Maghemite Particles Research Articles

Development of maghemite nanoparticles supported on cross-linked chitosan (γ-Fe2O3@CS) as a recoverable mesoporous magnetic composite for effective heavy metals removal

A mesoporous magnetic composite, γ-Fe2O3-functionalized cross-linked chitosan (γ-Fe2O3@CS), was developed as an efficient adsorbent to remove cadmium (Cd2+) ions from contaminated water media. The as-prepared composite was characterized by FESEM, TEM, EDS, VSM, BET and XRD techniques. Several parameters affecting the removal efficiency including surface area, solution pH, contact time, adsorbent dose, initial Cd2+ concentration and temperature were evaluated and discussed. The average crystallite size of γ-Fe2O3 was found to be 26.5nm. The highest magnetization saturation of adsorbent was 25.1emu/g. The adsorption rate belonged γ-Fe2O3@CS composite was much higher than that γ-Fe2O3 and CS, which reflects a synergistic effect between the maghemite and CS particles on the removal of Cd2+. Based on the adsorption capacity normalized by surface area, the value of Cd2+ adsorbed on adsorbents follows the order of γ-Fe2O3@CS>CS>γ-Fe2O3. The equilibrium time was 60min and the monolayer maximum adsorption capacity was found to be 15.2mg/g. Under optimized experimental conditions, complete removal of 5mg/L of Cd2+ was achieved. Cycling tests revealed that γ-Fe2O3@CS was recyclable to remove Cd2+ ions during five consecutive cycles and the removal efficiency still remains at 78.3%. Kinetic and isotherm of adsorption were in good agreement with pseudo-second-order and Langmuir models, respectively. The adsorption process was endothermic and spontaneous in nature. Cd2+ adsorption mechanism on γ-Fe2O3@CS follows ion-exchange and monolayer chemical adsorption.

Raw montmorillonite modified with iron for photo-Fenton processes: influence of iron content on textural, structural and catalytic properties

A raw montmorillonite was exchanged with the trinuclear Fe(III) acetate complex and calcined at 400°C. Ratios of 0.5, 1.0 and 3.5mmol of complex per gram of clay were employed. The pillared solids (Fe-PILCs) were analyzed by X-ray fluorescence spectroscopy, thermogravimetry analysis, scanning electron microscopy, Mössbauer spectroscopy, X-ray diffraction and nitrogen adsorption isotherms. Total iron amount incorporated by the clay increases with the complex/clay ratio used from 6.1% to 17.6%. Iron is incorporated mainly in the interlayer space when the clay is pillared with the smallest complex/clay ratio and a microporous network is generated. Adsorption of iron on the outer surface is favored for higher iron loads and results in the creation of a mesoporous structure. Mössbauer analysis shows the presence of iron as maghemite (γ-Fe2O3) particles with a wide particle size distribution. All the Fe-PILCs were active as catalysts for phenol degradation under photo-Fenton like conditions using UVA radiation and a maximum in their activity is achieved for an intermediate iron content (13.4%).

The impact of magnetic viscosity on time-domain electromagnetic data from iron oxide minerals embedded in rocks at Opemiska, Québec, Canada

The magnetic viscosity (MV) effects observed at time scales between 0.01 and 10 ms at Opemiska are associated with magnetic grains of variable size in rocks. Recent observations made during a ground time-domain electromagnetic (TDEM) survey at Opemiska are consistent with four aspects of the spatial and amplitude characteristics of a MV response: (1) the [Formula: see text] decay rate is roughly proportional to [Formula: see text], where [Formula: see text], (2) the anomalies are mainly visible on the [Formula: see text]-component, when the EM receiver sensor is located inside or just outside the transmitter loop, (3) there is no obvious [Formula: see text]- or [Formula: see text]-component response, and (4) the sites where MV effects are seen in the TDEM data are coincident with an airborne magnetic anomaly. Previous studies have demonstrated that MV could be caused by (1) fine-grained particles of maghemite or magnetite in the overburden, regolith, or soil that were formed through lateritic weathering processes, (2) volcanic glass shards from tuff containing approximately 1% by weight magnetite, which occur as grains approximately [Formula: see text] in size precipitated in a spatially uniform way, or (3) from the Gallionella bacterium that precipitates ferrihydrite that oxidizes to nanocrystalline maghemite aggregates. The sites investigated at Opemiska are outcropping and well-exposed with relatively little or no overburden, and they are unfavorable for the formation of maghemite; hence, it is assumed that the source of MV seen at Opemiska cannot be the maghemite, or the other aforementioned causes. Hand samples were collected from Opemiska to identify the minerals present. Polished thin sections observed under an optical reflecting microscope identified the accessory minerals magnetite, ilmenite, and pyrrhotite, all known for their relatively high magnetic susceptibility. The use of the scanning electron microscope confirmed fine-grained magnetite grains as small as [Formula: see text]. An electromagnetic induction spectrometer confirmed the viscous nature of the susceptibility of the Opemiska samples. This suggests that MV could originate not only from fine-grained magnetite and maghemite particles located in the weathered regolith but also from other iron oxides and magnetic minerals embedded in the rock itself.

