CuO Cu2O Research Articles

Photocatalysis, wettability and optical properties of N-doped Cu2O/CuO thin films for smart coating applications

Abstract Undoped and nitrogen (N)_doped Cu2O/CuO thin films were deposited via reactive DC magnetron sputtering. The deposition was carried out by sputtering the Cu targets under various Ar/N2/O2 gas flow ratios. The structural, optical, wettability, and photocatalytic performance of the deposited films were investigated. A simple cubic Cu2O crystallographic phase is observed for the undoped film, whereas mixed cubic Cu2O and monoclinic CuO phases (Cu2O/CuO) are observed for the N_doped films. EDAX revealed that as the N2 flow rate increased the amount of nitrogen incorporated into the film increased. The transmittance and reflectance are affected by the incorporation of nitrogen into the films. The transmittance values decreased with increasing N2 flow rate, whereas the reflectance values increased. Both the refractive index and extinction coefficient almost increased with increasing N2 flow rate. A noticeable optical band gap narrowing from 2.55 eV to 2.39 eV was detected upon increasing the N2 flow from 0.0 to 190 sccm. The photoluminescence spectrum of the undoped sample contains five distinct bands at 518, 612, 654, 714 and 825 nm. These five maxima are attributed to the radiative decay of bound and free excitons, and oxygen vacancies (VO) After nitrogen incorporation, the photoluminescence intensity decreases and then increases again with increasing N2 flow rate. A reduction in the water contact angle was observed with increasing N2 flow rate. Upon Vis-light illumination, the N_doped Cu2O/CuO films reached superhydrophilicity faster than the undoped film did. The photocatalytic performance of the deposited Cu2O/CuO films was strongly enhanced with a small amount of N doping. The deposited films are promising for self-cleaning and photocatalytic degradation of organic wastes.

Substrate temperature effect on the structural, morphological and optical properties of pyrolyzed bi-phase Cu2O–CuO thin films

Multiphase nanomaterials are fascinating due to the synergistic effect between the crystalline phases that lead to improved device performance. Publications are available for the synthesis of monophasic copper oxides, such as Cu2O and CuO, and the mixed-phase Cu2O–CuO counterpart using different synthesis methods. However, literature report is scarce that focuses on the fabrication of bi-phase Cu2O–CuO thin films by the spray pyrolysis technique without phase transformation to form the monophasic counterparts. The present work attempts to prepare solely mixed-phase Cu2O–CuO films through small incremental change in substrate temperature, in steps of 20 °C. Structural analysis of the pyrolyzed films revealed the formation of a bi-phase Cu2O–CuO crystal system. The crystallite size increased from 18.64 to 23.94 nm, microstrain decreased from 7.134 ×10−4 to 5.625 ×10−4, while stacking faults decreased from 3.753 ×10−3 to 2.942 ×10−3 with an increase in temperature. Microstructural analysis showed nanoaggregates with increased particle size at increasing temperature. The films exhibited a common optical bandgap of 2.61 eV. The values of the static refractive index and optical electronegativity were found to be 2.47 and 0.70, respectively. The surface roughness increased from 41.3 to 90.9 nm with substrate temperature.

Cu metallization of Al2O3 ceramics via CuO reduction: Role of SiO2 additive and sintering atmosphere

A Cu-coated Al2O3 substrates which can be used for power modules are prepared via sintering and reduction of CuO–SiO2 film onto the surface of Al2O3 ceramic without precious metal brazing filler or high-vacuum equipment. This method has a significant cost advantage over the existing technology. Effects of oxygen partial pressure from sintering atmosphere and SiO2 content on microstructure and mechanical properties of Cu/Al2O3 interface are systematically investigated. Phase compositions and morphologies of sintered Cu2O layer, reduced Cu layer and reactive layer are characterized via X-ray diffraction and scanning electron microscopy. In addition, physicochemical changes within CuO–SiO2 during sintering are characterized by thermogravimetry-differential scanning calorimeter. It is found that oxygen and SiO2 can promote the generation of Cu2O–CuO–SiO2 eutectic phase with low melting point upon sintering, which increases the thickness of reaction layer and the densification of Cu layer. The shear strength between the Cu layer and the Al2O3 substrate is enhanced with the increase in Cu layer densification degree, while varying in irregular manner with the thickness of reaction layer. In particular, the highest shear strength of 62.70 MPa is obtained at oxygen partial pressure of 0.02 atm and SiO2 content of 1.5 wt%.

