Preparation of flower-like CuO by a simple chemical precipitation method and their application as electrode materials for capacitor

A novel CuO electrode material with flower-like nanostructures was fabricated at a low temperature (80 °C) by a simple chemical precipitation method. Scanning electron microscopy (SEM) results showed that CuO with spherical and flower-like structure can be formed under a weak alkali (C₆H₁₂N₄), and CuO with sheets structure can be obtained under a strong alkali (NaOH). A possible growth mechanism of CuO nanocrystals was discussed. The flower-like CuO electrode exhibited a higher specific capacitance (133.6 Fg⁻¹) and an excellent cycle performance at a high current density of 10 mA/cm². Specific capacitance of flower-like CuO was 405.3% higher than globular CuO (26.44 Fg⁻¹) at 2 mA/cm².     

A facile one step synthesis of SnO<Subscript>2</Subscript>/CuO and CuO/SnO<Subscript>2</Subscript> nanocomposites: photocatalytic application

Here novel photocatalysts, SnO₂/CuO and CuO/SnO₂ nanocomposites were successfully synthesized by chemical method at room temperature. X-ray Diffraction (XRD), transmission electron microscopy (TEM), Fourier transform Infrared (FT-IR), UV–Visible (UV–Vis) and photoluminescence (PL) spectroscopy were utilized for characterization of the nanocomposites. The photocatalytic activity of the nanocomposites was investigated. The hybrid nanocomposites exhibited high photocatalytic activity as evident from the degradation of methylene blue (MB) dye. The result revealed substantial degradation of the MB dye (92 and 69.5% degradation of SnO₂/CuO and CuO/SnO₂, respectively) under visible light illumination with short period of 30 min. Their large conduction band potential difference and the inner electrostatic field formed in the p–n heterojunction provide a strong driving force for the photogenerated electrons to move from Cu₂O to SnO₂ under visible light illumination. The excellent photodegradation of methylene blue suggested that the heterostructured SnO₂/CuO nanocomposite possessed higher charge separation and photodegradation abilities than CuO/SnO₂ nanocomposite under visible light irradiation.     

Synthesis,defect characterization and photocatalytic degradation efficiency of Tb doped CuO nanoparticles

Monoclinic undoped and Tb doped CuO are prepared by solution combustion method and annealed at different temperatures. The effect of annealing and doping on their structural and optical properties of CuO are examined using XRD, FTIR and DRS. The surface and lattice defects in CuO and Tb doped CuO is analyzed qualitatively and quantitatively using positron lifetime and Doppler broadening spectroscopy. The average positron lifetime and electron momentum (energy) S parameter increases owing to the number of vacancies in the CuO lattice upon doping and decreases with increasing temperature. The migration of vacancies from grain to grain boundary region is observed at 600 °C annealed samples. At 800 °C, the overall behavior of lifetime value denotes that the vacancy type defect is recovered, cluster vacancy and microvoids exists with reducing size. The photocatalytic performance of undoped and Tb doped CuO on degradation of methylene blue (MB) and methyl orange (MO) is investigated under visible light for two different lamp power and dye concentration. The influence of annealing temperature and dopant ion on the efficiency is also elaborated. Enhanced photocatalytic efficiency in Tb doped CuO is observed upon annealing. X-ray photoelectron spectroscopy (XPS) result indicates that the valence states of Cu, O and Tb ions exist at the surface of the particles. Brunauer–Emmett–Teller N₂ adsorption–desorption analyses were employed to characterize specific surface area and porosity of Tb doped CuO. The doped CuO with pore size of about ～34 nm have a surface area of 16–28 m²/g. The surface area effect plays an important role in the enhanced catalytic performance on Tb doped catalysts.     

