the capacitive properties of CDC and WC-CDC. The capability of CDC and WC-CDC over-layers to undergo efficient double-layer-type charging/discharging should facilitate collection and transport of photoelectrons and inhibit recombination of photogenerated electron-hole pairs. The relatively higher photoelectrochemical activity of the Cu2O system over-coated with WC-CDC, relative to the one containing CDC only, seems to reflect specific interactions between CO2 and WC-CDC thus inducing reduction of CO2 adsorbates.

A DFT Study of Electronic Structures and Photocatalytic Properties of Mn–Cu2O

First-principle calculations have been performed to systematically analyze the electronic structure and photocatalytic properties of Cu2O with different Mn-doped concentrations and configurations. The results indicated that pure Cu2O showed semiconductor characteristics, the doping systems were stable and shown metallic properties. Compared with pure Cu2O, the visible range absorption intensity and photocatalytic efficiency are enhanced with increasing the doping concentrations and changed with different configurations. By analyzing the density of states, the enhanced light absorption of the doped systems is mainly attributed to the intraband transition of Mn 3d state electrons. Doping concentrations and configurations have a great influence in the longwave range, while the effect is small in the shortwave range. These works imply that Mn-doped Cu2O system may be a promising photocatalyst active under visible light.

Erratum to: Electrical conductivity of molten LiF−DyF3−Dy2O3−Cu2O system for Dy−Cu intermediate alloy production

Dy–Cu intermediate alloys have shown substantial potential in the field of magnetostrictive and magnetic refrigerant materials. Therefore, this study focused on investigating the electrical conductivity of molten-salt systems for the preparation of Dy–Cu alloys and on optimizing the corresponding operating parameters. The electrical conductivity of molten LiF–DyF3–Dy2O3–Cu2O systems was measured from 910 to 1030°C using the continuously varying cell constant method. The dependencies of the LiF–DyF3–Dy2O3–Cu2O system conductivity on the melt composition and temperature were examined herein. The optimal operating conditions for Dy–Cu alloy production were determined via analyses of the electrical conductivity and activation energies for conductance, which were calculated using the Arrhenius equation. The conductivity of the molten system regularly increases with increasing temperature and decreases with increasing concentration of Dy2O3 or Cu2O or both. The activation energy Eκ of the LiF–DyF3–Dy2O3 and LiF–DyF3–Cu2O molten-salt systems increases with increasing Dy2O3 or Cu2O content. The regression functions of conductance as a function of temperature (t) and the addition of Dy2O3 (W(Dy2O3)) and Cu2O (W(Cu2O)) can be expressed as κ = −2.08435 + 0.0068t − 0.18929W(Dy2O3) −0.07918W(Cu2O). The optimal electrolysis conditions for preparing the Dy–Cu alloy in LiF–DyF3–Dy2O3–Cu2O molten salt are determined to be 2.0wt% > W(Dy2O3) + W(Cu2O) > 3.0wt% and W(Dy2O3): W(Cu2O) = 1:2 at 970 to 1000 °C.

Electrical conductivity of molten LiF–DyF3–Dy2O3–Cu2O system for Dy–Cu intermediate alloy production

Dy–Cu intermediate alloys have shown substantial potential in the field of magnetostrictive and magnetic refrigerant materials. Therefore, this study focused on investigating the electrical conductivity of molten-salt systems for the preparation of Dy–Cu alloys and on optimizing the corresponding operating parameters. The electrical conductivity of molten LiF–DyF3–Dy2O3–Cu2O systems was measured from 910 to 1030°C using the continuously varying cell constant method. The dependencies of the LiF–DyF3–Dy2O3–Cu2O system conductivity on the melt composition and temperature were examined herein. The optimal operating conditions for Dy–Cu alloy production were determined via analyses of the electrical conductivity and activation energies for conductance, which were calculated using the Arrhenius equation. The conductivity of the molten system regularly increases with increasing temperature and decreases with increasing concentration of Dy2O3 or Cu2O or both. The activation energy Eκ of the LiF–DyF3–Dy2O3 and LiF–DyF3–Cu2O molten-salt systems increases with increasing Dy2O3 or Cu2O content. The regression functions of conductance as a function of temperature (t) and the addition of Dy2O3 (W(Dy2O3)) and Cu2O (W(Cu2O)) can be expressed as κ = −2.08435 + 0.0068t − 0.18929W(Dy2O3) −0.07918W(Cu2O). The optimal electrolysis conditions for preparing the Dy–Cu alloy in LiF–DyF3–Dy2O3–Cu2O molten salt are determined to be 2.0wt% > W(Dy2O3) + W(Cu2O) > 3.0wt% and W(Dy2O3): W(Cu2O) = 1:2 at 970 to 1000 °C.