Some characteristics of Cu/Cu2O/CuO nanostructure heterojunctions and their applications in hydrogen generation from seawater: effect of surface roughening

Cu/Cu2O/CuO heterojunction were synthesized, using thermal oxidation under the flow of argon and oxygen gas mixture, as efficient photoelectrode for hydrogen generation. The Cu/Cu2O/CuO heterojunction were synthesized using un-roughed and roughed Cu foils. The resulting heterojunction samples were characterized using various techniques. The evaluated oxide layer (Cu2O/CuO) thicknesses for un-roughed and roughed samples are 4.2 and 8.5 μm, respectively. XRD revealed that the oxide layer is a mix cubic Cu2O and monoclinic CuO crystalline phases with higher CuO ratio in the roughed sample. The surface morphology of the un-roughed sample is a porous surface that consisting of nanoflakes whereas surface morphology of the roughed sample is randomly oriented nanowires. The Cu/Cu2O/CuO nanostructured surface is superhydrophilic, with water contact angles of 11.12 and 0° for un-roughed and roughed samples, respectively. The roughed sample has higher absorbance over the entire studied wavelength range. The obtained values of the optical band gap for un-roughed and roughed samples are 2.48 and 2.39 eV, respectively. The photocurrent density of the roughed photoelectrode is much greater than that of un-roughed photoelectrode. The roughed photoelectrode has a photocurrent density of—0.151 mA cm−2 at—0.85 V and a photoconversion efficiency of 0.55% when illuminating with 340 nm light. This work offers a promised Cu/Cu2O/CuO photoelectrode for hydrogen generation from seawater.

Copper Precursor Salt‐Dependent Antimicrobial Activity of Graphite Oxide Composites Against Escherichia coli and Staphylococcus Aureus: Synthesis and Characterization

Graphite oxide (GrO) is doped with Cu(NO3)2 (CuN/GrO) and CuSO4 (CuS/GrO). Face‐centered cubic Cu, monoclinic CuO, and cubic Cu2O mixed crystalline phases are observed. The ID/IG ratio on average is 1.0 for all composites, associated with similar structural disorders and defects. CuN/GrO and CuS/GrO composites increase the C:O ratio by 30% compared to GrO. In Cu(NO3)2‐ and CuSO4‐doped GrO composites, the copper particle dispersion is on the GrO surface and GrO edges, respectively. By agarwell diffusion assay, the CuN/GrO composite presents only inhibition against the Staphylococcus aureus microorganism at 10 mg mL−1 per well. However, using the CuS/GrO composite, the minimum inhibitory concentration is 5 mg mL−1 per well against Escherichia coli and S. aureus microorganisms. In general, the copper precursor salt influences the copper particle localization in the GrO matrix in a different way, modulating the antimicrobial behavior. In this way, it is possible to establish a possible electrostatic adsorption caused by the Cu+ or Cu2+ ions and the negative charges of the bacterial cell membrane, where the adsorption and mass diffusion mechanisms between charged composites and Gram‐positive and Gram‐negative microorganisms are affected by the copper particle arrangement in the composites.

