Fast microwave synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag magnetic nanoparticles using Fe<Superscript>2+</Superscript> as precursor

A simple and quick microwave method to prepare high performance magnetite nanoparticles (Fe₃O₄ NPs) directly from Fe has been developed. The as-prepared Fe₃O₄ NPs product was fully characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results show that the as-prepared Fe₃O₄ NPs are quite monodisperse with an average core size of 80 × 5 nm. The microwave synthesis technique can be easily modified to prepare Fe₃O₄/Ag NPs and these NPs possess good magnetic properties. The formation mechanisms of the NPs are also discussed. Our proposed synthesis procedure is quick and simple, and shows potential for large-scale production and applications for catalysis and biomedical/biological uses.     

Synthesis and microwave absorption properties of sandwich-type CNTs/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/RGO composite with Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> as a bridge

A novel sandwich-type CNTs/Fe₃O₄/RGO composite with Fe₃O₄ as a bridge was successfully prepared through a simple solvent-thermal and ultrasonic method. The structure and morphology of the composite have been characterized by Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. This new structure can effectively prevent the agglomeration of GO and the combination of CNTs/Fe₃O₄ and RGO shows a strong reflection loss (R_L) (?50 dB) at 8.7 GHz with absorber thickness of 2.5 mm. Moreover, compared with CNTs/Fe₃O₄/GO composite, it is found that the thermal treating process is beneficial to enhance the microwave absorption properties, which may be attributed to high conductivity of RGO. On this basis, the microwave absorbing mechanism is systematically discussed. All the data show that the CNTs/Fe₃O₄/RGO composite exhibits excellent microwave absorption properties with light density and is expected to have potential applications in microwave absorption.     

An efficientfficient,controllable and facile two-step synthesis strategy: Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@RGO composites with various Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles and their supercapacitance properties

An efficient,controllable,and facile two-step synthetic strategy to prepare graphene-based nanocomposites is proposed.A series of Fe3O4-decorated reduced graphene oxide (Fe3O4@RGO) nanocomposites incorporating Fe3O4 nanocrystals of various sizes were prepared by an ethanothermal method using graphene oxide (GO) and monodisperse Fe3O4 nanocrystals with diameters ranging from 4 to 10 nm.The morphologies and microstructures of the as-prepared composites were characterized by X-ray diffraction,Raman spectroscopy,nitrogen adsorption measurements,and transmission electron microscopy.The results show that GO can be reduced to graphene during the ethanothermal process,and that the Fe3O4 nanocrystals are well dispersed on the graphene sheets generated in the process.The analysis of the electrochemical properties of the Fe3O4@RGO materials shows that nanocomposites prepared with Fe3O4 nanocrystals of different sizes exhibit different electrochemical performances.Among all samples,Fe3O4@RGO prepared with Fe3O4 nanocrystals of 6 nm diameter possessed the highest specific capacitance of 481 F/g at 1 A/g,highlighting the excellent capability of this material.This work illustrates a promising route to develop graphene-based nanocomposite materials with a wide range of potential applications.     

Magnetic Fe<Subscript>2</Subscript>P nanowires and Fe<Subscript>2</Subscript>P@C core@shell nanocables

We report the synthesis of one-dimensional (1-D) magnetic Fe₂P nanowires and Fe₂P@C core@shell nanocables by the reactions of triphenylphosphine (PPh₃) with Fe powder (particles) and ferrocene (Fe(₅H₅)₂), respectively, in vacuum-sealed ampoules at 380–400 °C. The synthesis is based on chemical conversion of micrometer or nanometer sized Fe particles into Fe₂P via the extraction of phosphorus from liquid PPh₃ at elevated temperatures. In order to control product diameters, a convenient sudden-temperature-rise strategy is employed, by means of which diameter-uniform Fe₂P@C nanocables are prepared from the molecular precursor Fe(C₅H₅)₂. In contrast, this strategy gives no obvious control over the diameters of the Fe₂P nanowires obtained using elemental Fe as iron precursor. The formation of 1-D Fe₂P nanostructures is ascribed to the cooperative effects of the kinetically induced anisotropic growth and the intrinsically anisotropic nature of hexagonal Fe₂P crystals. The resulting Fe₂P nanowires and Fe₂P@C nanocables display interesting ferromagnetic-paramagnetic transition behaviors with blocking temperatures of 230 and 268 K, respectively, significantly higher than the ferromagnetic transition temperature of bulk Fe₂P (T _C = 217 K).      

