Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocrystal anode materials with improved cyclic stability for lithium ion batteries

The cyclic stability of Cr₂O₃ is very poor due to the large volume change during lithiation/delithiation. In this study, we have found that Cr₂O₃ nanocrystals synthesized by using a simple hydrothermal method can improve its cyclic stability. Sample calcined at 430 °C has uniform size, compact structure and high crystallization degree. These Cr₂O₃ nanocrystals exhibit a stable cyclic performance of 185 mAh g^?1 after 100 cycles at 100 mA g^?1. It is useful in real life, such as providing power consumption for minitype device, etc.     

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.     

Fabrication of Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite nanofibers by electrospinning

PVA(Polyvinyl alcohol)/chromium nitrate/aluminum nitrate composite nanofibers were prepared by using sol–gel processing and electrospinning technique. By high temperature calcinating the above precursor fibers, Cr₂O₃/Al₂O₃ composite nanofibers were successfully obtained. The fibers were characterized by XRD, IR, and SEM, respectively. The results showed that the crystalline phase and the morphology of the fibers depended on the calcination temperatures.     

Synthesis of well-defined Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods/N-doped graphene for lithium-ion batteries

The geometric size and distribution of magnetic nanoparticles are critical to the morphology of graphene (GN) nanocomposites, and thus they can affect the capacity and cycling performance when these composites are used as anode materials in lithium-ion batteries (LiBs). In this work, Fe₃O₄ nanorods were deposited onto fully extended nitrogen-doped GN sheets from a binary precursor in two steps, a hydrothermal process and an annealing process. This route effectively tuned the Fe₃O₄ nanorod size distribution and prevented their aggregation. The transformation of the binary precursor was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). XPS analysis indicated the presence of N-doped GN sheets, and that the magnetic nanocrystals were anchored and uniformly distributed on the surface of the flattened N-doped GN sheets. As a high performance anode material, the structure was beneficial for electron transport and exchange, resulting in a large reversible capacity of 929 mA·h·g^–1, high-rate capability, improved cycling stability, and higher electrical conductivity. Not only does the result provide a strategy for extending GN composites for use as LiB anode materials, but it also offers a route for the preparation of other oxide nanorods from binary precursors.

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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.     

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.     

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.     

Novel porous starfish-like Co<Subscript>3</Subscript>O<Subscript>4</Subscript>@nitrogen-doped carbon as an advanced anode for lithium-ion batteries

A Co-based metal-organic framework (Co-MOF) with a unique three-dimensional starfish-like nanostructure was successfully synthesized using a simple ultrasonic method.After subsequent carbonization and oxidation,a nanocomposite of nitrogen-doped carbon with a Co3O4 coating (Co3O4@N-C) with a porous starfish-like nanostructure was obtained.The final hybrid exhibited excellent lithium storage performance when evaluated as an anode material in a lithiumion battery.A remarkable and stable discharge capacity of 795 mAh·g-1 was maintained at 0.5 A·g-1 after 300 cycles.Excellent rate capability was also obtained.In addition,a full Co3O4@N-C/LiFePO4 battery displayed stable capacity retention of 95％ after 100 cycles.This excellent lithium storage performance is attributed to the unique porous starfish-like structure,which effectively buffers the volume expansion that occurs during Li+ insertion/deinsertion.Meanwhile,the nitrogendoped carbon coating enhances the electrical conductivity and provides a buffer layer to accommodate the volume change and accelerate the formation of a stable solid electrolyte interface layer.     

Electrical properties of some Y<Subscript>2</Subscript>O<Subscript>3</Subscript> and/or Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-containing lithium silicate glasses and glass-ceramics

