Growth kinetics of nanograins in Co3O4 fibers

The growth kinetics of nanograins in Co₃O₄ nanofibers has been investigated. Individual fibers were made up of nanograins. The nanograins were observed to coalesce and grow at the expense of the smaller ones, similar to the phenomenon observed in the sintering process of bulk ceramics. The activation energy and the growth kinetics of nanograins were estimated, showing the dominant growth mechanism of nanograins to be likely related to a lattice diffusion process.     

Synthesis and magnetic properties of nanoporous Co3O4 nanoflowers

Nanoporous Co₃O₄ hierarchical nanoflowers have been prepared through sequential process of a hydrothermal reaction and heat treatment. These nanoflowers consisting of a great deal of Co₃O₄ nanofibers have bimodal pore structures and Brunauer–Emmett–Teller surface area of 34.61 m²/g. The temperature dependence curves of magnetization in zero-field-cooled and field-cooled exhibit main antiferromagnet and weak ferromagnet of Co₃O₄ nanoflowers at blocking temperature of 34 K, respectively. In addition, analysis of their optic properties obviously indicates red shift of absorption peaks, exhibiting quantum-confined effect and traits of semiconductor.     

Morphology effects of Co3O4 on the catalytic activity of Au/Co3O4 catalysts for complete oxidation of trace ethylene

Au/Co₃O₄ catalysts with different morphologies (nanorods, nanopolyhedra and nanocubes) were successfully synthesized and evaluated for ethylene complete oxidation. We found that support morphology has a significant effect on catalytic activity, which is related to the exposed planes of different morphological Co₃O₄. HRTEM revealed the Co₃O₄-nanorods predominantly exposes {110} planes, while the dominant exposed planes of Co₃O₄-nanopolyhedra and -nanocubes are {011} and {001} planes, respectively. Compared with {011} and {001} planes, {110} planes exhibit the maximum amount of oxygen vacancies, which play a major role in ethylene oxidation. Therefore, Au/Co₃O₄-nanorods exhibits extraordinary catalytic activity, yielding 93.7% ethylene conversion at 0 °C.     

Co3O4 thin film prepared by a chemical bath deposition for electrochemical capacitors

Co₃O₄ thin film is synthesized on ITO by a chemical bath deposition. The prepared Co₃O₄ thin film is characterized by X-ray diffraction, and scanning electron microscopy. Electrochemical capacitive behavior of synthesized Co₃O₄ thin film is investigated by cyclic voltammetry, constant current charge/discharge and electrochemical impedance spectroscopy. Scanning electron microscopy images show that Co₃O₄ thin film is composed of spherical-like coarse particles, together with some pores among particles. Electrochemical studies reveal that capacitive characteristic of Co₃O₄ thin film mainly results from pseudocapacitance. Co₃O₄ thin film exhibits a maximum specific capacitance of 227 F g⁻¹ at the specific current of 0.2 A g⁻¹. The specific capacitance reduces to 152 F g⁻¹ when the specific current increases to 1.4 A g⁻¹. The specific capacitance retention ratio is 67% at the specific current range from 0.2 to 1.4 A g⁻¹.     

Rapid synthesis of nanocrystalline Co3O4 by a microwave-assisted combustion method

A facile and rapid microwave-assisted combustion method was developed to synthesize the nanocrystalline Co₃O₄. The study suggested that application of microwave heating to produce the homogeneous porous Co₃O₄ was achieved in a few minutes. The structure and morphology of the as-prepared nanocrystalline Co₃O₄ were investigated by means of X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), Raman spectra, UV-vis absorbance spectra and scanning electron microscopy (SEM). The XRD, FTIR and Raman spectra confirmed the formation of spinel structural Co₃O₄, and the SEM results indicated the porous surface characteristic of the products. Magnetic measurement was carried out using a vibrating sample magnetometer (VSM). The field dependence of the magnetization at room temperature showed a tiny hysteresis loop with a coercivity of 56.7 Oe.     

Preparation and electrochemical capacitance of cobalt oxide (Co3O4) nanotubes as supercapacitor material

Cobalt oxide (Co₃O₄) nanotubes have been successfully synthesized by chemically depositing cobalt hydroxide in anodic aluminum oxide (AAO) templates and thermally annealing at 500 °C. The synthesized nanotubes have been characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The electrochemical capacitance behavior of the Co₃O₄ nanotubes electrode was investigated by cyclic voltammetry, galvanostatic charge-discharge studies and electrochemical impedance spectroscopy in 6 mol L⁻¹ KOH solution. The electrochemical data demonstrate that the Co₃O₄ nanotubes display good capacitive behavior with a specific capacitance of 574 F g⁻¹ at a current density of 0.1 A g⁻¹ and a good specific capacitance retention of ca. 95% after 1000 continuous charge-discharge cycles, indicating that the Co₃O₄ nanotubes can be promising electroactive materials for supercapacitor.     

