A novel CoFe2O4/polyacrylate nanocomposite prepared via an in situ polymerization in emulsion system

A CoFe₂O₄/polyacrylate nanocomposite was synthesized by in situ emulsion polymerization of an acrylic acid monomer in the presence of CoFe₂O₄ magnetic fluid. X-ray diffraction and FT-IR spectra confirmed the formation of the CoFe₂O₄/polyacrylate nanocomposite. Transmission electron microscopy images showed that CoFe₂O₄ nanoparticles with the particle sizes of about 12 nm were well dispersed in the polymer matrix. The nanocomposite exhibited superparamagnetic behavior at room temperature under an applied magnetic field. The formation mechanism of the nanocomposite was investigated as well.     

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.     

Polyaniline (PANI)–Co0.5Mn0.5Fe2O4 nanocomposite: Synthesis,characterization and magnetic properties evaluation

Polyaniline (PANI)/Cobalt-manganese ferrite, (PANI)/Co_0.5Mn_0.5Fe₂O₄, nanocomposite was synthesized by oxidative chemical polymerization of aniline in the presence of ammonium peroxydisulfate (APS). Microwave assisted synthesis method was used for the fabrication of core CoFe₂O₄ nanoparticles. The structural, morphological, thermal and magnetic properties of the nanocomposite were investigated in detail by X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The average crystallite size of (PANI)/Co_0.5Mn_0.5Fe₂O₄ nanocomposite by the line profile method was 20±9 nm. The magnetization measurements revealed that (PANI)/Co_0.5Mn_0.5Fe₂O₄ nanocomposite has superparamagnetic behavior with blocking temperature higher than 300 K. The saturation magnetization of the composite is considerably low compared to that of CoFe₂O₄ nanoparticles due to the partial replacement of Co²⁺ ions and surface spin disorder. As temperature decreases, both coercivity and strength of antiferromagnetic interactions increase which results in unsaturated magnetization of the nanocomposite.     

Soft chemistry routes for the preparation of Ag-CoFe2O4 nanocomposites

Silver-cobalt ferrite nanocomposites (Ag-CoFe₂O₄) were synthesized through wet ferritization process and self-propagating combustion method. The structure, morphology, surface chemistry and magnetic properties of the nanocomposites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). X-ray diffraction patterns confirmed the formation of CoFe₂O₄ and Ag nanoparticles with cubic symmetry. The average crystallite size of CoFe₂O₄ by wet ferritization ranged between 60 Å and 87 Å; for those obtained by self-propagating combustion was in the range 232–290 Å. SEM micrographs revealed different morphological features of nanocomposites. Ag-CoFe₂O₄ obtained by wet ferritization exhibited typical superparamagnetic behaviour. The antimicrobial and anti-biofilm properties of all silver-cobalt ferrites were evaluated. The results revealed that the Ag-CoFe₂O₄ nanocomposites exhibited good microbicidal and anti-biofilm features.     

Halloysite nanotubes coated with magnetic nanoparticles

Co nanoparticles were assembled on the surface of halloysite nanotubes (HNTs) to prepare one-dimensional magnetic Co-HNTs via electroless deposition. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry (EDXS) and vibrating sample magnetometer (VSM). The cobalt nanoparticles of 3–7 nm in size were uniformly deposited on the surface of the nanotubes. The remanent magnetization (M_r), saturation magnetization (M_s) and coercivity (H_c) values of the Co-HNTs were 13.9 emu/g, 27.05 emu/g and 1659 O_e, respectively, larger than that of the pure Co nanoparticles (580.72 O_e). A mechanism of the deposition of the magnetic nanoparticles on the surface of the halloysite nanotubes is suggested. Co-HNTs showed an interesting potential in the field of magnetic devices.     

