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Iron (Fe)-based nanoparticles are extremely valuable in biomedical applications owing to their low toxicity and high magnetization values at room temperature. In this study, we synthesized nearly monodisperse iron oxide (Fe₃O₄) and Fe@Fe₃O₄ (core: Fe, shell: Fe₃O${}_4)$ nanoparticles in aqueous medium under argon flow and then, coated them with various biocompatible ligands and silica. In this study, eight types of surface-modified nanoparticles were investigated, namely, Fe₃O₄@PAA (PAA = polyacrylic acid; $M_w$ of PAA = 5100 amu and 15,000 amu), Fe₃O₄@PAA–FA (FA = folic acid; $M_w$ of PAA = 5100 amu and 15,000 amu), Fe₃O₄@PEI–fluorescein (PEI = polyethylenimine; $M_w$ of PEI = 1300 amu), Fe@Fe₃O₄@PEI ($M_w$ of PEI = 10,000 amu), Fe₃O₄@SiO₂ and Fe@Fe₃O₄@SiO₂ nanoparticles. We characterized the prepared surface-modified nanoparticles using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) absorption spectroscopy, a superconducting quantum interference device (SQUID), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy and confocal microscopy. Finally, we measured the cytotoxicity of the samples. The results indicate that the surface-modified nanoparticles are biocompatible and are potential candidates for various biomedical applications.

Graphene/Fe₃O₄/Ni nano-composite materials were prepared by one-step hydrothermal method from RGO, FeCl₃ ⋅ 6H₂O and purity Ni. The structure and electromagnetic microwave absorbing properties were investigated systematically by field emission scanning electron microscope (FESEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and vector network analyzer (VNA). The reflectance was simulated based on the electromagnetic parameters to evaluate the absorption properties of the sample. The results show that Fe₃O₄ and Ni are on the surface of graphene evenly, the composites exhibit excellent microwave absorption properties, reflection loss and broad effective absorption bandwidth are −16.38 dB and 3.60 GHz, as the paraffin wax is 40% and the matching thickness is 2.00–3.50 mm.

This paper analyzes the employment of nanotechnology and FHD effect on the transportation of fluid within a container. Carrier fluid is a combination of H₂O and iron oxide and homogeneous model was incorporated to guess the features. The complex equations can be achieved by incorporating the source terms of Kelvin force and gravity term and in order to solve them, the control volume-based FEM approach was applied. To examine the accuracy, previous article of on FHD flow was examined and the achieved data showed nice accuracy. Laminar flow was analyzed and the influences of Kelvin and gravity forces were examined along with the role of the nano-sized particles. As Mn${}_F$ augments, impingement of fluid with wall enhances and bigger Nu was obtained. The effect of Ra on the characteristics of ferrofluid is same as Mn${}_F$. Disperse of nanosized material makes Nu to rise to about 12.8% owing to greater conductivity of ferrofluid. Given $\mathrm{\text{Ra}}=1$E4, the augment of Kelvin force causes Nu to intensify to about 27.09%.

In virtue of the particle swarm optimization (PSO) algorithm, the global minimum candidate structures with the lowest energy for ${({\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4)}_n(n=1-3)$ clusters were obtained by first-principles structural searches. The geometric structures and spin configurations of three cationic ${({\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4)}_n^{+}(n=1-3)$ clusters have been identified for the first time by comparing the experimental IR spectra with the calculated results from density functional theory by using different exchange-correlation functionals. It is found that the lowest energy structures of these clusters are of a shape of hat, boat and tower, respectively, with a ferrimagnetic arrangement of spins, and M06L functional is more suitable for ${\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4$ clusters than other ones.

Magnetite (Fe₃O₄) nanoparticles (MPs) capped with polyethylene glycol (PEG) were prepared by a hydrothermal method, and their antibacterial activity was examined against Staphylococcus aureus, Escherichia coli and Psudomonas aeruginosa. The functionalized NPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), Fourier transform infrared (FTIR) spectroscopy, and Thermogravimetry (TG). The average size of the Fe₃O₄ was in the range 9–20nm, while the functionalized PEG–Fe₃O₄ had an average size of 5–15nm. The PEG–Fe₃O₄ exhibited superparamagnetism and high saturation magnetization at room temperature. The antibacterial activity of the Fe₃O₄ and PEG–Fe₃O₄ were evaluated against E. coli, S. aureus, and P. aeruginosa using the agar well diffusion method. The changes in the morphology of the studied bacterial species were observed via SEM, while the mode of action of the studied agents was determined via the detection of reactive oxygen species (ROS) using Acridine orange-ethidium bromide (AO/EtBr) staining method. The results showed that PEG-functionalized magnetic (Fe₃O₄) NPs as a novel DNA-mediated antibacterial agent. The PEG–Fe₃O₄ NPs were observed to destroy the bacterial cells by permeating the bacterial nucleic acid and cytoplasmic membrane, resulting in the loss of cell-wall integrity, nucleic acid damage, and increased cell-wall permeability. The PEG–Fe₃O₄ NPs could serve as a potential antibacterial agent in future biomedical and pharmaceutical applications.

