Showing papers on "Magnetite published in 2004"
IBM1
TL;DR: As-synthesized iron oxide nanoparticles have a cubic spinel structure as characterized by HRTEM, SAED, and XRD and can be transformed into hydrophilic ones by adding bipolar surfactants, and aqueous nanoparticle dispersion is readily made.
Abstract: High-temperature solution phase reaction of iron(III) acetylacetonate, Fe(acac)3, with 1,2-hexadecanediol in the presence of oleic acid and oleylamine leads to monodisperse magnetite (Fe3O4) nanoparticles. Similarly, reaction of Fe(acac)3 and Co(acac)2 or Mn(acac)2 with the same diol results in monodisperse CoFe2O4 or MnFe2O4 nanoparticles. Particle diameter can be tuned from 3 to 20 nm by varying reaction conditions or by seed-mediated growth. The as-synthesized iron oxide nanoparticles have a cubic spinel structure as characterized by HRTEM, SAED, and XRD. Further, Fe3O4 can be oxidized to Fe2O3, as evidenced by XRD, NEXAFS spectroscopy, and SQUID magnetometry. The hydrophobic nanoparticles can be transformed into hydrophilic ones by adding bipolar surfactants, and aqueous nanoparticle dispersion is readily made. These iron oxide nanoparticles and their dispersions in various media have great potential in magnetic nanodevice and biomagnetic applications.
3,244 citations
TL;DR: Magnetite nanoparticles coated with (3-aminopropyl)triethoxysilane, NH2(CH2)3Si(OC2H5)3 were prepared by silanization reaction and characterized by X-ray diffractometry, transmission electron microscopy, atomic force microscopy and Fourier transform infrared spectroscopy and magnetization measurements as mentioned in this paper.
727 citations
TL;DR: Iron oxide (Fe(3)O(4), magnetite) nanocrystals of 6 to 30 nm with narrow size distributions (sigma = 5-10%) were prepared by the pyrolysis of iron carboxylate salts.
597 citations
TL;DR: In this article, the reaction between dissolved sulfide and synthetic iron (oxyhydr)oxide minerals was studied in artificial seawater and 0.1 M NaCl at pH 7.5 and 25°C.
550 citations
TL;DR: In this article, it was suggested that the intermediate iron oxide nanoparticles (before aeration) were formed by the competing processes of oxidation and crystal growth after decomposition of Fe(CO)5.
Abstract: Easy preparation of iron oxide nanoparticles [5- and 11-nm maghemite (γ-Fe2O3) and 19-nm magnetite (Fe3O4)] by thermal decomposition of Fe(CO)5 in the presence of residual oxygen of the system and by consecutive aeration were investigated by TEM/HRTEM, XRD, and Mossbauer spectroscopy. Also, the magnetic properties of the nanoparticles were studied by SQUID magnetometer and optical microscopy. It was suggested that the intermediate iron oxide nanoparticles (before aeration) were formed by the competing processes of oxidation and crystal growth after decomposition of Fe(CO)5. At room temperature, the aerated 5-nm particles were superparamagnetic without interaction among the particles, whereas the 19-nm particles were ferrimagnetic. The 11-nm iron oxide nanoparticles were superparamagnetic with some interactions among the particles.
521 citations
TL;DR: In this paper, the simultaneous entrapment of biological macromolecules and nanostructured silica-coated magnetite in sol−gel materials using a reverse-micelle technique leads to a bioactive, mechanically stable, nanometer-sized, and magnetically separable particles.
Abstract: The simultaneous entrapment of biological macromolecules and nanostructured silica-coated magnetite in sol−gel materials using a reverse-micelle technique leads to a bioactive, mechanically stable, nanometer-sized, and magnetically separable particles. These spherical particles have a typical diameter of 53 ± 4 nm, a large surface area of 330 m2/g, an average pore diameter of 1.5 nm, a total pore volume of 1.427 cm3/g and a saturated magnetization (MS) of 3.2 emu/g. Peroxidase entrapped in these particles shows Michaelis−Mentan kinetics and high activity. The catalytic reaction will take place immediately after adding these particles to the reaction solution. These enzyme entrapping particles catalysts can be easily separated from the reaction mixture by simply using an external magnetic field. Experiments have proved that these catalysts have a long-term stability toward temperature and pH change, as compared to free enzyme molecules. To further prove the application of this novel magnetic biomaterial in...
489 citations
TL;DR: In this paper, Amino-silane was covalently coupled to the surface of the magnetic silica nanospheres and activated by glutaraldehyde, and the morphology and magnetic properties of the magnetite particles were examined.
