Iron Oxide Particle Size Research Articles

Alumina-supported iron oxide nanoparticles as Fischer–Tropsch catalysts: Effect of particle size of iron oxide

The Fischer–Tropsch synthesis of unpromoted and nano-sized iron oxide supported on δ-Al 2O 3 was investigated using a fixed-bed reactor. The catalysts prepared from pre-synthesized iron oxide with varying particle size (2–12 nm) showed much higher catalytic activities than the one prepared by using conventional impregnation method. The best results for CO conversion were obtained when the catalyst had Fe particle size of 6.1 nm. With an increase in particle size, the reduction degree and C 5+ selectivity was increased, whereas CH 4 selectivity and the uptake of adsorbed CO were decreased. Turnover frequency (TOF) at 300 °C was increased from 0.02 to 0.16 s −1 when d(Fe 0) was increased from 2.4 to 6.2 nm, and then it remains almost constant up to a particle size of 11.5 nm. Particle sizes of prepared iron oxide were analyzed by XRD and TEM, and the reduction behaviors of Fe/Al 2O 3 catalysts were studied by H 2-TPR. The effective iron size, metal dispersion and reduction degree of Fe/Al 2O 3 catalysts were measured by CO chemisorption and O 2 titration.

High transversal relaxivities of silica coated multicore iron oxide nanoparticles suitable for magnetic resonance imaging

AbstractWe report on high transversal relaxivity values of composite iron oxide-silica nanoparticles. To obtain the material, pre-formed maghemite nanoparticles were coated with silica by sol-gel chemistry, using supercritical fluids as the reaction media. The composite particles were monodisperse and consisted of a core of several maghemite nanoparticles, surrounded by a thick silica shell. The high pressure and high temperature process did not affect the iron oxide particle size but induced an increase on their saturation magnetization values, possibly due to an improvement of the particle crystallinity. These iron oxide-based materials present very high transversal relaxivity values which can be correlated to the magnetic moment and to the silica shell width of the composite particles. Moreover, composite particles are not cytotoxic and they are dispersable in polar solvents.

Synthesis and Characterization of Iron Oxide Nanoparticles by Solid State Chemical Reaction Method

The iron oxide nanoparticles were synthesized by solid state chemical reaction method. The synthesized powders were characterized by XRD, SEM, EDAX and TG-DTA techniques. An average grain size of 10–20 nm for Maghemite and 80–85 nm for Hematite was calculated using XRD line broadening and SEM. The effect of different parameters such as annealing temperature, milling time, Fe+3:Fe+2 concentration ratio have been investigated on the particle size and phase formation. Heat treatment of the produced powders in which Fe+3:Fe+2 ratio equal to 2:1, resulted in tetragonal (Maghemite) and rombohedral (Hematite) structures at 300 and 600 °C, respectively. It was found that by changing Fe+3:Fe+2 ratios from 2:1 to 1:2, hematite phase and from 2:1 to 1:1, Maghemite phase were formed at 300 °C. In addition with increasing milling time, the iron oxide particle size decreases, but there was no changing in the kind of phase.

Controlled flame synthesis of αFe2O3 and Fe3O4 nanoparticles: effect of flame configuration, flame temperature, and additive loading