The anisotropic spindle-like Fe₃O₄ hybrid nanocomposites blended with multi-wall carbon nanotubes (MWCNTs) have been prepared to function as an ideal lightweight candidate for electromagnetic (EM) wave absorption with decent performance in high frequency. The microstructure, morphology, magnetic properties, charge-transfer behavior and EM wave absorbing performance have been characterized by powder X-ray diffractometer, transmission electron microscope, vibrating sample magnetometer, Raman spectrometer and vector network analyzer, respectively. A maximum reflection loss reaches around $-$40dB with 5% MWCNTs loading density. Compared with the monomer Fe₃O₄, the complex permittivity and permeability of the Fe₃O₄–MWCNTs nanocomposites are kept in balance, achieving a better impedance matching with a larger dielectric loss and magnetic loss. The optimization may be attributed to the synergistic effect between spindle-like Fe₃O₄ nanoparticles and MWCNTs. Moreover, the EM microwave absorbing performance can be optimized by tuning the Fe₃O₄–MWCNTs mass ratio and layer thickness of the samples, indicating promising application prospects for outstanding performance EM attenuation materials in high frequency.

A unique CdS/Fe₃O₄/rGO composite photocatalyst is successfully synthesized by the microwave method. It displays promising photocatalytic activity towards the photo-degrading of tetracycline (TC) in aqueous solution, the degradation rate of TC is 69% with adding 0.1g CdS/Fe₃O₄/rGO photocatalyst into 20mg/L tetracycline for 2h under visible light irradiation. Furthermore, the mechanism was systematically investigated by active species trapping experiment. It can be known that ${\mathrm{\text{e}}}^{-}\mathrm{\text{was}}$ the major active species in the photodegradation process and the possible process of charge transfer for CdS/Fe₃O₄/rGO was proposed based on the experimental results. The as-prepared samples were carefully evaluated by XRD, TEM, XPS, VSM, PL spectra, Raman spectrometer.

ZnO nanocrystals were introduced into Fe₃O₄/MWCNTs composites to improve the impedance matching and electromagnetic (EM) wave attenuation of the system. The as-synthesized ZnO/Fe₃O₄/MWCNTs composites were characterized by X-ray diffraction, vibrating sample magnetometer, field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy. SEM and TEM images showed that Fe₃O₄ microspheres 100–200nm in size connected MWCNTs. Analysis of EM parameters revealed that the impedance matching of the ZnO/Fe₃O₄/MWCNTs composites was considerably improved after ZnO nanocrystals were introduced. The ZnO/Fe₃O₄/MWCNTs composites exhibited a highly efficient microwave absorption (MA) capacity within the tested frequency range of 2–18GHz. The optimal reflection loss of EM waves was $-38.2$dB at 6.08GHz with an absorber thickness of 3.5mm. The excellent MA properties of the composites could be attributed to the improved impedance matching, interfacial polarization, and combined effects of dielectric and magnetic losses.

Polydopamine-coated Fe₃O₄ (Fe₃O₄@PDA) nanoparticles (NPs) were prepared as synergistic redox mediators for the catalytic reduction, by NaBH₄, of azo dyes such as methyl orange (MO) and methyl red (MR). Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were applied to determine their surface morphology, surface chemistry and detailed chemical composition, respectively. The latter technique confirmed the presence of quinone moieties. Moreover, a vibrating sample magnetometer (VSM) was used to confirm the superparamagnetic properties of these NPs. The characteristic optical absorption maximum of MO at 462nm was used to monitor the decolorization process. This was employed to determine the catalytic activity in the reaction. An enhancement of the catalytic activity of the magnetic-separable Fe₃O₄@PDA nanocatalyst over that of PDA microspheres (MPs) was observed. Moreover, their reusability and stability were also investigated. A synergistic electron transfer mechanism involving both Fe₃O₄ and PDA moieties was proposed as follows: the quinone moieties and Fe (III) species in Fe₃O₄@PDA NPs served as systematic redox mediators, with quinone receiving an electron from NaBH₄. The reduced quinone next transfers an electron to the Fe (III) moiety, generating an Fe (II) species that in turn transfers an electron to the azo dye. We determined that this process resulted in enhanced reductive degradation of azo dyes when compared with PDA MPs. Moreover, Fe₃O₄@PDA NPs could be magnetically separated and recycled. We therefore concluded that these NPs show great potential in the immobilization of homogeneous catalysts in the chemical reduction processes of azo dyes.

