The synthesis and selected properties of Co<Subscript>2</Subscript>InV<Subscript>3</Subscript>O<Subscript>11</Subscript>

It has been demonstrated that Co₂V₂O₇ and InVO₄ react with each other forming a new compound of the Co₂InV₃O₁₁ formula, when their molar ratio is equal to 1:1, or among CoCO₃, In₂O₃ and V₂O₅, mixed at a molar ratio of 4:1:3. This compound melts incongruently at the temperature of 960±5°C, depositing crystals of InVO₄. It crystallizes in the triclinic system and the unit cell parameters amount to: a=0.6524(6) nm, b=0.6885(5) nm, c=1.0290(4) nm, α=96.5°, β=104.1°, γ=100.9°, Z=2. The phase equilibria being established in the Co₂V₂O₇–InVO₄ system over the whole components concentration range up to the solidus line were described.     

Synthesis,characterization and thermal analysis of polyaniline (PANI)/Co<Subscript>3</Subscript>O<Subscript>4</Subscript> composites

Conducting polyaniline/Cobaltosic oxide (PANI/Co₃O₄) composites were synthesized for the first time, by in situ deposition technique in the presence of hydrochloric acid (HCl) as a dopant by adding the fine grade powder (an average particle size of approximately 80 nm) of Co₃O₄ into the polymerization reaction mixture of aniline. The composites obtained were characterized by infrared spectra (IR) and X-ray diffraction (XRD). The composition and the thermal stability of the composites were investigated by TG-DTG. The results suggest that the thermal stability of the composites is higher than that of the pure PANI. The improvement in the thermal stability for the composites is attributed to the interaction between PANI and nano-Co₃O₄.     

Electrochemical dissolution of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> in acidic solutions

The cyclic voltammetry method was used to study the regularities of the electrochemical behavior of cobalt cobaltite in an acidic medium. It is shown that cathodic reduction of Co₃O₄ in the studied range of potentials of +1.0 to −0.8 V is a multistage process occurring according to the scheme:      

Promoted porous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for ammonia decomposition

Transition metal catalysts have been considerably used for NH₃ decomposition because of the potential application in CO_x-free H₂ generation for fuel cells. However, most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components. Here, we adopted an efficient method, aerosol-assisted self-assembly approach (AASA), to prepare the optimized cobalt-alumina (Co₃O₄-Al₂O₃) catalysts. The Co₃O₄-Al₂O₃ catalysts exhibited excellent catalytic performance in the NH3 decomposition reaction, which can reach 100% conversion at 600 °C and maintain stable for 72 h at a gaseous hourly space velocity (GHSV) of 18000 cm³ g_cat^?1 h^?1. The catalysts were characterized by various techniques including transmission electron microscope (TEM), scanning electron microscope (SEM), nitrogen sorption, temperature-programmed reduction by hydrogen (H₂-TPR), ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction (XRD) to obtain the information about the structure and property of the catalysts. H₂-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species, which influences the redox properties of the catalysts. It is found that even a low content of alumina (10 at%) is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components, which ensures the high activity and superior stability of the cobalt-alumina catalysts.     

Thermal oxide synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

Fe₃O₄ nanorods and Fe₂O₃ nanowires have been synthesized through a simple thermal oxide reaction of Fe with C₂H₂O₄ solution at 200–600°C for 1 h in the air. The morphology and structure of Fe₃O₄ nanorods and Fe₂O₃ nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals Fe₃O₄ nanorods with cubic structure and the average diameter of 0.5–0.8 μm grow after reaction at 200–500°C for 1 h in the air. When the temperature was 600°C, the samples completely became Fe₂O₃ nanowires with hexagonal structure. It was found that C₂H₂O₄ molecules had a significant effect on the formation of Fe₃O₄ nanorods. A possible mechanism was also proposed to account for the growth of these Fe₃O₄ nanorods. Supported by the Fund of Weinan Teacher’s University (Grant No. 08YKZ008), the National Natural Science Foundation of China (Grant No. 20573072) and the Doctoral Fund of Ministry of Education of China (Grant No. 20060718010)     

Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/BiFeO<Subscript>3</Subscript> heterostructure: preparation,characterization, and photocatalytic activity

