Cobalt terephthalate MOF-templated synthesis of porous nano-crystalline Co3O4 by the new indirect solid state thermolysis as cathode material of asymmetric supercapacitor

In this work, two different types of Co₃O₄ nano-crystals were synthesized by (i) conventional direct solid state thermolysis of cobalt terephthalate metal-organic framework (MOF-71) and (ii) new indirect solid state thermolysis of Co(OH)₂ derived by alkaline aqueous treatment of MOF-71. The products were then characterized by X-ray diffraction technique (XRD), Fourier transforms infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Reflection electron energy loss spectroscopy (REELS), Brunauer, Emmett, and Teller (BET), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. By REELS analysis the energy band gap of MOF-71 was determined to be 3.7 eV. Further, electrochemical performance of each Co₃O₄ nanostructure was studied by the cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) in a three-electrode system in KOH electrolyte. An asymmetric supercapacitor was fabricated using indirect Co₃O₄ nanoparticles as cathode and electrochemically reduced graphene oxide as anode, and the electrochemical properties were studied and showed a high energy density of 13.51 Wh kg⁻¹ along with a power density of 9775 W kg⁻¹ and good cycling stability with capacitance retention rate of 85% after 2000 cycles.     

Hydrothermal synthesis of mesoporous Co3O4 nanobelts by means of a compound precursor

In the present work, high surface area mesoporous cobalt oxide (Co₃O₄) nanobelts have been synthesized by thermal treatment of cobalt hydroxide carbonate (CHC) precursors. CHC nanobelts were prepared by a facile hydrothermal method. Control experiments with variations in reaction time, solvent and different cobalt source revealed that temperature and sulfates are key factors in determining the formation of CHC nanobelts. Scanning electron microscopy and transmission electron microscopy images showed that the Co₃O₄ nanobelts consisted of mesoporous nanobelts with the average width of 40 nm. Brunauer–Emmett–Teller (BET) gas adsorption measurement further indicated that the products presented a rather large surface area (172.09 m² g^?1).     

Electrochemical supercapacitor studies of hierarchical structured Co2+-substituted SnO2 nanoparticles by a hydrothermal method

Hierarchical structured Co-doped SnO₂ nanoparticles are prepared by a low temperature hydrothermal process. The structural and surface morphologies of the SnO₂ and Sn_1?xCo_xO₂ nanoparticles are studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The Sn_1?xCo_xO₂ nanoparticles form with a tetragonal rutile structure during the hydrothermal process without further calcination. The pseudocapacitance behavior of the Sn_1?xCo_xO₂ nanoparticles is characterized by cyclic voltammetry (CV) in 1.0 M H₂SO₄ electrolyte. The specific capacitance (SC) is found to increase with an increase in cobalt content. A maximum SC of 840 F g^?1 is obtained for a Sn_0.96Co_0.04O₂ composite at a 10 mV s^?1 scan rate.     

Co3O4-ZnO hierarchical nanostructures by electrospinning and hydrothermal methods

A new hierarchical nanostructure that consists of cobalt oxide (Co₃O₄) and zinc oxide (ZnO) was produced by the electrospinning process followed by a hydrothermal technique. First, electrospinning of a colloidal solution that consisted of zinc nanoparticles, cobalt acetate tetrahydrate and poly(vinyl alcohol) was performed to produce polymeric nanofibers embedding solid nanoparticles. Calcination of the obtained electrospun nanofiber mats in air at 600 °C for 1 h, produced Co₃O₄ nanofibers with rough surfaces containing ZnO nanoparticles (i.e., ZnO-doped Co₃O₄ nanofibers). The rough surfaced nanofibers, containing ZnO nanoparticles (ZnNPs), were then exploited as seeds to produce ZnO nanobranches using a specific hydrothermal technique. Scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to characterize the as-spun nanofibers and the calcined product. X-ray powder diffractometery (XRD) analysis was used to study the chemical composition and the crystallographic structure.     

Syntheses and characterization of Mg(OH)2 and MgO nanostructures by ultrasonic method

Magnesium hydroxide nanostructures have been synthesized by the reaction of magnesium acetate with sodium hydroxide via sonochemical method. Reaction conditions such as the Mg²⁺ concentration, aging time and the ultrasonic device power show important roles in the size, morphology and growth process of the final products. The magnesium oxide nanoparticles have been prepared by calcination of magnesium hydroxide nanostructures at 400 °C. The magnesium hydroxide and magnesium oxide nanostructures were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), thermal gravimetric (TG) and differential thermal analyses (DTA).     