Superparamagnetic iron oxide nanoparticles are used in diverse applications, including optical magnetic recording, catalysts, gas sensors, targeted drug delivery, magnetic resonance imaging, and hyperthermic malignant cell therapy. Combustion synthesis of nanoparticles has significant advantages, including improved nanoparticle property control and commercial production rate capability with minimal post-processing. In the current study, superparamagnetic iron oxide nanoparticles were produced by flame synthesis using a coflow flame. The effect of flame configuration (diffusion and inverse diffusion), flame temperature, and additive loading on the final iron oxide nanoparticle morphology, elemental composition, and particle size were analyzed by transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy. The synthesized nanoparticles were primarily composed of two well known forms of iron oxide, namely hematite αFe2O3 and magnetite Fe3O4. We found that the synthesized nanoparticles were smaller (6–12 nm) for an inverse diffusion flame as compared to a diffusion flame configuration (50–60 nm) when CH4, O2, Ar, and N2 gas flow rates were kept constant. In order to investigate the effect of flame temperature, CH4, O2, Ar gas flow rates were kept constant, and N2 gas was added as a coolant to the system. TEM analysis of iron oxide nanoparticles synthesized using an inverse diffusion flame configuration with N2 cooling demonstrated that particles no larger than 50–60 nm in diameter can be grown, indicating that nanoparticles did not coalesce in the cooler flame. Raman spectroscopy showed that these nanoparticles were primarily magnetite, as opposed to the primarily hematite nanoparticles produced in the hot flame configuration. In order to understand the effect of additive loading on iron oxide nanoparticle morphology, an Ar stream carrying titanium-tetra-isopropoxide (TTIP) was flowed through the outer annulus along with the CH4 in the inverse diffusion flame configuration. When particles were synthesized in the presence of the TTIP additive, larger monodispersed individual particles (50–90 nm) were synthesized as observed by TEM. In this article, we show that iron oxide nanoparticles of varied morphology, composition, and size can be synthesized and controlled by varying flame configuration, flame temperature, and additive loading.

Iron oxide modified minerals

Composites of iron oxide nanoparticles immobilized on the surface of various clay mineral matrices (muscovite, montmorillonite and vermiculite) have been prepared by the alkaline oxidative hydrolysis of iron sulphate in the presence of mineral matrices. The composites have been studied by Mossbauer spectroscopy, XRD, TEM and SQUID. Correspondence between the hyperfine parameters and the iron oxide particle size and magnetic behaviour has been proved. The prepared composites differ in magnetic properties, size and morphology of the iron oxide particles.

Surfactant effects on the particle size of iron (III) oxides formed by sol–gel synthesis

In this work, we probed the effects of a common surfactant, sodium dodecylbenzene sulfonate (NaDDBS), on the particle size of iron (III) oxides formed via a modified sol–gel synthesis. The goal was to create tunable nanosized particles via a method that combines the efficiency and advantages of the sol–gel process, but inhibits the formation of a gel. Two different metal salt precursors were used, ferric nitrate nonahydrate, Fe(NO 3) 3 · 9H 2O, and ferric chlorate hexahydrate, FeCl 3 · 6H 2O. The particle size of the dried gel was 4.5 nm for Fe(NO 3) 3 · 9H 2O and 3.6 nm for FeCl 3 · 6H 2O. In the presence of the surfactant FeCl 3 · 6H 2O formed a gel and Fe(NO 3) 3 · 9H 2O was unable to gel, but the new particle sizes were 4.9 nm and 3.2 nm, respectively. The addition of the surfactant in the later stages of the process afforded the stabilization of independent nanoparticles of the same size as those obtained in the systems that gelled.

Size, charge and concentration dependent uptake of iron oxide particles by non-phagocytic cells

A promising new direction for contrast-enhanced magnetic resonance (MR) imaging involves tracking the migration and biodistribution of superparamagnetic iron oxide (SPIO)-labeled cells in vivo. Despite the large number of cell labeling studies that have been performed with SPIO particles of differing size and surface charge, it remains unclear which SPIO configuration provides optimal contrast in non-phagocytic cells. This is largely because contradictory findings have stemmed from the variability and imprecise control over surface charge, the general need and complexity of transfection and/or targeting agents, and the limited number of particle configurations examined in any given study. In the present study, we systematically evaluated the cellular uptake of SPIO in non-phagocytic T cells over a continuum of particle sizes ranging from 33 nm to nearly 1.5 μm, with precisely controlled surface properties, and without the need for transfection agents. SPIO labeling of T cells was analyzed by flow cytometry and contrast enhancement was determined by relaxometry. SPIO uptake was dose-dependent and exhibited sigmoidal charge dependence, which was shown to saturate at different levels of functionalization. Efficient labeling of cells was observed for particles up to 300 nm, however, micron-sized particle uptake was limited. Our results show that an unconventional highly cationic particle configuration at 107 nm maximized MR contrast of T cells, outperforming the widely utilized USPIO (<50 nm).

