CuO Nanowires Research Articles

Ag Nanoparticles Decorated CuO@RF Core-Shell Nanowires for High-Performance Surface-Enhanced Raman Spectroscopy Application

Vertical-aligned CuO nanowires have been directly fabricated on Cu foil through a facile thermal oxidation process by a hotplate at 550 °C for 6 h under ambient conditions. The intermediate layer of resorcinol-formaldehyde (RF) and silver (Ag) nanoparticles can be sequentially deposited on Cu nanowires to form CuO@RF@Ag core-shell nanowires by a two-step wet chemical approach. The appropriate resorcinol weight and silver nitrate concentration can be favorable to grow the CuO@RF@Ag nanowires with higher surface-enhanced Raman scattering (SERS) enhancement for detecting rhodamine 6G (R6G) molecules. Compared with CuO@Ag nanowires grown by ion sputtering, CuO@RF@Ag nanowires exhibited a higher SERS enhancement factor of 5.33 × 108 and a lower detection limit (10-12 M) for detecting R6G molecules. This result is ascribed to the CuO@RF@Ag nanowires with higher-density hot spots and surface-active sites for enhanced high SERS enhancement, good reproducibility, and uniformity. Furthermore, the CuO@RF@Ag nanowires can also reveal a high-sensitivity SERS-active substrate for detecting amoxicillin (10-10 M) and 5-fluorouracil (10-7 M). CuO@RF@Ag nanowires exhibit a simple fabrication process, high SERS sensitivity, high reproducibility, high uniformity, and low detection limit, which are helpful for the practical application of SERS in different fields.

Photoinduced Cu+/Cu2+ interconversion for enhancing energy conversion and storage performances of CuO based Li-ion battery

Pursuing appropriate photo-active Li-ion storage materials and understanding their basic energy storage/conversion principle are pretty crucial for the rapidly developing photoassisted Li-ion batteries (PA-LIBs). Copper oxide (CuO) is one of the most popular candidates in both LIBs and photocatalysis. While CuO based PA-LIBs have never been reported yet. Herein, one-dimensional (1D) CuO nanowire arrays in situ grown on a three-dimensional (3D) copper foam support were employed as dual-functional photoanode for both ‘solar-to-electricity’ and ‘electricity-to-chemical’ energy conversion in the PA-LIBs. It is found that light energy can be indeed stored and converted into electrical energy through the assembled CuO based PA-LIBs. Without external power source, the photo conversion efficiency of CuO based photocell reaches about 0.34%. Impressively, at a high current density of 4000 mA g−1, photoassisted discharge and charge specific capacity of CuO based PA-LIBs respectively receive 64.01% and 60.35% enhancement compared with the net electric charging and discharging process. Mechanism investigation reveals that photogenerated charges from CuO promote the interconversion between Cu2+ and Cu+ during the discharging/charging process, thus forcing the lithium storage reaction more completely and increasing the specific capacity of the PA-LIBs. This work can provide a general principle for the development of other high-efficient semiconductor-based PA-LIBs.

CuO Nanowires Fabricated by Thermal Oxidation of Cu Foils towards Electrochemical Detection of Glucose

In view of the various stability issues and high cost of enzymatic glucose biosensors, non-enzymatic biosensors have received great attention in recent research and development. Copper oxide (CuO) nanowires (NWs) were fabricated on Cu foil substrate using a simple thermal oxidation method. The phase and morphology of the CuO NWs could be controlled by synthesis temperature. Variation in oxidation states enables CuO NWs to form Cu (III) species, which is crucial in catalysing the eletro-oxidation of glucose. The Cu-based metal/oxide composite electrode works as a non-enzymatic biosensor that adapts to the fast, dynamic change in glucose concentration, with a low saturation concentration (~0.7 mM) and a lower detection limit of 0.1 mM, making CuO NWs an excellent sensor towards impaired fasting glucose. The simplicity, cost-effectiveness and non-toxicity features of this study might make a way for potentially scalable application in glucose biosensing.

