Cobalt Ferrite Particles Research Articles

Cobalt Ferrite Bearing Nitrogen-Doped Reduced Graphene Oxide Layers Spatially Separated with Microporous Carbon as Efficient Oxygen Reduction Electrocatalyst.

The present work discloses how high-quality dispersion of fine particles of cobalt ferrite (CF) could be attained on nitrogen-doped reduced graphene oxide (CF/N-rGO) and how this material in association with a microporous carbon phase could deliver significantly enhanced activity toward electrochemical oxygen reduction reaction (ORR). Our study indicates that the microporous carbon phase plays a critical role in spatially separating the layers of CF/N-rGO and in creating a favorable atmosphere to ensure the seamless distribution of the reactants to the active sites located on CF/N-rGO. In terms of the ORR current density, the heat-treated hybrid catalyst at 150 °C (CF/N-rGO-150) is found to be clearly outperforming (7.4 ± 0.5 mA/cm(2)) the state-of-the-art 20 wt % Pt-supported carbon catalyst (PtC) (5.4 ± 0.5 mA/cm(2)). The mass activity and stability of CF-N-rGO-150 are distinctly superior to PtC even after 5000 electrochemical cycles. As a realistic system level exploration of the catalyst, testing of a primary zinc-air battery could be demonstrated using CF/N-rGO-150 as the cathode catalyst. The battery is giving a galvanostatic discharge time of 15 h at a discharge current density of 20 mA/cm(2) and a specific capacity of ∼630 mAh g(-1) in 6 M KOH by using a Zn foil as the anode. Distinctly, the battery performance of this system is found to be superior to that of PtC in less concentrated KOH solution as the electrolyte.

Effect of the thermal treatment on the magnetic and structural properties of cobalt ferrite particles

We herein report a study on the sol-gel synthesis of CoFe2O4 and the effect of thermal treatment on the product outcome. Xerogels treated at 750, 800 and 850°C had their structural and magnetic properties thoroughly studied, in order to correlate their synthesis conditions to the positions in which the cations are inserted in the spinel structure. X-ray diffractograms exhibit reflections representative of the spinel structure and demonstrate that the thermal treatment does not affect the lattice parameters of the material. Mossbauer spectroscopy studies indicate a very low inversion degree in the synthesized spinels, which is very unusual for CoFe2O4. A maximum in coercivity of 1405.2 Oersted was achieved for the sample treated at 800°C.

Preparation and characterization of nanosized cobalt ferrite particles by co-precipitation method with citrate as chelating agent

Cobalt ferrite (CoFe2O4) nanoparticles were synthesized by a facile novel co-precipitation method with citrate as chelating agent. The synthesized cobalt ferrite nanoparticles were calcinated at 400, 600 and 800 °C and characterized by using XRD and TGDTA. From XRD it confirms that CoFe2O4 nano particles belongs to spinel type lattice of space group Fd3m. The CoFe2O4 nano particles calcinated at 600 °C were further characterized by using FE-SEM with EDAX, FE-TEM with SAED pattern, DLS zeta potential and CV. The linear relationship between particle size and calcination temperatures of CoFe2O4 nanoparticles was noticed. The surface morphology of CoFe2O4 studied through FE-SEM and FE-TEM indicate that the particles are found crystalline and are in cubic shape. EDAX analysis revealed the presence of Co, Fe and O. Zeta potential exposes the good stability of the prepared CoFe2O4 nanoparticles. Capacitance value 609 F g−1 was observed for the scanning rate of 2 mV s−1 from the CV study and concluded it is suitable for super capacitor application.

Structural and magnetic characteristics of PVA/CoFe2O4 nano-composites prepared via mechanical alloying method

In this research, polyvinyl alcohol/cobalt ferrite nano-composites were successfully synthesized employing a two-step procedure: the spherical single-phase cobalt ferrite of 20±4nm mean particle size was synthesized via mechanical alloying method and then embedded into polymer matrix by intensive milling. The results revealed that increase in polyvinyl alcohol content and milling time causes cobalt ferrite particles disperse more homogeneously in polymer matrix, while the mean particle size and shape of cobalt ferrite have not been significantly affected. Transmission electron microscope images indicated that polyvinyl alcohol chains have surrounded the cobalt ferrite nano-particles; also, the interaction between polymer and cobalt ferrite particles in nano-composite samples was confirmed. Magnetic properties evaluation showed that saturation magnetization, coercivity and anisotropy constant values decreased in nano-composite samples compared to pure cobalt ferrite. However, the coercivity values of related nano-composite samples enhanced by increasing PVA amount due to domain wall mechanism.

