Showing papers on "Iron oxide published in 2006"

Self‐Assembled 3D Flowerlike Iron Oxide Nanostructures and Their Application in Water Treatment

Abstract: 3D nanostructures have attracted much attention because of their unique properties and potential applications. The simplest synthetic route to 3D nanostructures is probably selfassembly, in which ordered aggregates are formed in a spontaneous process. However, it is still a big challenge to develop simple and reliable synthetic methods for hierarchically selfassembled architectures with designed chemical components and controlled morphologies, which strongly affect the properties of nanomaterials. Iron oxides have been extensively studied in diverse fields including catalysis, environment protection, sensors, magnetic storage media, and clinical diagnosis and treatment. Various iron oxide structures, such as nanocrystals, particles, cubes, spindles, rods, wires, tubes, and flakes, have been successfully fabricated by a variety of methods. However, the self-assembly of these low-dimensional building blocks into complex 3D ordered nanostructures is still considerably more difficult. In order to further understand the mechanism of self-organization and expand the applications of iron oxide nanomaterials, self-assembled iron oxide 3D nanostructures need to be explored in more detail. Herein, we report the synthesis of novel 3D flowerlike iron oxide nanostructures by an ethylene glycol (EG)-mediated self-assembly process. Such a method has been adopted previously for the preparation of V2O5 hollow microspheres, [7]

Sorption of Perfluorinated Surfactants on Sediments

Abstract: The sorption of anionic perfluorochemical (PFC) surfactants of varying chain lengths to sediments was investigated using natural sediments of varying iron oxide and organic carbon content. Three classes of PFC surfactants were evaluated for sorptive potential: perfluorocarboxylates, perfluorosulfonates, and perfluorooctyl sulfonamide acetic acids. PFC surfactant sorption was influenced by both sediment-specific and solution-specific parameters. Sediment organic carbon, rather than sediment iron oxide content, was the dominant sediment-parameter affecting sorption, indicating the importance of hydrophobic interactions. However, sorption also increased with increasing solution [Ca2+] and decreasing pH, suggesting that electrostatic interactions play a role. Perfluorocarbon chain length was the dominant structural feature influencing sorption, with each CF2 moiety contributing 0.50−0.60 log units to the measured distribution coefficients. The sulfonate moiety contributed an additional 0.23 log units to the ...

Iron nanoparticles: the core-shell structure and unique properties for Ni(II) sequestration.

Abstract: It is demonstrated that iron nanoparticles function as a sorbent and a reductant for the sequestration of Ni(II) in water. A relatively high capacity of nickel removal is observed (0.13 g Ni/g Fe, or 4.43 mequiv Ni(II)/g), which is over 100% higher than the best inorganic sorbents available. High-resolution X-ray photoelectron spectroscopy (HR-XPS) confirms that the zerovalent iron nanoparticles have a core-shell structure and exhibit characteristics of both hydrous iron oxides (i.e., as a sorbent) and metallic iron (i.e., as a reductant). Ni(II) quickly forms a surface complex and is then reduced to metallic nickel on the nanoparticle surface. The dual properties of iron nanoparticles may offer efficient and unique solutions for the separation and transformation of metal ions and other environmental contaminants.

Iron oxide particles are the active sites for hydrogen peroxide sensing at multiwalled carbon nanotube modified electrodes.

Abstract: We demonstrate that the "electrocatalytic" hydrogen peroxide detection reported at multiwalled carbon nanotube modified electrodes is due to iron oxide particles arising from the chemical vapor deposition nanotube fabrication process rather than due to intrinsic catalysis attributable to the carbon nanotubes arising, for example, from edge plane-like sites/defects.

