Showing papers on "Iron oxide published in 2003"

Comparison of arsenic(V) and arsenic(III) sorption onto iron oxide minerals: implications for arsenic mobility.

Abstract: Arsenic derived from natural sources occurs in groundwater in many countries, affecting the health of millions of people. The combined effects of As(V) reduction and diagenesis of iron oxide minerals on arsenic mobility are investigated in this study by comparing As(V) and As(III) sorption onto amorphous iron oxide (HFO), goethite, and magnetite at varying solution compositions. Experimental data are modeled with a diffuse double layer surface complexation model, and the extracted model parameters are used to examine the consistency of our results with those previously reported. Sorption of As(V) onto HFO and goethite is more favorable than that of As(III) below pH 5−6, whereas, above pH 7−8, As(III) has a higher affinity for the solids. The pH at which As(V) and As(III) are equally sorbed depends on the solid-to-solution ratio and type and specific surface area of the minerals and is shifted to lower pH values in the presence of phosphate, which competes for sorption sites. The sorption data indicate tha...

Characterization of Biophysical and Metabolic Properties of Cells Labeled with Superparamagnetic Iron Oxide Nanoparticles and Transfection Agent for Cellular MR Imaging

Abstract: PURPOSE: To evaluate the effect of using the ferumoxides–poly-l-lysine (PLL) complex for magnetic cell labeling on the long-term viability, function, metabolism, and iron utilization of mammalian cells. MATERIALS AND METHODS: PLL was incubated with ferumoxides for 60 minutes, incompletely coating the superparamagnetic iron oxide (SPIO) through electrostatic interactions. Cells were coincubated overnight with the ferumoxides-PLL complex, and iron uptake, cell viability, apoptosis indexes, and reactive oxygen species formation were evaluated. The disappearance or the life span of the detectable iron nanoparticles in cells was also evaluated. The iron concentrations in the media also were assessed at different time points. Data were expressed as the mean ± 1 SD, and one-way analysis of variance and the unpaired Student t test were used to test for significant differences. RESULTS: Intracytoplasmic nanoparticles were stained with Prussian blue when the ferumoxides-PLL complex had magnetically labeled the huma...

Low-temperature selective catalytic reduction of NO with NH3 over iron and manganese oxides supported on titania

Abstract: A series of catalysts of manganese oxide supported on TiO 2 and iron–manganese oxide supported on TiO 2 with different amounts of manganese and iron were studied for low-temperature selective catalytic reduction (SCR) of NO with ammonia in the presence of excess oxygen. It was found that the addition of iron oxide not only increased the NO conversion and N 2 selectivity but also increased the resistance to H 2 O and SO 2 . The Fe–Mn/TiO 2 catalysts yield high activities and high N 2 product selectivity. The N 2 O product selectivity increased with the amount of MnO x as well as temperature. Crystalline phase of MnO x was present at ≥15% Mn on TiO 2 , and the amount increased with Mn content. In addition, SO 2 and H 2 O decreased the activities only slightly, while such effect was reversible. The Fe–Mn/TiO 2 with Mn/Fe=1 showed the highest activity. The results showed that this catalyst yielded nearly 100% NO conversion at 120 °C at a space velocity of 15,000 h −1 . The effect of oxygen was also studied. Reversible transient behaviors similar to that on other oxide catalysts, including vanadia and chromia, were observed for the Fe–Mn/TiO 2 catalyst.

The removal of carbon monoxide by iron oxide nanoparticles

Abstract: NANOCAT ® Superfine Fe 2 O 3 nanoparticles were evaluated both as a catalyst and as an oxidant for carbon monoxide oxidation. It was found that the nanoparticles are much more effective as carbon monoxide catalysts than the non-nano oxide powder. For the Fe 2 O 3 nanoparticles, the reaction order is first-order with respect to the partial pressure of carbon monoxide, and zero-order with respect to the partial pressure of oxygen. The apparent activation energy was 14.5 kcal mol −1 and the normalized reaction rate was 19 s −1 m −2 at 300 °C. In the absence of oxygen, Fe 2 O 3 nanoparticles oxidize carbon monoxide directly as an oxidant. The resulting reduced forms of Fe 2 O 3 also catalyze a disproportionation reaction for a considerable amount of carbon monoxide. The significant amount of carbon monoxide it can remove through the catalytic oxidation, direct oxidation, and the disproportionation reaction make it a very promising material in certain special applications, such as removing the carbon monoxide from a burning cigarette, where the potential toxicity of other, more conventional catalysts would be undesirable. The higher activity of Fe 2 O 3 nanoparticles over non-nano Fe 2 O 3 powders was attributed to a small particle size (3 nm), the presence of an hydroxylated phase of iron oxide (FeOOH), as revealed by both high resolution transmission electron microscopy (HRTEM) and a comparable study of FeOOH (goethite) powder.