CuO nanomesh hierarchical structure for directional water droplet transport and efficient fog collection

Collecting water from fog is a promising approach to solve the shortage of water resources by micro-nano scale hierarchical structure material surface. Inspired by the structures of cactus and pine needles, CuO micro-nano scale structures attached to the surface of Cu foam are designed to increase the efficiency of fog collection and droplet transport. The structural evolution from CuO nanowires to CuO nanomesh and CuO nanosheets is achieved by regulating the synthesis conditions. The results show that the synthesized CuO nanomesh hierarchical structure is more favorable for fog collection, and the collection efficiency can achieve a rate of up to 34.6 mg/cm2 s. The tip structure can rapidly capture and coalesce small droplets in a foggy environment, which significantly improves the fog collection efficiency. In addition, the synthesized mesh structure and inter-neighborhood gaps have a strong ability to confine air, making the surface has small adhesion and enabling water droplets to fall quickly, which realizes the transport of the collected water efficiently and sustainably. The research work opens a new path for constructing surface structures to improve fog collection performance and has reference value and promotion for the design and development of fog collectors.

Integrated one–dimensional CuO–nanowire arrays/Cu–foam nanoarchitecture for ultrahigh sensitive and non–enzymatic electrochemical determination of histamine levels in different–bacteria fermented mandarin fish

Integrated one–dimensional CuO–nanowire arrays/Cu–foam (CuO–NWAs/Cu–foam) nanostructure, which was fabricated by oxidation and calcination, has been newly utilized as non–enzymatic electrocatalytic electrode for exploring histamine level. Under optimal condition of pH at 13 and potential at 0.55 V (vs Ag/Ag/Cl), the sensitivity of CuO–NWAs/Cu–foam electrode towards non–enzymatic electrochemical histamine determination presented as high as 12.94 mA mM−1 cm−2, linear range spanned between 0.5 and 1046 μM, a detection limit (S/N = 3) was about 44 nM. The unprecedented causes of ultrahigh sensitivity were physically contributed to enhancing active surface area and declining charge transfer resistance. More crucially, the outstanding selectivity, stability and reproducibility facilitated its practical capacity on evaluating histamine levels in different–bacteria fermented mandarin fish, which triggered the potential feasibility for commercializing non–enzymatic electrochemical determination of histamine with high sensitivity, reliable precision and low expenditure.

Understanding the Growth of Copper Oxide Nanowires and Layers by Thermal Oxidation over a Broad Temperature Range at Atmospheric Pressure

In this paper, we explore the development of copper oxide layers and their evolution into nanowires on thermally oxidized copper and underlying chemical processes governing the growth of unidirectional, one-dimensional copper oxide (CuO), especially focusing on the role of underlying oxide layers. Extensive experimental data sets of grown nanowires in an ambient atmosphere at different oxidation temperatures and times were collected, analysed, and correlated with theoretical modeling of growth processes. Detailed microstructural analysis revealed that upon annealing in air, the Cu2O layer of randomly oriented columnar grains forms first, followed by preferentially oriented CuO grains, evolving into CuO nanowires. Our results highlight the importance of copper and oxygen diffusion and concentration in equilibrium between Cu2O and CuO phases in the oxide film and indicate that CuO nanowires originate in twinned CuO grains, which elongate due to the twin boundary’s instability. With broad experimental data sets on growth conditions, we obtain the complete picture of experimental and modeled growth of copper oxide nanowires, which will enable the tailored design of nanowires and their implementation in catalysis, sensing, and other applications.