Mesoporous silica beads embedded with semiconductor quantum dots and iron oxide nanocrystals : Dual-function microcarriers for optical encoding and magnetic separation

Abstract: Mesoporous beads are promising materials for embedding functional nanoparticles because of their nanometer-sized pores and large surface areas. Here we report the development of silica microbeads embedded with both semiconductor quantum dots (QD) and iron oxide (Fe3O4) nanocrystals as a new class of dual-function carriers for optical encoding and magnetic separation. The embedding (doping) process is carried out by either simultaneous or sequential addition of quantum dots and iron oxide (Fe3O4) nanocrystals in solution. The doping process is fast and quantitative, but the incorporated iron oxide strongly attenuates the signal intensity of QD fluorescence. We find that this attenuation is not due to conventional fluorescence quenching but is caused by the broad optical absorption spectrum of mixed-valence Fe3O4. For improved biocompatibility and reduced nonspecific binding, the encoded beads are further coated with amphiphilic polymers such as octylamine poly(acrylic acid). The results indicate that the polymer-coated beads are well suited for target capturing and enrichment, yielding magnetic separation efficiencies higher than 99%. By combining the multiplexing capability of QDs with the superparamagnetic properties of iron oxide nanocrystals, this class of encoded beads is expected to find broad applications in high-throughput and multiplexed biomolecular assays.

Fe(0) Nanoparticles for Nitrate Reduction: Stability, Reactivity, and Transformation

Abstract: The pyrophoric character of zerovalent iron nanoparticles and cumbersome handling of this material has been a drawback in practical applications, despite the expectation of an enhanced reactivity. We have been interested in how the iron nanoparticles can gain stability in air without significantly sacrificing reactivity. The freshly synthesized iron nanoparticles ignited spontaneously upon exposure to air. However, when exposed slowly to air, an approximately 5 nm coating of iron oxide was formed on the surface of particles. The oxide shell did not thicken for at least two months, indicating no sign of further corrosion of iron particles. The reactivity studies on nitrate reduction showed that the freshly synthesized iron reacted at the fastest rate. After formation of the oxide shell the rate constants decreased by ca. 50% of that of fresh iron, but were still higher than that of commercial grade micro- or milli-sized iron powder. Nitrate (50 ppm/350 mL) can be recharged 6 times into a bottle containing 0.5 g of iron nanoparticles. The reduction rate of the second cycle was the fastest among the six cycles, which can be attributed to the increase of surface area and the fresh iron surfaces that were bared by the dissolution of oxidized iron species on the surface. The oxidized iron was transformed to crystalline magnetite (Fe3O4) in solution.

Facile autoreduction of iron oxide/carbon nanotube encapsulates.

Abstract: Facile autoreduction of iron oxide encapsulated within carbon nanotubes has been observed at a temperature 200 °C lower than those on the outer surface. This opens a new route to tune the state of confined nanoparticles of d-band metals by the confinement of CNTs.

The concept of delayed nucleation in nanocrystal growth demonstrated for the case of iron oxide nanodisks

Abstract: A comprehensive study of iron oxide nanocrystal growth through non-hydrolitic, surfactant-mediated thermal reaction of iron pentacarbonyl and an oxidizer has been conducted, which includes size control, anisotropic shape evolution, and crystallographic phase transition of monodisperse iron oxide colloidal nanocrystals. The reaction was monitored via in situ UV-vis spectroscopy, taking advantage of the color change accompanying the iron oxide colloid formation, allowing measurement of the induction time for nucleation. Features of the synthesis such as the size control and reproducibility are related to the occurrence of the observed delayed nucleation process. As a separate source of iron and oxygen is adopted, phase control could also be achieved by sequential injections of oxidizer.

Selective catalytic reduction of nitrogen oxides by ammonia on iron oxide catalysts

