Preparation of Co3O4/graphene Oxide Composites by a Depositing‐decompostion Method and its Application for Electrochemical Determination of Glucose

Co₃O₄/graphene oxide (GO) nanocomposites were successfully prepared by a depositing‐decomposition method. The as‐prepared samples were characterized by scanning electron microscopy (SEM) and Raman spectroscopy. Cyclic voltammetry (CV) was used to evaluate the electrochemical response of a glass carbon electrode (GCE) modified with Co₃O₄/GO nanocomposite towards glucose. Compared with the Co₃O₄/GCE, the Co₃O₄/GO/GCE exihibits higher electrocatalytic activity due to the synergistic effects of electrocatalytic ability of Co₃O₄ and large surface of GO. The Co₃O₄/GO/GCE was applied for glucose detection in alkaline solution. The linear current response range of glucose on Co₃O₄/GO/GCE covered the range from 9 × 10^?5 to 6.03 × 10^?3 M, with a detection limit of 5.2 × 10^?7 M (S/N = 3).     

Nickel‐substituted cobalt ferrite nanoparticles supported on arginine‐modified graphene oxide nanosheets: Synthesis and catalytic activity

The amino acid arginine was used to modify the surface of graphene oxide nanosheets and then nickel‐substituted cobalt ferrite nanoparticles were supported on those arginine‐grafted graphene oxide nanosheets (Ni_0.5Co_0.5Fe₂O₄@Arg–GO). The prepared Ni_0.5Co_0.5Fe₂O₄@Arg–GO was characterized using flame atomic absorption spectroscopy, inductively coupled plasma optical emission spectrometry, energy‐dispersive spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, Raman spectroscopy, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. The application of Ni_0.5Co_0.5Fe₂O₄@Arg–GO as a catalyst was examined in a one‐pot tandem oxidative cyclization of primary alcohols with o ‐phenylenediamine to benzimidazoles under aerobic oxidation conditions. The results showed that 2‐phenylbenzimidazole derivatives were successfully achieved using Ni_0.5Co_0.5Fe₂O₄@Arg–GO nanocomposite catalyst via the one‐pot tandem oxidative cyclization strategy.     

One‐pot synthesis of magnetic palladium–NiFe2O4–graphene oxide composite: an efficient and recyclable catalyst for Heck reaction

A magnetically separable NiFe₂O₄@GO–Pd composite (GO = graphene oxide) was successfully prepared by a facile one‐pot hydrothermal strategy. This new kind of hybrid material was fully characterized using powder X‐ray diffraction, Raman spectroscopy, X‐ray photoelectron spectroscopy, transmission electron microscopy and vibrating sample magnetometry. Structural characterizations confirmed the formation of NiFe₂O₄ and Pd nanocrystals, and the close anchoring between nanoparticles and GO sheets. Additionally, the as‐prepared NiFe₂O₄@GO–Pd nanocomposite was effectively employed in the palladium‐catalyzed Heck reaction in an ethanol–water system as a green solvent. The catalyst was completely recoverable with the simple application of an external magnetic field and with no obvious loss of catalytic activity even after six repeated cycles. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of W‐doped TiO2 by low‐temperature hydrolysis: Effects of annealing temperature and doping content on the surface microstructure and photocatalytic activity

A series of tungsten‐doped Titania photocatalysts were synthesized using a low‐temperature method. The effects of dopant concentration and annealing temperature on the phase transitions, crystallinity, electronic, optical, and photocatalytic properties of the resulting material were studied. The X‐ray patterns revealed that the doping delays the transition of anatase to rutile to a high temperature. A new phase W_yTi_1‐yO₂ appeared for 5.00 wt% W‐TiO₂ annealed at 900 °C. Raman and diffuse reflectance UV–Vis spectroscopy showed that band gap values decreased slightly up to 700 °C. X‐ray photoelectron spectroscopy showed that surface species viz. Ti³⁺, Ti⁴⁺, O^2?, oxygen‐vacancies, and adsorbed OH groups vary depending on the preparation conditions. The photocatalytic activity was evaluated via the degradation of methylene blue using LED white light. The degradation rate was affected by the percentage of dopants. The best photocatalytic activity was achieved with the sample labeled 5.00 wt% W‐TiO₂ annealed at 700 °C.     

