Magnetically recoverable CoFe1.9Gd0.1O4 ferrite/polyaniline nanocomposite synthesized via green approach for radar band absorption

The gadolinium substituted cobalt ferrite (CoFe_1.9Gd_0.1O₄) nanoparticles and CoFe_1.9Gd_0.1O₄/Polyaniline (PANI) microwave absorber were synthesized by sol-gel auto combustion technique using lemon juice and in-situ polymerization method respectively. X-ray patterns confirmed the formation of single phase cubic structure. The crystallite size of the synthesized CoFe_1.9Gd_0.1O₄ nanoparticles are within the range of 15–68 nm. The saturation magnetization of CoFe_1.9Gd_0.1O₄ ferrite/Polyaniline (PANI) composite was reduced due to nonmagnetic PANI. The reflection loss for microwave absorbing properties of CoFe_1.9Gd_0.1O₄ ferrite nanoparticles and CoFe_1.9Gd_0.1O₄/PANI nanocomposite were investigated and minimum value of reflection loss was found to be −16.85 dB at 13.52 GHz for nanoparticles of thickness 2.5 mm and −25.59 dB at 11.92 GHz for CoFe_1.9Gd_0.1O₄/PANI nanocomposite of thickness 2.0 mm) respectively. The prepared samples have low density, high surface resistivity and enhanced attenuation constant. The nanocomposite exhibits excellent absorption performance over a broad band range in the radar band.     

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.     

Size-controlled high magnetization CoFe2O4 nanospheres and nanocubes using rapid one-pot sonochemical technique

Highly crystalline single phase spherical and monodisperse cobalt ferrite (CoFe₂O₄) nanoparticles (NPs) with uniform shape and size distribution have been synthesized by one pot-rapid sonochemical method. The effect of different solvents, such as aqueous, alcoholic, and a mix of water/ethanol in 1:1 volume ratio on the shape, size, and crystalline structure of CoFe₂O₄ NPs were studied using X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy and Fourier transform infrared spectroscopy. The size of CoFe₂O₄ nanoparticle was controlled in the range from 20 to 110 nm based on the solvent medium used in the synthesis process. Furthermore, the evolution from spherical to cubic morphology of cobalt ferrite NPs is achieved by simply changing the solvent medium from aqueous to alcoholic medium. The magnetic properties of all the synthesized CoFe₂O₄ NPs were studied by vibrating sample magnetometer (VSM) at room temperature. The magnetization value was found to be particle size dependent, and high magnetization (Ms) of 92.5 emu/g was obtained for the CoFe₂O₄ NPs sample synthesized in a mixed solution of water and ethanol. A possible reaction mechanism for the formation of cobalt ferrite NPs by the sonochemical technique was discussed. The facile method adopted in our study appears to be a promising route for synthesis of highly crystalline nanoparticles within short times and without the need for using any calcination process.     

The effect of the ethylene glycol to metal nitrate molar ratio on the phase evolution,morphology and magnetic properties of single phase BiFeO3 nanoparticles

In this work, single phase BiFeO₃ nanoparticles have been synthesized by thermal decomposition of a glyoxylate complex achieved by the redox reaction between ethylene glycol and nitrate anions. The effects of different molar ratios of ethylene glycol to metal nitrate anions on the phase evolution, morphology and magnetic properties were investigated by infrared spectroscopy, thermal analysis, X-ray diffraction, electron microscopy and vibrating sample magnetometry methods. The single phase bismuth ferrite nanoparticles synthesized with the ethylene glycol to nitrate anions molar ratio of 5 showed the weak ferromagnetism behavior with saturation magnetization of 1.3 emu/g, due to the size confinement effect. Furthermore, the BiFeO₃ nanoparticles were used for the degradation of methylene blue (MB) as a typical dye pollutant under direct sunlight irradiation.     

