A novel one-step electron beam irradiation method for synthesis of Ag/Cu2O nanocomposites

In this paper, a novel method for fabrication of silver/cuprous oxide (Ag/Cu₂O) nanocomposites is reported. The method involves the reduction of Ag⁺ and Cu²⁺ in the aqueous solution to Ag/Cu₂O without adding any reducing reagent under electron beam (EB) irradiation. Dye methyl orange is used as the pollutant model to investigate the photocatalytic properties of these nanocomposites. The results reveal that they have higher photocatalytic efficiencies than that of Cu₂O under visible light. These visible light-sensitive catalysts may have potential application in the field of environmental remediation.     

Cu2O/Ag复合物的合成及SERS原位分析其可见光催化降解活性

A multifunctional Cu₂O/Ag micro-nanocomposite, which has the characteristics of high catalytic activities under the visible light and high surface-enhanced Raman scattering (SERS) activity, was fabricated via a facile method and employed for the in situ SERS monitoring of the photocatalytic degradation reaction of crystal violet. Through the variation of the AgNO₃ concentration, Ag content on the Cu₂O template can be controllably tuned, which has great influence on the SERS effect. The results indicate that Ag nanoparticles form on the Cu₂O nanoframes to obtain the Cu₂O/Ag nanocomposite, which can act as an excellent bifunctional platform for in situ monitoring of photocatalytic degradation of organic pollutions by SERS.     

High-performance hierarchical cypress-like CuO/Cu<Subscript>2</Subscript>O/Cu anode for lithium ion battery

Composite CuO/Cu₂O/Cu anode for lithium ion battery was designed and synthesized via facile electrodeposition and the subsequent in situ thermal oxidation in air at 300 °C for 1 h. The as-prepared composite CuO/Cu₂O/Cu anode was studied in terms of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), galvanostatic charge/discharge, cyclic voltammetry (CV), and AC impedance. As expected, the composite CuO/Cu₂O/Cu with CuO-rich surface displayed hierarchical cypress-like morphology; furthermore, the hierarchical cypress-like CuO/Cu₂O/Cu anode also delivered satisfactory electrochemical performances. For example, the reversible discharge capacity remained at 534.1 mAh/g even after 100 cycles. The enhanced electrochemical performances were attributed to the hierarchical cypress-like porous structure and the synergistic effect among the composite active copper oxides and highly conductive Cu current collector.     

Shape evolution, photoluminescence and degradation properties of novel Cu2O micro/nanostructures

Three kinds of novel cuprous oxide (Cu₂O) micro/nanostructures are synthesized via a facile template-free hydrothermal method. Two factors are critical for the growth process of typical samples: the concentration of copper ions (Cu(II)) and the addition of Polyvinylpyrrolidone (PVP) as surfactant. It is found that the application of ethanol as solvent speeds up the reduction rate of Cu(II), and it promotes the aggregating of Cu₂O nanocrystals at the preliminary stage to form irregular spherical structures. Photoluminescence (PL) properties of the three kinds of samples and their photocatalytic activities for degradation of Methyl Orange (MO) are also measured. The sample with higher concentration of copper vacancy (V _Cu) defects has better photocatalytic ability, indicating that besides the morphology of Cu₂O nano/microcrystals, the defects in crystalline structures can also influence their electrical characteristics, and thus change their photocatalytic activity. This provides a potential method to improve the photocatalytic performances of Cu₂O crystals.     

Evaluating the electric property of different crystal faces and enhancing the Raman scattering of Cu2O microcrystal by depositing Ag on the surface

The surface electric property of Cu₂O microcrystal affects the interaction of facets with substance in the aqueous solution, and hence plays a key role in determining the photocatalytic activity. In this paper, the capability of Cu₂O microcrystals with exclusive {111}, {110} or both lattice surfaces in reducing Ag⁺ to Ag⁰ were investigated. Ag particles selectively deposited on {111} surfaces of Cu₂O, while not on {110} surfaces. The different behaviors of the two surfaces are mainly attributed to their different electric properties: negatively-charged {111} surfaces absorb Ag⁺ ions while positively-charged {110} surfaces repel them. Raman scattering of Cu₂O {111} surfaces was enhanced by the photo-deposition of Ag particles.     

Silver-tracer diffusion in Cu2O

The diffusion of¹¹⁰Ag in Cu₂O has been measured by a serial-sectioning technique as a function of temperature (700–1132°C) and oxygen partial pressure (6 × 10^?6 ?8 × 10^?2 atm). The data are fit to the defect model for Cu₂O developed by the authors in the preceding paper. Silver ions have a larger impurity-vacancy binding free energy and/or a larger jump frequency for the singly charged cation vacancies relative to that for the neutral cation vacancies. The activation enthalpies for the diffusion of copper and silver ions in Cu₂O are nearly equal, but the absolute value of D¹_Ag is about three times larger than D¹_Cu even though the silver ion is 31% larger than the copper ion.     

