The influence of solvent composition in the sol-gel synthesis of cobalt ferrite (CoFe2O4): A route to tuning its magnetic and mechanical properties

This work presents a successful, environmentally-friendly route for tuning the magnetic and mechanical properties of CoFe₂O₄ sintered ceramics. The precursor powders were prepared from mixtures containing 100, 50 and 20% water, with the remaining volume composed of isopropanol. The synthesised powders were pressed into pellets and sintered at 1150 and 1200 °C. SEM micrographs indicate that the solvent exerts a major influence over the morphology of the ferrite grains. Vickers hardness shows a maximum for products from a medium containing 50% water, which could be directly related to the smaller average size of the CoFe₂O₄ grains. The coercivity of the pellets is strongly influenced by the reactional medium, with a maximum of 501.7 Oe (sample prepared at 20% water and fired at 1150 °C). This work opens up possibilities for fine tuning of the final properties of CoFe₂O₄ sintered ceramics, further enabling the utilisation of this material in advanced applications.     

Magnetic interactions and hysteresis loops study of Co/CoFe2O4 nanoparticles

Co/CoFe₂O₄ nanoparticles with the mean size of 8.8, 10.8 and 16.9 nm were prepared by thermal decomposition of metal salts in the presence of citric acid. The X-ray diffraction patterns and Rietveld refinements confirmed coexistence of Co-ferrite and metallic cobalt phases in the nano-powders. Scanning electron microscope images showed an increase in particles aggregates mean diameter with increasing the annealing temperature. Magnetic hysteresis loops showed a demagnetization jump at low fields, which was attributed to different reversal fields of ferrite and the cobalt phases. Field-dependent behavior of maximum magnetization (M_max), remanence (M_r), squareness (S) and coercivity (H_c) were studied through minor loops measurements. The calculated S value of the loops showed a maximum, between anisotropy and coercive fields. A sharp increase in H_c of larger particles was observed with increasing the applied field when compared to smaller particles. Henkel plots showed that the samples are interacting. Negative deviation of Henkel plots from linear behavior and negative δm plots revealed the dominant role of dipole–dipole interactions in the nano-aggregates.     

Synthesis of CoFe2O4 powders with high surface area by solution combustion method: Effect of fuel content and cobalt precursor

High surface area cobalt ferrite (CoFe₂O₄) powders were synthesized by solution combustion method. The dependence of the adiabatic temperature and the released gases during combustion reaction on the fuel content and cobalt precursor type, cobalt nitrate and cobalt acetate, was thermodynamically calculated. Thermal analysis, infrared spectroscopy, X-ray diffractometry, nitrogen adsorption–desorption, electron microscopy and vibrating sample magnetometer were used for investigation of the phase evolution, surface areas, morphology and magnetic properties of the synthesized CoFe₂O₄ powders. The specific surface area decreased from 285.4 to 35.7 m²/g with increasing of fuel to oxidant molar ratio, ϕ, from 0.5 to 1.25 for the cobalt nitrate precursor, while the maximum surface area of 182.1 m²/g was attained at ϕ=1 for the cobalt acetate precursor. The synthesized CoFe₂O₄ powders from the cobalt nitrate precursor exhibited the higher saturation magnetization and coercivity on account of the higher purity and crystallinity.     

CoFe2O4的制备及其活化过硫酸盐降解磺胺甲恶唑

采用简单的共沉淀法在不同煅烧温度下成功合成了一系列铁酸钴材料（CoFe2O4-X），通过SEM，XRD，BET，XPS等表征手段对其结构组成进行了分析，并将其用于活化过一硫酸盐（PMS）以降解磺胺甲恶唑（SMX）。考察了催化剂投加量、PMS用量、pH值和无机离子对SMX降解的影响。结果表明，550℃煅烧温度下获得的CoFe2O4-550具有最佳的催化性能，在最佳反应条件下，20 min内，SMX的降解率可高达95%，且TOC去除率可达80%。同时，CoFe2O4-550/PMS反应体系具有较广的pH适用范围（pH=5.00-9.00）。CoFe2O4-550催化剂可磁性回收，具有较好的稳定性和重复使用性。自由基淬灭实验表明，在该降解反应过程中产生了大量的SO4-?和?OH自由基，并提出了相应的催化降解机理。这项工作将为有效处理含有SMX化合物的废水提供一种新思路。     