479 citations
TL;DR: In this article, the specific absorption rate (SAR) values of aqueous suspensions of magnetite particles with different diameters varying from 7.5 to 416nm were investigated by measuring the time-dependent temperature curves in an external alternating magnetic field (80 kHz, 32.5 kA/m).
473 citations
TL;DR: The catalytic properties of FeNi3 allow complex organic compounds to form within serpentinite and, when mixed with atmospherically produced complex organic matter and waters that circulated through basalts, constitutes an attractive prebiotic substrate.
Abstract: Metamorphic hydration and oxidation of ultramafic rocks produces serpentinites, composed of serpentine group minerals and varying amounts of brucite, magnetite, and/or FeNi alloys. These minerals buffer metamorphic fluids to extremely reducing conditions that are capable of producing hydrogen gas. Awaruite, FeNi3, forms early in this process when the serpentinite minerals are Fe-rich. Olivine with the current mantle Fe/Mg ratio was oxidized during serpentinization after the Moon-forming impact. This process formed some of the ferric iron in the Earth's mantle. For the rest of Earth's history, serpentinites covered only a small fraction of the Earth's surface but were an important prebiotic and biotic environment. Extant methanogens react H2 with CO2 to form methane. This is a likely habitable environment on large silicate planets. The catalytic properties of FeNi3 allow complex organic compounds to form within serpentinite and, when mixed with atmospherically produced complex organic matter and waters that circulated through basalts, constitutes an attractive prebiotic substrate. Conversely, inorganic catalysis of methane by FeNi3 competes with nascent and extant life.
472 citations
TL;DR: Water-soluble magnetite nanocrystals of different sizes have been prepared by a one-pot reaction through thermal decomposition of ferric triacetylacetonate in 2-pyrrolidone.
Abstract: Water-soluble magnetite nanocrystals of different sizes have been prepared by a one-pot reaction through thermal decomposition of ferric triacetylacetonate in 2-pyrrolidone.
347 citations
TL;DR: It is substantiated that increasing the concentration of oxidants in water and maintaining flowing conditions can reduce the amount of iron release from corroded iron pipes, and that the microstructure and composition of corrosion scales are important parameters that can influence the amounts of iron released from such systems.
TL;DR: Silica-magnetite composites were prepared for eventual applications in biomolecular separations (nucleic acids) Their production on large scale has been extensively characterised in a physical and chemical context They perform at least as well, if not better than a commercially available equivalent at adsorbing and eluting DNA Several methods for the preparation of magnetite were compared in order to select one, which produced particles, possessing high magnetic susceptibility, low rate of sedimentation and good chemical stability.
TL;DR: In this article, the average particle size varies from 5 to 15 nm, depending on the concentration and the nature of the polyelectrolyte, and the presence of only magnetite phase.
Abstract: Magnetite nanoparticles of nearly uniform size have been prepared by precipitating ferrous ions in the presence of two different polyelectrolytes, viz., poly(acrylic acid) and the sodium salt of carboxymethyl cellulose at high pH (∼13). The size of the magnetite nanoparticles can be controlled easily by varying the concentration of the polyelectrolyte in the medium. Transmission electron microscopy study indicates that the average particle size varies from 5 to 15 nm, depending on the concentration and the nature of the polyelectrolyte. X-ray diffraction study shows the presence of only magnetite phase. FTIR spectroscopy and thermogravimetric analysis confirmed the presence of polyelectrolyte on the magnetite surface. The magnetization and Mossbauer studies were performed on two samples with mean diameters 7.0 and 14.7 nm. Magnetization measurements suggest that both of these particles are of single magnetic domain. The measurements also estimate the superparamagnetic blocking temperature, TB = 145 K for ...
TL;DR: The transition from magnetite to maghemite nanoparticles was confirmed by X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) and electron diffraction photography as discussed by the authors.
TL;DR: In a series of water-rock reaction simulations, the authors assess the processes of serpentinization of harzburgite and related calcium metasomatism resulting in rodingite-type alteration, and seafloor carbonate chimney precipitation.
TL;DR: In this paper, the formation of the porosity of hematite was due to the decomposition of FeCO 3 and FeOOH, which played a key role in the forming of the iron oxide nanorods.
TL;DR: Magnetite nanoparticles were synthesized by sol-gel method and the highly crystalline nature of the magnetite structure with diameter of around 10 nm was characterized with transmission electron microscopy and X-ray diffractometry as discussed by the authors.
TL;DR: In this paper, the graft densities of polymers on the surfaces of magnetite particles were estimated at 0.12−0.20 chains/nm2 by thermogravimetric analysis (TGA).
