CoFe2O4 Particles Research Articles

Fiber-guided and particle-localized microwave absorption of nanoscale CoFe2O4 derived from citric acid-based precursor

CoFe2O4 fibers and particles were prepared by directly annealing electrospun citric acid-based precursor fibers and dried precursor gel under protective atmosphere, respectively. Their electromagnetic parameters were measured and CoFe2O4 nanofibers exhibit excellent microwave absorption performance. When the matching thickness of CoFe2O4 fibers is 3 mm, the bandwidth corresponding to reflection loss below −10 dB (over 90% microwave absorption) can reach 10.0 GHz and cover the entire X-band and Ku-band. Typical Cole-Cole semicircles suggest that both CoFe2O4 particles and fibers have multiple dielectric relaxation processes. The nanoconfinement of the electrospun CoFe2O4 fibers can result in an improved mutual interfacial polarization. For the intrinsic shape anisotropy of the fibrous structure, CoFe2O4 fiber with higher coercivity increases the magnetic loss. Based on comprehensive experimental investigation, the relationship between the microwave energy loss and the morphology of CoFe2O4 is discussed.

Magnetic Traits in CoO‐Core@CoFe2O4‐shell Like Nanoparticles

AbstractAntiferromagnetic (AF) CoO pseudo‐single crystals 125±20 nm in diameter were prepared by forced hydrolysis in polyol and used as seeds to grow a poly‐ and nano‐crystalline (5 nm in diameter) ferrimagnetic (F) CoFe2O4 shell. Transmission electron microscopy (TEM) showed a certain epitaxy between the face‐centered cubic lattices of the AF rock‐salt core and the F spinel shell. Magnetometry measurements do not evidence any exchange bias feature between the two phases in direct contact. The hysteresis loops recorded between 7 and −7 T after cooling the composite particles from 400 K (between the Néel and the Curie temperatures of the AF and F phases, respectively) to 5 K, with and without a cooling magnetic field (μ0HFC=+7 T), are the same, meaning that the AF core does not allow any spin pinning on the CoFe2O4 nanocrystals. Nevertheless, differences exist between these magnetic data and those collected on two CoFe2O4 reference particles: the low temperature coercive field of the composite is between those of 5 nm sized single‐crystals and their assembly as submicrometer polycrystals. This order was also observed for the blocking temperature, although the constituting CoFe2O4 nanocrystals of all these particles, the composite and the two references, were the same. Advanced analysis by X‐ray diffraction and TEM established that the coherent crystallographic domain length of the ferrite phase and the magnetic behavior of the three systems are interdependent. Depending on the growth conditions of the CoFe2O4 phase, a relative epitaxy between the nanocrystals may exist. It is much greater in the polycrystalline CoFe2O4 particles than in their CoO−CoFe2O4 core‐shell counterparts, and does not occur in free single crystal CoFe2O4 particles.

Phase formation and magnetic properties of CoFe2O4/CoFe2 nanocomposites

Abstract Nanosize CoFe2O4 particles were synthesized via thermal decomposition of a mixed oxalate precursor; the mean ferrite particle size between 5 nm and 35 nm is tailored through variations of the decomposition temperature. Ferrite particles of 22 nm and 14 nm size were subsequently heated in Ar/5%H2 atmosphere at 315 °C for various holding times. The resulting nanocomposites consist of spinel ferrite, CoO and CoFe2, with the alloy concentration increasing with dwell time. Room temperature hysteresis loops exhibit a single-phase reversal behavior and remanence enhancement. An increase of the maximum energy product was observed as well. Hysteresis loops at 5 K, however, show two-phase behavior indicating that no exchange coupling is active.

