Fabrication of magnetic polybenzoxazine-based carbon nanofibers with Fe3O4 inclusions with a hierarchical porous structure for water treatment

Hierarchical porous, magnetic Fe₃O₄@carbon nanofibers (Fe₃O₄@CNFs) based on polybenzoxazine precursors have been synthesized by a combination of electrospinning and in situ polymerization. The benzoxazine monomers could easily form thermosetting nanofibers by in situ ring-opening polymerization and subsequently be converted into CNFs by carbonization. The resultant fibers with an average diameter of 130 nm are comprised of carbon fibers with embedded Fe₃O₄ nanocrystals, and could have a high surface area of 1885 m² g^?1 and a porosity of 2.3 cm³ g^?1. Quantitative pore size distribution and fractal analysis were used to investigate the hierarchical porous structure using N₂ adsorption and synchrotron radiation small-angle X-ray scattering measurements. The role of precursor composition and activation process for the effects of the porous structure is discussed, and a plausible correlation between surface fractal dimension and porous parameter is proposed. The Fe₃O₄@CNFs exhibit efficient adsorption for organic dyes in water and excellent magnetic separation performance, suggesting their use as a promising adsorbent for water treatment, and also provided new insight into the design and development of a carbon nanomaterial based on a polybenzoxazine precursor.     

Preparation of Fe3Si‐Al2O3 Nanocomposite Powders by Mechanochemical Reaction of Fe3O4‐Si‐Al Powder Mixtures

Phase evolution and morphology of Fe₃O₄‐Si‐Al powder mixtures during ball milling from 30 min to 20 h were investigated. A 3‐h critical milling was necessary for the occurrence of mechanically activated combustion reaction. The reaction results in the formation of Fe (Si), Fe₃Si, and α‐Al₂O₃. During ball milling from 3 to 20 h, Fe (Si) and Fe₃Si were combined into disordered Fe₃Si intermetallic and Fe₃Si‐Al₂O₃ composite powder was formed. The presence of in situ formed alumina leads to a decrease in crystallite and particle sizes. The Fe₃Si‐Al₂O₃ particles after milling for 20 h had a crystalline size of 10~12 nm.     

Low Temperature Synthesis of Needle‐like α‐FeOOH and Their Conversion into α‐Fe2O3 Nanorods for Humidity Sensing Application

In this study, we report template and surfactant‐free, low temperature (70°C) synthesis of needle‐like α‐FeOOH and its conversion at 400°C into α‐Fe₂O₃ nanorods using Fe(+2) and Fe(+3) chlorides and urea as a hydrolysis‐controlling agent. The isolated needle‐like α‐FeOOH indicates asparagus‐type growth pattern having length ca. 600 nm with 80 nm diameter at base and apex diameter of around 10 nm. The sample on heating (α‐Fe₂O₃) shows nanorod‐like morphology. The samples were characterized using various physicochemical characterization techniques such as XRD, Raman spectroscopy, UV‐Vis spectroscopy, particle size distribution analysis, Field Emission Scanning Electron Microscopy (FE‐SEM), and humidity sensing performance. The humidity sensing behavior of both α‐FeOOH and α‐Fe₂O₃ was studied. The α‐FeOOH shows quicker (10 s) and higher response toward change in humidity from 20%RH to 90%RH as compared with α‐Fe₂O₃ (60 s). Their typical morphology and crystalline structure plays an important role in humidity sensing behavior.     