Magnetic targeting, which utilizes a magnetic field to specifically deliver therapeutic agents to the targeted regions, can greatly improve the treatment efficiency. Herein, ibuprofen-loaded brain targeting magnetic nanoparticles (AA-Ibu-PEG-DA@MNPs) modified with ascorbic acid (AA) for central nervous system (CNS) drug delivery was designed and synthesized in order to effectively deliver ibuprofen to the brain through Na${}^{+}$-dependent vitamin C transporter 2 (SVCT₂) and glucose transporter 1 (GLUT₁). The brain targeting magnetic nanoparticles, AA-Ibu-PEG-DA@MNPs, have a particle size of 82.5nm, 2% drug loading capacity and limited cytotoxicity against bEnd.3 cells. What’s more, the nanoparticles maintained the magnetic property with a saturation magnetization level at 52.17emu/g and could release ibuprofen when incubated in different mediums, including various buffers, mice plasma and brain homogenate. The results indicate that the magnetic nanoparticles may have the potential to be a promising approach to selectively deliver drugs into the brain. This study may be conducive to the field of CNS drugs delivery.

A simple pyrolysis, activation and hydrothermal method was utilized to synthesize composite materials (Fe₃O₄/SFP) of ferroferric oxide and nitrogen self-doped sunflower plate-derived carbon for the simultaneous electrochemical sensing of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The Fe₃O₄/SFP had synergistic catalytic effect on target molecules, and the oxidation peak potential of AA, DA and UA was well distinguished in the differential pulse voltammetry determination. Under the optimal conditions, the linear response ranges of AA, DA and UA are 3–150$\mu$M, 5–450$\mu$M and 15–1200$\mu$M, respectively. The detection limits of AA, DA and UA ($S$/$N=3$) are 1.0$\mu$M, 0.4$\mu$M and 1.48$\mu$M, respectively, and the sensitivity is 1.87$\mu \mathrm{\text{A}}\cdot \mu {\mathrm{\text{M}}}^{-1}\cdot {\mathrm{\text{cm}}}^{-2}$ (3–20$\mu$M) and 0.64$\mu \mathrm{\text{A}}\cdot \mu {\mathrm{\text{M}}}^{-1}\cdot {\mathrm{\text{cm}}}^{-2}$ (20–150$\mu$M) for AA, 3.90$\mu \mathrm{\text{A}}\cdot \mu {\mathrm{\text{M}}}^{-1}\cdot {\mathrm{\text{cm}}}^{-2}$ (5–20$\mu$M) and 1.21$\mu \mathrm{\text{A}}\cdot \mu {\mathrm{\text{M}}}^{-1}\cdot {\mathrm{\text{cm}}}^{-2}$ (20–450$\mu$M) for DA and 1.12$\mu \mathrm{\text{A}}\cdot \mu {\mathrm{\text{M}}}^{-1}\cdot {\mathrm{\text{cm}}}^{-2}$ (15–100$\mu$M) and 0.31$\mu \mathrm{\text{A}}\cdot \mu {\mathrm{\text{M}}}^{-1}\cdot {\mathrm{\text{cm}}}^{-2}$ (100–1200$\mu$M) for UA. In addition, satisfactory results have been obtained for the determination of AA, DA and UA in normal human serum, which provides a new research direction for the construction of electrochemical sensors in the future.

Fe₃O₄ nanoparticles have been widely used as drug carriers, but their toxicity is rarely reported. Herein, we compared the toxicity of novel Fe₃O₄ nanorings, nanotubes and conventional Fe₃O₄ nanospheres. The structure, morphology and magnetic properties of Fe₃O₄ nanoparticles were characterized via X-ray diffraction, scanning electron microscope and vibrating sample magnetometer. Scanning electron microscope images revealed that the morphologies of Fe₃O₄ particles were annular, tubular or spherical. The magnetic property measurements demonstrated that saturation magnetization values of nanorings, nanotubes and nanospheres were 85.3, 90.1 and 74.8emu/g, respectively. In addition, the cytotoxic effects on the 264.7 mouse macrophages cells of Fe₃O₄ nanorings, nanotubes and nanospheres were determined by cck-8 test and TUNEL staining assay. Cell viability was slightly decreased on spherical Fe₃O₄ nanoparticles compared to annular and tubular Fe₃O₄ nanoparticles.

