Streptomycin-modified Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–Au@Ag core–satellite magnetic nanoparticles as an effective antibacterial agent

The fabrication of ideal Ag-modified magnetic nanoparticles (MNPs) as a recyclable antibacterial agent that possesses good dispersibility, strong magnetic responsiveness, and high bactericidal activity is still a challenge. In this study, we described a simple polyethyleneimine (PEI)-assisted connection method for fabricating high-performance Au@Ag-loaded MNPs (Fe₃O₄–Au@Ag). The Fe₃O₄ cores are first modified with uniform PEI shell (2 nm) through self-assembly under sonication. And then, the negatively charged Au@Ag NPs with a uniform size of 5 nm are adsorbed on the surface of the Fe₃O₄ cores through electrostatic interaction. The Au@Ag-loaded MNPs were obtained within 30 min, and they were highly uniform in size and shape with good dispersibility and strong magnetic responsivity. With the aid of the magnetic core, the residual nanoparticles can be recycled from solution through an external magnetic field. These dense Au@Ag NPs acted as antibacterial satellites in highly active areas for Ag ion releasing and bacteria contacting. The Fe₃O₄–Au@AgMNPs exhibited good antibacterial activity against both Gram-negative and Gram-positive bacteria. Moreover, the antibacterial activity of Fe₃O₄–Au@AgMNPs was significantly improved by streptomycin antibiotic modification. Enhancement of the bactericidal efficiency of Fe₃O₄–Au@Ag-streptomycin revealed the presence of a synergistic effect between the MNPs and the introduced antibiotic.     

Extending LaMer's mechanism using open system for increasing forced and controlled growth of Au nano particles: Desired decreasing Fe3O4 nano particles size during simultaneous synthesis in optimized conditions

The most effective parameters were found to obtain Au/Fe₃O₄ nano particles (NPs)-oleylamine composite. Having Au NPs with the controlled maximum mean size under the forced conditions was the main aim of this study. We used the continuous flow rates of oleylamine 75% to produce Au NPs under an open system by extended LaMer mechanisms. This process decreased the mean size of Fe₃O₄ NPs synthesized simultaneously, by classic LaMer mechanism. The Fe₃O₄ NPs production was carried out without continuous adding of any iron reactant, viz. as a closed system. In the absence of gold ions, the mean size of the synthesized Fe₃O₄ NPs using 2.5 ml/min oleylamine was about 35.0 nm at 2.0 ± 0.5 °C after 120 min. This mean size was decreased to 27.2, 21.4, 16.8 and 8.7 nm, when Au NPs were simultaneous prepared using 0.5, 0.75, 1.5 and 2.5 ml/min of oleylamine, respectively, at the same conditions. Surface Plasmon Resonance (SPR) adsorption was used to evaluate Au NPs production at first 30 min, while Small Angle X-ray Scattering (SAXS) method was used to monitor the reaction progression for near-real time analysis of increasing the growth of Au NPs up to 280 min, at the optimum conditions. Changing the properties of Fe₃O₄ NPs during processes was determined by studying Magnetization, Potentiometric titration, Inductive heating and Zeta potential.     

Electrospun Fe3O4/PVP//Tb(BA)3phen/PVP magnetic–photoluminescent bifunctional bistrand aligned composite nanofibers bundles

Fe₃O₄/PVP//Tb(BA)₃phen/PVP magnetic–photoluminescent bifunctional bistrand aligned composite nanofibers bundles based on Fe₃O₄ nanoparticles (NPs) and terbium complex Tb(BA)₃phen (BA = benzoic acid) were fabricated by employing a parallel axial electrospinning setup and were characterized by X-ray diffraction, field-emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscopy, fluorescence spectroscopy, and vibrating sample magnetometer. It is found that Fe₃O₄ NPs were only dispersed into one strand of the bistrand aligned composite nanofibers bundles, but no nanoparticles in the other strand. And the average diameter of the individual strand fiber was 200 ± 25 nm. The bistrand aligned composite nanofibers bundles exhibit strong green emissions under the excitation of 275 nm ultraviolet light, and the ⁵ D ₄ → ⁷ F ₅ hypersensitive transition at 545 nm was the predominant emission peak of Tb³⁺ ions. The newly obtained bifunctional nanofibers bundles exhibit excellent magnetism and high fluorescence intensity and are expected to apply in biology cell separation, magnetic resonance imaging, drug deliver, and fluorescence immunoassays/imaging.     

