Co3O4 Concentration Research Articles

Preparation and optical properties of high-quality green cobalt sapphires

A series of (Al2O3)100-x(Co3O4)x (x = 0, 0.04, 0.1, 0.2, 0.3, 0.4) single crystals were successfully prepared by the optical floating zone method for the first time, even though natural cobalt-containing sapphires have not been observed. It has been found that the (Al2O3)99.70(Co3O4)0.30 single crystal is a high-quality, beautiful, and stable green cobalt sapphire like an emerald, and its density is 3.984 g/cm3. XRD and Raman spectra of the (Al2O3)100-x(Co3O4)x crystals show that cobalt is successfully incorporated in the Al2O3 which retains its hexagonal structure. Two strong broad absorption peaks at 436 nm and 652 nm were observed in the UV–Vis absorption spectra, which are assigned to the 1A1→1T1 and 1A1→1T2 transitions of Co3+, respectively. Whilst the optical band gaps were in the range 4.43–3.95 eV. Under excitation at 436 nm, one strong emission peak at 864 nm and a weak emission peak at 692 nm were found in the photoluminescence (PL) spectra of the cobalt sapphires. At Co3O4 concentrations lower than 0.30 mol%, the intensities of both emission peaks increase with Co3O4 concentration, and reach their maxima at 0.30 mol%, then decrease with the further increases in Co3O4. Also, X-ray excited luminescence (XEL) spectra show that the cobalt sapphires have a high sensitivity for X-ray detection. Overall, cobalt sapphires can have various potential uses, such as in jewelry, as ultraviolet detectors, in X-ray detection, and in near-infrared emission devices.

Nanocomposite Co3O4-ZnO Thin Films for Photoconductivity Sensors.

Thin nanocomposite films based on zinc oxide (ZnO) added with cobalt oxide (Co3O4) were synthesized by solid-phase pyrolysis. According to XRD, the films consist of a ZnO wurtzite phase and a cubic structure of Co3O4 spinel. The crystallite sizes in the films increased from 18 nm to 24 nm with growing annealing temperature and Co3O4 concentration. Optical and X-ray photoelectron spectroscopy data revealed that enhancing the Co3O4 concentration leads to a change in the optical absorption spectrum and the appearance of allowed transitions in the material. Electrophysical measurements showed that Co3O4-ZnO films have a resistivity up to 3 × 104 Ohm∙cm and a semiconductor conductivity close to intrinsic. With advancing the Co3O4 concentration, the mobility of the charge carriers was found to increase by almost four times. The photosensors based on the 10Co-90Zn film exhibited a maximum normalized photoresponse when exposed to radiation with wavelengths of 400 nm and 660 nm. It was found that the same film has a minimum response time of ca. 26.2 ms upon exposure to radiation of 660 nm wavelength. The photosensors based on the 3Co-97Zn film have a minimum response time of ca. 58.3 ms versus the radiation of 400 nm wavelength. Thus, the Co3O4 content was found to be an effective impurity to tune the photosensitivity of radiation sensors based on Co3O4-ZnO films in the wavelength range of 400-660 nm.

Blue emission: Optical properties of Co2+ doping towards Zn2SiO4 glass-ceramics

This article reports the fabrication of Zn2SiO4:Co2+ using composition (Co3O4)y[(ZnO)55.0(WRHA)45.0]1−y where y = 0.0, 0.01, 0.05 and 0.10 wt. % via melt and quenching technique. The effect of Co3O4 concentration dopant towards willemite also reported as in their physical characteristics, UV–visible, optical bandgap, and photoluminescence spectroscopy. The samples of Zn2SiO4:Co2+ became bluer as the dopant increased which imply the incorperation of Co2+ towards the willemite lattice and the density increasing from 3.1472 to 3.4592 gcm−3 when the dopant increased. XRD results showed presence of the stable state of willemite phase, α-Zn2SiO4 after sintered at 950 °C. In addition, there appeared two absorptions spectra in the optical absorption. First is the triply split absorption band centred at 475–700 nm spectral range assigned to 4A2 → 4T1 (4P) spin allowed optical transition of Co2+ ions whilst second absorption centred at ∼325 nm assigned to scattering by the Zn2SiO4. The optical bandgap decreases first as the dopant was introduced, then increased at highest value of Co3O4 concentration dopant. The PL spectra showed the undoped-Zn2SiO4 (sample B1) emits nine minor peaks in the blue, green, and yellow region centred at 382, 395, 415, 443, 460, 469, 482, 511 and 532 nm then, when Co3O4 was introduced, the Zn2SiO4:Co2+ presents five peaks correspond to blue emission (∼420 nm, ∼444 nm, ∼461 nm and ∼485 nm) and green emission (∼525 nm). Lastly, the CIE 1931 chromaticity showed all sample fall in the blue region which support the PL spectra and proves the possibility to produce blue emissions.