Lattice Expansion in Metal Oxide Nanoparticles: MgO,Co3O4, & Fe3O4

Uniform sets of mono‐crystalline nanoparticles ranging from 6 nm to over 100 nm were prepared for the MgO, Co₃O₄, and Fe₃O₄ oxide systems. The nanoparticles were characterized by transmission electron microscopy (TEM) and x‐ray diffraction (XRD). A careful analysis shows increased lattice parameter for smaller nanoparticles of each oxide system: 0.47% expansion from bulk for 7 nm MgO crystallites, 0.15% expansion from bulk for 9 nm Co₃O₄ crystallites, and 0.13% expansion from bulk for 6 nm Fe₃O₄ crystallites. The compressive surface stresses and expansion energies against hydrostatic pressure for each oxide system were calculated, respectively, to be 4.13 N/m and 1.8 meV/formula unit for MgO, 3.09 N/m and 0.87 meV/formula unit for Co₃O₄, and 1.26 N/m and 0.67 meV/formula unit for Fe₃O₄. The fundamental understanding of oxide nanoparticle mechanics as presented here will facilitate integration of these materials into technological applications in a rationally designed manner.     

Preparation and properties of electrospun PAN/Fe3O4 magnetic nanofibers

Polyacrylonitrile (PAN)/Fe₃O₄ composite nanofibers were prepared via the electrospinning of the PAN spinning solutions with magnetite Fe₃O₄ nanoparticles. The experimental results showed that the morphology and diameter of the nanofibers strongly depended upon concentrations of PAN and salt additives in the spinning solutions. A suitable PAN concentration and LiCl additives could effectively prevent the occurrence of beads in the electrospinning process and affected the diameters of the electrospun nanofibers. The breaking strength and breaking strain decreased when the magnetite Fe₃O₄ nanoparticles were incorporated. The prepared PAN/Fe₃O₄ nanofibers were superparamagnetic at room temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of fibres diameter on the AC and DC magnetic characteristics of Fe/Fe3O4 fibres based soft magnetic composites

Fibres-based soft magnetic composites (FSMCs) have been prepared by using Fe fibres of different diameters (65, 125, 250 and 500 μm). The Fe fibres were coated with a 3 μm thick layer of Fe₃O₄ via the blackening process and subsequently compacted at 700 MPa. The X-ray diffraction analysis (XRD) was used to prove the formation of the Fe₃O₄ coating on the surface of the fibres. The thickness and the uniformity of the coating were analysed via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The DC measurements performed on the composite cores revealed that the saturation induction increase from 1.36 to 1.68 T, the maximum relative permeability increase from 550 to 940, and the coercive field decrease from 796 to 454 A/m as the fibre's diameter increase from 65 to 500 μm. By using thinner fibres (65 and 125 μm), composites with low losses and stable initial relative permeability, in the frequency range 50 Hz–10 kHz, can be obtained. To distinguish between different types of losses dissipated by our compacts, and the influence of the fibre's diameter on the different components of the total losses, a numerical model for loss separation is proposed. The comparative evolution of the AC magnetic characteristics of the FSMCs and powder-based SMCs is presented. According to the presented results, this new type of composites can be successfully used to prepare magnetic cores designated to work in the medium to high-frequency range.     

Superior thermal stability of polymer capped Fe3O4 magnetic nanoclusters

In general, the technologically important ferrites nanoparticles, magnetite and maghemite, are converted from cubic to the more stable rhombohedral structure above 500°C‐700°C under air/vacuum/inert atmosphere. Here, we report, the superior thermal stability of polymer capped Fe₃O₄ (PCIO) nanocluster (synthesized using microwave‐assisted polyol approach) up to 1000°C under vacuum and inert atmosphere. Raman spectra of post annealed PCIO nanoclusters show the Fe₃O₄ phase with carbon signature due to the decomposition of polymer matrix. The carbon layer seems to act as a thermal shield and increases the activation energy thereby preventing the intrusion of heat, oxygen, volatiles mass into the magnetic core. The presence of carbon layer was further confirmed from the high‐resolution transmission electron microscopic image. After thermal annealing at 1000°C, PCIO nanoclusters showed superparamagnetic behavior with a saturation magnetization of 89 emu/g, close to the bulk saturation magnetization of Fe₃O₄ phase. In contrast, the uncoated Fe₃O₄ (UCIO) nanoclusters decompose at 700°C into α‐Fe₂O₃ and FeO phases under similar annealing conditions. Our findings open up new possibilities of stabilizing nanomaterials for high‐temperature applications.     