Low-temperature growth of well-crystalline Co3O4 hexagonal nanodisks as anode material for lithium-ion batteries

Uniform hexagonal-shaped cobalt oxide (Co₃O₄) nanodisks were prepared in large scale via facile aqueous solution based hydrothermal process at 110 °C. The detailed structural characterizations confirmed that the synthesized products are hexagonal cobalt oxide nanodisks, possessing very well-crystalline cubic spinel structure. A coin cell of type −2032 was assembled using the synthesized Co₃O₄ nanodisks and its charge–discharge profile was analyzed between the voltages 0.01 and to 2.5 V vs. Li/Li⁺ reference electrode. The electrochemical cell composed of Li/Co₃O₄ delivered an initial lithium insertion capacity of 2039 mAh/g. Although the cell exhibited high irreversible capacity during the first four cycles, the columbic efficiency has been improved upon cycling.     

硫修饰的多孔Co3O4活化过一硫酸盐降解亚甲基蓝

以Na₂S₂O₃为硫源，采用改进的草酸盐-热解法制备了一系列硫修饰的Co₃O₄多孔催化剂[S_x@Co₃O₄,x=0.25、0.50、0.75、1,x为硫的修饰量，以Co(NO₃)₂·6H₂O的物质的量为基准，下同]。以亚甲基蓝(MB)为降解模型，考察了不同催化剂活化过一硫酸盐(PMS)的性能。探讨了催化剂用量、PMS浓度、反应温度、常见阴离子种类在S_x@Co₃O₄-PMS体系下对MB降解率的影响，并评价了催化剂的循环稳定性。结果表明，随着硫修饰量的增加，Co₃O₄的催化性能逐渐升高，S₁@Co₃O₄表现出最佳的催化性能。硫元素以SO₄^2–     

Optimization of preparation for Co3O4 by calcination from cobalt oxalate using response surface methodology

The conditions of technique to prepare Co₃O₄ by calcination from cobalt oxalate were optimized using response surface methodology. A quadratic equation model for decomposition rate was built and effects of main factors and their corresponding relationships were obtained. The statistical analysis of the results showed that in the range studied the decomposition rate of cobalt oxalate was significantly affected by the calcination temperature and calcination time. The optimized calcination conditions were as follows: the calcination temperature 680.86 K, the calcination time 44.7 min, and the mass of material 3.04 g, respectively. Under these conditions the decomposition rate of cobalt oxalate was 99.06%. The validity of the model was confirmed experimentally and the results were satisfactory.     

Porous Co3O4 nanoplatelets by self-supported formation as electrode material for lithium-ion batteries

In this paper, we have reported a simple and rapid approach for the large-scale synthesis of β-Co(OH)₂ nanoplatelets via the microwave hydrothermal process using potassium hydroxide as mineralizer at 140 °C for 3 h. Calcining the β-Co(OH)₂ nanoplatelets at 350 °C for 2 h, porous Co₃O₄ nanoplatelets with a 3D quasi-single-crystal framework were obtained. The process of converting the β-Co(OH)₂ nanoplatelets into the Co₃O₄ nanoplatelets is a self-supported topotactic transformation, which is easily controlled by varying the calcining temperature. The textural characteristics of Co₃O₄ products have strong positive effects on their electrochemical properties as electrode materials in lithium-ion batteries. The obtained porous Co₃O₄ nanoplatelets exhibit a low initial irreversible loss (18.1%), ultrahigh capacity, and excellent cyclability. For example, a reversible capacity of 900 mAh g⁻¹ can be maintained after 100 cycles.     

Calibrated Co3O4 nanoparticles patterned in SBA-15 silicas: Accessibility and activity for CO oxidation

The catalytic performances in CO oxidation of Co₃O₄ nanoparticles patterned in the porosity of SBA-15 silicas are investigated. Accessibility limitations of the reactants to the catalytic sites are clearly revealed, when the Co₃O₄ nanoparticles are embedded in the SBA-15 pores. Despite these limitations, the synthesised Co₃O₄ nanoparticles exhibit promising CO oxidation properties.     

