Influence of iron (III) acetylacetonate on structure and electrical conductivity of Fe3O4/carbon composite nanofibers

Fe₃O₄/carbon composite nanofibers were prepared by electrospinning polyacrylonitrile (PAN), iron (III) acetylacetonate (AAI) and dimethyl formamide (DMF) compound solutions, followed by stabilization and carbonization processes. Emphasis was put on the influence of AAI on reactions during stabilization and carbonization. The effect of Fe₃O₄ on catalytic graphitization and electrical conductivity was also studied. Experimental results show that AAI has participated in the reactions and structural changes of PAN during stabilization and carbonization, and is evidenced to promote the processes. Fe₃O₄ nanoparticles exhibit catalytic effect on carbonization process that promote graphitization by a catalytic effect at low AAI content and inhibit the formation of graphitized layers when AAI content is excessive. Therefore, there exists an optimum AAI content (C_o) where composite nanofibers show the maximum graphitization degree and electrical conductivity. With proper amount of AAI addition, Fe₃O₄/carbon composite nanofibers showing high graphite degree and electrical conductivity could be achieved.     

Electromagnetic interference shielding effectiveness of hybrid multifunctional Fe3O4/carbon nanofiber composite

Electromagnetic interference shielding effectiveness (EMI SE) of multifunctional Fe₃O₄/carbon nanofiber composites in the X-band region (8.2–12.4 GHz) is studied. Here, we examine the contributing effects of various parameters such as Fe₃O₄ content, carbonization temperature and thickness on total shielding efficiency (SE_total) of different samples. The maximum EMI SE of 67.9 dB is obtained for composite of 5 wt.% Fe₃O₄ (0.7 mm thick) with the dominant shielding by absorption (SE_A) of electromagnetic radiation. The enhanced electromagnetic shielding performance of Fe₃O₄/carbon nanofiber composites is attributed to the increment of both magnetic and dielectric losses due to the incorporation of magnetite nanofiller (Fe₃O₄) in electrically conducting carbon nanofiber matrix as well as the specific nanofibrous structure of carbon nanofiber mats, which forms a higher aspect ratio structure with randomly aligned nanofibers. Furthermore, we prove that the addition of elastomeric polydimethylsiloxane (PDMS) as a coating for carbon nanofiber composite strengthens the composite structure without interfering with its electromagnetic shielding efficiency.     

Synthesis and strengthened microwave absorption properties of three-dimensional porous Fe3O4/graphene composite foam

The three-dimensional porous Fe₃O₄/graphene composite foam as a new kind of absorbing composite with electrical loss and magnetic loss was successfully synthesized by a facile method. Fe₃O₄ was evenly attached on structure of graphene sheets which overlapped with each other to form three-dimensional porous graphene foam. The results revealed that when the mass ratio of graphene oxide (GO) and Fe₃O₄ was 1:1, the Fe₃O₄/graphene composite foam possessed the best absorption properties: the minimum reflection loss was up to ??45.08?dB when the thickness was 2.5?mm and the bandwidth below ??10?dB was 6.7?GHz when the content of the composite foam absorbents was just 8%. The micron-sized three-dimensional porous structure provided more propagation paths, enhancing the energy conversion of incident electromagnetic waves. The addition of Fe₃O₄ contributed to improving the impedance matching performance and magnetic loss. The three-dimensional porous Fe₃O₄/graphene composite foam was a kind of high-efficiency wave absorber, providing a new idea for the development of microwave absorbing materials.     

Modulation of electromagnetic wave absorption by carbon shell thickness in carbon encapsulated magnetite nanospindles–poly(vinylidene fluoride) composites

A series of Fe₃O₄/C core–shell nanospindles with different shell thickness have been synthesized by a wet chemical method and subsequent high-temperature carbonization. The thickness of carbon shell can be well adjusted from 9 to 32 nm by changing the addition amounts of resorcinol and formaldehyde precursors during the coating process. Structure and morphology characterizations reveal that the carbon shell is amorphous structure and uniformly encapsulates on porous Fe₃O₄ nanospindles. For the first time, a flexible Fe₃O₄/C/poly(vinylidene fluoride) (PVDF) composite absorber was prepared by embedding the core–shell Fe₃O₄/C nanospindles in PVDF matrix. The electromagnetic properties of the composite show strong dependence on the carbon-shell thickness. The impedance matching for electromagnetic absorption is improved by the synergy effect between Fe₃O₄ nanospindles and encapsulated carbon shell. The Fe₃O₄/C/PVDF composite with thick carbon shell exhibits strong electromagnetic wave absorbing ability with thin absorber thickness. The minimum reflection loss for the absorber with thickness of 2.1 mm can reach −38.8 dB.     