Hydrothermal deposition of CoFe2o4 with a micro nano binary structure onto a wood surface with related magnetic property and microwave absorption

In this study, magnetic CoFe2O4 with a micro/nano binary structure was deposited onto a wood surface using a hydrothermal process. Several samples of CoFe2O4-modified wood composites were obtained by varying the initial parameters of the process. The morphology and structure of the samples demonstrated the influence of varying temperature during the hydrothermal process. The results indicated that CoFe2O4 particles, which comprise a variety of microscale and nanoscale structures, precipitated on the wood surface through the Ostwald ripening process under alkali treatment. Additionally, temperature was found to be a critical factor that influenced the resultant morphology, magnetic property, and microwave absorption property of the CoFe2O4-modified wood. Moreover, the CoFe2O4-modified wood had a high saturation magnetization (Ms) of 30.7 emu·g−1 and a minimum value of reflection of −16.2 dB at 16.6 GHz at room temperature. This work suggested that the CoFe2O4-modified wood composites can be used to design and manufacture microwave absorbers.

Effect of heat treatment conditions on properties of carbon-fiber-based electromagnetic-wave-absorbing composites

Hybridization of carbon materials with magnetic metals and oxides has become a research hotspot in electromagnetic (EM) wave loss of reinforced materials. In this study, EM wave-absorbing composites were prepared by a one-step, high-temperature process using a polyacrylonitrile (PAN)-based pre-oxidized felt impregnated with a metal salt solution containing Fe, Co, and Ni. The structures, chemical compositions, and morphologies of the obtained composites were analyzed in detail. The carbon fiber (CF)/FeCoNi composites are composed of carbon fibers and Fe3O4, NiFe2O4, CoFe2O4, and Ni3Fe particles with magnetic loss properties. The magnetic particles are distributed uniformly along the axial direction of the fiber, and EM waves are reflected by multiple reflections in the fiber felt. In addition, the CF/FeCoNi composites exhibit excellent performances owing to the synergistic effect of electric loss and magnetic loss materials, and different wave-absorbing properties. The maximum reflection loss of CF/FeCoNi was − 30.62 dB at 11.74 GHz, and the absorption bandwidth with a reflection loss exceeding − 10 dB was 7.4 GHz (from 8.7 to 16.1 GHz) with 1 h of heat treatment at 650 °C. By adjusting the treatment temperature and time, composite materials can be obtained to serve as lightweight and high-performance EM wave-absorbing materials.

Catalytic Ozonation of Melanoidin in Aqueous Solution over CoFe2O4 Catalyst

In this work, cobalt ferrite (CoFe2O4) was synthesized by solvothermal route for application as a catalyst in the ozonation reaction for the decolorization and mineralization of melanoidin from aqueous solution. The structural properties of CoFe2O4 sample were investigated by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, Fourier-transform infrared spectroscopy (FTIR), particle-size distribution, scanning electron microscopy (SEM) and X-ray dispersive energy spectroscopy (EDS). Single-phase CoFe2O4 particles with a predominantly mesoporous structure containing a high specific surface area were obtained. Results showed that the CoFe2O4-catalyzed ozonation reaction has higher activity for the decolorization and mineralization of melanoidin when compared with the ozonation reaction without the presence of catalyst. Therefore, this material can be very promising for the application in catalytic ozonation systems for the melanoidin removal from liquid effluents.

Effects of nitriding temperature on the structure and magnetic properties of CoFe2 alloy

It has been reported that the nitridation can increase the magnetization of α-Fe by 20%. The CoFe2 alloy has the highest magnetization among all binary alloys, thus whether the nitridation can further enhance its magnetization. In the present work, the uniform and dispersed 16-nm CoFe2O4 particles were separated by the MgO matrix in order to prepare the fine CoFe2 particles, beneficial for the nitridation reaction. With increasing the nitridation temperature, the crystal structure of the Co–Fe–N alloy experiences α″-Fe16N2 below 250 °C, γ′-Fe4N at 300 °C and e-Fe3N between 350 °C and 500 °C. The single-phase e-CoFe2N was synthesized at 400 °C, a much lower temperature than that previously reported. The results of magnetic measurement at 10 K show that the nitridation at 200 °C increases the magnetization of CoFe2 from 228 to 292 emu/g by 28%; the nitridation at temperatures of 200, 250 and 300 °C enhances both the magnetization and coercivity of the CoFe2 alloy. These CoFe2 nitrides are very interesting and of importance both from physical and industrial aspects, which deserves further investigations.

