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.     

Electromagnetic synergetic actuators based on polypyrrole/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> hybrid nanotube arrays

Conducting polymer actuators that can undergo complex and coordinated motions are generally obtained by using complex microfabrication methods to pattern several conducting polymer components. Herein, we describe a facile approach for fabricating electromagnetic synergetic actuators based on polypyrrole/Fe₃O₄ hybrid nanotube arrays. The actuator can perform biomimetic movements like arm-hand coordination. In this case, a magnetic field is used for primary actuation like an arm, i.e., large-scale angular movement, and an electric potential is used for secondary adjustment like a hand, i.e., small-scale angular movement.     

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.     

Preparation and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag composite magnetic nanoparticles

Fe₃O₄ magnetic nanoparticles being used as seeding materials, Ag⁺ ions on the Fe₃O₄ magnetic nanoparticles reduced to the metal form by tartaric acid using heated treatment. Thus, Fe₃O₄/Ag composite core-shell magnetic nanoparticles were synthesized. The products were characterized by transmission electron microscope (TEM) and x-ray diffraction (XRD). Both TEM and XRD results showed that the Ag nanoparticles were well distributed on the surface of Fe₃O₄ magnetic nanoparticles. The size for Fe₃O₄/Ag composite magnetic nanoparticles which were spherical shape was ≃40 nm. Furthermore, the magnetic properties of samples were characterized on a vibrating sample magnetometer. Under optimal conditions, Fe₃O₄/Ag composite nanoparticles showed higher magnetism than pure Fe₃O₄ nanoparticles. The text was submitted by the authors in English.     

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.     

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.     

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.     

Magnetic properties of Nd-Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> nanoparticles

Nb³⁺-substituted garnet nanoparticles Y_3−xNd_xFe₅O₁₂ (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were fabricated by a sol-gel method and their crystalline structures and magnetic properties were investigated by using X-ray diffraction (XRD), thermal analysis (DTA/TG), and vibrating sample magnetometer (VSM). The XRD patterns of Y_3−xNd_xFe₅O₁₂ have only peaks of the garnet structure and the sizes of particles range from 34 to 70 nm. From the results of VSM, it is shown that when the Nd concentration x ( 1.0, the saturation magnetization of Y_3−xNd_xFe₅O₁₂ increases as the Nd concentration (x) is increased, and gets its maximum at x = 1.0, but when x ( 1.0, the saturation magnetization decreases with increasing the Nd concentration (x), this may be due to the distortion of the microstructure of Y_3−xNd_xFe₅O₁₂, which leads to the decrease of the effective moment formed by Fe³⁺. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the particle size is increased.     

Removal and reuse of Ag nanoparticles by magnetic polyaniline/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanofibers

For the treatment of wastewater containing Ag nanoparticles (NPs), PANI/Fe₃O₄ nanofibers were firstly prepared by a novel self-assemble. And then, the efficiency for the removal of Ag NPs from wastewater was investigated. The magnetic performance of PANI/Fe₃O₄ nanofibers could be optimized by adjusting the pH of the self-assemblied system. Under pH of 3, the as-prepared nanofibers exhibited the highest magnetism and also displayed good efficiency (>?12 mg g^?1) for the removal of Ag NPs. Importantly, the resulted product (PANI/Fe₃O₄/Ag composite) could act as a catalysis for cleaning durable pollutant, 4-nitrophenol. After 10 cycles, only slight decrease in rate constant was found, indicating excellent reusability. Those approaches provide a new way to merge the recovery of Ag NPs as pollutants and reuse of recovered Ag NPs as recyclable material for environmental remediation.     

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.     

Study on the endocytosis and the internalization mechanism of aminosilane-coated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles in vitro

In this study, the endocytosis and the internalization mechanism of aminosilane-coated Fe₃O₄ nanoparticles into human lung cancer cell line SPC-A1 was studied compared with human lung cell line WI-38 in vitro. The particle endocytosis behavior was studied by using Transmission Electron Microscope (TEM) and Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). It was found that aminosilane-coated Fe₃O₄ nanoparticles could be greatly taken up by SPC-A1 human cancer cells (202 pg iron/cell) but not by WI-38 human lung cells (13 pg iron/cell). The particles could be retained in SPC-A1 cells over a number of generations in vitro. Different endocytosis was observed by TEM after SPC-A1 cells were treated with different temperature or with/without Cytochalasin B (Inhibitor of phagocytosis) at 37 °C. No nanoparticles were taken up by SPC-A1 after the endocytosis inhibited in low temperature. Restoring the endocytosis activity at 37 °C, the process of nanoparticles from coated pit to endosomes and lysosomes was observed by TEM. Endocytosis activity was effectively inhibited by the presence of Cytochalasin B at 37 °C, while a lot of nanoparticles were uptaken to the cytoplasm of SPC-A1 cells in the control group. Our results suggest that the process of endocytosis of aminosilane-coated Fe₃O₄ nanoparticles can efficiently takes place in lung cancer cells and nanoparticles can be kept in cancer cells for generations. Phagocytosis may be involved in the internalization process of aminosilane-coated Fe₃O₄ nanoparticles.     