The role of Co ion substitution in SnFe2O4 spinel ferrite nanoparticles: Study of structural,vibrational, magnetic and optical properties

In order to accurately investigate the effect of cobalt substitutions in tin ferrite (SnFe₂O₄) properties, we prepared Co_xSn_1-xFe₂O₄ nanoparticles for different Co concentrations, x?=?0.0, 0.25, 0.50, 0.75, and 1.00 using a simple co-precipitation method. X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX) and diffuse reflectance spectra (DRS) are used to study of structural, magnetic, morphology, and optical properties. The XRD and FTIR results confirmed the formation of cubic spinel structure. The lattice parameter and unit cell volume of tin ferrite nanoparticles were found to increase by entering and increasing Co⁺² content in 0.25, and then significantly decrease for higher contents. In accordance with the XRD results, a slight shift in main band υ₁ (${\mathit{Fe}}_{\mathrm{tetra}}^{+3}?O)$ to lower wavenumber and then to higher wavenumber were observed in the IR spectra of Co content x?<?0.25 and x?>?0.25, respectively. In turn to, saturation magnetization, remanent magnetization and anisotropy constant of SnFe₂O₄ nanoparticles were gradually increased for x?=?0.50 and then decreased for x?>?0.50.     

Anisotropy investigation of cobalt ferrite nanoparticles embedded in polyvinyl alcohol matrix: A Monte Carlo study

The magnetic properties of the cobalt ferrite/polyvinyl alcohol nanocomposites have been studied experimentally and theoretically. For investigation the impact of polymeric matrix on magnetic properties of magnetic nanoparticles, four different processes have been considered for synthesizing the polymer based nanocomposites by co-precipitation method. The effective magnetic anisotropy obtained by Monte Carlo simulation and law of approach to the saturation magnetization showed a significant decrease relative to the bulk and bare cobalt ferrite nanoparticles. The polymeric matrix interacted with the surface of particles by different strength and made them approximately non-interacting. The as synthesized samples characterized by X-Ray diffractions (XRD) and Fourier transform infrared spectroscopy (FT-IR). Magnetic measurements were carried out at room temperature using a vibrating sample magnetometer (VSM).     

尖晶石型铁氧体CuFe_2O_4的制备及其Fenton反应效能研究

本文采用溶胶-凝胶法制备了不同煅烧温度下的尖晶石型铁氧体Cu Fe2O4系列样品。利用XRD、SEM对样品的结构、形貌进行了表征。结果表明,煅烧温度在800℃以上时,所合成的样品均为单相尖晶石型铁氧体CuFe2O4,样品的形貌呈现球状。在尖晶石型铁氧体CuFe2O4体系中加入H2O2,利用Fenton反应,能够有效地降解亚甲基蓝染料废水。     

Faujasite zeolite decorated with cobalt ferrite nanoparticles for improving removal and reuse in Pb2+ ions adsorption

Water pollution caused by heavy metals ions has been gaining attention in recent years, increasing the interest in the development of methodologies for their efficient removal focusing on the adsorption process for these purposes. The current challenge faced by adsorption processes is the adequate adsorbent immobilization for removal and reuse. Thus, the present work aimed at producing a faujasite zeolite nanocomposite decorated with cobalt ferrite nanoparticles for Pb~(2+) ions adsorption in an aqueous medium improving magnetic removal and reuse.As a result, a high surface area(434.4 m~2·g~(-1)) for the nanocomposite and an 18.93 emu·g~(-1) saturation magnetization value were obtained, indicating magnetic removal in a promising material for adsorption process. The nanocomposite regeneration capacity evaluated by magnetic recovery after 24 h suspension presented a high Pb~(2+) ion adsorptive capacity(98.4%) in the first cycle. Around 98% of the Pb~(2+) ions were adsorbed in the second cycle. In this way, the synthesized faujasite:cobalt ferrite nanocomposite reveals itself as a promising alternative in adsorption processes, aiming at a synergic effect of FAU zeolite high adsorptive activity and the cobalt ferrite nanoparticles magnetic activity, allowing for adsorbent recovery from the aqueous medium via magnetic force and successive adsorptive cycles.     