Abstract: In this study, new Fe 2 O 3 based materials are developed for the selective catalytic reduction (SCR) of NO x by NH 3 in diesel exhaust. As a result of the catalyst screening, performed in a synthetic model exhaust, ZrO 2 is considered to be the most effective carrier for Fe 2 O 3 . The modification of the Fe 2 O 3 /ZrO 2 system with tungsten leads to drastic increase of SCR performance as well as pronounced thermal stability. These results show that tungsten acts as bifunctional component. The highest catalytic activity is observed for ZrO 2 that is coated with 1.4 mol% Fe 2 O 3 and 7.0 mol% WO 3 (1.4Fe/7.0W/Zr). By the use of this catalyst quantitative conversion of NO x is obtained between 285 and 430 °C with selective formation of N 2 . Here, the turnover frequency of NO x per Fe atom is found to be 35 × 10 −5 s −1 that indicates a high catalytic performance. The SCR activity of the 1.4Fe/7.0W/Zr material is decreased in the presence of H 2 O and CO 2 , whereas it is increased by NO 2 . Temperature programmed reduction by H 2 (HTPR) analyses show that the Fe sites of the 1.4Fe/7.0W/Zr catalyst are mainly in the form of crystalline Fe 2 O 3 , whereby relatively small oxide entities are also present. The strongly aggregated Fe 2 O 3 species are associated with the presence of the promoter tungsten. Based upon stationary catalytic examinations as well as diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) studies we postulate an Eley Rideal type mechanism for SCR on 1.4Fe/7.0W/Zr catalyst. The mechanistic model includes a redox cycle of the active Fe sites. As first reaction step, we assume dissociative adsorption of NH 3 that leads to partial reduction of the iron as well as to production of very reactive amide surface species. These amide intermediates are supposed to react with gaseous NO to form N 2 and H 2 O. In the final step, the reduced Fe sites be regenerated by oxidation with O 2 . As a side reaction of SCR, imide species, originated from decomposition of amide, are oxidized by NO 2 or O 2 into NO.

Magnetic enhancement is linked to and precedes hematite formation in aerobic soil

Abstract: [1] Soil formation usually increases magnetic susceptibility, most often by increasing the concentrations of magnetite and maghemite, which are two ferrimagnetic iron oxides. Here we provide evidence that magnetic enhancement in aerobic soils not affected by detrital magnetic inputs or thermal transformation of other iron oxides is mostly due to the formation of maghemite, which is later transformed into hematite—the iron oxide that gives red color to soil. We show that the maghemite/hematite ratio is influenced by the particular environment and the degree of soil development, so it constitutes an effective tool for paleoenvironmental and planetary studies.

Iron/iron oxide core-shell nanoclusters for biomedical applications

Abstract: Biocompatible magnetic nanoparticles have been found promising in several biomedical applications for tagging, imaging, sensing and separation in recent years. Most magnetic particles or beads currently used in biomedical applications are based on ferromagnetic iron oxides with very low specific magnetic moments of about 20–30 emu/g. Here we report a new approach to synthesize monodispersed core-shell nanostructured clusters with high specific magnetic moments above 200 emu/g. Iron nanoclusters with monodispersive size of diameters from 2 nm to 100 nm are produced by our newly developed nanocluster source and go to a deposition chamber, where a chemical reaction starts, and the nanoclusters are coated with iron oxides. HRTEM Images show the coatings are very uniform and stable. The core-shell nanoclusters are superparamagnetic at room temperature for sizes less than 15 nm, and then become ferromagnetic when the cluster size increases. The specific magnetic moment of core-shell nanoclusters is size dependent, and increases rapidly from about 80 emu/g at the cluster size of around 3 nm to over 200 emu/g up to the size of 100 nm. The use of high magnetic moment nanoclusters for biomedical applications could dramatically enhance the contrast for MRI, reduce the concentration of magnetic particle needs for cell separation, or make drug delivery possible with much lower magnetic field gradients

Characterization of iron oxides in mineral dust aerosols: Implications for light absorption