Al-doped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles and Their Magnetic Properties

Al-doped Fe₃O₄ nanoparticles were synthesized for the first time via the Composite-Hydroxide-Mediated (CHM) method from Fe₃O₄ and Al₂O₃ without using any capping agent. The synthesis technique was one-step and cost effective. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersion spectroscopy (EDS). Samples with a tunable size of 500–1500 nm, 200–800 nm, and 100–700 nm could be obtained by adjusting the reaction time and temperature. Magnetic property of the as-synthesized Al-doped Fe₃O₄ nanoparticles was investigated. Magnetic hysteresis loops measured in the field range of −10 kOe<H<10 kOe, indicated the ferromagnetic behavior with coercivity (H _c) of 470 and 110 Oe and remanence magnetization (M _r) of 13 and 6.4 emu/g at the temperature of 5 and 300 K, respectively. The saturation intensity (M _s) was 46.1 emu/g at 5 K, while it was about 43.6 emu/g at 300 K.     

Local amorphization of atomic structure in Mg<Subscript>0.54</Subscript>Zn<Subscript>0.46</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrites

The structure of Mg_0.54Zn_0.46Fe₂O₄ ferrites has been studied using x-ray diffraction techniques. It is established that high-temperature annealing (T = 1280°C, τ = 0.5–8.0 h) leads to a change in the crystal structure of samples, which is accompanied by their local amorphization.     

Morphological control of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> particles via glycothermal process

Acicular magnetite (Fe₃O₄) powders were synthesized through new glycothermal dehydration by using crystalline α-FeOOH as precursor and glycols as solvent. When ethylene glycol was used as solvent, the phase was in-situ transformed from acicular α-FeOOH to α-Fe₂O₃ and finally to Fe₃O₄ at 270 °C for 6 h without morphological change. When water was added as a co-solvent in glycothermal reaction, Fe₃O₄ powders were synthesized through dissolution–recrystallization process at 230 °C for 3 h. The volume ratio of ethylene glycol to water (E/W) in the reaction has a strong effect on the morphology of the synthesized Fe₃O₄ particles. The particle shape of Fe₃O₄ particles changed from needle to sphere when the water content in E/W volume ratio increased from 0.5 to 1 mL in mixed glycothermal condition. When the water were added by more than 10 ml, the particle shape of Fe₃O₄ changed from sphere to octahedron truncated with the {100} faces and finally distinct octahedron with only {111} faces. Also, it is demonstrated that the size of Fe₃O₄ particles can be controlled from 1–2 μm to 100–200 nm by varying the reaction conditions such as the volume ratio of water to ethylene glycol and additive in glycothermal reaction.     

Hydrogen-induced diffusion phase transformations in Nd<Subscript>2</Subscript>Fe<Subscript>14</Subscript>B and Sm<Subscript>2</Subscript>Fe<Subscript>17</Subscript> magnetically hard alloys

The Nd₂Fe₁₄B and Sm₂Fe₁₇ magnetically hard alloys become thermodynamically unstable under the action of hydrogen and suffer hydrogen-induced direct and inverse phase transformations at elevated temperatures. The kinetics of these transformations is investigated. It is shown that they are diffusion-controlled and develop according to the mechanism of nucleation and growth. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 5, pp. 105–111, September–October, 2008.     

Synthesis and applications of fluorescent-magnetic-bifunctional dansylated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanoparticles

Bifunctional magnetic-luminescent dansylated Fe₃O₄@SiO₂ (Fe₃O₄@SiO₂-DNS) nanoparticles were fabricated by the nucleophilic substitution of dansyl chloride with primary amines of aminosilane-modified Fe₃O₄@SiO₂ core–shell nanostructures. The morphology and properties of the resultant Fe₃O₄@SiO₂-DNS nanoparticles were investigated by transmission electron microscopy, FT–IR spectra, UV–vis spectra, photoluminescence spectra, and vibrating sample magnetometry. The Fe₃O₄@SiO₂-DNS nanocomposites exhibit superparamagnetic behavior at room temperature, and can emit strong green light under the excitation of UV light. They show very low cytotoxicity against HeLa cells and negligible hemolysis activity. The T ₂ relaxivity of Fe₃O₄@SiO₂-DNS in water was determined to be 114.6 Fe mM⁻¹ s⁻¹. Magnetic resonance (MR) imaging analysis coupled with confocal microscopy shows that Fe₃O₄@SiO₂-DNS can be uptaken by the cancer cells effectively. All these positive attributes make Fe₃O₄@SiO₂-DNS a promising candidate for both MR and fluorescent imaging applications.     

Electrical properties of Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Mn<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> + BaTiO<Subscript>3</Subscript> ME composites

Polycrystalline samples of mixed composites of Ni_0.93Co_0.02Mn_0.05Fe₂O₄ + BaTiO₃ were prepared by conventional double sintering ceramic method. The phase analysis was carried out by using X-ray diffraction technique. Variation of dc resistivity and thermo emf was studied as a function of temperature. AC conductivity (σ_ac) was investigated in the frequency range 100 Hz–1 MHz. The loss tangent (tan δ) measurements conclude that the conduction mechanism in these samples is due to small polaron hopping. The magnetoelectric conversion factor, i.e. dc(ME) _H was studied as a function of intensity of magnetic field and the maximum value 407 μV/cm/Oe was observed at a field of 0.8 kOe in a composite with 85% BaTiO₃ and 15% Ni_0.93Co_0.02Mn_0.05Fe₂O₄ phase.     