Hydrothermal synthesis,magnetic properties and characterization of CoFe2O4 nanocrystals

Magnetic cobalt ferrite (CoFe₂O₄) nanocrystals were synthesized via the hydrothermal method and the crystallite size was measured using Sherrer's equation. Instrumental broadening was a significant parameter for determining crystallite size. The effect of annealing time and calcination on crystallite size and magnetic properties was discussed. It was found that the coercivity was highly dependent on the crystallite size. As the crystallite size increased from 61 to 68.2 nm, room temperature coercivity increased from 1488 Oe to 1700 Oe, while high coercivity (5.2 kOe) was achieved at lower temperature (80 K). It was found that the presence of hematite could affect the crystallite size after calcination.     

Antimony removal from aqueous solutions using magnetic nickel ferrite (NiFe2O4) nanoparticles

In this study, magnetic nickel ferrite (NiFe₂O₄) nanoparticles were synthesized via microwave assisted combustion method and these particles were used as adsorbent for antimony removal. The most effective parameters for the removal efficiency are adsorbent dosage and temperature, while the impact of pH is insignificant. In order to determine the most suitable kinetic model, the compatibility of pseudo-first order, pseudo-second order and the intraparticle diffusion model was compared and the most suitable kinetic model was determined to be pseudo-second-order. Langmuir and Freundlich isotherms were assessed and the most suitable isotherm was observed to be Freundlich model.     

Rietveld structure refinement,cations distribution and magnetic features of CoFe2O4 nanoparticles synthesized by co-precipitation,hydrothermal, and combustion methods

Cobalt ferrite nanoparticles were synthesized by chemical co-precipitation, hydrothermal and sol gel auto-combustion methods. X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM) and vibrating sample magnetometer (VSM) were used to investigate the structural characteristics and magnetic properties of cobalt ferrite nanocrystals. X-ray patterns revealed the production of a broad single cubic phase with the average crystallite size of 16, 18 and 178 nm for co-precipitation, hydrothermal and combustion methods, respectively. The FTIR measurements between 400 and 4000 cm⁻¹ confirmed the intrinsic cation vibrations of spinel structure. The FE-SEM micrographs of the synthesized samples indicated the presence of two distinct groups of grains exhibiting different sizes and, different shapes for hydrothermal route. The results of magnetic hysteresis at a room temperature showed that the magnetic properties depend on the particle size and shape of particles, whereas the role of particle size is more significant.     

Effect of annealing on the structure and magnetic properties of CoFe2O4:SiO2 nanocomposites

The decomposition of succinate type precursors obtained by a modified sol-gel method using cobalt and iron nitrates, 1,4-butanediol and tetraethylorthosilicate, followed by the formation of single phase cobalt ferrite embedded in the silica matrix by annealing at 400–1100 °C was studied. The thermal analysis indicated the formation temperature of succinate type precursors, while the Fourier transform infrared spectroscopy (FT-IR) data confirmed the formation of the precursors in the pores of silica matrix. The formation of CoFe₂O₄ was investigated by X-ray diffraction and FT-IR, the size and shape of the nanoparticles by transmission electron microscopy, while the resulted microstructures by scanning electron microscopy. The crystallinity and crystallites size increased with the annealing temperature. The hysteresis loops revealed a direct relationship between annealing temperature and saturation magnetization in constant coercive field. The particle size of ferrite powders is critically dependent on the annealing temperature.     