Magnetic properties of polymer matrix composites with embedded ferrite particles

Polymeric composite materials offer advantages for many applications because of a combination of properties, which includes high specific mechanical strength and elastic modulus and corrosion resistance. However, the non-magnetic nature of these materials impedes the use of non-destructive evaluation (NDE) techniques using magnetic sensors. In this work, glass fiber-reinforced epoxy magnetic composites were produced with the addition of 10wt% of cobalt or barium ferrite particles. Circular plates with notches of 1, 5 and 10mm in diameter were produced and characterized using magnetic flux leakage (MFL) technique. The effect of particle size on the magnetic properties of the composites was also investigated for the barium ferrite. The results indicated a good correlation between the measured magnetic signals and the presence of notches. Smaller average particle sizes hindered the identification of the smallest notch. However, it resulted in better signal-to-noise ratio for the intermediate and larger size notches.

Synthesis of Cobalt Ferrite Particles by Utilized Sol-Gel Method

Cobalt ferrite (CoFe2O4) nanoparticles were successfully synthesized by utilized sol gel method with controlled pH and temperature solution during reflux process in order to obtain monodispersed nanoparticles with high magnetic properties. The obtained cobalt ferrite particles are oval with the size vary from 100 nm to 220 nm. The Co˗O and Fe˗O bonds are formed as confirmed by FTIR measurement. The sample has high quality crystal with spinel structure as indicated by similar XRD pattern of the sample and the JCPDS (00-001-1121) data without impurity peaks. From the Vibrating Sample Magnetometer (VSM) measurement, magnetic remnant around 0.2303 emu/cc and coercive field around 2.7039 kOe are obtained.

Magnetic properties of cobalt ferrite synthesized by hydrothermal method

In this study, the magnetic properties of nanocrystalline cobalt ferrite synthesized via the hydrothermal method have been investigated. The structural properties of the produced powders were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The observed XRD pattern confirmed the spinel/cubic structure of the prepared cobalt ferrite. The SEM pictures show that the simple hydrothermal method produces uniform sphere-shaped nanopowders. Moreover, infrared spectroscopy was used to confirm the formation of cobalt ferrite particles. Magnetic hysteresis was measured using a vibrating sample magnetometer in a maximum field of 10 kOe. The magnetization of the prepared nanoparticles was investigated, and the saturation magnetization (M s), remanence (M r), and coercivity (H c) were derived from the hysteresis loops. The results revealed that the cobalt ferrite nanoparticles synthesized via the simple hydrothermal method exhibit superior magnetic properties.

Influence of pH and fuels on the combustion synthesis, structural, morphological, electrical and magnetic properties of CoFe2O4 nanoparticles

Nanocrystalline spinel cobalt ferrite particles are synthesized by simple combustion method using aspartic acid and glycine as fuels. The single phase cubic structure of CoFe2O4 is revealed through X-ray diffraction analysis (XRD). Further the Rietveld refinement confirms the formation of inverse spinel structure of CoFe2O4. The characteristic functional groups of Co–O and Fe–O are identified from Fourier Transform Infrared (FT-IR) analysis. Uniform distribution of of nearly spherical particles with the size range of 40–80nm is identified through field emission scanning electron microscope (FESEM) images. The calculated DC conductivity is 1.469×10−7 and 2.214×10−8Scm−1, for CoFe2O4 synthesized using aspartic acid and glycine, respectively. The dielectric behavior obeys the Maxwell–Wagner interfacial polarization. The ferromagnetic behavior of CoFe2O4 is identified using VSM analysis and the calculated coercivity is 27Oe and saturation magnetization is 68emu/g.

Enhanced electrocatalytic activity of PANI and CoFe2O4/PANI composite supported on graphene for fuel cell applications

New catalysts of reduced graphene oxide (rGO) with poly aniline (PANI) and cobalt ferrite (CF) have been successfully prepared by simple chemical reduction method. Their electrocatalytic activity for oxygen reduction reaction (ORR) was evaluated. Semi-crystalline nature of CF was analyzed by X-ray diffraction (XRD) study. Surface morphology by HR-SEM showed features of CF particles and PANI film on graphene sheets. FT-IR studies revealed changes in C–N and CN stretching vibrations of PANI confirming bonding of PANI to graphene sheets. Raman spectrum showed presence of PANI on distorted graphene layers. TG/DTA revealed thermal stability and extent of loading of CF in composite. ORR performance was studied using catalyst modified rotating disc electrode (RDE). A maximum kinetic current density of −3.46 mA cm−2 at −0.2 V was obtained for CF/PANI/rGO. Tafel slope, onset and half wave potentials for the catalyst were obtained from ORR response. Durability studies showed that synthesized electrocatalyst has better stability and methanol tolerance than commercial Pt/C catalyst. To the best of our knowledge, this is the first study aiming enhancement of ORR activity using PANI and CoFe2O4 on graphene support. A trace amount of Pt in the composite boosted the performance of single PEM fuel cell.