Synthesis,characterization and excellent photocatalytic activity of Ag/AgBr/MoO3 composite photocatalyst

A novel composite photocatalyst Ag/AgBr/MoO₃ was successfully synthesized via a simple precipitation method at room temperature. The obtained products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and UV–vis diffuse reflectance spectroscopy in detail. The photocatalytic activity of the samples was evaluated by monitoring the degradation of rhodamine B (RhB) solution under visible-light irradiation. The results showed that the photocatalytic activity of Ag/AgBr/MoO₃ composite significantly enhanced and the degradation ratio of RhB reached 97.7 % after 15 min only. The excellent photocatalytic activity might be closely related to the large surface area, porosity structure and efficient separation of photoinduced electron–hole pairs. The possible reaction mechanism was also discussed.     

Synthesis of starfish-like Cu2O nanocrystals through ��-irradiation and their application in lithium-ion batteries

In this study, single-crystalline starfish-like cuprous oxide (Cu₂O) nanocrystals with the backbones lengths in the range of 660 nm~16 ??m are successfully prepared through ??-irradiation, the cetyltrimethylammonium bromide (CTAB) is used as a capping material or soft colloidal templates. Without the addition of CTAB in the reaction system, irregular Cu₂O nanoclusters were obtained and their diameter is about 200 nm~1 ??m. Controlling the concentration ratio of CTAB to the copper ions, starfish-like morphology of Cu₂O can be obtained in high yield. Their structures are characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The possible growth mechanism of the starfish structure is discussed in the text. For potential application in lithium-ion batteries, an electrode made of the starfish-like Cu₂O shows excellent electrochemical cycling performance and high-rate capability. Compared with the Cu₂O nanoclusters, the starfish-like Cu₂O exhibits an improved electrochemical cycling stability. The capacity of the starfish-like Cu₂O can maintain 340 and 215 mAh g^?1 after 50 cycles at the rate of 0.1 C and 5 C, respectively. The reversible capacity holds 60% as the discharge?Ccharge rate even increases by 50 times.     

Photocatalytic degradation of methyl orange by gold silver nano-core/silica nano-shell

The silica nanoparticles (SiO₂ NPs), silver (Ag) NPs and gold (Au) NPs coated with SiO₂ NPs (core-shell) were prepared. The sizes and morphology of the particles were indicated. The three prepared NPs were used for photocatalytic degradation of methyl orange (MO) dye by xenon lamp. Rate of photocatalytic degradation reaction constant and lifetime were calculated for each catalyst. Moreover, the mechanism of the photocatalytic reaction was studied.     

Bifunctional photocatalysis of TiO2/Cu2O composite under visible light: Ti in organic pollutant degradation and water splitting

Photocatalytic experiment results under visible light demonstrate that both TiO₂ and Cu₂O have low activity for brilliant red X-3B degradation and neither can produce H₂ from water splitting. In comparison, TiO₂/Cu₂O composite can do the both efficiently. Further investigation shows that the formation of Ti³⁺ under visible light has great contribution. The mechanism of photocatalytic reaction is proposed based on energy band theory and experimental results. The photogenerated electrons from Cu₂O were captured by Ti⁴⁺ ions in TiO₂ and Ti⁴⁺ ions were further reduced to Ti³⁺ ions. Thus, the photogenerated electrons were stored in Ti³⁺ ions as the form of energy. These electrons trapped in Ti³⁺ can be released if a suitable electron acceptor is present. So, the electrons can be transferred to the interface between the composite and solution to participate in photocatalytic reaction. XPS spectra of TiO₂/Cu₂O composite before and after visible light irradiation were carried out and provided evidence for the presence of Ti³⁺. The image of high-resolution transmission electron microscopy demonstrates that TiO₂ combines with Cu₂O tightly. So, the photogenerated electrons can be transferred from Cu₂O to TiO₂.     

Synthesis of ZnO-SnO2 composite oxides by CTAB-assisted co-precipitation and photocatalytic properties

ZnO-SnO₂ composite oxides with various molar ratios of Sn:Zn have been synthesized at different calcination temperatures via a facile cetyltrimethylammonium bromide (CTAB)-assisted co-precipitation method with Zn(NO₃)₂·6H₂O and SnCl₄·5H₂O as starting materials. XRD, TEM, SEM and BET were employed to characterize the as-prepared samples. It has been found that amorphous intermediates appear between the evolutions of ZnO and SnO₂ crystals. The photocatalytic properties of the composite oxides were investigated using photocatalytic degradation of methyl orange as the probe reaction. The results show that the ZnO-SnO₂ composite oxide with a cube morphology exhibits the best photocatalytic activity, which was prepared with a molar ratio of Zn:Sn of 2:1 and calcination temperature of 700 °C.     