Synthesis of LiNi0.9Co0.1O2 from Li2CO3, NiO or NiCO3, and CoCO3 or Co3O4 and their electrochemical properties

Cathode active materials with a composition of LiNi_0.9Co_0.1O₂ were synthesized by a solid-state reaction method at 850 °C using Li₂CO₃, NiO or NiCO₃, and CoCO₃ or Co₃O₄, as the sources of Li, Ni, and Co, respectively. Electrochemical properties, structure, and microstructure of the synthesized LiNi_0.9Co_0.1O₂ samples were analyzed. The curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂ for the first charge–discharge and the intercalated and deintercalated Li quantity Δx were studied. The destruction of unstable 3b sites and phase transitions were discussed from the first and second charge–discharge curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂. The LiNi_0.9Co_0.1O₂ sample synthesized from Li₂CO₃, NiO, and Co₃O₄ had the largest first discharge capacity (151 mA h/g), with a discharge capacity deterioration rate of −0.8 mA h/g/cycle (that is, a discharge capacity increasing 0.8 mA h/g per cycle).     

Novel promoting effect of SO2 on the selective catalytic reduction of NOx by ammonia over Co3O4 catalyst

Spinel nano-Co₃O₄ was prepared by solid-state reaction at room temperature and investigated for selective catalytic reduction of NO_x by NH₃ (NH₃-SCR). Although suffering from pore filling and plugging, treatment of this catalyst by SO₂ showed novel promoting effect on NH₃-SCR above 250 °C. Bulk cobalt sulfate was observed over the sulfated Co₃O₄ with XRD, which would be an active component for NH₃-SCR. The sulphated Co₃O₄ catalyst exhibited good resistance to SO₂ (500 ppm, 100 ppm) and 10% H₂O at a space velocity of about 25 000 h⁻¹ at 300 °C, as tested for 12 h.     

Comparison of AlPO4- and Co3(PO4)2-coated LiNi0.8Co0.2O2 cathode materials for Li-ion battery

Electrochemical and thermal properties of Co₃(PO₄)₂- and AlPO₄-coated LiNi_0.8Co_0.2O₂ cathode materials were compared. AlPO₄-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 170.8 mAh g⁻¹ and had a capacity retention (89.1% of its initial capacity) between 4.35 and 3.0 V after 60 cycles at 150 mA g⁻¹. Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 177.6 mAh g⁻¹ and excellent capacity retention (91.8% of its initial capacity), which was attributed to a lithium-reactive Co₃(PO₄)₂ coating. The Co₃(PO₄)₂ coating material could react with LiOH and Li₂CO₃ impurities during annealing to form an olivine Li_xCoPO₄ phase on the bulk surface, which minimized any side reactions with electrolytes and the dissolution of Ni⁴⁺ ions compared to the AlPO₄-coated cathode. Differential scanning calorimetry results showed Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathode material had a much improved onset temperature of the oxygen evolution of about 218 °C, and a much lower amount of exothermic-heat release compared to the AlPO₄-coated sample.     

Soft template synthesis of mesoporous Co3O4/RuO2·xH2O composites for electrochemical capacitors

Co₃O₄/RuO₂·xH₂O composites with various Ru content (molar content of Ru = 5%, 10%, 20%, 50%) were synthesized by one-step co-precipitation method. The precursors were prepared via adjusting pH of the mixed aqueous solutions of Co(NO₃)₂·6H₂O and RuCl₃·0.5H₂O by using Pluronic123 as a soft template. For the composite with molar ratio of Co:Ru = 1:1 annealed at 200 °C, Brunauer-Emmet-Teller (BET) results indicated that the composite showed mesoporous structure, and the specific surface area of the composite was as high as 107 m² g⁻¹. The electrochemical performances of these composites were measured in 1 M KOH electrolyte. Compared with the composite prepared without template, the composite with P123 exhibited a higher specific capacitance. When the molar content of Ru was rising, the specific capacitance of the composites increased significantly. It was also observed that the crystalline structures as well as the electrochemical activities were strongly dependent on the annealing temperature. A capacitance of 642 F/g was obtained for the composite (Co:Ru = 1:1) annealed at 150 °C. Meanwhile, the composites also exhibited good cycle stability. Besides, the morphologies and textural characteristic of the samples were also investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM).     