The accelerating effect of silver ion on the degradation of methyl orange in Cu2O system

In this paper we reported an interesting phenomenon that additive Ag+ ion can rapidly and continuously capture the activated electrons which accumulated on the surface of as-prepared Cu2O catalyst, resulting in residual holes directly and rapidly reacting with methyl orange (MO) to be degraded. When 10−2M Ag+ was added rapidly into the suspension containing 800mg/L MO, the decolorizing rate immediately reached 38%, and rapidly increased to 88% in 30min. This accelerating effect of Ag+ ion on MO degradation was first observed in Cu2O system. Although the as-prepared Cu2O shows a very large particle size (∼2.2μm), it possesses loose crystal structure with rough multiple surfaces and various defect levels in the interior and on the surface to promote the massive accumulation and fast migration of electron and hole. As a result, when Ag+ ion was added into the suspension, it immediately reacted with the accumulated electron to turn into metallic Ag and deposited on the surface of Cu2O to form a core-shell structured catalyst Cu2O@Ag, resulting in fast degradation of MO via directly reacting with residual hole. The Schottky barriers which generate at the junctions of Cu2O and metallic Ag crystals can speed up the directional migration of electron and hole, resulting in effective separation of electron–hole pair. In addition, Cu2O@Ag catalyst shows strong light absorption in UV, vis and NIR region. These results indicate that the as-prepared Cu2O catalyst exhibits a very high photocatalytic activity in the case of adding high concentration Ag+ ion.

Superhydrophobic ceramic coatings enabled by phase-separated nanostructured composite TiO2–Cu2O thin films

By exploiting phase-separation in oxide materials, we present a simple and potentially low-cost approach to create exceptional superhydrophobicity in thin-film based coatings. By selecting the TiO2–Cu2O system and depositing through magnetron sputtering onto single crystal and metal templates, we demonstrate growth of nanostructured, chemically phase-segregated composite films. These coatings, after appropriate chemical surface modification, demonstrate a robust, non-wetting Cassie–Baxter state and yield an exceptional superhydrophobic performance, with water droplet contact angles reaching to ∼172° and sliding angles <1°. As an added benefit, despite the photo-active nature of TiO2, the chemically coated composite film surfaces display UV stability and retain superhydrophobic attributes even after exposure to UV (275 nm) radiation for an extended period of time. The present approach could benefit a variety of outdoor applications of superhydrophobic coatings, especially for those where exposure to extreme atmospheric conditions is required.

Measurement and modeling of decomposition kinetics for copper oxide-based chemical looping with oxygen uncoupling

Chemical looping combustion with oxygen uncoupling (CLOU) is a promising CO2-capture ready energy technology that employs oxygen carriers with thermodynamic properties that cause oxygen to be spontaneously liberated as gaseous O2 in the fuel reactor, where it can react directly with solid fuels. One of the promising CLOU carrier metals is copper, cycling between CuO and Cu2O. Experimentally-determined rate expressions for these reactions are needed for proper development, modeling and scale-up of CLOU technology. The CuO–Cu2O system presents an interesting challenge in that the rate of decomposition depends on the thermodynamic driving force imparted by the difference between equilibrium and actual partial pressures of oxygen, and the equilibrium partial pressure is strongly temperature dependent in the range useful for combustion. This study investigates decomposition of two different copper-based oxygen carriers, from CuO to Cu2O oxidation states, to develop a universal kinetic expression to describe the observed rate of reaction as a function of temperature, conversion and gas environment. The kinetic model developed is compared to results of a third support type (silica) using two different CuOwt% loadings (64wt% CuO and 16wt% CuO) to demonstrate applicability to other support types and copper oxide loadings.

