Narrow Results

Magnetorheological (MR) suspensions, composed of colloidal particles dispersed in a carrier liquid, possess tunable rheological characteristics by applying an external magnetic field, showing dramatic changes of yield stress and shear viscosity caused by transformation between solid-like to liquid-like state. As a new MR material, we synthesized hollow polystyrene/magnetite (PS/Fe₃O₄) microspherical composite. Morphology of the PS obtained and the loaded magnetite were examined via SEM, and TGA spectra confirmed the composition. Magnetic property was tested by VSM data. MR characteristics of MR suspension based on PS/Fe₃O₄ composites were studied via both steady shear and oscillatory tests using a rotational rheometer equipped with a magnetic field generator.

In the presented work, nanocomposites based on poly (vinylidene fluoride) (PVDF) and magnetite Fe₃O₄ nanoparticles were prepared. The structure and content of nanocomposite materials were studied by using scanning electron microscope (SEM), atomic-force microscope (AFM) and X-Ray diffraction (XRD). Magnetic properties of PVDF+Fe₃O₄ nanocomposites have been studied upon increasing nanoparticle content in polymer matrix upto 20%, revealing superparamagnetic behavior as Fe₃O₄ nanoparticles in polymer matrix act out like single-domain particles. It has also been observed that PVDF+Fe₃O₄-based nanocomposites can absorb the electromagnetic waves in the high frequency range 0.1–30 GHz. It has been shown that the absorption of high frequency radio waves by PVDF+Fe₃O₄ nanocomposites can be explained by the different molecular structures and also by the scattering of the radio waves at the boundary of nanoparticle-polymer matrix.

The structures and magnetic properties of the PP+Fe₃O₄ nanocomposites manufactured by different technological techniques were studied in this work. Polymeric nanocomposite materials based on PP+Fe₃O₄ were obtained by two technological methods: hot pressing and extrusion. Scanning electron microscopy (SEM) and AFM investigations of nanocomposites were carried out for structure analysis. It was found that the distribution of Fe₃O₄ nanoparticles in the polymer matrix for nanocomposites obtained by the hot pressing method is uniform and monodisperse. Compared to this, the heterogeneous and inhomogeneous distribution of nanoparticles in the polymer matrix for the samples that were produced through extrusion method was observed. Furthermore, the nanocomposite samples produced via the extraction method have a lower surface regularity rather than those obtained by hot pressing. M(H) and M(T) studies of polymer nanocomposite samples synthesized through both technological methods were performed. Studies have shown that for relatively low concentrated samples — PP+10% Fe₃O₄, the values of the saturation magnetization were close, but the magnetization of nanocomposites obtained by heat pressing was slightly higher than the other samples. This is because the samples obtained by hot pressing method are characterized by higher uniformity and structure that is called “flat packaging”.

The natural oxidation process is studied in the case of 15 nm iron nanoparticles produced by the thermal decomposition of Fe(CO)₅. X-ray diffraction spectra of the nanoparticles at different timescales after exposure to air revealed the instant oxidation of iron and the formation of wüstite and magnetite. Wüstite mainly occupies the interior of nanoparticles, as evidenced by microscopy, but is slowly transformed to a spinel structure. The shape, the dispersion and the role of surfactant were investigated by conventional microscopy and Fourier Transformed-Infrared (FT-IR) spectroscopy. Magnetic hysteresis loops confirmed the expected variation of magnetic properties till the steady state.

We investigated pseudo-Josephson current effects in magnetite. Compared with the original Josephson junctions applied to superconductors, we obtained theoretical results that correlate well with experimental current data. Even though we applied a pseudo-Josephson junction to the current along the axis of energy (i.e. the momentum space), the theoretical form of DC-type currents was proportional to a tan function for the time parameter or a tanh function for the temperature parameter, which agrees with the experimental data. These pseudo-Josephson junctions occur in momentum space rather than in real space. The currents in magnetite are not primarily due to the electron–phonon interactions that induce a gap opening in band structures. We hypothesize that the Verwey Transition (VT) mechanism is pseudo-Josephson in nature.