Mössbauer study of the reduction of synthesized ferrihydrite by the alkaliphilic iron-reducing bacterium Fuchsiella ferrireducens

Samples of biogenic iron minerals obtained during the growth of the anaerobic alkaliphilic ironreducing bacterium Fuchsiella ferrireducens (strain Ζ-7101Т) in the presence of synthesized ferrihydrite used as electron acceptor are studied by 57Fe Mossbauer spectroscopy. Two series of samples, differing by electron acceptor, are analyzed. Ethanol and acetate are used as electron donors in the first and second series, respectively. Mossbauer studies are performed at room temperature and at 82 K. Phases containing ferrous iron (siderite) form in both series, while a magnetically ordered phase (a mixture of hematite and maghemite particles) forms only in the series with ethanol.

Magnetic properties of nanoparticle compacts with controlled broadening of the particle size distribution

Binary random compacts with different proportions of small (volume V) and large (volume 2V) bare maghemite nanoparticles (NPs) are used to investigate the effect of controllably broadening the particle size distribution on the magnetic properties of magnetic NP assemblies with strong dipolar interaction. A series of eight random mixtures of highly uniform 9.0 and 11.5 nm diameter maghemite particles prepared by thermal decomposition are studied. In spite of severely broadened size distributions in the mixed samples, well defined superspin glass transition temperatures are observed across the series, their values increasing linearly with the weight fraction of large particles.

Single-phase γ-Fe2O3 nanoparticles synthesized by green ionothermal method and their magnetic characterization

The γ-Fe2O3 nanoparticles were prepared by ionothermal method in ionic liquids. A wide range of maghemite particle sizes within the nanometer scale are obtained by this method. The structural and magnetic properties of these γ-Fe2O3 particles were studied by using XRD, SEM and IR. Magnetic properties of the prepared nanoparticles were evaluated on a vibrating sample magnometer (VSM). By changing the ionic liquids, particles with an average diameter from 5 to 10nm were prepared. The size of the final particle decreases with the longer alkyl chain of ionic liquid in this method while the template is bounded to the particle surface. Also magnetic properties of the products change with different ionic liquids. A longer alkyl chain in ionic liquid causes an increase in the magnetic properties in this method.

Frequency Mixing Magnetic Detection Scanner for Imaging Magnetic Particles in Planar Samples.

The setup of a planar Frequency Mixing Magnetic Detection (p-FMMD) scanner for performing Magnetic Particles Imaging (MPI) of flat samples is presented. It consists of two magnetic measurement heads on both sides of the sample mounted on the legs of a u-shaped support. The sample is locally exposed to a magnetic excitation field consisting of two distinct frequencies, a stronger component at about 77 kHz and a weaker field at 61 Hz. The nonlinear magnetization characteristics of superparamagnetic particles give rise to the generation of intermodulation products. A selected sum-frequency component of the high and low frequency magnetic field incident on the magnetically nonlinear particles is recorded by a demodulation electronics. In contrast to a conventional MPI scanner, p-FMMD does not require the application of a strong magnetic field to the whole sample because mixing of the two frequencies occurs locally. Thus, the lateral dimensions of the sample are just limited by the scanning range and the supports. However, the sample height determines the spatial resolution. In the current setup it is limited to 2 mm. As examples, we present two 20 mm × 25 mm p-FMMD images acquired from samples with 1 µm diameter maghemite particles in silanol matrix and with 50 nm magnetite particles in aminosilane matrix. The results show that the novel MPI scanner can be applied for analysis of thin biological samples and for medical diagnostic purposes.