Self-powered illuminating glucose sensor

Nowadays, the development of various electricity generation methods via dynamic water motions has been intensively focused on. While verifying the exact electricity generation mechanism, another important task of making full use of the electricity generated by the solid-liquid interaction is being considered. Herein, we demonstrated a self-powered illuminating glucose sensor with high sensitivity (∼ 22.61 V·M−1) and selectivity, and a wide detection range (0.5–100 mM), utilizing the electricity generated from the water infiltration into a glycine-coated porous CuO nanowires film. Fundamentally, the sensing mechanism could be comprehensively verified by an ionovoltaic effect that attributes the electricity generation to the adsorption/desorption of ions or protons at the solid-liquid interface. As the concentration of adsorbed glucose increases, the generated open-circuit voltage decreases accordingly. Moreover, by selectively turning on LEDs with different threshold voltages, the glucose concentration that is harmful to the human body is successfully distinguished. Overall, the self-powered illuminating sensor platform utilizing electricity generated by the water-infiltration phenomenon provides the feasibility of novel biosensors.

Plasma-Assisted Anion Exchange Reactions in Thermally Grown Copper Oxide Nanowires

Copper oxide nanowires represent a popular topic in recent research due to their potential use in gas sensors, batteries, supercapacitors etc. One of their advantages is facile synthesis, as they can be synthesized merely by heating metallic copper in the air. Moreover, their parameters, such as length and diameter, can be easily tailored by adjusting the conditions at which they are synthesized. Once obtained, nanowires can be further processed to enhance their properties. Common processing includes a partial or complete transformation of grown nanowires to another phase via cation or anion exchange. There are many existing methods for achieving such transformations, which are mostly solution-based. On the other hand, great unused potential lies in methods that exploit plasmas to achieve phase transformations in nanomaterials.Even though there are a lot of reports on the synthesis of CuO nanowires, there are still a lot of knowledge gaps when it comes to their production and ion exchange reactions. In both cases, the challenges are associated with fundamental science behind processes during nanowire growth and phase transformations, as mechanisms behind NW growth and ion exchange reactions are not completely understood. In our present research, we tackle challenges connected to the thermal growth of CuO nanowires as well as the fundamental science behind phase transformations in them. In order to study mechanisms of nanowire growth, we performed thermal oxidation of copper to obtain nanowires at different times and temperatures. With detailed microstructural analysis of nanowires and oxide layers on which they grow as well as utilization of theoretical simulations, we obtained valuable information about growth of one dimensional metal oxide nanomaterials. Furthermore, mechanisms of anion exchange reactions were studied in the copper oxide – copper sulfide system. To achieve the oxide to sulfide transformations, copper oxide nanowires were subjected to plasma treatment with sulfur-containing gasses, which allowed us to study anion exchange in non-equilibrium plasma environments.

Ag-decorated CuO NW@TiO2 heterojunction thin film for improved visible light photocatalysis

Herein, Ag-decorated CuO@TiO2 (CuO@TiO2-Ag) semiconductor heterojunctions are prepared using a porous CuO nanowire (NW) matrix for visible light photocatalysis applications. The CuO NW matrix is synthesized by wet-oxidation-based growth on a commercial Cu plate. Conformal coating of TiO2 on the CuO NW surfaces is successively achieved by atomic layer deposition, following which Ag nanoparticles (NPs) are deposited to synthesize a Ag-decorated CuO@TiO2 photocatalyst film. Microstructural and chemical analyses reveal uniform synthesis of a CuO@TiO2 heterojunction as well as a binding energy shift at the interface to form balanced Fermi energy, respectively. The performance of CuO@TiO2-Ag as a visible-light photocatalyst is evaluated under 20-W low-power visible-light LED illumination for the photodegradation of methylene blue. In addition, the effects of the TiO2 layer and the Ag NPs on the decomposition efficiency are investigated. To control the thickness of TiO2 and the dosage of Ag NPs, the photodegradation of CuO@TiO2-Ag is optimized at a rate of 0.0133 min−1, which is approximately 3 and 2.5 times higher than those of a bare CuO@TiO2 heterojunction and Ag-deposited CuO, respectively. The high decomposition efficiency achieved in this study results from the combined effects of the conformal core–shell heterojunction formed by atomic layer deposition and the well-distributed Ag NPs.

