Magnetic Fe Nanoparticles Research Articles

Lightweight Fe@C hollow microspheres with tunable cavity for broadband microwave absorption

Lightweight and high-performance microwave absorption materials with wide effective bandwidth are highly required due to the increasingly severe electromagnetic radiation. It is now still imperative to elaborately tune the constituents and microstructures of absorbers for improving microwave absorption capability over wide frequency ranges. Herein, sulfonated polystyrene@Fe(OH)3@polydopamine (SPS@Fe(OH)3@PDA) microspheres are firstly synthesized with ferric sulphate and dopamine as precursors of Fe(OH)3 and amorphous carbon, and then thermally annealed at 600 °C to generate lightweight Fe@C hollow microspheres. The thermal annealing effectively decomposes SPS templates to gases, and carbonizes the PDA shell to amorphous carbon, which also reduces the ferric irons to magnetic Fe nanoparticles via the carbothermal reduction reaction. Interestingly, the microwave absorption performances of the Fe@C hollow microspheres are obviously improved by increasing the cavity sizes. The Fe@C hollow microspheres with the largest cavity of 780 nm exhibit the broadest effective absorption bandwidth of 7.5 GHz and the superior maximum reflection loss of −37.7 dB. These outstanding performances are attributed not only to the favourable synergistic effect of dielectric and magnetic losses, but also to the optimized hollow structure enhancing the attenuation capability and improving impedance matching. This work provides an efficient approach for designing and fabricating high-performance and broad-band microwave absorbers with tunable peak frequency.

Mechanochemically Synthesized Supported Magnetic Fe-Nanoparticles as Catalysts for Efficient Vanillin Production

Magnetically separable nanocatalysts were synthesized by incorporating ironnanoparticles on a mesoporous aluminosilicate (Al-SBA-15) through a mechanochemical grindingpathway in a single step. Noticeably, magnetic features were achieved by employing biomass wasteas a carbon source, which additionally may confer high oxygen functionalities to the resultingmaterial. The resulting catalysts were characterized using X-ray diffraction, X-ray photoelectronspectroscopy, transmission electron microscopy, scanning electron microscopy, porosimetry, andmagnetic susceptibility. The magnetic nanocatalysts were tested in the selective oxidative cleavagereaction of isoeugenol and vanillyl alcohol to vanillin. As a result, the magnetic nanocatalystsdemonstrated high catalytic activity, chemical stability, and enormous separation/reusabilityqualities. The origin of catalytic properties and its relationship with the iron oxide precursor wereanalyzed in terms of the chemical, morphological, and structural properties of the samples. Suchanalysis allows, thus, to highlight the superficial concentration of the iron entities and the interactionwith Al as key factors to obtain a good catalytic response.

Fabrication of MnO2@Fe rod-like composite with controllable weight ratios of Fe/MnO2 and excellent wideband electromagnetic absorption performance

In this research, we designed a rod-like shaped MnO2/Fe binary composite by loading magnetic Fe nanoparticles on MnO2 rods. The co-existence of MnO2 and Fe shows balanced impedance match and dual magnetic-dielectric loss ability. When MnO2/Fe sample presenting rod-like shape, the dielectric loss ability can be further boosted, owing to the formation of conductive network. After tuning weight ratio of Fe in a suitable value, the minimum reflection loss value (RLmin) can up to 35.0 dB with a matched thickness of 1.5 mm. Meanwhile, the effective frequency absorption region (fE) covers 5.6 GHz. To better understand the electromagnetic attenuation mechanism, the effects of components, microstructure as well as weight ratios on the electromagnetic absorption properties have been discussed in depth.

Fabrication and comparative study of magnetic Fe and α-Fe2O3 nanoparticles dispersed hybrid polymer (PVA + Chitosan) novel nanocomposite film