Bi₂O₃/BiFeO₃ composite was successfully fabricated by a conventional sol–gel method and structural properties were characterized based on X-ray diffractometer, scanning electron microscope, transmission electron microscope, energy-dispersive X-ray analyzer, nitrogen adsorption–desorption measurement, and UV–visible diffuse reflectance spectroscopy. Bi₂O₃/BiFeO₃ had a good absorption for visible light, which was benefit to photocatalytic activity. The highest degradation efficiency was obtained when the content of Bi₂O₃ in Bi₂O₃/BiFeO₃ was 63.9%. Effect of experimental conditions was investigated, and the highest photocatalytic activity of Bi₂O₃/BiFeO₃ was observed at photocatalyst dosage of 0.5 g/L, initial BPA concentration of 10 mg/L, and solution pH of 6.3. Bi₂O₃/BiFeO₃ photocatalyst exhibited enhanced photocatalytic activity for BPA, and the reaction rate constant over Bi₂O₃/BiFeO₃ composite was 2.23, 3.65, and 8.71 times higher than that of BiFeO₃, Bi₂O₃ and commercial TiO₂ (P25), respectively. Bi₂O₃/BiFeO₃ showed high photocatalytic activity after three cycles, suggesting that it was a stable photocatalyst. The possible photocatalytic mechanism has been discussed on the basis of the theoretical calculation and the experimental results. The hydroxyl and superoxide radicals together with photogenerated holes played significant roles in the photocatalytic reaction.     

Facile synthesis of single-crystalline Co<Subscript>3</Subscript>O<Subscript>4</Subscript> cubes as high-performance anode for lithium-ion batteries

Transition metal oxides have great potential as anode for lithium-ion batteries (LIBs), owing to their high theoretical capacity and low cost. However, the poor cycling stability and electron conductivity have limited the widely expected application of transition metal oxides. In this work, highly single-crystalline Co₃O₄ cubes with 400 nm in the average side length are successfully synthesized by a facile hydrothermal method. When used as anode for LIBs, the Co₃O₄ single-crystalline cubes exhibit highly stable and substantial discharge capacities of the amount to 877 mA h g^?1 at 200 mA g^?1 after 110 cycles with remarkable capacity retention of 98%, and 576 mA h g^?1 even at a high rate of 2000 mA g^?1. The scalability of the preparation method and the impressive results achieved here demonstrate the potential for the application to the future development of transition metal oxides anodes. These results suggest that the single-crystalline Co₃O₄ is a promising electrode material for the high-performance energy storage devices.     

2-pyrrolidone - capped Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals

Water-soluble Mn₃O₄ nanocrystals have been prepared through thermal decomposition in a high temperature boiling solvent, 2-pyrrolidone. The final product was characterized with XRD, SEM, TEM, FTIR and Zeta Potential measurements. Average crystallite size was calculated as ∼15 nm using XRD peak broadening. TEM analysis revealed spherical nanoparticles with an average diameter of 14±0.4 nm. FTIR analysis indicated that 2-pyrrolidone coordinates with the Mn₃O₄ nanocrystals only via O from the carbonyl group, thus confining their growth and protecting their surfaces from interaction with neighboring particles.      

Preparation of Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9</Subscript> by polyacrylamide gel processing and its thermoelectric properties

Ca₃Co₄O₉ powder was prepared by a polyacrylamide gel route in this paper. The effect of the processing on microstructure and thermoelectric properties of Ca₃Co₄O₉ ceramics via spark plasma sintering were investigated. Electrical measurement shows that the Seebeck coefficient and conductivity are 170 μV/K and 128 S/cm, respectively, at 700 °C, yielding a power factor value of 3.70 × 10⁻⁴ W m⁻¹ K⁻² at 700 °C, which is larger than that of Ca₃Co₄O₉ ceramics via solid-state reaction processing. The polyacrylamide gel processing is a fast, cheap, reproducible and easily scaled up chemical route to improve the thermoelectric properties of Ca₃Co₄O₉ ceramics by preparing the homogeneous and pure Ca₃Co₄O₉ phase.     

Synthesis and characterization of Co<Subscript>0.8</Subscript>Zn<Subscript>0.2</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Cobalt zinc ferrite, Co_0.8Zn_0.2Fe₂O₄, nanoparticles have been synthesized via autocatalytic decomposition of the precursor, cobalt zinc ferrous fumarato hydrazinate. The X-ray powder diffraction of the ‘as prepared’ oxide confirms the formation of single phase nanocrystalline cobalt zinc ferrite nanoparticles. The thermal decomposition of the precursor has been studied by isothermal, thermogravimetric and differential thermal analysis. The precursor has also been characterized by FTIR, and chemical analysis and its chemical composition has been determined as Co_0.8Zn_0.2Fe₂(C₄H₂O₄)₃·6N₂H_4. The Curie temperature of the ‘as-prepared oxide’ was determined by AC susceptibility measurements.     

