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Showing papers on "Magnetite published in 2012"


Journal ArticleDOI
TL;DR: In this article, the size of the magnetite nanoparticles was carefully controlled by varying the reaction temperature and through surface modification, which significantly affected the particle size, the electrical conductivity, and the magnetic properties.
Abstract: Magnetite nanoparticles were synthesized via the chemical co-precipitation method using ammonium hydroxide as the precipitating agent. The size of the magnetite nanoparticles was carefully controlled by varying the reaction temperature and through the surface modification. Herein, the hexanoic acid and oleic acid were introduced as the coating agents during the initial crystallization phase of the magnetite. Their structure and morphology were characterized by the Fourier transform infrared spectroscopy (FTIR), the X-ray diffraction (XRD) and the field-emission scanning electron microscopy (FE-SEM). Moreover, the electrical and magnetic properties were studied by using a conductivity meter and a vibrating sample magnetometer (VSM), respectively. Both of the bare magnetite and the coated magnetite were of the cubic spinel structure and the spherical-shaped morphology. The reaction temperature and the surface modification critically affected the particle size, the electrical conductivity, and the magnetic properties of these particles. The particle size of the magnetite was increased through the surface modification and reaction temperature. In this study, the particle size of the magnetite nanoparticles was successfully controlled to be in the range of 10–40 nm, suitable for various biomedical applications. The electrical conductivity of the smallest particle size was 1.3 × 10−3 S/cm, within the semi-conductive materials range, which was higher than that of the largest particle by about 5 times. All of the magnetite nanoparticles showed the superparamagnetic behavior with high saturation magnetization. Furthermore, the highest magnetization was 58.72 emu/g obtained from the hexanoic acid coated magnetite nanoparticles.

589 citations


Journal ArticleDOI
12 Jan 2012-Nature
TL;DR: The full low-temperature superstructure of magnetite is determined by high-energy X-ray diffraction from an almost single-domain, 40-micrometre grain, and the emergent order is identified, suggesting trimerons may be important quasiparticles in magnetite above the Verwey transition and in other transition metal oxides.
Abstract: X-ray diffraction is used to show that the structural distortion of magnetite below 125 kelvin is to a first approximation caused by charge ordering of its constituent iron ions, but that the localized electrons are distributed over three iron sites to form ‘trimeron’ quasiparticles. In a letter to Nature in 1939, Evert Johannes Willem Verwey described the first example of a low-temperature charge-ordering transition in a solid — the Verwey transition — in the mineral magnetite, Fe3O4 (see go.nature.com/3h2pp1 ). This phenomenon has since been observed in other transition metal oxides, yet despite decades of study, the precise structure of the charge-ordered state in magnetite has remained elusive. The complex structural distortions that characterize the Verwey state have now been determined, revealing an anomalous shortening of some inter-atomic distances. These are suggestive of an unusual charge configuration in which the localized electrons are each distributed over three neighbouring Fe sites. The mineral magnetite (Fe3O4) undergoes a complex structural distortion and becomes electrically insulating at temperatures less than 125 kelvin. Verwey proposed in 1939 that this transition is driven by a charge ordering of Fe2+ and Fe3+ ions1, but the ground state of the low-temperature phase has remained contentious2,3 because twinning of crystal domains hampers diffraction studies of the structure4. Recent powder diffraction refinements5,6,7 and resonant X-ray studies8,9,10,11,12 have led to proposals of a variety of charge-ordered and bond-dimerized ground-state models13,14,15,16,17,18,19. Here we report the full low-temperature superstructure of magnetite, determined by high-energy X-ray diffraction from an almost single-domain, 40-micrometre grain, and identify the emergent order. The acentric structure is described by a superposition of 168 atomic displacement waves (frozen phonon modes), all with amplitudes of less than 0.24 angstroms. Distortions of the FeO6 octahedra show that Verwey’s hypothesis is correct to a first approximation and that the charge and Fe2+ orbital order are consistent with a recent prediction17. However, anomalous shortening of some Fe–Fe distances suggests that the localized electrons are distributed over linear three-Fe-site units, which we call ‘trimerons’. The charge order and three-site distortions induce substantial off-centre atomic displacements and couple the resulting large electrical polarization to the magnetization. Trimerons may be important quasiparticles in magnetite above the Verwey transition and in other transition metal oxides.