Study of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nano-Magnetic Ferrofluid by Atomic Force Microscope

The magnetic ferrofluid is a special intelligent material and its many properties can be controlled by external magnetic field. This paper introduces the preparation, performance and applications of Fe₃O₄ nano-ferrofluid, principally observed by the microstructure characterization by Atomic Force Microscopy (AFM), and we measured the particle size and morphology of nano-ferrofluid. The magnetic property was analyzed from the microstructure characterization, and the analysis results show that the size of the Fe₃O₄ nano-particle is about 5 nm; the magnetic property is closely related to the chain microstructure and is influenced by the nano-particle distribution in the Fe₃O₄ magnetic ferrofluid.     

Room-Temperature Photomagnetic Effect of Fe<Subscript>3</Subscript>Ga<Subscript>4</Subscript> Grown on GaAs Substrates

Ga–As–Fe composite films prepared by molecular beam epitaxy at 600°C on GaAs(100) substrates with the stacking sequence of [100-nm GaAs/50-nm Fe₃Ga_{2− x} As _x /100-nm GaAs] exhibit the distinct photo-enhanced magnetization at room temperature. Transmission electron microscopy reveals the formation of metamagnetic Fe₃Ga₄ grains on the sample surface. Illumination power dependence of the enhanced magnetization has been carefully compared with the antiferromagnetic-type magnetization–temperature (M–T) curve (Neel temperature of T _N = 340–390 K), from which we have discussed the existence of photon-mode photo-enhanced magnetization of some sort in addition with the enhancement due to the light-induced heating.     

Solvothermal synthesis and characterization of size-controlled monodisperse Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles

Monodisperse Fe₃O₄ nanoparticles with narrow size distribution could be successfully synthesized in large quantities by a facile solvothermal synthetic method in the presence of oleic acid and oleylamine. Well-defined assembly of uniform nanoparticles with average sizes of 8 nm can be obtained without a further size-selection process. The sizes of final products could be readily tuned from 5 to 12 nm by adjusting the experimental parameters such as reaction time, temperature, and surfactants. The phase structures, morphologies, and magnetic properties of the as-prepared products were investigated in detail by X-ray diffraction, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, and magnetometry with a superconducting quantum interference device. The magnetic study reveals that the as-synthesized nanoparticles are ferromagnetic at 2 K while they are superparamagnetic at 300 K.     

Dual-mode protein detection based on Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-Au hybrid nanoparticles

A facile method of synthesizing Fe₃O₄-Au hybrid nanoparticles is reported utilizing the multifunctional nature of polyethyleneimine (PEI). An abundance of 5 nm gold nanoparticles were attached to 50 nm Fe₃O₄ nanoparticles via the covalent binding between the -NH₂ groups of the PEI and Au nanoparticles, as well as the electrostatic interaction between the negatively charged citrate-coated Au nanoparticles and the positively charged PEI-coated Fe₃O₄ nanoparticles. The as-prepared Fe₃O₄-Au hybrid nanoparticles, which combine the merits of magnetic materials and gold, were successfully employed for the first time in the dual-mode detection of carcinoembryonic antigen (CEA) via electrochemical and surface-enhanced Raman scattering (SERS) methods. Both methods make clever use of Fe₃O₄-Au nanoparticles and can accurately verify the presence of antigens. In particular, the electrochemical immunosensor detection displays a wide linear range (0.01–10 ng/mL) of response with a low detection limit (10 pg/mL), while the SERS method responds to even lower antigen concentrations with a wider detection range. The Fe₃O₄-Au hybrid nanoparticles therefore exhibit great potential for biomedical applications.      

Magnetically separable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@TiO<Subscript>2</Subscript> nanospheres: preparation and photocatalytic activity

A facile and efficient approach for the fabrication of Fe₃O₄@TiO₂ nanospheres with a good core–shell structure has been demonstrated. Products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results showed that Fe₃O₄@TiO₂ nanocomposites exhibited high degree of crystallinity, excellent magnetic properties at room temperature. Furthermore, the as-prepared Fe₃O₄@TiO₂ nanocomposites exhibited good photocatalytic activity toward the degradation of Rhodamine B (RhB) solution. Additionally, the recycling experiment of Fe₃O₄@TiO₂ nanocomposites had been done, demonstrating that Fe₃O₄@TiO₂ nanocomposites have high efficiency and stability.     