Synthesis and Electrocatalytic Properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanocrystallites with Various Morphologies

Co₃O₄ crystallites with particle, plate-, tube-, rod- and sheet-like morphologies were successfully prepared by the calcination of the corresponding precursors synthesized via a precipitation or hydrothermal procedure. The morphologies of the precursors and Co₃O₄ nano-tubes were detected by field emission scanning electron microscopy (FE-SEM). The as-obtained Co₃O₄ samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and special surface area measurement (BET). The electrocatalytic activity of p-nitrophenol reduction with the Co₃O₄ products decorated on a glassy carbon electrode (GCE) was tested, respectively, using cyclic voltammetry (CV) in a basic solution. The results indicated that p-nitrophenol was reduced with higher current density but almost at a constant potential on the Co₃O₄/GCE in contrast with that on a bare GCE at the same conditions. The highly catalytic activity of the as-prepared Co₃O₄ in a basic solution suggested their wide applications in environmental treatment or organic synthesis.     

Magnetic nanoparticles (Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> &amp; Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) and their applications in urea biosensing

Nanobiotechnology has opened a new and exciting opportunities for exploring urea biosensor based on magnetic nanoparticles (NPs) mainly Fe₃O₄ and Co₃O₄. These NPs have been extensively exploited to develop biosensors with stability, selectivity, reproducibility and fast response time. This review gives an overview of the development of urea biosensor based on Fe₃O₄ and Co₃O₄ for in vitro diagnostic applications along with significant improvements over the last few decades. Additionally, effort has been made to elaborate properties of magnetic nanoparticles (MNPs) in biosensing aspects. It also gives details of recent developments in hybrid nanobiocomposite based urea biosensor.     

Novel Visible-Light-Driven Photocatalyst Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/FeWO<Subscript>4</Subscript> for Efficient Decomposition of Organic Pollutants

A highly efficient and visible light (λ ≥ 420 nm) responsive composite photocatalyst, Co₃O₄/FeWO₄ was prepared by simple impregnation method. The heterojunction semiconductors Co₃O₄/FeWO₄ demonstrated notably high photocatalytic activity over a wide range of composition than the individual component Co₃O₄ or FeWO₄ for the complete degradation of 1,4-dichlorobenzene (DCB) in aqueous phase under visible light irradiation. The photocatalytic activity of composite was optimized at 1/99 Co₃O₄/FeWO₄ composition. After 2 h of visible light irradiation 51% decomposition of 1,4-dichlorobenzene (DCB) was observed utilizing 1/99 Co₃O₄/FeWO₄ photocatalyst while the end members demonstrated a negligible degradation under the same experimental condition. The valence band (VB) and conduction band (CB) of Co₃O₄ is located above the VB and CB of FeWO₄, respectively. Both the semiconductors Co₃O₄ and FeWO₄ exhibit strong absorption over the wide range of visible light. The obviously enhanced photocatalytic performance of Co₃O₄/FeWO₄ composite has been discussed on the hole (h⁺) as well as electron (e^?) transfer mechanism between the VB and CB of individual semiconductors.     

Cellulose nanocrystals prepared in H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>-acetic acid system

Cellulose nanocrystals (CNC) were prepared by destruction of cotton cellulose using phosphotungstic acid in acetic acid medium. The study shows the influence of the heteropolyacid concentration, pre-activation, and hydrogen peroxide addition on the size of CNC particles. CNC were characterized using the methods of dynamic light scattering, FTIR-spectroscopy, thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, scanning and transmission electron microscopy, and potentiometric titration. CNC particles have highly-crystalline structure and rod-like morphology. Freeze-dried CNC hydrosols form lamellar or fibrous agglomerates, depending on the initial concentration of the CNC sol. Potentiometric titration results show increase in surface activity index and offset of pK_a values for CNC active centers in comparison to initial cellulose material.     

Effect of the preparation method on the catalytic performance of Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9</Subscript> for methane oxidation

The layered structure oxide Ca₃Co₄O₉ particle was synthesized by two routes of citrate sol–gel method. The structure, morphology and surface property of Ca₃Co₄O₉ was characterized by XRD, SEM and XPS, respectively. The catalytic activity of Ca₃Co₄O₉ for methane combustion was tested in a fixed bed quartz tubular microreactor. The catalysis results reveal that the catalytic activity is sensitive to the texture of Ca₃Co₄O₉ by different route. TG measures confirm that the small particle size of Ca₃Co₄O₉ favors the oxygen transformation on the surface, which can be ascribed the random distribution of the crystal axes in irregular Ca₃Co₄O₉ particle.     