CuO/CeO2 catalysts prepared with different cerium supports for CO oxidation at low temperature

The activity of a catalyst depends on the nature of its support, its active site, and its preparation method. This study aimed to employ various types of CeO₂ supports such as commercial CeO₂ and self-prepared CeO₂ for the preparation of copper catalysts. The CuO/CeO₂ catalysts were prepared using the polyol process and impregnation method. The catalysts were characterized using Brunauer–Emmett–Teller analysis, scanning electron microscopy, and X-ray analysis, and their catalytic activity for CO removal was evaluated in a microcatalytic reactor. The experimental results showed that the catalytic activity of the CuO/CeO₂ catalysts with different calcination temperatures decreased in the following order: 500 °C > 300 °C > 700 °C. Compared to the impregnation method, the polyol process generated well-dispersed metal particles over the support and showed higher CO removal efficiency with low activation energy. Compared to CuO/CeO₂ catalysts with commercial CeO₂, those with CeO₂ that was self-prepared by pyrolysis had a large pore volume and good crystal structure of CeO₂ and showed good performance. The catalytic activity for CO removal was in the following order: CuO/CeO₂-P (pyrolysis) > CuO/CeO₂-C (commercial) > CuO/CeO₂-D (deposition precipitation). CuO/CeO₂-P catalysts showed good activity even at low temperature. The CuO/CeO₂-P(300)-P-120 min catalyst was found to possess the good CO removal rate when the oxygen content was 6%, CO concentration was 500 ppm, catalyst weighed 1.0 g, pollutant gas velocity was 500 mL min⁻¹, SV was 3.7 × 10⁴ h⁻¹, and reaction temperature was 150 °C.     

Preparation and characterization of high surface area nanosheet titania with mesoporous structure

High surface area nanosheet TiO₂ with mesoporous structure were synthesized by hydrothermal method at 130 °C for 12 h. The samples were characterized by XRD, SEM, TEM, SAED, and BET surface area. The nanosheet structure was slightly curved and approximately 50–100 nm in width and several nanometers in thickness. The as-synthesized nanosheet TiO₂ had an average pore diameter about 3–4 nm. The BET surface area and pore volume of the sample are about 642 m²/g and 0.774 cm³/g, respectively.     

CuO/TiO2 nanocrystals grown on graphene as visible-light responsive photocatalytic hybrid materials

CuO/TiO₂ nanocrystals grown on graphene (CuO/TiO₂?CGR) were prepared by a simple hydrothermal method using Cu(CH₃COO)₂·H₂O and (NH₄)₂TiF₆ as precursors and graphene oxide (GO) as templates. The as-prepared composites were characterizated by TEM, XRD, FT?CIR to determine composition and phase purity. The photocatalytic activity of the samples was evaluated by photo-degradation of methylene blue (MB) aqueous solution under UV and visible light illumination. This work may provide new insights into preparing other inorganic graphene-based composites.     

A facile decoration of anatase Fe3O4/TiO2 nanocomposite with graphene quantum dots: Synthesis,characterization, and photocatalytic activity

A combination of electron-rich graphene quantum dots (GQDs) with Fe₃O₄/TiO₂ nanocomposites may develop an efficient electron transfer for enhanced photocatalytic activity. In this report, a facile decoration of GQDs with maltose precursor was synthesized and loaded onto magnetic anatase TiO₂ nanocomposites under hydrothermal methods. The as-synthetized magnetic TiO₂/GQDs nanocomposite resulted in a specific surface area of 38.00 m²/g and a total pore volume of 0.186 cm³/g. The HRTEM images showed a lattice plane distance of 0.350 nm related to the interplanar spacing of the anatase TiO₂ (1 0 1) plane and that of 0.299 nm observed for the in-plane lattice part of GQDs. The effects of magnetic loading ratio and GQDs loading onto TiO₂, pH, photocatalyst dosage, and methylene blue (MB) concentration were thoroughly evaluated to find the optimum conditions of mineralization MB for getting the highest photocatalytic efficiency. The removal efficiency of around 86.08 ± 3.62% was obtained at pH11, photocatalytic dose 400 mg/100 mL, and MB concentration 10 mg/L. Moreover, the photogenerated electron transfers and MB degradation mechanism by the resulting Fe₃O₄/TiO₂/GQD_S under irradiation of UVA light are proposed. The as-synthesized material improved meaningfully greater photocatalytic efficiency for degrading MB under UVA light irradiation than merely pure anatase TiO₂. Also, the predominant mechanism of MB degradation was direct oxidative decomposition through the photogenerated holes. The photocatalytic destruction of MB complied with the apparent first-order models under UVA light irradiation.     

