Colloidal Magnetite Research Articles

Ultrasmall Mixed Ferrite Colloids as Multidimensional Magnetic Resonance Imaging, Cell Labeling, and Cell Sorting Agents

One area that has been overlooked in the evolution of magnetic nanoparticle technology is the possibility of introducing informational atoms into the iron oxide core of the coated colloid. Introduction of suitable atoms into the iron oxide core offers an opportunity to produce a quantifiable probe, thereby adding one or more dimensions to the magnetic colloid's informational status. Lanthanide-doped iron oxide nanoparticles have been synthesized to introduce informational atoms through the formation of colloidal mixed ferrites. These colloids are designated ultrasmall mixed ferrite iron oxides (USMIOs). USMIOs containing 5 mol % europium exhibit superparamagnetic behavior with an induced magnetization of 56 emu/g Fe at 1.5 T, a powder X-ray diffraction pattern congruent with magnetite, and R1 and R2 relaxivity values of 15.4 (mM s) (-1) and 33.9 (mM s) (-1), respectively, in aqueous solution at 37 degrees C and 0.47 T. USMIO can be detected by five physical methods, combining the magnetic resonance imaging (MRI) qualities of iron with the sensitive and quantitative detection of lanthanide metals by neutron activation analysis (NA), time-resolved fluorescence (TRF), X-ray fluorescence, along with detection by electron microscopy (EM). In addition to quantitative detection using neutron activation analysis, the presence of lanthanides in the iron oxide matrix confers attractive optical properties for long-term multilabeling studies with europium and terbium. These USMIOs offer high photostability, a narrow emission band, and a broad absorption band combining the high sensitivity of time-resolved fluorescence with the high spatial resolution of MRI. USMIO nanoparticles are prepared through modifications of traditional magnetite-based iron oxide colloid synthetic methods. A 5 mol % substitution of ferric iron with trivalent europium yielded a colloid with nearly identical magnetic, physical, and chemical characteristics to its magnetite colloid parent.

Spontaneous Oil-in-Water Emulsification Induced by Charge-Stabilized Dispersions of Various Inorganic Colloids

Charge-stabilized dispersions of inorganic colloids are shown to induce spontaneous emulsification of hydrophobic (TPM) molecules to stable oil-in-water emulsions, with monodisperse, mesoscopic oil droplet diameters in the range of 30-150 nm, irrespective of the polydispersity of the starting dispersions. The results for cobalt ferrite particles and commercial silica sols extend our first study (Sacanna, S.; Kegel, W. K.; Philipse, A. Phys. Rev. Lett. 2007, 98, 158301) on spontaneous emulsification induced by charged magnetite colloids and show that this type of self-assembly is quite generic with respect to the composition of the nanoparticles adsorbing at the oil-water interface. Moreover, we provide additional experimental evidence for the thermodynamic stability of these mesoemulsions, including spontaneous oil dispersal imaged by confocal microscopy and monitored in situ by time-resolved dynamic light scattering. We discuss the possibility that thermodynamic stability of the emulsions is provided by the negative tension of the three-phase line between oil, water, and adsorbed colloids.

One‐Step Synthesis of Highly Water‐Soluble Magnetite Colloidal Nanocrystals

A high-temperature solution-phase hydrolysis approach has been developed for the synthesis of colloidal magnetite nanocrystals with well-controlled size and size distribution, high crystallinity, and high water solubility. The synthesis was accomplished by the hydrolysis and reduction of iron(III) cations in diethylene glycol with a rapidly injected solution of sodium hydroxide at an elevated temperature. The high reaction temperature allows for control over size and size distribution and yields highly crystalline products. The superior water solubility is achieved by using a polyelectrolyte, that is, poly(acrylic acid) as the capping agent, the carboxylate groups of which partially bind to the nanocrystal surface and partially extend into the surrounding water. The direct synthesis of water-soluble nanocrystals eliminates the need for additional surface modification steps which are usually required for treating hydrophobic nanocrystals produced in nonpolar solvents through the widely recognized pyrolysis route. The abundant carboxylate groups on the nanocrystal surface allow further modifications, such as bioconjugation, as demonstrated by linking cysteamine to the particle surface. The monodisperse, highly water-soluble, superparamagnetic, and biocompatible magnetite nanocrystals should find immediate important biomedical applications.

Purity of Colloidal Magnetite Particles Used as a Model Corrosion Product

Abstract Synthesis of magnetite as a model corrosion product by oxidation of ferrous hydroxide precipitated from ferrous sulfate by nitrate is a classical protocol to obtain monodisperse pseudosphe...

