Showing papers on "Iron oxide published in 2013"

Photochemical Route for Accessing Amorphous Metal Oxide Materials for Water Oxidation Catalysis

Abstract: Large-scale electrolysis of water for hydrogen generation requires better catalysts to lower the kinetic barriers associated with the oxygen evolution reaction (OER). Although most OER catalysts are based on crystalline mixed-metal oxides, high activities can also be achieved with amorphous phases. Methods for producing amorphous materials, however, are not typically amenable to mixed-metal compositions. We demonstrate that a low-temperature process, photochemical metal-organic deposition, can produce amorphous (mixed) metal oxide films for OER catalysis. The films contain a homogeneous distribution of metals with compositions that can be accurately controlled. The catalytic properties of amorphous iron oxide prepared with this technique are superior to those of hematite, whereas the catalytic properties of a-Fe100-y-zCoyNizOx are comparable to those of noble metal oxide catalysts currently used in commercial electrolyzers.

Octapod iron oxide nanoparticles as high-performance t2 contrast agents for magnetic resonance imaging

Abstract: Disclosed are nanoparticles comprising octapod iron oxide having eight trigonal bipyramidal arms and a method of preparing the same. The nanoparticles are prepared by heating a mixture of a ferric carboxylate, a carboxylic acid, a chloride salt, water, and a non-polar solvent, to a temperature above about 300° C. Also disclosed is a method of magnetic resonance imaging a tissue in a mammal, comprising use of the aforesaid nanoparticles.

Core-shell structure dependent reactivity of Fe@Fe₂O₃ nanowires on aerobic degradation of 4-chlorophenol.

Abstract: In this study, core-shell Fe@Fe₂O₃ nanowires with different iron oxide shell thickness were synthesized through tuning water-aging time after the reduction of ferric ions with sodium borohydride without any stirring. We found that these Fe@Fe₂O₃ nanowires exhibited interesting core-shell structure dependent reactivity on the aerobic degradation of 4-chlorophenol. Characterization results revealed that the core-shell structure dependent aerobic oxidative reactivity of Fe@Fe₂O₃ nanowires was arisen from the combined effects of incrassated iron oxide shell and more surface bound ferrous ions on amorphous iron oxide shell formed during the water-aging process. The incrassated iron oxide shell would gradually block the outward electron transfer from iron core for the subsequent two-electron molecular oxygen activation, but more surface bound ferrous ions on iron oxide shell with prolonging aging time could favor the single-electron molecular oxygen activation, which was confirmed by electron spin resonance spectroscopy with spin trap technique. The mineralization of 4-chlorophenol was monitored by total organic carbon measurement and the oxidative degradation intermediates were analyzed by gas chromatography-mass spectrometry. This study provides new physical insight on the molecular oxygen activation mechanism of nanoscale zerovalent iron and its application on aerobic pollutant removal.

Systematic Review of the Preparation Techniques of Iron Oxide Magnetic Nanoparticles

Abstract: Magnetism being one of the oldest scientific disciplines has been continuously studied since 6 th century BC, which still offers scientific innovations today in realm of nanomagnetism. Iron oxide nanomaterials have been growing excessive importance because of their magnetic characteristics and wide applications. Iron oxides magnetic nanoparticles with appropriate surface chemistry are prepared either by wet chemical method such as colloid chemical or sol-gel methods or by dry processes such as vapour deposition techniques. This review summarizes comparative and brief study of the methods for the preparation of iron oxide magnetic nanoparticles with a control over the size, morphology and the magnetic properties. Applications of microwave irradiation for magnetic particle synthesis are also addressed.

Naturally occurring iron oxide nanoparticles: morphology, surface chemistry and environmental stability

Abstract: The widespread nanostructures of iron oxides and oxyhydroxides are important reagents in many biogeochemical processes in many parts of our planet and ecosystem. Their functions in various aspects are closely related to their shapes, sizes, and thermodynamic surroundings, and there is much that we can learn from these natural relationships. This review covers these subjects of several phases (ferrihydrite, goethite, hematite, magnetite, maghemite, lepidocrocite, akaganeite and schwertmannite) commonly found in water, soils and sediments. Due to surface passivation by ubiquitous water in aquatic and most terrestrial environments, the difference in formation energies of bulk phases can decrease substantially or change signs at the nanoscale because of the disproportionate surface effects. Phase transformations and the relative abundance are sensitive to changes in environmental conditions. Each of these phases (except maghemite) displays characteristic morphologies, while maghemite appears frequently to inherit the precursor's morphology. We will see how an understanding of naturally occurring iron oxide nanostructures can provide useful insight for the production of synthetic iron oxide nanoparticles in technological settings.