Fe3O4 nanoparticle-coated boron nitride nanospheres: Synthesis,magnetic property and biocompatibility study

Hybrid nanocomposites consisting of uniform Fe₃O₄ nanoparticles and boron nitride (BN) nanospheres were synthesized via an ethanol-thermal reaction method. The spherical BN nanoparticles (BNNSs) with average diameter 150 nm have been uniformly coated with dense ultra-small Fe₃O₄ nanoparticles (with average diameter of 10 nm), forming novel Fe₃O₄@BNNS nanocomposites. Magnetic measurement by using vibrating sample magnetometer (VSM) indicates that the Fe₃O₄ coating is superparamagnetic, and the nanocomposites can be physically manipulated at a low magnetic field. Preliminary biocompatibility study has also been performed to evaluate the toxicity of the nanocomposites. The nanocomposites show cytocompatibility at low concentration and have little effect on cell viability of MCF-7, MCF-10 and Hela cell lines. The Fe₃O₄@BNNS nanocomposites may find a wide range of potential applications including water treatment, catalysts, carriers for boron neutron capture therapy and magnetic-targeted drug delivery.     

Synthesis and characterization of nanocomposite Fe3O4/SiO2 core–shell abrasives for high-efficiency ultrasound-assisted magneto-rheological polishing of sapphire

A functional Fe₃O₄/SiO₂ core–shell abrasive was synthesized via hydrolysis of tetraethyl orthosilicate. A silica shell was successfully coated on a Fe₃O₄ core, resulting in a core-shell particle with an average diameter of 140 nm. The prepared core–shell abrasives was utilized for ultrasound-assisted magneto-rheological polishing (UAMP) of sapphire substrate. The experimental results showed that the Fe₃O₄/SiO₂ core–shell abrasives exhibited a remarkable polishing performance for the sapphire material, resulting in smooth and detect-free surfaces with a high material removal rate (MRR) compared to mixed abrasives (Fe₃O₄ and SiO₂) and pure Fe₃O₄ particles. The application of ultrasonic vibration to the sapphire wafer further improved the MRR, which was approximately 3.4 times higher than that of traditional magneto-rheological polishing. The largest MRR (1.974 μm/h) and comparatively low surface roughness (0.442 nm) of the polished sapphire wafer were achieved by UAMP with the Fe₃O₄/SiO₂ core–shell abrasives. The polishing mechanism of the sapphire wafer is discussed in terms of chemical reactions and mechanical polishing.     

Continuous ferrimagnetic Y3Fe5O12 layers on the ceramic PbZr0·45Ti0·55O3 substrates

For the first time, continuous layers of yttrium iron garnet (YIG, Y₃Fe₅O₁₂) with a thickness of about 2 μm were synthesized on ferroelectric ceramic substrates based on lead titanate zirconate (PZT, PbZr_0·45Ti_0·55O₃). The Y₃Fe₅O₁₂ layer was deposited by ion-beam sputtering – deposition on PZT substrates of 400 μm thick by sputtering a polycrystalline target of the composition Y₃Fe₅O₁₂ with a mixture of argon and oxygen ions. Due to preliminary planarization of the PZT surface with a TiO₂ layer, a high-quality plane-parallel YIG/PZT interface was obtained, which is confirmed by scanning electron microscopy in combination with the focused ion beam technique. Atomic force microscopy showed that planarization makes it possible to achieve surface smoothness of 10 nm.The YIG/PZT heterostructures obtained in this work are potentially attractive for use in logic circuits based on low-scattering spin waves, memory elements, as well as electrically controlled microwave devices.     

