Functionalized Fe₃O₄@Au superparamagnetic nanoparticles: in vitro bioactivity

The interaction of nanoparticles with cells has been a focus of interest during the past decade. We report the fabrication and characterization of hydrosoluble Fe?O?@Au nanoparticles functionalized with biocompatible and fluorescent molecules and their interaction with cell cultures by visualizing them with confocal microscopy. Gold covered iron oxide nanoparticles were synthesized by reducing metal salts in the presence of oleylamine and oleic acid. The functionalization of these particles with an amphiphilic polymer provides a water soluble corona as well as the possibility to incorporate different molecules relevant for bio-applications such as poly(ethylene glycol), glucose or a cadaverine derived dye. The particle size, and the presence of polymer layers and conjugated molecules were characterized and confirmed by transmission electron microscopy, thermogravimetric measurements and infrared spectroscopy. A complete magnetic study was performed, showing that gold provides an optimum coating, which enhances the superparamagnetic behaviour observed above 10-15 K in this kind of nanoparticle. The interaction with cells and the cytotoxicity of the Fe?O?@Au preparations were determined upon incubation with the HeLa cell line. These nanoparticles showed no cytotoxicity when evaluated by the MTT assay and it was demonstrated that nanoparticles clearly interacted with the cells, showing a higher level of accumulation in the cells for glucose conjugated nanoparticles.     

Constructing carbon-coated Fe₃O₄ microspheres as antiacid and magnetic support for palladium nanoparticles for catalytic applications

Fe?O? microsphere is a good candidate as support for catalyst because of its unique magnetic property and large surface area. Coating Fe?O? microspheres with other materials can protect them from being dissolved in acid solution or add functional groups on their surface to adsorb catalyst. In this paper, a carbon layer was coated onto Fe?O? microspheres by hydrothermal treatment using polyethylene glycol as the connecting agents between glucose and Fe?O? spheres. Through tuning the added amounts of reactants, the thickness of the carbon layer could be well-controlled. Because of the abundant reductive groups on the surface of carbon layer, noble metal ions could be easily adsorbed and in situ reduced to nanoparticles (6-12 nm). The prepared catalyst not only had unique antiacid and magnetic properties, but also exhibited a higher catalytic activity toward the reduction of methyl orange than commercially used Pd/C catalyst.     

Graphene-encapsulated hollow Fe₃O₄ nanoparticle aggregates as a high-performance anode material for lithium ion batteries

Graphene-encapsulated ordered aggregates of Fe(3)O(4) nanoparticles with nearly spherical geometry and hollow interior were synthesized by a simple self-assembly process. The open interior structure adapts well to the volume change in repetitive Li(+) insertion and extraction reactions; and the encapsulating graphene connects the Fe(3)O(4) nanoparticles electrically. The structure and morphology of the graphene-Fe(3)O(4) composite were confirmed by X-ray diffraction, scanning electron microscopy, and high-resolution transmission microscopy. The electrochemical performance of the composite for reversible Li(+) storage was evaluated by cyclic voltammetry and constant current charging and discharging. The results showed a high and nearly unvarying specific capacity for 50 cycles. Furthermore, even after 90 cycles of charge and discharge at different current densities, about 92% of the initial capacity at 100 mA g(-1) was still recoverable, indicating excellent cycle stability. The graphene-Fe(3)O(4) composite is therefore a capable Li(+) host with high capacity that can be cycled at high rates with good cycle life. The unique combination of graphene encapsulation and a hollow porous structure definitely contributed to this versatile electrochemical performance.     

Preparation and lithium storage performances of mesoporous Fe₃O₄@C microcapsules

Fe(3)O(4)@C microcapsules were prepared using carbon-coated α-FeOOH nanorods as precursors, which were synthesized via two-step hydrothermal reactions. During the subsequent sintering procedure, α-FeOOH was reduced to Fe(3)O(4) by carbon, accompanied by the formation of mesopores. In Fe(3)O(4)@C microcapsules, mesoporous Fe(3)O(4) nanorods are coated with amorphorous carbon layers. The Fe(3)O(4)/C composites with such special structures demonstrate high specific capacity and good cyclic stability as anode materials in Li test cells.     