Structure and magnetic properties of CoFe2O4/SiO2 nanocomposites obtained by sol-gel and post annealing pathways

The influence of the CoFe₂O₄ nanoparticles concentration in silica matrix on the structural and magnetic properties of xCoFe₂O₄/(100−x)SiO₂ nanocomposites with x=10, 30, 50, 70 and 90 was studied. Magnetic CoFe₂O₄ nanoparticles dispersed in silica matrix was obtained by sol-gel method, followed by annealing at 1100 °C. The X-ray diffraction pattern and FT-IR spectra revealed the single spinel ferrite structure for all samples. The FT-IR spectra also suggested the formation of the amorphous silica matrix. The results showed that the increase of cobalt ferrite concentration (x) in the silica matrix leads to high crystallinity, specific surface area and particle size. The magnetic CoFe₂O₄ nanoparticles have spherical shapes and size in the 6–35 nm range. The Mössbauer measurements were fitted with two Zeeman sextets, indicating that all the samples were completely magnetically ordered. The vibrating sample magnetometer studies showed that the saturation magnetization (Ms) and coercivity (Hc) of the CoFe₂O₄ nanocrystals embedded in silica matrix possessed a linear relationship with the mean crystallite size. Also, the saturation magnetization of the studied nanocomposites increases with the increase of cobalt ferrite concentration (x) in the silica matrix.     

Electrospun nanocomposite polyacrylonitrile fibers containing carbon nanotubes and cobalt ferrite

Nanocomposite fibers made from polyacrylonitrile (PAN) containing carbon nanotubes (CNTs) and cobalt ferrite (CoFe₂O₄) nanoparticles were fabricated by electrospinning. The 10–25 nm CoFe₂O₄ nanoparticles were made by a simple hydrothermal process. Characterization by X‐ray diffraction confirmed that the CNTs and the CoFe₂O₄ nanoparticles were successfully incorporated into the PAN matrix. Scanning electron microscopy showed nanocomposite fibers with regular morphologies. Transmission electron microscopy revealed the internal distribution of the CNTs and CoFe₂O₄ nanoparticles. The nanocomposite fibers exhibited effective electromagnetic interference shielding attenuation of about 3.9 dB. Magnetic measurement using a vibrating sample magnetometer showed saturation magnetization of 4.7 emu g⁻¹, thus this property can be accurately tailored by adjusting the loading of CoFe₂O₄ nanoparticles. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Preparation,physicochemical characterization,and AC induction heating properties of colloidal aggregates of ferrimagnetic cobalt ferrite nanoparticles coated with a bio-compatible polymer

AC induction heating properties of colloidal nano-aggregates of ferrimagnetic cobalt ferrite magnetic nanoparticles (MNPs) are reported in this study. Bio-compatible chitosan polymer-coated CoFe₂O₄ MNPs are synthesized using a co-precipitation method. Powder X-ray diffraction indicates the formation of mixed spinel structures for the uncoated (CP) and chitosan-coated (CP–CHN) MNPs, which is also supported by the cation distributions obtained from the Mössbauer spectra. The presence of chitosan coating on the surface of the CP-CHN MNPs is confirmed using X-ray photoelectron and Fourier transform infrared spectroscopy studies. Transmission electron microscopy shows primary particle sizes of ∼13 nm, which is larger than the superparamagnetic size limit of the CoFe₂O₄ MNPs. Hence, the CP and CP-CHN MNPs exhibit ferrimagnetic behaviour at room temperature with estimated saturation magnetization values of ∼77.4 emu/g and ∼74.4 emu/g, respectively. The average hydrodynamic diameter is found to be ∼90 ± 8 nm for an aqueous dispersion of the CP-CHN MNPs, which indicate the formation of colloidal nano-aggregates due to the ferrimagnetic interaction of the primary MNPs. The CP-CHN sample exhibits a significantly high AC induction heating efficiency of ∼267.2 ± 4.0 W/g_Fe, where the higher heating efficiency is attributed to the combination of hysteresis and relaxation-mediated magneto-thermal energy conversion, as confirmed using Stoner-Wohlfarth model-based dynamic hysteresis loop calculations. Further, the heating efficiency decreases with increasing sample concentration due to an increase in dipolar interaction, which is confirmed using semi-empirical calculations, where a lowering of the initial susceptibility is observed at higher concentrations. The higher AC induction heating efficiency, coupled with the demonstrated significant bio-compatibility during in vitro cytotoxicity studies, make the cobalt ferrite nano-aggregates potential candidates for magnetic hyperthermia.     