Hydrogen-substituted graphdiyne encapsulated cuprous oxide photocathode for efficient and stable photoelectrochemical water reduction

Photoelectrochemical (PEC) water splitting is an appealing approach for “green” hydrogen generation. The natural p-type semiconductor of Cu2O is one of the most promising photocathode candidates for direct hydrogen generation. However, the Cu2O-based photocathodes still suffer severe self-photo-corrosion and fast surface electron-hole recombination issues. Herein, we propose a facile in-situ encapsulation strategy to protect Cu2O with hydrogen-substituted graphdiyne (HsGDY) and promote water reduction performance. The HsGDY encapsulated Cu2O nanowires (HsGDY@Cu2O NWs) photocathode demonstrates a high photocurrent density of −12.88 mA cm−2 at 0 V versus the reversible hydrogen electrode under 1 sun illumination, approaching to the theoretical value of Cu2O. The HsGDY@Cu2O NWs photocathode as well as presents excellent stability and contributes an impressive hydrogen generation rate of 218.2 ± 11.3 μmol h−1cm−2, which value has been further magnified to 861.1 ± 24.8 μmol h−1cm−2 under illumination of concentrated solar light. The in-situ encapsulation strategy opens an avenue for rational design photocathodes for efficient and stable PEC water reduction.

Engineering the surface chemical microenvironment over CuO nanowire arrays by polyaniline modification for efficient ammonia electrosynthesis from nitrate

Electrochemical nitrate reduction into ammonia offers an attractive alternative to value-added ammonia (NH3) production under benign conditions. The critical to achieve satisfactory NH3 production rate from nitrate electroreduction that can compare with industrial Haber–Bosch route is the development of highly efficient electrocatalysts. In this work, we descript a post-modification strategy for synthesizing polyaniline (PANI)-modified CuO nanowire arrays (CuO@PANI) for selective electrocatalytic nitrate-to-ammonia transformation. Surface modification of CuO with PANI can not only well-retain the nanowire array structure and large specific surface area, but also modulate the surface chemical microenvironment of catalyst, which promotes nitrate enrichment and hydrogenated species accumulation, and thus facilitates selective nitrate-to-ammonia transformation. As a result, the CuO@PANI exhibits high Faradaic efficiency (93.88%) and excellent NH3 selectivity (91.38%) for NH3 electrosynthesis from nitrate. The strategy is worthy for designing high-efficiency electrocatalysts by surface modification with organic molecular or polymers for selective nitrate reduction into ammonia.

Sculpting nanocavities via thermal stimulated Kirkendall effect oxidation

Controlling the shape, morphology, and porosity of hollow nanostructures is a pivotal issue for adjusting the characteristics of tailor-made nanomaterials to expand their application to more fields. Although many hollow metal oxides have been developed, studies on the construction of hollow bimetal oxide heterostructures with controllable nanocavities in different morphologies and high crystallinity through Kirkendall effect is still ascendant. Using this strategy, nickel nanotubes with smooth walls was acquired through continuous oxidation treatments on CuNi nanowires at 200 °C. Oxidation treatment at high temperature (300 °C) on CuNi nanowires produced nickel oxide nanotubes containing periodic copper nanoparticles, nickel oxide nanotubes with a bamboo-like structure and nanoforests. In addition, thin CuO nanowires with diameters of 5–10 nm grew on nanowires at 400 °C. Finally, the mechanisms of sculpting nanocavities at high and low temperatures were elucidated. An in-depth understanding of the thermally stimulated Kirkendall effect in bimetals has a significant influence on the design and fabrication of new hollow multifunctional hetero-nanostructures with potential applications in energy storage, catalysis, and gas sensing.