Ultrasensitive SERS-based detection of prostate cancer exosome using Cu2O–CuO@Ag composite nanowires

Exosome is a recently emerging cancer-associated biomarker for early diagnostic and prognostic owing to their noninvasive, intrinsic stability, and representativeness of primitive cell state. However, the development of convenient and quantitative methods for exosome analysis remains technically challenging. Here, we proposed a cost-effective assay for the direct capture and rapid monitoring of exosomes utilizing the multifunctional surface enhanced Raman scattering (SERS) substrate, which consisted of Cu2O–CuO nanowires prepared by a simple thermo-oxidative growth method and subsequently sputtered with Ag NPs. This reticulate substrate made up of interlaced one-dimensional nanowires that highly favored for exosome recognition and collection. Particularly, the electromagnetic hotspots with high density were uniformly distributed on the nanowires due to uniform physical deposition, facilitating robust SERS property with an enhancement factor (EF) of 3.3 × 108 and signal reproducibility with a relative standard deviation (RSD) of 13%. In addition, the presence of Cu2O–CuO heterojunction enabled further elevation of the SERS performance attributed to the effective charge transfer, triggering a significant chemical enhancement effect. Finally, clinical validation with the serum specimens of prostate cancer patients indicated that the proposed immunosensor possessed great potential for application in rapid cancer screening and diagnosis.

Synthesis, characterization and enhancing efficiency of composite CuO2/CuO nanostructures deposited on porous activated carbon for supercapacitors electrode applications

The efficiency of supercapacitor (SC) electrodes made from hydrothermally obtained composite Cu2O/CuO nanostructures/activated Cassia fistula dry seed pod carbon (CCu NSs) was improved. X-ray results indicated a mixed phase of monoclinic CuO and cubic Cu2O nanoparticles. Morphology and dispersion of both phases were revealed using field emission scanning electron microscopy and transmission electron microscopy. Raman spectra indicated the characteristic peaks of disordered and graphitic carbon in all samples. Fourier transform infrared spectra confirmed the vibrational modes of Cu and O atoms. Specific surface area and pore-size distribution of samples were determined using a nitrogen adsorption-desorption isotherm. X-ray photoelectron spectroscopy was employed to examine their chemical surfaces. Electrochemical properties were evaluated with cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy with three-electrode and symmetric SC cell experiments in KOH. After a 5000 cycle GCD test at 5 A g−1, CCu-2 NS electrode demonstrated an exceptional EDLC performance with 91.2 % capacity retention and specific capacitance 277.80 F g−1 at 0.5 A g−1. Additionally, the fabricated CCu-2//CCu-2 NSs SC cell showed an outstanding 62.3 % capacity retention at 1 A g−1 after a 5000 cycle GCD test with high energy (Esd) and power densities (Psd) of 11.39 Wh kg−1 and 629.34 W kg−1, respectively.

On the scope of mechanochemical activation: The case of Cu/ZnO catalytic systems

ZnO was submitted to different conditions of high-energy ball milling to thoroughly study the outcome of mechanochemical activation. Structural modifications led to a decrease in crystallite size and an increase in micro-strain and specific surface area (SBET) with milling time. Different copper amounts were added on pristine (reference) and activated support by incipient wetness impregnation. Cu deposited over activated support showed an enhanced metal-support interaction since part of Cu2+ could be introduced into milled ZnO lattice, replacing Zn2+ ions and/or locating in lattice interstitials. Moreover, further analyses suggested an electron transfer from activated support to metal, generating a mixture of Cu2O–CuO species, particularly at the interface between metal and support. N2O chemisorption studies gave Cu particle sizes of 1.3, 1.9 and 3.5 nm (for 0.2, 0.5 and 1 wt% Cu, respectively) and thus a good metal dispersion over ZnO was achieved. Hence, support's activation by milling process showed to be an excellent approach to improve both metal-support interaction and metal dispersion of supported catalysts.