Magnetic solid‐phase extraction of brominated flame retardants from environmental waters with graphene‐doped Fe3O4 nanocomposites

Graphene‐doped Fe₃O₄ nanocomposites were prepared by a solvothermal reaction of an iron source with graphene. The nanocomposites were characterized by transmission electron microscopy, atomic force microscopy, X‐ray diffraction, superconducting quantum interference, Raman spectroscopy, Fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy. This nanomaterial has been used as a magnetic solid‐phase extraction sorbent to extract trace brominated flame retardants from environmental waters. Various extraction parameters were optimized including dosage and reusability of the nanocomposites, and pH of sample matrix. The reliability of the magnetic solid‐phase extraction protocol based on graphene‐doped Fe₃O₄ nanocomposites was evaluated by investigating the recoveries of 2,4,6‐tribromophenol, tetrabromobisphenol A, 4‐bromodiphenyl ether, and 4,4?‐dibromodiphenyl ether in water samples. Good recoveries (85.0–105.0%) were achieved with the relative standard deviation ranging from 1.1–7.1%. Moreover, it is speculated from characterization and magnetic solid‐phase extraction experiment that there is not only π–π stacking but also possible hydrophobic interaction between the graphene‐doped Fe₃O₄ nanocomposites and analytes.     

Effect of the premelting temperature and sample thickness on the polymorphic behavior of syndiotactic polystyrene/clay nanocomposites

X‐ray diffraction methods and differential scanning calorimetry thermal analysis have been used to investigate the structural changes of syndiotactic polystyrene (sPS)/clay nanocomposites. sPS/clay nanocomposites have been prepared by the mixing of sPS polymer solutions with organically modified montmorillonite. X‐ray diffraction data and differential scanning calorimetry results indicate that the dominating crystal forms and their relative fractions in sPS and sPS/clay nanocomposites are different for various premelting temperatures (T_max's). Higher T_max's favor the formation of the thermodynamically more stable β‐crystalline form, and its relative fraction has been obtained from the X‐ray diffraction data in the range of 11.5–13°. The intensity of the X‐ray diffraction data in the range of 11.5–13° decreases as the thickness of sPS/clay nanocomposites decreases from 150 to 20 μm. At the same time, the intensity of the X‐ray data in the range of 6–7° becomes sharper as the thickness of sPS/clay nanocomposites decreases. The calculation ratio based on the peak intensities at 6.2 and 6.8° for sPS/clay nanocomposites of equal thickness and crystallinity in the pure β and α forms has also been determined in this study. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1730–1738, 2003     

Influence of thermal annealing on the microstructure,hardness and corrosion behavior of TiAlSiCuN nanocomposite films

Nanocomposite TiAlSiCuN films were deposited on high speed steels by filtered magnetic arc ion plating. Detailed properties of the films annealed at various temperatures are studied. After thermal annealing at different temperatures ranging from 400 to 800 °C, changes in the film micro‐structure, chemical and phase composition, surface morphology, hardness and polarization curve properties were systematically characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy, scanning electron microscopy, nano‐indenter and electrochemical workstation, respectively. It was found that the TiAlSiCuN films could be fully oxidized at 800 °C, Al and Ti atoms all diffused outwards and formed dense protective Al₂O₃ and TiO₂ layer. Simultaneously, the TiAlN phase gradually disappeared. The films annealed at 400 °C obtained the highest hardness because of the certain grain growth and little generated oxides. Besides, the certain formation of dense protective Al₂O₃ layer made the TiAlSiCuN film annealed at 600 °C present the least corrosion current density and the corrosion voltage. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of Ag Nanoparticle Doped MnO2/GO Nanocomposites at a Gas/Liquid Interface and its Application in H2O2 Detection

Ag/MnO₂/GO nanocomposites were synthesized via the method of gas/liquid interface based on silver mirror reaction, and a non‐enzymatic H₂O₂ sensor was fabricated through immobilizing Ag/MnO₂/GO nanocomposites on GCE. The composition and morphology of the nanocomposites were studied by energy‐dispersive X‐ray spectroscopy (EDS), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Electrochemical investigation indicated that it exhibited a favorable performance for the H₂O₂ detection. Its linear detection range was from 3 μM to 7 mM with a correlation coefficient of 0.9960; the sensitivity was 105.40 μA mM^?1 cm^?2 and the detection limit was estimated to be 0.7 μM at a signal‐to‐noise ratio of 3.     