Controlled synthesis of Fe3O4@SnO2/RGO nanocomposite for microwave absorption enhancement

A ternary nanocomposite of Fe₃O₄@SnO₂/reduced graphene oxide (RGO) with different contents of SnO₂ nanoparticles was synthesized by a simple and efficient three-step method. The transmission electron microscopy and field emission scanning electron microscopy characterization display that plenty of Fe₃O₄@SnO₂ core–shell structure nanoparticles are well distributed on the surface of RGO sheets. The X-ray diffractograms show that the products consist of highly crystallized cubic Fe₃O₄, tetragonal SnO₂ and disorderedly stacked RGO sheets. The magnetic hysteresis measurement reveals the ferromagnetic behavior of the products at room temperature. The microwave absorption properties of paraffin containing 50 wt% products were investigated at room temperature in the frequency range of 2–18 GHz by a vector network analyzer. The electromagnetic data show that the maximum reflection loss is −45.5 dB and −29.5 dB for Fe₃O₄@SnO₂/RGO-1 and Fe₃O₄@SnO₂/RGO-2 nanocomposite, respectively. Meanwhile, the reflection loss less than −10 dB is up to 14.4 GHz and 13.8 GHz for Fe₃O₄@SnO₂/RGO-1 and Fe₃O₄@SnO₂/RGO-2 nanocomposite, respectively. It is believed that such nanocomposite could be used as promising microwave absorbers.     

Preparation and Xylene‐Sensing Properties of Co3O4 Nanofibers

Co₃O₄ nanofibers were prepared by an electrospinning method and characterized by differential thermal and thermal gravimetric analyzer (DTA‐TGA), X‐ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FT‐IR), and scanning electron microscopy (SEM). Xylene‐sensing properties of the as‐prepared nanofibers were also investigated in detail. The results showed that the morphology of the as‐prepared fibers was largely influenced by the calcination temperature. The Co₃O₄ nanofibers calcined at 500°C exhibited the highest response to xylene in a wide concentration range. Moreover, Co₃O₄ nanofibers calcined at 500°C also exhibited good selectivity, fast response (15 s) and recovery (22 s) rate at a low operating temperatures of 255°C. These properties make the fabricated nanofibers good candidates for xylene detection.     

Controlled synthesis and electromagnetic wave absorption properties of core-shell Fe3O4@SiO2 nanospheres decorated graphene

Fe₃O₄/reduced graphene oxide (RGO) nanocomposite was synthesized by a simple hydrothermal method and then SiO₂ coated onto Fe₃O₄ by a modified Stӧber method. The transmission electron microscopy and field emission scanning electron microscopy characterization indicate that masses of Fe₃O₄@SiO₂ core-shell structure nanospheres attached to the RGO sheets, and that the thicknesses of SiO₂ shells are about 20–40 nm. The X-ray diffractograms and Raman spectra illustrate that the synthesized samples consist of highly crystallized cubic Fe₃O₄, amorphous SiO₂ and disorderedly stacked RGO sheets. The magnetic hysteresis loops reveal the ferromagnetic behavior of the samples at room temperature. In addition, the Fe₃O₄@SiO₂/RGO paraffin composite exhibit excellent electromagnetic wave absorption properties at room temperature in the frequency range of 2–18 GHz, which are attributed to the effective complementarities between the dielectric loss and magnetic loss. For Fe₃O₄@SiO₂/RGO-1 and Fe₃O₄@SiO₂/RGO-2 nanocomposite, the minimum reflection loss can reach −26.4 dB and −16.3 dB with the thickness of 1.5 mm, respectively. The effective absorption bandwidth of the samples can reach more than 10.0 GHz with the thickness in the range of 1.5–3.0 mm. It is demonstrated that such nanocomposite could be used as a promising candidate in electromagnetic wave absorption area.     