Influence of core size on the multiferroic properties of CoFe2O4@BaTiO3 core shell structured composites

Core shell structured magnetoelectric multiferroics have attracted great attentions due to their improved multiferroic properties and potential applications. In this paper, CoFe2O4 @BaTiO3 core shell structured composites with different core size were prepared by hydrothermal method and the effect of core size on the microstructure and multiferroic properties have been systematically studied. The results indicate that with the decrease of the core size, the dielectric, ferroelectric properties as well as the magnetoelectric coupling effect were increased dramatically. Improved interface area and the perfect distribution of CoFe2O4 particles into BaTiO3 matrix are ascribed to be the result of this enhancement of magnetoelectric properties. Our result may shield light on the improvement of multiferroic properties for composite multiferroic materials.

Structural, dielectric and magnetic properties of nano-sized CoFe2O4 employing various synthesis techniques for high frequency and magneto recording devices: a comparative analysis

CoFe2O4 consisting of nanocrystallites were synthesized using glycine nitrate auto combustion, co-precipitation method and solid-state techniques. Both glycine nitrate auto combustion and co-precipitation method yielded nanosized CoFe2O4 (∼30–50 nm) particles whereas solid-state technique produced micron-sized (∼150 nm) cobalt ferrite particles. XRD and FTIR analysis confirmed the formation of the spinel CoFe2O4 structure. The frequency dependence of the dielectric constant for all the samples in the range 100 Hz–1 MHz, investigated in temperature regime of room temperature to 300 °C exhibited Maxwell-Wagner type interfacial polarization in consonance with Koop’s phenomenological theory. Magnetic measurements were found to be strongly reliant on the particle size. Saturation magnetization decreased with decrease in particle size whereas the coercivity was found to increase from 1954 Oe to 2645 Oe as the particle size was reduced from 180 nm to about 24 nm. These deviations in the magnetic properties are ascribed to the grain size effects and cation redistribution, hence different synthesis techniques can lead to varied particle sizes and magnetic properties. Moreover, CoFe2O4 sample synthesized using sol-gel auto combustion technique find suitability in high frequency and magneto recording devices.

Paederia foetida Linn. promoted synthesis of CoFe 2 O 4 and NiFe 2 O 4 nanostructures and their photocatalytic efficiency

A facile method of synthesis of cobalt ferrite (CoFe2O4) and nickel ferrite (NiFe2O4) nanoparticles (NPs) was developed using urea as a hydroxylating agent and Paederia foetida Linn. (family: Rubiaceae) leaf extract as a bio-template. The synthesised ferrite NPs were characterised in a detailed manner by powder X-ray diffraction (XRD), transmission electron microscopy, Fourier transform-infrared spectroscopy and vibrating sample magnetometer analysis. The XRD patterns revealed the formation of cubic face-centred phase for both CoFe2O4 and NiFe2O4 NPs. These quasi-spherical particles of CoFe2O4 and NiFe2O4 were shown to have sizes in the range of 10–80 and 5–50 nm, respectively. The photocatalytic activity of metal ferrites was evaluated in H2O2 assisted oxidative degradation of methylene blue (MB) and rhodamine B (RhB) under irradiation of solar light. Both metal ferrite photocatalysts exhibited pronounced activity in degradation of MB and RhB, respectively, but relatively higher activity was observed for NiFe2O4. After completion, the catalysts were recovered using an external magnet. Recycling of these recovered catalysts up to five times showed no noticeable change in the efficiency.