Storage of luminescent nanoparticles in porous silicon: Toward a solid state “golden fleece”

Meso-porous silicon layers and free-standing membranes are studied as solid-state safe storing matrixes for luminescent Si and 3C–SiC nanoparticles. The porous silicon “fleece” is shown to soak efficiently and easily a great number of luminescent nanoparticles from ethanol solution. Incorporation of the nanoparticles inside the meso-pores after ethanol evaporation was illustrated by photoluminescence and reflection spectroscopies. Numerous reproducible extractions of the nanoparticles from the meso-porous network can be ensured by controlled adding a few drops of pure ethanol.     

Influence of plasmonic Au nanoparticles on the photoactivity of Fe₂O₃ electrodes for water splitting

An experimental study of the influence of gold nanoparticles on α-Fe(2)O(3) photoanodes for photoelectrochemical water splitting is described. A relative enhancement in the water splitting efficiency at photon frequencies corresponding to the plasmon resonance in gold was observed. This relative enhancement was observed only for electrode geometries with metal particles that were localized at the semiconductor-electrolyte interface, consistent with the observation that minority carrier transport to the electrolyte is the most significant impediment to achieving high efficiencies in this system.     

One-pot synthesis of uniform Fe₃O₄ nanospheres with carbon matrix support for improved lithium storage capabilities

Poly(acrylic acid) (PAA)-entangled Fe(3)O(4) nanospheres are synthesized via a facile solvothermal method. In this system, ethylenediamine plays a very important role to control the uniformity of the nanospheres, and the PAA molecules serve as the carbon source that transforms into a carbon matrix after the heat treatment under an inert atmosphere. These uniform Fe(3)O(4) nanospheres with carbon matrix support manifest greatly enhanced lithium storage properties over prolonged cycling, with a reversible capacity of 712 mA h g(-1) retained after 60 charge/discharge cycles. However, the carbon-free counterpart can only deliver a much lower capacity of 328 mA h g(-1).     

Ferromagnetic resonance of a magnetostatically stabilized domain wall in a nanowire–nanoparticle planar system

The results of micromagnetic simulation of induced high-frequency magnetization oscillations in a planar ferromagnetic system composed of a magnetostatically coupled nanowire and nanoparticle are reported. The possibility of transformation of the spectrum of this system by introducing a domain wall stabilized with the magnetic field of the nanoparticle into the nanowire is discussed. The dependences of the frequency and amplitude of resonant oscillations of the domain wall on the geometric parameters of the system are analyzed.     

SrTi1−x Fe x O3 nanoparticle: a study of structural,optical, impedance and magnetic properties

We investigate the effects of Fe-dopant concentration on the structure, as well as optical, electrical transport and magnetic properties of SrTi_{1? x} Fe _x O₃ (x?=?0.00, 0.10, 0.20, 0.30, 0.40 and 0.50) nanoparticles prepared by sol–gel method. The dopant-induced changes are studied by X-ray diffraction (XRD), Raman, optical absorption, impedance and magnetic measurements. The results show an average particle size of about 15–30?nm, depending on the Fe-doped concentration. The decrease in lattice parameters and the change of phonon modes related to structural changes, decreasing gap with increasing dopant concentration in conjunction with increasing grain boundary contribution to the impedance. The Fe-doped content has affected the structure, absorption and Raman spectroscopy of the samples. These indicate that the Fe ion has replaced the site of Ti in unit cell. By this method, we have decreased the annealing temperature considerably than that in the conventional solid-state reaction.     

One-pot synthesis of magnetic γ-Fe2O3 nanoparticles in ethanol-water mixed solvent

Maghemite (γ-Fe₂O₃) nanoparticles were synthesized via a low-temperature solution-based method using ferric chloride hexahydrate and ferrous chloride tetrahydrate as precursors in the mixed solvent of ethanol and water. X-ray diffraction, energydispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy revealed that the obtained product was pure γ-Fe₂O₃. Transmission electron microscopy showed the morphology of the nanoparticles to be approximately spherical in shape with an average diameter of 11 nm. Magnetization measurements indicated the dry powders exhibit ferromagnetic behavior with a maximum saturation magnetization of 41.1 emu/g at room temperature.     