Optically transparent polymer composites: A study on the influence of filler/dopant on electromagnetic interference shielding mechanism

Composite materials made of polymers and carbon-based ferromagnetic filler are attractive for electromagnetic interference shielding through a combination of reflection and microwave absorption. It is possible to enhance their shielding properties by controlling electrical conductivity, dielectric, and magnetic properties. In this work, the aforementioned properties are tailored to achieve optically transparent films with microwave absorbing properties. Nanocarbon materials, namely carbon nanotubes, graphene nanoribbons (GNR) and their ferromagnetic nanocomposites with Fe₃O₄ and cobalt in PVA-PEDOT:PSS matrix were made and tested in X-band. The highest shielding effectiveness for PVA films with nanocarbon filler was observed for 0.5 wt% GNR − Fe₃O₄ at 16.36 dB (9.7 GHz) with 79.8% transmittance.     

Porous Fe3O4/C microspheres for efficient broadband electromagnetic wave absorption

Porous Fe₃O₄/C microspheres, which were Fe₃O₄ nanocrystals (～8?nm) embedded in an open nanostructured carbon network, were successfully synthesized via a facile hydrothermal process. The porous Fe₃O₄/C microspheres possessed many distinct attributes that facilitate efficient broadband electromagnetic wave absorption (EMWA). EMWs were attenuated through multiple reflections and absorption in the 3D interconnected porous structure of the microspheres; these processes collectively improved the interaction between the EMWs and the absorber. Additionally, the carbon network and embedded Fe₃O₄ nanoparticles caused significant dielectric losses and magnetic losses, respectively, which also enhanced EMWA. The EMWA characteristics of the microspheres could be precisely tuned via changing the carbon content to achieve optimized impedance matching. Porous Fe₃O₄/C microspheres with a 71.5?wt% carbon content displayed particularly impressive EMWA properties: a maximum reflection loss (RL) value of ??31.75 across broad band frequencies in the range of 7.76–12.88?GHz (RL < ?10?dB) at an absorber thickness of 3.0?mm. These excellent EMWA properties may be attributed to both dielectric loss (carbon) and magnetic loss (Fe₃O₄). Additionally, the 3D interconnected porous structure of the Fe₃O₄/C microspheres is especially favorable for impedance matching.     

Magnetite/graphene oxide/Prussian blue composite with robust effectiveness for electromagnetic interference shielding

Considering the promising efficiency of composites, in the current study, a graphene oxide (GO)-magnetite-Prussian blue (PB) composite material was prepared. The composite exhibited electrical conductivity, magnetic permeability, and permittivity nature, and was evaluated using electromagnetic interference (EMI) shielding studies. GO was developed by the Hummer's method, ferrite (Fe₃O₄) was incorporated by the sol-gel method, and PB was introduced in the mixture by an in-situ process. The fabricated samples were studied by X-ray diffraction, Raman Spectroscopy, Fourier-transform infrared spectroscopy along with EMI shielding efficiency (SE) evaluation. The SE of ?71.66 dB of reflection losses was measured at a frequency of 1.5 MHz. The GO/Fe₃O₄/PB composite provided the best results for the detection in the 1–18 MHz frequency range because of its excellent electric and magnetic properties. The obtained results demonstrated that the GO/Fe₃O₄/PB composite has promising potential applications in EMI shielding.     

A study of the electrical properties of carbon nanotube-NiFe2O4 composites: Effect of the surface treatment of the carbon nanotubes

Novel carbon nanotube-NiFe₂O₄ composite materials have been prepared for the first time by in situ chemical precipitation of metal hydroxides in ethanol in the presence of carbon nanotubes (CNTs) and followed by hydrothermal processing. The obtained composite powders were characterized using XRD, TEM and EDS. The effect of surface oxidation treatment of CNTs on their properties was investigated by FTIR, zeta potential and hydrodynamic radius distribution characterization. Electrical conductivity measurements show that surface oxidation treatment of CNTs can improve the electrical conductivity of the composites more pronouncedly than pristine CNTs do. With 10 wt.% addition of surface treated CNTs, the electrical conductivity is increased by 5 orders of magnitude. The surface oxidized CNTs are crucial for this significant increase in electrical conductivity, which provides strong adhesion between the nanotubes and the matrix to give a homogeneous carbon nanotube-NiFe₂O₄ composite.     