Frequency Mixing Magnetic Detection Scanner for Imaging Magnetic Particles in Planar Samples

The setup of a planar Frequency Mixing Magnetic Detection (p-FMMD) scanner for performing Magnetic Particles Imaging (MPI) of flat samples is presented. It consists of two magnetic measurement heads on both sides of the sample mounted on the legs of a u-shaped support. The sample is locally exposed to a magnetic excitation field consisting of two distinct frequencies, a stronger component at about 77 kHz and a weaker field at 61 Hz. The nonlinear magnetization characteristics of superparamagnetic particles give rise to the generation of intermodulation products. A selected sum-frequency component of the high and low frequency magnetic field incident on the magnetically nonlinear particles is recorded by a demodulation electronics. In contrast to a conventional MPI scanner, p-FMMD does not require the application of a strong magnetic field to the whole sample because mixing of the two frequencies occurs locally. Thus, the lateral dimensions of the sample are just limited by the scanning range and the supports. However, the sample height determines the spatial resolution. In the current setup it is limited to 2 mm. As examples, we present two 20 mm × 25 mm p-FMMD images acquired from samples with 1 µm diameter maghemite particles in silanol matrix and with 50 nm magnetite particles in aminosilane matrix. The results show that the novel MPI scanner can be applied for analysis of thin biological samples and for medical diagnostic purposes.

High Visible-light Photocatalytic Activity of γ-Fe2O3/TiO2 Nanotube Heterojunction Arrays

Abstract This study presents the preparation and the application of γ -Fe 2 O 3 /TiO 2 nanotube magnetic heterojunction photocatalysts (MHPs) for photodegradation of methylene blue under visible light irradiation. The morphology, the microstructure, the magnetic properties and the photocatalytic activity of γ -Fe 2 O 3 /TiO 2 (NT) MHPs were studied. Results show that the MHPs are provided with highly ordered TiO 2 (titania) nanotube arrays (55 nm in diameter and 10 nm in wall thickness) and nano γ -Fe 2 O 3 (maghemite) particle (approximately 15 nm) co-deposition. The MHPs exhibit a superparamagnetic behavior of γ -Fe 2 O 3 /TiO 2 (NT) MHPs resulting from the small size of γ -Fe 2 O 3 particles. The photocatalytic activity of γ -Fe 2 O 3 /TiO 2 (NT) MHPs is greater than that of Fe 3 O 4 /TiO 2 (NT) MHPs or pure TiO 2 (NT) under visible light irradiation. The interaction between γ -Fe 2 O 3 and TiO 2 improves charge separation and extends TiO 2 response into the visible region. Moreover, the formed heterojunction between γ -Fe 2 O 3 and TiO 2 can further prevent the recombination between photoelectrons and holes.

Enzyme Immobilization by Using Apatite Microcapsules with Magnetic Properties

Apatite Nucleus (AN) was attached on the surfaces of maghemite (γ-Fe2O3) particles and soaked them in SBF. By this treatment, formation of bonelike apatite was induced by AN and the apatite covered the whole surface of the γ-Fe2O3 particles. Urease was immobilized on the surfaces of microcapsules and collected by a neodymium magnet. The immobilized urease has an ability of a urea decomposition in an aqueous solution.

Synthesis, characterization and electrochemical performances of γ-Fe2O3 cathode material for Li-ion batteries

Maghemite nanoparticles were successfully synthesized via a co-precipitation method and electrochemical-optical properties of three different sizes were studied. Using this material as a Li-ion battery cathode, the results of charge–discharge tests showed that decreasing the maghemite particle size increased the lithium hosting capacity. First discharge capacities for cathodes made of material of particle size 11 and 19 nm were 206 and 186 mAh g−1 respectively, while for micron-sized cathode material a discharge capacity of 26 mAh g−1 was obtained. Electrochemical impedance spectroscopy (EIS) was used to derive equivalent circuit elements, which confirmed a reduction in lithium insertion resistance for material with a smaller particle size. EIS investigations disclosed that the Rct and ZW reduced with reduction of particle size, which indicates cathode material with lower particle size is more suitable. Band-gaps of the materials were determined using the diffuse reflectance spectroscopy technique on the base of Kubelka–Munk theory. The results showed that the needed energy for electron conduction reduces with reduction of particle size, which results in capacity enhancement.