Fe 2O 3-filled carbon nanotubes as a negative electrode for an Fe–air battery

Fe 2O 3-filled carbon nanotube material was prepared by filling carbon nanotubes (CNTs) with iron nitrate and then heating in an argon flow. The morphology and structure of this material were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with X-ray energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) measurements. The morphology, particle size and amount of iron oxide that filled CNTs depended on the amount of iron nitrate precursor. When Fe:C = 1:17 wt%, almost all of the iron oxide particles resided inside CNTs and their particle size was smaller than that at Fe:C = 1:8 wt%. The electrochemical properties of this material were investigated using cyclic voltammetry (CV) and galvanostatic cycling.

Synthesis of iron oxide nanoparticles using chitosan and starch templates

Natural polymers like chitosan and starch have been employed as templates for the preparation of iron oxide nanoparticles. The templates offer selective binding sites for Fe(II) under aqueous conditions. Controlled drying and subsequent removal of the template backbone enables the synthesis of spatially separated iron oxide nanoparticles. The crystalline character of the iron oxide and near narrow particle size distribution pattern have been confirmed through powder XRD, Photon Correlation Spectroscopy, and TEM measurements. The crystallite sizes of the particles were found to be 26–35 nm irrespective of the nature of the template.

D-Mannose-Modified Iron Oxide Nanoparticles for Stem Cell Labeling

New surface-modified iron oxide nanoparticles were developed by precipitation of Fe(II) and Fe(III) salts with ammonium hydroxide according to two methods. In the first method, precipitation was done in the presence of D-mannose solution (in situ coating); the second method involved oxidation of precipitated magnetite with sodium hypochlorite followed by addition of D-mannose solution (postsynthesis coating). Selected nanoparticles were characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), elemental analysis, dynamic light scattering, infrared (IR), X-ray powder analysis, and ultrasonic spectrometry. While the first preparation method produced very fine nanoparticles ca. 2 nm in diameter, the second one yielded ca. 6 nm particles. Addition of D-mannose after synthesis did not affect the iron oxide particle size. UV-vis spectroscopy suggested that D-mannose suppresses the nonspecific sorption of serum proteins from DMEM culture medium on magnetic nanoparticles. Rat bone marrow stromal cells (rMSCs) were labeled with uncoated and d-mannose-modified iron oxide nanoparticles and with Endorem (Guerbet, France; control). Optical and transmission electron microscopy confirmed the presence of D-mannose-modified iron oxide nanoparticles inside the cells. D-mannose-modified nanoparticles crossed the cell membranes and were internalized well by the cells. Relaxivity measurements of labeled cells in gelatin revealed very high relaxivities only for postsynthesis D-mannose-coated iron oxide nanoparticles.

Dextran-modified iron oxide nanoparticles

Dextran-modified iron oxide nanoparticles were prepared by precipitation of Fe(II) and Fe(III) salts with ammonium hydroxide by two methods. Iron oxide was precipitated either in the presence of dextran solution, or the dextran solution was added after precipitation. In the second method, the iron oxide particle size and size distribution could be controlled depending on the concentration of dextran in the solution. The nanoparticles were characterized by size-exclusion chromatography, transmission electron microscopy and dynamic light scattering. Optimal conditions for preparation of stable iron oxide colloid particles were determined. The dextran/iron oxide ratio 0–0.16 used in precipitation of iron salts can be recommended for synthesis of nanoparticles suitable for biomedical applications, as the colloid does not contain excess dextran and does not coagulate.

Magnetically modified bentonite as a possible contrast agent in MRI of gastrointestinal tract

AbstractA composite of iron oxide nanoparticles and mineral matrix has been studied by XRD, Mössbauer spectroscopy, and TEM. Magnetite and superparamagnetic magnetite have been identified by Mössbauer spectroscopy in the nanocomposite. A relationship between the hyperfine parameters and iron oxide particle size has been confirmed by TEM. The optimal concentration of “magnetite—bentonite” composite, when the MRI signal is fully reduced, was found for using this composite as a negative contrast agent.

