Hierarchical CuO Microspheres Research Articles

Wireless Volatile Organic Compound Detection for Restricted Internet of Things Environments Based on Cataluminescence Sensors

Cataluminescence-based sensors do not require external light sources and complex circuitry, which enables them to avoid light scattering with high sensitivity, selectivity, and widely linear range. In this study, a wireless sensor system based on hierarchical CuO microspheres assembled from nano-sheets was constructed for Volatile Organic Compound (VOC) online detection. Through sensor characteristics and data process analysis, the results showed that the luminous sensor system has good luminous characteristics, including the intensity of visible light, high signal/noise (S/N) values, and very short response and recovery times. Different VOC concentration values can be detected on multiple wavelength channels and different Cataluminescence signal spectra separations can process multiple sets of Cataluminescence data combinations concurrently. This study also briefly studied the mechanism action of the Cataluminescence sensor, which can specifically be used for VOC detecting.

Synthesis of graphene quantum dots-coated hierarchical CuO microspheres composite for use as binder-free anode for lithium-ion batteries

There is an urgent need to develop improved anode materials for lithium-ion batteries (LIBs). Herein, we report the synthesis of a graphene quantum dots (GQDs)-coated hierarchical nanoflake-based CuO microspheres (H–CuO) composite on Cu foam via a one-pot hydrothermal technique for use as a binder-free anode for LIBs. The carboxyl-functionalized GQD coating on H–CuO not only results in lower charge-transfer resistance and enhanced electrical conductivity but also prevents the dissolution and agglomeration of the electrode. The GQDs/H–CuO composite anode exhibits a reversible capacity as high as 609 mAh g−1 (pristine H–CuO: 61 mAh g−1) after 200 cycles at 0.2 A g−1. It also shows long-term cycling stability, exhibiting a capacity retention rate of 79.4% after 1000 cycles (pristine H–CuO: 0.7%) at a high current density (2 A g−1) and improved initial coulombic efficiency at 88.2% (pristine H–CuO: 75.2%). The superior electrochemical properties of the GQDs/H–CuO composite anode are attributable to the graphene networks, which help maintain a high specific surface area and effectively protect the anodic active material from forming an unstable solid electrolyte interface layer. The proposed strategy for fabricating the GQD-coated metal oxide microsphere-based anode should contribute to the development of next-generation LIBs with improved electrochemical performance.

Bactericidal activity of Moringa oleifera leaf extract assisted green synthesis of hierarchical copper oxide microspheres against pathogenic bacterial strains

Hierarchical copper oxide (CuO) microspheres were prepared by Moringa oleifera (M. oleifera) leaf extract assisted green synthesis method. The structural, chemical, and morphological features of the hierarchical CuO microspheres were inspected by XRD, FTIR, SEM, and EDAX techniques. The XRD pattern unveiled the formation of monoclinic crystal structured CuO, which confirmed the conversion of Cu(NO3)2.3H2O to Cu2+ ions by phytochemicals present in the M. oleifera leaf extract. The SEM micrographs demonstrated that small CuO nanostructures have interacted with adjacent CuO nanostructures leading to the formation of cluster-like morphologies that resemble hierarchical CuO microspheres. The asymmetric stretching deformation vibration bands observed in the FTIR spectrum of the hierarchical CuO microspheres correspond to Cu–O bond along the (−2 0 2) direction that conveyed monoclinic unit crystal formation of the CuO. The detected Cu and O elements through the EDAX analysis reveal the pristine nature of the hierarchical CuO microspheres. The rich phytochemicals in the M. oleifera leaf extract played crucial roles towards the formation and stabilization of hierarchical CuO microspheres. The highest bactericidal activity was noticed against the Staphylococcus aureus strain with zone of inhibition (ZOI) of 30 and 32 mm for the hierarchical CuO microspheres dosage of 50 and 100 μL, respectively, followed by Klebsiella pneumoniae, Escherichia coli and Bacillus cereus strains. The better bactericidal activity observed against the selected bacterial strains could be credited to ideal interaction of the hierarchical CuO microspheres/small nanostructures with cell walls of the bacterial strains, favorable deliverance of copper ions inside the cells and subsequent production of reactive oxygen species.