An electrochemical impedance study of the oxygen evolution reaction at hydrous iron oxide in base

Abstract: The oxygen evolution reaction at multi-cycled iron oxy-hydroxide films in aqueous alkaline solution is discussed. Steady-state Tafel plot analysis and electrochemical impedance spectroscopy have been used to elucidate the kinetics and mechanism of oxygen evolution. Tafel slopes of ca. 60 mV dec−1 and 40 mV dec−1 are found at low overpotentials depending on the oxide growth conditions, with an apparent Tafel slope of ca. 120 mV dec−1 at high overpotentials. Reaction orders of ca. 0.5 and 1.0 are observed at low and high overpotentials, again depending on the oxide growth conditions. A mechanistic scheme involving the active participation of octahedrally coordinated anionic iron oxyhydroxide surfaquo complexes, which form the porous hydrous layer, is proposed. The latter structure contains considerable quantities of water molecules which facilitate hydroxide ion discharge at the metal site during active oxygen evolution. This work brings together current research in heterogeneous electrocatalysis and homogeneous molecular catalysis for water oxidation.

Arsenic Removal from Contaminated Water Using Three-Dimensional Graphene-Carbon Nanotube-Iron Oxide Nanostructures

Abstract: We report a highly versatile and one-pot microwave route to the mass production of three-dimensional graphene-carbon nanotube-iron oxide nanostructures for the efficient removal of arsenic from contaminated water. The unique three-dimensional nanostructure shows that carbon nanotubes are vertically standing on graphene sheets and iron oxide nanoparticles are decorated on both the graphene and the carbon nanotubes. The material with iron oxide nanoparticles shows excellent absorption for arsenic removal from contaminated water, due to its high surface-to-volume ratio and open pore network of the graphene-carbon nanotube-iron oxide three-dimensional nanostructures.

A new anode material for oxygen evolution in molten oxide electrolysis

Abstract: Molten oxide electrolysis (MOE) is an electrometallurgical technique that enables the direct production of metal in the liquid state from oxide feedstock, and compared with traditional methods of extractive metallurgy offers both a substantial simplification of the process and a significant reduction in energy consumption. MOE is also considered a promising route for mitigation of CO2 emissions in steelmaking, production of metals free of carbon, and generation of oxygen for extra-terrestrial exploration. Until now, MOE has been demonstrated using anode materials that are consumable (graphite for use with ferro-alloys and titanium) or unaffordable for terrestrial applications (iridium for use with iron). To enable metal production without process carbon, MOE requires an anode material that resists depletion while sustaining oxygen evolution. The challenges for iron production are threefold. First, the process temperature is in excess of 1,538 degrees Celsius (ref. 10). Second, under anodic polarization most metals inevitably corrode in such conditions. Third, iron oxide undergoes spontaneous reduction on contact with most refractory metals and even carbon. Here we show that anodes comprising chromium-based alloys exhibit limited consumption during iron extraction and oxygen evolution by MOE. The anode stability is due to the formation of an electronically conductive solid solution of chromium(iii) and aluminium oxides in the corundum structure. These findings make practicable larger-scale evaluation of MOE for the production of steel, and potentially provide a key material component enabling mitigation of greenhouse-gas emissions while producing metal of superior metallurgical quality.

Biodegradation of Iron Oxide Nanocubes: High-Resolution In Situ

Abstract: The long-term fate of nanomaterials in biological environment represents a critical matter, which determines environmental effects and potential risks for human health. Predicting these risks requires understanding of nanoparticle transformations, persistence, and degradation, some issues somehow ignored so far. Safe by design, inorganic nanostructures are being envisioned for therapy, yet fundamental principles of their processing in biological systems, change in physical properties, and in situ degradability have not been thoroughly assessed. Here we report the longitudinal visualization of iron oxide nanocube transformations inflicted by the intracellular-like environment. Structural degradation of individual nanocubes with two different surface coatings (amphiphilic polymer shell and polyethylene glycol ligand molecules) was monitored at the atomic scale with aberration-corrected high-resolution transmission electron microscopy. Our results suggest that the polymer coating controls surface reactivity and that availability and access of chelating agents to the crystal surface govern the degradation rate. This in situ study of single nanocube degradation was compared to intracellular transformations observed in mice over 14 days after intravenous injection, revealing the role of nanoparticle clustering, intracellular sorting within degradation compartments, and iron transfer and recycling into ferritin storage proteins. Our approach reduces the gap between in situ nanoscale observations in mimicking biological environments and in vivo real tracking of nanoparticle fate.