Photoelectrochemical Fabrication of CuO-Cu2O Nanocomposite Semiconductors by High-Frequency Potential-Switching in Copper(II)-Tartrate Complex Aqueous Solution and the Energy Band Structures

P-type CuO-Cu2O nanocomposite semiconductors composed of Cu2O-embedded CuO aggregations and Cu2O aggregation consisting of space-filling CuO grains have been fabricated by photoelectrochemical high-frequency potential-switching of 100 to 1000 cycles in an aqueous solution containing copper(II) sulfate hydrate, tartaric acid, and sodium hydroxide, and the size of both the CuO and Cu2O grains decreased from 40–44 nm to approximately 10 nm remaining the characteristic monoclinic and cubic lattices with an increase in cycle numbers. The bandgap energy of CuO components was almost a constant value of 1.5 eV, and the Cu2O components showed a decrease in bandgap energy from 2.05 eV to 1.85 eV with an increase in cycle number due to the Cu2+ state incorporation, and the CuO-Cu2O nanocomposites possessed an ionization energy of approximately 5.2 eV and work function of approximately 4.6 eV respectively, and were close to those for single CuO and Cu2O layers.

Features of the Interaction of Scheelite with HCl Solutions at 400 and 500°C, 100 MPa, and Various f(O2) (According to Experimental and Calculated Data)

Experimental studies were carried out on the solubility of scheelite in HCl solutions in the concentration range from 0.01 to 0.316 mol/kg H2O at 400 and 500°C, a pressure of 100 MPa and the fugacity of oxygen (hydrogen) specified by the buffers Cu2O–CuO, Fe3O4–Fe2O3, Ni–NiO, and Co–CoO. It was found that scheelite in HCl solutions at the specified parameters dissolves incongruently. In solutions containing from 0.01 to 0.0316 m HCl, minor amounts of WO3 and/or WO3 – x tungsten oxides are found in the run products, along with scheelite. In solutions containing from 0.1 to 0.316 m HCl, the formation of calcium tungsten bronzes CaxWO3 is observed, the average composition of which corresponds to the formula Ca0.07WO3. Based on the analysis of the experimental data obtained, the free energies of the formation of tungsten oxides WO3, WO2.9, scheelite, and calcium tungsten bronze were calculated. Using mutually agreed thermodynamic data, the solubility of Sch in solutions of HCl and (Na, K)Cl with the participation of aluminosilicates is calculated. It is shown that the scheelite has a wide area of congruent solubility in saline systems.

Spintronic filter via p-typed polaron state in photoelectron conversion integrating devices

High-performance Cu2O–CuO nanocube thin films water-splitting solar cells were achieved via polaron surface states-induced spin–orbital coupling, spintronic excitation, and migration.

A Low Temperature Growth of Cu2O Thin Films as Hole Transporting Material for Perovskite Solar Cells.

Copper oxide thin films have been successfully synthesized through a metal-organic chemical vapor deposition (MOCVD) approach starting from the copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate), Cu(tmhd)2, complex. Operative conditions of fabrication strongly affect both the composition and morphologies of the copper oxide thin films. The deposition temperature has been accurately monitored in order to stabilize and to produce, selectively and reproducibly, the two phases of cuprite Cu2O and/or tenorite CuO. The present approach has the advantages of being industrially appealing, reliable, and fast for the production of thin films over large areas with fine control of both composition and surface uniformity. Moreover, the methylammonium lead iodide (MAPI) active layer has been successfully deposited on the ITO/Cu2O substrate by the Low Vacuum Proximity Space Effusion (LV-PSE) technique. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM) analyses have been used to characterize the deposited films. The optical band gap (Eg), ranging from 1.99 to 2.41 eV, has been determined through UV-vis analysis, while the electrical measurements allowed to establish the p-type conductivity behavior of the deposited Cu2O thin films with resistivities from 31 to 83 Ω cm and carrier concentration in the order of 1.5-2.8 × 1016 cm-3. These results pave the way for potential applications of the present system as a hole transporting layer combined with a perovskite active layer in emergent solar cell technologies.