The influence of bias magnetization of nanoparticles on GMR sensor signal and sensitivity for the ultra-low concentration detection

In the broad research of the GMR bio-sensing technology, it is vital to explore appropriate magnetic labels and its influences on the detection signal. In this work, four kinds of ferrite particles of γ-Fe2O3, CoFe2O4, NiFe2O4 and NiZnFe2O4 were prepared through calcining the Dimethyl Formamide (DMF) solution of the transition metal nitrates [Fe(NO3)3 and X(NO3)2, X = Co, Ni, Zn] to study the effect of magnetic properties on detection signals using a DC in-plane measuring method. It was revealed that for four particles, the output voltage differences |ΔV| between with and without magnetic particles exhibit log-linear functions of the particles concentrations x in the range from 0.1 to 10 ng/mL. A very low limitation of detection (LOD) of 0.1 ng/mL for all the samples was obtained, which is two orders smaller than that in the previous work. Moreover, the change of output voltage difference at the LOD (|ΔVlim|) is proportional to the magnetization at bias field (bias magnetization, Mbias), which indicates that larger Mbias leads to a lower LOD. This work provides a useful guidance in selecting or preparing magnetic labels to enhance the sensitivity of GMR biosensors.

Optimising the magnetic performance of Co ferrite nanoparticles via organic ligand capping.

Ferrofluids of CoFe2O4 nanoparticles are gaining increasing interest due to their enhanced heating performance in biomedical applications (e.g. in magnetic hyperthermia as mediators for cancer treatment) or in energy applications (e.g. magneto-thermo-electric applications). Until now, the effect of an organic surfactant on the magnetic particle behaviour has been unintentionally overlooked. Here, we present the counterintuitive magnetic effect of two representative organic ligands: diethylene glycol (DEG) and oleic acid (OA) bonded at the surface of small (∼5 nm in size) CoFe2O4 particles. The combined results of the bulk dc susceptibility, local-probe Mössbauer spectroscopy and physical modelling, which is based on electronic structure calculations and Monte Carlo simulations, reveal the effect of different ionic distributions of the particles due to the different surfactant layers on their magnetic behaviour. They result in an unexpected increase of the saturation magnetisation and the blocking temperature, and a decrease of the coercive field of DEG coated CoFe2O4 nanoparticles. Our work provides a pathway for the production of colloidal assemblies of nanocrystals for the engineering of functional nano-materials.

Bifunctional CoNi/CoFe2O4 /Ni foam electrodes for efficient overall water splitting at a high current density

An electrocatalyst composed of CoNi(hydroxide) nanosheets and flower-like CoFe2O4 particles with multiple porous structure is successfully deposited on nickel foam and applied for overall water splitting.

Green Synthesis of CoFe2O4 and Investigation of its Catalytic Efficiency for Degradation of Dyes in Aqueous Medium

Abstract The catalytic wet oxidation is one the methods used for elimination of dyes from aqueous medium in which various metal based materials can be used as heterogeneous catalysts. Bimetallic oxides as heterogeneous catalysts have gained much attention as bimetallization improve the catalytic properties of the resulting particles. The biosynthetic green method is the most viable and simple method for synthesis of bimetallic oxides nanoparticles. Here, we report the green synthesis of CoFe2O4 particles using Azadirachata indica leaves extract as reducing and stabilizing agent. The synthesized particles were characterized using X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy and scanning electron microscopy. The synthesized CoFe2O4 particles were tested as a catalyst for mineralization of rhodamine B and methylene blue dyes in the presence of hydrogen peroxide in aqueous media. More than 95% dyes degraded in 120 min. The reaction kinetics was described in terms of Langmuir–Hinshelwood mechanism which suggests that molecules of dye and hydrogen peroxide adsorbed surface of CoFe2O4 and then react together.