CeO2-modified Fe2O3 for CO2 utilization via chemical looping

Abstract: Both pure and mixed CeO2–Fe2O3 were prepared for CO2 reduction to CO by chemical looping. The crystallographic structure of the investigated materials was monitored in situ during H2 reduction and CO2 oxidation. A solid solution of iron in ceria was identified. Up to 70 wt % CeO2, a distinct Fe2O3 hematite phase occurred next to the solid solution. At higher CeO2 content, no diffraction patterns corresponding to iron oxide phases were present, but upon H2 temperature programmed reduction, a metal iron phase appeared. The Fe2O3 phase at lower CeO2 content, during H2 temperature programmed reduction, completely reduced at 700 °C while the solid solution was only partially reduced. For all investigated samples, CO2 reoxidized iron in one-step to Fe3O4 from 500 °C during temperature programmed oxidation. Adding CeO2 to Fe2O3 was beneficial for the materials activity and stability. Isothermal redox cycles were performed without significant loss of CO2 conversion. The highest CO yield was obtained for 20 wt % C...

Effect of surface charge on the colloidal stability and in vitro uptake of carboxymethyl dextran-coated iron oxide nanoparticles

Abstract: Nanoparticle physicochemical properties such as surface charge are considered to play an important role in cellular uptake and particle-cell interactions. In order to systematically evaluate the role of surface charge on the uptake of iron oxide nanoparticles, we prepared carboxymethyl-substituted dextrans with different degrees of substitution, ranging from 38 to 5 groups per chain, and reacted them using carbodiimide chemistry with amine-silane-coated iron oxide nanoparticles with narrow size distributions in the range of 33-45 nm. Surface charge of carboxymethyl-substituted dextran-coated nano-particles ranged from -50 to 5 mV as determined by zeta potential measurements, and was dependent on the number of carboxymethyl groups incorporated in the dextran chains. Nanoparticles were incubated with CaCo-2 human colon cancer cells. Nanoparticle-cell interactions were observed by confocal laser scanning microscopy and uptake was quantified by elemental analysis using inductively coupled plasma mass spectroscopy. Mechanisms of internalization were inferred using pharmacological inhibitors for fluid-phase, clathrin-mediated, and caveola-mediated endocytosis. Results showed increased uptake for nanoparticles with greater negative charge. Internalization patterns suggest that uptake of the most negatively charged particles occurs via non-specific interactions.

Superparamagnetic Iron Oxide Nanoparticles with Variable Size and an Iron Oxidation State as Prospective Imaging Agents

Abstract: Magnetite nanoparticles in the size range of 32-75 nm were synthesized in high yields under variable reaction conditions using high-temperature hydrolysis of the precursor iron(II) and iron(III) alkoxides in diethylene glycol solution The average sizes of the particles were adjusted by changing the reaction temperature and time and by using a sequential growth technique To obtain γ-iron(III) oxide particles in the same range of sizes, magnetite particles were oxidized with dry oxygen in diethylene glycol at room temperature The products were characterized by DLS, TEM, X-ray powder diffractometry, TGA, chemical analysis, and magnetic measurements NMR r(1) and r(2) relaxivity measurements in water and diethylene glycol (for OH and CH(2) protons) have shown a decrease in the r(2)/r(1) ratio with the particle size reduction, which correlates with the results of magnetic measurements on magnetite nanoparticles Saturation magnetization of the oxidized particles was found to be 20% lower than that for Fe(3)O(4) with the same particle size, but their r(1) relaxivities are similar Because the oxidation of magnetite is spontaneous under ambient conditions, it was important to learn that the oxidation product has no disadvantages as compared to its precursor and therefore may be a better prospective imaging agent because of its chemical stability

Superior adsorption capacity of hierarchical iron oxide@magnesium silicate magnetic nanorods for fast removal of organic pollutants from aqueous solution

Abstract: Novel hierarchical core–shell iron oxide@magnesium silicate magnetic nanorods (HIO@MgSi) were fabricated via a versatile sol–gel process through hydrothermal reaction. They contain magnetic iron oxide (Fe3O4) cores and hierarchical shells (MgSi) made of ultrathin nanosheets (ca. 5 nm). Using methylene blue as a model compound, the HIO@MgSi nanorods showed fast adsorption kinetics and a superb adsorption capacity. 99.3% of methylene blue was adsorbed onto the surface of the HIO@MgSi nanorods in 40 min contact time. A maximum adsorption capacity of 2020.20 mg g−1 was achieved after 4 h. This study indicated that HIO@MgSi nanorods can be used as a potential super adsorbent to remove cationic organic pollutants effectively and rapidly from large volumes of industrial wastewater or drinking water.