Study of Structural and Magnetic Properties of Superparamagnetic Fe3O4–ZnO Core–Shell Nanoparticles

In this work, Fe₃O₄–ZnO core–shell nanoparticles have been successfully synthesized using a simple two-step co-precipitation method. In this regard, Fe₃O₄ (magnetite) and ZnO (zincite) nanoparticles (NPs) were synthesized separately. Then, the surface of the Fe₃O₄ NPs was modified with trisodium citrate in order to improve the attachment of ZnO NPs to the surface of Fe₃O₄ NPs. Afterwards, the modified magnetite NPs were coated with ZnO NPs. Moreover, the influence of the core to shell molar ratio on the structural and magnetic properties of the core–shell NPs has been investigated. The prepared nanoparticles have been characterized utilizing transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and vibrating sample magnetometer (VSM). The results of XRD indicate that Fe₃O₄ NPs with inverse spinel phase were formed. The results of VSM imply that the Fe₃O₄–ZnO core–shell NPs are superparamagnetic. The saturation magnetization of prepared Fe₃O₄ NPs is 54.24 emu/g and it decreases intensively down to 29.88, 10.51 and 5.75 emu/g, after ZnO coating with various ratios of core to shell as 1:1, 1:10 and 1:20, respectively. This reduction is attributed to core–shell interface effects and shielding. TEM images and XRD results imply that ZnO-coated magnetite NPs are formed. According to the TEM images, the estimated average size for most of core–shell NPs is about 12 nm.     

Synthesis and characterization of Fe–B nanoparticles for potential magnetic applications

The crystallization and structure of Fe–B nanoparticles (NPs) of different sizes formed in a single process by gas aggregation from Fe₈₀B₂₀ targets were analyzed by transmission electron microscopy. It is concluded that all NPs are covered by an amorphous Fe–B shell while the crystal structure of the NPs core depends on their size. Large NPs with diameters ≥30 nm are monocrystalline tetragonal Fe₃B, small diameter NPs (≤20 nm) are completely amorphous whereas in middle size NPs, with diameters between 20 and 30 nm, difference Fe–B phases (tetragonal Fe₃B and orthorhombic FeB) together with defaulted areas are observed. This work opens new possibilities to produce Fe–B NPs tailoring their magnetic properties by controlling their size and composition.     

Synthesis of Fe–Co alloy and cobalt–magnetite composites doped with Nd3+ by using iron disproportionation

Iron–cobalt alloy and cobalt–magnetite composites doped with Nd³⁺ (Co _x Fe_1?x /Co _y Fe_1?y Nd _z Fe_2?z O₄) in which the Fe alloy has either a bcc or a fcc structure and the oxide is a spinel phase, have been synthesized by using the disproportionation of Fe(OH)₂ and the reduction of Co(II) by Fe⁰ in a concentrated KOH solution. Powder X-ray diffraction, scanning electron microscope and vibrating sample magnetometer were employed to characterize the crystallite sizes, structure, morphology and magnetic properties of the composites. And the effect of the Co(II)/Fe(II) ratio (0 ≤ Co/Fe ≤ 1), concentration of KOH, reaction time and substitution Fe³⁺ ions by Nd³⁺ ions on structure, magnetic properties of the composites were investigated. From the perspective of thermodynamics, we explain the postulated mechanism of the disproportionation reaction.     

