CoFe2O4 Particles Research Articles

Bio-gel template synthesis of CoFe2O4 nano-catalysts and application in aerobic oxidation of cyclohexane

Magnetic cobalt ferrite (CoFe2O4) particles were synthesized via a solvothermal pathway by using the gel of natural lotus roots as bio-gel template. Samples with porous structure and of large specific area (∼95.6 m2/g) were prepared, which were assembled by CoFe2O4 particles of uniform sizes (ca. 15.0 nm). The annealed CoFe2O4 nanoparticles were proven to be highly efficient catalysts for aerobic oxidation of cyclohexane. Factors such as oxygen pressure, temperature, reaction time and self-catalysis by adding cyclohexanone have been studied in view of improving the conversion of cyclohexane as well as the selectivity of KA oil (cyclohexanone and cyclohexanol). Optimum parameters were found at an initial O2 pressure of 1.6 MPa when the reaction was conducted for 6.0 h at the temperature of 150 °C. The maximum conversion of cyclohexane oxidation reaches 16.43%, and the selectivity 90.3% for KA oil was obtained. This research provides a facile way of developing green catalysts in the aerobic oxidation of cyclohexane.

Evaluation and optimization of the magnetoelectric response of CoFe2O4/poly(vinylidene fluoride) composite spheres by computer simulation

Magnetoelectric (ME) composites exhibiting strain-mediated coupling are gaining increasing interest for applications. The most interesting ones are composed of piezoelectric polymers and magnetostrictive particles. In particular, low dimensional ME materials, such as the ones in the form of micro- and nano-spheres, show strong potentials for improved energy harvesters with higher volume efficiency, sensors and actuators. Nevertheless the ME characterization of such low dimensional ME structures remain a difficult and challenging task and, therefore, the use of mathematical models and simulations are an interesting and viable option to better understand and tailor materials towards applications.In this context, the ME coupling on microspheres based on piezoelectric poly(vinylidene fluoride) (PVDF) and magnetostrictive CoFe2O4 (CFO) particles was theoretically studied based on Finite Element Methods (FEM). The effect of sphere size and filler content on the ME response was evaluated, showing that the ME response of CFO/PVDF microspheres is strongly influenced by the magnetic field intensity, sphere diameter and CFO content, being the highest ME response achieved on composite sphere with 90 wt% of CFO and 1.2 μm.

Effect of Mn-substitution on the structure and magnetic properties of CoFe2O4/SiO2 nanocomposites

Mn-substituted CoFe2O4/SiO2 nanocomposites were prepared by sol–gel method using Mn-substituting for Co or Fe. The microstructural, morphological, and magnetic characterizations were carried out by X-ray diffraction, transmission electron microscope, X-ray photoelectron spectroscopy, vibrating sample magnetometer, and Mossbauer spectroscopy. It can be found that the Mn-substituted CoFe2O4 particles in obtained nanocomposites exhibit cubic spinel structure and the substitution of Co or Fe by Mn increase the lattice constant. The results of X-ray photoelectron spectroscopy, vibrating sample magnetometer and Mossbauer spectroscopy demonstrate that Mn ions exists as Mn2+ and tend to preferentially occupy octahedral A sites when it replaces Co ions as in Co0.8Mn0.2Fe2O4/SiO2 nanocomposites, which leads to the saturation magnetization Ms increasing and coercivity Hc decreasing. While Mn ions valence state is +3 as it substitutes to Fe ions as in CoFe1.8Mn0.2O4/SiO2. The presence of Mn3+ induces a decrease in Ms and Hc.

Novel method of preparing CoFe2O4/graphene by using steel rolling sludge for supercapacitor

Steel rolling sludge containing high amounts of iron was recycled for the first time via a facile hydrothermal method and used as ferric ions source for CoFe2O4/graphene nanocomposite electrode. CoFe2O4 agglomeration is weakened by introducting graphene, which is crucial for improving efficient ions transport pathways in energy storage devices. The CoFe2O4/graphene complex exhibits a rough morphology and a porous nanostructure with a high specific surface area of 191.5m2g−1. The material also shows excellent Faradaic redox reactions with high specific capacity of 166.5Cg−1 and 127.0Cg−1 at 0.5 and 10Ag−1, respectively, which are higher than that of simple, dense CoFe2O4 particles (121.6Cg−1 at 0.5Ag−1). Furthermore, the electrode demonstrates outstanding cycle stability with 79.3% capacitance retained after 5000 cycles. Hence, the proposed resource reuse strategy can be used to prepare CoFe2O4/graphene nanocomposites for supercapacitors.