Thickness Dependence of Dielectric,Leakage, and Ferroelectric Properties of Bi6Fe2Ti3O18 Thin Films Derived by Chemical Solution Deposition

We prepared Bi₆Fe₂Ti₃O₁₈ thin films on Pt/Ti/SiO₂/Si substrates with thickness ranging from ～300 to ～900 nm by using a chemical solution deposition route and investigated the thickness effects on the microstructure, dielectric, leakage, and ferroelectric properties of Bi₆Fe₂Ti₃O₁₈ thin films. Increasing thickness improves the surface morphology, dielectric, and leakage properties of Bi₆Fe₂Ti₃O₁₈ thin films and a well‐defined ferroelectric hysteresis loops can form for the thin films with the thickness above 400 nm. Moreover, the thickness dependence of saturation polarization is insignificant, whereas the remnant polarization decreases slightly with increasing thickness and it possesses a maximal value of ～20 μC/cm² for the 500 nm‐thick thin films. The mechanisms of the thickness dependence of microstructure, dielectric, and ferroelectric properties are discussed in detail. The results will provide a guidance to optimize the ferroelectric properties in Bi₆Fe₂Ti₃O₁₈ thin films by chemical solution deposition, which is important to further explore single‐phase multiferroics in the n = 5 Aurivillius thin films.     

A Novel Scheme to Obtain Y2O2S:Er3+ Upconversion Luminescent Hollow Nanofibers via Precursor Templating

Y₂O₃:Er³⁺ hollow nanofibers were prepared by calcination of the monoaxial electrospinning‐derived PVP/[Y(NO₃)₃+Er(NO₃)₃] composite nanofibers, and then Y₂O₂S:Er³⁺ hollow nanofibers were synthesized by sulfurization of the as‐obtained Y₂O₃:Er³⁺ hollow nanofibers via a double‐crucible method using sulfur powders as sulfur source. X‐ray diffraction (XRD) analysis shows that the Y₂O₂S:Er³⁺ hollow nanofibers are pure hexagonal phase with the space group of . Scanning electron microscope (SEM) observation indicates that the Y₂O₂S:Er³⁺ hollow nanofibers are obvious hollow‐centered with the outer diameter of 176 ± 25 nm. Upconversion emission spectrum analysis manifests that Y₂O₂S:Er³⁺ hollow nanofibers emit strong green and weak red upconversion emissions centering at 526, 546, and 667 nm, respectively. The green emissions and the red emission are, respectively, originated from ²H_11/2/⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_l5/2 energy levels transitions of the Er³⁺ ions. The emitting colors of Y₂O₂S:Er³⁺ hollow nanofibers are located in the green region in CIE chromaticity coordinates diagram. The formation mechanism of the Y₂O₂S:Er³⁺ hollow nanofibers is also advanced. This preparation technique can be applied to prepare other rare‐earth oxysulfides hollow nanofibers.     

Synthesis of nanofibrous chitosan/Fe3O4/TiO2@TiO2 microspheres with enhanced biocompatibility and antibacterial property

Multifunctional materials have received considerable attention as they could integrate different functional components in one-single platform. In this study, novel chitosan/Fe₃O₄/TiO₂@TiO₂ nanowire (NW) microspheres having extracellular matrix-like fibrous surface and photothermal antibacterial property were synthesized through in situ hydrothermal growth of TiO₂ NWs on chitosan/Fe₃O₄/TiO₂ microspheres. It is found that the microspheres were spherical in morphology with a diameter of 100–300 µm and exhibited a hierarchical and nanofibrous feature. Their surface was mainly constructed by numerous TiO₂ NWs with a diameter of 20– 30nm. In vitro biological evaluation indicates that the chitosan/Fe₃O₄/TiO₂@TiO₂ NW microspheres significantly enhanced attachment and proliferation of human umbilical vein endothelial cells compared with chitosan/Fe₃O₄/TiO₂ nanocomposite microspheres due to the presence of nanofibrous surface. Moreover, the microspheres showed photothermal antibacterial property to inhibit the growth of bacteria due to the presence of Fe₃O₄ component.     