Synthesis of amorphous silicon carbide nanoparticles in a low temperature low pressure plasma reactor

Commercial scale production of silicon carbide (SiC) nanoparticles smaller than 10?nm remains a significant challenge. In this paper, a microwave plasma reactor and appropriate reaction conditions have been developed for the synthesis of amorphous SiC nanoparticles. This continuous gas phase process is amenable to large scale production use and utilizes the decomposition of tetramethylsilane (TMS) for both the silicon and the carbon source. The influence of synthesis parameters on the product characteristics was investigated. The as-prepared SiC particles with sizes between 4 and 6?nm were obtained from the TMS precursor in a plasma operated at low temperature and low precursor partial pressure (0.001-0.02?Torr) using argon as the carrier gas (3?Torr). The carbon:silicon ratio was tuned by the addition of hydrogen and characterized by x-ray photoelectron spectroscopy. The reaction mechanism of SiC nanoparticle formation in the microwave plasma was investigated by mass spectroscopy of the gaseous products.     

Magnetic resonance study of γ-Fe2O3 nanoparticles dressed in oxygen based free radicals

Two composites consisting of γ-Fe₂O₃ (maghemite) nanoparticles covered by two different oxygen-based free radicals derived from a 4-(methylamino)phenol sulphate and 8-hydroxy-1,3,6-trisulfonic trisodium salt acid were prepared and investigated by the magnetic resonance method in the 4–300 K range. Both composites displayed broad and very intense ferromagnetic resonance (FMR) lines originating from γ-Fe₂O₃ agglomerated nanoparticles. The FMR spectrum was fitted satisfactorily at each temperature by two Landau-Lifshitz functions reflecting the existence of magnetic anisotropy in the investigated system. The temperature dependence of the obtained FMR parameters (resonance field, linewidth, integrated intensity) was studied and the results were interpreted in terms of magnetic interactions between free radicals and nanoparticle agglomerates. A comparison with previously studied similar systems containing maghemite nanoparticles was made and conclusions about the role of free radicals were drawn.     

Study of magnetic inhomogeneity in β-Cu3Fe4V6O24

The temperature dependence of dc magnetization and electron paramagnetic resonance (EPR) spectra of the ??-Cu₃Fe₄V₆O₂₄ multicomponent vanadate were investigated. Dc magnetic measurements showed the presence of strong antiferromagnetic interactions (Curie-Weiss temperature, ?? ?? 80 K) at high temperatures, while zero-field-cooled (ZFC) magnetization revealed a cusp-like maximum in low fields at T _f1 = 4.4 K, which coincides with the splitting of the ZFC and FC curves. Another maximum was registered at T _f2 = 3.0 K. These two temperatures (T _f1 and T _f2) could be regarded as freezing temperatures in the spin glass state of two magnetic sublattices of Fe1 and Fe2 ions. The EPR spectrum of ??-Cu₃Fe₄V₆O₂₄ is dominated by a nearly symmetrical, very intense and broad resonance line centered at g _eff ?? 2.0 that could be attributed to iron ions. Below 10 K, an additional EPR spectrum with g ₁ = 2.018(1) and g ₂ = 2.175(1) appears, as well as a very weak line at g_eff = 1.99(1). The former spectrum is probably is due to divalent copper ions, and the latter line due to vanadium V⁴⁺ complexes. The temperature dependence of EPR parameters (g-factor, linewidth, integrated intensity) was determined in the range of 3?C300 K. Two low-temperature maxima in the temperature dependence of the integrated intensity (at 40 and 6 K) were fitted with a function suitable for pairs of exchange-coupled Fe³⁺ ions. A comparison of dc magnetic susceptibility and EPR integrated intensity indicates the presence of spin clusters, which play an important role in determining the low-temperature magnetic response of _??-Cu₃Fe₄V₆O₂₄.     