Structural and Dielectric Properties of Bismuth Doped Cobalt Nano Ferrites Prepared by Sol-Gel Auto Combustion Method

The present study is focused on the preparation of a series of Bismuth doped CoFe2O4 (CFO) nanoparticles and its structural and dielectric properties. The CFO particles having chemical composition CoBixFe2-xO4 (where x = 0.0, 0.1, 0.5) has been synthesized using sol-gel auto combustion method. Phase formation study of the prepared samples is carried out using X -ray diffraction (XRD) technique. It reveals single phase spinel structure having space group Fd3m. The two absorption bands v1 and v2 are observed in Fourier transform infrared spectroscopy (FTIR) spectra corresponding to the tetrahedral and octahedral sites, which show mark of spinel structure of the samples. Morphological study is carried out using Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscopy (TEM) which revealed that the particle size obtained is around 40 nm to 120 nm. In addition, phase formation has been confirmed from the analysis of Raman spectra. Different types of conduction mechanism of the charge carriers have been analysed with DC resistivity and AC impedance measurement at room temperature. Results demonstrate the presence of dielectric relaxation, which is found to be of non-Debye type.

Efficient degradation of Azorubin S colourant in the commercial jam-jelly food samples using TiO2-CoFe2O4 nanocomposites in visible light

A series of TiO2-CoFe2O4 nanocomposites, with different compositions of TiO2 and CoFe2O4 was synthesized by ex-situ method to enhance the activity of bare TiO2. X-ray diffraction revealed the prominent characteristics of anatase phase for higher composition of TiO2 in the composites; while cubic-spinel structure for higher composition of CoFe2O4 in the composites. Electron microscopic images showed uniform particles with marigold shape of TiO2 particles and porous nature of CoFe2O4 particles. The catalytic activity of TiO2-CoFe2O4 was evaluated by using the photoremediation of Azorubin S under visible light irradiation and exhibited the higher activity for a composite consists of 95wt% TiO2 and 5wt% CoFe2O4 than the remaining composites. The optimized experimental conditions of photodegradation reaction were used for complete degradation of Azorubin S in the commercial jam-jelly food samples and reaction was monitored by using UV–vis as well as HPLC techniques.

Switchable 3-0 magnetoelectric nanocomposite thin film with high coupling.

A mixed precursor solution method was used to deposit 3-0 nanocomposite thin films of PbZr0.52Ti0.48O3 (PZT) and CoFe2O4 (CFO). The piezoelectric behavior of PZT and magnetostrictive behavior of CFO allow for magnetoelectric (ME) coupling through strain transfer between the respective phases. High ME coupling is desired for many applications including memory devices, magnetic field sensors, and energy harvesters. The spontaneous phase separation in the 3-0 nanocomposite film was observed, with 25 nm CFO particle or nanophases distributed in discrete layers through the thickness of the PZT matrix. Magnetic-force microscopy images of the nanocomposite thin film under opposite magnetic poling conditions revealed in-plane pancake-like regions of higher concentration of the CFO nanoparticles. The constraints on the size and distribution of the CFO nanoparticles created a unique distribution in a PZT matrix and achieved values of ME coupling of 3.07 V cm-1 Oe-1 at a DC bias of 250 Oe and 1 kHz, increasing up to 25.0 V cm-1 Oe-1 at 90 kHz. Piezo-force microscopy was used to investigate the ferroelectric domain structure before and after opposite magnetic poling directions. It was found that in this nanocomposite, the polarization of the ferroelectric domains switched direction as a result of switching the direction of the magnetization by magnetic fields.

Effect of composition and coating on the interparticle interactions and magnetic hardness of MFe2O4 (M = Fe, Co, Zn) nanoparticles

Single domain superparamagnetic ferrite nanoparticles with the composition MFe2O4 (M = Fe, Co, Zn) have been prepared by thermal decomposition of metal acetylacetonates in diphenyl ether or dibenzyl ether, using oleic acid in the presence of oleylamine as a stabilizing agent. The Fe, Co and Zn ferrite nanoparticles are monodisperse with diameters of 4.9, 4.4 and 4.7 nm, respectively. The TG and IR results indicate that four or six carboxylate groups per nm2 are bonded at the surface of the particles acting as chelating and/or bridging bidentate ligands depending on the composition. The oleate groups minimize the interparticle interactions in Fe and Zn ferrite samples, while in the Co ferrite sample dipolar interactions produce broad maxima in the ZFC and energy barriers distribution curves. The inversion degree has been estimated from the Raman spectra and the obtained x values have been used to calculate the saturation magnetization and compare them with the experimental MS values. Compared to bulk materials, the magnetization value is higher for the Zn ferrite sample due to its mixed spinel cation distribution. For the Co ferrite sample, and probably for the Fe one, the low value of saturation magnetization seems to be due to the surface disordered layer of canted spins. Compared to non-coated nanoparticles with the same composition and similar size, the oleate groups, covalently bonded to the superficial cations, increase the anisotropy field and decrease the magnetization.