Abstract: [1] We report on measurements that were specifically designed to determine iron oxides in mineral dust aerosols needed for improved optical modeling. Atmospheric dust samples as well as samples generated in a wind tunnel from soils were analyzed by a number of analytical techniques for their total and free iron content (bulk and size resolved), hematite and goethite, mineralogy, and size distribution. These samples are representative of several important dust sources in East Asia and northern Africa. A novel data set generated from these measurements enables us to perform an in-depth modeling study of dust optical properties in the solar spectrum. We modeled the iron oxide–clay aggregates, which are the key light-absorbing species, as well as their mixtures with nonabsorbing minerals. A volume fraction of iron oxide in aggregates was determined from measurements. Significant differences in the single-scattering albedo, ω0, were found between hematite- and goethite-clay aggregates, although these calculations involved several important assumptions about the partition of hematite and goethite in size-resolved aggregates. Furthermore, we found that variability of the free iron content is large enough to cause important differences in ω0 of mineral dust originating from different sources. In contrast, this variability has little effect on the extinction coefficient and optical depth. We demonstrate that for the same size distribution, ω0 calculated from data obtained for Chinese and Tunisian samples show higher values and more distinct wavelength dependence than those of Niger dust. All the above ω0 differ from ones calculated using the refractive indices of Patterson et al. (1977) or the OPAC model (Hess et al., 1998), which are often used in radiative transfer studies. We conclude that information on a size-resolved content of free iron and a fraction of hematite and goethite in aggregates will need to be known on a regional basis to improve the prediction of the single-scattering albedo at solar wavelengths and hence the radiative impact of atmospheric mineral dust.

Aqueous dispersion of monodisperse magnetic iron oxide nanocrystals through phase transfer

Abstract: A facile method was developed for completely transferring high quality monodisperse iron oxide nanocrystals from organic solvents to water. The as-prepared aqueous dispersions of iron oxide nanocrystals were extremely stable and could be functionalized for bioconjugation with biomolecules. These iron oxide nanocrystals showed negligible cytotoxicity to human breast cancer cells (SK-BR-3) and human dermal fibroblast cells. This method is general and versatile for many organic solvent-synthesized nanoparticles, including fluorescent semiconductor nanocrystals.

Removal of arsenite and arsenate using hydrous ferric oxide incorporated into naturally occurring porous diatomite.

Abstract: In this study, a simplified and effective method was tried to immobilize iron oxide onto a naturally occurring porous diatomite. Experimental resultsfor several physicochemical properties and arsenic edges revealed that iron oxide incorporated into diatomite was amorphous hydrous ferric oxide (HFO). Sorption trends of Fe (25%)-diatomite for both arsenite and arsenate were similar to those of HFO, reported by Dixit and Hering (Environ. Sci. Technol. 2003, 37, 4182-4189). The pH at which arsenite and arsenate are equally sorbed was 7.5, which corresponds to the value reported for HFO. Judging from the number of moles of iron incorporated into diatomite, the arsenic sorption capacities of Fe (25%)-diatomite were comparable to or higher than those of the reference HFO. Furthermore, the surface complexation modeling showed that the constants of [triple bond]SHAsO4- or [triple bond]SAsO4(2-) species for Fe (25%)-diatomite were larger than those reference values for HFO or goethite. Larger differences in constants of arsenate surface species might be attributed to aluminum hydroxyl ([triple bond]Al-OH) groups that can work better for arsenate removal. The pH-controlled differential column batch reactor (DCBR) and small-scale column tests demonstrated that Fe (25%)-diatomite had high sorption speeds and high sorption capacities compared to those of a conventional sorbent (AAFS-50) that is known to be the first preference for arsenic removal performance in Bangladesh. These results could be explained by the fact that Fe (25%)-diatomite contained well-dispersed HFO having a great affinity for arsenic species and well-developed macropores as shown by scanning electron microscopy (SEM) and pore size distribution (PSD) analyses.

Catalytic performance of various mesoporous silicas modified with copper or iron oxides introduced by different ways in the selective reduction of NO by ammonia