Studies of Nano－sized Co304 as Anode Materials for Lithium－ion Batteries

The structural evolution of the Co₃O₄ fine powders prepared by rheological phase reaction and pyrolysis method upon different temperature has been investigated using X‐ray diffraction (XRD) topography. The electrochemical performance of Co₃O₄ electrode materials for Li‐ion batteries is studied in the form of Li/Co₃O₄ cells. The reversible capacity as high as 930 mAh/g for the Co₃O₄ sample heat‐treated at 600 °C is achieved and sustained over 30 times charge‐discharge cycles at room temperature. The detailed information concerning the reaction mechanism of Co₃O₄ active material together with lithium ion is obtained through ex‐situ XRD topography, X‐ray photoelectron spectroscopy (XPS) analysis and cyclic voltammetry (CV) technique. And it is revealed that a “two‐step” reaction is involved in the charge and discharge of the Li/Co₃O₄ cells, in which Co₃O₄ active material is reversibly reduced into xCoO(3 ‐ x)CoO and then into metallic Co.     

Ein neuartiges Polyoxocobaltat(II)‐Anion in Rb2Co2O3

A New Polyoxocobaltate(II) Anion in Rb₂Co₂O₃ Rb₂Co₂O₃ was prepared via the azide/nitrate route. Mixtures of the precursors Co₃O₄, RbN₃ and RbNO₃ in the molar ratios 6:17:1 were heated in a special regime up to 450 °C and annealed at this temperature for 50 h in silver crucibles. Single crystals have been grown by subsequent annealing of prepared powder at 450 °C for 500 h in silver crucibles, which were sealed in glass ampoules under dried Ar. According to the X‐ray analysis of the crystal structure (Pnma, Z = 8, 11.729(2), 6.058 (1), 8.004(1) Å) cobalt is trigonal planar coordinated by oxygen atoms. The CoO₃‐units share through all corners and build up an infinite two‐dimensional Co₂O₃‐network.     

Magnetic ionic liquid‐assisted synthesis of polypyrrole/AgCl nanocomposites

The synthesis of polypyrrole (PPy)/AgCl nanocomposites with their size ranging around 70–100 nm are achieved by using magnetic ionic liquid as the oxidant in the interface polymerization system. The interface polymerization leads to the formation of uniform and unaggregated nanocomposites with a relatively narrow size distribution confined to submicrometer‐sized domains. The morphology and structure of the nanocomposites are characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and X‐ray diffraction (XRD). The potential application of PPy/AgCl nanocomposites as a H₂O₂ biosensor is also reported. Copyright © 2010 John Wiley & Sons, Ltd. Erratum: Magnetic ionic liquid‐assisted synthesis of polypyrrole/AgCl nanocomposites     

Evaluating the efficiency of the GO‐Fe3O4/TiO2 mesoporous photocatalyst for degradation of chlorpyrifos pesticide under visible light irradiation

In this work, the photocatalytic activity of the synthesized graphene oxide (GO)‐Fe₃O₄/TiO₂ mesoporous photocatalysts was evaluated using chlorpyrifos (CP) as a contaminant. The nano‐photocatalyst was characterized by X‐ray diffraction, field emission scanning electron microscopy with energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, and specific surface area by the Brunauer–Emmett–Teller method. Using visible light, the GO‐Fe₃O₄/TiO₂ mesoporous photocatalyst was investigated on the degradation of CP pesticide. The GO‐Fe₃O₄/TiO₂ photocatalyst displayed a good photocatalytic activity, which was achieving 97% of CP degradation after 60 min. Finally, experiments were performed to evaluate GO‐Fe₃O₄/TiO₂ mesoporous nanocatalyst activity on repeated applications; after several uses, its photocatalytic activity was retained, which indicated stability.     

Facile Synthesis of Graphene/Cobalt Oxide Nanohexagons for the Selective Detection of Dopamine

This work presents a simple green approach for the chemical synthesis of cobalt oxide nano hexagons (Co₃O₄ NHs) with an average size of 160±40 nm incorporated graphene nanosheets (GR). The techniques used to confirm the formation of GR−Co₃O₄ NHs are transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDX), and X‐ray diffraction spectroscopy (XRD). The dopamine (DA) sensor was fabricated by drop casting GR−Co₃O₄ NHs on the pre‐cleaned glassy carbon electrode (GCE). GR−Co₃O₄ modified GCE displayed a sensitive and selective electrochemical determination of DA compared to only GR and Co₃O₄ NHs modified GCE. Our fabricated sensor showed a wide linear range from 0.2 to 3443 μM with low limit of detection (84 nM) towards the determination of DA. The sensitivity of our fabricated sensor was calculated to be 108 μA mM⁻¹ cm⁻². As well, a significant storage stability, repeatability and reproducibility were attained by GR−Co₃O₄ NHs modified GCE. Human urine samples were targeted for the demonstration of practicality of our sensor.     