2D Cobalt Chalcogenide Heteronanostructures Enable Efficient Alkaline Hydrogen Evolution Reaction

The development of high-efficiency non-precious metal electrocatalysts for alkaline electrolyte hydrogen evolution reactions (HER) is of great significance in energy conversion to overcome the limited supply of fossil fuels and carbon emission. Here, a highly active electrocatalyst is presented for hydrogen production, consisting of 2D CoSe₂/Co₃S₄ heterostructured nanosheets along Co₃O₄ nanofibers. The different reaction rate between the ion exchange reaction and redox reaction leads to the heterogeneous volume swelling, promoting the growth of 2D structure. The 2D/1D heteronanostructures enable the improved the electrochemical active area, the number of active sites, and more favorable H binding energy compared to individual cobalt chalcogenides. The roles of the different composition of the heterojunction are investigated, and the electrocatalysts based on the CoSe₂/Co₃S₄@Co₃O₄ exhibited an overpotential as low as 165 mV for 10 mA cm⁻² and 393 mV for 200 mA cm⁻² in 1 m KOH electrolyte. The as-prepared electrocatalysts remained active after 55 h operation without any significant decrease, indicating the excellent long-term operation stability of the electrode. The Faradaic efficiency of hydrogen production is close to 100% at different voltages. This work provides a new design strategy toward Co-based catalysts for efficient alkaline HER.     

Flower-like CuO synthesized by CTAB-assisted hydrothermal method

Flower-like CuO nanostructures have been synthesized by cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method. Here, CuCl₂·2H₂O was used as copper raw material, and sodium hydroxide was used as precipitate. The resulting CuO powders were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). X-ray diffraction (XRD) pattern exhibited the nanocrystalline nature with monoclinic structure for the as-synthesized nanostructures. FESEM images indicated that the flower-like CuO nanostructures are composed of many interconnected nanosheets in size of several micrometres in length and width and 60–80 nm in thickness. The possible formation mechanism of flower-like CuO nanostructures was discussed.     

Hydrogen peroxide-assisted hydrothermal synthesis of hierarchical CuO flower-like nanostructures

Hierarchical CuO nanostructures were synthesized through a hydrogen peroxide-assisted hydrothermal route in which Cu(OH)₂ was the copper source. The CuO nanostructures were composed of numerous nanobelts that radiated from the center of the nanostructure and formed a flower-like shape with a diameter of 5-10 μm. The nanobelts had lengths of 2.5-5 μm and widths of 150-200 nm. The H₂O₂ concentration directly influenced the product morphology. As the concentration of H₂O₂ increased, the length and width of the nanobelts increased and the quantity of the nanobelts decreased. The possible formation mechanism of hierarchical CuO flower-like nanostructures was presented.     

Fabrication and efficient photocatalytic degradation of methylene blue over CuO/BiVO4 composite under visible-light irradiation

CuO/BiVO₄ composite photocatalysts were prepared by solution combustion synthesis method and impregnation technique. X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scan electron microscopy and UV-vis diffusion reflectance spectra were used to identify the physical properties and photophysical properties of CuO/BiVO₄ composite photocatalysts. The photocatalysts exhibit the enhanced photocatalytic properties for degradation of methylene blue under visible-light (λ > 420 nm). The mechanism of improved photocatalytic activity is also discussed.     

Stable controlled growth of 3D CuO/Cu nanoflowers by surfactant-free method for non-enzymatic hydrogen peroxide detection

Sensitive, convenient and rapid detection of hydrogen peroxide(H_2 O_2) is highly desirable in fields like fundamental biological research, food industries, and clinical environmental analysis. Herein, a hierarchical porous CuO/Cu flower-like active electrode material for non-enzymatic H_2 O_2 sensor was synthesized via a low-cost and one-step chemical oxidation of Cu powder in water bath without surfactants. In order to discuss the growth mechanism of the product, products with different growth time length were fabricated. The electro-catalysis of all products were first exhibited by cyclic-voltammetry,and the product under 6 h reaction shows the best result. The detailed electro-catalytic behaviors of the best product(under 6 h reaction) are characterized by cyclic-voltammetry and amperometry under alkaline conditions. The materials have high sensitivity of 103 μA mM~(-1) cm~(-2)(R~2= 0.9979), low detection limit of 2 μmol/L and wide concentration range(from 2 μmol/L to 19.4 mmol/L). Large specific surface area and stabled nanostructure enabled good features, such as stability and sensitivity for the H_2 O_2 determination.     

