Synthesis Of Co Research Articles

Synthesis of Co0·52Cu0·48/Cu@S–C arrays for the enhanced performance of hydrazine-assisted hydrogen production

The development of efficient bifunctional catalysts is the key technology to replace oxygen evolution reaction (OER) with hydrazine oxidation reaction (HzOR) with lower theoretical potential to achieve high efficiency and energy-saving hydrogen production. In this work, the Co0·52Cu0·48/Cu@S–C (−1.3 V) composite with flower-like array was prepared by two-step electrodeposition coupled pyrolysis method. The electrochemical measurements showed that the driving voltages of the optimal composite for HzOR and hydrogen evolution reaction (HER) are respectively −118 mV and 47 mV at a current density (j) of 10 mA cm−2. The excellent performance of Co0·52Cu0·48/Cu@S–C (−1.3 V) composite is attributed to the fact that the flower-like structure exposes more active areas and facilitates the diffusion of electrolyte, the strong electron interaction between Co0·52Cu0·48/Cu and S–C substrate, which can be verified by X-ray photoelectron spectroscopy (XPS), enhances the electrical conductivity, the Co0·52Cu0·48/Cu heterogeneous interface reduces the water dissociation barrier and facilitates the dehydrogenation kinetics of N2H4 determined by density functional theory (DFT) calculations. Due to the excellent performance of Co0·52Cu0·48/Cu@S–C (−1.3 V), the overall hydrazine splitting (OHzS) electrolytic cell was constructed with Co0·52Cu0·48/Cu@S–C (−1.3 V) as electrodes. The results showed the voltages required by the cell are 36, 210 and 282 mV at the current density values of 10, 100 and 200 mA cm−2 respectively, showing that Co0·52Cu0·48/Cu@S–C (−1.3 V) can be used for energy-saving hydrogen production by hydrazine assisted water electrolysis.

Metal Complexes of Schiff Bases of 3-Hydroxyquinoxaline-2-carboxaldehyde Encapsulated in Zeolite Y Cages: Potential Catalyst for Removing Phenol from Effluent Media

Transition metal complexes are known to be efficient catalyst for many organic transformations. Encapsulation of metal complexes in zeolite cage brings many significant modifications in the structure of the metal complexes, which are very interesting from the catalytic point of view. This study aims in a comparative evaluation of the influence of structure of neat and encapsulated complexes in their catalytic activity. Phenol is one of the major industrial pollutants. Heterogenizing transition metal Schiff bases by encapsulation inside the zeolite would help to minimize the reuse problem of transition metal complexes. This article deals with the synthesis, characterization and catalytic activity studies of Co(II), Ni(II) and Cu(II) complexes of 3-hydroxyquinoxaline-2-carboxaldehyde with ethylenediamine (L1) and an o-phenylene diamine (L2).

Enhancement in DC Electrical Resistivity and Dielectric Behaviour of Ti4+ Doped CoFe2O4 NP’s for Nanoelectronics Application

Inverse spinel structured cobalt ferrite is one of the capable nominee for information storage and also in nanoelectronics devices. The present paper reports the rietveld refined structural, elastic, electrical and dielectric behaviour of titanium doped CoFe2O4 NP’s. The synthesis of Co1+xTixFe2-2xO4 (where, 0.0  x  0.5) nanoparticles was performed using self generated combustion technique. The prepared NP’s were characterized by X-ray diffraction technique (XRD) and Fourier transform infrared spectroscopy (FT-IR) technique to analyze the structural and elastic properties. The analysis of XRD patterns confirms the formation of single phase spinel cubic structure of all the prepared samples. The diffractograms obtained at room temperature were used for Rietveld refinement to determine the lattice constant, oxygen position, average crystallite size etc. parameters. The elastic modules were investigated through vibrational bands in FTIR spectra. The band positions in FT-IR spectra confirmed the octahedral [B] and tetrahedral (A) stretching which evident the ferrite skeleton. The plot of DC electrical resitivity with respect to temperature shows the semiconducting behaviour of the nanoparticles. The activation energy determined through resistivity plots, show decreasing nature with incrementing Ti4+ doping in cobalt ferrite. The dielectric parameters decreased exponentially with increasing frequency and with Ti doping.