Abstract: Polymer-grafted magnetite (Fe3O4) nanoparticles (diameter about 10 nm) were prepared through a direct polymer grafting reaction from their surfaces. The chemisorbed initiator (TEMPO-based alkoxyamine) for nitroxide-mediated radical polymerization with a phosphoric acid group gave controlled polystyrene (PS) and poly(3-vinylpyridine) (P3VP) graft layers on the surface. The graft densities of polymers on the surfaces of magnetite particles were estimated at 0.12−0.20 chains/nm2 by thermogravimetric analysis (TGA). The improvement in the dispersibility of PS-modified magnetite in good solvents was verified by ultraviolet−visible (UV−vis) absorption spectroscopy, transmission electron microscopy (TEM), and dynamic light scattering (DLS). In the case of P3VP-modified magnetite, the particles were stably dispersed in good solvents, by protonation, in acid solution, and by quarternization with iodomethane, in neutral aqueous solution. The magnetic response of the polymer-grafted magnetite against an external mag...
TL;DR: In this article, superparamagnetic polymeric nanofibers were produced via an electrospinning technique from colloidally-stable suspensions of magnetite nanoparticles in polyethylene oxide and polyvinyl alcohol solutions.
TL;DR: This work presents the first direct observation of dipolar chain formation in zero field in a ferrofluid containing the largest synthetic single-domain magnetite particles studied so far, and is the only ferroluid system available at present that allows quantifying chain length and ring-size distributions of dipsolar structures as a function of concentration and particle size.
Abstract: Magnetite (Fe3O4) forms the basis of most dispersions studied in the field of magnetic fluids and magnetic colloids Despite extensive theory and simulations on chain formation in dipolar fluids in zero field, such structures have not yet been imaged in laboratory-made magnetite dispersions Here, we present the first direct observation of dipolar chain formation in zero field in a ferrofluid containing the largest synthetic single-domain magnetite particles studied so far To our knowledge, this is the only ferrofluid system available at present that allows quantifying chain length and ring-size distributions of dipolar structures as a function of concentration and particle size
TL;DR: In this paper, the authors compare the reducing capacity and Fe(II) sequestration mechanisms of goethite and hematite to 2-line ferrihydrite under advective flow within a medium mimicking that of natural groundwater supplemented with organic carbon.
TL;DR: Raman spectral features of chromite, ulvospinel, magnetite, ilmenite, hematite, and some of their solid solutions are presented in this article, where the relationship between Raman spectral features and mineral chemistry is used to interpret the Raman data of Fe-Ti-Cr oxides found during Raman point-count measurements on rock chips of Martian meteorite EETA79001.
Abstract: Raman spectral features of chromite, ulvospinel, magnetite, ilmenite, hematite, and some of their solid solutions are presented. Although most Fe-Ti-Cr-oxides produce relatively weak Raman signals compared to oxyanionic minerals, sufficient information can be extracted from their spectra to identify the end-member mineral phases as well as some information about compositional variations in solid solutions. Correlations between Raman spectral features and mineral chemistry are used to interpret the Raman data of Fe-Ti-Cr oxides found during Raman point-count measurements on rock chips of Martian meteorite EETA79001, as an analog to Mars on-surface planetary investigations. In general, ulvospinel, magnetite, and chromite end-members are readily distinguished by their Raman spectral patterns, as are ilmenite and hematite. In the low signal-to-noise (S/N) spectra generally obtained from the Raman point-count procedure, the position and shape of the strongest peak of Fe-Ti-Cr oxides in the region 660–680 cm−1 (A1g mode) is the most useful for discriminating Fe3+-Ti-Cr-Al substitutions in the magnetite-ulvospinel, ulvospinel-chromite, and chromite-spinel series, but minor peaks in the range 300–600 cm−1 also assist in discrimination. These spectral features are useful for investigating the variability among Fe-Ti-Cr-Al oxide solid solutions in natural samples. In EETA79001, a Martian basaltic meteorite, most of the oxide grains (as measured with the electron microprobe) are ulvospinel, chromian ulvospinel, and chromite, but ilmenite, titanian chromite, and titanomagnetite are also observed. The Fe-Ti-Cr-oxides identified by Raman point-count include end-member ilmenite, low-Al chromite-spinel solid solutions, ulvospinel-magnetite solid solutions, and more complex chromite-spinel-ulvospinel-magnetite solid solutions; the latter exhibit a wide range of main peak positions and broadened peak widths that may reflect structural disorder as well One Raman spectrum suggests end-member magnetite, and one spectrum from a different rock chip appears to be that of non-terrestrial hematite, reflecting local oxidizing alteration, which has not been observed previously in this meteorite. These results show that analyses done in an automated mode on the surface of an unprepared Martian rock sample can provide useful constraints on the Fe-Ti-Cr oxide mineralogy present and on compositional variations within those minerals, including an indication of oxygen fugacity.