A new strategy to assemble enhanced magnetic–photoluminescent bifunction into a flexible nanofiber

A new type of magnetic–photoluminescent bifunctional [Fe₃O₄@Y₂O₃:Eu³⁺]/polyvinyl pyrrolidone (PVP) flexible composite nanofibers were successfully prepared via electrospinning through dispersing Fe₃O₄@Y₂O₃:Eu³⁺ core–shell structured nanoparticles (NPs) into the PVP matrix. The structure, morphology, and properties of the flexible composite nanofibers were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and fluorescence spectroscopy. The diameter of [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP nanofibers is ca. 128.57 ± 36.72 nm. Fluorescence emission peaks of Eu³⁺ in both Fe₃O₄@Y₂O₃:Eu³⁺ NPs and [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP nanofibers are observed and assigned to the energy levels transitions of ⁵D₀ → ⁷F₀ (580 nm), ⁵D₀ → ⁷F₁ (533, 586, 592, 599 nm), ⁵D₀ → ⁷F₂ (612 nm), and ⁵D₀ → ⁷F₃ (629 nm) of Eu³⁺ ions. Compared with Fe₃O₄/Y₂O₃:Eu³⁺/PVP nanofibers, [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP nanofibers possess much stronger luminescence. The as-prepared [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP flexible composite nanofibers simultaneously exhibit excellent magnetism and photoluminescent performance. The intensities of magnetism and luminescence of the composite nanofibers can be simultaneously tuned by adjusting the amount of Fe₃O₄@Y₂O₃:Eu³⁺ NPs introduced into the nanofibers. The high performance [Fe₃O₄@Y₂O₃:Eu³⁺]/PVP flexible composite nanofibers have potential applications in bioimaging, cell separation, and future nanomechanics.     

A new tactics to fabricate flexible nanobelts with enhanced magnetic–luminescent bifunction

Novel magnetic–photoluminescent bifunctional [Fe₃O₄@Y₂O₃:Eu³⁺]/polymethyl methacrylate (PMMA) flexible composite nanobelts were successfully prepared by electrospinning via dispersing Fe₃O₄@Y₂O₃:Eu³⁺ core–shell structured nanoparticles (NPs) into the PMMA matrix. The morphology, structure and properties of the flexible composite nanobelts were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry and fluorescence spectroscopy. The width and thickness of [Fe₃O₄@Y₂O₃:Eu³⁺]/PMMA composite nanobelts are 3.58 ± 0.29 and 1.2 μm, respectively. Fluorescence emission peaks of Eu³⁺ in [Fe₃O₄@Y₂O₃:Eu³⁺]/PMMA flexible composite nanobelts are observed and assigned to the energy levels transitions of ⁵D₀ → ⁷F₀ (580 nm), ⁵D₀ → ⁷F₁ (533, 586, 592, 599 nm), ⁵D₀ → ⁷F₂ (612 nm) and ⁵D₀ → ⁷F₃ (629 nm) of Eu³⁺ ions. Compared with Fe₃O₄/Y₂O₃:Eu³⁺/PMMA nanobelts, [Fe₃O₄@Y₂O₃:Eu³⁺]/PMMA flexible composite nanobelts possess much stronger luminescent intensity. The as-prepared flexible composite nanobelts exhibit excellent magnetism and photoluminescent performance. The intensities of magnetism and luminescence of the flexible composite nanobelts can be simultaneously tuned by adjusting the amount of Fe₃O₄@Y₂O₃:Eu³⁺ NPs introduced into the nanobelts. The high performance [Fe₃O₄@Y₂O₃:Eu³⁺]/PMMA flexible composite nanobelts have potential applications in the fields of cell separation, magnetic resonance imaging, drug deliver and future nanodevices.     