Applying Co3O4@nanoporous Carbon to Nonenzymatic Glucose Biofuel Cell and Biosensor

A novel hierarchically nanoporous carbon (NPC) derived from Al‐based porous coordination polymer is prepared by two‐step carbonization method for immobilization of the Co₃O₄ in the application of the nonenzymatic biofuel cells and biosensors. The structure and morphology are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), and X‐ray diffraction (XRD). Brunauer‐Emmett‐Teller (BET) is to characterize the porous nature of the NPC, and X‐ray photoelectron spectroscopy (XPS) is to characterize the composition of Co₃O₄@nanoporous carbon (Co₃O₄@NPC). Without collapse in the high carbonization temperature (above 1600 °C), the NPC maintains the nanoporous structure and high specific surface area of 1551.2 m² g⁻¹. In addition, the NPC is composited with Co₃O₄ by hydrothermal method to form the Co₃O₄@NPC. When tested as the nonenzymatic electrocatalyst for glucose oxidation reaction (GOR), the Co₃O₄@NPC exhibits higher response to glucose, in which the current shifts up by 64 %, than pure Co₃O₄ in 0.1 M KOH. The limit of detection is 0.005 mM (S/N=3) and response time is within 3 s. The detection range can be divided into two sections of 0.02–1.4 mM and 1.4–10.7 mM with the sensitivity of 249.1 μA mM⁻¹ cm⁻² and 66.6 μA mM⁻¹ cm⁻², respectively. A glucose fuel cell is constructed with the Co₃O₄@NPC as the anode and Pt/C catalyst as the cathode. The open‐circuit potential of the nonenzymatic glucose/O₂ fuel cell was 0.68 V, with a maximum power density of 0.52 mW cm⁻² at 0.27 V. This work may contribute to exploring other nanoporous carbons for application in glucose fuel cells and biosensors.     

H3PMo12O40‐immobilized chitosan/Co3O4: A novel and recyclable nanocomposite for the synthesis of pyrimidinedione derivatives

An efficient three‐component reaction of aromatic aldehydes, 6‐aminouracil/6‐amino‐1,3‐dimethyluracil and 4‐hydroxycoumarin in the presence of a novel heterogeneous catalyst H₃PMo₁₂O₄₀‐immobilized Co₃O₄/chitosan led to a synthesis of a new class of pyrimidinedione derivatives under reflux conditions. The magnetically recoverable nanocomposite of Co₃O₄/chitosan/H₃PMo₁₂O₄₀ was fully characterized by Fourier transform‐infrared spectrophotometry, scanning electron microscopy, X‐ray powder diffraction, energy‐dispersive X‐ray spectroscopy, vibrating‐sample magnetometry and N₂ adsorption–desorption by Brunauer–Emmett–Teller analysis. Results show that Keggin‐type 12‐molybdophosphoric acid immobilized into the network of the cross‐linked chitosan with super‐paramagnetic Co₃O₄ nanoparticles. The present method offers several advantages, such as simple procedure, short reaction times and excellent yields of products. The novelty of the catalyst, high catalytic activity, easy separation from the reaction with an external magnetic field and reusability of the catalyst in six consecutive runs are additional eco‐friendly attributes of this catalytic system.     

Shape‐Controlled Synthesis of NiCo2O4 Microstructures and Their Application in Supercapacitors

The shape‐controlled synthesis of NiCo₂O₄ microstructures through a facile hydrothermal method and subsequent calcinations was explored. By employing CoSO₄, NiSO₄, and urea as the starting reactants, flower‐like NiCo₂O₄ microstructures were obtained at 100 °C after 5 h without the assistance of any additive and subsequent calcination at 300 °C for 2 h; dumbbell‐like NiCo₂O₄ microstructures were prepared at 150 °C after 5 h in the presence of trisodium citrate and subsequent calcination at 300 °C for 2 h. The as‐prepared NiCo₂O₄ microstructures were characterized by X‐ray powder diffraction, field‐emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and (high‐resolution) transmission electron microscopy. Both the flower‐like and dumbbell‐like NiCo₂O₄ microstructures could be used as electrode materials for supercapacitors, and they exhibited excellent electrochemical performance, including high specific capacitance, good rate capability, and excellent long‐term cycle stability. Simultaneously, the shape‐dependent electrochemical properties of the product were investigated.     