Bioactivity of catalase loaded into vaterite CaCO3 crystals via adsorption and co-synthesis

Protein therapy gained a reputation of the most direct and safe approach for treating various diseases, yet biodegradation and loss of bioactivity of fragile therapeutic proteins limit their wide medical use. Recently, a new hard templating technology using decomposable mesoporous vaterite CaCO3 crystals became extremely popular strategy for formulation of protein nano(micro)-vectors. This study deciphers how protein bioactivity depends on protein loading/release for this technology utilizing catalase as a promising antioxidant therapeutic agent. Catalase has been loaded into CaCO3 using two approaches: i) passive - via adsorption (ADS) into pre-formed crystals and ii) active - via co-synthesis (COS) in the pH range 8–10. Crystal morphology, protein secondary structure and enzymatic bioactivity, and protein retention upon washing are assessed. The activity reduction (∼70% for COS and ∼20% for ADS) is caused by both protein exposure to an alkaline medium and protein aggregation induced by Ca2+. The aggregation significantly governs protein release kinetics. Catalase loading into the crystals is pH-independent and van der Waals interactions dominate over the electrostatics, while catalase activity strongly depends on pH. This study implicates the prime role of loading/release mechanism in the preservation of protein bioactivity and guide for the control over the retention of protein bioactivity.

The mechanism of catalase loading into porous vaterite CaCO3 crystals by co-synthesis.

Porous vaterite CaCO3 crystals are nowadays extensively used as high-capacity bio-friendly sacrificial templates for the fabrication of such protein-containing nano- and micro-particles as capsules and beads. The first step in the protein encapsulation is performed through loading of the protein molecules into the crystals. Co-synthesis is one of the most useful and simple methods proven to effectively load crystals with proteins; however, the loading mechanism is still unknown. To understand the mechanism, in this study, we focus on the loading of a model protein catalase into the crystals by means of adsorption into pre-formed crystals (ADS) and co-synthesis (COS). Analysis of the physico-chemical characteristics of the protein in solution and during the loading and simulation of the protein packing into the crystals are performed. COS provides more effective loading than ADS giving protein contents in the crystals of 20.3 and 3.5 w/w%, respectively. Extremely high loading for COS providing a local protein concentration of about 550 mg mL-1 is explained by intermolecular protein interactions, i.e. formation of protein aggregates induced by CaCl2 during the co-synthesis. This is supported by a lower equilibrium constant obtained for COS (5 × 105 M-1) than for ADS (23 × 105 M-1), indicating a higher affinity of single protein molecules rather than aggregates to the crystal surface. Fitting the adsorption isotherms by classical adsorption models has shown that the Langmuir and BET models describe the adsorption phenomenon better than the Freundlich model, proving the aggregation in solution followed by adsorption of the aggregates into the crystals. We believe that this study will be useful for protein encapsulation through CaCO3 crystals using the COS method.

“Synthesis of Co1−xGdxFe2O4+δ (0 ≥ x ≤ 0.1) and study of their magnetic, electric, and magneto-optical properties”

In this investigation, pure and gadolinium-doped cobalt ferrites (Co1−xGdxFe2O4+δ, x= 0, 0.02, 0.04, 0.06, 0.08 y 0.1), were synthesized through a modified route of the coprecipitation method. X-ray diffraction technique shows a cubic phase of the spinel-type structure typically associated with these compounds. According to Scherrer's equation, the crystallite size can be tuned through the Gd3+ content (26 nm to x= 0 and 9 nm to x= 0.1) or through the temperature of the thermal treatment (21 nm to 400 °C and 28 nm to 700 °C). The obtained powders show a ferrimagnetic behavior, at room temperature, with magnetization (reached at the maximum applied field) and coercivity values showing a dependence on the substitution grade of cobalt (II) by gadolinium (III) ions. At x= 0.02 the magnetization shows an increase of 7% (even when the particle size decreases a 40%) and the coercivity shows a decrease of 45%. DC conductivity of sintered ferrites is enhanced up to 3 orders of magnitude in the x= 0.1 substituted materials; while, keeping a constant transverse magneto-optical Kerr effect around 0.35%.

Carbon Nanotubes Rooted in Porous Ternary Metal Sulfide@N/S‐Doped Carbon Dodecahedron: Bimetal‐Organic‐Frameworks Derivation and Electrochemical Application for High‐Capacity and Long‐Life Lithium‐Ion Batteries

Lithium ion battery is the predominant power source for portable electronic devices, electrical vehicles, and back‐up electricity storage units for clean and renewable energies. High‐capacity and long‐life electrode materials are essential for the next‐generation Li‐ion battery with high energy density. Here bimetal‐organic‐frameworks synthesis of Co0.4Zn0.19S@N and S codoped carbon dodecahedron is shown with rooted carbon nanotubes (Co‐Zn‐S@N‐S‐C‐CNT) for high‐performance Li‐ion battery application. Benefiting from the synergetic effect of two metal sulfide species for Li‐storage at different voltages, mesoporous dodecahedron structure, N and S codoped carbon overlayer and deep‐rooted CNTs network, the product exhibits a larger‐than‐theoretical reversible Li‐storage capacity of 941 mAh g−1 after 250 cycles at 100 mA g−1 and excellent high‐rate capability (734, 591, 505 mAh g−1 after 500 cycles at large current densities of 1, 2, and 5 A g−1 , respectively).