Sustainable synthesis of magnetically separable SiO2/Co@Fe2O4 nanocomposite and its catalytic applications for the benzimidazole synthesis

The Co(II) and Fe(III) centres magnetically separable two new mesoporous nanocatalyst were synthesised via chemical synthesis method. The transmission electron microscopic studies (TEM) show that, the particles are spherical shape with mean size of 20 nm. The Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) reveals that SiO2 is coating on the surface of the cobalt ferrate nanoparticle (CoFe2O4). The SiO2 coating is efficiently preventing the aggregated collision of nanoparticles. Magnetic measurements show that diamagnetic character of the SiO2 is unaffected to the coercivity of SiO2 coated CoFe2O4 particles. In addition, these nanoparticles are used as nanocatalyst for high yielding, facile and expeditious synthesis of various functionalized 2-arylbenzimidazoles via one-pot condensation. The cascade including imine formation, cyclization, condensation, and aromatization occurs, without addition of any reducing or oxidizing agents. In all situations, the desired product was synthesised with excellent yield. The shorter reaction time, mild reaction condition, simplicity, non-toxicity, safe reaction and easy workup are the impotent merits of this protocol. Statement of SignificanceIn SiO2 coated CoFe2O4 particles SiO2 serves as an efficient capping agent and prevent the aggregation of nanoparticles hence reducing the particle size, this cascade open up with stoichiometric quantity of using SiO2 with unaffected ferromagnetism of CoFe2O4 particles along with reducing the particle size. In addition SiO2 coated CoFe2O4 particles act as a highly efficient nanocatalytic, this method can be extended to the development of other catalytic system used in the synthesis of important pharmacological drungs. Moreover this catalyst employed economic large scale synthesis of cyclization reaction with recoverable and reusable properties without loss of catalytic activity for several cycles.

Synthesis, optical and magnetic properties of a new nanocomposite HAp/CoFe 2 O 4 /RGO

Magnetically separable CoFe2O4/reduced graphene oxide (CoFe2O4/RGO) and a new of magnetic hydroxyapatite/CoFe2O4/RGO nanocomposites (HAp/CoFe2O4/RGO) were prepared via co-precipitation along with hydrothermal methods. The characterisation and properties of the synthesised nanocomposite were analysed using Fourier transform infrared, X-ray powder diffraction, vibrating sample magnetometer, field emission scanning electron microscopy, transmission electron microscopy (TEM) and UV-visible spectroscopy. TEM images show that the synthetic RGO layers are decorated with 10 nm CoFe2O4 particles and HAp nanorods of about 10 nm diameter and 100 nm average length are well separated and uniformly distributed. In addition, separation of the layers from one another and approximately uniform distribution on nanosheets is completely visible. Due to the magnetic properties of HAp/CoFe2O4/RGO nanocomposite, it can be separated from the environment by an external magnetic field. In addition, the energy gap measurements represent the effective role of CoFe2O4/RGO inremarkable decreasing of the energy gap of the nano-HAp.

Bi-based superconductors prepared with addition of CoFe2O4 for the design of a magnetic probe

We have investigated the microstructure and the magnetoresistivity of bismuth based superconductor bulks added with nano-sized CoFe2O4 particles (10 nm in diameter). Samples were prepared through the solid state reaction (SSR) technique by addition of CoFe2O4 nanoparticles during the last step of heat treatment. Phase examination using X-ray diffraction (XRD), morphology investigation by scanning electron microscope (SEM), microstructure and local chemical composition analyses using transmission electron microscope (TEM) coupled with energy dispersive X-ray spectroscope (EDXS), electrical resistance versus temperature ρ(T) under applied magnetic fields (B) and electrical resistance versus B at 77 K, ρ(B), were carried out. The CoFe2O4 added sample shows a great magnetoresistance to weak magnetic field at the temperature of liquid nitrogen (77 K). This result is attractive for practical, because CoFe2O4 added samples can be utilized as active elements in magnetic fields sensor devices.

