Shape-controlled synthesis of cobalt oxide nanocrystals using cobalt acetylacetonate

Cobalt oxide nanocrystals (NCs) with different morphologies have been successfully synthesized through the decomposition of cobalt (II) acetylacetonate (Co(acac)₂) in nonpolar solvent. The growth temperature of NCs was set at 30 °C lower than the nucleation temperature to prepare monodisperse NCs. By tuning the injection speed of paraffin oil, CoO nanoparticles and nanoflowers have been obtained, respectively. The variation in ligand concentration changing speed due to different injection speed of extra paraffin oil is supposed to be the reason for the formation of CoO NCs with different nanostructures. The structure and shape properties of as-synthesized cobalt oxide NCs have been studied and characterized using XRD and TEM.     

Morphological investigation on cobalt oxide powder prepared by wet chemical method

In this paper cobalt oxide has been prepared by wet chemical method using Co(NO₃)₂ sol (Co: 80 g/L) and NaHCO₃ sol (100 g/L) as starting materials. When organic reagent: ethanol, acetone, and Polyethylene glycol-400 (PEG-400) (all are 2 mL) or three sodium salts: sodium chloride, sodium sulfate and sodium acetate (all are 1 g) had been introduced into reaction as inert additives once every time, and the measurement of PH value, zeta potential and viscosity in all solutions retains on the same level of magnitude, but the SEM shows that specific shapes of cobalt oxide particle is obtained after firing of CoCO₃ at 300 °C for 2 h in air. The DLVO theory discloses effect of dielectric constant of organic reagent and steric hindrance effect is the main factor for big molecular PEG-400. By replacing partly Co(NO₃)₂ with CoCl₂, the behavior of Cl⁻ is studied in the process of nucleus growth, the results show that Cl⁻ existed in the structure of nucleus with the content from 1300 to 2400 ppm, the structure, which can stand several time washing in an ultrasonic bath after reaction, but collapse as soon as it is fired at 300 °C for 2 h in air. It is reasonable to conclude that there may be directed anion chemical adsorption existed in cobaltous carbonate structure, which results in corresponding cobalt oxide particle morphology via anisotropic growth of nucleus.     

Thin cobalt oxide films for catalysis deposited by plasma-enhanced metal-organic chemical vapor deposition

The plasma-enhanced metal-organic chemical vapor deposition was used to prepare thin films of cobalt oxide starting with cyclopentadienyldicarbonyl-cobalt(I) (CpCo(CO)₂) mixed with argon and oxygen. The films were characterized by Raman and Fourier transform infrared spectroscopies, electron diffraction, and energy dispersive X-ray microanalysis. Their thickness was estimated by ellipsometric measurements. Catalytic properties of the films were tested in oxidation of n-hexane. It has been found that spinel-type Co₃O₄ nanoclusters with a crystallite size of 4-6 nm are formed in the deposits. Amorphous carbon and amorphous CoO_x phases are also observed in the films. The content of these phases depends on the molar fraction of oxygen in the gas mixture. Preliminary catalytic tests have shown that precalcined Cr-Al steel carrier covered by the plasma-deposited films reveals much higher catalytic effect then the non-deposited substrate.     

Electrochemical oxidation of phenol in a parallel plate reactor using ruthenium mixed metal oxide electrode

In this study, electrochemical oxidation of phenol was carried out in a parallel plate reactor using ruthenium mixed metal oxide electrode. The effects of initial pH, temperature, supporting electrolyte concentration, current density, flow rate and initial phenol concentration on the removal efficiency were investigated. Model wastewater prepared with distilled water and phenol, was recirculated to the electrochemical reactor by a peristaltic pump. Sodium sulfate was used as supporting electrolyte. The Microtox bioassay was also used to measure the toxicity of the model wastewater during the study. As a result of the study, removal efficiency of 99.7% and 88.9% were achieved for the initial phenol concentration of 200 mg/L and chemical oxygen demand (COD) of 480 mg/L, respectively. In the same study, specific energy consumption of 1.88 k Wh/g phenol removed and, mass transfer coefficient of 8.62 x 10(-6)m/s were reached at the current density of 15 mA/cm(2). Electrochemical oxygen demand (EOD), which can be defined as the amount of electrochemically formed oxygen used for the oxidation of organic pollutants, was 2.13 g O(2)/g phenol. Electrochemical oxidation of petroleum refinery wastewater was also studied at the optimum experimental conditions obtained. Phenol removal of 94.5% and COD removal of 70.1% were reached at the current density of 20 mA/cm(2) for the petroleum refinery wastewater.     