Effect of Fe doping on structure,magnetic and electrical properties La0.7Ca0.3Mn0.5Fe0.5O3 manganite

The crystal and magnetic structures of La_0.7Ca_0.3Mn_0.5Fe_0.5O₃ compound have been studied by neutron powder diffraction in the temperature range of 10–300 К. The magnetization and electrical resistivity measurements have been also performed in the temperature range of 5–300?K in magnetic fields up to 1?T. These experimental results indicate a formation of a complex magnetic state in which the long-range antiferromagnetic G-type phase coexists with the short-range ferromagnetic clusters. The electrical conductivity of La_0.7Ca_0.3Mn_0.5Fe_0.5O₃ demonstrates an anomalous temperature behavior suggesting a switching between different states. The origin of the unconventional magnetic state, the mechanisms of the electrical conductivity, and correlation between magnetic and transport properties in this manganite have been discussed.     

Electrospun magnetic carbon composite fibers: Synthesis and electromagnetic wave absorption characteristics

Electrospun polyacrylonitrile (PAN)‐based carbon composite fibers embedded with magnetic nanoparticles have been developed as materials for electromagnetic wave absorption. The nanocomposite fibers were prepared by electrospinning from a dispersion of magnetite (Fe₃O₄) nanoparticles stabilized by L ‐glutamic acid in a solution of PAN and N, N‐dimethyl formamide. The Fe₃O₄‐embedded PAN nanofibers were stabilized at 270°C in air and carbonized at 800°C in nitrogen. The Fe₃O₄ nanoparticles were crystalline with a particle size of about 7 nm, most of which was reduced to Fe₃C with agglomerates of up to 50 nm diameter in the carbon fibers. The carbon morphology was mostly disordered, but exhibited a layered graphitic structure in the vicinity of the nanoparticles. The carbon composite fiber exhibited ferromagnetic behavior, and the induced magnetic saturation per unit mass of fibers increased with increasing Fe₃O₄ content in the precursor. The complex relative dielectric permittivity was tuned by adjusting the amount of Fe₃O₄ in the carbon fiber precursor. With increasing Fe₃O₄ content, good electromagnetic wave absorption characteristics were observed below 6 GHz, even for samples with fiber loadings as low as 5 wt %. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Highly dispersible carbon composited Fe3O4 nanoparticles in an aqueous solvent via normal pressure liquid reaction

In this study, a simple fabrication of carbon composited Fe₃O₄ nanoparticles was carried out under reflux condition using glucose as a carbon precursor. The carbon composited Fe₃O₄ nanoparticles having a core-shell structure were synthesized in a low-temperature and low-pressure atmosphere instead of in an autoclave. Simple carbonization without inert gas and extra heating was complemented by adding sulfuric acid, which has an important role as a carbonization catalyst. In addition, sulfuric acid also acted as the controller of such surface properties as surface area by an etching effect. The prepared nanoparticles have uniform and continuous carbon layers, which have several functions, such as stable dispersibility and an increase of electron conductivity. carbon composited Fe₃O₄ nanoparticles were investigated with zeta-potential, particle size distribution, Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and a vibrating sample magnetometer. The results provide clear evidence that carbon-coated Fe₃O₄ nanoparticles are applicable in electrochemical industrial fields.     

Fabrication of PLA/MWCNT/Fe3O4 composite nanofibers for leukemia cancer cells

The efficient delivery of daunorubicin loaded poly (lactic acid) (PLA)/multiwalled carbon nanotubes (MWCNT)/Fe₃O₄ composite nanofibers was investigated. The synthesized nanofibers were characterized using SEM, TEM, and XRD analysis. The proliferation inhibition effect of PLA/MWCNT/Fe₃O₄ nanofibrous scaffolds on leukemia K562 cell lines was investigated. The effect of nanofiber concentration on the daunorubicin delivery in the absence and presence of external magnetic field was also evaluated. The results indicated that the incorporation of daunorubicin into the prepared nanofibrous scaffold under applied magnetic field could have synergistic cytotoxic effect on leukemia cancer cells. The drug release mechanism followed the non-Fickian transport.     

Synthesis and mechanical properties characterization of multiferroic BiFeO3-CoFe2O4 composite nanofibers

Multiferroic nanofibers with excellent mechanical properties have great potential applications in multifunctional nanodevices. BiFeO₃-CoFe₂O₄ (BFO-CFO) composite nanofibers with different molar ratios were successfully synthesized by sol-gel-based electrospinning method. The mechanical properties of BFO-CFO composite nanofibers were examined by nanoindentation technique, and further investigated by amplitude modulation-frequency modulation (AM-FM) method based on atomic force microscopy (AFM). The results of AM-FM showed that the elastic moduli of BFO-CFO composite nanofibers increased with the increase of CFO ratio, which was consistent with the results of nanoindentation. These results indicated that AFM-based AM-FM is a powerful method for nondestructively investigating the mechanical properties of materials at nanoscale, and that the results of BFO-CFO composite nanofibers are also of practical importance for the future applications of multifunctional nanodevices.     