Electrochemical Nonenzymatic Glucose Detection Based on the Nanostructures of NiCo2O4 Nanosheets Wrapped CuO Nanowires

A kind of NiCo2O4-based hierarchically-nanostructured composites has been synthesized for electrooxidation of glucose. The Cu(OH)2 nanowires were initially growth in situ on the surface of Cu foam (CF) and wrapped with Ni-Co precursor (Ni-Co Pre) to prepare nanocomposites (Ni-Co Pre@Cu(OH)2 NWs/CF). Then, the obtained composites were annealed in air to form the NiCo2O4 nanosheets wrapped CuO nanowires nanostructures which were supported on the Cu foam (NiCo2O4@CuO NWs/CF). Because of the synergism of Ni, Co and Cu, as well as the enhanced surface area by hierarchical nanostructure, the as-prepared NiCo2O4@CuO NWs/CF sensor exhibits outstanding electrooxidation activity for glucose detection, including high sensitivity (7.98 μA/μM cm−2), wide linear range (1.0 × 10−3−2.0 mM), low detection limit (0.68 μM) and fast response/recovery times (1.3/2.0 s). Meanwhile, the as-fabricated sensor also possesses good reproducibility, flexibility, selectivity and long-term stability, which is a promising platform for glucose electrooxidation and determination in serum sample.

Constructing Proton Transfer Channels Using CuO Nanowires and Nanoparticles as Porogens in High-Temperature Proton Exchange Membranes

Constructing Proton Transfer Channels Using CuO Nanowires and Nanoparticles as Porogens in High-Temperature Proton Exchange Membranes

Synthesis of ZnO and CuO Nanowires by Thermal Oxidation on Metallic Substrates

In this research work, brass (Cu - 37.2 wt% Zn) and Cu (99.9 wt%) wires having diameters of 200 μm were thermally oxidized in N2 containing 5% O2, at a flow rate of 200 sccm and in the ambient atmosphere respectively, to support the growth of nanowires. The oxidation temperature was varied from 300 to 600 °C and the as-grown nanowires were characterized by field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray (EDX) spectroscope, and transmission electron microscope (TEM). Results show that ZnO and CuO nanowires are formed on brass and Cu wires, respectively. The ZnO nanowires are branched and CuO nanowires are straight with tapered morphology. ZnO nanowires having hexagonal wurtzite structure grow along the <1 1 0> directions whereas, CuO nanowires have monoclinic structure. A diffusion based stress induced model is proposed to explain the growth mechanism of the nanowires. Thermal oxidation process is a suitable platform for synthesizing ZnO and CuO nanowires, which can be used in in-situ device fabrication.

Oxygen Adsorption and Desorption Kinetics in CuO Nanowire Bundle Networks: Implications for MOx-Based Gas Sensors

Copper oxide (CuO) nanostructures have demonstrated a good chemiresistive response for the sensing of various gases. The precise sensing mechanisms of this material and, in particular, the kinetics of the response to gases and the sensor recovery remain much less investigated. For metal oxide (MOx) chemiresistive gas sensors, oxygen adsorption and desorption reactions on a material surface play a major role in the sensor kinetics, as most other gases react with oxygen on the sensor surface in order to provide the sensing signal, and nanoscale materials are known to achieve faster response. Here we investigate the oxygen adsorption and desorption kinetics on CuO nanowire bundle (NWB) networks by analyzing the electrical response and recovery curves of sensing devices exposed to oxygen. The observation of multiple time constants for the response and recovery curves led us to discuss the various potential mechanisms related to surface reaction kinetics and diffusion of oxygen species. By comparing the reaction rate constants and diffusion constants extracted from the obtained time constants, we conclude that the diffusion of oxygen defects into the material might be the main reason for the observed large time constants. Surprisingly, we observe that the sensor devices based on as-deposited materials show 4–16 times faster response and recovery as compared to devices after being annealed, depending on the temperature. By comparing this result with detailed characterization using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, we discuss the role of the junctions between nanostructures in the network and of the hydroxylated CuO surface to explain this result. Our investigation on the kinetics of adsorption and desorption of oxygen of CuO NWB provides a direct understanding of the general response of the sensor and will be useful in order to further understand and optimize these materials for the sensing of various gases.