Tailoring the nanostructure of plasma-deposited CoOX-based thin films for catalytic applications – A step forward in designing nanocatalysts

Among the heterogeneous catalysts based on non-noble metals, cobalt oxides, mainly in the Co3O4 form, are particularly promising materials. Herein, we developed a facile bottom-up approach to synthesize a novel and sophisticated Co3O4-based thin-film material with a tailored nanostructure that is crucial for catalytic properties. The films were produced using a low-pressure plasma-enhanced chemical vapor deposition (PECVD) process that was thoroughly analyzed. The as-deposited films, in the amorphous form composed of Co, O, C, and H atoms (called CoOX-based films), were thermally treated (calcined), transforming them into films containing Co3O4 nanocrystallites. For a fundamental understanding of the transformation process, the calcination was performed in a controlled manner by Raman spectroscopy using the Raman laser as a heat source. An original model to describe the formation of Co3O4 nanocrystallites was proposed. We have shown that the concentration of Co3O4 and also the number and size of its nanocrystallites in the films can be rationally tailored to the specific needs by selecting the parameters of the PECVD and calcination processes. Our research provides a practical strategy for the molecular design of nanostructured thin-film catalysts in a controllable way using the PECVD process.

Oxygen Vacancy-Rich RuO2-Co3O4 Nanohybrids as Improved Electrocatalysts for Li-O2 Batteries.

Lithium oxygen (Li-O2) batteries have shown great potential as new energy-storage devices due to the high theoretical energy density. However, there are still substantial problems to be solved before practical application, including large overpotential, low energy efficiency, and poor cycle life. Herein, we have successfully synthesized a RuO2-Co3O4 nanohybrid with a rich oxygen vacancy and large specific surface area. The Li-O2 batteries based on the RuO2-Co3O4 nanohybrid shown obviously reduced overpotential and improved circulatory property, which can cycle stably for more than 100 cycles at a current density of 200 mA g-1. Experimental results and density function theory calculation prove that the introduction of RuO2 can increase oxygen vacancy concentration of Co3O4 and accelerate the charge transfer. Meanwhile, the hollow and porous structure leads to a large specific surface area about 104.5 m2 g-1, exposing more active sites. Due to the synergistic effect, the catalyst of the RuO2-Co3O4 nanohybrid can significantly reduce the adsorption energy of the LiO2 intermediate, thereby reducing the overpotential effectively.

Nonlinearity Characteristics of Low-Voltage Barium Titanate Based Zinc Oxide Varistor Ceramics Modified by Cobalt Dopants

Application of ZnO varistor at low voltage has increased significantly due to the high demands of low-voltage electronics with high nonlinearity characteristics and low leakage current. The varistor ceramics were developed via solid-state reaction method and the resultant sample was analyzed by means of SEM, EDS and XRD. The nonlinearity characteristics of ZnO varistor ceramics for different contents of cobalt oxide (Co3O4) at a given barium titanate (BaTiO3) amount were analyzed based on the J-E characteristics measurement. The increased value of nonlinear coefficient (α) equal to 4.8 was exhibited by the sample made with 12 wt.% BaTiO3 additive. As the concentration of dopant (Co3O4) incorporated was increased from 0.5 to 1.5 wt.%, the varistor voltage limit decreased from 8.9 V/mm to 7.0 V/mm, respectively. Additionally, the barrier height increased from 0.88 to 0.98 eV for 0.0 wt.% to 1.0 wt.% of Co3O4 concentration, respectively. The highest α of 7.2 was obtained at 0.5 wt.% Co3O4 and decreased with further doping content due to to the reduction of barrier height caused by the variation of electronic state at the grain boundaries.