Synthesis and rheological characterization of nano-magnetorheological fluid using inverse spinel ferrite (NiFe2O4)

In recent years, the utilization of nanoparticles for nano-magnetorheological fluid (NMRF) synthesis is gaining popularity in automotive applications. From this perspective, the nickel ferrite (NiFe₂O₄) nanoparticles were prepared by gel burning method and characterized using the X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy-energy dispersive X-ray analysis (FESEM-EDX), and vibration sample magnetometer (VSM). The XRD and FTIR results showed the phase formation and characteristic metal–oxygen M–O vibrations. The FESEM images showed quasi-spherical crystallites with considerable agglomeration. The magnetic properties measured showed the ferromagnetic nature of NiFe₂O₄. The nanosized NiFe₂O₄ was used for NMRF preparation and characterization.     

Controlled synthesis of L-cysteine coated cobalt ferrite nanoparticles for drug delivery

In the present work, we reported a facile synthesis of cobalt ferrite (CoFe₂O₄) nanoparticles in the presence of L-cysteine (Lys). The morphology and size of samples were characterized by SEM and TEM. The successful coating of Lys on the surface of CoFe₂O₄ was confirmed by XRD, XPS and TGA. The investigation of magnetic properties showed that both bare CoFe₂O₄ and Lys-coated CoFe₂O₄ nanoparticles exhibited room-temperature superparamagnetic behavior. The results of MTT experiments revealed insignificant cytotoxicity of Lys-coated CoFe₂O₄ nanoparticles even after 24?h incubation. More importantly, Lys-coated CoFe₂O₄ nanoparticles displayed an excellent drug loading capacity and a pH-sensitive drug release behavior. In summary, the prepared Lys-coated CoFe₂O₄ nanoparticles demonstrated a promising application potential in controlled drug delivery.     

Sol-gel synthesis of substoichiometric cobalt ferrite (CoFe2O4) spinels: Influence of additives on their stoichiometry and magnetic properties

Spinel cobalt ferrites (CoFe₂O₄) with varying levels of substoichiometry were prepared via sol-gel synthesis with different combinations of citric acid, dextrose and PVP (polyvinylpyrrolidone). The gels, prepared from the metal nitrates, were dried at 110?°C, further treated at 850?°C and finally subjected to thorough structural and magnetic characterization in order to correlate the composition of the gel to the structural and magnetic properties displayed by the ferrites. The materials synthesized in the present work have shown to be rather iron-depleted, reaching over 50% deficiency of the metal, which leaves the spinel lattice and forms Fe₂O₃ instead. The fuel/oxidant ratio and the thermal behavior of the xerogels exert a direct influence on the compositional variation of the prepared spinels, which could in turn be correlated to the magnetic properties displayed by the particles. A maximum in coercivity of 2154.4?Oe was achieved without the application of any additive to the nitrate precursors. On the other hand, the magnetic remanence displayed by the ferrites shows a linear relationship to the iron content in their chemical formula. The results open up the possibility of fine-tuning the structural and magnetic properties displayed by the spinel product via careful control of the composition of the reaction medium.     

Investigation of ZnFe2O4 spinel ferrite nanocrystalline screen-printed thick films for application in humidity sensing

Zinc ferrite nanocrystalline powder was obtained by solid state synthesis of starting zinc oxide and hematite nanopowders. Field emission scanning electron microscopy and transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy confirmed the formation of nanocrystalline zinc-ferrite powder with a mixed spinel structure with small amounts of remaining zinc oxide and hematite as impurities. Thick film paste was formed and screen printed on test interdigitated PdAg electrodes on alumina substrate. Formation of a porous nanocrystalline structure was confirmed by scanning electron microscopy and Hg porosimetry. Humidity sensing properties of zinc ferrite thick films were investigated by monitoring the change in impedance in the relative humidity interval 30%-90% in the frequency range 42 Hz-1 MHz at room temperature (25°C) and 50°C. At 42 Hz at both analyzed temperatures the impedance reduced ~46 times in the humidity range 30%-90%. The dominant influence of grain boundaries was confirmed by analysis of complex impedance with an equivalent circuit.     