Dechlorination of 3,3′,4,4′-tetrachlorobiphenyl in aqueous solution by hybrid Fe0/Fe3O4 nanoparticle system

The kinetics and efficiency of 3,3′,4,4′-tetrachlorobiphenyl (PCB77) degradation in aqueous solution by hybrid Fe⁰/Fe₃O₄ nanoparticle system were investigated. The results showed that nano-sized Fe⁰ and Fe₃O₄ could efficiently degrade PCB77, and the residual rate of PCB77 by nano-sized Fe⁰ and Fe₃O₄ were 67.70% ± 0.42% and 82.26% ± 2.96%, respectively after 240 min of reaction (for 5 mg·L^?1 PCB77 and 5 g·L^?1 nanoparticles). The combined use of nanoscale Fe⁰ and Fe₃O₄ could enhance the degradation of PCB77. The dose ratios of nano-sized Fe⁰ and Fe₃O₄ significantly affected the PCB77 degradation rate. At Fe⁰/Fe₃O₄ ratios of 1:0.1, 1:0.2 and 1:1, the residual rates of PCB77 were 6.46%, 10.23% and 38.20%, respectively. The PCB77 degradation efficiency was also greatly affected by solution pH, and was maximised at pH 6.8. The degradation of PCB77 by Fe⁰/Fe₃O₄ nanoparticle was a dechlorination process, and the chlorion concentration increased with the decreasing residual rate of PCB77 accordingly. Fe₃O₄ provided Fe²⁺ and Fe³⁺ for enhancing the PCB77 degradation by nanoscale Fe⁰, suggesting a synergy between Fe⁰ and Fe₃O₄.     

Crystallization of a Bi–Pb–Fe–Cd–O glass under magnetic annealing

Magnetic annealing with a tunable solenoid magnetic field from 0–240 G, was conducted on a Bi–Pb–Fe–Cd–O glass containing 20% Fe2O3, which was prepared by the melt-quenching process. The crystalline phases of the annealed samples were identified as -Bi2O3 and BiFeO3. Evidence of the formation of the crystalline BiFeO3 which was strongly magnetically enhanced at the surface of the samples, was obtained from X-ray diffraction patterns and EPR spectra. Based on the structure transition of Fe3+ ions, a crystallization mechanism for the BiFeO3 crystals under magnetic annealing has been proposed.     

Synthesis and characterization of core∕shell Fe(3)O(4)∕ZnSe fluorescent magnetic nanoparticles

We report on the successful preparation and characterization of fluorescent magnetic core∕shell Fe(3)O(4)∕ZnSe nanoparticles (NPs) with a spherical shape by organometallic synthesis. The 7 nm core∕3 nm shell NPs show good magnetic and photoluminescence (PL) responses. The observed PL emission∕excitation spectra are shifted to shorter wavelengths, compared to a reference ZnSe NP sample. A dramatic reduction of PL quantum yield is also observed. The temperature dependence of the magnetization for the core∕shell NPs shows the characteristic features of two coexisting and interacting magnetic (Fe(3)O(4)) and nonmagnetic (ZnSe) phases. Compared to a reference Fe(3)O(4) NP sample, the room-temperature Néel relaxation time in core∕shell NPs is three times longer.     

A new type of silica-coated Gd₂(CO₃)₃:Tb nanoparticle as a bifunctional agent for magnetic resonance imaging and fluorescent imaging

We report a new type of dual modal nanoprobe to combine optical and magnetic resonance bioimaging. A simple reverse microemulsion method and coating process was introduced to synthesize silica-coated Gd(2)(CO(3))(3):Tb nanoparticles, and the particles, with an average diameter of 16 nm, can be dispersed in water. As in vitro cell imaging of the nanoprobe shows, the nanoprobe accomplishes delivery to gastric SGC7901 cancer cells successfully in a short time, as well as NCI-H460 lung cancer cells. Furthermore, it presents no evidence of cell toxicity or adverse affect on kidney cell growth under high dose, which makes the nanoprobe's optical bioimaging modality available. The possibility of using the nanoprobe for magnetic resonance imaging is also demonstrated, and the nanoprobe displays a clear T(1)-weighted effect and could potentially serve as a bimodal T(1)-positive contrast agent. Therefore, the new nanoprobe formed from carbonate nanoprobe doped with rare earth ions provides the dual modality of optical and magnetic resonance imaging.     