Yolk–Shell Nanostructure: An Ideal Architecture to Achieve Harmonious Integration of Magnetic–Plasmonic Hybrid Theranostic Platform

Magnetic–plasmonic hybrid nanoparticles (MPHNs) have attracted great interest in cancer theranostics. However, the relaxivity of the magnetic component is typically reduced by the plasmonic component in conventional core–shell structured MPHNs, due to the presence of a water‐impenetrable coating which severely restricts the proximity of protons to the magnetic portion. To circumvent this issue, yolk–shell structured MPHNs comprising a Fe₃O₄ core within a hollow cavity encircled by a porous Au outer shell are designed. As expected, the introduction of hollow cavity between the magnetic and plasmonic portions significantly prevents the decline in relaxivity of the Fe₃O₄ core caused by the Au layer. Moreover, in addition to conferring high near‐infrared absorption to plasmonic component, the hollow cavity and the pores in the outer shell can also provide a large storage space and release channels for anticancer drugs. Furthermore, the multicomponent nanoparticles (NPs) still have a compact size of less than 100 nm to ensure efficient tumor accumulation. Taken together, the yolk–shell Fe₃O₄@Au NPs can be regarded as an ideal magnetic–plasmonic theranostic platform for magnetic resonance/photoacoustic/positron emission tomography multimodal imaging and light‐activated chemothermal synergistic therapy.     

Narrowing of ferromagnetic resonance linewidth in calcium substituted YIG powders by Zr4+/Sn4+ substitution

Ca _x+y Y_3?x?y Sn _x Zr _y Fe_5?x?y O₁₂ powders were synthesized by a citric acid combustion method. The phase, microstructure and ferromagnetic resonance linewidth (ΔH) of the powders were analyzed. Pure garnet phase Y₃Fe₅O₁₂ could be obtained at 1,200 °C, except for YFeO₃ phase appearing in the sample with x = 0.5, y = 0.2. The addition of Zr⁴⁺ ion and Sn⁴⁺ ion could lower ΔH by replacing Fe³⁺ ion, which could change the a–d superexchange interaction in YIG lattice. Moreover, Zr⁴⁺ ion could promote this replacement by enlarging the lattice. However, too much addition of Zr⁴⁺ ion would bring the second phase YFeO₃. The sample of Ca_0.76Y_2.24Sn_0.7Zr_0.06Fe_4.34O₁₂ shows excellent properties which are M _s  = 6.4 emu/g, H _c  = 10.9 Oe, ΔH = 113 Gs.     

A single nanobelt to achieve simultaneous photoluminescence–electricity–magnetism trifunction

In order to develop new-typed multifunctional composite nanobelts, polymethyl methacrylate (PMMA) is used as the matrix to construct composite nanobelts containing different amounts of Eu(BA)₃phen(BA = benzoic acid, phen = phenanthroline), polyaniline (PANI) and Fe₃O₄ nanoparticles (NPs), and Eu(BA)₃phen/PANI/Fe₃O₄/PMMA trifunctional composite nanobelts with simultaneous photoluminescence, electricity and magnetism have been successfully fabricated via electrospinning technology. The morphology and properties of the obtained composite nanobelts were characterized by X-ray diffractometry, scanning electron microscopy, vibrating sample magnetometry, fluorescence spectroscopy and Hall effect measurement system. The results indicate that the trifunctional composite nanobelts simultaneously possess excellent photoluminescence, electrical conduction and magnetic properties. Fluorescence emission peaks of Eu³⁺ ions in the composite nanobelts are observed and assigned to the energy levels transitions of ⁵D₀ → ⁷F₀ (580 nm), ⁵D₀ → ⁷F₁ (593 nm) and ⁵D₀ → ⁷F₂ (615 nm) of Eu³⁺ ions, and the ⁵D₀ → ⁷F₂ hypersensitive transition at 615 nm is the predominant emission peak. The electrical conductivity reaches up to the order of 10^?3 S/cm. Furthermore, the luminescent intensity, electrical conductivity and saturation magnetization of the composite nanobelts can be tunable by adjusting amounts of Eu(BA)₃phen, PANI and Fe₃O₄ NPs. The formation mechanism of the composite nanobelts is also proposed. The obtained photoluminescence–electricity–magnetism trifunctional composite nanobelts have potential applications in many areas such as electromagnetic interference shielding, microwave absorption, molecular electronics, biomedicine and future nanomechanics. More importantly, the design concept and construct technique are of universal significance to fabricate other trifunctional naonobelts.     