Magnetite nanoparticles (Fe₃O₄ NPs) are prepared using chemical reduction method. This is a simple, economical, nontoxic, facile, clean, and environment friendly process. Preparation of composite polymeric membrane of polyvinyl alcohol (PVA)/Fe₃O₄ has been performed using dry phase inversion technique for different medical/filtration applications. PVA coatings using magnetite NPs are focused to passivate the surface and decrease agglomeration and also reduce module biomedical absorption and most of the times increase dispersion stability. Therefore, research on PVA coatings on magnetite NPs are in trend now a days, as they are of high charge density that makes them stable in dispersion by electrostatic repulsion. The prepared samples (Fe₃O₄ NPs) and PVA/Fe₃O₄ composite membrane have been analyzed for their different properties by using X-ray direction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis) and thermogravimetric Analysis (TGA).

In this study, we aimed to modify polymeric membranes by incorporating magnetic nanoparticles (NPs) to enhance their properties. The structural and chemical properties of magnetic NPs of iron oxide were prepared via a wet chemical method. Iron oxide nanoparticles (IONPs) were used as the core and were coated with polymers polyvinyle alcohol (PVA) and polyvinylpyrrolidone (PVP). The prepared samples were cast on a glass substrate using a casting knife. The aim of this study is the use of a specific type of magnetic NPs, coated with a polymer, and their application in membrane modification. We employed a facile synthesis method to coat the IONPs with the polymer and characterized the resulting material using various techniques, including X-ray Diffraction (XRD), scanning electron microscope (SEM), Fourier Transform Infrared (FTIR) Spectroscopy, and UV/Visible (UV–Vis) Spectroscopy for structural, morphological, chemical bonding, and optical properties studies. Our results show that the modified polymeric membranes exhibited improved properties, such as increased permeability and selectivity. We also observed that the magnetic NPs helped in the easy recovery of the modified membranes using an external magnetic field. Some agglomeration of IONPs was also observed, and the polymer membrane caused a decrease in crystallinity of IONPs. Overall, this study presents a promising approach for enhancing the properties of polymeric membranes using magnetic NPs and can potentially have practical applications in various fields, such as water treatment, food processing, and biotechnology.

High-quality hydrophobic or hydrophilic ferrofluid based on magnetite (Fe₃O₄) nanoparticles can be synthesized by one-pot direct synthesis which involves thermolysis of Iron(III) acetylacetonate, Fe(acac)₃ in hydrophobic or hydrophilic stabilizing agent, respectively. The structure of the nanoparticles dispersed in the ferrofluid was studied using XRD, FTIR, XPS, and TGA analysis, while morphology and size of the nanoparticles were determined by TEM. The magnetic properties of the samples were measured using VSM and SQUID measurement. The results show that oleylamine (OM) and tri(ethylene glycol) (TREG) coated Fe₃O₄ nanoparticles which are well stabilized in hydrophobic and hydrophilic ferrofluid, respectively, are relatively monodisperse, single crystalline and superparamagnetic in nature with the blocking temperature at around 100 K.

Magnetite and biopolymer-magnetite nanoparticles coated with polyethylene glycol (PEG) and chitosan have been synthesized. The adsorption of the biopolymers on the magnetite nanoparticles is confirmed using Fourier Transform Infrared (FTIR) Spectroscopy. Atomic Force Microscopy (AFM) imaging revealed magnetite-biopolymer core–shell nanoparticles of typical size range 25–80 nm. We report a novel way of determining the thickness of the biopolymer coating using noncontact AFM imaging. AFM has been used to study the variation of the biopolymer coating thickness as a function of the magnetite core diameter, biopolymer type, and its concentration. The thickness of the chitosan coating varies in the range of 4–11 nm and increases linearly with increase in magnetite core size. PEG coating thickness has similar values as for the chitosan coating.