Structural, Optical Absorption and Conductivity of PIn/Co3O4 Composites

This article presents the results obtained from structural, optical absorption and dc conductivity studies of pure polyindole (PIn) and its Co3O4 doped composites. Polyindole has been prepared by chemical oxidation method at room temperature using APS as an oxidant. The composites with varied concentrations of Co3O4 were prepared by in situ polymerization method. The obtained powder XRD patterns of both PIn and its composites indicated amorphous nature. Shifting of aromatic alkene peaks in FTIR reveals interaction between PIn and Co3O4. DC electrical conductivity has been measured in the temperature range 303–393 K and its observed variation inferred semiconducting nature of both pure PIn and the composites. Optical absorption studies have carried out and the band gap for both direct and indirect allowed transitions has been determined to be in the range from 1.79 to 2.34 eV and 2.38 to 3.19 eV respectively. These sizes of band gap values make them to be suitable for opto electronic applications. Activation energy for dc conduction has been determined using Arrhenius expression and it is found to be in the range of 0.3252–0.3806 eV. Conductivity increased and activation energy for conduction decreased with increase of Co3O4 concentration. This is interpreted to be due to decrease of hopping distance of charge carriers with increase of Co3O4 in the composites.

Phase-separated Ce–Co–O catalysts for CO oxidation

As a major gas pollutant, the control of CO gas emission from chemical industry and vehicle exhausts has aroused global attention in the past years and it is extremely essential to develop efficient, low-cost and environmental friendly catalysts for CO conversion and removal. In this work, we report the facile synthesis of Ce–Co–O catalysts through a simple ultrasonic spray pyrolysis process and investigate their application for low-temperature CO oxidation. The Ce–Co–O catalysts comprising of separated CeO2 and Co3O4 phases show superior CO oxidation capability below 473 K (200 °C) without the assistance of any other co-catalyst or noble metal. With the increase of Co3O4 concentration, the CO oxidation temperature of Ce–Co–O catalysts decreases quickly and reaches a complete conversion temperature of 410 K (137 °C) in the case of the optimized Co content. Microstructure analysis using high-resolution transmission electron microscope reveals that the tiny CeO2 and Co3O4 phases assembled into porous particles are well crystallized and show high chemical purity. The porous feature of Ce–Co–O catalysts synthesized from feasible ultrasonic spray pyrolysis makes them more competitive and promising towards gaseous environmental pollution processing including CO oxidation, TWCs, SCR, etc.

Optical spectroscopic study of cobalt oxide doped boron glass and its ion effect on optical properties

In this paper, the optical spectroscopic properties of Co3O4 doped borate glass with chemical composition: 60 B2O3, 30 ZnO, (10-x) Na2O, x Co3O4, (where x= 0 (S0), 0.1 (S1), 0.2 (S2), 0.3 (S3), 0.4 (S4), 0.5 (S5) mol %) were investigated. The glass samples (S0-S5) were prepared by conventional melt quenching technique. The formability of all prepared glass samples was examined by XRD and UV–visible spectroscopy techniques. The amorphous nature of glass structure was confirmed by XRD- technique. Archimedes method was used to measure density and calculate the molar volume of the prepared glass composition. It was observed that the density and molar volume of processed glass samples increased by increasing concentration of Co3O4. The optical spectroscopic characteristics of the obtained borate glass have been carried out over the whole range (190-2500nm) for studying the bandpass glass filter and UV cut-off. Through experimental data it was observed that the optical energy gap decreased from 3.25 to 3.03 eV by increasing doped cobalt oxide contents on borate glass. Furthermore, UV cut-off regions increased by increasing concentration of cobalt oxide. The effect of doping concentration on the optical properties of the prepared glass samples (refractive index, extinction coefficient, permittivity, dielectric constants, electric susceptibility and polarizability) was determined and studied.