Patterned langmuir-blodgett films of monodisperse nanoparticles of iron oxide using soft lithography.

Abstract: Langmuir-Blodgett (LB) films of monodisperse iron oxide nanoparticles have been successfully deposited onto patterned poly(dimethylsiloxane) surfaces. These patterned LB films of iron oxide nanoparticles were transferred onto solid substrates using micro contact printing.

Ferritin: At the Crossroads of Iron and Oxygen Metabolism

Abstract: Iron and oxygen are central to terrestrial life. Aqueous iron and oxygen chemistry will produce a ferric ion trillions of times less soluble than cell iron concentrations, along with radical forms of oxygen that are toxic. In the physiological environment, many proteins have evolved to transport iron or modulate the redox chemistry of iron that transforms oxygen in useful biochemical reactions. Only one protein, ferritin, evolved to concentrate iron to levels needed in aerobic metabolism. Reversible formation and dissolution of a solid nanomineral-hydrated, iron oxide is the main function of ferritin, which additionally detoxifies excess iron and possibly dioxygen and reactive oxygen. Ferritin is a large multifunctional, multisubunit protein with eight Fe transport pores, 12 mineral nucleation sites and up to 24 oxidase sites that produce mineral precursors from ferrous iron and oxygen. Regulation of ferritin synthesis in animals uses both DNA and mRNA controls and genes encoding two types of related subunits with: 1) catalytically active (H) or 2) inactive (L) oxidase sites. Ferritin with varying H/L ratios is related to cell-specific iron and oxygen homeostasis. H-ferritin oxidase activity accelerates rates of iron mineralization in ferritins and, in animals, ferritin produces H(2)O(2) as a byproduct. Properties of ferritin mRNA and ferritin protein pore structure are new targets for manipulating iron homeostasis. Recent observations of the high bioavailability of iron in soybean ferritin and efficient utilization of soybean and ferritin iron by iron-deficient animals, and of soybean iron by humans with borderline deficiency, indicate a role for ferritin in managing global iron deficiency in humans.

Size-dependent oxidation in iron/iron oxide core-shell nanoparticles

Abstract: We report a detailed morphological and structural characterization of iron/iron oxide core-shell nanoparticles with x-ray diffraction and x-ray absorption spectroscopy performed at both the Fe and O $K$ edges. Core-shell nanoparticles with core size ranging from 7 to 21 nm were synthesized using the inert gas condensation technique followed by 12 h of controlled surface oxidation. Rietveld analysis of diffraction patterns shows the presence of \ensuremath{\alpha}-Fe nanoparticles surrounded by a 2--3 nm-thick oxide layer with a disordered cubic spinel structure. Magnetite $({\mathrm{Fe}}_{3}{\mathrm{O}}_{4})$ and maghemite $(\ensuremath{\gamma}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}),$ two different iron oxides, share this lattice structure, but x-ray diffraction was not able to distinguish between the two. An analysis of the Fe and O x-ray absorption spectra in both the near-edge and the extended energy regions is described. The analysis of the extended spectra was performed using the ab initio calculation of all significant contributions to the absorption cross section. We show that there are size-dependent changes in the local structure and oxidation state of the oxide shell, the relative fraction of maghemite increasing at the expense of magnetite as the core dimensions decrease. This size/structure correlation has been explained in terms of morphological and structural disorder arguments

Size and support effects for CO adsorption on gold model catalysts

Abstract: CO adsorption on gold particles deposited on well-ordered alumina and iron oxide films was studied with temperature-programmed desorption. Scanning tunneling microscopy was used to provide correlative structural characterization. The results show that the adsorption of CO on gold exhibits a size effect in that small particles adsorb CO more strongly. For a given particle size (∼3 nm), CO desorption temperature (at ∼170 K) is essentially independent of the supports studied. Therefore, support effects seen in CO oxidation on real catalytic systems must arise from the interaction of oxygen rather than CO with these catalysts.

A review of binders in iron ore pelletization

Abstract: The majority of iron ores must be ground to a fine particle size to allow the iron oxides they contain to be concentrated, and the concentrate must then be agglomerated back into large enough particles that they can be processed in blast furnaces. The most common agglomeration technique is pelletization, which requires the use of binders to hold the iron oxide grains together so that the agglomerates can be sintered into high-strength pellets. Although bentonite clay is the most commonly used binder, there are many other possibilities that could be competitive in a number of situations. This article reviews the numerous types of binders (both organic and inorganic) that have been considered for iron ore pelletization, including discussion of the binding mechanisms, advantages and limitations of each type, and presentation of actual pelletization results, so that the performance of the various types of binders can be compared and evaluated.