Sonochemical synthesis of Dy2(CO3)3 nanoparticles,Dy(OH)3 nanotubes and their conversion to Dy2O3 nanoparticles

Dysprosium carbonates nanoparticles were synthesized by the reaction of dysprosium acetate and NaHCO₃ by a sonochemical method. Dysprosium oxide nanoparticles with average size about 17 nm were prepared from calcination of Dy₂(CO₃)₃·1.7H₂O nanoparticles. Dy(OH)₃ nanotubes were synthesized by sonication of Dy(OAC)₃·6H₂O and N₂H₄. The as-synthesized nanostructures were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). Photoluminescence measurement shows that the nanoparticles have two emission peaks around 17,540 cm^?1 and 20,700 cm^?1, which should come from the electron transition from ⁴F_9/2 → ⁶H_15/2 levels and ⁴F_9/2 → ⁶H_13/2 levels, respectively. The effect of calcination temperature and sonication time was investigated on the morphology and particle size of the products. The sizes could be controlled by the feeding rate of the precipitating agent (NaHCO₃ and N₂H₄) and slower feeding rate lead to smaller nanoparticles.     

Laser power influence on Raman spectra of ZnO(Co) nanoparticles

Influence of laser power on nanocrystalline samples of ZnO(Co) prepared by commonly used wet chemistry method followed by calcination was investigated. Previous confirmation of the existence of ZnO and Co₃O₄ phases was based on the X-ray diffraction measurements. Here we report the experimental spectra of non-resonant Raman scattering in the range between 100 cm⁻¹ and 1600 cm^–1, for a series of samples irradiated with four different laser power densities. The laser power density has different influence on relative intensity of peaks that belong to ZnO phase than on those corresponding to Co₃O₄ phase. Both peak types show characteristic broadening and red shift toward lower frequencies. The laser power densities used in our study did not cause thermal destruction in any of the investigated samples. Laser-induced local heating effects in samples caused formation of cobalt dimers on the surface of Co₃O₄.     

Effects of doping with nanoscale Co3O4 particles on the superconducting properties of powder-in-tube processed MgB2 tapes

Nanoscale Co₃O₄ particles were doped into MgB₂ tapes with the aim of developing superconducting wires with high-current-carrying capacity. Fe-sheathed MgB₂ tapes with a mono-core were prepared using the in situ powder-in-tube (PIT) process with the addition of 0.2–1.0 mol% Co₃O₄. The critical temperature decreased monotonically with an increasing amount of doped Co₃O₄ particles for all heat-treatment temperatures from 600 to 900 °C. However, the transport critical current density (J_c) at 4.2 K varied with the heat-treatment temperatures. The J_c values in magnetic fields ranging from 7 to 12 T decreased monotonically with increasing Co₃O₄ doping level for a heat-treatment temperature of 600 °C. In contrast, some improvements on the J_c values of the Co₃O₄ doped tapes were observed in the magnetic fields below 10 T for 700 and 800 °C. Furthermore, J_c values in all the fields measured increased as the Co₃O₄ doping level increase from 0 to 1 mol% for 900 °C. This heat-treatment temperature dependence of the J_c values could be explained in terms of the heat-treatment temperature dependence of the irreversibility field with Co₃O₄ doping.     

Structure sensitivity of propene oxidation over Co-Mn spinels

Single-phase cobalt–manganese spinel oxides (Co_3?nMn_nO₄, CMO) were studied for the catalytic oxidation of propene in a systematic optimization strategy. CMO films were synthesized by pulsed-spray evaporation chemical vapor deposition (PSE–CVD) and characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman and Ultraviolet–Visible (UV–Vis) spectroscopy. The effect of Co/Mn ratio in the mixed oxide systems on their catalytic activity was investigated in a fixed-bed reactor at T = 100–800 °C, with a space velocity of 90,000 mL/g_cat h and a feed of 2% C₃H₆/20% O₂/78% Ar. XRD patterns, FTIR and Raman spectroscopy reveal that a cubic single-phase spinel structure is obtained for n ? 1.23, while a tetragonal spinel structure is observed for n > 1.23. With increasing of the manganese content, the temperature–programmed analysis demonstrates a lower reducibility, a general decrease of the temperature required for the reduced samples to be re-oxidized and increasing thermal stability. The catalytic tests show that the involvement of cobalt–manganese oxides in propene oxidation suppresses the formation of reaction intermediates, favoring the selectivity toward CO₂ at low temperatures. Co_2.35Mn_0.65O₄ exhibits the best catalytic performance, which follows in line with its better reducibility compared with the other compositions in the series of CMO oxides. These results show the great potential of CMO for future industrial application as a low-temperature catalytic system which does not rely on precious metals.     