Abstract: Mesoporous silicas (MCM-48, SBA-15, MCF), reflecting various porous structures, were modified with copper and iron oxides by two different methods. For a first series of the samples the molecular designed dispersion (MDD) method using acetylacetonate complexes of copper and iron was applied for the deposition of transition metal oxides on the silica supports. A second series of the catalysts was obtained by the incipient impregnation technique using aqueous solutions of the suitable metal nitrates. The modified materials were characterized with respect to the texture (BET), composition (electron microprobe analysis), coordination of the transition metals (UV–vis–DRS) and surface acidity (NH3-TPD, FTIR). The mesoporous silica supports modified with transition metal oxides were tested as catalysts of the selective reduction of NO with ammonia. The catalytic performance of the studied samples depended on the method used for the deposition of transition metal oxide as well as the kind of mesoporous silica used as a catalytic support. In general, the Cu-containing mesoporous samples effectively operated at lower temperatures than silicas modified with iron. The samples obtained by the MDD method have been found to be more active and selective compared to the analogous samples prepared by the impregnation technique. An introduction of water vapor into the reaction mixture only slightly decreased the NO conversion and selectivity towards N2 over the MCF mesoporous silica modified with copper or iron oxide.

Development of chromium-free iron-based catalysts for high-temperature water-gas shift reaction

Abstract: Chromium-free iron-based catalysts were prepared and studied in regard to their performance in the high-temperature water-gas shift reaction (HTS). The effects of various catalyst preparation variables (i.e., Fe/promoter ratio, pH of precipitation medium, calcination and reduction temperatures) and preparation methods were investigated. Aluminum is a potential chromium replacement in HTS catalysts. Further improvement in WGS activity of Fe–Al catalysts can be achieved by the addition of small amounts of copper or cobalt. Catalysts were characterized using BET surface area measurements, temperature-programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). As a textural promoter, aluminum and chromium prevent the sintering of iron oxides and stabilize magnetite phase by retarding its further reduction to FeO and metallic Fe. The promotional effect of Cu is found to be strongly dependent on the preparation method.

Growth and characterization of iron oxide nanorods/nanobelts prepared by a simple iron-water reaction.

Abstract: Single-crystalline hexagonal alpha-Fe(2)O(3) nanorods/nanobelts have been created by a simple iron-water reaction in the low-temperature range of 350-450 degrees C. Scanning electron microscopy examination shows that the needle-like products, radiating from and perpendicular to the original large iron particle surfaces, are up to a few micrometers in length with an average diameter from 20 nm (tip) to 100 nm (base). X-ray photoelectron spectroscopy and FTIR spectroscopy reveal that the outermost surface of the nanorods consists of Fe(2)O(3) without organic impurity contaminants, which could possibly result from other methods, such as hydrothermal growth. Nanobelt-like structures are believed to result from a combination of increased reaction temperature and time. The initial formation and subsequent growth of alpha-Fe(2)O(3) nanorods may be explained by the iron metal corrosion mechanism.

Defluidization Conditions for a Fluidized Bed of Iron Oxide-, Nickel Oxide-, and Manganese Oxide-Containing Oxygen Carriers for Chemical-Looping Combustion

Abstract: For combustion with CO2 capture, chemical-looping combustion with inherent separation Of CO2 is a promising technology. Chemical-looping combustion uses oxygen carriers that are composed of metal oxide to transfer oxygen from the combustion air to the fuel. The defluidization of oxygen-carrier particles was investigated to improve the understanding of when particle agglomeration may occur. The study was made in a laboratory fluidized-bed reactor at 950 degrees C, simulating a chemical-looping combustion system by exposing the sample to reducing and oxidizing conditions in an alternating manner. The oxygen-carrier particles used were based on oxides of iron, nickel, and manganese and produced by freeze granulation. For iron oxide particles, there was no defluidization of the bed when the content of available oxygen in the particle was high. The defluidization occurred during the oxidation period after long reduction periods, in which a significant reduction of the magnetite to wustite occurred. This is an important observation, because the reduction to wustite is not expected in chemical-looping combustion with high fuel conversion. Thus, laboratory experiments with iron oxide performed with long reduction times may give an unduly exaggerated impression of the risks of agglomeration. For nickel oxide, the defluidization was dependent on the sintering temperature with no defluidization in experiments conducted with particles sintered at 1300 and 1400 degrees C. The nickel oxide particles that were sintered at 1500 degrees C only defluidized once in a total of 49 cycles, whereas the particles that were sintered at 1600 degrees C defluidized already in the first cycle. For the nickel oxide particles, it was not possible to see any effect of the length of the reducing period on the defluidization. There was no defluidization of the manganese oxide particles. The defluidization of the bed leads to agglomeration for the iron oxide particles, but not for the particles of nickel oxide, where the bed was still loosely packed. Carbon was formed on the particles based on nickel oxide and manganese oxide.