Bioactive magnetic nanoparticles of Fe–Ga synthesized by sol–gel for their potential use in hyperthermia treatment

Hyperthermia is one of the most recents therapies for cancer treatment using particles with nanometric size and appropriate magnetic properties for destroying cancer cells. Magnetic nanoparticles (MNP’s) of Fe–Ga and synthesized using a polycondensation reaction by sol–gel method were obtained. MNP’s of Fe_1.4Ga_1.6O₄ that posses an inverse spinel structure were identified by X-Ray Diffraction, Transmission Electron Microscopy, Scanning Electron Microscopy and Energy Dispersive Spectroscopy. The results showed that the MNP’s are composed only by Fe, Ga and O and their size is between 15 and 20 nm. The magnetic properties measured by Vibration Sample Magnetometry demonstrated a saturation magnetization value of 37.5 emu/g. To induce the MNP’s bioactivity, a biomimetic method was used which consisted in the immersion of MNP’s in a Simulated Body Fluid (SBF) for different periods of time (7, 14 and 21d) along with a wollastonite disk. The formation of a bioactive layer, which closely resembles that formed on the existing bioactive systems and with a Ca/P atomic ratio within a range of 1.37–1.73 was observed on the MNP’s. Cytotoxicity of MNP’s was evaluated by in vitro hemolysis testing using human red blood cells at concentrations between 0.25 and 6.0 mg/mL. It was found that the MNP’s were not cytotoxic at none of the concentrations used. The results indicate that Fe–Ga MNP’s are potential materials for cancer treatment of both hard and soft tissue by hyperthermia and drug carriers, among other applications.     

Preparation of nanocomposite materials containing WS2, δ-WN,Fe3O4, or Fe9S10 in a silica aerogel host

Nanocomposite materials based on silica aerogel hosts have been produced using chemical vapour infiltration/decomposition methods and characterized by X-ray diffraction and electron microscopy. Amorphous tungsten in SiO₂ aerogel was formed by the decomposition of W(CO)₆ at 250 °C. Alternatively, reaction of this material with sulphur at 700 °C produced needle-shaped WS₂ crystals with lengths ranging from 25–230 nm. Reaction of the W/SiO₂ composite with anhydrous NH₃ formed crystals of -WN with diameters of 1–5 nm. Fe(CO)₅ is readily absorbed into the silica aerogel, forming an amorphous iron oxide/SiO₂ composite after slow oxidation in air. Treatment of this material with additional Fe(CO)₅ produced an Fe₃O₄/SiO₂ aerogel composite. Fe₃O₄ particle sizes were 20–55 nm. After additional heat treatment, this composite exhibited soft ferromagnetic behaviour with a coercivity of 170 Oe. Fe₉S₁₀ crystals with diameters of 30–90 nm were formed by the reaction of the amorphous iron oxide/SiO₂ composite with H₂S at 900 °C.     

Effects of a high-gradient magnetic field on the migratory behavior of primary crystal silicon in hypereutectic Al–Si alloy

Abstract

The migration of primary Si grains during the solidification of Al–18 wt%Si alloy under a high-gradient magnetic field has been investigated experimentally. It was found that under a gradient magnetic field, the primary Si grains migrated toward one end of the specimen, forming a Si-rich layer, and the thickness of the Si-rich layer increased with increasing magnetic flux density. No movement of Si grains was apparent under a magnetic field below 2.3 T. For magnetic fields above 6.6 T, however, the thickness of the Si-rich layer was almost constant. It was shown that the static field also played a role in impeding the movement of the grains. The primary Si grains were refined in the Si layer, even though the primary silicon grains were very dense. The effect of the magnetic flux density on the migratory behavior is discussed.