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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.