Magnetoconductive maghemite core/polyaniline shell nanoparticles: Physico-chemical and biological assessment

Nanoparticles of various compositions are increasingly being used in many areas of medicine. The aim of this study was to develop nanoparticles, which would possess both magnetic and conductive properties and, thus improve their suitability for a wider range of biomedical applications. Namely, it would enable both the particle manipulation and imaging using their magnetic properties and simultaneous stimulation of electro-sensitive cell types using their magnetic properties, which can be used in tissue therapy, engineering and as biosensors. Maghemite (γ-Fe2O3) particles were prepared by the co-precipitation of Fe2+ and Fe3+ salts with ammonium hydroxide, followed by the controlled oxidation with NaOCl. The polyaniline (PANI) shell on the γ-Fe2O3 nanoparticles was obtained by the polymerization of aniline hydrochloride with ammonium peroxydisulfate in an aqueous solution of poly(N-vinylpyrrolidone) at two reaction temperatures (0 and 25°C). The resulting γ-Fe2O3&PANI particles were characterized by both the light and transmission electron microscopies, dynamic light scattering, magnetic measurements, UV–vis and energy dispersive X-ray (EDAX) spectroscopy. The size of the starting γ-Fe2O3 particles was 11nm, that increased to 25nm after the modification with PANI. The incubation of both the γ-Fe2O3 and γ-Fe2O3&PANI nanoparticles with the human neuroblastoma derived SH-SY5Y cells for 8 days showed neither significant decrease in the cell viability, nor detectable changes in the cell morphology. This indicates, that the particles have no detectable cytotoxicity in cell culture and represent a promising tool for further use in biomedical applications.

Laboratory Investigation of Antibiotic Interactions with Fe2O3 Nanoparticles in Water

AbstractThe movement and degradation of drugs in soil and water environments are related to surface interactions with oxide nanoparticles. These nanoparticles could be stationary substrates or suspended in aqueous solution. In this study, different pH solutions of the common antibiotic ampicillin (AMP) were mixed with ≤50-nm Fe2O3 (maghemite) particles. Both sorption and breakdown of AMP were observed. For initial drug concentrations from ∼3 μM to 2.9 mM, the overall AMP removal from solution can be described by linear isotherms with removal coefficients (Kr) of 394 (±43) L kg−1 at pH 2, 551 (±37) L kg−1 at pH 6, and 256 (±37) L kg−1 at pH 8. At pH 4, AMP removal can be described by a Freundlich isotherm of log Kf=3.27 (±0.19) and n=0.57 (±0.15). AMP solutions were separated from maghemite nanoparticles after mixing and analyzed by liquid chromatography/mass spectroscopy (LC/MS) techniques, resulting in the detection of penicilloic and penilloic acid breakdown products.

Synthesis, surface characterization and electrokinetic properties of colloidal silica nanoparticles with magnetic core