Electrochemical reduction of carbon dioxide to formate via nano-prism assembled CuO microspheres

Electrochemical reduction of CO2 has been demonstrated as one of the promising technologies to reduce the greenhouse effect. In this study, nano-prism assembled hierarchical CuO microspheres (Prism-CuO) were designed and used for CO2 electroreduction. The Prism-CuO coated gas diffusion electrode showed high activity for CO2-to-formate conversion with overpotential as low as ∼200 mV, and achieved maximum faradaic efficiency of 65.1% at −1.6 V vs. Ag/AgCl. Moreover, it maintained the stable performance for continuous 20 h of electrolysis. The better performance was mainly attributed to the unique prism feature as it provided abundant corner- and edge-based low-coordinated active reaction sites. These sites could further arouse strong local-electric field to lower the barrier of CO2 adsorption and motivate CO2 activation by accelerating charges transfer process. The result implied designing the nano-prism constructed hierarchical framework would be an efficient strategy to develop the advanced electrocatalyst for efficient CO2 reduction in aqueous solution.

Hierarchical copper oxide microspheres prepared in an ordinary household microwave oven

Hierarchical copper oxide (CuO) microspheres were prepared by a simple microwave-assisted preparation method in an ordinary household microwave oven under ambient pressure. The CuO microspheres were characterised by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermal gravimetric analysis. Characterisation results show that the hierarchical CuO microspheres are assembled by spine-like nanorods and have high Brunauer–Emmett–Teller surface area of 25.0 m2/g.

A simple chemical solution synthesis of nanowire-assembled hierarchical CuO microspheres with enhanced photochemical properties

Hierarchical micro/nanostructures manifest attractive prospects for photocatalytic application. Nevertheless, large-scale hierarchical micro/nanostructures for industrial application with facile, low-cost and eco-friendly routes remain difficult. Herein, nanowire-assembled hierarchical CuO microspheres (HCMAW) are synthesized for the first time by CO32- ions induced synthesis route. The time-dependent SEM images reveal that the growth mechanism for HCMAW is the well-known Ostwald ripening with self-assembly. The specific surface area of the HCMAW is 7.265 m2 g-1, which is higher than that of hierarchical CuO microspheres assembled with nanosheets (HCMAS) (4.952 m2 g-1) prepared by direct self-assembly scheme without the introduction of CO32- ions. Meanwhile, the HCMAW possess strong light absorption around a broadband wavelength from 300 nm to 800 nm. As a result, the photodegradation activity test demonstrates that the HCMAW shows the degradation efficiency of 98.8% for rhodamine B (RhB) under white light irradiation for 30 min in the presence of H2O2 higher than those of HCMAS (66.3%) and commercial CuO (48.3%) under the same condition, which is one of the highest reported till date related to CuO nanomaterials for the degradation of RhB. The novel HCMAW synthesized by the ion-induced protocol is worth being generalized to more assembled hierarchical micro/nanostructures for versatile applications.

Synthesis of porous CuO microspheres assembled from (001) facet-exposed nanocrystals with excellent glucose-sensing performance

Hierarchical porous CuO microspheres are successfully synthesized through a facile hydrothermal method using Na2HPO4-NaOH buffer solution as solvent. The SEM and TEM results reveal that the CuO microspheres are assembled by (001) facet-exposed nanocrystals. The BET result indicates that the CuO microspheres have a surface area of 61.9 m2 g−1 and an average pore size of ∼3.7 nm. Moreover, it is found that the buffer solution not only serves as reactant and medium, but also affects the final shape of the CuO microspheres. The buffer solution can supply a suitable amount of OH− ions, which leads to no extra OH− ions absorb on the original crystals, thus favoring to form into 3D spherical microstructure. In addition, the CuO microspheres are used as the electrodic material for non-enzymatic glucose sensor, which present low detection limit (0.50 μM), fast amperometric response time (3 s), and wide linear range (0.001–4.0 mM). The improved electrocatalytic performance is ascribed to the synergistic effect of exposure of (001) facet, large special surface area, and porous structure.