Promoting the Hole Extraction with Co3O4 Nanomaterials for Efficient Carbon‐Based CsPbI2Br Perovskite Solar Cells

Carbon‐based perovskite solar cells (PSCs) have gathered much attention due to their excellent thermal stability and low cost. However, the typically used hole‐conductor‐free PSCs based on carbon electrodes show the worst performance due to the serious charge recombination at the perovskite/carbon interface. In this work, the efficient and stable carbon‐based CsPbI2Br PSCs using Co3O4 as the hole transport material (HTM) are fabricated and their photoelectric properties are systematically investigated. It is found that the Co3O4 inorganic HTM effectively promotes photo‐generated charges separation and extraction, and suppresses charge recombination at the CsPbI2Br/carbon electrode interface, resulting in the improved photovoltaic performance. At the optimal Co3O4 concentration, the carbon‐based CsPbI2Br PSCs achieve the maximum efficiency of 11.21% with a negligible J–V hysteresis. This work provides a novel strategy to fabricate efficient and stable all‐inorganic PSCs.

Effect of Sintering Process with Co3O4 on the Performance of LSCF-Based Cathodes for Solid Oxide Fuel Cells

The impact of the sintering process, especially in terms of sintering temperature and sintering aid concentration, on the ohmic transport and electrode performance of (La0.80Sr0.20)0.95CoO3–δ–gadolinia-doped ceria (LSCF-GDC) cathodes is studied. The ohmic and charge-transfer kinetics exhibit a highly coupled Co3O4 concentration dependency, showing the best performances at an optimum range of 4–5 wt%. This is ascribed to small grain sizes and improved connection between particles. The addition of Co3O4 was also found to have a dominant impact on charge-transfer kinetics in the LSCF-GDC composite layer and a moderate impact on the electronic transport in the current-collecting LSCF layer. Care should be taken to avoid a formation of excessive thermal stresses between layers when adding Co3O4.

Effect of Cobalt Oxide Nanoparticles on the Nano-scale Free Volume and Optical Properties of Biodegradable CMC/PVA Films

Chemically prepared cobalt oxide nanoparticles (NPs) were added to biodegradable carboxymethyl cellulose (CMC) (20%)/polyvinyl alcohol (PVA) (80%) blend films. The structural properties of these films were investigated by X-ray diffraction, Fourier transformation infrared spectroscopy (FTIR) and differential thermal analysis (DTA). Co3O4/(CMC + PVA) films show a semi-crystalline structure and the degree of crystallinity decreases with adding Co3O4 NPs. FTIR confirms the good interaction between the blend chains and Co3O4 NPs. The melting temperature Tm for CMC/PVA is about 212 °C then decreased with increasing Co3O4 content, due to some decrease in the ordered association of the blend which results in a decrease in the blend crystallinity. Positron annihilation lifetime spectroscopy (PALS) measurements were carried out with a conventional fast–fast coincidence spectrometer. It was found that ortho-positronium lifetime τ 3 and free volume Vf increase while o-Ps intensity I3 still constant as Co3O4 concentration increases. This is because adding Co3O4 NPs encourages the formation of o-Ps. The swelling ratio SR% as a function of Co3O4 concentration was also studied and its value increases with Co3O4 addition. The optical study illustrated the decrease of the transmittance T of the films from 87 to 35.5% with increasing Co3O4 content from 0 to 0.9 wt%. Also, both the direct and indirect optical band gaps of the films red-shifted from 4.05 to 3.75 eV and 3.3 to 2.75 eV, respectively. The influence of Co3O4 on the refractive index of the films is also reported.

Cobalt Oxide/Reduced Graphene Oxide Composite with Enhanced Electrochemical Supercapacitance Performance

Abstract Binary nanocomposite materials comprised of cobalt oxide (Co3O4) nanocrystals embedded in reduced graphene oxide (RGO) sheet were fabricated using one-pot hydrothermal synthetic route without using any structure guiding surfactant. We succeeded to visualize a 1/8 corner of a single cubic shape Co3O4 crystal under transmission electron microscopy (TEM). Shape and size of Co3O4 crystals varies from particle-type (size ∼10 nm), octahedral (size ∼20 nm) and aggregates of particles (size in the range of 50–80 nm) with increase in concentration of Co3O4 in the Co3O4/RGO composite. Cyclic voltammetry and charge/discharge measurements in aqueous KOH electrolyte (2 M) revealed that the Co3O4/RGO composite material exhibits electrochemical supercapacitive performance giving specific capacitance of 487 F g−1 at scan rate of 5 mV s−1 followed by outstanding cyclic stability sustaining 96.6% of capacitance after 2000 cycles.