Facile and green synthesis of highly dispersed cobalt oxide (Co3O4) nano powder: Characterization and screening of its eco-toxicity

A novel green synthesis of cobalt oxide (Co₃O₄) nanoparticles using latex of Calotropis procera via simple precipitation method at room temperature was investigated. An extensive characterization of the product was carried out using X-ray diffractometry (XRD), Differential scanning calorimetry (DSC), Transmission electron microscopy (TEM), Energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR) and UV–Visible spectroscopy. The results of the characterization confirmed that the synthesized nanomaterial is highly dispersed. TEM analysis revealed that the nano particles are having an average size around 10?nm. The eco-toxic investigation suggested that the particles are non-toxic and safe towards the environment. This green strategy proves to be an effective, fast, simple and cost-effective approach for the synthesis of Co₃O₄ nanoparticles for various applications.     

Removal of Co ions from aqueous solution by cation exchange sorption onto NiO

Batch adsorption technique was used to study the adsorption of cobalt on NiO. The aim of this work was to examine the effect of pH, concentration and temperature on the ion exchange removal of Co²⁺ from aqueous solution by the NiO surface. We used Langmuir model to interpret the adsorption data. The Kurbatov-type plots were tested to determine the adsorption mechanism. The kinetics of Co²⁺ adsorption on NiO was best described by film diffusion model. A well-known thermodynamic equation was used to assess the enthalpy and entropy of the system. The thermodynamic data were indicative of the spontaneous nature of the endothermic sorption process of Co²⁺ onto the NiO.     

Sol-gel derived zinc oxide films alloyed with cobalt and aluminium

ZnO films codoped with 5 at.% Co and 1 at.% Al were prepared by sol-gel technique on corning glass and silicon substrates with precursor sols of different pH values. The pH was varied from 5.4 to 11 by adding varying amounts of monoethanolamine to the sol. Since pH plays an important role in controlling the properties of films, we discuss in detail the effect of pH value on the structural, morphological and optical properties of the grown films. X-ray diffraction and atomic force microscopy images reveal that the size of crystallites increases with pH of the sol. The variation of pH in the reaction system influences the density of homogeneous nucleation and the crystal growth along the c-axis. High quality Co and Al codoped ZnO films annealed at 600 °C have been obtained using a sol with pH = 9. These sol-gel derived films find their suitability to be used as dilute magnetic semiconductors.     

Influence of deposition conditions on the morphology and phase of tungsten oxide nanorods synthesized by thermal oxidation

When synthesizing tungsten oxide nanorods using thermal oxidation,the deposition conditions play an important role in the morphology and phase structure.The evaporation voltage greatly influences the a...     

Formation and characterization of cobalt oxide layers on polyimide films via surface modification and ion-exchange technique

Polyimide (PI) films with thin cobalt oxide (Co₃O₄) layers on both film sides have been prepared via a surface modification and ion-exchange technique. The method works by hydrolyzing the PI film surfaces in aqueous potassium hydroxide solution and incorporating Co²⁺ into the hydrolyzed layers of PI film via subsequent ion exchange, and followed by thermal treatment in ambient atmosphere. The PI composite films were characterized by Attenuated total reflection-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractions, scanning electron microscopy, transmission electron microscopy and thermogravimetric analyses, as well as surface resistance and mechanical measurements. By varying the absorbed cobalt ion content, a series of PI/Co₃O₄ composite films with insulative to semiconductive surfaces were obtained. The room temperature surface resistances of the semiconductive composite films reached to about 10⁷ Ω. The Co₃O₄ particle formed on PI film surfaces was in the range of 10-40 nm. The final composite films maintained the essential mechanical properties and thermal stability of the pristine PI films. The adhesion between surface Co₃O₄ layers and PI matrix was acceptable.     