Abstract Incorporation of nanoparticles into polymer matrix allows the development of new features that differs from the pure materials. In this research, magnetic nanoparticles reinforced organic biodegradable polymer matrix based biocompatible nanocomposite films were fabricated. This work covered, synthesis of Iron (Fe) and Iron oxide (α-Fe2O3) nanoparticles by chemical reduction and sol-gel method respectively, fabrication of Fe/Polyvinyl alcohol (PVA)/Chitosan and α-Fe2O3/PVA/Chitosan nanocomposites by solvent casting method, and evaluation and comparison of their mechanical properties to find the superior biocompatible nanocomposite. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDX) analysis confirmed the size, structure, morphology and formation of Fe and α-Fe2O3 nanoparticles. Magnetic study showed that, synthesized α-Fe2O3 nanoparticle possess better magnetic properties than the Fe nanoparticle. The Fourier-transform infrared spectroscopy (FTIR) spectra confirmed the successful interaction of Fe and α-Fe2O3 nanoparticles with the polymer matrix. The Iron oxide dispersed (16.67 wt%) nanocomposite α-Fe2O3/PVA/Chitosan showed highest tensile strength and elastic modulus that is respectively 45% and 40% higher than the PVA polymer alone. This novel nanocomposite may potentially be useful in various biomedical applications.

Encapsulation of metallic iron magnetic nanoparticles by polyacrylamide in water suspensions

Theoretical consideration of the factors of the stability of metallic iron magnetic nanoparticles (MNPs) in water suspensions was done using extended DLVO (Derjaguin-Landau-Verwey-Overbeek) approach based on the balance among Van der Waals, electrostatic, magnetic and steric interactions. Magnetic and steric interactions dominate over other in suspensions of Fe MNPs. To test the theory Fe MNPs with average diameter 84 nm were synthesized by electrical explosion of wire and encapsulated by polyacrylamide in water suspension to provide steric repulsion. It was shown that encapsulation resulted in the efficient diminishing of the aggregation of metallic iron MNPs in water.

Encapsulation of metallic iron magnetic nanoparticles by polyacrylamide in water suspensions

Theoretical consideration of the factors of the stability of metallic iron magnetic nanoparticles (MNPs) in water suspensions was done using extended DLVO (Derjaguin-Landau-Verwey-Overbeek) approach based on the balance among Van der Waals, electrostatic, magnetic and steric interactions . Magnetic and steric interactions dominate over other in suspensions of Fe MNPs. To test the theory Fe MNPs with average diameter 84 nm were synthesized by electrical explosion of wire and encapsulated by polyacrylamide in water suspension to provide steric repulsion. It was shown that encapsulation resulted in the efficient diminishing of the aggregation of metallic iron MNPs in water.

Using Fe magnetic nanoparticles for reducing evaporation from water surface in small scale

Using Fe magnetic nanoparticles for reducing evaporation from water surface in small scale

In-situ one-step synthesis of carbon-encapsulated naked magnetic metal nanoparticles conducted without additional reductants and agents.

C-encapsulated highly pure Ni, Co, and Fe magnetic nanoparticles (MNPs/C) were synthesized by an innovative one-step in-situ plasma in liquid method (solution plasma processing, SPP) without any additional reductants, agents, or treatment. Successful encapsulation of MNPs was demonstrated by using inductively coupled plasma-atomic emission spectrometry and cyclic voltammetry techniques. The obtained X-ray diffraction patterns and transmission electron microscopy images corresponded to MNPs with average diameters of 5 nm and good crystalline structure. The C capsules with spherical shapes (containing onion-like layers) were characterized by uniform sizes (ranging from 20 nm to 30 nm) and chain-like morphologies. The synthesized MNPs/C exhibited superparamagnetic properties at room temperature and might be utilized in data storage, biomedical, and energy applications since various NPs (including bimetallic ones) could be easily prepared by changing working electrodes. This study shows the potential of SPP to be a candidate for the next-generation synthesis method of NPs/C.

Photocatalytic degradation of bromophenol blue in aqueous medium using chitosan conjugated magnetic nanoparticles

