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1.
Superparamagnetic silica-coated magnetite (Fe3O4) nanoparticles with immobilized metal affinity ligands were prepared for protein adsorption. First, magnetite nanoparticles were synthesized by co-precipitating Fe2+ and Fe3+ in an ammonia solution. Then silica was coated on the Fe3O4 nanoparticles using a sol–gel method to obtain magnetic silica nanoparticles. The condensation product of 3-Glycidoxypropyltrimethoxysilane (GLYMO) and iminodiacetic acid (IDA) was immobilized on them and after charged with Cu2+, the magnetic silica nanoparticles with immobilized Cu2+ were applied for the adsorption of bovine serum albumin (BSA). Scanning electron micrograph showed that the magnetic silica nanoparticles with an average size of 190 nm were well dispersed without aggregation. X-ray diffraction showed the spinel structure for the magnetite particles coated with silica. Magnetic measurement revealed the magnetic silica nanoparticles were superparamagnetic and the saturation magnetization was about 15.0 emu/g. Protein adsorption results showed that the nanoparticles had high adsorption capacity for BSA (73 mg/g) and low nonspecific adsorption. The regeneration of these nanoparticles was also studied.  相似文献   

2.
In this study, we developed a convenient one-pot method with sodium oleate as both the surfactant and precipitant to synthesize pure magnetite nanoparticles in the water/ethanol/toluene system. The initial molar ratio of [Fe3+]/[Fe2+] and the concentration of iron salts were changed in order to systematically investigate their influences on the chemical and physical properties of nanoparticles, such as the crystal structure, morphology, particle sizes, dispersion and magnetism. Samples were determined by XRD, XPS, FTIR, DLS, and VSM. The oleate coating steadily existed on the surface of the nanoparticles to profit them of excellent monodispersibility and stability in non-polar solvents with very narrow size distribution and extremely approximate mean diameters of ~7 nm. Particles consisted mainly of magnetite with a little or no maghemite phase with the molar ratio of [Fe3+]/[Fe2+] decreasing from 2:1 to 1:1, but they all exhibited superparamagnetism at room temperature. After the optimization, pure magnetite nanoparticles could be prepared with the saturation magnetization successfully increasing to 75 emu/g(Fe), when the molar ratio of [Fe3+]/[Fe2+] was 1.5:1 and the concentration of iron precursors was 95 mM.  相似文献   

3.
Tropical soils often contain high amounts of iron oxides. Hematite (αFe2O3) and goethite (αFeOOH) are the most widespread iron oxides, but magnetite (Fe3O4) and maghemite (γFe2O3) occur in magnetic pedons. A wide range of spinel compositions in the Fe3O4-γFe2O3 series has been identified in magnetic Brazilian soils. Isomorphic substitution of mainly Ti4+, Al3+ and Mg2+, but also of Cr3+ and Mn2+ and other minor elements for iron are related to changes in their structural stability and magnetic properties. Magnetic iron oxides of selected Brazilian pedodomains are discussed, distinguishing those produced from mafic rocks (tuffite, basalt), where primary magnetite transforms to maghemite, from those produced in non-mafic lithologies (such as steatite), where inherited magnetite may be exceptionally stable in the soil. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

4.
The stoichiometric conditions for the formation of ferrous hydroxide Fe(OH)2, by mixing Fe2+ ions with caustic soda NaOH, leads by oxidation to magnetite, irrelevant of the foreign anions, e.g. Cl? or SO4 2?, as demonstrated from Mössbauer spectroscopy. The electrochemical potential Eh and pH value of the initial conditions correspond to the drastic change from basic to acidic medium, observed when varying the initial Fe2+/OH? ratio. Mössbauer analysis of the end products of oxidation at various temperatures shows that magnetite is only obtained at stoichiometry at very low temperature, but extends off stoichiometry at higher temperatures. The mechanism of formation of magnetite through an intermediate compound is discussed.  相似文献   

5.
Mössbauer, magnetic, and X-ray studies of magnetic microspheres separated from energy ashes have been performed. The major component of the composition of the microspheres is an imperfect magnetite with cation vacancies in which iron is located in trivalent and mixed-valence positions characteristic of stoichiometric magnetite. Moreover, the Fe3+ and Fe2.5+ positions with a cation vacancy among the nearest neighbors and the positions with a partial localization of 3d electrons have been identified.  相似文献   

6.
The present paper analyzes the valence-coordination state of iron atoms in polymer composite materials fabricated from polystyrene and iron-ore concentrates – magnetite and hematite – upon exposure to fast electrons with energy of 6.2 MeV and fluence of 1018 electrons/cm2. Changes in the phase content and valence-coordination and magnetic states of iron atoms are established. After irradiation, the hematite phase is transformed into the magnetite phase with a predominance of Fe3+ ions with [FeO4] coordination, and the magnetite phase forms the wüstite-type (FeO) phase in which Fe2+ ions are arranged in [FeO6] coordination.  相似文献   

7.
Synthesis of magnetite (Fe3O4) nanoparticles under oxidizing environment by precipitation from aqueous media is not straightforward because Fe2+ gets oxidized to Fe3+ and thus the ratio of Fe3+:Fe2+=2:1 is not maintained during the precipitation. A molar ratio of Fe3+:Fe2+ smaller than 2:1 has been used by many to compensate for the oxidation of Fe2+ during the preparation. In this work, we have prepared iron oxide nanoparticles in air environment by the precipitation technique using initial molar ratios Fe3+:Fe2+?2:1. The phases of the resulting powders have been determined by several techniques. It is found that the particles consist mainly of maghemite with little or no magnetite phase. The particles have been suspended in non-aqueous and aqueous media by coating the particles with a single layer and a bilayer of oleic acid, respectively. The particle sizes, morphology and the magnetic properties of the particles and the ferrofulids prepared from these particles are reported. The average particle sizes obtained from the TEM micrographs are 14, 10 and 9 nm for the water, kerosene and dodecane-based ferrofluids, respectively, indicating a better dispersion in the non-aqueous media. The specific saturation magnetization (σs) value of the oleic-acid-coated particles (∼53 emu/g) is found to be lower than that for the uncoated particles (∼63 emu/g). Magnetization σs of the dodecane-based ferrofluid is found to be 10.1 emu/g for a volume fraction of particles ?=0.019. Zero coercivity and zero remanance on the magnetization curves indicate that the particles are superparamagnetic (SPM) in nature.  相似文献   