Facile synthesis of nanosheets-assembled hierarchical copper oxide microspheres and their ethanol gas sensing properties

Hierarchical CuO microspheres assembled with monocrystalline nanosheets based sensors exhibit favorable ethanol gas sensing properties, particularly rapid response/recovery speed.

Facile synthesis and photocatalytic performance of self-assembly CuO microspheres

Hierarchical CuO microspheres have been successfully synthesized by chemical bath deposition, during which Cu(OH)2 nanorobs firstly transform into CuO nanosheets and then these nanosheets spontaneously self-assemble to form CuO microspheres. Detailed characterization of the synthesized nanomaterials was performed utilizing X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and UV–Vis absorption spectra to study their crystalline phase, morphology and optical property. Additionally, photocatalytic performance of Cu(OH)2/CuO composite and pure CuO nanostructures was evaluated. Optical gaps of them are 2.75eV and 1.33eV respectively, showing a significant enhancement in the photocatalytic property in comparison with commercial CuO as demonstrated in photodegradation of methyl blue (MB). A growth mechanism for the formation of CuO nanostructure was also proposed.

Photocatalytic activity of hierarchical CuO microspheres synthesized by facile reflux condensation method

Flower-shaped hierarchical CuO microspheres consisting of interpenetrating nanosheets were successfully synthesized by reflux condensation method without using any surfactant or templates. X-ray diffraction revealed the formation of single phase CuO exhibiting monoclinic crystal structure. Scanning electron microscopy and transmission electron microscopy confirmed the formation of hierarchical flower-shaped CuO microspheres made up of nanosheets as building blocks. UV–vis diffused reflectance spectroscopy showed a steep absorption between 700 and 950nm, and the corresponding band gap of CuO nanoparticles was found to be 1.59eV. To explore the potential capability of flower-shaped CuO microspheres for wastewater treatment, the photocatalytic activity of CuO nanostructures was evaluated by monitoring the photodegradation of methyl orange (MO) and methylene blue (MB) dyes in the presence of hydrogen peroxide under UV light irradiation. Experimental results demonstrated that CuO hierarchical architecture possesses good photocatalytic activity towards MO and MB dyes, indicating the feasibility of using CuO for the effective removal of organic contaminants from wastewater.

Facile Synthesis of Hierarchical CuO Microspheres and their Gas Sensing Properties for NOx at Room Temperature

In this research, hierarchical CuO microspheres have been successfully synthesised by a facile reflux method. Scanning electron microscopy results clearly revealed that the hierarchical CuO microspheres were composed of two-dimensional nanosheets. The morphology of the prepared products could be tailored by changing the precursor concentration. The CuO-2 sample shows a higher NOx gas sensing performance with a low detection limit of 0.97 ppm, high gas response of 64.93 %, and short response time of 5.33 s to 97.0 ppm NOx at room temperature. The CuO-2 sensor also presents good selectivity and stability. The significantly improved gas response was concluded to be related to the well aligned microstructures and the improved conductivity of the CuO-2 sample. The unique hierarchical structure allows effective and rapid gas diffusion towards the sensing surfaces. In addition, the sensing mechanism based on the hierarchical CuO microspheres is discussed.

Carbonate-assisted hydrothermal synthesis of porous, hierarchical CuO microspheres and CuO/GO for high-performance lithium-ion battery anodes

Porous, hierarchical CuO microspheres were synthesized by a facile carbonate-assisted hydrothermal method and encapsulated with GO sheets through engineering the ionic strength in NaCl solution.

Solvothermal synthesis and sensing properties of meso-macroporous hierarchical CuO microspheres composed of nanosheets

The meso-macroporous hierarchical CuO microspheres composed of nanosheets were prepared by a simple solvothermal method combined with post-annealing. The samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscope (HRTEM) and Brunauer–Emmett–Teller N2 adsorption–desorption analyzes. The results reveal that the meso-macroporous hierarchical CuO microspheres are monoclinic structure and are assembled by porous nanosheets. The Brunauer–Emmett–Teller N2 adsorption–desorption analysis indicates that the as-prepared meso-macroporous hierarchical CuO microspheres have a surface area of 42 m2 g−1 with pore size of 8–60 nm. The meso-macroporous hierarchical CuO microspheres exhibited a low working temperature and excellent response, especially to the low concentration of ethanol. The response of the meso-macroporous CuO microspheres composed of porous nanosheets to 100 ppm ethanol reached 13.7 at a working temperature of 150 °C. The enhancement of the response was attributed to the large specific surface area and thin platelet-like building blocks.