Enhanced oxygen exchange near the oxide/silicon interface during silicon thermal oxidation

The effect of the SiO₂/Si interface on oxygen exchange diffusion during oxidation was investigated using oxygen isotopes. A 40-nm thick Si¹⁸O₂ layer was first grown in ¹⁸O₂ and then the sample was reoxidized in ¹⁶O₂ at 1100 °C. The ¹⁸O diffusion in Si¹⁶O₂ during the ¹⁶O₂ oxidation was investigated by secondary ion mass spectrometry measurements. A significant broadening of the ¹⁸O profile toward the newly grown Si¹⁶O₂ was observed. The average oxygen diffusivity was initially about one order of magnitude larger than the reported thermal diffusivity in the SiO₂ network. In addition, the ¹⁸O diffusion became slower with oxidation time and hence with increasing distance between ¹⁸O diffusion region and the interface. This distance-dependent ¹⁸O self-diffusion was simulated taking into account the effect of Si¹⁶O molecules generated at the interface upon oxidation and diffusing into SiO₂ to enhance the oxygen exchange. The simulation fits the SIMS profiles and shows that the SiO diffusion is greatly retarded by the oxidation with O₂ from the oxygen-containing atmosphere. Therefore, the Si¹⁶O concentration becomes smaller as the interface leaves the ¹⁸O region and the oxygen exchange becomes slower with time.     

Preparation of a novel zwitterionic graphene oxide-based adsorbent to remove of heavy metal ions from water: Modeling and comparative studies

A novel zwitterionic graphene oxide-based adsorbent was first synthesized in a multistep procedure including the successive grafting of bis(2-pyridylmethyl)amino groups (BPED) and 1,3-propanesultone (PS) onto graphene oxide (GO) sheets. Then, the as-prepared materials were used as adsorbent for the removal of metal ions from aqueous solutions. The influence of solution pH, contact time, metal ion concentration, and temperature onto the adsorption capacity of the zwitterionic GO-BPED-PS adsorbent was investigated and compared with the GO-BPED adsorbent. In particular, it was shown that the maximum adsorption capacities of the GO-BPED-PS adsorbent were as high as 4.174 ± 0.098 mmol.g^?1 for the Ni(II) ions and 3.902 ± 0.092 mmol.g^?1 for the Co(II) ions under optimal experimental conditions (metal ion concentration = 250 mg.L^?1, pH = 7 and T = 293 K). In addition, the adsorption behaviors of Ni(II) and Co(II) ions onto both the GO-BPED and GO-BPED-PS adsorbents fitted well with a pseudo-second-order kinetic model and a Jossens isotherm model. Moreover, adsorption thermodynamics of Ni(II) and Co(II) ions have been studied at various temperatures and confirmed the exothermic adsorption nature of the adsorption process onto the GO-BPED-PS adsorbent. Furthermore, the zwitterionic GO-BPED-PS adsorbent retained good adsorption properties after recycling 18 times which is much better than the conventional adsorbents.     

Evolution of potential distributions during the charging of nano-structured metal oxide films in air as response to sudden voltage application

Using metal oxide film structures, which were originally designed for gas sensing applications, we measured the charging and discharge currents and potential distributions on several metal oxide coatings after the application of an electrical potential against earth. The potential distributions show a specific charging of the surface with oxygen ions through the gas phase. The accumulated charge corresponds to that of the pseudocapacitors. Influence of air humidity has been found to be low, voltaic and temperature dependences of the charge are presented. The activation energy of discharge indicates a weak chemisorption of the charging oxygen species on the metal oxide surface.     

Stress and oxidation of nickel according to its purity

Abstract

The effect of impurities on the oxidation mechanism of nickel and on mechanical characteristics of the NiO scale was studied on two industrial grades and one pure nickel.

The oxidation mechanism at 800°C was clarified using kinetics approach, microstructure observations, EDX and XPS analyses, profilometry, oxygen isotopic exchange and SIMS.

The mechanical characteristics were determined mainly by three point bending tests performed in a scanning microscope.