Ultrasonic wave aided selective epoxidation of mixed styrene and α-pinene with air over nanosized Co3O4

Catalytic selective epoxidation of mixed biolefins with air over nanosized Co₃O₄ catalyst under mild ultrasonic conditions has been first reported. When the styrene/α-pinene molar ratio was 1:5, the highest conversions were, respectively, reached 81.8 mol% for styrene and 76.1 mol% for α-pinene, with the epoxidation selectivity of 84.1% (styrene oxide) and 94.6% (α-pinene oxide), notably higher than those of the conventional reactions under magnetic stirring. An intermolecular electron-transfer phenomenon between conjugated styrene and electron-rich α-pinene was revealed by UV–vis spectra, which was considerably important for the enhancement of reactivities of both olefinic molecules observed experimentally.     

Synthesis and electrochemical characteristics of Al2O3-coated LiNi1/3Co1/3Mn1/3O2 cathode materials for lithium ion batteries

LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials have been coated with Al₂O₃ nano-particles using sol-gel processing to improve its electrochemical properties. The X-ray diffraction (XRD) pattern of the as-prepared Al₂O₃ nano-particles was indexed to the cubic structure of the γ-Al₂O₃ phase and had an average size of ∼4 nm. The XRD showed that the structure of LiNi_1/3Co_1/3Mn_1/3O₂ was not affected by the Al₂O₃ coating. However, the Al₂O₃ coatings on LiNi_1/3Co_1/3Mn_1/3O₂ improved the cyclic life performance and rate capability without decreasing its initial discharge capacity. These electrochemical properties were also compared with those of LiAlO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ cathode material. The electrochemical impedance spectroscopy (EIS) was studied to understand the enhanced electrochemical properties of the Al₂O₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ compared to uncoated LiNi_1/3Co_1/3Mn_1/3O₂.     

A novel kojic acid amperometric sensor based on hollow CuO/Fe2O3 hybrid microspheres immobilized in chitosan matrix

Hollow CuO/Fe₂O₃ hybrid microspheres with small uniform holes were synthesized using a convenient hydrothermal method and were applied to fabricated an amperometric sensor for kojic acid. The resulting materials were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) and then were immobilized into the chitosan (Chi) matrix onto a glassy carbon electrode to obtain CuO/Fe₂O₃–Chi/GCE. The potential utility of the constructed electrodes were demonstrated by applying them to the analytical determination of kojic acid concentration. The electrochemical behavior of kojic acid on CuO/Fe₂O₃–Chi/GCE was explored. The modified electrode displayed excellent amperometric response for kojic acid with a linear range from 0.2 μM to 674 μM with a detection limit of 0.08 μM at a signal-to-noise ratio of 3. In order to validate feasibility, the CuO/Fe₂O₃–Chi/GCE has been used for quantitative detecting kojic acid in real samples.     

Influence of CuO on the formation and coexistence of 3CaO·SiO2 and 3CaO·3Al2O3·CaSO4 minerals

The influence of CuO on the formation and coexistence of 3CaO·SiO₂ and 3CaO·3Al₂O₃·CaSO₄ minerals in Portland cement containing 3CaO·3Al₂O₃·CaSO₄ mineral is reported in this paper. The results show that a suitable amount of CuO can lower the clinkering temperature and improve the burn-ability of clinkers. It can also promote the formation of 3CaO·SiO₂ and 3CaO·3Al₂O₃·CaSO₄ minerals and facilitate the coexistence of the two minerals in the clinkers. But adding 1% CuO to the raw material can cause the decomposition of 3CaO·3Al₂O₃·CaSO₄.     

Aging characteristics of high-power lithium-ion cells with LiNi0.8Co0.15Al0.05O2 and Li4/3Ti5/3O4 electrodes

The impedance rise that results from the accelerated aging of high-power lithium-ion cells containing LiNi_0.8Co_0.15Al_0.05O₂-based positive and graphite-based negative electrodes is dominated by contributions from the positive electrode. Data from various diagnostic experiments have indicated that a general degradation of the ionic pathway, apparently caused by surface film formation on the oxide particles, produces the positive electrode interface rise. One mechanistic hypothesis postulates that these surface films are components of the negative electrode solid electrolyte interphase (SEI) layer that migrate through the electrolyte and separator and subsequently coat the positive electrode. This hypothesis is examined in this article by subjecting cells with LiNi_0.8Co_0.15Al_0.05O₂-based positive and Li_4/3Ti_5/3O₄-based negative electrodes to accelerated aging. The impedance rise in these cells was observed to be almost entirely from the positive electrode. Because reduction products are not expected on the 1.55 V Li_4/3Ti_5/3O₄ electrode, the positive electrode impedance cannot be attributed to the migration of SEI-type fragments from the negative electrode. It follows then that the impedance rise results from mechanisms that are “intrinsic” to the positive electrode.