A rapid one-pot synthesis of hierarchical hollow mesoporous CuO microspheres and their catalytic efficiency for the decomposition of H2O2

Hierarchical hollow mesoporous CuO microspheres were synthesized by a rapid one-pot hydrothermal method at 150 °C for 2 h, using aqueous based precursors like copper acetate, urea and water. The as-prepared (uncalcined) and calcined (300–500 °C) particles were characterized by differential thermal analysis (DTA), thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), multipoint BET (Brunauer–Emmett–Teller) surface area, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The catalytic efficiency of the synthesized microspheres was examined by tracking the decomposition of H2O2. The size of the hollow microspheres was 3–8 μm comprised of small particles (100–300 nm) which were formed by the self-assembly of nanometer sized (5–20 nm) particles with a stone-wall-like structure. The formation mechanism of the hierarchical hollow CuO microspheres is discussed. The BET surface area and total pore volume of the 300 °C-treated sample were found to be 51 m2 g−1 and 0.25 cm3 g−1, respectively, and it exhibited the highest catalytic performance for the decomposition of H2O2 with a rate constant of 27.49 × 10−3 min−1, the highest value ever published. The catalytic activity was studied in terms of the textural properties and calcination temperatures of the microspheres. The hollow CuO microspheres were used as recyclable catalyst.

Synthesis of hierarchical CuO microspheres: Photocatalytic and antibacterial activities

In this work, hierarchical CuO micropeony was synthesized by an environmentally benign reflux condensation approach without using any surfactant or templates. X-ray diffraction (XRD) analysis revealed the formation of CuO exhibiting monoclinic crystal structure. Fourier transform infrared spectroscopy (FTIR) further confirmed the formation of single phase CuO. Scanning electron microscopy (SEM) analysis showed that the hierarchical CuO architecture is composed of numerous interpenetrating nanosheets that radiated from the center to form floral pattern with a diameter of 1–2μm. Photoluminescence (PL) spectra of CuO exhibited both UV and visible emissions. The photocatalytic activity of hierarchical CuO microsphere was evaluated by monitoring the photodegradation of methyl orange dye while the antibacterial activity was studied against gram-positive and gram-negative bacteria's. Results demonstrated that CuO hierarchical architecture possesses good photocatalytic as well as antibacterial activity.

Organic free synthesis of flower-like hierarchical CuO microspheres by reflux condensation approach

In the present work, CuO nanostructures with different morphologies were synthesized by a simple one-pot reflux condensation approach using different alkaline precursors. Structural analysis by X-ray diffraction and Fourier transform infrared spectroscopy revealed the formation of single phase CuO with a monoclinic crystal structure. Morphological analysis by scanning electron microscopy showed the formation of spindle-shaped and flower-like CuO architecture when NaOH and NH4OH were used as alkaline precursors, respectively. The flower-like CuO architecture is found to be made up of 2D nanosheets as building blocks, which were self-assembled to form spherical assemblies. Optical analysis by UV–VIS diffused reflectance spectroscopy showed blue-shift in the optical band gap due to quantum confinement effect. Photoluminescence spectra showed both UV and visible emission. The plausible growth mechanism for the formation of different CuO nanostructures was proposed.

Facile Fabrication and Enhanced Sensing Properties of Hierarchically Porous CuO Architectures

Hierarchically porous CuO architectures were successfully fabricated via copper basic carbonate precursor obtained with a facile hydrothermal route. The shape of the precursor is preserved after its conversion to porous CuO architectures by calcination. The obtained CuO are systemically characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller N(2) adsorption-desorption analysis. The results reveal that hierarchical CuO microspheres are monoclinic structure and are assembled by porous single-crystal sub-microplatelets. The Brunauer-Emmett-Teller N(2) adsorption-desorption analysis indicates that the obtained CuO has a surface area of 12.0 m(2)/g with pore size of around 30 nm. The gas sensing performance of the as-prepared hierarchical CuO microspheres were investigated towards a series of typical organic solvents and fuels. They exhibit higher sensing response than that of commercial CuO powder. Their sensing properties can be further improved by loading of Ag nanoparticles on them, suggesting their potential applications in gas sensors.