In-situ preparation of carbon nanotubes on CuO nanowire via chemical vapor deposition and their growth mechanism investigation

In-situ growth of carbon nanotubes (CNTs) on CuO nanowires is realized by chemical vapor deposition method, in which hydrogen/argon mixed gas and acetylene are used as pretreatment gas and carbon source, respectively. CuO nanowires are formed uniformly on the surface of copper wire (CW) through thermal oxidation method, which generates CW@CuO@CNTs with a good hierarchical structure. Also, many copper nanoparticles are formed on the surface of CNTs. The growth mechanisms of CNTs and copper nanoparticles are investigated in this paper.

Ultrafast Photoresponse Using Axial n-ZnO/p-CuO Heterostructure Nanowires Array-Based Photodetectors

Photodetector (PD) based on axial n-ZnO/p-CuO heterostructure (HS) nanowires (NWs) array was fabricated on Si substrate by using glancing angle deposition (GLAD) technique. The field emission scanning electron microscope (FE-SEM) image shows the formation of a well-aligned and vertical NW structure. A typical high-resolution transmission electron microscope (HR-TEM) image confirms the formation of an axial HS NW consisting of ZnO NW at the top and CuO NW at the bottom. A twofold enhanced photo-absorption was observed for axial n-ZnO/p-CuO HS NW as compared to pristine ZnO NWs. Moreover, X-ray photoelectron spectroscopy (XPS) analysis prove that there is no deviation in electronic state after the formation of HS. The axial n-ZnO/p-CuO HS NW based PD exhibited a very high rectification ratio of 1200, low dark current ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{d}$ </tex-math></inline-formula> ) of 0.09 nA and an ultrafast photoresponse with rise time and fall time of 0.49 and 0.11 ms, respectively.

Boosting activity of Ni(OH)2 toward alkaline energy storage by Co and Mn co-substitution

Ni-based hydroxides nanomaterials are widely used in alkaline storage devices. Under the guidance of density functional theory calculations and experimental investigations, here, (Ni0.8Co0.1Mn0.1)(OH)2 is designed and prepared on CuO nanowire arrays, demonstrating Co and Mn co-substitution resulted in enhanced capacity and stability of Ni(OH)2. The enhanced performance is mainly thanks to the low deprotonation energy and the facile electron transport, which results from the synergistic interactions among Ni, Co and Mn. Ni-Zn battery and alkaline hybrid supercapacitor with (Ni0.8Co0.1Mn0.1)(OH)2 (8.4 mg cm−2) as positive electrode can achieve infusive energy density of 605.2 and 270.1 Wh kg−1, respectively. The finding lay a foundation for further the design and fabrication of high-performance Ni-based nanomaterials for alkaline energy storage.

Rapid Conversion of Co2+ to Co3+ by Introducing Oxygen Vacancies in Co3O4 Nanowire Anodes for Nitrogen Removal with Highly Efficient H2 Recovery in Urine Treatment

Urine is a nitrogenous waste biomass but can be used as an appealing alternative substrate for H2 recovery. However, urine electrolysis suffers from sluggish kinetics and requires alkaline condition. Herein, we report a novel system to decompose urine to H2 and N2 under neutral conditions mediated by Cl• using oxygen-vacancy-rich Co3O4 nanowire (Ov-Co3O4) anodes and CuO nanowire cathodes. The Co2+/Co3+ cycle in Co3O4 activates Cl- in urine to Cl•, which rapidly and selectively converts urea into N2. Thus, electron transfer is boosted for H2 production, eliminating the kinetic limitations. The shuttle of Co2+ to Co3+ is the key step for Cl• yield, which is accelerated due to the introduction of Ov. Electrochemical analysis shows that Ov induces positive charge on the Co center; therefore, Co2+ loses electrons more efficiently to form Co3+. H2 production in this system reaches 716 μmol h-1, which is 320% that of non-radical-mediated urine electrolysis. The utilization of Ov-Co3O4 further enhances H2 generation, which is 490 and 210% those of noble Pt and RuO2, respectively. Moreover, urine is effectively degraded in 90 min with the total nitrogen removal of 95.4%, and N2 is the final product. This work provides new insights for efficient and low-cost recovery of H2 and urine remediation.