Preparation of Cu 2 O nanoparticles dispersed in NH 2 -terminated polyethyleneoxide matrix

Small Copper (I) oxide, Cu₂O, nanoparticles dispersed in diamine-terminated polyethyleneoxide (PEO-NH₂) matrix have been successfully prepared by vacuum evaporation of copper onto the molten PEO-NH₂. The obtained composite were characterized by TEM, electron diffraction, TG-DTA and FT-IR spectroscopy. The stable composite, in which the Cu₂O nanoparticles are stabilized through interaction between NH₂ chain end groups of PEO molecules and Cu₂O nanoparticles was obtained when the samples were heat-treated at 110 ^° C. The mean size of the Cu₂O nanoparticles increased from 2.5 to 3.5 nm in diameter upon increasing the amount of initial Cu deposition. The obtained composite material having a waxy texture was soluble in many solvents without aggregation and can be handled as a simple chemical compound for starting material in various applications. Received 29 November 2000     

Au/Cu2O core/shell nanostructures with efficient photoresponses

Metal/semiconductor nanoscale heterojunctions are of pronounced attention because of their specific structures and properties that vary in their individual counterparts and anticipated applications in photo-driven fields. A modified facile method is reported in this connection for the formation of cuprous-oxide coated gold (Au/Cu₂O) nanostructures including octahedral, cuboctahedral and flower-like structures using cubic and multi-faceted gold nanostructures as the core material. The well-organized shape growth of the Cu₂O-shell is accomplished via an adequate adjustment of the ratio H₂O:NH₂OH^·HCl in the solution. The effect of nanoparticle's shape and thickness of the shell on the optical properties of truncated-octahedra, cuboctahedra and flower-like Au/Cu₂O nanostructures (having sizes within 90–230 nm) shows a bathochromatic shift in the surface plasmon resonance (SPR) band of the Au-core with the increase of shell thickness. A comparative study to correlate the photoluminescence analyses of core/shell nanostructures with their photocatalytic activities shows that truncated-octahedra and nanoflowers, bounded by {111} facets, are photocatalytically more active. On the other hand, cuboctahedra with more {100} catalytically inactive sites reveal a comparatively sharp emission peak. These photoresposes are also appeared to be affected by SPR coupling between plasmonic metal-core and semiconducting-shell.     

Synthesis and characterization of Ag/BiVO4 composite photocatalyst

Ag/BiVO₄ composite photocatalysts were hydrothermal synthesized and characterized by XRD, SEM, XPS and DRS techniques. Their photocatalytic activities were determined by oxidative decomposition of methyl orange in aqueous solution under visible light irradiation. It revealed that the doped Ag species greatly improved the visible light absorption abilities and morphologies of the composites, and thus lead to enhanced photocatalytic activities compared with that of the pure BiVO₄.     

Photocurrent characteristics in Cu2O/Pt and Cu2O/TiO2 photoelectrochemical cells in aqueous and non-aqueous electrolytes

Photocurrent characteristics of the Cu₂O/Pt and Cu₂O/TiO₂ photoelectro-chemical cells have been presented. In aqueous solution, a slow deterioration of power output occurs approximately at the rate of 50% per day. Operation in non-aqueous solutions (acetonitrile and ethanol) also produced a deterioration of power output. However in ethanol, it was found that the deterioration reversed itself and a new cycle of deterioration and rejuvenation began. These suggest that the deterioration is not due to a chemical reduction process at the electrode surface but other factors such as migration of charged defect centres in the depletion layer or chemical reaction on the electrode surface.     

Photocatalytic properties of zinc oxide nanorods grown by different methods

A comparison of photocatalytic properties of ZnO nanostructures fabricated by different methods was carried out. The photocatalytic properties of as grown and Ar-ion-treated ZnO materials were tested using photocatalytic degradation of an aqueous solution of methyl orange dye serving as a model water contaminant. The reaction rate constants of methyl orange photodegradation for untreated ZnO nanorods grown by the method of gas-transport reactions and hydrothermal method were equal to 5.3 × 10^?5 and 3.7 × 10^?4 s^?1, respectively, whereas for the case of the Ar-ion-treated samples they reached 1.85 × 10^?4 and 5.9 × 10^?4 s^?1, respectively. Based on the analysis of the photoluminescence spectra, it is assumed that the difference in photocatalytic activity is connected with different type of defects predominant on the surfaces of ZnO nanorods grown by the hydrothermal and gas-transport reactions methods. The experimental results show that ZnO nanostructures grown by the hydrothermal method would be promising for producing efficient catalysts.     