In order to obtain functionalized silica colloids with magnetic properties, the three-step reaction, was carried out. The aqueous suspension of iron oxide nanoparticles as magnetic core (maghemite—γ-Fe2O3) was synthesized according to the Massart’s method (Massart in IEEE Trans Magn 17:1247–1248, 1981). A silica shell was obtained onto maghemite employing a modified sol–gel method by Salgueirino (Salgueirino-Maceira et al. in Adv Mater 19:4131–4144, 2006). As-synthesized magnetic silica core/shell nanocomposites were further functionalized by the post-grafting approach, using (3-Aminopropyl)-trimethoxysilane (APTMS) (Pham et al. in Langmuir 18:4915–4920, 2002). The obtained materials were characterized by nitrogen adsorption/desorption measurements, X-ray powder diffractometry (XRD), transmission electron microscopy (TEM). Particle sizes were measured by diffraction laser (DL). In order to establish colloidal stability of the system, zeta potential were measured. The syntheses routes led to obtain both, good purity of maghemite particles (more than 90 %) and their good coverage by outer silica shell. Thanks to their nanometer size and surface properties (especially, presence of amino groups which can ensure the electrostatic interaction between surface of adsorbent and adsorbate molecules), as-prepared nanocomposites can be considered as promising adsorbents. It can be found in the literature, that such systems are used in medicine as targeted drug delivery systems (Chen et al. in J Magn Magn Mater 322:2439–2445, 2010; Bele et al. in J Chromatogr B 867:160–164, 2008) or in environment protection as magnetically removable adsorbents (Giakisikli and Anthemidis in Anal Chim Acta 789:1–16, 2013; Tural et al. in J Phys Chem Solids 72:968–973, 2011).

Scanning Nanospin Ensemble Microscope for Nanoscale Magnetic and Thermal Imaging.

Quantum sensors based on solid-state spins provide tremendous opportunities in a wide range of fields from basic physics and chemistry to biomedical imaging. However, integrating them into a scanning probe microscope to enable practical, nanoscale quantum imaging is a highly challenging task. Recently, the use of single spins in diamond in conjunction with atomic force microscopy techniques has allowed significant progress toward this goal, but generalization of this approach has so far been impeded by long acquisition times or by the absence of simultaneous topographic information. Here, we report on a scanning quantum probe microscope which solves both issues by employing a nanospin ensemble hosted in a nanodiamond. This approach provides up to an order of magnitude gain in acquisition time while preserving sub-100 nm spatial resolution both for the quantum sensor and topographic images. We demonstrate two applications of this microscope. We first image nanoscale clusters of maghemite particles through both spin resonance spectroscopy and spin relaxometry, under ambient conditions. Our images reveal fast magnetic field fluctuations in addition to a static component, indicating the presence of both superparamagnetic and ferromagnetic particles. We next demonstrate a new imaging modality where the nanospin ensemble is used as a thermometer. We use this technique to map the photoinduced heating generated by laser irradiation of a single gold nanoparticle in a fluid environment. This work paves the way toward new applications of quantum probe microscopy such as thermal/magnetic imaging of operating microelectronic devices and magnetic detection of ion channels in cell membranes.

Functional micelles formed by branched polymeric surfactants: Synthesis, characteristics, and application as nanoreactors and carriers

Branched polymeric surfactants composed of grafted non-ionic polyethylene glycol (PEG) and anionic polyelectrolyte chains were synthesized via radical polymerization initiated by the comb-like PEG-containing polyperoxide. Above definite concentration in solution, these surfactants form micelle-like structures (MLS). The MLS formed by branched polymeric molecules are of larger size in comparison with size of MLS formed by the initial PEG-containing polyperoxide that is caused mainly by different mechanism of their self-organization and morphology of formed MLS. The availability of grafted polyelectrolyte chains in the MLS provides a possibility of their use as the containers for immobilization of bio-active substances and nucleation of the inorganic nanoparticles, as well as formation of their stable colloidal systems in water in a wide pH range. Noticeable compaction and narrowed size distribution of the MLS were revealed after immobilization of doxorubicin (Dox) molecules or Fe2O3 nanocrystals. MLS-based systems were used for delivery of Dox and maghemite particles at treatment of tumor cells. Both MLS-based formulations of Dox and Fe2O3 were efficiently engulfed by rat glioma C6 cells. A significant (10 times) decrease in the effective therapeutic dose of Dox was found when this drug was delivered by a MLS-based formulation of Dox. That effect might be explained by a specific structure and functionality of the novel carrier used for immobilization of drug that should be delivered to target cells.

Hypericin-bearing magnetic iron oxide nanoparticles for selective drug delivery in photodynamic therapy.