8.
Magnetic contrast at the atomic level has been observed for the first time in scanning tunneling microscopy experiments on a magnetite (Fe3O4(001)) surface using in-situ prepared ferromagnetic Fe tips. A periodic corrugation with a 12 Å periodicity is clearly observed along the rows of FeB-sites which corresponds to the repeat period of Fe2+ and Fe3+ along these rows. This periodicity is not observed by using non-magneticW tips although the rows of FeB-sites can be resolved as well. The magnetic contrast observed with Fe tips is attributed to the different spin configurations of the magnetic ions Fe2+ and Fe3+ in Fe3O4.  相似文献   

9.
The element iron plays a crucial role in the study of the evolution of matter from an interstellar cloud to the formation and evolution of the planets. In the Solar System iron is the most abundant metallic element. It occurs in at least three different oxidation states: Fe(0) (metallic iron), Fe(II) and Fe(III). Fe(IV) and Fe(VI) compounds are well known on Earth, and there is a possibility for their occurrence on Mars. In January 2004 the USA space agency NASA landed two rovers on the surface of Mars, both carrying the Mainz Mössbauer spectrometer MIMOS II. They performed for the first time in-situ measurements of the mineralogy of the Martian surface, at two different places on Mars, Meridiani Planum and Gusev crater, respectively, the landing sites of the Mars-Exploration-Rovers (MER) Opportunity and Spirit. After about two Earth years or one Martian year of operation the Mössbauer (MB) spectrometers on both rovers have acquired data from more than 150 targets (and more than thousand MB spectra) at each landing site. The scientific measurement objectives of the Mössbauer investigation are to obtain for rock, soil, and dust (1) the mineralogical identification of iron-bearing phases (e.g., oxides, silicates, sulfides, sulfates, and carbonates), (2) the quantitative measurement of the distribution of iron among these iron-bearing phases (e.g., the relative proportions of iron in olivine, pyroxenes, ilmenite and magnetite in a basalt), (3) the quantitative measurement of the distribution of iron among its oxidation states (e.g., Fe2+, Fe3+, and Fe6+), and (4) the characterization of the size distribution of magnetic particles. Special geologic targets of the Mössbauer investigation are dust collected by the Athena magnets and interior rock and soil surfaces exposed by the Athena Rock Abrasion Tool and by trenching with rover wheels. The Mössbauer spectrometer on Opportunity at Meridiani Planum, identified eight Fe-bearing phases: jarosite (K,Na,H3O)(Fe,Al)(OH)6(SO4)2, hematite, olivine, pyroxene, magnetite, nanophase ferric oxides (npOx), an unassigned ferric phase, and a metallic Fe–Ni alloy (kamacite) in a Fe–Ni-meteorite. Outcrop rocks consist of hematite-rich spherules dispersed throughout S-rich rock that has nearly constant proportions of Fe3+ from jarosite, hematite, and npOx (28%, 35%, and 19% of total Fe). Jarosite is mineralogical evidence for aqueous processes under acid–sulfate conditions because it has structural hydroxide and sulfate and it forms at low pH. Hematite-rich spherules, eroded from the outcrop, and their fragments are concentrated as hematite-rich soils (lag deposits) on ripple crests (up to 68% of total Fe from hematite). Olivine, pyroxene, and magnetite are primarily associated with basaltic soils and are present as thin and locally discontinuous cover over outcrop rocks, commonly forming aeolian bedforms. Basaltic soils are more reduced (Fe3+/Fetotal ~0.2?0.4), with the fine-grained and bright aeolian deposits being the most oxidized. Basaltic soil at Meridiani Planum and Gusev crater have similar Fe-mineralogical compositions. At Gusev crater, the Mössbauer spectrometer on the MER Spirit rover has identified 8 Fe-bearing phases. Two are Fe2+ silicates (olivine and pyroxene), one is a Fe2+ oxide (ilmenite), one is a mixed Fe2+ and Fe3+ oxide (magnetite), two are Fe3+ oxides (hematite and goethite), one is a Fe3+ sulfate (mineralogically not constrained), and one is a Fe3+ alteration product (npOx). The surface material in the plains have a olivine basaltic signature (Morris, et al., Science, 305: 833, 2004; Morris, et al., J. Geophys. Res., 111, 2006, Ming, et al., J. Geophys. Res., 111, 2006) suggesting physical rather than chemical weathering processes present in the plains. The Mössbauer signature for the Columbia Hills surface material is very different ranging from nearly unaltered material to highly altered material. Some of the rocks, in particular a rock named Clovis, contain a significant amount of the Fe oxyhydroxide goethite, α-FeOOH, which is mineralogical evidence for aqueous processes because it is formed only under aqueous conditions.  相似文献   

10.
The partial substitution of oxygen by fluorine, in magnetite, has allowed us to increase the concentration of the Fe2+ ions and to modify the ratio (Fe2+Fe3+)oct. without introducing a foreign cation. Studies of specific heat and X-ray diffraction at temperatures near that of the Verwey temperature show that the crystallographic transformation is linked to the existence of octahedral Fe2+ ions.  相似文献   

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