Cluster Structural CoFe2O4 Particles Loaded onto Graphene and Its Li-Storage Performance

以氧化石墨为碳前驱体, 利用含氧官能团与金属离子的价键结合, 一步水热工艺同时实现石墨烯的制备及均匀负载团簇结构CoFe 2 O 4 。微观形貌显示CoFe 2 O 4 为一次颗粒组成的团簇结构。复合材料独特的结构有助于充分发挥石墨烯高导电性、大比表面积的优势, 相比单纯的CoFe 2 O 4 , 该复合材料具有优异的倍率特性和循环稳定性。石墨烯的高导电性提升了复合材料的整体导电和导锂特性。同时, 独特的团簇结构及石墨烯的限制作用抑制了活性纳米颗粒在充放电过程中的体积变化, 提高了活性材料的稳定性。

Multifunctional Polymeric Platform of Magnetic Ferrite Colloidal Superparticles for Luminescence, Imaging, and Hyperthermia Applications.

Adequately designed multiresponsive water-soluble graft copolymers were used to serve as a multifunctional polymeric platform for the encapsulation and transfer in aqueous media of hydrophobic magnetic nanoparticles (MNPs). The backbone of the graft copolymers was composed of hydrophilic sodium methacrylate units, hydrophobic dodecyl methacrylate units, and luminescent quinoline-based units, while either the homopolymer poly(N-isopropylacrylamide) or a poly(N,N-dimethylacrylamide-co-N-isopropylacrylamide) copolymer was used as thermosensitive pendent side chains. The polymeric platform forms micellar-type assemblies in aqueous solution, and exhibits pH-responsive luminescent properties and a lower critical solution temperature behavior in water. Depending on the design of the side chains, the cloud point temperatures were determined at 38 and 42 °C, close or slightly above body temperature (37 °C). Above the critical micelle concentration (CMC), both graft copolymers can effectively stabilize in aqueous media as magnetic colloidal superparticles (MSPs), oleylamine-coated MnFe2O4 MNPs, as well as 1:1 mixture of oleylamine-coated MnFe2O4 and CoFe2O4 MNPs. When CoFe2O4 particles were mixed with MnFeO4 in equal amounts, the specific loss power increased significantly, while an opposite trend was observed in the magnetic resonance imaging (MRI) studies, probably due to the anisotropy of cobalt. As a consequence, fine-tuning of the chemical structure of the copolymers and the composition of the MSPs can lead to materials that are able to act simultaneously as luminescent, hyperthermia, and contrast MRI agents.

Magnetic properties of the nanocomposite CoFe2O4/FeCo-FeO at a high H/T regime

The low temperature magnetic properties of nanopowders of CoFe2O4 and of CoFe2O4/FeCo-FeO with average particle size of about 6nm were investigated for temperatures down to 5K and for applied magnetic fields up to 350kOe. Highly enhanced coercive fields were obtained for the CoFe2O4 nanoparticles. The values of the saturation magnetization MS and of the anisotropy constant K1 were also found to be enhanced for the nanocomposite powder sample. The overall results are discussed in terms of a particle model which takes into account a thin amorphous layer present in the CoFe2O4 particles and due to a FeCo-FeO layer grown during an annealing procedure. Moreover, the temperature dependence of K1 was found to be in good agreement with a model proposed by Tachiki.

Synthesis and properties of precipitated cobalt ferrite nanoparticles

The formation and properties of cobalt ferrite were investigated with XRD, FT-IR, FE-SEM, Mössbauer and magnetometry. Cobalt ferrite samples were prepared (a) by combining coprecipitation Co(OH)2/2Fe(OH)3, using NaOH between pH 5.2 and 11.4 and autoclaving, and (b) by autoclaving the Co(OH)2/2Fe(OH)3 coprecipitate in a very strong alkaline medium. XRD and FE SEM showed that both CoFe2O4 crystallites and particles were in the nanosize range. The FT-IR spectra were typical of spinel ferrites. Cobalt ferrite precipitated at pH 7.2 and at 11.4 contained a small fraction of α-Fe2O3, whereas in the sample precipitated at pH 11.4 a very small amount (traces) of α-FeOOH were detected by FT-IR, additionally. Parameters obtained by Mössbauer spectroscopy suggested a structural migration of cobalt and iron ions in prepared cobalt ferrite spinels with the prolonged time of autoclaving. Magnetic measurements showed the magnetic behaviour typical of spinel ferrite nanoparticles.