PTh/Co3O4 nanocomposites as new conducting materials for micro/nano‐sized electronic devices

This paper reports polythiophene/cobalt (II,III) oxide (PTh/Co3O4) nanocomposites synthesized via in situ polymerization of thiophene in the presence of Co3O4 at various molar concentrations. Samples were characterized by Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), Energy‐dispersive X‐ray (EDX) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and atomic force microscopy (AFM). The alternating current (ac) conductivity of the samples was studied depending on the temperature. XRD analyses indicated that the filling process decreased the π − π stacking distance of PT chains. The most significant shift was observed in the C‐S band of PTh depending on the filling process. Thermal stability of the PTh increased with increasing concentration of Co3O4. Filling process reduced the surface roughness of PTh. The ac conductivity analyses indicated that charge transport mechanism of the samples was consistent with corraleted barrier hopping (CBH) model. The conductivity of PTh increased about 18 times for maximum filling level depending on temperature and frequency. The thermal stability and controllable ac conductivity properties of PTh/Co3O4 nanocomposites showed that they can be used in the production of micro/nano‐sized electronic circuit elements with lower cost. POLYM. ENG. SCI., 57:1168–1178, 2017. © 2017 Society of Plastics Engineers

The influence of Co3O4 concentration on quasi-solid state dye-sensitized solar cells with polymer electrolyte

In this work the effects of Co3O4 concentration on the properties of agarose polymer electrolyte and the corresponding DSSCs are studied with/without magnetic field treatments. The surface morphology, ion concentration, and ionic conductivity of agarose electrolytes with different Co3O4 concentrations are compared under 0 and 35mT magnetic field using various characterization methods. The photovoltaic performances of quasi-solid-state DSSCs with Co3O4 modified polymer electrolyte are examined. After applying magnetic fields, the ionic conductivity and photo-to-electric conversion efficiency of DSSCs are obviously improved in the Co3O4 concentrations below 4wt.%. The highest ionic conductivity of 6.00mScm−1 is obtained with electrolyte modified by 3wt.% Co3O4. The DSSCs with the optimal Co3O4 content show the best conversion efficiency under both 0 and 35mT magnetic fields.

Spectroscopic and structural studies of isochronally annealed cobalt oxide nanoparticles

X-ray absorption near edge structure (XANES) spectroscopy, X-ray photoelectron spectroscopy (XPS), and Synchrotron X-ray diffraction (SXRD) techniques are used to study as synthesized and isochronally annealed samples of cobalt oxide nanoparticles (NPs) grown using the wet chemical route. Quantitative phase composition determined using Linear Combination Fitting (LCF) on XANES data is found to be in reasonably good agreement with that obtained from Rietveld refinement on SXRD data. XPS data qualitatively indicate that Co3O4 concentration increases with increase in the annealing temperature, in confirmation with SXRD and XANES data. Larger shifts in the satellite peaks from the main peaks compared to these in bulk suggest larger crystal field splitting in nanoparticles as compared to the bulk.

Towards high purity graphene/single-walled carbon nanotube hybrids with improved electrochemical capacitive performance