Experimental and first-principles theoretical studies on Ag-doped cuprous oxide as photocathode in photoelectrochemical splitting of water

Nanostructured thin films of undoped and Ag-doped cuprous oxide were deposited on indium tin oxide-coated glass substrate using simple spray pyrolysis method for their use as photocathode in photoelectrochemical (PEC) cell for solar energy based water splitting. Combination of experiments and first-principles density functional theory based calculations was used to determine and understand the effect of Ag substitution on electronic structure and PEC performance. Thin films were characterized using XRD, FE-SEM, UV–Vis spectroscopy and PEC measurements. The results of DFT calculations show that the top of valence band and bottom of conduction band of undoped Cu2O lie at Г point of brillouin zone, respectively, suggesting that pure Cu2O is a direct band gap material. Minimal changes appear in the band gap and band gap energies in the Ag-doped Cu2O system, keeping it still a direct band gap material. A defect band appearance can be seen between −4 and −5 eV in the valence band consisting mainly of Ag 4d states and can be explained by a stronger interaction between the Ag 4d and O 2p, due to the larger Ag size. Ag-doped samples exhibit improved conductivity and fourfold increase in photocurrent density with respect to undoped samples.

Zn Doping-Induced Shape Evolution of Microcrystals: The Case of Cuprous Oxide

Zn-doped Cu2O polyhedrons with various crystal morphologies, from 50-facet and 26-facet to 8-facet, were synthesized via a mild, low-temperature process based on the hydrothermal method. Addition of zinc salt to the reaction mixture might allow the introduction of Zn ions into the Cu2O crystal lattice, which is shown by X-ray photoelectron spectroscopy and energy dispersive spectroscopy. Doping of Cu2O crystals with Zn affects not only their morphologies but also significantly influences their optoelectronic properties. UV–visible and photoluminescence (PL) tests showed that the Zn-doped Cu2O system displays an increased band gap and enhanced photoluminescence properties. The open circuit potential-time (Ocp-t) method shows that a pure Cu2O crystal is an n-type semiconductor, while the Zn-doped Cu2O crystal shows p-type characteristics.

NO dissociation on Cu(111) and Cu2O(111) surfaces: a density functional theory based study

NO dissociation on Cu(111) and Cu2O(111) surfaces is investigated using spin-polarized density functional theory. This is to verify the possibility of using Cu-based catalyst for NO dissociation which is the rate limiting step for the NOx reduction process. The dissociation of molecularly adsorbed NO on the surface is activated for both cases. However, from the reaction path of the NO–Cu2O(111) system, the calculated transition state lies below the reference energy which indicates the possibility of dissociation. For the NO–Cu(111) system, the reaction path shows that NO desorption is more likely to occur. The geometric and electronic structure of the Cu2O(111) surface indicates that the surface Cu atoms stabilize themselves with reference to the O atom in the subsurface. The interaction results in modification of the electronic structure of the surface Cu atoms of Cu2O(111) which greatly affects the adsorption and dissociation of NO. This phenomenon further explains the obtained differences in the dissociation pathways of NO on the surfaces.

Rules governing the formation of photolysis products in the lead azide-copper(I) oxide system

It was found that, along with a decrease in the rate of photolysis and photocurrent in the region of lead azide intrinsic absorption, the addition of copper(I) oxide broadened the range of spectral sensitivity, and preliminary treatment of the PbN6(Ab)-Cu2O system with light (λ = 365 nm) increased the rate of photolysis. The rate constants for photolysis were estimated. An analysis of the results of current-voltage characteristic, contact potential difference, and contact photo-electromotive force measurements was used to construct a diagram of energy zones and suggest a model of the photolysis of the PbN6(Ab)-Cu2O system including stages of the generation, recombination, and redistribution of nonequilibrium carriers in a contact field, formation of microheterogeneous PbN6(Ab)-Pb (photolysis product) systems, and formation of final photolysis products.