PVA assisted coprecipitation synthesis and characterization of MgFe2O4 nanoparticles

Single phase magnesium ferrite (MgFe₂O₄) nanoparticles were prepared by the coprecipitation method followed by calcination at 700 °C for 1 h. The effects of polyvinyl alcohol (PVA) agent on the structural, microstructure, magnetic properties and AC magnetically induced heating characteristics of MgFe₂O₄ nanoparticles were investigated. The structure and cation distributions investigated by X-ray diffraction method showed single phase MgFe₂O₄ powders had partially inverse spinel structure in which the inversion coefficient increased by adding more PVA. The small particle size and narrow size distribution of the coprecipitated MgFe₂O₄ powders characterized by scanning electron microscopy were achieved using PVA agent. Magnetic properties of MgFe₂O₄ nanoparticles studied by vibrating sample magnetometry showed ferrimagnetic characteristics with the highest saturation magnetization and coercivity of 24.6 emu/g and 17 Oe, respectively. The coprecipitated MgFe₂O₄ nanoparticles assisted by PVA exhibited the lower AC heating temperature of 5.6 °C and specific loss power of 2.4 W/g in comparison with 6.1 °C and 2.7 W/g for the powders coprecipitated without using PVA.     

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.     

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.     

Coupling CoFe2O4 and SnS2 nanoparticles with reduced graphene oxide as a high-performance electromagnetic wave absorber

The reduced graphene oxide (RGO)/CoFe₂O₄/SnS₂ composites have been successfully synthesized by two-step hydrothermal processes. TEM results show that CoFe₂O₄ and SnS₂ nanoparticles with both diameters about 5–10 nm are well dispersed on the surface of graphene. Compared with RGO/CoFe₂O₄ composites, the as-prepared RGO/CoFe₂O₄/SnS₂ composites exhibit excellent electromagnetic (EM) wave absorption properties in terms of both the maximum reflection loss and the absorption bandwidth. The maximum reflection loss of RGO/CoFe₂O₄/SnS₂ composites is −54.4 dB at 16.5 GHz with thickness of only 1.6 mm and the absorption bandwidth with the reflection loss below −10 dB is up to 12.0 GHz (from 6.0 to 18.0 GHz) with a thickness in the range of 1.5–4.0 mm. And especially, they cover the whole X band (8.0–12.0 GHz), which could be used for military radar and direct broadcast satellite (DBS).     

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.     

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.     

A sonochemical method for synthesis of Fe3O4 nanoparticles and thermal stable PVA-based magnetic nanocomposite

Fe₃O₄ nanoparticles were synthesized via a simple surfactant-free sonochemical reaction. Room temperature synthesis without using inert atmosphere is the novelty of this work. The effect of different parameters on the morphology of the products was investigated. The magnetic properties of the samples were also investigated using an alternating gradient force magnetometer. Fe₃O₄ nanoparticles exhibit a ferromagnetic behavior with a saturation magnetization of 66 emu/g and a coercivity of 39 Oe at room temperature. For preparation magnetic nanocomposite, Fe₃O₄ nanoparticles were added to the polyvinyl alcohol (PVA). Nanoparticles can enhance the thermal stability and flame retardant property of the PVA matrix.     

Re-formation of metastable ε-Fe2O3 in post-annealing of Fe2O3/SiO2 nanostructure: Synthesis,computational particle shape analysis in micrographs and magnetic properties

Several Fe₂O₃/SiO₂ nanostructures were synthesized by the combination of the microemulsion and a sol-gel methods. Based on X-ray powder diffraction (XRD) and magnetic measurements (giant coercivity ~2.13 T) we identified ε-Fe₂O₃ (hard magnet) as the dominant crystalline phase. TEM analysis showed a wide size distribution of iron oxide nanoparticles (from 4 to 50 nm) with various morphologies (spherical, ellipsoidal and rod-like). We quantitatively described (computational analysis, MATLAB code) morphological properties of nanoparticles using the ellipticity of the shapes. The as-synthesized hard magnetic material was subjected to a post-annealing treatment at different temperatures (200, 500, 750, 1000 and 1100 °C) in order to investigate stability, formation and transformation of the ε-Fe₂O₃ polymorph. We found decreasing coercivity in the thermally treated samples up to the temperature of 750 °C (H_c=1245 Oe), followed by an observation of a surprising jump in coercivity H_C~1.5 T after post-annealing at 1000 °C. We conclude that the re-formation of the ε-Fe₂O₃ structure during post-annealing at 1000 °C is the origin of the observed phenomena. The phase transformation ε-Fe₂O₃→α-Fe₂O₃ and crystallization of amorphous silica in quartz and cristobalite were observed in the sample treated at 1100 °C.     