Magnetic Properties of Annealed CoFe2O4 Nanoparticles Synthesized by the PEG-Assisted Route

Annealed cobalt inverse spinel-type ferrite nanoparticles were synthesized using polyethylene glycol assisted co-precipitation. The structure, magnetic properties and effect of annealing temperature was investigated in detail. Saturation magnetization, coercivity and remanence magnetization were observed to decrease with increasing temperature. The magnetic hysteresis curves supported the proposition that the CoFe₂O₄ nanoparticles showed ferromagnetic character from 10 to 400 K. Magnetization measurements showed the blocking temperature to be higher than 400 K. Unsaturated magnetization behavior suggested the existence of disordered spins in the surface layer of the CoFe₂O₄ nanoparticles.     

Photocatalytic and antibacterial characteristics of decorated polyester textile with ceramic nanoparticles of cobalt ferrite

In this study, a multifunctional textile profiting from photocatalytic activity, magnetic, and antibacterial properties was generated through decorating polyester fabric with cobalt ferrite (CoFe₂O₄) nanoparticles using the co-precipitation technique. The X-ray diffraction (XRD) results supported the successful decoration of fabrics with CoFe₂O₄ magnetic nanoparticles. Field emission electron scanning microscopy (FESEM) images accompanied by energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses demonstrated the morphology, dispersion, and chemical structure of particles on the surface. The mean particle size of cobalt ferrite was measured to be approximately 40 nm. Vibrating sample magnetometer (VSM) results confirmed the ferrimagnetic behavior of the decorated fabrics with saturation magnetization (M_s) and coercivity (H_c) of 1.8 emu/g and 1902 Oe, respectively. The UV–vis diffuse reflectance spectrum (DRS) and photoluminescence (PL) data indicated the appropriate performance under visible light irradiation and postponed electron-hole recombination of the decorated fabric, respectively. The maximum MB degradation efficiency of 97% after 180 min of visible light illumination was obtained. The active species trapping analyses indicated that hydroxyl radicals (^●OH) were the effective species in the photocatalytic degradation mechanism. The decorated sample with the best photocatalytic activity revealed more than 99% reduction in the number of colonies against gram-negative and gram-positive bacteria after 24 h contact time, which validated its excellent potential for antibacterial applications. Outstanding photocatalytic and antibacterial characteristics of the decorated textile with cobalt ferrite nanoparticles turn it into promising composite material for self-cleaning purposes.     

Fabrication and characterization of magnetic cobalt ferrite/polyacrylonitrile and cobalt ferrite/carbon nanofibers by electrospinning

An electrospinning process was used to fabricate cobalt ferrite (CoFe₂O₄)-embedded polyacrylonitrile (PAN) nanofibers. Oleic acid-modified CoFe₂O₄ nanoparticles were dispersed in the PAN before spinning. The surface morphologies and structures of the nanofibers were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM observation showed that the average diameter of the CoFe₂O₄/PAN nanofibers was 110 nm, and the magnetic CoFe₂O₄ nanoparticles were embedded in the PAN nanofibers. X-ray photoelectron spectroscopy was used to characterize the CoFe₂O₄/PAN and CoFe₂O₄/carbon nanofibers. Fiber magnetic properties were measured by vibrating sample magnetometry, showing that the saturation magnetization of the CoFe₂O₄/PAN nanofibers was 45 emu/g and that the fibers demonstrated superparamagnetic behavior.     

Influence of Gd content on the structural,Raman spectroscopic and magnetic properties of CoFe2O4 nanoparticles synthesized by sol-gel route

The structural and magnetic properties of sol-gel synthesized Gd doped (x = 0.00 to 0.15) CoFe₂O₄ nanoparticles (NPs) have been studied. The x-ray diffraction (XRD) and FTIR spectroscopy along with Raman spectra confirmed the formation of face centered cubic inverse spinel structure. TEM images showed the NPs are well-dispersed with average particle size 30 nm. Room temperature magnetic measurement showed the value of coercivity fluctuates from 353 Oe to 1060 Oe for different % of Gd content. The maximum coercivity, saturation magnetization, magnetic moment, magnetic anisotropy, remnant magnetization found for 0.03% Gd content are 1060.19 Oe, 77.53 emu/gm, 3.29 μ, 4.11 × 10⁴ erg/cm³, 32.38 emu/gm, respectively. The large value of coercivity indicated that the interparticle interactions and crystalline anisotropy are high. Thus CoFe_2-xGd_xO₄ magnetic NPs might be a potential candidate for data processing, automotive and telecommunications.     