Sol–gel proteic method using orange albedo pectin for obtaining cobalt ferrite particles

Cobalt ferrite particles (CoFe 2 O 4 ) were synthetized using the proteic sol–gel method with pectin extracted from the albedo of orange peel as the gelling agent. The sol–gels were obtained by mixing pectin in different concentrations (4, 6 and 8 %) with salts of cobalt (II) nitrate hexahydrate and iron (III) nitrate nonahydrate. After gelling, the samples were calcined from 4 to 48 h at 1373 K. The formation of the spinel phase was investigated using X-ray diffraction, Fourier transform infrared and Mossbauer spectroscopy. Data analyses showed that 4 % pectin concentration is sufficient to produce cobalt ferrite particles. The grain size slightly increases with the thermal treatment time. The particles were successfully used to move a drop of sparged oil on water subjected to the action of a magnetic field.

Structural and Magnetic Properties of Ultrafine CoFe2O4 Nanoparticles

Nanosized Cobalt ferrite (CoFe2O4) particles are prepared through the sol-gel method using polyvinyl alcohol (PVA) as a chelating agent. The powder as prepared is annealed at three different temperatures (400oC, 500oC and 1000oC) for one hour. The X-ray diffraction patterns confirm the spinel structure of the samples. The XRD patterns of the samples indicate broad peaks and the full width at half maximum decreased with increasing annealing temperature. Infrared (IR) spectra of the samples confirm the presence of metal - oxygen complexes within the spinel lattice. The average particle size obtained from TEM micrographs demonstrates ultrafine particles having spherical morphology. The particle size of the annealed samples is in between 4.5-6.8nm. The saturation magnetization (Ms) and remnant magnetization (Mr) of the samples show dependence on particle size and crystallinity of the samples. The highest saturation magnetization (78.1 emu/g) is achieved for the sample annealed at 10000C having average particle size of 6.8nm. The high saturation magnetization of the samples suggests the present method is suitable for obtaining nanocrystalline magnetic ferrites which is desirable for practical applications.

Related magnetic properties of CoFe2O4 cobalt ferrite particles synthesised by the polyol method with NaBH4 and heat treatment: new micro and nanoscale structures

In this contribution, hierarchical CoFe2O4 particles are successfully prepared via a modified polyol elaboration method with NaBH4 and a proposed heat treatment process.

The influence of material properties on the assembly of ferrite nanoparticles into 3D structures

The fabrication of patterned arrays consisting of magnetic nanoparticles is gaining more and more research activities due to the possibility of enhancing a material's properties for the use in various fields (i.e. magneto-electrics). Here we present the influence of the particle size, the magnetic interactions between the particles and the strength of the applied magnetic field on the magnetically-directed assembly of ferrite nanoparticles. The assemblies were prepared from cobalt ferrite and maghemite suspensions using the drop-deposition technique without or with applied magnetic fields of different strengths. The cobalt ferrite particles with diameter of 6, 8, 10, 12, 20 nm, and maghemite nanoparticles with a diameter of 14 nm were used. The particles' size influences their magnetic properties, the magnetic interactions between the particles and, consequently, the assemblies' morphology. At an applied magnetic field of 0.5 T the morphology of the assembled structures was gradually changing as the particles' size was increasing from flat films for the 6 nm-sized cobalt ferrite nanoparticles to ordered 3-dimensional structures with columnar shape for the 20 nm-sized cobalt ferrite and 14 nm-sized maghemite nanoparticles. The assembled 3-dimensional structures displayed promising magnetic properties and can be used as a basis for the preparation of magneto-electric composites.

Highly sinterable cobalt ferrite particles prepared by a modified solution combustion synthesis

Highly sinterable CoFe2O4 particles were prepared by a modified solution combustion synthesis, starting from a stoichiometric mixture of cobalt acetate (instead of cobalt nitrate), iron nitrate and 5-aminotetrazole. The resulted cobalt ferrite powder had large surface area (44m2/g), small crystallite size (11nm) and a saturation magnetization of 38.9Am2/kg. CoFe2O4 pellets sintered at 1100°C for 2h developed a fine compact microstructure, reaching 99% of the theoretical density. After sintering, the saturation magnetization increased to 71.3Am2/kg whilst the coercivity decreased to 21.8kA/m.

Interaction of electromagnetic radiation and adsorption-mobile particles of metal ferrites in film composite materials

The technique of chemical synthesis of metal ferrite nanoparticles in a porous filler structure is developed. It is shown that cobalt ferrite particles located in the pores of carbon weaken the electromagnetic radiation flow passing through a sample of composite material.