Fabrication of magnetic-luminescent bifunctional composite nanofibers via facile electrospinning

Fe₃O₄/Eu(BA)₃phen/polyvinyl pyrrolidone (PVP) magnetic-luminescent bifunctional composite nanofibers have been successfully fabricated based on ferroferric oxide (Fe₃O₄) nanoparticles (NPs) and europium complexes Eu(BA)₃phen (BA = benzoic acid, phen = phenanthroline) via electrospinning technology. The as-prepared samples were characterized by X-ray diffractometry, field-emission scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, fluorescence spectroscopy and vibrating sample magnetometry. The as-prepared Fe₃O₄/Eu(BA)₃phen/PVP composite nanofibers possess good fibrous morphology, and Fe₃O₄ NPs are evenly dispersed into nanofibers. Under the excitation of 274-nm ultraviolet light, Fe₃O₄/Eu(BA)₃phen/PVP composite nanofibers exhibit red emissions of predominant peaks at 592 and 616 nm, which are respectively attributed to the ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ energy levels transitions of Eu³⁺ ions. The optimum mass percentage of Eu(BA)₃phen to PVP is 15 %. The fluorescence intensity of composite nanofibers is decreased when more Fe₃O₄ NPs were added. The saturation magnetization is increased with the increase of Fe₃O₄ NPs, indicating that the magnetism of the composite nanofibers can be tuned by adjusting Fe₃O₄ NPs content. The magnetic-luminescent bifunctional composite nanofibers are expected to apply in the fields of cell separation and biological labeling imaging, etc.     

Rational synthesis and tailored optical and magnetic characteristics of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–Au composite nanoparticles

To minimize saturation magnetization (Ms) degradation and simultaneously maintain the optical and magnetic responsiveness characteristics of Fe₃O₄/Au nanocomposites, we successfully prepared Fe₃O₄–Au seeds composite nanoparticles (NPs) by a novel seed deposition process. The effects of gold seeds coating amounts and the concentration of Fe₃O₄ NPs on the morphologies of final products are extensively characterized. The results of energy-dispersive spectrometry mapping show that the gold seeds are uniformly adhered onto the Fe₃O₄ NPs surfaces in precisely controlled amount. Importantly, with the electronic redistribution between Fe₃O₄ and Au NPs interfaces, the obvious position shifting of Fe 2p and Au 4f electronic binding energy peaks is observed. Upon increasing surface coatings of gold seeds, the electron deficiency on the gold NPs leads to the redshift of the absorption peak. Though Ms declines slightly due to the diamagnetic contribution from decorated gold seeds, the developed Fe₃O₄–Au seeds composite NPs possess the robust magnetic responsiveness and they are amenable to be separated and recycled by the external magnet, which facilitates great potential applications in biological, medical and photocatalytic fields.     

Effect of Zn<Superscript>2+</Superscript> doping on the structural,magnetic and dielectric properties of MnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> prepared by the sol–gel method

Mn_1?xZn_xFe₂O₄ (x?=?0.2–0.8) ferrite samples were successfully prepared by the sol–gel method. X-ray diffraction study reveals that single cubic spinel phase was formed in Mn_1?xZn_xFe₂O₄ samples. The SEM micrographs revealed that the microstructures change significantly with different Zn²⁺ doping concentration and sintering temperature while the grain size grow up to 9.48 μm for Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100 °C. Further, the dielectric and magnetic measurements indicated that both Zn²⁺ doping and sintering temperature could affect both electrical and magnetic parameters such as dielectric constant and saturation magnetization in a great manner. The Mn_0.6Zn_0.4Fe₂O₄ sample sintered at 1100 °C for 8 h is found to show the largest M _s value (77.30 emu/g) in this work. These results indicate that Zn²⁺ doping or sintering temperature can adjust the microstructures, dielectric and magnetic properties of Mn_1?xZn_xFe₂O₄ ferrites.     