Hydrazine-mediated Reduction of Nitro and Azide Functionalities Catalyzed by Highly Active and Reusable Magnetic Iron Oxide Nanocrystals

Abstract: Iron oxide (Fe3O4) nanocrystals generated in situ from an inexpensive and readily available iron source catalyze the reduction of nitroarenes to anilines with unparalleled efficiency. The procedure is chemoselective, avoids the use of precious metals, and can be applied under mild reflux conditions (65 or 80 °C) or using sealed vessel microwave heating in an elevated temperature regime (150 °C). Utilizing microwave conditions, a variety of functionalized anilines have been prepared in nearly quantitative yields within 2-8 min at 150 °C, in a procedure also successfully applied to the reduction of aliphatic nitro compounds and azides. The iron oxide nanoparticles are generated in a colloidal form, resulting in homogeneous solutions suitable for continuous flow processing. Selected examples of anilines of industrial importance have been prepared in a continuous regime using this protocol.

Kinetics and mechanism of solar-thermochemical H2 production by oxidation of a cobalt ferrite–zirconia composite

Abstract: Accurate knowledge of water splitting kinetics is essential for the design and optimization of high-temperature thermochemical cycles for solar-driven fuel production, but such crucial data are unavailable for virtually all redox materials of potential practical value. We describe an investigation of the redox activity and oxidation kinetics of cobalt ferrite, a promising material for this application that is representative of a broader class of metal-substituted ferrites. To enable repetitive cycling, ferrites must be supported on another oxide to avoid sintering and deactivation. Consequently, we synthesized a composite material using atomic layer deposition of cobalt and iron oxides on zirconia, a commonly used ferrite “support”, to create a well-controlled, uniformly distributed composition. Our results show that the support is not an innocent bystander and that dissolved iron within it reacts by a different mechanism than embedded iron oxide particles in the matrix. Samples were thermally reduced at 1450 °C under helium and oxidized with steam at realistic process temperatures ranging from 900 °C to 1400 °C. Experiments within a fluid-dynamically well-behaved stagnation-flow reactor, coupled with detailed numerical modelling of the transient H2 production rates, allow us to effectively deconvolve experimental artefacts from intrinsic material behaviour over the entire time domain of the oxidation reaction. We find that second-order reaction and diffusion-limited mechanisms occur simultaneously at different oxidation rates and involve iron in two separate phases: (1) reduced Fe dissolved in the ZrO2 support and (2) iron oxide located at the interface between embedded ferrite particles and the zirconia matrix. Surprisingly, we also identified a catalytic mechanism occurring at the highest temperatures by which steady-state production of H2 and O2 occurs. The results reported here, which include Arrhenius rate constants for both oxidation mechanisms, will enable high-fidelity computational simulation of this complex, but promising approach to renewable fuel production.

Reduction Behavior of Panzhihua Titanomagnetite Concentrates with Coal

Abstract: The reduction behavior of the Panzhihua titanomagnetite concentrates (PTC) briquette with coal was investigated by temperature-programmed heating under argon atmosphere in a vertical tube electric furnace. The mass loss behavior of the PTC-coal mixture was checked by thermogravimetric analysis method in argon with a heating rate of 5 K (5 °C)/ min. It was found that there are five stages during the carbothermic reduction process of the PTC. The devolatilization of coal occurred in the first stage, and reductions of iron oxides mainly occurred in the second and third stages. The reduction rate of iron oxide in the third stage was much higher than that in the second stage because of the significant rate of carbon gasification reaction. The iron in the ilmenite was reduced in the fourth stage. In the final stage, the rutile was partially reduced to lower valence oxides. The phase transformation of the briquette reduced at different temperatures was investigated by X-ray diffraction (XRD). The main phases of sample reduced at 1173 K (900 °C) are metallic iron, ilmenite (FeTiO3), and titanomagnetite (Fe3–x Ti x O4). The traces of rutile (TiO2) were observed at 1273 K (1000 °C). The iron carbide (Fe3C) and ferrous-pseudobrookite (FeTi2O5) appeared at 1473 K (1200 °C). The titanium carbide was found in the sample reduced at 1623 K (1350 °C). The shrinkages of reduced briquettes, which increased with increase in the temperature, were found to depend greatly on the temperature. With increasing the reduction temperature to 1573 K (1300 °C), the iron nuggets were observed outside of the samples reduced. The nugget formation can indicate a new process of ironmaking with titanomagnetite similar to ITmk3 (Ironmaking Technology Mark 3).