Surface-modified CuO layer in size-stabilized single-phase Cu2O nanoparticles

Activated reactive evaporation has been used to grow copper oxide nanoparticles in the size range of 8–100 nm. X-ray diffraction spectra clearly show the presence of a single Cu2O phase. Detailed x-ray photoelectron spectroscopy studies show an increase in the ionicity of the Cu2O system with decreasing particle size. Depth profiling and finger printing of x-ray photoelectron spectra reveal that the Cu2O nanoparticles are capped with a CuO surface layer of thickness ≈1.6 nm. This study strongly suggests that the stabilization of the cubic Cu2O nanophase is enhanced by the formation of a CuO surface layer.

Compatible phases of the Y2O3–CuO–Cu2O system in air

The phase diagram of the Y2O3–CuO–Cu2O system was constructed as a function of temperature in air by means of thermal analysis and x-ray diffraction. The phase Y2Cu2O5 was found to be stoichiometric and melted peritectically at about 1110 °C. A new intermediate phase with the composition YCu2O2.5 was discovered. It exists between 990 and 1105 °C in air and quenching did not preserve it to room temperature. High temperature x-ray diffraction established its pattern and confirmed its peritectic decomposition. Above 1110 °C YCu2O2.5 consists of Y2O3 and liquid. The results of this system are shown on a ternary system as well as on a pseudo-binary phase diagram. The solid state reactions were established. Melting occurs with isothermal oxygen loss or gain, depending on the initial composition.

低エネルギー酸素イオンアシスト蒸着により作製したＣｕ‐Ｏ薄膜

Ion assisted deposition is very useful method for obtaining the films with desired properties. The role of ions in this method is to give kinetic energy and chemical activity to a substrate or a growing film. Using a reactive gas ion, it is able to react on the deposition atoms. Consequently various compounds are formed. Control of the incident ion energy, curret and/or the ion species makes to be possible to regulate the film properties such as density, crystal structure, electrical resistivity and so on. We have ever developed a new type of ion source with low energy and high current density. It was discussed that the effects of ion kinetic energy and ion current on the crystal structure of Cu-O thin films prepared by oxygen ion assisted deposition using the ion source developed by us.The crystal structure of Cu-O films were prepared in various ion energy and current was studied by X-ray diffraction measurement. The following results were obtained:(1) The X-ray diffraction peaks due to Cu2O crystal structure are appeared, in spite of low current bombardment of oxygen ion (ion current : O.1mA).(2) As ion current is increased from 0.1mA to 1.2mA and from 1.2mA to 4.4mA at adequate acceleration voltage, the crystal structure of the prepared films is changed as follows, Cu-Cu2O system --> Cu2O system --> CuO system.

SrTiO3 Base BL Capacitors Prepared by Vapor Phase Diffusion

When a PbO–Bi2O3–Cu2O system vapor phase diffusion was applied to an SrTiO3–base semiconductive ceramic, a BL capacitor with a high apparent permittivity of 28500, a low dissipation factor of 0.3%, and a high resistivity of 2.6×1011 Ω cm was obtained.

Phase equilibrium in The TeO2Cu2O System

AbstractPhase equilibrium in the TeO2Cu2O system was determined in air at atmospheric pressure. Differential thermal analysis (DTA), X‐ray powder diffraction and optical microscopy were used to identify the phase transitions. Two congruently melting compounds Te3Cu2O7 and TeCu2O3 were obtained. They possess monoclinic and hexagonal symmetry respectively. The morphology, optical properties and indexed powder pattern up to 1.3 Å are submitted for these compounds. Experiments realized by the DTA indicated the existence of an oxidation process with beginning and rate dependent on the composition. The glass formation limits determined for 2 g and 10 g tellurite glass melts correlate with the invariant points in the system.