Simple and efficient CVD synthesis of graphitic P-doped 3D cubic ordered mesoporous carbon at low temperature with excellent supercapacitor performance

Heteroatom doping is a promising strategy for improving the electrochemical performance of carbon materials. Herein, we spotlight an advantageous, simple, and efficient CVD synthesis of P-doped 3D cubic ordered mesoporous carbon (POMC) for the first time. The POMC was prepared by pyrolysis of acetylene/triphenylphosphine (C₂H₂/Ph₃P) mixture at relatively low temperature over Fe-KIT-6 as a sacrificial template. The ensuing P-doped OMC showed an enhanced porous texture than an undoped counterpart with a specific surface area of 403.5 m²/g, pore volume of 0.545 cm³/g, average pore size of 4.64 nm and suitable heteroatom functionalities with P and O contents of 0.13% and 9.83%, correspondingly. The obtained POMC exhibited a much higher specific capacitance of 288F/g at 0.2 A/g (175F/g for OMC), good cyclic stability of 97.6 %, and good rate capability than pristine OMC in 6 M KOH. It is equivalent to or improved than various stated mono doped and even dual doped porous carbon electrodes. Furthermore, a symmetric supercapacitor (POMC//POMC) was fabricated with 1 M Na₂SO₄ aqueous neutral electrolyte exhibits high cycling stability (89.3%) even with a wide potential window (2.0 V) and offers a relatively high energy density (10.01 Wh/kg) with a power density of 300 W/kg.     

Synthesis of flower-like CuO nanostructures via a simple hydrolysis route

We describe a facile route for the synthesis of flower-like CuO nanostructures by hydrolyzing of Cu(OAc)₂ solution without any surfactants. SEM and TEM observations indicate that the CuO products are composed of microspheres with diameters of 0.4-0.8 μm. The microspheres are in fact built from small needle-like nanocrystals with diameters of 10-15 nm. The method provides a convenient, low-cost, nontoxic route for the synthesis of nanostructures of oxide materials, and it is important for exploring oxide-based nanostructures for applications in nanodevices.     

Ultrasound assisted quick synthesis of square-brick-like porous CuO and optical properties

Square-brick-like CuC₂O₄ intermediate was synthesized quickly by an ultrasound and microwave assisted solution route in the presence of sodium dodecyl benzene sulfonate (SDBS) surfactant using CuCl₂ and K₂C₂O₄ as raw materials. The CuC₂O₄ was transformed into CuO with a preserved morphology by heating at 300 °C for 2 h. The products were characterized by XRD, TG-DTA, XPS, SEM, TEM, HRTEM and N₂ adsorption–desorption measurement. The light harvesting capability, photoluminescence and surface photovoltage properties of the CuO were investigated. The width and thickness of the obtained porous CuO square bricks are ca. 0.5–1 μm and 200 nm, respectively. Its average primary particle size is 12 nm. The formation mechanism of this square-brick-like CuO was investigated on the basis of series of controlling experiments. The results show that SDBS, C₂O₄^2? and ultrasonic processing play important roles in the formation of this square-brick-like morphology.     

Growth and characterization of flower-like Ag/ZnO heterostructure composites with enhanced photocatalytic performance

Flower-like Ag/ZnO heterostructure composites were prepared through a solvothermal method without surfactants or templates. The products were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and photoluminescence (PL) spectroscopy. Results demonstrate that flower-like Ag/ZnO heterostructure composites were composed of wurtzite ZnO flowers coated by face-center-cubic Ag nanoparticles. The growth process of flower-like ZnO crystals was investigated, and a possible growth mechanism was proposed. The photocatalytic activity of the as-prepared flower-like Ag/ZnO samples, pure ZnO samples, and commercial TiO₂ (Degussa, P-25) was tested with the photocatalytic degradation of methylene blue. Results show that the Ag/ZnO heterostructures were superior in photocatalytic activity to the pure ZnO samples and the commercial TiO₂ (Degussa, P-25), but the mixture of Ag (0.1 wt%) particles and ZnO flowers did not, which implies that the heterostructure promoted the separation of photogenerated electron–hole pairs, enhancing the photocatalytic activity. That was primarily verified by the PL results.     