Preparation of hierarchical dandelion-like CuO microspheres with enhanced catalytic performance for dimethyldichlorosilane synthesis

Hierarchical dandelion-like CuO (HD–CuO) microspheres composed of nanoribbons were prepared via a facile hydrothermal method. The samples were characterized by nitrogen adsorption, X-ray diffraction, temperature-programmed reduction, thermogravimetric analysis, transmission electron microscopy and scanning electron microscopy. It was found that the reaction temperature, reaction time and reagent amounts had a significant effect on the morphology and structure of HD–CuO. The obtained HD–CuO microspheres possessed a surface area of 10.6–57.5 m2 g−1 and a diameter of 3–6 μm. In the formation process, ethylene glycol was adsorbed on the surface of the CuO nanoribbons and it acted as the structure-directing agent and thereafter the CuO nanoribbons were self-assembled into HD–CuO. The investigation of the Rochow reaction showed that the HD–CuO catalyst had a better catalytic performance in dimethyldichlorosilane synthesis than the commercial CuO microparticles and commercial CuO–Cu2O–Cu catalyst, owing to its well-developed hierarchically porous structure and higher specific surface area, leading to the increased contact interface among reaction gas, solid catalyst and solid silicon, together with enhanced mass transportation.

Hierarchical CuO hollow microspheres: Controlled synthesis for enhanced lithium storage performance

In this work, hierarchical CuO hollow microspheres were hydrothermally prepared without use of any surfactants or templates. By controlling the formation reaction conditions and monitoring the relevant reaction processes using time-dependent experiments, it is demonstrated that hierarchical CuO microspheres with hollow interiors were formed through self-wrapping of a single layer of radically oriented CuO nanorods, and that hierarchical spheres could be tuned to show different morphologies and microstructures. As a consequence, the formation mechanism was proposed to proceed via a combined process of self-assembly and Ostwald's ripening. Further, these hollow microspheres were initiated as the anode material in lithium ion batteries, which showed excellent cycle performance and enhanced lithium storage capacity, most likely because of the synergetic effect of small diffusion lengths in building blocks of nanorods and proper void space that buffers the volume expansion. The strategy reported in this work is reproducible, which may help to significantly improve the electrochemical performance of transition metal oxide-based anode materials via designing the hollow structures necessary for developing lithium ion batteries and the relevant technologies.

Fabrication of Hierarchical CuO Microspheres

Hierarchical microstructures of metal oxides comprised of nanoparticles, nanorods, and nanobelts as building blocks have been attracted great interests due to their novel structures, properties, and applications. In most systems, hierarchical assembly involves two distinct steps: 1) synthesizing the appropriate precursors, and 2) assembling them into larger structures. Copper oxide (CuO) is a narrow bandgap semiconducting oxide that has been widely used in electrochemical cells, in photothermal and photoconductive materials, and as a heterogeneous catalyst. Various techniques have been used to synthesize CuO nanostructures such as nanoparticles, nanorods, nanobelts, nanoribbons and nanotubes. However, the methods for fabricating CuO hierarchical microstructures were examined by a few groups. Dandelion-like CuO hollow microspheres have been synthesized by a solvothermal process. CuO microspheres have been generated by a simple solution method using sodium tartrate as a chelating agent and CuO whisker assemblies have been fabricated using a microwave-induced polyol process. Here we report a simple method for fabricating hierarchical CuO microspheres with an average diameter of 1.5-2.5 μm under the microwave irradiation. In this method, the CuO microspheres are built from small flakes, each comprised of several nanoplates of 15-25 nm wide and about 400 nm long. The effect of capping reagent concentration on the morphologies of the CuO products was also investigated.