Size-Dependent Photodynamic Anticancer Activity of Biocompatible Multifunctional Magnetic Submicron Particles in Prostate Cancer Cells.

In this study, newly designed biocompatible multifunctional magnetic submicron particles (CoFe2O4-HPs-FAs) of well-defined sizes (60, 133, 245, and 335 nm) were fabricated for application as a photosensitizer delivery agent for photodynamic therapy in cancer cells. To provide selective targeting of cancer cells and destruction of cancer cell functionality, basic cobalt ferrite (CoFe2O4) particles were covalently bonded with a photosensitizer (PS), which comprises hematoporphyrin (HP), and folic acid (FA) molecules. The magnetic properties of the CoFe2O4 particles were finely adjusted by controlling the size of the primary CoFe2O4 nanograins, and secondary superstructured composite particles were formed by aggregation of the nanograins. The prepared CoFe2O4-HP-FA exhibited high water solubility, good MR-imaging capacity, and biocompatibility without any in vitro cytotoxicity. In particular, our CoFe2O4-HP-FA exhibited remarkable photodynamic anticancer efficiency via induction of apoptotic death in PC-3 prostate cancer cells in a particle size- and concentration-dependent manner. This size-dependent effect was determined by the specific surface area of the particles because the number of HP molecules increased with decreasing size and increasing surface area. These results indicate that our CoFe2O4-HP-FA may be applicable for photodynamic therapy (PDT) as a PS delivery material and a therapeutic agent for MR-imaging based PDT owing to their high saturation value for magnetization and superparamagnetism.

Liquid-Solid-Solution Assembly of CoFe2O4/Graphene Nanocomposite as a High-Performance Lithium-Ion Battery Anode

CoFe2O4/graphene composites were fabricated via a novel one-pot liquid-solid-solution (LSS) hydrothermal process. Through ions electrostatic adsorption onto graphene sheets and oil microemulsion encapsulation, CoFe2O4 nanoparticles can be uniformly anchored on crumpled graphene sheets without aggregation, and the size distribution of CoFe2O4 particles can be controlled by the microemulsion shell in the range of 50–100nm. With the synergistic effect between CoFe2O4 and graphene, the CoFe2O4/graphene hybrid exhibits a high reversible specific capacity of 1102mAhg−1 at 0.2Ag−1 after 100 cycles, and a good cycling stability as well. Moreover, the composite has good rate capability. The specific capacity can reach a high value of 410mAhg−1 even under a high current density of 6.4Ag−1 (corresponds to a charge time of ∼230s), indicating its promising application as an anode material for lithium ion batteries.

In situ chemical vapor deposition growth of carbon nanotubes on hollow CoFe2O4 as an efficient and low cost counter electrode for dye-sensitized solar cells

Abstract The composites of hollow CoFe2O4 and carbon nanotubes (h-CoFe2O4@CNTs) are successfully prepared by using a simple hydrothermal process coupling with the in-situ chemical vapor deposition (CVD) as electrocatalytic materials for counter electrode of dye-sensitized solar cells. The CNTs are uniformly grown on the surface of hollow CoFe2O4 particles verified by X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) measurements. The electrochemical performances of hollow CoFe2O4@CNTs composites are evaluated by the EIS, Tafel polarization and CV measurements, and exhibiting high electrocatalytic performance for the reduction of triiodide. The presence of conductive polypyrrole nanoparticles could further improve the conductivity and catalytic performance of the resultant composites. Controlling the thickness of composites film, the optimum photovoltaic conversion efficiency of 6.55% is obtained, which is comparable to that of the cells fabricated with Pt counter electrode (6.61%). In addition, the composites exhibit a good long-term electrochemical stability in I3−/I− electrolyte.