Cu2O Nanoparticles Deposited on Y2O3 and CuO: Synthesis and Antimicrobial Properties

This paper reports the preparation of copper(I) oxide nanoparticles deposited on yttrium oxide and copper(II) oxide in the presence of acerola and white willow extracts. Through the use of natural compounds, it was possible to modify the surface of the Y2O3 and CuO carriers allowing Cu2O to be deposited to a greater extent, thus improving the antibacterial properties of the materials. Cu2O nanoparticles, by being deposited on a carrier, enable an increase in the contact surface of the nanoparticles with microorganisms, which react to form reactive oxygen species. Cu2O nanoparticles with sizes of about 38 nm and 76 nm were obtained for Y2O3- and CuO-deposited nanoparticles, respectively. The Gram-negative bacteria Escherichia coli shown a greater sensitivity to the degree of inhibition compared to Staphylococcus Aureus already at a concentration of 250 mg/L. For almost all materials, the inhibition level remained above 50% after 48 h. Analysis of the effect of the antimicrobial properties of the materials against Candida albicans fungus shown high activity which was obtained only at the highest concentrations of 8000 mg/L, for which the degree of growth inhibition was 100% also after 48 h for both Y2O3–Cu2O and CuO–Cu2O.

Sputtering-Assisted Synthesis of Copper Oxide-Titanium Oxide Nanorods and Their Photoactive Performances.

A TiO2 nanorod template was successfully decorated with a copper oxide layer with various crystallographic phases using sputtering and postannealing procedures. The crystallographic phase of the layer attached to the TiO2 was adjusted from a single Cu2O phase or dual Cu2O–CuO phase to a single CuO phase by changing the postannealing temperature from 200 °C to 400 °C. The decoration of the TiO2 (TC) with a copper oxide layer improved the light absorption and photoinduced charge separation abilities. These factors resulted in the composite nanorods demonstrating enhanced photoactivity compared to that of the pristine TiO2. The ternary phase composition of TC350 allowed it to achieve superior photoactive performance compared to the other composite nanorods. The possible Z-scheme carrier movement mechanism and the larger granular size of the attached layer of TC350 under irradiation accounted for the superior photocatalytic activity in the degradation of RhB dyes.

Copper-containing polymethylsilsesquioxane nanocomposites in catalytic olefination reaction

New copper-containing organosilicon hybrid materials were synthesized by the reaction of branched polymethyl- silsesquioxane with copper nanoparticles prepared by the metal-vapor synthesis. Hybrid materials showed a high activity in the catalytic olefination of p-chlorobenzaldehyde hydrazone with polyhaloalkanes such as CBrCl3, CBr4 and CF CBr to afford the corresponding halostyrenes in the yields above 80%. The structure and composition of the prepared nanocomposites were studied by X-ray using synchrotron radiation to show that the active sites of the catalysts are mixed copper(I)–copper(II) oxides (Cu–Cu2O–CuO) in nature.

In Situ Synthesis of Monolithic Cu2O–CuO/Cu Catalysts for Effective Ozone Decomposition

Nowadays, ozone (O3) has become a worldwide pollutant, and it is challenging to prepare monolithic O3 decomposition catalysts substituting the conventional complicated process of adhering catalyst powders onto porous substrates. Herein, monolithic Cu2O–CuO/Cu catalysts are obtained facilely by in situ thermal oxidizing–reducing copper foam. After optimization, the CuO nanowires (NWs) are first produced by annealing Cu foam in O2 at 400 °C for 2 h and then the NW surface is reduced into Cu2O by annealing in Ar/H2 at 350 °C for 2 h. The obtained Cu2O–CuO/Cu monolithic catalyst exhibits high catalytic activity to 20 ppm O3, maintaining 100% at a space velocity of 11,000 h–1 and even about 94% at 38,000 h–1. The catalytic ability toward O3 can be attributed to the generated Cu+/Cu2+ redox couples, the donor/acceptor-type point defects, and the Cu2O–CuO p–p heterojunction. This demonstrates the successful and convenient preparation of the monolithic catalyst for rapid, controllable, and productive O3 removal applications.