Effect of heat treatment on structural,morphological, dielectric and magnetic properties of Mg–Zn ferrite nanoparticles

Green combustion was used to prepare a ferrite composition of Mg_0.4Zn_0.6Fe₂O₄ using a blend of fresh lemon juice as a natural fuel-reductant. Effect of heat treatment on phase, morphological, dielectric, and humidity sensor properties is discussed. The formation of a cubic spinel ferrite has been established by XRD-diffraction and vibrational spectroscopic studies. The experimental lattice parameter ranges from 8.3721 to 8.3631 Å. The broadening of octahedral band (υ₂) in the vibrational spectra is an identification for the existence of ferrite nanoparticles in various sizes. The typical crystallite size ranges from 10.2 to 36.9 nm. Using micrographs obtained from field-effect scanning electron microscopy (FESEM), researchers observed a spherical-shaped microstructure with agglomerated nanoparticles. Dielectric investigations have shown that the current ferrite composition has typical dielectric dispersion. The highest reported value for saturation magnetization (M_s) in the present study is 33 emu/g. Magnetic behaviour is primarily influenced by magnetocrystalline anisotropy, cation distribution, and crystallite size. The existence of void spaces in the sintered samples, as well as their porous nature, rendered them suitable for humidity sensor applications. Sintered samples have good sensing capability at 900 °C. The current findings are integrated in terms of cation distribution and magnetocrystalline anisotropy, assuming fine size effects of ferrite nanoparticles.     

Sonochemical synthesis of CoFe2O4 nanoparticles and their application in magnetic polystyrene nanocomposites

CoFe₂O₄ (CoFe) nanoparticles were synthesized via a facile surfactant-free sonochemical reaction. For preparation of magnetic polymeric films, CoFe₂O₄ nanoparticles were added to polystyrene (PS). Nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Magnetic properties of the samples were investigated using an alternating gradient force magnetometer (AGFM). CoFe₂O₄ nanoparticles exhibit a ferromagnetic behaviour with a saturation magnetization of 62 emu/g and a coercivity of 640 Oe at room temperature. By preparing magnetic films the coercivity is increased. The coercivity of PS/CoFe₂O₄ (10%) nanocomposites is higher than that obtained for PS/CoFe₂O₄ (30%).     

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 the rare-earth substitution on the structural,magnetic and adsorption properties in cobalt ferrite nanoparticles

Rare-earth (RE) substituted cobalt ferrite CoFe_1.9RE_0.1O₄ (RE=Pr³⁺, Sm³⁺, Tb³⁺, Ho³⁺) nanoparticles are synthesized by a facile hydrothermal method without any template and surfactant. The effects of RE³⁺ substitution on structural, magnetic and adsorption properties of cobalt ferrite nanoparticles are investigated. Structure, morphology, particle size, chemical composition and magnetic properties of the ferrite nanoparticles are studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), high solution transmission electron microscopy (HRTEM), energy-dispersive spectrometer (EDS), Fourier transform spectroscopy (FTIR), Raman spectra and vibrating sample magnetometry (VSM). The results indicate that the as-synthesized samples have the pure spinel phase, uniform crystallite size and narrow particle size distribution. Meanwhile, the RE³⁺ substitution leads to the decrease in the particle size, magnetization and coercivity of the CoFe₂O₄ ferrite. Notably, it demonstrates that the RE³⁺ doping can apparently enhance the adsorption capacity for Congo red (CR) onto ferrite nanoparticles. Adsorption equilibrium studies show that adsorption of CR follows the Langmuir model. The monolayer adsorption capacities of CoFe_1.9Sm_0.1O₄ and CoFe_1.9Ho_0.1O₄ are 178.6 and 158.0 mg/g, respectively. The adsorption kinetics can be described by the pseudo-second-order model.     