Conventional versus microwave combustion synthesis of CoFe2O4 nanoparticles

Cobalt ferrite (CoFe2O4) nanoparticles have been synthesized by sol–gel autocombustion method ignited by conventional and microwave heating techniques. The precursor solutions were prepared with different fuel types such as citric acid and urea. The ignition technique and fuel type affected the phase evolution, microstructure, and magnetic properties of CoFe2O4 nanoparticles. X-ray diffraction results revealed that the single-phase and well-crystallized CoFe2O4 nanoparticles would only be formed using citric acid as fuel and after calcination at 600 °C. Microwave ignition resulted in the formation of larger sphere-like CoFe2O4 particles, possibly due to the contribution of microwave-absorbing products in attaining of higher temperatures. Furthermore, the single-phase CoFe2O4 nanoparticles synthesized by microwave ignition exhibited the higher saturation magnetization (Ms = 77 emu/g) compared to that of conventional method (Ms = 53 emu/g), due to their larger particle size and higher inversion coefficient. Magnetization curves of the as-combusted and as-calcined samples (CCA: conventional ignition with citric acid fuel, MCA: microwave ignition with citric acid fuel, CU: conventional ignition with urea fuel, and MU: microwave ignition with urea fuel).

Innovative study of superparamagnetism in 3 nm CoFe2O4 particles

Superparamagnetic moment evolution with temperature and applied magnetic field, corresponding to 3 nm particles of CoFe2O4.

Magnetoelectric Properties of Low Temperature Sintered CoFe2O4-(PZN-PZT) Multiferroic Composite Materials

CoFe2O4-(PZN-PZT) multiferroic composite ceramics were prepared by low temperature sintering using traditional ceramic method. The influences of mixed mode, PZT shell and composition on structure, magnetic and magnetoelectric coupling properties were studied. XRD and TEM results show that CoFe2O4/PZT core-shell nanos- tructured particles are prepared by the Sol-Gel method. A 10-20 nm thick PZT shell formed on the surface of CoFe2O4 particle. EDS analyses show that low temperature sintering and barrier layer effectively inhibit the elements diffusion of the two phases. SEM images and magnetoelectric property measurement show that PZT shell coated on CoFe2O4 particles and the stirring process improve the magnetic particles content in com-position, match the sintering process perfectly, and improve the magnetoelectric coupling properties effectively. The coated and stirred sample CoFe2O4-(PZN-PZT) with volume ratio of 4:6 which sintered at 1000℃ show maximum magnetoelectric coupling coefficient of (18.3 mV/(cm·Oe)) at 10 kHz.

Preparation and adsorption properties of magnetic CoFe2O4–chitosan composite microspheres

Magnetic chitosan microspheres made from novel polymer materials show outstanding applied characteristics. Magnetic chitosan microspheres are rather cheap, non-toxic, tasteless, alkali resistant, corrosion resistant, easily degradable, easily recyclable, and so on. It can be widely used in many fields. In this paper, magnetic CoFe2O4/chitosan core-shell microspheres are prepared by means of emulsification cross-linking technique using CoFe2O4 as core and glutaric dialdehyde as crosslinking agent. The results demonstrated that the different calcining temperature of magnetic (CoFe2O4) particles, CoFe2O4/chitosan ratio and stirring time of the suspension medium are the most effective parameters that control the size, size distribution, morphology and magnetism of the described microspheres. Finally, the size, morphology and chemical structure of the prepared materials are studied by different methods. The results show that the optimal calcination temperature of magnetic particles is 700°C, the optimal ratio of CoFe2O4/chitosan is 1: 1, ultrasonic dispersion time is 30 min. The prepared chitosan magnetic microspheres have small size and are well dispersed when the stirring time is 3 h. The prepared magnetic chitosan microspheres are well shaped spheres with a diameter from 1 to 50 μm, in which CoFe2O4 particles are dispersed uniformly. The magnetic chitosan microspheres show excellent magnetic response and have good adsorption characteristics.

Growth of CoFe2O4 particles on wood template using controlled hydrothermal method at low temperature

Magnetic wood would be a potential for electromagnetic shielding, indoor electromagnetic wave absorber and special decoration. This work focuses on the development of a method to make magnetic wood/CoFe2O4 composites using a hydrothermal process. A particular emphasis is devoted to the understanding of the role of the chemical parameters involved in the hydrothermal technique, and of the hydrothermal treatment on the structures and properties of the materials obtained. The magnetic wood/CoFe2O4 composites could be obtained at 90°C within 8h. The crystallization of the spinel ferrites that precipitated on the wood template was promoted by the increase in reaction temperature. The saturation magnetization of the magnetic wood composites increases with holding time rapidly, attaining a maximum value of 2.59emu/g at 8h. Moreover, it has been found that the concentration of KNO3 and NaOH have a critical influence on the resultant structure, morphology and magnetic property of the magnetic wood composites.