The ac electrical properties of some lithium silicate glasses and glass-ceramics containing varying proportions of Y₂O₃ and/or Fe₂O₃ were measured to investigate their electronic hopping mechanism. There is a clear variation of these properties with composition. The obtained results were related to the concentration and role of Y₂O₃ and/or Fe₂O₃ in the lithium silicate glass structure. In crystalline solids the electrical properties data obtained were correlated to the type and content of the mineral phases formed as indicated by X-ray diffraction analysis (XRD). The conductivity, dielectric constant and dielectric loss of the studied glasses were studied using the frequency response in the interval 30 Hz–100 KHz and the effect of compositional changes on the measured properties was investigated. The measurements revealed that the electrical responses of the samples were different and complex. The addition of Y₂O₃ generally, decreased the ac conductivity, dielectric constant and dielectric losses of the lithium silicate glasses. The addition of Fe₂O₃ in Y₂O₃-containing glasses increases the conductivity, while, the dielectric constant and dielectric losses were found to be decreased. However, the addition of Fe₂O₃ instead of Y₂O₃ led to decrease the ac conductivity and increased their dielectric constant and dielectric losses. The obtained data were argued to the internal structure of the lithium silicate glass and the nature or role-played by weakness or rigidity of the structure of the sample. Lithium disilicate-Li₂Si₂O₅, lithium metasilicate-Li₂SiO₃, two forms of yttrium silicate Y₂Si₂O₇ & Y₂SiO₅, iron yttrium oxide-YFeO₃, lithium iron silicate-LiFeSi₂O₆ and α-quartz phases were mostly developed in the crystallized glasses. The conductivity of the crystalline materials was found to be relatively lower than those of the glass. At low frequency, as the Y₂O₃ content increased the ac conductivity, dielectric constant and dielectric loss data of the glass-ceramics decreased. However, the addition of Fe₂O₃ to the Y₂O₃ containing glass-ceramic led to increase the conductivity. The addition of high content of Fe₂O₃ instead of Y₂O₃ in the glass ceramic led to increase the ac conductivity.     

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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Structural changes induced by Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> addition in strontium-borate glass matrix

Glasses of the xFe₂O₃·(100−x)[B₂O₃·SrO] system, with 0 ≤ x ≤ 30 mol% were studied by X-ray diffraction, density, optical microscopy and FT-IR spectroscopy measurements. The X-ray patterns for the prepared system show that vitreous phase is present only in the sample with x < 40 mol%. For x ≥ 40 mol% in the studied samples is evidenced crystalline phase of Fe₂O₃. SEM measurements for the sample with x = 40 mol% shows that there are formed Fe₂O₃ microcrystallites with 10–20 μm dimension. FT-IR spectroscopy measurements shown that BO₃ and BO₄ are the main structural units of the glass system and the iron ions are located in the glass network.     

Electrical conductivity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Tm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> solid solutions

New solid solutions, Bi_2?x?y Tm _x Nb _y O_3+δ, with tetragonal and cubic structures have been synthesized in the Bi₂O₃-Tm₂O₃-Nb₂O₅ system, and their electrical conductivity has been measured at temperatures from 670 to 1020 K. The 1020-K conductivity of the tetragonal solid solution Bi_1.8Tm_0.15Nb_0.05O_3+δ is comparable to that of Bi_1.75Tm_0.25O₃, the best conductor in the Bi₂O₃-Tm₂O₃ system.     

Effect of Eu<Subscript>2</Subscript>O<Subscript>3</Subscript> doping on the crystallization behavior of BaO-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

We gave studied the crystallization behavior of 30BaO · 25Bi₂O₃ · 45B₂O₃ glasses doped with Eu₂O₃ to different levels. At a Eu₂O₃ content of 7 mol % or higher, the glasses undergo volume crystallization. The only precipitating phase is a solid solution between europium and bismuth oxides. With increasing europium concentration in the glass, the structure of the crystallites changes from cubic to rhombohedral. We have investigated the morphology, physicochemical properties, and luminescence spectra of the glasses and glass-ceramics.     

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.     

Preparation of magnetic composites through SrO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass crystallization

Glasses with nominal compositions 11SrO · 5.5Fe₂O₃ · 4.5Al₂O₃ · 4B₂O₃ (1) and 15SrO · 5.5Fe₂O₃ · 4.5Al₂O₃ · 4B₂O₃ (2) were prepared by rapidly quenching oxide melts between counterrotating steel rollers. The glasses were then heat-treated in the range 650–950°C to produce glass-ceramic samples. The samples were characterized by X-ray diffraction, electron microscopy, and magnetic measurements. The phase composition of the glass-ceramics was determined, and their microstructure and magnetic properties were studied. The annealing temperature was shown to have a strong effect on the coercivity of the materials, which reaches 650 and 570 kA/m for compositions 1 and 2, respectively.     

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.     

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.     

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.     

Biocompatibility of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanoparticles for the Activation of Glia Cell Migration

We study the biocompatibility, the magnetic clustering, and the possible transfection effect of iron particles on glia cells. Results indicate that iron particles can coexist quite well with glia cells, and the inductive migration of the cell through the vanishing of the Fe compound particles around the cell is examined. Transfection experiments also prove the feasibility of using iron particles with glia cells.