CuO particles and plates: Synthesis and gas-sensor application

We reported on the synthesis and gas-sensor application of copper oxide particles and plates. CuO particles were prepared by a thermal decomposition method, while CuO plates were obtained by a hydrothermal route. The sensitivity of the as-prepared CuO to NO₂ gas and alcohol at varied temperatures was studied systematically. The results revealed that the as-synthesized products had high sensitivity and quick response/recovery time at an operating temperature of 200 °C. Furthermore, the CuO plates displayed higher sensitivity to NO₂ gas than that of the corresponding particles. This research indicated that CuO plates have potentials in the applications of sensors.     

Photocatalytic degradation and mineralization of dye pollutants from wastewater under visible light using synthetic CuO-VO2/TiO2 nanotubes/nanosheets

CuO-VO₂/TiO₂ as a new nanocomposite was synthesized through hydrothermal method and identified by various spectroscopic techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray analysis (EDX), UV–visible, differential reflectance spectroscopy (DRS), and Mott–Schottky. The presence of nanotubes/nanosheets in the synthesized nanocomposite was confirmed by HR-TEM. The anatase and rutile crystalline forms of TiO₂ were detected by Raman spectroscopy and X-ray diffraction (XRD). XPS analysis confirmed the presence of CuO and VO₂ in the nanocomposite. The surface area and the band-gap energy of the nanocomposite were determined via N₂ adsorption–desorption analysis and DRS. The presence of a p–n junction between TiO₂ (n-type) and CuO/VO₂ (p-type) was confirmed by the Mott–Schottky analysis. The photocatalytic activity of the nanocomposite against methylene blue (MB), methyl orange (MO), and cango red (CR) was studied under visible-light irradiation. The times of degradation for the decomposition of the dyes were 10–25 min. The rate constants of degradation for MB, MO, and CR were calculated as 0.34, 0.090, and 0.155 min^?1, respectively. The catalyst was recovered four times. In addition, the mineralization of the dyes was investigated by chemical oxygen demand (COD). The reaction was performed in the presence of different radical scavengers, and the ·OH was found to be the predominantly active species in the photodegradation of the dyes.

     

Synthesis and characterization of large mesoporous silica SBA-15 sheets with ordered accessible 18 nm pores

Mesoporous silica SBA-15 in the form of 10–30 µm sized sheets with unusually large ordered pores has been synthesized using heptane as a cosolvent in the presence of NH₄F. The resulting morphology of 400 nm thick sheets that contain easily accessed, hexagonally arranged, 18 nm sized pores running parallel to sheet normal has not been previously reported. The material has a BET surface area of 541 m²/g, large pore volume of 1.69 cm³/g and ordered mesopore structure with a narrow pore size distribution around 18 nm. A mechanism for sheet formation based on heptane droplets acting as sites for self assembling of silica crystallites is suggested.     

Controlled synthesis of mesoporous α-Fe2O3 nanorods and visible light photocatalytic property

Porous α-Fe₂O₃ nanorods with typical pore size of 2–4 nm were controlled prepared by a facile hydrothermal process of Fe(NO₃)₃·9H₂O aqueous solution in the presence of NaOH, followed by a calcination treatment. Contrast experiments indicate that the morphology and crystalline structure of the hydrothermal products depend greatly on the quantity of NaOH. Hematite nanoparticles and microplates were respectively obtained under conditions without or with excess NaOH. The porous α-Fe₂O₃ nanorods exhibit a high BET surface area of 105.1 m² g^?1 and a pore volume of 0.13 m³ g^?1. UV–vis measurement shows wide absorption to visible light and an obvious blue-shift of the adsorption edge due to the quantum size effect. The visible-light photocatalytic performances of the as-prepared samples were evaluated by photocatalytic decolorization of methylene blue at ambient temperature. The results indicate that the photocatalytic activity of the porous α-Fe₂O₃ nanorods is superior to hematite nanoparticles and platelets and exhibit good reusable feature. The photocatalytic process of porous structure is determined to be pseudo-first-order reaction with apparent reaction rate constant of 1.04 × 10^?2 min^?1. And the optimum photocatalyst dosage is 20 mg per 100 mL of dye solution. The porous α-Fe₂O₃ nanorods are considered potential photocatalyst for practical application due to the excellent photocatalytic behavior and good reusability.