Microstructure and multiferroic properties of BaTiO3/CoFe2O4 films on Al2O3/Pt substrates fabricated by electrophoretic deposition

BaTiO₃/CoFe₂O₄ bilayer films on high temperature resistant Al₂O₃/Pt substrates were fabricated using the electrophoretic deposition (EPD) method. Powder synthesis, suspension preparation and kinetics of deposition were investigated in detail. Two different sintering temperatures were tested and the resultant microstructure and properties of ceramic films were investigated. The composite films sintered at a temperature of 1200 °C/2 h yielded optimal microstructures and properties. The obtained bilayer films had a dense structure with no phase diffusion or passive layer. Besides to ferroelectric and magnetic properties, magnetoelectric (ME) coupling properties were also confirmed by the magnetic anisotropy and magnetic field induced polarization investigation. The composite films showed a increased P_s from 16.2 to 16.85 μC/cm² with variations ΔP_s of 4% when the magnetic field was applied in parallel direction and a decreased P_s from 16.2 to 14.9 μC/cm² with variations ΔP_s of ?8% when a normal direction field was applied.     

Structural,morphological and magnetic parameters investigation of multiferroic (1-x)Bi2Fe4O9- xCoFe2O4 nanocomposite ceramics

(1-x)Bi₂Fe₄O₉- xCoFe₂O₄ (0.0≤ x ≤1.0) multiferroic nanocomposites were prepared by wet chemical procedures combining reverse chemical co-precipitation and Pechini-type sol–gel techniques followed by mechanical blending process. The XRD and SAED results showed that the diffraction patterns are perfectly indexed to the constituent phases present in composite samples. The crystallite sizes of the constituent phases were 35.4 and 39.4 nm for cobalt and bismuth ferrites, respectively. The characteristic peaks in FT-IR spectra confirmed formation and purity of all specimens. FESEM micrographs revealed the uniform phase distribution with the mean grain size of approximately 40 and 230 nm for CoFe₂O₄ and Bi₂Fe₄O₉, respectively. TEM micrograph indicated suitable distribution in the as-prepared composite sample. The VSM results revealed that saturation and remnant magnetization increase by increasing CFO content in composites. Based on the results obtained from M-H curves, magnetic properties of composites did not originate only from linear combination of parent phases. The recorded coercivity values of all nanocomposites, for example 1443 Oe for x = 0.4 were higher than those of each parent phase i.e. 708 Oe for CoFe₂O₄ and 149 Oe for Bi₂Fe₄O_9, showing a noticeable improvement in magnetic properties.     

MnFe2O4 bulk,nanoparticles and film: A comparative study of structural and magnetic properties

MnFe₂O₄ bulk sample was synthesized by conventional solid state reaction method, at 1350 °C. Nanoparticles with mean size of 〈D〉_TEM=10.4(±1.1) nm were prepared by thermal decomposition of metal nitrates, at 350 °C. And a film sample was prepared by pulsed laser deposition of bulk ferrite on MgO(100) at substrate temperature of 600 °C. Then a comparative study of the structural and magnetic properties of the samples has been carried out using different measurements. X-ray diffraction pattern of bulk and nanoparticles samples confirmed formation of spinel phase. The film sample showed an epitaxial growth on MgO in (400) direction. Saturation magnetization of nanoparticles at 300 K, M_S=33 emu/g, was comparable with film sample, M_S=38 emu/g, both being ∼2.5 times smaller than that of bulk sample (M_S=82 emu/g). The results showed the importance of surface effects in the film sample and nanoparticles. The obtained zero coercivity of bulk sample at 300 K and the low value of 8 Oe at 5 K is attributed to soft magnetic behavior of the MnFe₂O₄. On the other hand, nanoparticles showed superparamagnetic behavior at 300 K; and blocked state with a large coercivity of 730 Oe at 5 K. The film sample showed non-zero corecivity at both 5 and 300 K which reveals higher magnetic anisotropy of film compared to the bulk ferrite.     