Effect of Surfactants on Structural and Dielectric Properties of Cobalt Ferrite

Cobalt ferrite (Cofe2o4) particles were synthesized with and without presence of surfactants using a co-precipitation method. Three surfactants Cetyl Tri methyl Ammonium Bromide (CTAB-cationic), Sodium dodecylbenzenesulphonate (anionic), Triton X-100 (nonionic), were used and investigate their effects on the structural and dielectric properties of CoFe2O4 particles. The ferrite precursors were first pre calcined in a muffle furnace at 500°C and then calcined at 950°C. Structural, dielectric and magnetic properties of prepared particles were investigated using X-ray powder diffraction, Dielectric and Low field ac magnetic susceptibility measurement. Phase purity of prepared samples was confirmed by X-ray diffraction. The sample with surfactant Triton X-100 shows the highest values of dielectric constant at low frequency.

Self-biased cobalt ferrite nanocomposites for microwave applications

Oriented CoFe2O4 nanoparticles, dispersed in polymethyl methacrylate (PMMA) matrix, were fabricated by magnetophoretic deposition of functionalized nanocolloidal cobalt ferrite particles into porous alumina membrane. Their magnetic behavior exhibits an out-of-plane easy axis with a large remanent magnetization and coercitivity. This orientation allows high effective internal magnetic anisotropy that contributes to the permanent bias along the wire axis. The microwave studies reveal a ferromagnetic resonance at 46.5 and 49.5GHz, depending on the filling ratio of the membrane. Ansoft High Frequency Structure Simulator (Ansoft HFSS) simulations are in good agreement with experimental results. Such nanocomposite is presented as one of the promising candidates for microwave devices (circulators, isolators, noise suppressors etc.).

Nickel and cobalt ferrites nanoparticles: synthesis, study of magnetic properties and their use as magnetic adsorbent for removing lead(II) ion

Nano-sized nickel ferrite (NiFe2O4) and cobalt ferrite particles (CoFe2O4) were successfully synthesized using a hydrothermal method. Techniques of X-ray diffraction, scanning electron microscope, Fourier transform infrared spectrometer, energy dispersive X-ray spectroscopy, vibrating sample magnetometer and transmission electron microscope have been used to characterize and study the as-synthesized NiFe2O4 and CoFe2O4 products. The results showed that the average size of the nickel and cobalt ferrite nanoparticles is smaller than 10 and 100 nm, respectively. The results of magnetic measurement showed that the synthesized NiFe2O4 and CoFe2O4 nanoparticles were superparamagnetic and soft ferromagnetic materials, respectively. Study of adsorption behavior showed that these nanoparticles can act as a good adsorbent for removing Pb2+.

Core–shell hybrid nanomaterials based on CoFe2O4 particles coated with PVP or PEG biopolymers for applications in biomedicine

Monodisperse core–shell hybrid nanoparticles based on cobalt ferrite (CoFe2O4) particles coated with polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG) biopolymers were obtained employing a two-step procedure: the CoFe2O4 of 21 nm mean particle size were first synthesized by coprecipitation method assisted by PVP soft template and then were coated by PVP or PEG biopolymers. The effect of the thermal treatment upon the phase evolution of the obtained precursor from the coprecipitation step was monitored by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses. The FTIR spectra also indicated the interaction between the cobalt ferrite particles and the two polymers were used as biocompatible coatings. Transmission electron microscopy (TEM) and Selected Area Electron Diffraction (SAED) analyses revealed the formation of approximately 22 nm CoFe2O4-PVP and CoFe2O4-PEG hybrid nanoparticles. The magnetic measurements indicated that all synthesized hybrids were appropriate for applying in biomedical field. Testing the bioeffect of the uncoated cobalt ferrite nanoparticles and corresponding hybrids on Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, Salmonella enterica serovar typhimurium bacteria and Candida scotti yeast it was clear that no significant toxic activity was obtained. Moreover, all the prepared nanohybrids and their components possess antioxidant activity.

Synthesis, Characterization and Effects of Citric Acid and PVA on Magnetic Properties of CoFe2O4

Cobalt ferrite (CoFe2O4) particles were synthesized by sol–gel method using metal nitrates, citric acid (CA) and polyvinyl alcohol (PVA). X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), thermogravimetry/differential scanning calorimetry analysis and vibrating sample magnetometer were used to study the structural, thermal and magnetic properties of the CoFe2O4 powder. XRD results indicate that the resultant particles have crystalline, pure single phase spinel structure. From HR-SEM images, a systematic decrease in particle size is observed with an increase in PVA concentration, along with addition of CA. CA at various concentrations of PVA significantly enhance the magnetic properties of the materials.