Change in the intensity of light scattering in a magnetite colloid under the simultaneous action of electric and magnetic fields

The change in the intensity of light scattering in a colloidal solution of magnetite particles in kerosene under the simultaneous action of coaxial and mutually perpendicular electric and magnetic fields has been studied. It has been found that, at certain strengths of mutually perpendicular fields, the change in the scattering intensity is maximal. The effect observed has been interpreted on the basis of the Rayleigh-Debye-Gans anisotropic approximation within the model of orientation of aggregates of magnetite particles under the joint action of the fields.

Microwave dielectric properties of magnetite colloidal particles in magnetic fluids

Measurements performed over the frequency range 700 MHz to 3 GHz, of the complexdielectric permittivity of (i) a kerosene-based magnetic fluid sample with magnetiteparticles stabilized with oleic acid, (ii) oleic acid and (iii) kerosene, are presented.The biphasic dielectric model describing the dielectric behaviour of magnetic fluids wasredefined based on the experimental results of Rocchiccioli-Deltcheff et al. According tothis proposed new model, the magnetic fluids can be considered as being biphasic systemsin which one phase consists of surfacted colloidal particles electrically charged byadsorbed or chemisorbed ions and the other phase consists of the carrier liquid.Using the Sillars theory for heterogeneous dielectrics, in the biphasic approximation, wehave determined the dielectric permittivity, electric conductivity and shape factor of thecolloidal magnetite particles within the investigated magnetic fluid, in the microwave range.The values obtained for the colloidal magnetite particles are the shape factorn = 2.27, the real part of the dielectric permittivityε1′ = 36.8, and the effectiveconductivity σ1 eff = 1.5 Ω−1 m−1.The differences between the experimental results and the values of conductivity andpermittivity of bulk magnetite are explained in terms of the proposed biphasic model.

Effect of Dispersant on Preparation of Colloidal Magnetite Nanocrystals

Nanometer scale magnetite particles were prepared in a very low concentration dispersing system with a dispersant. The average size of the particles prepared under optimum conditions was determined by transmission electron microscopy to be approximately 1.8 nm. The magnetic properties were investigated using a superconducting quantum interference device (SQUID) magnetometer. The dried samples exhibited approximately superparamagnetic behavior. Rhelogical property measurement shows that the colloidal magnetite both with and without polyurethane reveals shear thinning. The surface morphology of the films of the magnetite nanoparticles on the glass, as shown by atomic force microscopy (AFM) images, produces well-formed surface structures that are evenly spaced by the magnetite nanoparticles. It also shows that this is an effective method of surface modification for nanometer scale magnetite.

Deposition of Magnetic Colloidal Particles on Graphite and Mica Surfaces Driven by Solvent Evaporation

The deposition of colloidal magnetite particles onto graphite and mica surfaces induced by solvent evaporation is studied using atomic force microscopy. After evaporation under ambient conditions we observe polydisperse beadlike aggregates; the mean aggregate diameter is larger on graphite than on mica. After evaporation at elevated temperatures we observe a variety of effects, including enhanced particle aggregation and spinodal-like deposition patterns. To explain these trends, we propose mechanisms involving the wetting properties of the solvent. We have also made a brief study of the effects of applied magnetic fields on the formation of aggregates. A field applied parallel to the surface enhances aggregation and favors deposition patterns characteristic of hole-nucleation processes. A perpendicular field leads to a reduction in aggregate size and favors a homogeneous distribution of particles on the surface. These effects are explained in terms of the likely orientation of the dipolar particles on the surface.

Internal magnetic field effects on the photochemistry of a xanthone derivate covalently anchored to magnetite nanoparticles

Irradiation of azaxanthone in the presence of colloidal magnetite nanoparticles gives rise to the generation of the corresponding azaxanthone triplet, whose lifetime is influenced by internal magnetic field effects. In contrast, covalent tethering between magnetite and azaxanthone promotes photoinduced electron transfer leading to the observation of azaxanthone radical anion.

Stability of mixtures of charged silica, silica–alumina, and magnetite colloids

We report experiments on the stability of aqueous mixtures of charged colloidal magnetite and charged silica and silica covered with alumina particles of similar size. First, positively charged magnetite dispersions were mixed with negatively charged silica dispersions at pH 4, at different volume ratios and low colloid volume fractions, producing mixtures which were stable over a period of weeks despite the expected electrostatic attraction between the oppositely charged particles. When magnetite particles were mixed with positively charged silica covered with alumina at pH 4 under exactly the same conditions, some of the systems separated to form a magnetite sediment. When the volume fraction of the initial dispersions was increased, the behavior of the mixtures was the opposite: positive magnetite/negative silica mixtures were unstable at intermediate volume ratios. The unexpected behavior of the mixtures was investigated by means of electrophoretic mobility, initial susceptibility, and dynamic light scattering measurements as well as sedimentation experiments.