The high-temperature oxidation behavior of hot-dipping Al–Si coating on low carbon steel

Abstract: Low carbon steel was coated by hot-dipping into a molten bath containing Al-10 wt.% Si. The high-temperature oxidation behavior of the specimen was tested at 750, 850 and 950 °C for 72 h in air using a thermobalance. The element distribution, phase composition, and morphology of the aluminide layer and the oxide scale were characterized by OM, XRD and SEM/EDX. After hot-dip treatment, the coating layers consisted of three phases, where Al, FeAl 3 , and Fe 2 Al 5 were detected from external topcoat to the aluminide/steel substrate. The result of high-temperature oxidation test showed oxidation kinetics basically followed the parabolic rate law at all temperatures. The Fe 2 Al 5 formed during the immersion process completely transformed to FeAl 2 , FeAl and α-Fe(Al) phases because of the composition gradient and the chemical diffusion by oxidation. In the present study, Kirkendall voids were found to form at the coating/substrate interface due to the rapid inter-diffusion of iron and aluminum during oxidation and, therefore, the adherence of the coatings should be compromised. Afterwards, loss of protective behavior of coating layer occurred only by iron oxide nodules formed on the coating specimen exposed at 850 °C for 24 h.

A Two-Step Thermochemical Water Splitting by Iron-Oxide on Stabilized Zirconia

Abstract: The thermochemical two-step water splitting cycle was examined by using an iron oxide supported on yttrium-stabilized, cubic zirconia (YSZ) as the working material with a view toward direct conversion of solar high-temperature heat to clean hydrogen energy In the first step of the cycle, the YSZ-supported Fe3O4 was thermally decomposed to the reduced phase at 1400°C under an inert atmosphere The reduced solid phase was oxidized back to the original phase (the YSZ-supported Fe3O4) with steam to generate hydrogen below 1000°C A new redox pair, which is different from the Fe3O4–FeO pair previously examined by others, served as the working solid material on this YSZ-supported Fe3O4 Our new redox reaction proceeded as follows The Fe3O4 reacted with YSZ to produce an Fe2+-containing ZrO2 phase by releasing oxygen molecules in the first step: The Fe2+ ions entered into the cubic YSZ lattice In the second step, the Fe2+-containing YSZ generated hydrogen via steam splitting to reproduce Fe3O4 on the cubic YSZ support This cyclic reaction could be repeated with a good repeatability of the reaction below 1400°C

Cellular MRI contrast via coexpression of transferrin receptor and ferritin.