In this article, we describe synthesis of a novel drug delivery vector (DDV) for photodynamic therapy (PDT). The DDV consists of a magnetite core surrounded by a thin layer of functionalized silica. These core–shell structures are loaded with a photosensitizer (PS) drug "Methylene Blue" (MB). Magnetite nanostructures are produce by the well-established chemical co-precipitation technique and encapsulated in silica shell by modified process of hydrolysis and condensation of tetraethyl orthosilicate (TEOS). MB is grafted into the pores of silica shell by demethylation reaction. Reaction kinetics has been established for tunable loading of PS in DDV. Physical and chemical properties of composite nanostructures are determined by X-ray diffraction (XRD), dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometry (VSM). Amount of PS loading in DDV is measured by UV-Visible spectroscopy. Smaller size, biocompatibility, tunable loading of PS and capabilities of magnetic guidance, makes this DDV, a potential candidate for the treatment of malignant tumors by PDT.

Magnetic nanoparticles (MNPs) comprising magnetite (Fe₃O₄) were functionalized with 3-aminopropyl-triethoxysilane forming amino functionalized magnetite nanoparticles (AMNPs). The amino group allows for conjugation with zinc octacarboxyphthalocyanine (ZnOCPc) via the carboxyl group to form an amide bond. Transmission electron microscopy showed a change in morphology after conjugation. The covalent linkage of AMNPs to ZnOCPc has shown improvements in the photophysical behavior of the Pc in the presence of the MNP, increasing the triplet quantum yield (Φ_T), singlet oxygen quantum yield (Φ_Δ), triplet lifetime (τ_T) and singlet oxygen lifetime (τ_Δ) of the ZnOCPc and thus improving the efficiency of the ZnOCPc as a photosensitizer.

Nitrated lignosulfonates were used to synthesize a water-based magnetic fluid. Lignosulfonates were nitrated by nitric acid under mild conditions and without further purification were used to synthesize a magnetic fluid. Part of the iron(II) were oxidized with an excess of nitric acid, so that the magnetoactive phase under the condensation by action of sodium hydroxide was formed. Optimum conditions for nitration of lignosulfonates and synthesis of a magnetic fluid were experimentally established. The optimum consumption of iron(II) was 1.3–1.5g per 1g of sodium lignosulfonate. Unlike the initial lignosulfonates, nitrated lignosulfonates have peptizing properties, due to which the precipitate formed during condensation was dispersed to nanoparticles (15–30nm). The resulting magnetic fluid had a high magnetic activity and was stable for a long time.

Facile procedures to synthesize large quantities of uniform and well dispersed magnetite particles in water were developed through a solvothermal method. Magnetite microspheres were obtained by using FeCl₃ · 6H₂O, urea and polyethylene glycol as the starting materials in ethylene glycol at 200°C for 8 h. The samples were characterized by using X-ray diffraction, transmission electron microscopy, scanning electron microscopy and vibrating sample magnetometry. Experimental results revealed that the particles were well dispersed with uniform particle size and diameters in the range 260 to 280 nm. The saturation magnetization value was 71.5 emu/g with negligible remanence.

Fe₃O₄/carbon nanotubes (CNTs) nanocomposites are successfully prepared by a facile hydrothermal method, without any reducing agents. SEM shows that the CNTs are dispersed well in the Fe₃O₄ nanoparticles of 50 to 100 nm in size. The electrochemical properties of the prepared nanocomposites as anode materials are further evaluated by galvanostatic charge/discharge cycling and cyclic voltammetry (CV). Results show that the nanocomposites display an initial discharge capacity of 1421 mAh⋅g^-1 and maintain 1100 mAh⋅g^-1 up to 40 cycles in the voltage of 0.005–3.0 V at 100 mAh⋅g^-1. When the current density is to 0.5, 1, 2, 5 and 1 C, the nanocomposites still exhibit discharge capacity of 1615.8, 817.0, 585.0, 391.0 and (585.0 ± 45.0) mAh⋅g^-1, respectively, which are potential for anode materials in lithium-ion batteries.