Preliminary evaluation of nanoscale biogenic magnetite in Alzheimer's disease brain tissue

Abstract: Elevated iron levels are associated with many types of neurodegenerative disease, such as Alzheimer's, Parkinson's and Huntington's diseases. However, these elevated iron levels do not necessarily correlate with elevated levels of the iron storage or transport proteins, ferritin and transferrin. As such, little is known about the form of this excess iron. It has recently been proposed that some of the excess iron in neurodegenerative tissue may be in the form of the magnetic iron oxide magnetite (Fe(3)O(4)). We demonstrate, for the first time to our knowledge, using highly sensitive superconducting quantum interference device (SQUID) magnetometry, that the concentrations of magnetite are found to be significantly higher in three samples of Alzheimer's disease tissue than in three age- and sex-matched controls. These results have implications, not only for disease progression, but also for possible early diagnosis.

Efficient Formation of Iron Nanoparticle Catalysts on Silicon Oxide by Hydroxylamine for Carbon Nanotube Synthesis and Electronics

Abstract: Iron containing nanoparticles are found to spontaneously form on hydroxylated SiO2 substrates when immersed in a freshly mixed aqueous solution of FeCl3 and hydroxylamine. Upon calcination, a submonolayer of uniformly distributed iron oxide nanoparticles can be derived and used to catalyze the growth of single-walled carbon nanotubes by chemical vapor deposition. This simple method affords clean single-walled nanotube films on SiO2. The solution phase catalyst deposition approach allows for submicron scale catalyst patterning. Patterned growth of nanotubes with this catalyst retains high degrees of surface cleanliness and leads to arrays of nanotube electronic devices including field effect transistors. The population of hydroxyl groups on SiO2, reaction time, and pH of the solutions are found to be important to the deposition of nanoparticles through a surface-mediated hydroxylamine/FeCl3 chemistry.

Inorganic Macroporous Films from Preformed Nanoparticles and Membrane Templates: Synthesis and Investigation of Photocatalytic and Photoelectrochemical Properties

Abstract: Colloidal dispersions of titania, zirconia, tin oxide, indium oxide, and ceria have been successfully used to impregnate membrane templates and form the respective metal oxide (MO) porous films. The use of alumina and iron oxide sols in the same procedure, however, resulted in compact structures. By mixing different nanoparticle solutions before impregnation, final inorganic films containing two metal oxides, of variable metal oxide ratios, were obtained. The porous inorganic materials were analyzed in terms of surface area, pore size, film thickness, and crystallinity. The mechanism of nanoparticle infiltration and particle adsorption to the template walls is proposed based on the stability of the inorganic film and a study of the influence of either the sol concentration or washing times on the amount of inorganic substance incorporated in the hybrid material. The photocatalytic decomposition of an organic pollutant, 2-chlorophenol, was demonstrated for the porous titania material along with the structures containing mixtures of titania with zirconia, indium oxide, and tin oxide. A ratio of 9:1 TiO2/MO gave the highest photocatalytic activity, which was higher than the activity of Degussa P25 for the TiO2/In2O3 and TiO2/SnO2 systems under the same conditions. The titania films have also been attached to substrates—glass or indium tin oxide (ITO) surfaces—and the photoelectrochemical properties of the porous film attained. A comparison with a spin-coated titania film (prepared from the same colloidal dispersion) showed that the structured porous inorganic film has two times the photoelectrochemical efficiency as the spin-coated film.

Characterization of Bacteriogenic Iron Oxide Deposits from Axial Volcano, Juan de Fuca Ridge, Northeast Pacific Ocean

Abstract: Iron oxides from the caldera of Axial Volcano, a site of hydrothermal vent activity along the Juan de Fuca Ridge, are characterized by abundant bacterial structures that closely resemble the sheaths of Leptothrix ochracea , the stalks of Gallionella ferruginea , and the filaments of a novel iron oxidizing PV-1 strain. These bacteria are commonly associated with iron-oxide precipitates and are proposed to play two causal roles in the formation of iron oxides at Axial Volcano. First, by increasing the rate of Fe 2+ oxidation, and second, by lowering the concentration of Fe 3+ required for precipitation by providing a reactive surface for heterogeneous nucleation. Rapid rates of oxidation and precipitation caused by the bacteria likely contribute to the poorly ordered nature of the iron oxides, determined to be primarily 2-line ferrihydrite, and in one case, poorly ordered goethite. The iron-oxide precipitates consist dominantly of iron, silicon (mostly diatoms), and organic carbon with a suite of sorbed tra...