CoMgAl layered double hydroxides were prepared as catalysts for the in situ synchronous growth of graphene and single-walled carbon nanotubes (SWCNTs) from methane by chemical vapor deposition. The as-calcined CoMgAl layered double oxide (LDO) flakes served as the template for the deposition of graphene, and Co nanoparticles (NPs) embedded on the LDOs catalyzed the growth of SWCNTs. After the removal of CoMgAl LDO flakes, graphene (G)/SWCNT/Co3O4 hybrids with SWCNTs directly grown on the surface of graphene and 27.3wt.% Co3O4 NPs encapsulated in graphene layers were available. Further removal of the Co3O4 NPs by a CO2-oxidation assistant purification method induced the formation of G/SWCNT hybrids with a high carbon purity of 98.4wt.% and a high specific surface area of 807.0m2/g. The G/SWCNT/Co3O4 hybrids exhibited good electrochemical performance for pseudo-capacitors due to their high Co3O4 concentration and the high electrical conductivity of SWCNTs and graphene. In another aspect, the G/SWCNT hybrids can be used as excellent electrode materials for double-layer capacitors. A high capacity of 98.5F/gelectrode was obtained at a scan rate of 10mV/s, 78.2% of which was retained even when the scan rate increased to 500mV/s.

Effect of the location of cobalt species on NO adsorption and NOx-SCR over Co–mordenite

Abstract A thorough characterization of Co–mordenite was carried out using NO-TPD, H2-TPR, Raman, DRX and FTIR with NO as probe molecule. Different cobalt-loading catalysts (8.85, 5.70, 2.91, 2.45 and 1.15 wt.%) were prepared by ion exchange over NH4–mordenite and treated with different procedures (heated on He, O2 and H2). The effect of adding water to the reaction stream at 500 °C on the location of the cobalt species was also analyzed. All catalysts were evaluated for the SCR of NOx with methane as a test reaction both under dry and wet conditions. The NO adsorption capacity depended not only on the Co/Al ratio and pretreatments but also on the presence of Co oxides. In fact, for similar Co/Al ratios, Co2.91MOR showed a lower NO/Co ratio than Co2.45MOR due to the higher Co3O4 concentration in the former. These species probably blocked the main mordenite channels and/or produced the formation of some Co island on the zeolite surface, lowering the amount of surface Co. The main NO surface species detected were dinitrosyl and mononitrosyl. Their stability and relative amount depended on the cobalt species and the pretreatments. Heating in He or H2 induced the stabilization of part of the exchanged Co in less gas-accessible sites, whereas the calcination with O2 involved the mobilization of Co to more external sites. However, those effects were less significant for samples containing Co oxides suggesting that the spinel hinders the Co migration. During the wet reaction treatment, the cobalt mobilization to hidden positions occurred along with the formation of Co-oxides, which negatively affected both the catalytic activity and the NO adsorption capacity.

Electrochemical deposition and properties of PbO2 + Co3O4 composites

Abstract Electrolysis of suspensions of Co3O4 particles in Pb2+-containing electrolytes has been used for depositing PbO2 + Co3O4 composite layers on Ni rotating dise anodes. A sufficiently high angular speed of the electrode is necessary to obtain layers of homogeneous thickness and Co3O4 concentration. The volume fraction of Co3O4 particles in the deposit α reaches a limiting value of ca. 0.1 when the volume fraction of particles in suspension C exceeds 0.008. The current density j has little effect on α as long as it is in the range 1 to 20 mA cm−2; if j increases further, α decreases. PbO2 + Co3O4 composite layers have been studied as electrode materials for the oxygen evolution reaction (mainly in NaOH solution). The overpotential and Tafel slope decrease upon increasing α. At a fixed potential, j is roughly proportional to OH− concentration. The PbO2 + Co3O4 electrode performance is fairly stable at 25°C but declines with time at higher temperature.

Spectroscopic determination of the kinetic model and of activation energies of Co3O4 surface dissociation on γ-Al2O3 and SiO2 modified with alkaline earth cations

The kinetic model which follows the surface dissociation of Co3O4 on γ-Al2O3 and SiO2 modified with alkaline earth cations has been investigated using the Arrhenius kinetic law as an approximate criterion. It was found that on both classes of modified carriers a “phase boundary reaction control” mechanism fits the experimental points. Using this model, the activation energies were calculated. The modification of γ-Al2O3 brings about a decrease of Ea values whereas that of SiO2 causes an increase in activation energy. These effects, in conjunction with the “initial values” of the Co3O4 concentration, explain the influence of alkaline earth cations on the Co3O4/γ-Al2O3 and Co3O4/SiO2 catalytic systems and support the tentative mechanism proposed earlier.