Effects of Gd2O3 on structure and magnetic properties of Ni-Mn ferrite

The emulsion method was used to prepare nanocrystalline Ni_0.7Mn_0.3Gd _x Fe_2-x O₄ ferrites. The growth of particles, the structure and the magnetic properties were investigated by X-ray diffraction (XRD), Mössbauer spectroscopy and vibrating sample magnetometer (VSM). Furthermore, the influence of Gd₂O₃ on magnetic properties of Ni-Mn ferrite powders has been investigated in detail. When the crystallite sizes are about 30–40 nm, all the samples have the similar Ms values. The variational rules of saturation magnetization (Ms) and coercivity (Hc) along with doped-Gd contents at different sintering temperatures show that the maximum Gd ions content doped into ferrite lattices is x = 0.06. When Gd-doped content x is larger than 0.06, the doped Gd ions can’t enter into the ferrite lattice totally but reside at grain boundary, as the ionic radii of the Gd³⁺ ions are larger than that of Fe³⁺ ions. The ferrimagnetism have not disappeared completely, even if the crystallite size is 7.8 nm.     

Green synthesis and characterisation of L-Serine capped magnetite nanoparticles for removal of Rhodamine B from contaminated water

ABSTRACT

This paper describes a green one-pot synthesis of L-Serine (L-Ser) capped magnetite nanoparticles (Fe₃O₄ NPs) and its potential application for adsorption of RhB dye from aqueous solution. The surface property, structure, morphology and magnetic properties of as prepared L-Ser capped Fe₃O₄ NPs were characterised through UV-Visible spectroscopy, Fourier transform-infrared spectroscopy, X-Ray Diffraction (XRD), scanning electron microscope, transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). The XRD results were indicated the formation of high crystalline spinel type Fe₃O₄ NPs. TEM images were shown the spherical shape of L-Ser capped Fe₃O₄ NPs with particle size of 5.9 nm. The VSM curve showed the superparamagnetic behaviour of L-Ser capped Fe₃O₄. A plausible interaction mechanism of L-Ser and Fe₃O₄ NPs was also investigated. L-Ser capped Fe₃O₄ NPs due to its large surface area and a strong magnetism was shown potential adsorption efficiency towards RhB dye from aqueous solution. The adsorption isotherm data fitted well with Langmuir isotherm model and the monolayer adsorption capacity (q_e,exp) was found to be 6.82 mg/g at pH 7.4 and 300 K. The experimental kinetic data fitted very well with the pseudo-second-order model. The thermodynamic studies reveal that adsorption efficiency is critically dependent on temperature.     

Photoluminescence–electricity–magnetism trifunction simultaneously assembled into one flexible nanofiber

In order to develop new-typed multifunctional composite nanofibers, Eu(BA)₃phen/PANI/Fe₃O₄/PVP trifunctional composite nanofibers with photoluminescence, electricity and magnetism have been successfully fabricated via electrospinning technology. Polyvinyl pyrrolidone (PVP) is used as a matrix to construct composite nanofibers containing different amounts of Eu(BA)₃phen, polyaniline (PANI) and magnetite Fe₃O₄ nanoparticles (NPs). X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometry, fluorescence spectroscopy and Hall effect measurement system are used to characterize the morphology and properties of the obtained composite nanofibers. The results indicate that the trifunctional composite nanofibers possess excellent luminescent, electrical conductivity and magnetic properties. Fluorescence emission peaks of Eu³⁺ are observed in the Eu(BA)₃phen/PANI/Fe₃O₄/PVP photoluminescent-electrical-magnetism trifunctional composite nanofibers and assigned to the of ⁵D₀ → ⁷F₀ (580 nm), ⁵D₀ → ⁷F₁ (593 nm) of Eu³⁺, and the ⁵D₀ → ⁷F₂ hypersensitive transition at 615 nm is the predominant emission peak. The electrical conductivity reaches up to the order of 10^?3 S/cm. The luminescent intensity, electrical conductivity and saturation magnetization of the composite nanofibers can be tunable by adding various amounts of Eu(BA)₃phen, PANI and Fe₃O₄ NPs. The multifunctional composite nanofibers are expected to possess many potential applications in areas such as electromagnetic interference shielding, microwave absorption, molecular electronics and biomedicine.     