Whatever the nickel grade, the oxide toughness varies with the scale thickness and tends towards the value of massive NiO. The main difference related to Ni purity consists in the fact that spalling occurs at an oxide/oxide interface for the industrial grades, while it appears at the metal/oxide interface for pure Ni.

Indeed, due to the presence of impurities, internal oxidation, extrusion of metallic nickel along grain boundaries of the substrate and formation of an inner equiaxed oxide film are observed in industrial grades. This induces mechanical keying of the oxide, and therefore crack propagation in a mixed mode is easier at the oxide/oxide interface.

With pure nickel, only a single oxide film is formed by outward diffusion of Ni and there is no internal oxidation. Thus crack propagation occurs along the metal/oxide interface.     

Heavy metal ions adsorption and photodegradation of remazol black XP by iron oxide/silica monoliths: Kinetic and equilibrium modelling

The adsorption of heavy metal ions (Cr³⁺, Pb²⁺ and Cd²⁺) by metal oxide monoliths (Fe₂O₃ and Fe₂O₃/SiO₂) synthesized via nanocasting method using SiO₂ monoliths as a template was studied. The adsorption experiments were performed in different batches by varying key parameters and the equilibrium between the adsorbents and metal ion solution was achieved in ～120?min at pH 6. The maximum monolayer adsorption efficiency for Pb (II), Cr (III) and Cd (II) ions was 850, 770 and 690?mg/g, respectively, for the magnetic Fe₂O₃/SiO₂ monoliths. The experimental data show best fit with the pseudo-second-order reaction type. The adsorption data found to be well fitted using Freundlich and Langmuir adsorption isotherms. The adsorption process was exothermic and spontaneous in nature, as confirmed by the thermodynamic parameters. Furthermore, the photocatalytic degradation of an industrial dye e.g., remazol black XP (RxP) by Fe₂O₃/SiO₂ monoliths was done from wastewater and the photocatalytic efficiency of the monoliths (using different amount) has been evaluated under visible light source which gives the best results (97.8%) for the monolith concentration 0.10?g/L.     

石墨化对微螺旋炭纤维热氧化动力学的影响

以乙炔为碳源,镍粉为催化剂,噻吩为助催化剂,采用化学气相沉积法制备微螺旋炭纤维;在氩气气氛中,2500℃下对所制微螺旋炭纤维进行石墨化处理.通过扫描电子显微镜观察微螺旋炭纤维的螺旋形貌和微观结构,用热重法研究微螺旋炭纤维的耐氧化性能,并探讨了微螺旋炭纤维的氧化动力学行为.结果表明:石墨化处理对微螺旋炭纤维具有显著的纯化作用,其螺旋形貌基本保持不变.微螺旋炭纤维的氧化反应较好地服从一级反应.微螺旋炭纤维石墨化前后的氧化反应活化能分别为263.004kJ/mol和297.191kJ/mol.石墨化处理明显提了微螺旋炭纤维的抗氧化性能.     

Deep oxidation of pollutants using gold deposited on a high surface area cobalt oxide prepared by a nanocasting route

A new acrylic anion exchanger with both tertiary and quaternary ammonium as well as ketone groups in the structural unit has been prepared by the nucleophilic substitution reaction of aminolyzed vinylacetate:acrylonitrile:divinylbenzene copolymer of porosity structure in the swelling state with 2-chloroacetone as a halogenated compound. The new compound exhibits better qualities of strong base exchange capacity than the weak base anion exchangers. The obtained acrylic anion exchanger was used to remove Cr(VI) from the aqueous solution. Batch adsorption studies have been carried out to determine the effect of contact time, concentration of hexavalent chromium in the solution and pH on the sorption capacity. The kinetic parameters were determined on the basis of the static results. The thermodynamic parameters of Cr(VI) sorption process on the anion exchanger were calculated based on the Langmuir and Freundlich isotherms. Sorption was studied in the pH range of 1.5-7 and it was found that it depends on the solution acidity. At the pH values of 3.5 and 7 the anion exchanger exhibited large values of chromium sorption capacity. The speciation of chromium was investigated in the studied pH range by the Diffuse Reflectance Spectroscopy (DRS) method. Reduction of chromium(VI) to chromium(III) under acidic conditions was observed. The performed acrylic strong base anion exchanger is superior compared to the conventional one based on the styrene:divinylbenzene matrix due to its ability for reposition of the long spacer arm for providing exchange sites, hydrophilic character of matrix, and possible hydrogen bonds provided by carbonyl functional groups.     