Activated carbon/CoFe2O4 composites: Facile synthesis,magnetic performance and their potential application for the removal of malachite green from water

Activated carbon/CoFe₂O₄ composite (AC/CFO) was synthesized by a simple one-step refluxing route and was used as adsorbent for the removal of malachite green (MG) dye from water. The structure, morphology and magnetic properties of as-prepared composite were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). The results indicated that CoFe₂O₄ particles deposited on the surface of activated carbon in the composite were uniform with the particle size in the range of 14–20 nm. The composite adsorbents exhibited a clearly hysteretic behavior under applied magnetic field, which allowed their magnetic separation from water. Batch experiments were carried out to investigate adsorption isotherms and kinetics of MG onto the composite. The experimental data fitted well with the Langmuir model with a monolayer adsorption capacity of 89.29 mg g^?1. The adsorption kinetics was found to follow pseudo-second-order kinetic model. It was indicated that the as-prepared composite could be used as a promising and effective adsorbent for the removal of MG from water.     

Electrophoretic deposition of CoFe2O4 films from aqueous suspensions

CoFe₂O₄ nano-particles with average size of ～40 nm were synthesized via the chemical coprecipitation method. PAMANH₄ was used as dispersant to improve the stability of aqueous suspensions. Zeta potential and sediment volumes were tested to study the effects of pH and dispersant amounts on the stability of suspensions. The most stable suspension was obtained when using 0.6 wt.% PAMANH₄ as dispersant at pH = 10. Conductivity results showed that thoroughly dispersed suspensions were formed after being ultrasonic agitated for 30 min. CoFe₂O₄ films on Al₂O₃/Pt substrates fabricated via EPD sintered at 1250 °C exhibited preferentially oriented structure. The XRD analyses showed (2 2 0) and (5 1 1) were the preferential orientations. Anisotropy was also observed in magnetic hysteresis loops. Stronger ferromagnetic effect was observed in the in-plane orientation, with saturation magnetization of ～290 emu/cm³.     

Synthesis of magnetically recoverable ferrite (MFe2O4, M Co,Ni and Fe)-supported TiO2 photocatalysts for decolorization of methylene blue

Effects of ferrite materials as supports (CoFe₂O₄, NiFe₂O₄, and Fe₃O₄) on nano-TiO₂ were elucidated by their use in the oxidation of methylene blue. These photocatalysts, which were synthesized by co-precipitation, were characterized by XRD, SEM, EDS and VSM. The crystalline phase of TiO₂ onto magnetic MFe₂O₄ was formed by anatase and rutile. TiO₂/CoFe₂O₄ exhibited the strongest magnetic property of the prepared catalysts, and the photocatalytic efficiencies followed the order TiO₂/CoFe₂O₄ > TiO₂/NiFe₂O₄ > TiO₂/Fe₃O₄. MB decolorization was enhanced with the amount of TiO₂ on the photocatalyst, and was moderately affected by the extent of structural distortion of ferrite supports.     

Synthesis and characterization of magnetic polyHIPEs with humic acid surface modified magnetic iron oxide nanoparticles

Magnetic macroporous polymer monoliths have been prepared using styrene/divinylbenzene (S/DVB) high internal phase emulsions (HIPEs) as templates. Humic acid surface modified iron oxide magnetic nanoparticles (Fe₃O₄@HA) have been used to prepare magnetic emulsion templates. The effect of magnetic particle concentration has been investigated by changing the ratio of Fe₃O₄@HA nanoparticles in the continuous phase. Highly macroporous polymers with magnetic response were obtained by the removal of the internal phase after the curing of emulsions at 80 °C. Fe₃O₄@HA particles were characterized by XRD and FTIR. The porosity, pore morphology and magnetic properties of the macroporous polymers were characterized as a function of the Fe₃O₄@HA concentration by scanning electron microscopy (SEM), Brunauer–Emmet–Teller (BET) molecular adsorption method and vibrating sample magnetometry (VSM), respectively. BET and VSM measurements demonstrated that the specific surface area and the saturation magnetization of the polymer monoliths were changed according to the Fe₃O₄@HA concentration between 8.77–35.08 m² g^?1 and 0.63–11.79 emu g^?1, respectively. Resulting magnetic monoliths were tested on the adsorption of Hg(II) and atomic absorption spectroscopy (AAS) was used to calculate the adsorption capacities. The maximum adsorption capacity of the magnetic monoliths was calculated to be 20.44 mmol g^?1 at pH 4.