Abstract: Over the past decade several novel approaches for achieving specific cellular MRI contrast have focused on iron as the contrast agent. The broad categories of such cellular contrast methods include efforts to label cells with exogenous contrast agents consisting of crystalline iron oxide encapsulated in a biologically benign shell, or to label cells with endogenously available iron through recruitment of cellular iron metabolism machinery. Researchers in both categories have recognized the advantages of genetic methods for improving cell labeling specificity. Specifically, overexpression of cell surface proteins, such as the transferrin receptor (TfR) (1) and Her-2/neu receptor (2), have enabled targeted labeling with iron oxide particles conjugated to receptor ligand (1) or antibody (2). An advantage of genetic methods for accumulating endogenous iron is that the challenges of delivering contrast agent can be largely avoided. Because most existing iron oxide contrast agents remain primarily within the blood, labeling with exogenous contrast agent is effective for targeting vascular cells or tumor cells associated with leaky vasculature, but is substantially less effective for targeting nonvascular cells. In contrast, endogenous iron is efficiently transported in extracellular fluid throughout the organism, even across the notoriously challenging blood–brain barrier. Brain iron levels have been observed to correlate with darkening on T2-weighted MRI, indicating that differential iron levels in normal tissues may be sufficient to provide MRI contrast (3–6). This contrast effect is the result of varied approaches to iron management among cell types; molecularly, the result of varying expression patterns of proteins involved in iron metabolism. As biologically-controlled contrast mechanisms, iron metabolism genes have become targets for manipulation to provide an MRI reporter of gene expression in vivo, or to tag cells with an inheritable MRI marker to monitor, for example, future gene transfer or stem cell therapies. Although the ultimate cellular contrast agent is semi-crystalline iron within the core of the ferritin (FT) complex, several components of the iron metabolism pathway have been targeted in attempts to induce cellular iron accumulation, including TfR, the main cellular protein involved in iron uptake, and the two subunits of the FT complex, the H-subunit (FTH) and L-subunit (FTL). In one report, TfR overexpressing tumors were observed to have significantly decreased T2 values (7). However, a subsequent effort using a TfR overexpressing tumor line reported no significant signal change in the absence of exogenous transferrin conjugated to an iron oxide contrast agent (1). Iron response protein 2 (IRP-2) mutant mice, a neurodegenerative disease model, cellularly demonstrated elevated endogenous FT with a coincident decrease in TfR (8). Although tissue iron levels were found to be increased, minimal T2 contrast was observed, which was likely due to the opposing T2 effects of cell vacuolization, an indicator of cellular toxicity (8,9). To date, the most notable success has been achieved with overexpression of one or both of the FT subunits as critical components of the ultimate molecular contrast agent, the iron-loaded FT complex (10,11). Considerable work has been done to explore the contrast effects of FT, including the dependence on iron loading factor (12), and field strength (13–15). FT-bound iron, like the iron oxide contrast agents, is a much more effective contrast agent for T2 than for T1, and it has been suggested that the T2 effect is due to superparamagnetic iron in the FT core (16,17). Most studies have shown a linear correlation of R2 (=1/T2) relaxivity with increasing field strength up to 1.5 T (3,18–20) and a less clear correlation of R2 with tissue iron content that has been suggested to be due to variable clustering of FT in tissues (3,14). Fewer studies have explored the R2∗ effects of FT (21), and field strength influence above 1.5 T (21,22); however, the results indicate that R2∗ is more sensitive to superparamagnetic iron within FT, particularly at high field strengths. We took the approach of inducing MRI contrast in an in vitro system via expression of the TfR and FTH proteins in a transfected mouse neural stem cell line. We demonstrate that the transfected cells are able to accumulate more iron than control cells, and that the difference in iron accumulation results in a pronounced increase in T2 and T2∗ contrast effects at 7 T. Furthermore, we characterize the field dependence of the iron-based contrast in this system by MR relaxometry at both 7 T and at 1.5 T. Finally, we show that the increased contrast effect of the iron accumulation in the transfected cells is preserved following transplantation into mouse forebrain with T2∗-weighted brain imaging and R2∗ relaxometry.

Creating a Synergy Effect by Using Mixed Oxides of Iron- and Nickel Oxides in the Combustion of Methane in a Chemical-Looping Combustion Reactor

Abstract: Chemical-looping combustion is a new technology that could help reconcile the contradictory requirements of an increasing energy demand and the reduction of greenhouse gas emissions. This technique involves combustion of fossil fuels with inherent CO2 capture by means of an oxygen carrier that is circulated between air and fuel reactors. In this article, synergy effects of the combustion of methane by using a small amount of nickel oxide in a bed of iron oxide are presented. Reactivity was investigated on particles 125−180 μm in a laboratory fluidized bed reactor of quartz. Reduction was performed in 50% CH4/50% H2O. The two oxygen carriers used are 60% NiO/40% MgAl2O4 sintered at 1400 °C and 60% Fe2O3/40% MgAl2O4 sintered at 1100 °C. It is shown that, at 950 °C, a bed consisting of the mixed system of 3 wt % nickel oxides with 97 wt % iron oxides produces almost two times as much carbon dioxide per time unit in comparison to the sum of carbon dioxide when the oxygen carriers were tested separately. This ...