A comparative study of magnetic properties using the method of magnetometry with vibration magnetometer and spectra of electron paramagnetic resonance (EPR) nanocomplexes (NCs) of nanoparticles Fe₂O₃, Fe₃O₄ and antitumor antibiotic doxorubicin (DOXO) have shown that changes in saturation magnetic moments are similar to changes in integral intensity of EPR spectra. The greatest magnetic moments of saturation and integral intensity of EPR spectra were demonstrated by samples of Fe₃O₄ in NC with doxorubicin, which had the highest antitumor effect in radiofrequency hyperthermia of Walker-256 carcinosarcoma. The presented research provides the evidence of stronger antitumor effect of Fe₃O₄ and DOXO NC in comparison to NC from γ-Fe₂O₃ and DOXO at combined action of constant magnetic field and electromagnetic field. This can be a basis for development of bioengineering technology of magnetic cancer nanotherapy in conditions of moderate hyperthermia (< 39°C).

Magnetite nano-particles have been synthesized by reverse co-precipitation method using iron salts in alkaline medium in the presence of diethylene glycol (DEG). Effect of DEG on the nano-particle characteristics was investigated by XRD, FE-SEM, FTIR and VSM techniques. From XRD results it was concluded that in the presence of DEG the composition of magnetite did not change, however the mean crystallite size reduced from 10 to 5 nm. SEM micrograph showed that DEG decreased the size of spherical magnetite nano-particles from 50 to 20 nm. Fourier transform infrared spectra (FTIR) indicated that the DEG molecules chemisorbed on the magnetite nano-particles. Under the given experimental conditions, the rate of crystallization and growth reduced, which is probably due to the capping of DEG to the magnetite nano-particles. The agglomeration was also decreased which is attributed to the coating of magnetite nano-particles by DEG which prevents the formation of hydrogen bonding between magnetite and water molecules.

In this paper, we report an interesting approach for efficient synthesis of uniform sub-micrometer carbon supported Fe₃O₄ hollow spheres. Fe₃O₄ precursor was first coated on the surface of sulfonated polystyrene hollow microspheres. Then, the precursor and sulfonated polystyrene hollow microspheres were converted into Fe₃O₄ and carbon hollow spheres when heated at 550°C in N₂ atmosphere. The obtained Fe₃O₄ @ carbon hollow microspheres exhibit enhanced lithium storage properties compared with Fe₂O₃ hollow spheres as anode materials, delivering a reversible capacity of 612 mA hg⁻¹ after 50 cycles at a high current density of 400 mA g⁻¹.

To observe acute toxicity of naked Fe₃O₄-nanoparticles in mice, ICR mice were selected and exposed once to naked Fe₃O₄-nanoparticles by tail intravenous injection with different doses, i.e. 0, 102.4, 128, 160, 200, 250 mg/kg of body weight. 15 days later, Fe₃O₄ distribution and pathologic changes in main organs were investigated. By tail intravenous injection, LD₅₀ of naked Fe₃O₄-nanoparticles in mice was 163.60 mg/kg of body weight (147.58, 181.37 mg/kg of body weight, 95% confidence interval). Deaths of mice mainly caused by decompensation and twitching were observed. Immediately after injection, nanoparticles performed fast distribution in lung, liver, spleen etc, yet little were traced in brain, heart and kidney. 15 days after injection, apparent decline of nanoparticles content in lung and spleen was observed, whereas in liver the content rose. Pathologic detection indicated local particle denaturation and necrosis in the cardiac tissue. Protein cast was seen in several kidney tubules, and extravasated blood in carunculae papillaris, yet no pathologic changes were observed in other organs. LD₅₀ of Fe₃O₄ nanoparticles (9 nm) by means of tail intravenous injection is 163.60 mg/kg, and they mainly distributed in liver, spleen, lung and caused denaturation and necrosis in the cardiac muscle and malfunction of kidney. Also, the process of excreting the particles takes a long time.