Combining the concept of magnetic drug targeting and photodynamic therapy is a promising approach for the treatment of cancer. A high selectivity as well as significant fewer side effects can be achieved by this method, since the therapeutic treatment only takes place in the area where accumulation of the particles by an external electromagnet and radiation by a laser system overlap. In this article, a novel hypericin-bearing drug delivery system has been developed by synthesis of superparamagnetic iron oxide nanoparticles (SPIONs) with a hypericin-linked functionalized dextran coating. For that, sterically stabilized dextran-coated SPIONs were produced by coprecipitation and crosslinking with epichlorohydrin to enhance stability. Carboxymethylation of the dextran shell provided a functionalized platform for linking hypericin via glutaraldehyde. Particle sizes obtained by dynamic light scattering were in a range of 55–85 nm, whereas investigation of single magnetite or maghemite particle diameter was performed by transmission electron microscopy and X-ray diffraction and resulted in approximately 4.5–5.0 nm. Surface chemistry of those particles was evaluated by Fourier transform infrared spectroscopy and ζ potential measurements, indicating successful functionalization and dispersal stabilization due to a mixture of steric and electrostatic repulsion. Flow cytometry revealed no toxicity of pure nanoparticles as well as hypericin without exposure to light on Jurkat T-cells, whereas the combination of hypericin, alone or loaded on particles, with light-induced cell death in a concentration and exposure time-dependent manner due to the generation of reactive oxygen species. In conclusion, the combination of SPIONs’ targeting abilities with hypericin’s phototoxic properties represents a promising approach for merging magnetic drug targeting with photodynamic therapy for the treatment of cancer.

Magnetoelectrocatalysis of the Oxygen Reduction Reaction (ORR)

Fundamental kinetic studies of the catalytic effect of localized magnetic fields on the oxygen reduction reaction (ORR) are conducted at platinum electrodes in the organic solvent acetonitrile with tetrabutylammonium tetrafluoroborate (TBABF4) electrolyte. Electrodes are modified with magnetic particles suspended in a Nafion film. The magnetic particles are SiMag C1 (ChemiCell Gmbh) superparamagnetic maghemite particles coated with methyl silane to make them chemically inert. Cyclic voltammetric results for a Nafion film in oxygen free and oxygen saturated conditions are shown. For the composite of magnetic particles in Nafion, data for saturated oxygen are shown. Enhanced heterogeneous electron transfer kinetics are observed. Currents increase by 20% and the peak splitting is reduced by 400 mV (from 1.8 V to 1.4 V). The overpotential as measured at current half height is decreased by 200 mV. Particles with different magnetic field strengths are examined as well as demagnetized particles. Figure 1

Lithium Adsorption on Magnetite, Lepidocrocite, and Maghemite at Elevated Temperatures

Lithium adsorption on the surface of magnetite, lepidocrocite, and maghemite particles was studied at different pH values in LiOH and Li2CO3 solutions under redox conditions and temperatures relevant to the water chemistry of CANadian Deuterium Uranium (CANDU) reactors. Lithium adsorption on maghemite shows a different behavior than on lepidocrocite and magnetite. It is concluded that specific adsorption is the dominant adsorption mechanism on maghemite while lithium adsorption on lepidocrocite and magnetite is nonspecific. However, lithium intercalation into the spinel structure of magnetite and maghemite is also likely. The introduction of O2 reduces lithium adsorption on magnetite. The adsorption behavior of lithium on iron oxides is important to understand the lithium hideout and return in the heat transport system during shutdown and restart of CANDU reactors.

Collective magnetic behavior of biocompatible systems of maghemite particles coated with functional polymer shells

Abstract Three series of core–shell maghemite nanoparticles were prepared by a template synthesis using surface active oligoperoxides and further surface initiated grafting functional polymers, forming shell suitable for biomedical applications. Because the polymer shells prevent exchange coupling between maghemite particles, the overall magnetic properties of the samples studied are dominated by dipolar interparticle interactions. Only the sample with the highest polymer fraction displays superparamagnetic relaxation phenomena close to the room temperature. On cooling, the magnetostatic interactions lead to a disordered collective magnetic state that should be described in terms of a spin-glass phenomenology. This collective freezing cannot however be considered as a generic spin-glass phase transition at a well-defined temperature but rather as freezing to a metastable glass-like state of locally correlated structural domains (clusters) without a long-range order. A quasi static spin ordering is only achieved at temperatures much below the freezing temperature.