Plasma oxidation of Al thin films on Si substrates

In this study, Al thin films deposited on silicon wafers by direct current magnetron sputtering were oxidized under radio frequency 13.56 MHz O₂ plasma at temperatures up to 550 °C. During oxidation, plasma powers as well as oxidation temperature and time were varied to investigate the oxidation behavior of the Al films. X-ray photoelectron spectroscopy and Auger electron spectroscopy results show that the apparent alumina could be observed after O₂ plasma treatment with powers above 200 W as well as at temperatures above 250 °C. However, no alumina increment could be discerned after individual either heat treatment at 550 °C or plasma treatment at room temperature. The thickness of alumina layers increased remarkably with plasma power and could reach about 60 nm when undergone 400 W O₂ plasma treatment at 550 °C for 2 h. Moreover, the thickness of alumina increased parabolically with time during plasma oxidation aided by thermal treatment. The deduced activation energy of such plasma oxidation was 19.1 ± 0.5 kJ/mol.     

Characteristics of titania supported copper oxide catalysts for wet air oxidation of phenol

Various techniques have been used to characterize the CuO(x)/TiO(2) catalysts with different copper loading. Surface area, pore volume and pore size distribution of the prepared catalysts were estimated from nitrogen adsorption isotherm. Temperature programmed reduction (TPR), X-ray diffraction (XRD), electron spin resonance (ESR), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) experiments were performed to investigate the chemical state of the copper species. The chemical state of copper in the CuO(x)/TiO(2) catalysts varied with copper loading (1-25wt.%): highly dispersed Cu(2+) cluster for 1 and 5wt.%, and bulk CuO for 7-25wt.%. The activity and mineralization selectivity of the CuO(x)/TiO(2) catalysts increased with copper loading up to 20wt.%, and remained almost constant for higher copper loading. The optimum copper loading was 20wt.% for the wet air oxidation of phenol over the CuO(x)/TiO(2) catalysts in this work. The stability of the CuO(x)/TiO(2) catalysts with different copper loading was also studied with respect to carbonaceous deposits and copper leaching.     

Effects of cobalt doping on nonlinearity of zinc oxide

The microstructures and electrical properties of ZnO–Bi₂O₃–CoO (ZBC), ZnO–Bi₂O₃ (ZB) and ZnO–CoO (ZC) ceramics were investigated. Cobalt oxide addition could reduce bismuth loss at high sintering temperature. The same amount of cobalt within ZnO grains was found in both specimens, ZBC and ZC, suggesting that bismuth had no effect on the dissolution of cobalt in ZnO and cobalt substitution for zinc in the ZnO structure. The highest nonlinear coefficient of about 19 was found in the ZBC varistor sintered at 1000–1100 °C. For the ZC specimens, nonlinear properties could also be obtained in this sintering temperature range.     

氧化处理时间对Ti6Al4V微弧氧化陶瓷膜的影响

采用交流微弧氧化法于：Na：SiO3-KOH-(NaPO3)6溶液中在％6A14V表面形成了氧化物陶瓷膜．利用扫描电镜、电子探针及X射线衍射研究了陶瓷膜的组织形貌、元素的分布和相组成．研究表明：在恒定的微弧氧化电参数(U =500V,U-=100V和f=600Hz)下,随氧化时间延长,电流密度逐渐降低,膜层厚度不断增加;相对致密均匀的膜分为3层：过渡层、致密层与疏松层．膜层主要由TiO2(锐钛矿和金红石)相组成,延长处理时间,锐钛矿相及金红石相的相对含量发生变化,金红石相TiO2逐渐增多,而锐钛矿相TiO2减小．膜层相的形成过程可分为两个阶段。