Three different chitosan conjugated magnetic nanoparticles (CCMN) of Co, Ni and Fe were prepared using co-precipitation method. The prepared CCMN were characterized by scanning electron microscopy (SEM), Xray diffraction (XRD) and Fourier transform infra-red (FT-IR) spectroscopic techniques. The SEM results showed a smooth surface morphology with almost uniform particle size and irregular shape structure for all CCMN. The XRD study revealed the crystalline structure in case of Co-CCMN and Ni-CCMN, while amorphous nature of Fe-CCMN was observed. The particle size of the prepared CCMN was found to be <95 nm, as confirmed from SEM and XRD analyses. Similarly, FT-IR analysis showed the incorporation and conjugation of Co, Ni and Fe magnetic nanoparticles into the chitosan polymer matrix. The point of zero charge (PZC) was found to be 7.41 for Co-CCMN and Ni-CCMN and 7.70 for Fe-CCMN. The photocatalytic activity of the prepared CCMN was investigated under UV light irradiation (254 nm and 15 W) in the aqueous medium using bromophenol blue (BPB). The photocatalytic process was monitored by UV-visible spectrophotometer for different irradiation times (0 to 10 h). The results showed that all the prepared CCMN displayed good to excellent photocatalytic property where the highest degradation was exhibited by Fe-CCMN (94.5%), followed by Co-CCMN (85.1%) and Ni-CCMN (83.0%). The prepared catalysts were recycled and reused, maintaining good photocatalytic activity for four consecutive batches.

Microbial-Physical Synthesis of Fe and Fe3O4 Magnetic Nanoparticles Using Aspergillus niger YESM1 and Supercritical Condition of Ethanol

Magnetic Fe and Fe3O4 (magnetite) nanoparticles are successfully synthesized using Aspergillus niger YESM 1 and supercritical condition of liquids. Aspergillus niger is used for decomposition of FeSO4 and FeCl3 to FeS and Fe2O3, respectively. The produced particles are exposed to supercritical condition of ethanol for 1 hour at 300°C and pressure of 850 psi. The phase structure and the morphology measurements yield pure iron and major Fe3O4 spherical nanoparticles with average size of 18 and 50 nm, respectively. The crystal size amounts to 9 nm for Fe and 8 nm for Fe3O4. The magnetic properties are measured to exhibit superparamagnetic- and ferromagnetic-like behaviors for Fe and Fe3O4 nanoparticles, respectively. The saturation magnetization amounts to 112 and 68 emu/g for Fe and Fe3O4, respectively. The obtained results open new route for using the biophysical method for large-scale production of highly magnetic nanoparticles to be used for biomedical applications.

Magnetic γ-Fe2O3, Fe3O4, and Fe nanoparticles confined within ordered mesoporous carbons as efficient microwave absorbers.

A series of magnetic γ-Fe2O3, Fe3O4, and Fe nanoparticles have been successfully introduced into the mesochannels of ordered mesoporous carbons by the combination of the impregnation of iron salt precursors and then in situ hydrolysis, pyrolysis and reduction processes. The magnetic nanoparticles are uniformly dispersed and confined within the mesopores of mesoporous carbons. Although the as-prepared magnetic mesoporous carbon composites have high contents of magnetic components, they still possess very high specific surface areas and pore volumes. The magnetic hysteresis loops measurements indicate that the magnetic constituents are poorly-crystalline nanoparticles and their saturation magnetization is evidently smaller than bulky magnetic materials. The confinement of magnetic nanoparticles within the mesopores of mesoporous carbons results in the decrease of the complex permittivity and the increase of the complex permeability of the magnetic nanocomposites. The maximum reflection loss (RL) values of -32 dB at 11.3 GHz and a broad absorption band (over 2 GHz) with RL values <-10 dB are obtained for 10-Fe3O4-CMK-3 and 10-γ-Fe2O3-CMK-3 composites in a frequency range of 8.2-12.4 GHz (X-band), showing their great potentials in microwave absorption. This research opens a new method and idea for developing novel magnetic mesoporous carbon composites as high-performance microwave absorbing materials.

Magnetic Carbon Nanofiber Networks as Support for Ionic Liquid Based Catalyst

In this work, the ionic liquid (IL) 1-hexyl-3-methyl-imidazolium bromide (HMIm.Br) containing Pd suspended nanoparticles was supported on a nanostructured magnetically recoverable carbon nanofiber network. The magnetic material was prepared by a simple reaction of ethanol directly with a nanostructured hematite. SEM, XRD, Mössbauer, Raman, TG/DTA, BET surface area and magnetization analyses suggested that the network is based on carbon nanofibers with carbon coated magnetic Fe nanoparticles. These magnetic networks offer a high exposed carbon fiber area, which has a good interaction with the IL to form a thin layer. Preliminary studies with a Pd dispersed in supported IL as catalyst for the hydrogenation of 1,5-cyclooctadiene showed a membrane effect, which leads to an important increase on the selective hydrogenation of 1,5-cyclooctadiene to cyclooctene.