Sonochemical synthesis and characterization of new nanostructures cobalt(II) metal-organic complexes derived from the azo-coupling reaction of 4-amino benzoic acid with anthranilic acid,salicylaldehyde and 2-naphtol

Nanostructures of three new cobalt(II) complexes, (CoL₁)·0.5DMF·1.5MeOH (1), [H₂L₁ = 5-(4-Carboxy phenyl azo) anthranilic acid], (Co(L₂)₂)·1.5MeOH (2), [HL₂ = 5-(4-Carboxy phenyl azo) salicylaldehyde] and (Co(L₃)₂)·0.5 DMF·0.5MeOH (3), [HL₃ = 1-(4-Carboxy phenyl azo) 2-naphtol], have been synthesized by the reaction of H₂L₁, HL₂ and HL₃ with Co(OAc)₂·4H₂O through sonochemical process. Calcination of the nano-sized compounds 1–3 yield Co₃O₄ nanoparticles at 450 °C under air atmosphere. These nanostructures were characterized by X-ray powder diffraction (XRD) and Scanning Electron Microscopy (SEM). Thermal stability of compounds 1–3 was studied by thermogravimetric (TG) and differential thermal analyses (DTA).     

Sonochemical synthesis of cobalt aluminate nanoparticles under various preparation parameters

Cobalt aluminate (CoAl₂O₄) nanoparticles were synthesized using a precursor method with the aid of ultrasound irradiation under various preparation parameters. The effects of the preparation parameters, such as the sonochemical reaction time and temperature, precipitation agents, calcination temperature and time on the formation of CoAl₂O₄ were investigated. The precursor on heating yields nanosized CoAl₂O₄ particles and both these nanoparticles and the precursor were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The use of ultrasound irradiation during the homogeneous precipitation of the precursor reduces the duration of the precipitation reaction. The mechanism of the formation of cobalt aluminate was investigated by means of Fourier transformation infrared spectroscopy (FT-IR) and EDX (energy dispersive X-ray). The thermal decomposition process and kinetics of the precursor of nanosized CoAl₂O₄ were investigated by means of differential scanning calorimetry (DSC) and thermogravimetry (TG). The apparent activation energy (E) and the pre-exponential constant (A) were 304.26 kJ/mol and 6.441 × 10¹⁴ s^?1, respectively. Specific surface area was investigated by means of Brunauer Emmett Teller (BET) surface area measurements.     

Sonochemical fabrication of Fe3O4 nanoparticles on reduced graphene oxide for biosensors

This study synthesized Fe₃O₄ nanoparticles of 30–40 nm by a sonochemical method, and these particles were uniformly dispersed on the reduced graphene oxide sheets (Fe₃O₄/RGO). The superparamagnetic property of Fe₃O₄/RGO was evidenced from a saturated magnetization of 30 emu/g tested by a sample-vibrating magnetometer. Based on the testing results, we proposed a mechanism of ultrasonic waves to explain the formation and dispersion of Fe₃O₄ nanoparticles on RGO. A biosensor was fabricated by modifying a glassy carbon electrode with the combination of Fe₃O₄/RGO and hemoglobin. The biosensor showed an excellent electrocatalytic reduction toward H₂O₂ at a wide, linear range from 4 × 10^?6 to 1 × 10^?3 M (R² = 0.994) as examined by amperometry, and with a detection limit of 2 × 10^?6 M. The high performance of H₂O₂ detection is attributed to the synergistic effect of the combination of Fe₃O₄ nanoparticles and RGO, promoting the electron transfer between the peroxide and electrode surface.     

Synthesis and characterization of L10 FePt nanoparticles from Pt–Fe3O4 core-shell nanoparticles

Pt/Fe₃O₄ core-shell nanoparticles have been prepared by a modified polyol method. Pt nanoparticles were first prepared via the reduction of Pt(acac)₂ by polyethylene glycol-200 (PEG-200), and layers of iron oxide were subsequently deposited on the surface of Pt nanoparticles by the thermal decomposition of Fe(acac)₃. The nanoparticles were characterized by XRD and HR-TEM. The as-prepared Pt/Fe₃O₄ nanoparticles have a chemically disordered FCC structure and transformed into chemically ordered fct structure after annealing in reducing atmosphere (4% H₂, 96% Ar) at 700 °C. The ordered fct FePt phase has high magnetic anisotropy with coercivity reaching 7.5 kOe at room temperature and 9.3 kOe at 10 K.     

Theoretical investigation of the inversion parameter in Co3 − sAlsO4 (s = 0–3) spinel structures

The structural, energetic, and thermodynamic properties of the Co_3 ? sAl_sO₄ (s = 0, 1, 2, and 3) crystal family are studied using periodic DFT calculations. We provide a quantitative discussion of the cation distribution effect on the cell parameter, the oxygen Wyckoff position, the interatomic distances and the energies of the structures. It is demonstrated that the low cobalt containing CoAl₂O₄ spinel is the most stable structure of the Co_3 ? sAl_sO₄ (s = 0, 1, 2, and 3) crystal family.     