EPIR effect of Cu2O films by electrochemical deposition

Cuprous oxide (Cu₂O) films and Cu/Cu₂O/Cu/FTO sandwich structures were prepared by electrochemical deposition on conductive FTO substrates with different pH value conditions but constant deposition potential. The phase composition, crystal structure and microstructure of the Cu₂O films were characterized by XRD, SEM and EDS as well as by Electric–Pulse–Induced–Resistance (EPIR) perturbation. In particular, the switching effects of the Cu/Cu₂O/Cu/FTO device are examined in this work. The result shows that the EPIR-effect is large for the Cu/Cu₂O/Cu/FTO device at room temperature and strongly related to the pH value of the solution. In both acidic and neutral conditions, for example at pH = 5, 6 and 7, the EPIR effect is significant and decreases with increasing pH value. It disappears when the pH value goes further into the alkaline regime, i.e. pH = 8, 9 and 10. Space charge barriers at the interface of electrode and Cu₂O are used to explain the I–V characteristic of the layer structure and the EPIR-effect.     

Photo-induced charge separation and photocatalytic activity of Ga-doped SnO2

Ga-doped SnO₂ with different molar ratios of Ga/Sn (1, 2, 3, and 4 %) was prepared by a facile co-precipitation route. The photocatalysts prepared were characterized by N₂ adsorption–desorption measurements, X-ray diffraction, UV/Vis diffuse reflectance spectroscopy, and scanning electron microscope. The separation efficiency of photo-generated charge was studied using benzoquinone as scavenger. Hydroxyl radicals produced during photocatalytic process were detected by a terephthalic acid photoluminescence probing technique. Doping Ga³⁺ into SnO₂ can greatly enhance the separation efficiency of photo-induced charge and the formation rate of hydroxyl radicals. The superoxide radical is the main active species during the photocatalytic process. The catalytic activity of photocatalysts for decolorization of methyl orange in aqueous solution was investigated. Among the photocatalysts prepared, Ga-doped SnO₂ with 3 %Ga possesses the best photocatalytic activity and the underlying mechanism is suggested.     

Magnetic and structural properties of Cu0.85Fe0.15O system synthesized by co-precipitation

Cu_0.94Fe_0.06O and Cu_0.85Fe_0.15O samples were synthesized by using the co-precipitation chemical method. Starting from aqueous solutions of copper nitrate, CuO (NO₃)₂ 3H₂O, iron nitrate, Fe (NO₃)₃ 9H₂O and sodium hydroxide as precipitating agent, NaOH. The precipitate of three samples for Cu_0.94Fe_0.06O and five for Cu_0.85Fe_0.15O of fine powder were calcined for 5 h at different temperatures. The obtained X rays diffraction patterns refined by the Rietveld method show the CuO characteristic pattern, showing that the Fe atoms enter to replace Cu atoms. Furthermore, it was obtained that the crystallite size decreases with calcination temperatures for Cu_0.94Fe_0.06O. The transmission Mössbauer spectroscopy showed that the samples present a disordered paramagnetic behavior due to the big value of the half-width of line of the quadrupolar splitting. Vibrating sample magnetometry confirms the paramagnetic character. The XRD results indicate that the material is nanostructured, due that the crystallite sizes are of the order of 10 nm for Cu_0.94Fe_0.06O and 40 nm for Cu_0.85Fe_0.15O.     

Unusually Large Lattice Mismatch‐Induced Optical Behaviors of Au@Cu–Cu2O Core–Shell Nanocrystals with Noncentrally Located Cores

To extend the optical property characterization of metal–Cu₂O polyhedra, 50 nm Au@Cu cubic cores are used to fabricate Au@Cu–Cu₂O core–shell cubes, octahedra, and rhombic dodecahedra with tunable sizes. Despite the unusually large lattice mismatch of 15.1% between Cu and Cu₂O, fine adjustment in the volumes of reagents introduced allows the formation of these heterostructures. To relieve the lattice strain, the metal cores are essentially never found to locate at the particle center, and slight lattice spacing shifts are recorded. Although efforts are made to reduce the heterostructure sizes, the Cu₂O shells are generally too thick to reveal surface plasmon resonance (SPR) absorption band from the metal cores. Only the Au@Cu–Cu₂O cubes with many cores located near the particle corners show observable SPR band red‐shift, but UV–vis spectra of all particle shapes are still dominated by Cu₂O absorption and light scattering bands. Au@Cu–Cu₂O cubes consistently show the most red‐shifted absorption bands than those of octahedra resulting from the optical facet effects.