Preparation and characterization of ω-functionalized polystyrene–magnetite nanocomposites

Magnetite (Fe 3O 4) nanoparticles were prepared by in situ precipitation and oxidation of ferrous ions in the presence of ω-functionalized polystyrenes having carboxylate, sulfonate, thiol, and thiolated groups. Based on the results for the orthogonal experimental design, both the ratio of the concentration of iron precursor to polymer and the reaction temperature were the major factors controlling the particle size and its shape morphology. By adjusting the reaction conditions, the iron oxide particle size can be effectively controlled in the range between 2 and 20 nm. The magnetite-based polymer composite was characterized by UV–vis spectroscopy, thermogravimetric analysis, transmission electron microscopy, and X-ray diffraction. Magnetization measurements revealed that the nanocomposite materials exhibit superparamagnetic behavior at room temperature.

Mechanochemical Synthesis of Fe-Based Nanocomposites and Their Application in the Catalytic Formation of Carbon Nanostructures

Mechanochemical process was employed to prepare Fe/MgO and Fe/NaCl nanocomposites. The carbon nanostructures (nanotubes and carbon-encapsulated Fe nanoparticles) were successfully synthesized using two nanocomposites as the catalyst. Our wok revealed that the morphology of Fe nanoparticles in the Fe/MgO nanocomposites depended on the distribution and particle size of iron oxides in the precursors. The size of Fe nanoparticles greatly affected their catalytic properties and the morphologies of carbon nanotubes. The successful carbon encapsulation of Fe nanoparticles was achieved by using the mechanochemically derived Fe/NaCl catalyst.

Preparation, characterization and catalytic behavior in methanol decomposition of nanosized iron oxide particles within large pore ordered mesoporous silicas

Nanosized iron oxide particles within various ordered mesoporous silicas (SBA-15, SBA-16, Fm3m, Ia3d) have been prepared from the corresponding nitrate and acetylacetonate precursors. N 2 physisorption, X-ray diffraction and Moessbauer spectroscopy are used for their characterization. The reductive properties of the modified materials were investigated by temperature-programmed reduction with hydrogen. Methanol decomposition to H 2, CO and methane was used as a test reaction. Some differences in the iron state, its phase transformations in reductive medium and also some variations in its catalytic behavior were observed and discussed in view of the iron oxide particle size dispersion and its dependency on the pore geometries of the silica supports.

Soluble Paramagnetic Chelates and Stabilized Colloidal Particle Solutions of Iron Oxides as Contrast Agents for Magnetic Resonance Imaging

The development of contrast agents shortening the relaxation times of protons began more than 20 years ago in order to improve the capability of diagnosing disease by means of magnetic resonance imaging (MRI). A variety of extracellular and tissue specific contrast agents were developed based on two types of molecules. One type was related to soluble paramagnetic chelates and the other type to stabilized colloidal particle solutions of iron oxides. The chelate or metal complex of gadopentetate dimeglumine was the pioneering magnetic resonance (MR) contrast agent used in 1988. Chemical modifications of this chelate and the design of new chelates led to tissue or blood pool specificity in MRI. Similarly, modifications in coating materials and variations in size of iron oxide particles allowed for tissue specificity or blood pool properties in MRI. Both types of contrast agents offer excellent perspectives for clinical MRI and for molecular imaging.

Some factors influencing forced hydrolysis of FeCl 3 solutions

Phase composition, size and shape of iron oxide particles produced by forced hydrolysis of Fe 3+ ions depended on the concentrations of FeCl 3 and HCl, and on the presence of 0.005 M quinine hydrogen sulphate (QHS). After 7 days of forced hydrolysis, α-Fe 2O 3 was produced from the 0.01 M FeCl 3 solution, the mixture of β-FeOOH and α-Fe 2O 3 was produced from 0.02 M FeCl 3 solution, whereas β-FeOOH was produced from the 0.1 M FeCl 3 solution. Forced hydrolysis of the 0.1 M FeCl 3+0.1 M HCl solution yielded α-Fe 2O 3. In the presence of 0.005 M QHS, the formation of β-FeOOH and α-Fe 2O 3 was partially or completely suppressed in dependence on the conditions of forced hydrolysis of Fe 3+ ions. Specific shapes of β-FeOOH particles (cigar-type, X-, Y-, and star-shapes) were not obtained in the presence of 0.005 M QHS. The bundles of β-FeOOH needles with irregular ends were obtained instead. Also, in the presence of 0.005 M QHS, the formation of α-FeOOH is favoured. The preferential adsorption of sulphate groups and a possible influence of quinine group at the very beginning of FeCl 3 hydrolysis were suggested as responsible for the effects observed.