Magnetically-separable hierarchically porous carbon monoliths with partially graphitized structures as excellent adsorbents for dyes

Magnetically-separable hierarchically porous carbon monoliths with partially graphitized structures were synthesized through confinement self-assembly in polyurethane (PU) foam associated with a direct carbonization process from triblock copolymer F127, phenolic resol and ferric nitrate. It was observed that the magnetic Fe nanoparticles were embedded in the walls of graphitic porous carbon matrix, and the resulting materials exhibited hierarchically porous structure with macropores of 100–450 μm, mesopore size of 4.8 nm, BET surface area of 723 m2/g, pore volume of 0.46 cm3/g, and saturation magnetization of 3.1 emu/g. Using methylene blue as model dye pollutant in water, the carbon monolith materials showed high adsorption capacity of 190 mg/g, exhibiting excellent adsorption characteristics desirable for the application in adsorption of dyes and easy separation under an external magnetic field.

Synthesis and microwave absorption properties of Fe–C nanofibers by electrospinning with disperse Fe nanoparticles parceled by carbon

The Fe–C nanofibers were achieved using electrospinning technique. The microstructure was characterized by field emission scanning electron microscope and high resolution transmission electron microscopy equipped with energy-dispersive X-ray analysis. The results indicated that magnetic Fe nanoparticles uniformly dispersed along nanofibers and were parceled by carbon matrix. For the Fe–C nanofibers/paraffin composite, a minimum reflection loss (RL) value of −44dB was observed at 4.2GHz. Moreover, the frequency range with RL peak value below −10dB was achieved in a wide frequency range from 2.2 to 13.2GHz. The excellent microwave absorption properties were due to the combination of complex permeability and permittivity resulting from magnetic Fe particles and lightweight carbon.

Immobilization of DNA on Fe nanoparticles and their hybridization to functionalized surface

Magnetic Fe nanoparticles were fabricated using a magnetron–sputtering-based gas-phase condensation method, and they have an average size of 20 nm. The Fe nanoparticles were modified by 3-aminopropyltriethoxy silane, and were subsequently activated by glutaraldehyde, and then amino modified DNA oligomers were loaded on glutaraldehyde activated Fe nanoparticles. Their surface was investigated and confirmed by X-ray photoelectron spectroscopy (XPS). The concentrations of 3-aminopropyltriethoxy silane and glutaraldehyde play important roles for subsequent DNA immobilization, and their optimal concentrations are 0.5 vol% and 5.0 wt%, respectively. The loading level of DNA oligomers on Fe nanoparticles was quantitatively evaluated. We found that the presence of sodium dodecyl sulfate (SDS) surfactant can significantly increase the DNA loading level and the highest loading value reached to 47 mol DNA/mol Fe nanoparticles. The DNA–Fe complexes can be selectively hybridized to the DNA functionalized surface.

In situ modification of Fe and Ni magnetic nanopowders produced by the electrical explosion of wire

Iron and nickel spherical magnetic nanoparticles (MNPs) with mean diameter 50–80 nm were prepared by the electric explosion of wire. The advantage of this method is that it provides a very high production rate up to 200 g/h and requires low energy consumption of 25 kW h/kg. The as-prepared MNPs were modified in situ in hexane, toluene, chloroform, and the solutions of polystyrene in toluene, in an inert atmosphere at room temperature in order to provide both the stability at ambient conditions and tunable surface properties. Hexane was an inert liquid for Fe and Ni MNPs. In the case of toluene the surface of as-prepared Fe or Ni MNPs acted as a catalyst for the condensation reaction of aromatic organic compounds forming irregular polycyclic structures. The treatment with toluene led to the deposition of carbon and formation of “hair-like” ordered structures on the surface of the MNPs. Chloroform chemically interacted with Fe MNPs, forming FeCl2. The treatment of MNPs with the solution of polystyrene in toluene resulted in the adsorption of polymer and the formation of 3–6 nm polymeric coatings on the surface. The obtained magnetic properties (like the magnetization value for Ni MNPs up to 52 emu/g and Fe MNPs up to 179 emu/g) at room temperature make these MNPs competitive candidates for nanocomposites for microwave and other technological applications.