Synthesis,characterization and lithium-intercalation properties of rod-like CaMoO<Subscript>4</Subscript> nanocrystals

Rod-like CaMoO₄ nanocrystals were synthesized via a template-based rheological phase reaction route as a novel method. The physical characterization was carried out by thermogravimetric/differential thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and elected-area electron diffraction (SAED). A structure-directed role of hexamethylene tetramine (HMTA) was observed during the formation of CaMoO₄ nanocrystals. The electrochemical performance of CaMoO₄ as anode for lithium ion batteries has also been investigated by galvanostatic cycling and AC impedance spectroscopy. CaMoO₄/Li cell can deliver superior capacity than theoretical value in the initial cycle, and the much improved capacity was attributed to the contribution of oxygen besides the reduction of molybdenum during lithium insertion. Furthermore, a charge capacity of 276 and 438 mAh/g was retained after 50 cycles in the range of 0.01–2.50 V vs Li at a current density of 100 and 200 mA/g, respectively. The particle size and morphological properties were found to play an important role in fast lithium insertion/extraction performance and cycling stability at high rate.     

NH<Subscript>4</Subscript>V<Subscript>3</Subscript>O<Subscript>7</Subscript>: Synthesis,morphology, and optical properties

The effect of the method used for the synthesis of NH₄V₃O₇ on its morphology, textural parameters, and optical properties was studied. Ammonium vanadate NH₄V₃O₇ was prepared by treating NH₄VO₃ in the presence of citric acid under hydrothermal (4.0 ≤ pH ≤ 5.5, T = 180–200°C, 48 h) and microwave–hydrothermal (3.5 ≤ pH ≤ 5.0, T = 180–220°C, 20 min) conditions. Self-assembled NH₄V₃O₇ microcrystals crystallizing in monoclinic system with unit cell parameters a = 12.247(5) Å, b = 3.4233(1) Å, c = 13.899(4) Å, β = 89.72(3)°, and V = 582.3(4) ų (space group P2₁) were shown to be formed independently of the method used to treat the reaction mixture. The morphology of NH₄V₃O₇ particles was shown to depend on рН of the reaction mass and the method of synthesis. The structural features of NH₄V₃O₇ were studied by IR, UV, and Vis spectroscopy, and the optical bandgap was determined.     

Effect of Pd and rare earth oxides (La<Subscript>2</Subscript>O<Subscript>3</Subscript>, CeO<Subscript>2</Subscript>) on the properties of a Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/cordierite catalyst in reduction of O<Subscript>2</Subscript> and no by hydrogen

We have established that introducing a promoter (Pd) and modifying additives (La₂O₃, CeO₂) into the composition of a Co₃O₄/cordierite catalyst leads to an increase in its activity and selectivity during reduction of oxygen by hydrogen in the presence of nitrogen(II) oxide.     

Oxygen evolution on Ti/Co<Subscript>3</Subscript>O<Subscript>4</Subscript>-coated electrodes in alkaline solution

The electrochemical performances of Co₃O₄ nanopowders, obtained by the sol-gel method, were investigated and compared with those of commercial Co₃O₄ powders, for oxygen evolution reaction in alkaline solution. The active oxide powder was mixed with teflon and assembled on Ti substrate to form thin catalyst film. Cyclic voltammetry, polarization curves, and electrochemical impedance spectroscopy were used to assess the mechanism of oxygen evolution reaction, chemical structure, and morphology of the catalyst. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

Preparation and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>composite particles

Using Fe₃O₄ nano-particles as seeds, a new type of Fe₃O₄/Au composite particles with core/shell structure and diameter of about 170 nm was prepared by reduction of Au³⁺ with hydroxylamine in an aqueous solution. Particle size analyzer and transmission electron microscope were used to analyze the size distribution and microstructure of the particles in different conditions. The result showed that the magnetically responsive property and suspension stability of Fe₃O₄ seeds as well as reduction conditions of Au³⁺to Au⁰are the main factors which are crucial for obtaining a colloid of the Fe₃O₄/Au composite particles with uniform particle dispersion, excellent stability, homogeneity in particle sizes, and effective response to an external magnet in aqueous suspension solutions. UV-Vis analysis revealed that there is a characteristic peak of Fe₃O₄/Au fluid. For particles with d(0.5)=168 nm, the λmax is 625 nm.