Synthesis and characterization of porous flowerlike alpha-Fe2O3 nanostructures for supercapacitor application

Abstract: Porous flower-like alpha-Fe2O3 nanostructures synthesized by an ethylene glycol mediated self-assembly process are crystalline and porous with BET surface area of 64.6 m(2) g(-1). The discharge capacitance is 127 F g(-1) when the electrodes are cycled in 0.5 M Na2SO3 at a current density of 1 A g(-1). Capacitance retention after 1000 cycles is about 80% of the initial capacitance. The high discharge capacitance and its retention are attributed to high surface area and porosity of the iron oxide. As the iron oxides are inexpensive, the nano alpha-Fe2O3 is expected to be of potential use for supercapacitor application.

Electron transfer between iron minerals and quinones: estimating the reduction potential of the Fe(II)-goethite surface from AQDS speciation.

Abstract: Redox reactions at iron mineral surfaces play an important role in controlling biogeochemical processes of natural porous media such as sediments, soils and aquifers, especially in the presence of recurrent variations in redox conditions. Ferrous iron associated with iron mineral phases forms highly reactive species and is regarded as a key factor in determining pathways, rates, and extent of chemically and microbially driven electron transfer processes across the iron mineral-water interface. Due to their transient nature and heterogeneity a detailed characterization of such surface bound Fe(II) species in terms of redox potential is still missing. To this end, we used the nonsorbing anthraquinone-2,6-disulfonate (AQDS) as a redox probe and studied the thermodynamics of its redox reactions in heterogeneous iron systems, namely goethite-Fe(II). Our results provide a thermodynamic basis for and are consistent with earlier observations on the ability of AQDS to "shuttle" electrons between microbes and iron oxide minerals. On the basis of equilibrium AQDS speciation we reported for the first time robust reduction potential measurements of reactive iron species present at goethite in aqueous systems (EH,Fe-GT ≈ -170 mV). Due to the high redox buffer intensity of heterogeneous mixed valent iron systems, this value might be characteristic for many iron-reducing environments in the subsurface at circumneutral pH. Our results corroborate the picture of a dynamic remodelling of Fe(II)/Fe(III) surface sites at goethite in response to oxidation/reduction events. As quinones play an essential role in the electron transport systems of microbes, the proposed method can be considered as a biomimetic approach to determine "effective" biogeochemical reduction potentials in heterogeneous iron systems.

Iron Oxide with Facilitated O2– Transport for Facile Fuel Oxidation and CO2 Capture in a Chemical Looping Scheme

Abstract: The chemical looping strategy offers a potentially viable option for efficient carbonaceous fuel conversion with a reduced carbon footprint. In the chemical looping process, an oxygen carrier is reduced and oxidized in a cyclic manner to convert a carbonaceous fuel into separate streams of concentrated carbon dioxide and carbon-free products such as electricity and/or hydrogen. The reactivity and chemical and physical stability of the oxygen carrier are of pivotal importance to chemical looping processes. A typical oxygen carrier is composed of a multi-valence transition metal oxide supported on an “inert” support. Although the support does not get reduced or oxidized at any significant extent, numerous studies have indicated that certain supports such as TiO2 and Al2O3 can improve oxygen carrier stability and/or reactivity. This study reports the use of mixed ionic–electronic conductive support in iron-based oxygen carriers. By incorporating a perovskite-based mixed conductive support such as lanthanum s...

Anisotropically Alignable Magnetic Boron Nitride Platelets Decorated with Iron Oxide Nanoparticles

Abstract: To effectively utilize the anisotropic characteristics of hexagonal boron nitride (h-BN), we have developed magnetic h-BN hybrid platelets decorated with iron oxide (Fe3O4) nanoparticles, which are used as magnetic carriers for tailoring the anisotropy of h-BN. The as-synthesized Fe3O4-coated h-BN powders can easily move under a relatively low magnetic field. With the aid of iron oxide nanoparticles, h-BN platelets randomly dispersed in an epoxy matrix are successfully reoriented in a direction vertical to the film plane. Moreover, by utilizing the anisotropic characteristics of h-BN platelets, Fe3O4-coated h-BN/epoxy composites exhibit exceptional performance in terms of in-plane thermal conductivity. This result is attributed to an improvement in the heat-transport pathways in composite films due to the anisotropic ordering of thermally conductive h-BN sheets. The Fe3O4-decorated h-BN platelets will be promising candidates for significantly improving the performances of advanced electronic devices that ...