The synthesis of magnetically exchange coupled CoFe2O4/CoFe2 composites through low temperature CaH2 reduction

CoFe2O4 sub-micron particles were synthesized through a hydrothermal method. The as-synthesized CoFe2O4 particles were then mixed with CaH2 and heated at 180 °C for reduction. In three parallel experiments, the reduction time was controlled to be 10, 20 and 30 h, respectively. The effects of reduction time on the particle morphology and magnetic properties were investigated. The results showed that the reduction time did not affect the morphology of CoFe2O4 under 180 °C, indicating that these particles had a good thermal stability at reduction temperature. The XRD patterns showed that long reduction time resulted in a stronger peak of CoFe2. The magnetic hysteresis loops of reduced products showed that magnetic exchange coupling was presented when the reduction time was 10 h. Further extended reduction time resulted in the kinks in the magnetic hysteresis loop, and magnetic decoupling.

Hydrothermal synthesis of reduced graphene oxide-CoFe2O4 heteroarchitecture for high visible light photocatalytic activity: Exploration of efficiency, stability and mechanistic pathways

RGO-CoFe2O4 heterostructure nanocomposite was prepared by hydrothermal method and was characterized by various analytical techniques such as Powder X-ray Diffraction method (PXRD), UV–vis absorbance, Photoluminescence (PL), Fourier Transform Infra Red (FTIR) spectroscopic techniques, BET surface area measurements, Field Emission Scanning Electron Microscopy (FESEM), Raman Spectroscopy and Vibrating Sample Magnetometer (VSM). The results confirmed the formation of hybrid structure with CoFe2O4 particles embedded in RGO sheets. Photocatalytic activity of the nanocomposites was probed for the degradation of 4-Chlorophenol (4-CP) as the model compound under the visible light illumination. The photocatalytic activity decreases in the following order RGO-CoFe2O4>CoFe2O4>RGO. Further the activity of RGO-CoFe2O4 composite was explored in the presence of peroxymonosulfate (PMS) as an oxidant. LUMO of PMS can accommodate photogenerated electrons, thereby suppresses the recombination process. The enhanced activity of RGO-CoFe2O4 hybrid is compared to its individual counterparts and the higher activity is accounted to its unique electronic structure. RGO serves as electron acceptor from CoFe2O4 and electron donor to the oxygen molecule. During the photocatalysis, transformation of the native structure from normal spinel to inverse spinel and vice versa may take place continuously from the process of electron trapping and detrapping by Fe3+ and Co2+ions. The observed continuous absorption for RGO-CoFe2O4 composite in the UV–vis spectra implies active d–d transitions involving transition metals present in the nanocomposite.

Magnetic studies of SiO2 coated CoFe2O4 nanoparticles

Oleic acid capped CoFe2O4 nanoparticles which exhibit a high coercivity of ∼9.47kOe at room temperature were coated with a robust coating of SiO2. We have used chemical synthesis method to obtain SiO2 coated CoFe2O4 nanoparticles with different weight percentages of CoFe2O4 in SiO2 (1.5, 3.1 and 4.8wt.%). The morphological investigation of the coated nanoparticles by transmission electron microscopy shows that the particles are spherical with average size ∼160nm. Infrared spectroscopy reveals that oleic acid capping on the surface of CoFe2O4 nanoparticles is retained after silica coating process. The complete coating of SiO2 on CoFe2O4 nanoparticles is confirmed by X-ray photoelectron spectroscopy as there is no signature of cobalt or iron ions on the surface. Magnetic measurements show that coercivity of SiO2 coated CoFe2O4 particles remains more or less unaffected as in CoFe2O4 nanoparticles at room temperature. In addition, the temperature dependent magnetic measurements show that at 5K the CoFe2O4 and SiO2 coated 1.5wt.% CoFe2O4 samples exhibit a very high value of coercivity (∼20kOe) which is more than twice as compared to room temperature coercivity value (∼9.47kOe). We conclude that silica coating in our study does not significantly affect the coercivity of CoFe2O4 nanoparticles.