The effect of reaction temperature on the structural and magnetic properties of nano CoFe2O4

Nano cobalt ferrites (CoFe₂O₄) were co-precipitated at various reaction temperatures (60, 70 and 80 °C) for 1 h. The reaction temperature greatly influenced the crystallite size and the magnetic behaviours of the nano CoFe₂O₄. The mean crystallite size ranged from 9 to 15 nm with the increase in the reaction temperature and the intensity of metal oxide vibrations at 568–550 cm⁻¹ were also inclined. The synthesized samples were in the stoichiometric ratio of 1:2 (Co:Fe) with roughly spherical morphology. The synthesized cobalt nanoferrites exhibited ferromagnetism at room temperature and 5 K, and the saturation magnetization increased from 6.4 to 20 emu/g with the crystallite size.     

Effect of lemon juice on microstructure,phase changes,and magnetic performance of CoFe2O4 nanoparticles and their use on release of anti-cancer drugs

Cobalt ferrite magnetic nanoparticles were synthesized and developed by a modified Pechini method using iron nitrate, cobalt nitrate, ethylene glycol (EG), and sucrose with different volumes of lemon juice (10, 20, 30, 40, 50, 60, and 70 ml) as the source of chelating agent as well as nonmagnetic elements such as Ca and Mg ions. The XRD patterns confirmed that all samples synthesized by different contents of extracted lemon juice had a cubic crystal structure with single-phase spinel. Scanning electron microscopy revealed that cobalt ferrite nanoparticles had a semi-spherical morphology. Also, the vibrating sample magnetometer indicated that the saturation magnetization of CoFe₂O₄ nanoparticles prepared with different values of extracted lemon juice increased from 18.6 emu/g for 10 ml extracted lemon juice to 75.7 emu/g for 50 ml extracted lemon juice, after which the saturation magnetization diminished. Afterwards, the CoFe₂O₄ nanoparticles were coated with polyethylene glycol (PEG) and doxorubicin (DOX) drugs, whereby drug delivery was detected at different pH levels. The CoFe₂O₄-PEG-DOX nanocomposite could release doxorubicin by more than 42% at pH = 5.4 in 75 h.     

Synthesis and magneto-structural properties of chitosan coated ultrafine cobalt ferrite nanoparticles for magnetic fluid hyperthermia in viscous medium

AC induction heating mediated magnetic fluid hyperthermia of superparamagnetic nanoparticles (MNPs) is being widely explored for localized thermo-therapy of tumours. One of the primary hindrances for rapid adaptation of this technique is the loss of heating efficiency when the MNPs are placed within the viscous tissue medium, which necessitates undesired increase in MNP concentrations or exposure time during practical applications. With an objective to mitigate this, here we report the viscosity independent magnetic hyperthermia properties of biocompatible ultrafine (average size ～ 2.5 nm) chitosan-coated superparamagnetic CoFe₂O₄ MNPs synthesized using a low-cost co-precipitation technique. The presence of the chitosan coating is confirmed from Fourier transform infrared and X-ray photoelectron spectroscopy. The superparamagnetic nature of the synthesized MNPs at 300 K is confirmed from Mössbauer spectroscopy, isothermal and temperature dependent magnetization studies. Experimental findings indicate a higher field-induced heating efficiency for the chitosan-coated MNPs due to superior colloidal stability. The ultrafine size, combined with higher anisotropy energy density, results in viscosity independent Nèel relaxation-dominated magneto-thermal energy conversion for the CoFe₂O₄ MNPs. Experimental results reveal negligible loss of heating efficiency due to partial abrogation of Brownian relaxation when the chitosan-coated MNPs are immobilized in a tissue-equivalent agar medium, which is beneficial for practical applications. The heating efficiency of ～72.1 ± 2.8 W/g_Fe (at 33.1 kA/m and 126 kHz), obtained in the present study for the chitosan-coated MNPs, is higher than the previously documented values for ultrafine CoFe₂O₄ MNPs, which is useful for reducing the exposure time during practical applications. Further, the chitosan coating rendered the ultrafine CoFe₂O₄ MNPs bio-compatible against L929 cell line. The satisfactory magnetic fluid hyperthermia efficiency, negligible room temperature coercivity, retention of the field-induced heating efficiency in tissue-equivalent agar medium due to Nèel-dominated relaxation dynamics and superior biocompatibility, make the chitosan-coated ultrafine CoFe₂O₄ MNPs an attractive candidate for practical MFH applications.