In this study, proanthocyanidins-functionalized Fe₃O₄ magnetic nanocomposites were synthesized by the hydrothermal method. The prepared Fe₃O₄ nanocomposites were characterized by Fourier transform infrared spectrometer (FTIR), X-ray powder diffractometer (XRD), physical property measurement system (PPMS), particle size analyzer, scanning electron microscope (SEM), and transmission electron microscope (TEM). FTIR results indicated that the obtained products were coated with proanthocyanidins. The SEM and TEM results, as well as particle size distribution analysis, revealed that the obtained products were spherical particles with average diameter of $328.62\pm 26.75$nm. XRD and PPMS characterization confirmed that the Fe₃O₄ nanoparticles have a cubic spinel structure with magnetic properties. The performance of the Fe₃O₄ nanocomposites for removing organic dyes in an aqueous solution was investigated. The synthesized products were found to be effective on removing various organic dyes, such as Methylene blue (MB), neutral red (NR) and Rhodamine B (RhB), indicating their considerable potential as efficient dyes adsorbents for wastewater treatment.

Recently, utilizing biomass to synthesize novel functional materials has been a focus of significant interests in a myriad of fields such as environmental remediation. Herein, Ca–Fe–O porous materials were successfully synthesized by utilizing oyster shells and K₂FeO₄ according to a simple one-pot method. According to the result of TEM, Fe₃O₄ was obtained by reducing K₂FeO₄ and then deposited in situ on the Ca(OH)₂ nanosheets derived by CaO precursor. Such Ca–Fe–O porous materials showing outstanding adsorption capacity for RhB (146.11mg/g) and MB (135.70mg/g), additionally, would generate abundant H₂O₂ and remove the organic compounds through a Fenton-like reaction. It is hoped that our work could spur further interest in utilizing biomass to rationally design a variety of promising functional materials for environmental remediation.

In this paper, we fabricated graphene/Fe₃O₄ heterostructure devices by stacking monolayer graphene on magnetite (Fe₃O₄) substrate and investigated their magneto-transport properties. Interestingly, graphene/Fe₃O₄ heterostructure devices exhibit a giant magnetoresistance (MR) of 70% at a low magnetic field of 0.65T and at 11K, which is three times greater than that of graphene on SiO₂. Based on standard two-fluid model and LDA$+$U simulation, we showed that the observed enhanced MR effect is due to the increased disorder in graphene induced through the charge polarization via the alignment of C atoms of graphene over the charge ordered B-site cations of Fe₃O₄. Our results demonstrate a potential way to enhance graphene MR effect through coupling graphene with a suitable substrate with charge orbital ordering.

More and more scholars were committed to loading the iron oxide nanoparticles on the graphene. Shown in the studies, there were many nucleation sites on the graphene for the Fe₃O₄ particles, meanwhile, the distance between the graphene was lengthened due to the magnetic Fe₃O₄ particles, and the reunion of the graphene could be avoided. The excellent performance of the two materials was combined perfectly in this way. To facilitate the researchers work better in the future, in this paper, the synthesis of Fe₃O₄/graphene were reviewed from its applications such as waste water treatment, magnetic targeting drugs, biosensor, and the anode materials for lithium-ion battery. Simultaneously, the prospects of the composite material were discussed.

Fe₃O₄-graphene oxide composite nanocrystals with diameter of about 20 nm were prepared at 200°C for 12 h in a closed vessel containing an appropriate amount of ferrocene powder, grapheme oxide and distilled water. Magnetic measurements show 38.18 emu/g of saturation magnetization (Ms) of a typical sample, which is lower than 66.77 emu/g of the corresponding metal Fe₃O₄ bulk material. This is attributed to the considerable mass of the graphene oxide and nature of the magnetic nanocrystals.

A novel kind of magnetically photocatalyst Fe₃O₄@SiO₂@BiOBr was synthesized by hydrothermal method. Fe₃O₄ nanoparticles were firstly synthesized, and then got coated by SiO₂. The as-prepared product was coated by BiOBr finally. The character of Fe₃O₄@SiO₂@BiOBr was fully analyzed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and reflectance spectroscopy (DRS). The as-prepared Fe₃O₄@SiO₂@BiOBr show good photocatalytic performance in degradation of rhodamine B under visible light irradiation. In addition, Fe₃O₄ performs good magnet, which plays an important role in Fe₃O₄@SiO₂@BiOBr samples, moreover, its nontoxicity, easy and cheap to get also give it many priority.