Low temperature synthesis of Co<Subscript>2</Subscript>SiO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposite using a modified sol–gel method

The paper presents a study on the preparation of Co₂SiO₄/SiO₂ nanocomposites by a new modified sol–gel method. We have prepared gels starting from tetraethylorthosilicate (Si(OC₂H₅)₄), cobalt nitrate Co(NO₃)₂·6H₂O and some diols: ethylene glycol (C₂H₆O₂), 1,2propanediol (C₃H₈O₂) and 1,3propanediol (C₃H₈O₂), for a final composition: 30% CoO/70% SiO₂. During the heating of the gels at 140 °C, a redox reaction takes place between NO₃ ⁻ ions and diol with formation of some carboxylate anions. These carboxylate anions react with the Co(II) ions to form coordination compounds embedded in silica matrix, as evidenced by FT-IR spectrometry and thermal analysis. These Co(II) coordinative compounds thermally decompose in the range 250–300 °C to the corresponding oxides: CoO and/or Co₃O₄ inside the matrices pores. When CoO results, it reacts with SiO₂ at low temperature leading to Co₂SiO₄, which crystallizes at 700 °C. XRD patterns of the samples annealed at temperatures lower than 700 °C were characteristic to amorphous phases. The samples annealed at temperatures ≥700 °C, contain Co₂SiO₄ (olivine) as unique crystalline phase inside the amorphous silica matrix, according to XRD patterns. As evidenced by TEM images, Co₂SiO₄ nanoparticles are homogenously dispersed inside the silica matrix.     

Synthesis and Photocatalytic Properties of Nano‐crystalline In2O3

A nano‐crystalline In₂O₃ was synthesized using calcinations methods and was used as a photocatalyst to degrade sulfan blue (SB) dye. In addition, this study addresses the conditions of the degradation and the factors that influenced the catalysis. In₂O₃ was prepared by calcining In(OH)₃ at heat ranges of 100–700 °C for 24 h. The In₂O₃ was characterized using field emission scanning electron microscopy (FE‐SEM), an X‐ray diffractometer (XRD), thermogravimetric analysis (TGA), and high‐resolution X‐ray photoelectron spectroscopy (HR‐XPS). The activities of these samples were tested for the photocatalytic degradation of SB dye. The results indicated that the In(OH)₃ that was calcined at 300 °C for 24 h had the best performance.     

ZnO/Co3O4 Porous Nanocomposites Derived from MOFs: Room‐Temperature Ferromagnetism and High Catalytic Oxidation of CO

ZnO/Co₃O₄ porous nanocomposites were successfully fabricated by the thermal decomposition of Prussian Blue analogue (PBA) Zn₃[Co(CN)₆]₂ nanospheres obtained at room temperature. Interestingly, ZnO/Co₃O₄ porous nanocomposites exhibit room‐temperature ferromagnetism. Moreover, the ZnO/Co₃O₄ porous nanocomposites show good catalytic activity for CO oxidation, and the CO conversion rate reaches 100 % at 250 °C. It is suggested that the synergistic effect of each component, relative high surface area (32 m² g^?1) and porous structure lead to the promising catalytic properties.     

Deposition of copper‐doped iron sulfide (CuxFe1−xS) thin films using aerosol‐assisted chemical vapor deposition technique

Copper‐doped iron sulfide (Cu_xFe_1?xS, x = 0.010–0.180) thin films were deposited using a single‐source precursor, Cu(LH)₂Cl₂ (LH = monoacetylferrocene thiosemicarbazone), by aerosol‐assisted chemical vapor deposition technique. The Cu‐doped FeS thin films were deposited at different substrate temperatures, i.e. 250, 300, 350, 400 and 450 °C. The deposited thin films were characterized by X‐ray diffraction (XRD) patterns, Raman spectra, scanning electron microscopy, energy dispersive X‐ray analysis (EDX) and atomic force microscopy. XRD studies of Cu‐doped FeS thin films at all the temperatures revealed formation of single‐phase FeS structure. With increasing substrate temperature from 250 to 450 °C, there was change in morphology from wafer‐like to cylindrical plate‐like. EDX analysis showed that the doping percentage of copper increased as the substrate temperature increased from 250 to 450 °C. Raman data supports the doping of copper in FeS films. Copyright © 2010 John Wiley & Sons, Ltd.