Magnetic hydrophilic methacrylate-based polymer microspheres designed for polymerase chain reactions applications

Magnetic hydrophilic non-porous P(HEMA- co-EDMA), P(HEMA- co-GMA) and PGMA microspheres were prepared by dispersion (co)polymerization of 2-hydroxyethyl methacrylate (HEMA) and ethylene dimethacrylate (EDMA) or glycidyl methacrylate (GMA) in the presence of several kinds of magnetite. It was found that some components used in the preparation of magnetic carriers interfered with polymerase chain reaction (PCR). Influence of non-magnetic and magnetic microspheres, including magnetite nanoparticles and various components used in their synthesis, on the PCR course was thus investigated. DNA isolated from bacterial cells of Bifidobacterium longum was used in PCR evaluation of non-interfering magnetic microspheres. The method enabled verification of the incorporation of magnetite nanoparticles in the particular methacrylate-based polymer microspheres and evaluation of suitability of their application in PCR. Preferably, electrostatically stabilized colloidal magnetite (ferrofluid) should be used in the design of new magnetic methacrylate-based microspheres by dispersion polymerization.

Uranium (VI) sorption on colloidal magnetite under anoxic environment: experimental study and surface complexation modelling

Magnetite is one of the most important end member of iron corrosion products under a reducing environment; therefore, it may be one of the first products interacting with radionuclides in a radioactive waste disposal after the canister failure. Nanocrystalline magnetite was synthetised in the laboratory and its main physico-chemical properties (microstructure, surface area, surface charge) were analysed. The stability of the oxide was also investigated under the experimental conditions used in sorption studies. The sorption behaviour of U VI onto magnetite was analysed under O 2- and CO 2-free conditions in a wide range of pH, ionic strengths and radionuclide concentrations. The uranyl binding to magnetite is characterised by a sorption edge between pH 4 and 5.5, and sorption was found to be independent on the electrolyte concentration, which indicates the formation of inner sphere complexes. The sorption isotherms showed a linear behaviour up to the saturation of the sorption sites with a Langmuir-type behaviour. One of the aims of this work was to find the simplest model capable to reproduce the experimental data. Sorption data were fitted using a classical approximation (diffuse double layer model), considering only one type of surface site and evaluating two different options: the first one involving two different monodentate complexes, and the second one a single binuclear bidentate complex. A highly satisfactory fit of the experimental data was obtained by both approaches in the range of the experimental conditions investigated.

Magnetite and Co ferrite- based clay composites

AbstractThe synthesis of clay composites modified with magnetite and Co ferrite magnetic nanoparticles is described. The synthetic method relies on the adsorption of colloidal magnetite or Co ferrite particles onto the external surfaces of a Na-saturated clay mineral to give magnetic clay composites that can be converted easily, through ion exchange reactions, to valuable clay derivatives, e.g. organoclays, which maintain the magnetic properties of the parent composite. The magnetic solids were characterized by XRD, EPR, Mössbauer, magnetic measurement and TEM techniques.

Fabrication and characterization of a rigid magnetic matrix for protein adsorption

This article describes the fabrication and characterization of a novel magnetic poly(glycidyl methacrylate–triallyl isocyanurate–divinylbenzene) matrix containing magnetite colloids. The results showed that the matrix was superparamagnetic and could be separated magnetically from a suspension in a few seconds. Protein adsorption properties of diethylamine-derivatized matrix were characterized with bovine serum albumin (BSA) as a model protein. The static capacity determined by batch adsorption was 79 mg/ml wet matrix. Kinetic study gave an effective diffusivity of BSA of 5.0·10 −13 m 2/s in the matrix at an initial BSA concentration in the liquid phase of 1.0 mg/ml. Stability of the matrix was confirmed by recycling of the matrix in protein adsorptions.

Quartz surface contamination due to its processing in the Magstream model 100

The processing of quartz in the Magstream, a piece of equipment used to separate minerals according to their specific gravities, leads to the formation of colloidal magnetite and iron ligninsulphonate precipitates on its surface. These precipitates activate quartz for flotation with amine, especially in pH ranges less than 9.0 and over 10.5. These results indicate a restriction of the use of Magstream to separate minerals when further studies involve surface properties.