Preparation and characterization of Fe3O4(1 1 1) nanoparticles and thin films on Au(1 1 1)

Fe₃O₄ nanoparticles and thin films were prepared on the Au(1 1 1) surface and characterized using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Fe₃O₄ was formed by annealing α-Fe₂O₃(0 0 0 1) structures on Au(1 1 1) at 750 K in ultrahigh vacuum (UHV) for 60 min. Transformation of the α-Fe₂O₃(0 0 0 1) structures into Fe₃O₄ nanoparticles and thin films was supported by XPS. STM images show that during the growth procedure used, Fe₃O₄ initially appears as nanoparticles at low coverages, and forms thin films at ～2 monolayer equivalents (MLE) of iron. Two types of ordered superstructures were observed on the Fe₃O₄ particles with periodicities of ～50 and ～42 Å, respectively. As the Fe₃O₄ particles form more continuous films, the ～50 Å feature was the predominant superstructure observed. The Fe₃O₄ structures at all coverages show a hexagonal unit cell with a ～3 Å periodicity in the atomically resolved STM images.     

Cobalt oxide nanolayers on Pd(100): The thickness-dependent structural evolution

The growth of interface-stabilized cobalt oxide (CoO_x) nanolayers on Pd(100) has been investigated and their structures are reported as a function of coverage. Several different phases have been observed by LEED and STM experiments, and they have been characterized spectroscopically by photoemission and X-ray absorption. The data indicate that in the low coverage regime (up to Θ_Co ≈ 2–3 ML) rock-salt CoO type phases are formed (defective in the single layer regime, and stoichiometric in multilayers) with (100) or (111) termination. At higher coverage (Θ_Co ≈ 10–20 ML) spinel Co₃O₄(111) and CoO(100) layers have been detected, in ratios dependent on the preparation conditions. The observed structures are discussed in relation to similar structures reported recently for CoO_x films on Ir(100) [W. Meyer et al., J. Phys.: Condens. Matter 20 (2008) 265011].     

Synthesis of Sm2Co17 alloy nanoparticles by mechanochemical processing

Sm₂Co₁₇ alloy nanoparticles of 10–250 nm in size were prepared by mechanochemical processing involving the co-reduction of Sm₂O₃ and CoO with Ca. The crystal structure of the nano-sized Sm₂Co₁₇ particles was mainly of the ordered Th₂Zn₁₇-type. When embedded in the CaO matrix the Sm₂Co₁₇ nanoparticles exhibited a high coercivity of 14.2 kOe. The CaO by-product could be removed by a carefully controlled washing process without significant oxidation of the ultrafine alloy particles. After washing, the cold-pressed powder exhibited a coercivity value of 11.8 kOe and a maximum magnetization of 92.0 emu/g under an applied field of 50 kOe.     

Ionic conductance of composite electrolytes based on network polymer with ceramic powder

Effects of ceramic fillers (α-Al₂O₃, γ-Al₂O₃ and BaTiO₃) have been investigated on the ionic conductance of polymeric complexes consisting of poly(ethylene oxide)-modified poly(methacrylate) (PEO-PMA) and lithium bis(trifluoromethylsulfonyl)imide, Li(CF₃SO₂)₂N, and ceramic powder. The addition of ceramic powder increased the ionic conductivity over an ambient temperature range. Conductivity of 4.9 × 10^− 5 S cm^− 1 at 333 K (60 °C) was obtained for the composite containing 15 wt.% α-Al₂O₃ prepared by photo-polymerization. The optimum content of Al₂O₃ was different among the methods of polymerization. The highest conductivity was obtained for the composite containing 5 wt.% of α-, or γ-Al₂O₃ prepared by thermal polymerization. The addition of the ceramic filler scarcely influenced the thermal properties of the polymer matrix. XRD and NMR experiments showed that the ionic mobility could be enhanced in the composites by addition of α-Al₂O₃. The addition of small amounts of ferroelectric BaTiO₃ also increased the ionic conductivity of the polymeric complex, but its extent was smaller than the case of the Al₂O₃ addition.     

Electric property of mixed conductor BaIn1−xCoxO3−δ

We synthesized BaIn_1−xCo_xO_3−δ (x = 0–0.8) with a defective perovskite structure by partly replacing In with Co in Ba₂In₂O₅. Based on XRD measurements, the synthesized compound was found to have cubic perovskite and orthorhombic brownmillerite structures depending on the amount of Co. BaIn_1−xCo_xO_3−δ (x = 0.2 and 0.3) showed high total electrical conductivities without undergoing the structural transformation that the original Ba₂In₂O₅ undergoes. Some of the samples showed both electronic and oxide ionic conductivities. At the same time, the oxide ionic conductivity was comparable with that of Ba₂In₂O₅. For example, the sample with x = 0.1 had a total electrical conductivity of 4.7 × 10^− 1 S cm^− 1 and an oxide ion transport number of 0.52 at 850 °C.