Low temperature solventless synthesis and characterization of Ni and Fe magnetic nanoparticles

We have successfully implemented a facile, one-pot solventless synthesis procedure starting from acetylacetonate salts and CaH(2) to obtain carbon-coated ferromagnetic metallic Ni and Fe nanoparticles at low temperature. The use of CaH(2) as a reductant drastically reduces reaction temperature down to 140 °C.

Synthesis and characterization of superparamagnetic core–shell micrometre-sized particles of narrow size distribution by a swelling process

In previous publications we described several methods to prepare iron oxide and Fe magnetic nanoparticles entrapped within poly(divinyl benzene) or carbon composite microspheres for various biomedical applications. However, these methods involved relatively complex synthetic processes, the size of the entrapped nanoparticles could hardly be manipulated and the obtained particles were mostly ferromagnetic. The present work describes a new simple approach to overcome these obstacles. For this purpose, core–shell polystyrene/(poly(divinyl benzene)/ferrocene) and polystyrene/(poly(divinyl benzene–styrene)/ferrocene) micrometre-sized particles of narrow size distribution were prepared by a room temperature swelling of uniform polystyrene template microspheres dispersed in an aqueous continuous phase with emulsion droplets of a swelling solvent, such as toluene containing the monomers styrene and/or divinyl benzene, and the initiators azoisobutyronitrile and ferrocene. The monomer(s) within the swollen uniform polystyrene template microspheres were then polymerized at elevated temperature. Superparamagnetic and ferromagnetic poly(divinyl benzene)–Fe3O4 and poly(styrene–divinyl benzene)–Fe3O4 composite microspheres of narrow size distribution were then formed by annealing the previous micrometre-sized composite particles containing ferrocene at 330 °C for 2 h under ambient atmosphere in a sealed cell, followed by the dissolution of the polystyrene template part. This study shows that the size of the Fe3O4 nanoparticles entrapped within the poly(divinyl benzene) and poly(divinyl benzene–styrene) matrices can be controlled by adjusting the [divinyl benzene]/[styrene] volume ratio. Superparamagnetic C–Fe micrometre-sized particles of narrow size distribution were formed by annealing the PDVB–Fe3O4 particles at 450 °C under hydrogen atmosphere for 2 h.

Onion-like carbon-encapsulated Co, Ni, and Fe magnetic nanoparticles with low cytotoxicity synthesized by a pulsed plasma in a liquid

We synthesized onion-like carbon-encapsulated Co, Ni, and Fe (Co–C, Ni–C, and Fe–C) magnetic nanoparticles with low cytotoxicity using pulsed plasma in a liquid. The pulsed plasma is induced by a low-voltage spark discharge submerged in a dielectric liquid. The face-centered cubic Co and Ni, and body-centered cubic Fe core nanoparticles showed good crystalline structures with an average size between 20 and 30nm were encapsulated in onion-like carbon coatings with a thickness of 2–10nm. Vibrating-sample magnetometer measurements revealed the ferromagnetic properties of as-synthesized samples at room temperature (Co–C=360Oe, Fe–C=380Oe, and Ni–C=211Oe). Raman-spectroscopy analysis found onion-like carbon shells composed of well-organized graphitic structures. Thermal gravimetric analysis showed a high stability of the as-synthesized samples under thermal treatment and oxidation. Cytotoxicity measurements showed higher cancer cell viability than samples synthesized by different methods.

A feasible approach for preparing remanence enhanced NdFeB based permanent magnetic composites

NdFeB based permanent magnetic nanocomposites were prepared by depositing soft magnetic Fe, Co, or Fe65Co35 nanoparticles on the melt spun NdFeB powders with near single phase composition by a chemical reduction method. The effects of the reduction process, the composition, and the concentrations of metal ions on the magnetic properties of nanocomposites were investigated. Introducing and increasing soft nanoparticle content improved the remanence and maximum energy product of the nanocomposites at the expense of coercivity. Fe65Co35 coated NdFeB powders had higher remanence and energy product than Co or Fe coated powders. The inter-grain exchange coupling between hard and soft magnetic grains was demonstrated by the smooth demagnetization curve with high remanent polarization. Remanence enhanced bulk magnets were also fabricated by consolidating the nanocomposite powders using spark plasma sintering (SPS) technique.