Influence of the silica based matrix on the formation of iron oxide nanoparticles in the Fe2O3–SiO2 system, obtained by sol–gel method

Composite iron oxide–SiO2 materials were prepared by a sol–gel method starting with two types of precursors, tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS), as the SiO2 source. As the iron source a soluble Fe2+ salt, mainly Fe(SO4)2·7H2O, was used, the iron oxides were generated during the sol–gel process. The amorphous gels obtained were thermally treated up to 1000 °C in order to obtain iron oxides with different structures and grain size. The initial gels and the thermally treated samples were characterised by DTA/TGA analysis, DR-UV–VIS and IR-spectroscopy, EPR measurements, transmission electron microscopy (TEM) and BET surface area methods. The matrices obtained from the precursors play a major role in the evolution of the process. In both cases the initial gels are amorphous. In the non-porous matrix obtained by thermal treatment using methyltriethoxysilane (MTEOS), the tendency for crystallisation increases, and the iron oxide particle size is increased.

Superparamagnetic iron oxide contrast agents: physicochemical characteristics and applications in MR imaging.

Superparamagnetic iron oxide MR imaging contrast agents have been the subjects of extensive research over the past decade. The iron oxide particle size of these contrast agents varies widely, and influences their physicochemical and pharmacokinetic properties, and thus clinical application. Superparamagnetic agents enhance both T1 and T2/T2* relaxation. In most situations it is their significant capacity to reduce the T2/T2* relaxation time to be utilized. The T1 relaxivity can be improved (and the T2/T2* effect can be reduced) using small particles and T1-weighted imaging sequences. Large iron oxide particles are used for bowel contrast [AMI-121 (i.e. Lumirem and Gastromark) and OMP (i.e. Abdoscan), mean diameter no less than 300 nm] and liver/spleen imaging [AMI-25 (i.e. Endorem and Feridex IV, diameter 80-150 nm); SHU 555A (i.e. Resovist, mean diameter 60 nm)]. Smaller iron oxide particles are selected for lymph node imaging [AMI-227 (i.e. Sinerem and Combidex, diameter 20-40 nm)], bone marrow imaging (AMI-227), perfusion imaging [NC100150 (i.e. Clariscan, mean diameter 20 nm)] and MR angiography (NC100150). Even smaller monocrystalline iron oxide nanoparticles are under research for receptor-directed MR imaging and magnetically labeled cell probe MR imaging. Iron oxide particles for bowel contrast are coated with insoluble material, and all iron oxide particles for intravenous injection are biodegradable. Superparamagnetic agents open up an important field for research in MR imaging.

Synthesis, and structural and morphological characterization of iron oxide–ion‐exchange resin and –cellulose nanocomposites

AbstractThe synthesis and the comparative structural and morphological study of iron oxide nanoparticles in polystyrene‐based ion‐exchange resins and cellulosics are reported. The synthesis of magnetite was performed under nitrogen atmosphere by an in situ method in the presence of the matrix itself. Scanning and transmission electron microscopy measurements led to a detailed characterization of matrix morphology and of magnetic particle structure, size and morphology. The results show that the matrix influences the iron oxide particle size; the average size is about 7 nm in the resins and 25 nm in the celluloses. In the resins, particles are present inside the pores and as aggregates on the surface of the resin beads, whereas in the cellulose they are present on the surface and in the swollen network of the microfibers constituting the single fibers. Copyright © 2001 John Wiley &amp; Sons, Ltd.