Preparation of Fe3O4 particles from copper/iron ore cinder and their microwave absorption properties

In this study, magnetic Fe₃O₄ particles were prepared from copper/iron ore cider by precipitation oxidization method. The yield of Fe was 82.6 at%. XRD, TEM, SEM, EDS and microwave network analyzer were used to characterize the particles. The results showed that Fe₃O₄ particles were well crystallized and possessed an octahedral morphology, and the crystal size was about 200 nm; the sample with 70 wt% Fe₃O₄ exhibited the optimal absorbing ability, the minimum reflection loss was ?42.7 dB at 14.08 GHz and the bandwidth less than ?10 dB was about 4.2 GHz when the sample thickness was 1.9 mm. It was clearly demonstrated that the Fe₃O₄ particles prepared from copper/iron ore cider could be used as an effective microwave absorbing material.     

Luminomagnetic Nd3+ doped fluorapatite coated Fe3O4 nanostructures for biomedical applications

Luminomagnetic nanostructured Nd³⁺ doped fluorapatite (FAP) coated Fe₃O₄ nanoparticles were produced by hydrothermal method. X-ray diffraction analysis indicates that the prepared nanoparticles contain both FAP and Fe₃O₄ phases. Electron microscope analysis shows the formation of nanoparticles of Fe₃O₄ encased in rod shaped FAP nanoparticles of average length 40 nm. Magnetic measurements confirm the room temperature superparamagnetic nature of the nanoparticles with saturation magnetization value up to 7.8 emu/g. The prepared nanoparticles display strong near infrared (NIR) emission at 1060 nm under 800 nm excitation. Cell viability studies for 72 hour demonstrate the survival rate of over 84% with 500 μg/mL concentration indicating the good cytocompatibility of the prepared materials. The present Nd³⁺ doped FAP coated Fe₃O₄ nanostructure provides an excellent multifunctional platform for diagnostics and therapeutic applications.     

Magnetic-Fluorescent Nanocomposites Fe3O4@SiO2@ZnSe: Preparation and Characterization

Fe₃O₄@SiO₂@ZnSe composite nanoparticles with superparamagnetism and luminescence have been prepared by a facile chemical method. Nontoxic fluorescent ZnSe quantum dots were assembled around the Fe₃O₄-silica core–shell nanocomposite via chemical bonds formed between –COOH and –NH₂. Transmission electron microscopy images show that the nanocomposites are approximately spherical and between 50 nm and 80 nm in size. The bifunctional nanocomposites exhibit superparamagnetic behavior and good fluorescence intensity. Magnetic attraction test, vibrating sample magnetometer at 300 K, UV–visible absorption and fluorescence emission spectroscopy were applied to characterize the magnetic/fluorescent properties of the nanocomposites.     

Fabrication and Upconversion Luminescent Properties of Er3+‐Doped and Er3+/Yb3+ Codoped La2O2CN2 Nanofibers

La₂O₂CN₂:Er³⁺and La₂O₂CN₂:Er³⁺/Yb³⁺ upconversion (UC) luminescence nanofibers were successfully fabricated via cyanamidation of the respective relevant La₂O₃:Er³⁺ and La₂O₃:Er³⁺/Yb³⁺ nanofibers which were obtained by calcining the electrospun composite nanofibers. The morphologies, structures, and properties of the nanofibers are investigated. The mean diameters of La₂O₂CN₂:Er³⁺ and La₂O₂CN₂:Er³⁺/Yb³⁺ nanofibers are 179.46 ± 12.58 nm and 198.85 ± 17.07 nm, respectively. It is found that intense green and weak red emissions around 524, 542, and 658 nm corresponding to the ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_l5/2 energy levels transitions of Er³⁺ ions are observed for La₂O₂CN₂:Er³⁺ and La₂O₂CN₂:Er³⁺/Yb³⁺ nanofibers under the excitation of a 980‐nm diode laser. Moreover, the emitting colors of La₂O₂CN₂:Er³⁺ and La₂O₂CN₂:Er³⁺/Yb³⁺ nanofibers are all located in the green region. The upconversion luminescent mechanism and formation mechanism of the nanofibers are also proposed.