Synthesis of water-based Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic nanoparticles,stabilized by oleic acid and mannitol

Water-based Fe₃O₄ magnetic nanoparticles were synthesized and studied, stabilized by oleic acid and mannitol. Nanoparticles were prepared by dropwise introduction of aqueous salt solution of iron (II) and (III) into aqueous ammonia. The double salts of iron were taken as a source of iron ions: ferric alum and Mohr’s salt.     

A wrinkle to sub-100 nm yolk/shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanoparticles

Yolk/shell nanoparticles (NPs), which integrate functional cores (likes Fe₃O₄) and an inert SiO₂ shell, are very important for applications in fields such as biomedicine and catalysis. An acidic medium is an excellent etchant to achieve hollow SiO₂ but harmful to most functional cores. Reported here is a method for preparing sub-100 nm yolk/shell Fe₃O₄@SiO₂ NPs by a mild acidic etching strategy. Our results demonstrate that establishment of a dissolution–diffusion equilibrium of silica is essential for achieving yolk/shell Fe₃O₄@SiO₂ NPs. A uniform increase in the silica compactness from the inside to the outside and an appropriate pH value of the etchant are the main factors controlling the thickness and cavity of the SiO₂ shell. Under our “standard etching code”, the acid-sensitive Fe₃O₄ core can be perfectly preserved and the SiO₂ shell can be selectively etched away. The mechanism of regulation of SiO₂ etching and acidic etching was investigated.

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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.     

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.     

Sandwich-structured nanocomposites of N-doped graphene and nearly monodisperse Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles as high-performance Li-ion battery anodes

Iron oxides have attracted considerable interest as abundant materials for high-capacity Li-ion battery anodes. However, their fast capacity fading owing to poorly controlled reversibility of the conversion reactions greatly hinders their application. Here, a sandwich-structured nanocomposite of N-doped graphene and nearly monodisperse Fe₃O₄ nanoparticles were developed as high-performance Li-ion battery anode. N-doped graphene serves as a conducting framework for the self-assembled structure and controls Fe₃O₄ nucleation through the interaction of N dopants, surfactant molecules, and iron precursors. Fe₃O₄ nanoparticles were well dispersed with a uniform diameter of ~15 nm. The unique sandwich structure enables good electron conductivity and Li-ion accessibility and accommodates a large volume change. Hence, it delivers good cycling reversibility and rate performance with a capacity of ~1,227 mA·h·g^–1 and 96.8% capacity retention over 1,000 cycles at a current density of 3 A·g^–1. Our work provides an ideal structure design for conversion anodes or other electrode materials requiring a large volume change.

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Characterization and electrical properties of semiconducting Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> glasses

Semiconducting glasses of the Fe₂O₃-Bi₂O₃-K₂B₄O₇ system were prepared by the press-quenching method and their dc conductivity in the temperature range 223–393 K was measured. The glass transition temperature values (T_g) of the present glasses were larger than those of tellurite glasses. This indicates a higher thermal stability of the glass in the present system. The density for these glasses was consistent with the ionic size, atomic weight and amount of different elements in the glasses. Mössbauer results revealed that the relative fraction of Fe increases with increasing Fe₂O₃ content. Electrical conductivity showed a similar composition dependency as the fraction of Fe. The glasses had conductivities ranging from 10 to 10 Scm at temperatures from 223 to 393 K. Electrical conduction of the glasses was confirmed to be due to non-adiabatic small polaron hopping and the conduction was primarily determined by hopping carrier mobility.     

Plasma-chemical Synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles for Doping of High-Temperature Superconductors

Ferrite nanoparticles (Fe₃O₄) have been produced by the direct low-pressure plasma-chemical synthesis. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), vibration magnetometry (VSM), and Mössbauer spectroscopy (NGR) were used for measurements, showing that the produced nanoparticles have an average size of 9.4 nm, a crystalline phase of magnetite, possess a property of superparamagnetism at room temperature, and have a blocking temperature of 89 K. The peculiarities of nanoparticle behavior in the magnetic field, related to a large specific surface area, are discussed.     

Enhancement of the optical and mechanical properties of chitosan using Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

In this work, the optical and mechanical properties of Fe₂O₃ nanoparticles (NPs)/chitosan nanocomposite films have been investigated. Nanocomposite films of different weight ratios of Fe₂O₃ NPs/chitosan (0, 1, 5, 10, 20 and 30 wt%) were fabricated using casting technique. The optical properties of colloidal Fe₂O₃ NPs and Fe₂O₃ NPs/chitosan nanocomposite films were recorded using UV–visible spectrophotometer. As the ratio of Fe₂O₃ NPs to chitosan increases from 0 to 30%, the energy band gap of Fe₂O₃ NPs/chitosan films decreases from 3.16 to 2.11 eV. This decrease is due to quantum confinement effect. The mechanical properties of the nanocomposite films as a function of sweeping temperature were measured using a dynamic mechanical analyzer. An enhancement in storage modulus, stiffness and glass transition temperature (T_g) has been observed as the ratio of Fe₂O₃ NPs/chitosan increases. T_g of Fe₂O₃ NPs/chitosan nanocomposite film shifts towards higher temperature side with respect to pure chitosan film from 152.1 to 166.3?°C as the ratio of Fe₂O₃ NPs/chitosan increases from 0 to 30 wt%. The increase in T_g is mainly attributed to the decrease in free volumes and vacancies in the nanocomposite films as the weight ratio of Fe₂O₃ NPs/chitosan increases.