Anomalous Attraction between Colloidal Magnetite and Silica Spheres in Apolar Solvents

We demonstrate the existence of an anomalous, strong attraction between small (9 nm) oleic acid-grafted magnetite particles and octadecanol-grafted silica spheres (420 nm) in apolar solvents. This attraction manifests itself by irreversible adsorption of magnetite particles onto silica spheres, with surface coverages up to 30%. This “heteroflocculation” is, quite surprisingly, orders of magnitude slower than a diffusion-limited process. The adsorption can be reversed by transferring covered silica particles to solvents with a higher dielectric constant. The findings practically rule out van der Waals forces or Coulomb forces between any pre-existing surface charges as the source of attraction.

CHARACTERIZATION OF PVA-BASED MAGNETIC AFFINITY SUPPORT FOR PROTEIN ADSORPTION

A magnetic fluid was prepared by an oxidization-precipitation with FeCl2 and H2O2 in polyvinyl alcohol (PVA) solution. Cross-linked directly with glutaraldehyde, a magnetic support with magnetic particles entrapped by cross-linked PVA gel was produced. Cibacron blue 3GA (CB) was immobilized to the magnetic support to prepare the magnetic affinity support (MAS). The MAS was characterized by transmission electron microscopy (TEM) and infrared spectrum analysis. The TEM showed that the MAS ranged from 1 to 10 μm and consisted of nanometer-sized colloidal magnetite particles. It was determined that the MAS had a saturation magnetization of 1.16 × 103 A/m and showed no hysteresis in an external magnetic field of up to 5.6 × 105 A/m. The adsorption kinetics and equilibrium of bovine serum albumin (BSA) confirmed rapid adsorption and large capacity of the MAS. BSA adsorption reached equilibrium in 5 min. At a CB coupling density of 23 μmol/g, the adsorption capacity of the MAS was 35 mg/g at an aqueous phase concentration of 0.1 mg/mL. The possibility of repetitive uses of the MAS was also demonstrated, indicating the stability of the magnetic support for protein adsorption.

Redox reactions of nitrite ions on the surface of colloidal magnetite particles coated with chondroitin sulfate

Colloidal magnetite particles coated with chondroitin sulfate (abbreviated as Fe/CS) were prepared under conditions of varying Fe(II) fractions at a fixed Fe concentration and a given concentration of CS. The average size of the magnetite core region was estimated as 7 nm from transmittance electron microscopy measurements, while the size of the Fe/CS particles ranged 155–175 nm, as estimated using Rayleigh scattering measurements by reference to a control size derived from the dynamic light scattering. The reaction of various Fe/CS with NO−2 in aqueous solutions was determined by fluorometry using 2,3-diaminonaphthalene as a probe and by gas chromatography–mass spectrometry. The concentrations of NO−2 in the reaction mixtures decreased in the presence of Fe/CS to a greater extent under Ar compared with aerobic conditions. The reactivity of Fe/CS toward NO−2 under aerobic conditions increased with decreasing the size of Fe/CS particles or with increasing content of Fe(III) in the Fe/CS solutions, but was independent of the Fe(II) fraction in the preparation process. While CS molecules had no influence on the NO−2 decomposition, those coated with the magnetite core may prevent the diffusion of NO−2 to be adsorbed on the core surfaces. NO−2 was concluded to undergo redox reactions with Fe(II) and Fe(III) located on the core surface of magnetite crystalline structures of Fe/CS.

Characterisation and removal of iron from fly ash of talcher area, Orissa, India

Morphology, mineralogy and physico-chemical parameters of fly ash from Talcher area were studied. Morphologically it consists of spherical particles of varying size. Major minerals are quartz, mullite, hematite and magnetite. Elemental analysis and fusion characteristics of the material indicate the presence of class C type pozzolan with excellent pozzolonic properties and low slagging with medium fouling nature. In an attempt to remove iron from fly ash by selective magnetic coating followed by magnetic separation, the effects of pH, magnetic intensity, colloidal magnetite concentration and addition of sodium oleate have been studied. It is possible to remove around 92% iron at an optimum pH of ∼ 7.1 and magnetic intensity of ∼11.8 K gauss.

Birefringence in Concentrated Ferrocolloids

Magnetic birefringence in concentrated kerosene-based magnetite colloids was experimentally studied. It was shown that field, frequency, and temperature dependences of a signal can be satisfactorily described already in terms of one-particle model, however with obligatory allowance for particle polydispersity. The role of aggregates in the evolution of this effect was shown to be insignificant.