Synthesis and characterization of poly(styrene-co-fluorescein O-methacrylate)/poly(N-isopropylacrylamide)-Fe3O4 core/shell composite particles

We demonstrate the synthesis and characteristics of multifunctional poly(styrene-co-fluorescein O-methacrylate)/poly(N-isopropylacrylamide)-Fe₃O₄ [P(St/FMA)/PNIPAAm-Fe₃O₄] core/shell composite particles, in which the core consists of fluorescent materials and the shell consists of magnetic and thermo-responsive components. First, core/shell particles consisting of a fluorescent P(St/FMA) core and thermo-responsive PNIPAAm-rich shell were prepared by two-stage shot-growth emulsion polymerization. Next, Fe₃O₄ nanoparticles were immobilized via electrostatic interactions and then covalently linked to the shell via surface coordinated Aphen by a coupling reaction in order to obtain magnetic properties. The morphology of P(St/FMA)/PNIPAAm-Fe₃O₄ composite particles, confirmed by transmission electron microscopy (TEM), reveals that Fe₃O₄ nanoparticles are located in the PNIPAAm shell. The thermo-sensitivity of composite particles to hydrodynamic diameter was confirmed by using dynamic light scattering (DLS). Photoluminescence (PL) spectra indicate that the fluorescence emission intensity of core/shell particles is highly sensitive to the pH of an aqueous medium. The core/shell composite particles exhibited a combination of fluorescent, magnetic, pH and thermo-responsive behavior.     

Synthesis of magnetically separable ordered mesoporous carbons from F127/[Ni(H2O)6](NO3)2/resorcinol-formaldehyde composites

An easy method is described for the synthesis of a mesostructured Ni/ordered mesoporous carbon (OMC) composite with a highly ordered cubic structure (space group Im3m). This synthesis was carried out by the carbonization of the F127/[Ni(H₂O)₆](NO₃)₂/RF (resorcinol-formaldehyde) composite self-assembled in an alkaline medium. The effects of nickel loading content and carbonization temperature on the morphologies, pore features, structures and magnetic properties of these Ni/OMC composites were investigated using the thermogravimetric analysis, X-ray diffraction, nitrogen sorption, transmission electron microscopy and vibrating-sample magnetometer measurements. It was found that Ni²⁺ was captured by the network of F127/RF and further reduced into metallic Ni nanoparticles during the carbonization. The nickel nanoparticles were well-dispersed in the ordered mesoporous carbon walls. The Ni/OMC composites exhibit the soft ferromagnetic behavior and the magnetization parameters can be adjusted by the content of nickel and the carbonization temperatures. The excellent acid-resistant property of the magnetic materials makes them useful in magnetic separation.     

Enhanced microwave absorption properties of electrospun PEK‐C nanofibers loaded with Fe3O4/CNTs hybrid nanoparticles

The phenolphthalein polyetherketone (PEK‐C) nanofibers loaded with Fe₃O₄/carbon nanotubes (CNTs) hybrid nanoparticles were synthesized by electrospinning technique. The morphology, composition, and thermal stability of composite nanofibers were characterized by scanning electron microscope, energy dispersive spectrometer, and thermogravimetric analysis, respectively. The complex permittivity and permeability of composite nanofibers in the microwave frequency range of X band (8.2–12.4 GHz) were measured by vector network analyzer using wave‐guide method. The results show that the permittivity and dielectric loss were enhanced obviously by adding CNTs. With the W _CNTs increasing to 5%, the minimum R _L value reaches ?41.4 dB at 9.3 GHz with a matching thickness of 1.7 mm and exceeds ?10 dB with thickness of 1.4–1.8 mm in the whole X band. The enhanced microwave absorption properties are mainly attributed to tunable electromagnetic parameters and thus a better impedance matching characteristic by mixing CNTs with Fe₃O₄ nanoparticles within proper ranges loaded in PEK‐C nanofibers. POLYM. ENG. SCI., 57:1186–1192, 2017. © 2017 Society of Plastics Engineers     

New Magnetic Polymer Nanocomposites on the Basis of Isotactic Polypropylene and Magnetite Nanoparticles for Adsorption of Ultrahigh Frequency Electromagnetic Waves