Effect of Ho3+ substitution on magnetic and microwave absorption properties of Sr(ZnZr)0.5Fe12O19 hexagonal ferrite nanoparticles

Sr_1?x Ho _x (ZnZr)_0.5Fe₁₁O₁₉ (x = 0.03, 0.06 and 0.09) hexaferrite nanocrystallites of average sizes in the range of 46–60 nm are synthesized by the citrate sol–gel method. Crystalline structure, morphology, magnetic properties, and microwave absorption properties of powders were studied via X-ray diffraction, field emission scanning electron microscope vibrating sample magnetometer, and vector network analyzer, respectively. The magnetic properties such as saturation magnetization (M _s ) and coercivity (H _c ) were calculated from hysteresis loops. The XRD patterns show that the main phase is M-type strontium hexaferrite without other impurity phases. Microwave absorption properties of hexaferrite (70 wt%)–acrylic resin (30 wt%) composites were measured by the standing-wave-ratio (SWR) method in the range from 12 to 20 GHz. Results showed that substitution of Ho³⁺ ions for Sr²⁺ ions in Sr(ZnZr)_0.5Fe₁₁O₁₉ resonance frequency moves to higher frequency. For samples with x = 0.03, a minimum reflection loss of ?42 dB was obtained at 16.6 GHz for a layer of 1.7 mm in thickness. It was concluded that the prepared composites could be good candidates for electromagnetic compatibility and other practical applications at high frequency.     

Preparation of yolk–shell Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@N-doped carbon nanocomposite particles as anode in lithium ion batteries

The yolk–shell-structured Fe₃O₄ nanocomposite particles (Fe₃O₄@Void@C–N NPs) with Fe₃O₄ as the yolk and N-doped carbon as the shell were prepared by using melamine formaldehyde resin as the N and C sources. When used as anode material for lithium ion battery, the yolk–shell structure could not only afford adequate void to accommodate the large volume change during charge/discharge process but also improve structural stability and electrical conductivity. The anode material demonstrated superior long-term and high-rate performance because of the novel structure and the N-doped carbon shell with mesopore. Thus, Fe₃O₄@Void@C–N NPs exhibited a high reversible capacity of 1530 mAh g^?1 after 300 cycles at a current density of 500 mA g^?1, which were approximately 1.5 and 6 times higher than Fe₃O₄@C–N NPs and pure Fe₃O₄ particles, respectively. Even at the higher current density of 2000 mA g^?1, the reversible capacity remained at 651 mAh g^?1 after 500 cycles.     

Metal–Organic Gel‐Derived FexOy/Nitrogen‐Doped Carbon Films for Enhanced Lithium Storage

The development of cost‐effective and flexible electrodes is demanding in the field of energy storage. Herein, flexible Fe_xO_y/nitrogen‐doped carbon films (Fe_xO_y/NC‐MOG) are prepared by facile electrospinning of Fe‐based metal–organic gels (MOGs) followed by high‐temperature carbonization. This approach allows the even mixing of fragile coordination polymers with polyacrylonitrile into flexible films while reserving the structural characteristics of coordination polymers. After thermal treatment, Fe_xO_y/NC‐MOG films possess uniformly distributed Fe_xO_y nanoparticles and larger accessible surface areas than traditional Fe_xO_y‐NC films without MOG. Taking advantage of the unique structure, Fe_xO_y/NC‐MOG exhibits a superior rate performance (449.8 mA h g^?1 at 5000 mA g^–1) and long cycle life (629.3 mA h g^–1 after 500 cycles at 1000 mA g^–1) when used as additive‐free anodes in lithium‐ion batteries.