New NiO/Co3O4 and Fe2O3/Co3O4 Nanocomposite Catalysts: Synthesis and Characterization

Abstract: Two nanocomposite oxides, NiO/Co3O4 and Fe2O3/Co3O4, are considered. The nanocomposite oxides were obtained by wet impregnation and characterized by means of X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray diffraction (XRD), thermal analysis, atomic force microscopy (AFM), and transmission electron microscopy (TEM). The microscopy images suggest a different growing mechanism for the NiO/Co3O4 and Fe2O3/Co3O4 nanocomposite oxides: small clusters of iron oxide wet the surface of Co3O4, whereas NiO grows as isolated particles characterized by a big diameter. Both XPS and TEM data indicate the possible formation of Fe3O4. A marked decrease of OH groups on the Fe2O3/Co3O4 and NiO/Co3O4 sample surfaces is revealed by XPS and DRIFT data and suggests the grafting of supported and supporting oxides by hydroxyl condensation. The acidic and basic sites present on Fe2O3/Co3O4 and NiO/Co3O4 powder surfaces are investigated and compared with those obse...

Simultaneous conversion of nitrogen oxides and soot into nitrogen and carbon dioxide over iron containing oxide catalysts in diesel exhaust gas

Abstract: This paper deals with the simultaneous catalytic conversion of NO x and soot into N 2 and CO 2 in diesel exhaust gas. Several iron containing oxide catalysts were partially modified by the alkali metal potassium and were used for NO x –soot reaction in a model exhaust gas. Fe 1.9 K 0.1 O 3 has shown highest catalytic performance for N 2 formation in the so far investigated catalysts. Further studies have shown that Fe 1.9 K 0.1 O 3 was deactivated in a substantial way after about 20 TPR experiments due to the agglomeration of the promoter potassium. Experiments carried out over the aged Fe 1.9 K 0.1 O 3 catalyst have shown that NO x –soot reaction was suppressed at higher O 2 concentration, since O 2 –soot conversion was kinetically favored. In contrast to that, the catalytic activity was increased in presence of NO 2 and H 2 O. Mechanistic examinations suggest that (CO) intermediates, formed at the soot surface, are the reactive sites in the NO x –soot reaction. Higher catalytic performance in presence of NO 2 could be explained by the enhanced formation of these (CO) species. Moreover, nitrate species formed at the catalyst surface might also play an important role in NO x –soot conversion.

Adsorption of Heavy Metals on Mixed Fe-Al Oxides in the Absence or Presence of Organic Ligands

Abstract: A study was carried out on the adsorption of Co2+, Cu2+, Pb2+, and Zn2+ ions on mixed Fe-Al oxides inthe absence or presence of increasing concentrations of oxalate or tartrate. Mixed Fe-Al oxides were prepared by precipitating at pH 5.5 mixtures of Fe and Al ions at initial Fe/Al molar ratios (R) of 0, 1, 2, 4, 10 and ∞ (R0, R1, R2, R4, R10 and R∞).The oxides aged 7 days at 20 °C or 30 days at 50 °C showed different chemical composition and physico-chemical and mineralogical properties. All the mixed Fe-Al oxides showed presence of poorly crystalline materials (ferrihydrite) even after prolonged aging. The heavy metals wereselectively adsorbed on the oxides. For all the precipitates aged7 days at 20 °C, the selectivity sequence wasPb2+> Cu2+ > Zn2+ > Co2+, but the pH at which 50% ofeach cation was adsorbed (pH50) was different from sample tosample. It was found that usually the greater the amounts of Fe in Fe-Al gels the lower the pH50 for each metal, but the adsorption of a heavy metal was not linearly related to Fe content. The pH50 usually did not change significantly when the oxides were aged 30 days at 50 °C. Competitive adsorption of Cu and Zn on ferrihydrite (R∞) showed thatCu strongly prevented Zn adsorption even at an initial Zn/Cu molar ratio of 8, whereas Cu sorption was not inhibited. In thepresence of oxalate (OX) or tartrate (TR) (organic ligand/Pb molar ratio (rL) from 0 to 7) the quantities of Pb adsorbedon the Fe-Al oxides usually increased with increasing rL. The adsorption increase of Pb was particularly high on the oxidesricher in Fe (R4-R∞), but a significant increase was also observed on R0-R2 samples. The adsorption of Pb on the oxides hasbeen influenced not only by the presence and concentration of organic ligands but also by the sequence of addition of Pb and tartrate on the sorbents. It has been ascertained that on each oxide the greater amounts of Pb were adsorbed when tartrate wasadded before Pb and usually according to the following sequence: Tr before Pb > Pb before Tr > Pb + Tr > Pb.