TL;DR: In this paper, mesoporous silica coatings were created on micrometer-sized magnetite (Fe3O4) particles using cetyltrimethylammonium chloride micelles as molecular templates.
Abstract: A new concept is proposed to synthesize mesoporous magnetic nanocomposite particles of great scientific and technological importance. Mesoporous silica coatings were created on micrometer-sized magnetite (Fe3O4) particles using cetyltrimethylammonium chloride micelles as molecular templates. The characterization by transmission electron microscopy (TEM), nitrogen adsorption–desorption, diffuse-reflectance Fourier-transform infrared spectroscopy, and zeta-potential measurements confirmed the deposition of mesoporous silica thin layers on the magnetite particles. The synthesized particles showed a drastic increase in specific surface area with an average pore size of 2.5 nm. The coating material showed a negligible effect on the saturation magnetization of the original particles that were fully protected by silica coatings. The synthesized mesoporous magnetic nanocomposite particles have a wide range of applications in toxin removal, waste remediation, catalysis, reactive sorbents, and biological cell separations.
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TL;DR: In this article, a simple precipitation route was developed to synthesize magnetite (Fe3O4) nano-particles with controlled size without any requirement of calcination step at high temperatures.
Abstract: We have developed a simple precipitation route to synthesize magnetite (Fe3O4) nano-particles with controlled size without any requirement of calcination step at high temperatures. The study of these nano-particles indicates an enhancement in saturation magnetization with reduction in size down to ~10 nm beyond which the magnetization reduces. The latter is attributed to surface effects becoming predominant as surface to core volume ratio increases. From the view -point of applications, 10 nm size of magnetite particles seems to be the optimum.
TL;DR: In this paper, a simple precipitation route was developed to synthesize magnetite (Fe3O4) nanoparticles with controlled size without any requirement of calcination step at high temperatures.
TL;DR: These crystalline nanoarchitectures of iron oxide that exhibit superparamagnetic behavior while still retaining the desirable bicontinuous pore-solid networks and monolithic nature of an aerogel are developed.
Abstract: We have developed crystalline nanoarchitectures of iron oxide that exhibit superparamagnetic behavior while still retaining the desirable bicontinuous pore−solid networks and monolithic nature of an aerogel. Iron oxide aerogels are initially produced in an X-ray-amorphous, high-surface-area form, by adapting recently established sol−gel methods using Fe(III) salts and epoxide-based proton scavengers. Controlled temperature/atmosphere treatments convert the as-prepared iron oxide aerogels into nanocrystalline forms with the inverse spinel structure. As a function of the bathing gas, treatment temperature, and treatment history, these nanocrystalline forms can be reversibly tuned to predominantly exhibit either Fe3O4 (magnetite) or γ-Fe2O3 (maghemite) phases, as verified by electron microscopy, X-ray and electron diffraction, microprobe Raman spectroscopy, and magnetic analysis. Peak deconvolution of the Raman-active Fe−O bands yields valuable information on the local structure and vacancy content of the va...
TL;DR: The importance of the magnetic iron sulfide minerals, greigite and pyrrhotite, is often underappreciated in geochemical studies because they are metastable with respect to pyrite (FeS2), whereas magnetite is more abundant in coarse-grained sediments as discussed by the authors.
TL;DR: In this paper, the results from two rock magnetic analyses, the low-temperature Moskowitz test and ferromagnetic resonance (FMR), were applied to dozens of samples of magnetite and other materials.
TL;DR: In this paper, the effect of pressure on the apparent equilibrium constant, K′, for magnetite solubility and the relative iron-carrying capacities of magmatic vapor and brine were examined in a rhyolite melt-vapor-brine-magnetite system at 800°C.
TL;DR: The preparation of hybrid temperature-sensitive microgels which include magnetite nanoparticles in their structure, which possess a low critical solution temperature (LCST) in water solutions, with a rapid decrease of the particle size being observed at elevated temperatures.
Abstract: In the present paper, we report the preparation of hybrid temperature-sensitive microgels which include magnetite nanoparticles in their structure. Polymeric microgels have been prepared by surfactant-free emulsion copolymerization of acetoacetoxyethyl methacrylate (AAEM) and N-vinylcaprolactam (VCL) in water with a water-soluble azo-initiator. The obtained microgels possess a low critical solution temperature (LCST) in water solutions, with a rapid decrease of the particle size being observed at elevated temperatures. Magnetite was deposited directly into microgels, leading to the formation of composite particles which combine both temperature-sensitive and magnetic properties. The influence of magnetite load on microgel size, morphology, swelling-deswelling behavior, and stability is discussed.