Electromagnetic wave absorption in reduced graphene oxide functionalized with Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Fe nanorings

We report the preparation of nanocomposites of reduced graphene oxide with embedded Fe₃O₄/Fe nanorings (FeNR@rGO) by chemical hydrothermal growth. We illustrate the use of these nanocomposites as novel electromagnetic wave absorbing materials. The electromagnetic wave absorption properties of the nanocomposites with different compositions were investigated. The preparation procedure and nanocomposite composition were optimized to achieve the best electromagnetic wave absorption properties. Nanocomposites with a GO:α-Fe₂O₃ mass ratio of 1:1 prepared by annealing in H₂/Ar for 3 h exhibited the best properties. This nanocomposite sample (thickness = 4.0 mm) showed a minimum reflectivity of–23.09 dB at 9.16 GHz. The band range was 7.4–11.3 GHz when the reflectivity was less than–10 dB and the spectrum width was up to 3.9 GHz. These figures of merit are typically of the same order of magnitude when compared to the values shown by traditional ferric oxide materials. However, FeNR@rGO can be readily applied as a microwave absorbing material because the production method we propose is highly compatible with mass production standards.

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Corrosion resistance of amorphous Fe<Subscript>82</Subscript>P<Subscript>16</Subscript>Si<Subscript>2</Subscript> in 0.1 M Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>

A soft-magnetic amorphous Fe-P-Si alloy prepared using ferrophosphorus waste was tested for corrosion in 0.1 M Na₂SO₄. In a nonequilibrium state, the Fe₈₂P₁₆Si₂ alloy interacts with the medium, but annealing and relaxation reduce the interaction, without influencing the magnetic properties of the alloy. The corrosion resistance of the alloy is comparable to that of Finemet (Fe-Si-B-Nb-Cu) materials.     

Preparation of TiO<Subscript>2</Subscript>/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/CF composites for enhanced microwave absorbing performance

To meet the demand of electromagnetic absorption, cheap and easily available microwave absorbents are urgently required. As an important functional material, carbon fibers (CFs) have been widely reported, however, too high conductivity easily leads to the impedance mismatch, which is not favorable to the microwave absorbing performance (MAP). To address this challenge, in this study, novel TiO₂/Fe₃O₄/CF composites with tunable magnetic were synthesized by hydrothermal method and characterized by SEM, XRD, XPS and VSM. As absorbents, the minimum reflection loss (R_L) value is ??41.52 dB at a thickness of 2.1 mm, and the corresponding bandwidth with effective attenuation (R_L?<???10 dB) is up to 5.65 GHz (4.54–10.19 GHz). More importantly, the plausible mechanisms for the enhanced MAP are explored.     

Magnetically active Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods loaded with tissue plasminogen activator for enhanced thrombolysis

Systemic thrombolysis with intravenous tissue plasminogen activator (tPA) remains the only proven treatment that is effective in improving the clinical outcome of patients with acute ischemic stroke. However, thrombolytic therapy has some major limitations such as hemorrhage, neurotoxicity, and the short time window for the treatment. In this study, we designed iron oxide (Fe₃O₄) nanorods loaded with 6% tPA, which could be released within ~30 min. The Fe₃O₄ nanorods could be targeted to blood clots under magnetic guidance. In addition, the release of tPA could be significantly increased using an external rotating magnetic field, which subsequently resulted in a great improvement in the thrombolytic efficiency. Systematic and quantitative studies revealed the fundamental physical processes involved in the enhanced thrombolysis, while the in vitro thrombolysis assay showed that the proposed strategy could improve thrombolysis and recanalization rates and reduce the risk of tPA-mediated hemorrhage in vivo. Such a strategy will be very useful for the treatment of ischemic stroke and other deadly thrombotic diseases such as myocardial infarction and pulmonary embolism in clinical settings.

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Dielectric and ferromagnetic properties of BaTiO<Subscript>3</Subscript>/Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Cu<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> composites

xBaTiO₃ + (1 − x)Ni_0.93Co_0.02Cu_0.05Fe₂O₄ (x = 0.5, 0.6, 0.7, 0.8) composites with ferroelectric–ferromagnetic characteristics were synthesized by the ceramic sintering technique. The presence of constituent phases in the composites was confirmed by X-ray diffraction studies. The average grain size was calculated by using a scanning electron micrograph. The dielectric characteristics were studied in the 100 kHz to 15 MHz. The dielectric constant changed higher with ferroelectric content increasing; and it was constant in this frequency range. The relation of dielectric constant with temperature was researched at 1, 10, 100 kHz. The Curie temperature would be higher with frequency increasing. The hysteresis behavior was studied to understand the magnetic properties such as saturation magnetization (M _s). The composites were a typical soft magnetic character with low coercive force. Both the ferroelectric and ferromagnetic phases preserve their basic properties in the bulk composite, thus these composites are good candidates as magnetoelectric materials.