In this study, we report about the preparation of magnetic polymer nanocomposites on the basis of isotactic polypropylene and magnetite Fe₃O₄ nanoparticles. The structure and composition of polymer nanocomposite materials have been studied by scanning electron microscopy, atomic force microscopy, and X-ray dispersive analysis. The magnetic properties of polymer nanocomposites based on PP+Fe₃O₄have been investigated. It is found that not significant adhesion and agglomeration of nanoparticles occur, by increasing the nanoparticle content in polymer matrix up to 40%, and therefore they act as single-domain nanoparticles. The samples of nanocomposites based on PP+Fe₃O₄, with up to 40% content of Fe₃O₄, exhibit superparamagnetic properties. It was also found out that the magnetic polymer nanocomposite material based on PP+Fe₃O₄ is able to absorb ultrahigh frequency electromagnetic waves in the frequencies range from 0.1 to 30?GHz. The increase in Fe₃O₄ concentration from 5 to 40% at the 400?µm thicknesses of the films leads to an increase in absorption of electromagnetic waves of high frequency from 15 to 22.7%.     

Novel electromagnetic interference shielding effectiveness in the microwave band of magnetic nitrile butadiene rubber/magnetite nanocomposites

A novel nitrile butadiene rubber (NBR)/magnetite (Fe₃O₄) nanocomposite for electromagnetic interference (EMI) shielding at microwave frequency was successfully fabricated. The structural features of as-synthesized magnetite and NBR/Fe₃O₄ were examined by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The number of elastically effective chains, volume fraction of rubber, interparticle distance among conductive sites, polymer–filler interaction, and porosity of the nanocomposites were evaluated. The mechanical properties, including the tensile strength, elongation at break, and hardness, of the composites were measured. The static electrical properties, such as the electrical conductivity, carrier mobility, and number of charge carriers, as a function of magnetite content were evaluated. The interrelation between the electrical conductivity, shielding effectiveness (SE), dielectric constant, and skin depth of the composites are discussed. Finally, the EMI SE versus frequency was tested. The results reveal that an SE of 28–91 dB against EMI in the 1–12 GHz range depended on the loading of the conducting magnetite within the NBR matrix. Accordingly, these nanocomposites may used in the field of microwave absorption devices. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Fabrication and characterization of polymer composites surface coated Fe3O4/MWCNTs hybrid buckypaper as a novel microwave‐absorbing structure

A naval hybrid buckypaper was fabricated by vacuum filtration method with monodispersion solution of Fe₃O₄ decorated Multiwalled carbon nanotubes (MWCNTs). The morphology, element composition and phase structure of hybrid buckypaper were characterized by field‐emission scanning electron microscope, energy dispersive spectrometer, and X‐ray diffraction. The microwave absorption and complex electromagnetic properties of the composites surface coated MWCNTs buckypaper (or Fe₃O₄/MWCNTs hybrid buckypaper) have been investigated in the frequency range of 8–18 GHz. The results indicate that the microwave absorption properties of composite structure have been evidently improved due to the Fe₃O₄/MWCNTs hybrid buckypaper' high magnetic loss and suitable dielectric loss properties. The reflection loss of composite surface coated Fe₃O₄/MWCNTs hybrid buckypaper (with a matching thickness d = 0.1 mm) is below ?10 dB in the frequency range of 13–18 GHz, and the minimum value is ?15.3 dB at 15.7 GHz. Thus, Fe₃O₄/MWCNTs hybrid buckypaper can become a promising candidate for electromagnetic‐wave‐absorption materials with strong‐absorption, thin‐thickness and light‐weight characteristics. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41974.     

Crystallinity,conductivity, and magnetic properties of PVDF‐Fe3O4 composite films

The formation of Fe₃O₄ nanoparticles by hydrothermal process has been studied. X‐ray Diffraction measurements were carried out to distinguish between the phases formed during the synthesis. Using the synthesized Fe₃O₄ nanoparticles, poly(vinyledene fluoride)‐Fe₃O₄ composite films were prepared by spin coating method. Scanning electron microscopy of the composite films showed the presence of Fe₃O₄ nanoparticles in the form of aggregates on the surface and inside of the porous polymer matrix. Differential Scanning calorimetry revealed that the crystallinity of PVDF decreased with the addition of Fe₃O₄. The conductitivity of the composite films was strongly influenced by the Fe₃O₄ content; conductivity increased with increase in Fe₃O₄ content. Vibration sample magnetometry results revealed the ferromagnetic behavior of the synthesized iron oxide nanoparticles with a Ms value of 74.50 emu/g. Also the presence of Fe₃O₄ nanoparticles rendered the composite films magnetic. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011