Effects of annealing on the structural and magnetic properties of flame spray pyrolyzed MnFe2O4 nanoparticles

In this study, manganese ferrite (MnFe₂O₄) nanoparticles were produced through flame spray pyrolysis (FSP). To investigate the effects of heat treatment, the nanoparticles were annealed between 400 and 650°C for 4 h in air in a comparative manner. The structural, chemical, morphological, and magnetic properties of the nanoparticles were evaluated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), dynamic light scattering (DLS), and vibrating sample magnetometry (VSM), respectively. The XRD results showed that the nanoparticles synthesized by the FSP method exhibited the MnFe₂O₄ spinel ferrite structure. The annealing process led to the decomposition of MnFe₂O₄ into various phases. According to the morphological analysis, the as-synthesized particles were hemispherical–cubic in shape and had an average particle size of less than 100 nm. In addition, the chemical bond structures of the nanoparticles were confirmed in detail by XPS elemental analysis. The highest saturation magnetization was recorded as 33.50 emu/g for the as-produced nanoparticles. The saturation magnetization of the nanoparticles decreased with increasing annealing temperature, while coercivity increased.     

Structure and magnetic properties of multi-morphological CoFe2O4/CoFe nanocomposites by one-step hydrothermal synthesis

Multi-morphological CoFe₂O₄/CoFe nanocomposites have been synthesized using a facile hydrothermal process. The effects of hydrazine hydrate amount during hydrothermal reaction on the structure and magnetic property of the specimens were studied. With increasing hydrazine hydrate amount, the CoFe₂O₄ transformed to CoFe and the morphology of the specimen changed from granular particles to faceted particles. The saturation magnetization monotonically increased and the coercivity monotonically decreased with increasing hydrazine hydrate amount. The magnetic interactions, determining the magnetic properties of the composites, result from the dominant dipole coupling and relative weak exchange coupling between CoFe₂O₄ and CoFe nanoparticles. The CoFe₂O₄/CoFe nanocomposite prepared with 2?mL hydrazine hydrate exhibited the optimal magnetic properties, with the saturation magnetization of 81?emu/g and coercivity of 636?Oe.     

Single-phase and binary phase nanogranular ferrites for magnetic hyperthermia application

The study demonstrates the performance of heating efficiency in single-phase and binary phase spinel ferrite nanosystems. Ferrimagnetic cobalt ferrite (CoFe₂O₄) (CFO) and superparamagnetic copper ferrite/copper oxide (CuFe₂O₄/CuO) (CuF) nanosystems of different particle sizes were synthesized through a microwave-assisted coprecipitation method. The heating behavior was observed in range of both field amplitudes (8-24 kA/m at 516 kHz) and frequencies (325-973 kHz at 12 kA/m). The heating efficiency was analyzed and compared by means of particle size, magnetization, effective anisotropy constant, and Néel relaxation mechanism. Indeed, the heating rate was maximized in larger ferrite particles with low effective anisotropy constant. Moreover, though the magnetization and effective anisotropy constant of single-phase CoFe₂O₄ nanoparticles were higher, the binary phase CuFe₂O₄/CuO nanosystems of similar crystallite size (28 nm) exhibited superior heating efficiency (4.21°C/s). For a field amplitude and frequency of 24 kA/m and 516 kHz, the heating rate of CuF and CFO ferrites with different crystallite sizes decreased in the order of 4.21 > 2.14 > 0.58 > 0.52°C/s for 29 nm > 25 nm > 12 nm > 15 nm, respectively. The results emphasize that binary phase ferrite nanoparticles are better thermoseeds than the single-phase ferrites for the magnetic hyperthermia application.     

Effects of the fuel type and fuel content on the specific surface area and magnetic properties of solution combusted CoFe2O4 nanoparticles

In this work, the different fuels (citric acid, glycine and urea) at the various fuel to oxidant ratios (ϕ=0.5, 0.75, 1 and 1.25) were used for solution combustion synthesis of CoFe₂O₄ nanoparticles. The phase evolution, microstructure, specific surface area and magnetic properties of the solution combusted CoFe₂O₄ nanoparticles were investigated by X-ray diffraction, thermal analysis, electron microscopy, adsorption-desorption isotherms and vibrating sample magnetometry techniques. The specific surface area of the combusted products decreased with the increase of fuel to oxidant ratio (ϕ), irrespective of the fuel type. However, the specific surface area for the glycine fuel was higher than the others, due to the higher combustion rate for releasing gaseous products. Furthermore, the solution combusted CoFe₂O₄ powders by the glycine fuel exhibited the higher saturation magnetization (63.6 emu/g) on account of their higher crystallinity and particle size.     

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.