The synthesis of Co1−xDyxFe2O4 nanoparticles and thin films as well as investigating their magnetic and magneto-optical properties

The modification and optimization of the magnetic and magneto-optical properties of cobalt ferrite are of great importance due to their various applications in well-known scientific and industrial categories. In order to observe the effect of adding Dy3+ to the cobalt ferrite composition, Co1−xDyxFe2O4 (0≤x≤0.1) ceramic nanoparticles were synthesized by the co-precipitation chemical method and then their microstructure and magnetism were investigated through x-ray diffractometry, TEM micrography, IR spectroscopy and VSM magnetometry. The polar magneto-optical Kerr effect of the thin film specimens was also studied. The results reveal that the doping of Dy3+ ions could effectively alter the inversion degree of the spinel structure and the following magnetic and magneto-optical features. The ferrite coercivity was enhanced by 150% after adding Dy. The perceptible shifts of peak rotations were observed in the Kerr spectra for the Dy-doped CoFe2O4 films. Furthermore, TC had a descending trend with the addition of Dy from 440°C to 420°C for Co0.95Dy0.05Fe2O4.

Synthesis, non-isothermal crystallization and magnetic properties of Co0·75Zn0·25Fe2O4/poly(ethylene-co-vinyl alcohol) nanocomposite

The synthesis of Co0·75Zn0·25Fe2O4/poly(vinyl alcohol-co-ethylene) (ferrite/PEVA) nanocomposite was carried out through two steps: impregnation of the ferrite particules by PEVA and then mixing the ferrite/PEVA impregnated with PEVA solution. A non-isothermal study of the crystallization kinetic of ferrite/PEVA nanocomposite was carried out by differential scanning calorimetry (DSC), scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. It was observed that the Ozawa equation describes perfectly the primary process of non-isothermal crystallization of ferrite/PEVA system. There is a strong dependence of the ferrite/PEVA composition on the crystallization parameters. The crystallization activation energy (E a ) calculated from the Xu and Uhlmann model increased by increasing the ferrite content in ferrite/PEVA nanocomposites between 3 and 7 wt% and decreased dramatically beyond these values. The results revealed that the ferrite nanoparticles were uniformly distributed throughout the PEVA matrix. The percentage of magnetization of the composite decreases as the concentration of the ferrite increases.

Synthesis of Co1.5Fe1.5O4 spinel ferrite with high magnetic squareness and study its magnetic property by annealing the chemical routed sample at different temperatures

Ferromagnetic property of Co1.5Fe1.5O4 ferrite has been studied in a wide range of measurement temperature and magnetic field. Grain size effect on the ferromagnetic parameters has been examined by annealing the chemical routed sample at different temperatures up to 1150°C. The evolution from hard to soft ferromagnetism of the material has been correlated with undergoing changes of crystal structure, grain morphology, crystalline anisotropy, and transformation of the ferromagnetic grains from single domain to multi-domain structure during annealing process. The present ferrite samples also showed some interesting low temperature features, e.g., blocking of ferromagnetic grains that started above 300K and its control by varying magnetic field intensity, competition of the crystalline anisotropy between uniaxial and cubic character, large magnetic squareness and variable coercivity as the function of annealing temperature of the samples. The material seems to be technologically interesting for its high squareness value.

Co(OH)3 nanobelts: synthesis, characterization and shape-preserved transformation to pseudo-single-crystallineCo3O4 nanobelts

In this paper, we demonstrated a facile hydrothermal route leading to the generation of a new cobalt hydroxide,Co(OH)3, nanobelt. Thisnew product of Co(OH)3 nanobelts was well characterized and identified by SEM, TEM, XRD, EDX,XPS, EXAFS, Raman, TGA and SQUID. Additionally, through systematicinvestigations on morphological evolution, it was found that the size and shape ofCo(OH)3 nanobelts were adjustable in large scale, e.g. from 50 to 1.5 µm in lengthand 5 µm to 20 nm in width, by means of fine experimental parametercontrol. Furthermore, the unique pseudo-single-crystallineCo3O4 nanobelts wereproduced from Co(OH)3 precursors via heating treatment. This is the first synthesis ofCo(OH)3 with tunable shapes and sizes, which may find important applications as gas sensors,catalysts, and electrode materials, owing to the specific large surface-to-volume ratio andother unique properties endowed by typical 1D nanobelts.