Optical characterization of RF sputtered copper oxide for thin film solar cell applications

The structural and optical properties of copper oxide thin film have been investigated using various characterization techniques. These thin films have potential applications in thin film solar cells that utilize the visible and UV regions of the solar spectrum. Copper oxide thin films are deposited using RF magnetron sputtering equipped with mass flow controllers. The samples are in-situ annealed post deposition at 300 °C in oxygen ambient to improve the structural properties. Such annealed sample exhibit narrow (002) and (020) CuO peaks and (111)Cu2O peak. X-ray diffraction results confirm the formation of polycrystalline CuO and mixed phases of CuO -Cu2O. A Lowest FWHM of 0.00079 rad has been observed in the XRD spectrum, indicative of excellent crystalline quality of copper oxide thin films. UV–Visible Spectroscopy measurement performed on the copper oxide samples, showed a wide range of absorption edge ranging from 3.9 eV to 3.75 eV for various deposition temperatures ranging from 50 °C to 150 °C. The annealing effect at high temperature for longer duration results in the formation of CuO phase as confirmed by absorption edge at 2.85 eV and the presence of (002) and (020) CuO XRD peaks. In-situ annealing also showed the onset of Urbach effect due to the transitions at tail states and band to tail states.

Fabrication of CuO mesh for efficient oil/water separation

In this work, we have fabricated superhydrophobic copper oxide mesh by simply annealing copper mesh followed by surface modification with octadecanoic acid. The XRD analysis of the sample revealed the presence of cubic Cu2O and monoclinic CuO phases of copper oxide. The FESEM analysis of the samples demonstrated the presence of wire-like structures of copper oxide. The successful deposition of octadecanoic acid was confirmed by FT-IR analysis. The wettability study has confirmed that the sample modified with octadecanoic acid showed excellent superhydrophobic behavior with a water contact angle of 156° and superoleophilic behavior with oil contact angles of 0°. Owing to the excellent superhydrophobic-superoleophilic behavior, the modified copper oxide mesh allows oil to penetrate while restricting the passage of water through its surface, which results in the separation of the oil/water mixture. The modified mesh showed ∼98% separation efficiency and high flux for different oil/water mixtures. Moreover, this mesh exhibited excellent recyclability by maintaining its high efficiency even after 10 separation cycles. Owing to its high separation efficiency (∼98%), recyclability and high flux, the modified copper oxide mesh meets the current need for the separation of oil/water mixtures in real-world applications.

Effect of aqueous inorganic anions on the photocatalytic activity of CuO–Cu2O nanocomposite on MB and MO dyes degradation

In this study, CuO–Cu2O nanocomposite was synthesized via a facile chemical-thermal oxidation method. The prepared nanocomposite was characterized by several techniques. X-ray diffraction (XRD) result affirmed that the synthesized nanocomposite was composed of CuO and Cu2O phases. X-Ray Photoelectron Spectroscopy (XPS) result confirmed the presence of Cu+, Cu2+, and O2− in the synthesized nanocomposite structure. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) results revealed the formation of string-bead-like nanoparticles with an average diameter of 40 nm. The optical band gap energy of 1.9 eV was estimated by diffuse reflectance spectroscopy (DRS). Besides, the photoluminescence (PL) spectrum shows the outstanding peak of the excitonic process at 550 nm. The photocatalytic performance of the synthesized compound was evaluated on methyl orange (MO) and methylene blue (MB) dyes. The degradation experiments were performed for 240 min under visible light irradiation. The photodegradation of the MB was higher than MO dye. Type II charge transfer was proposed for the photocatalytic mechanism of the synthesized nanocomposite. The degradation was further studied in the presence of sulfate, chloride, and nitrate ions in different concentrations. Sulfate anions had the most significant effect on MB inhibiting degradation, while chloride ions at the concentration of 0.5 mM increased the degradation of MB. Chloride anions also had the greatest inhibitory effect on the degradation of MO. Sulfate ions only negligibly affected MO degradation over CuO–Cu2O photocatalyst. Recyclability experiment revealed that the photodegradation process was only influenced 5 and 6%, respectively for MB and MO solutions after three runs.

Thermal evolution of morphological, optical, and photocatalytic properties of Au–Cu2O–CuO nanocomposite thin film

Thermal evolution of morphological, optical, and photocatalytic properties of Au–Cu2O–CuO nanocomposite thin film