410 citations


Journal ArticleDOI
TL;DR: This is the first demonstration of highly photoactive hematite nanowire arrays at a relatively low activation temperature without a dopant element and shows substantially enhanced photoactivity compared to the pristine hematites prepared in air.
Abstract: A promising photoelectrode material for solar-driven water splitting, hematite (a-Fe2O3) is non-toxic, abundant, chemically stable, low-cost, and has a bandgap of approximately 2.1 eV, which accounts for a maximum theoretical solar-tohydrogen (STH) efficiency of 15%. This last property compares favorably with the most studied metal oxide materials for photoeletrochemical (PEC) water splitting, including TiO2, [6–10] ZnO, and WO3. [12–15] However, the reported STH efficiencies of hematite photoelectrodes are substantially lower than the theoretical value, owing to several limiting factors such as poor conductivity, short excited-state lifetime (< 10 ps), poor oxygen evolution reaction kinetics, low absorption coefficient, short diffusion length for holes (2–4 nm), and lower flat-band potential in energy for water splitting. Enormous efforts have been made to overcome these limitations of hematite, including the incorporation of oxygen evolving catalysts to reduce the kinetic barrier for water oxidation on the hematite surface, the development of nanostructures to increase the effective surface area and to reduce diffusion length for carriers, as well as the development of element-doped hematite for improving electrical conductivity and/or light absorption. Recently, we demonstrated that TiO2 nanowires thermally treated in hydrogen showed increased donor density and PEC performance as a result of the formation of oxygen vacancies. We anticipated that creating oxygen vacancy (VO), and thereby Fe, sites in hematite could significantly increase the conductivity of the material through a polaron hopping mechanism. Although VO can be created by sintering hematite in a reductive atmosphere such as hydrogen, it may introduce hydrogen as a dopant into the structure. Additionally, hematite can be easily reduced in hydrogen to produce magnetite (Fe3O4), which is photo-inactive. [27] Herein, we report an alternative method for the preparation of highly conductive and photoactive hematite through thermal decomposition of b-FeOOH in an oxygen-deficient atmosphere (N2+ air). The resulting hematite sample showed substantially enhanced photoactivity compared to the pristine hematite prepared in air. The oxygen content during thermal activation significantly affects the formation of VO and thereby the photoactivity of hematite nanowires for water oxidation. This is the first demonstration of highly photoactive hematite nanowire arrays at a relatively low activation temperature without a dopant element. Akaganeite nanowires were prepared through the hydrolysis of FeCl3 (0.15m) in an environment with a high ionic strength (1m NaNO3) and low pH value (pH 1.5, adjusted by HCl) at 95 8C for 4 h. The resulting yellow film on a fluorine-doped tin oxide (FTO) substrate was covered with nanowire arrays with an average diameter and length of 70 nm and 700 nm, respectively (Figure 1a). X-ray diffraction

346 citations


Journal ArticleDOI
TL;DR: In this paper, a facile one-step reverse precipitation method was proposed to synthesize water-dispersible, biocompatible, and carboxylate-functionalized superparamagnetic magnetite (Fe3O4) nanoparticles with the help of a sodium citrate salt.
Abstract: Hydrophilic functionalization of nanoparticle surface is essential for their biomedical applications. Herein, we report a facile one-step reverse precipitation method to synthesize water-dispersible, biocompatible, and carboxylate-functionalized superparamagnetic magnetite (Fe3O4) nanoparticles with the help of biocompatible sodium citrate salt. Transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), zeta potential measurement, dynamic light scattering (DLS), and superconducting quantum interference device (SQUID) were used to characterize the as-prepared magnetite nanoparticles. The size of the as-prepared magnetite nanoparticles was tuned from 27 ± 3.8 to 4.8 ± 1.9 nm by changing the sodium citrate concentration from 25 to 125 mM. The sodium citrate concentration also influenced the water-dispersible stability of the as-prepared magnetite nanoparticles, which was due to the electrostatic repulsion.

325 citations


Journal ArticleDOI
TL;DR: In this paper, the authors report on the use of synthetic and natural Fe (hydr)oxides as catalysts in environmental remediation procedures using an advanced oxidation process, more specifically the Fentonlike system, which is highly efficient in generating reactive species such as hydroxyl radicals, even at room temperature and under atmospheric pressure.
Abstract: Iron is the fourth most common element by mass in the Earth’s crust and forms compounds in several oxidation states. Iron (hydr)oxides, some of which form inherently and exclusively in the nanometre-size range, are ubiquitous in nature and readily synthesized. These facts add up to render many Fe (hydr)oxides suitable as catalysts, and it is hardly surprising that numerous studies on the applications of Fe (hydr)oxides in catalysis have been published. Moreover, the abundant availability of a natural Fe source from rocks and soils at minimal cost makes the potential use of these as heterogeneous catalyst attractive. Besides those Fe (hydr)oxides that are inherently nanocrystalline (ferrihydrite, Fe5HO8·4H2O, and feroxyhyte, δ′-FeOOH), magnetite (Fe3O4) is often used as a catalyst because it has a permanent magnetization and contains Fe in both the divalent and trivalent states. Hematite, goethite and lepidocrocite have also been used as catalysts in their pure forms, doped with other cations, and as composites with carbon, alumina and zeolites among others. In this review we report on the use of synthetic and natural Fe (hydr)oxides as catalysts in environmental remediation procedures using an advanced oxidation process, more specifically the Fenton-like system, which is highly efficient in generating reactive species such as hydroxyl radicals, even at room temperature and under atmospheric pressure. The catalytic efficiency of Fe (hydr)oxides is strongly affected by factors such as the Fe oxidation state, surface area, isomorphic substitution of Fe by other cations, pH and temperature.

311 citations


Journal ArticleDOI
15 Aug 2012-Talanta
TL;DR: An efficient and cost-effective method for the preconcentration of trace amounts of Pb(II), Cd( II) and Cu(II) in environmental and biological samples using this novel magnetic solid phase is developed and satisfactory results were obtained.

299 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of thermal annealing on uncoated and coated magnetite nano-particles has been investigated using transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy, infrared (IR) and Raman spectrographic analysis (TGA).

283 citations


Journal ArticleDOI
30 May 2012-Talanta
TL;DR: A convenient method is proposed to assess the presence of magnetite-maghemite mixture and to further quantify its phase composition using the conventional peak deconvolution technique and it is believed that the proposed method would be a convenient tool for the study of the magnetites-magemite mixture which otherwise requires highly sophisticated equipments and techniques.

273 citations


Journal ArticleDOI
Taebin Ahn1, Jong Hun Kim1, Hee-Man Yang1, Jeong Woo Lee1, Jong-Duk Kim1 
TL;DR: In this paper, the reaction pathways leading to the production of the magnetite phase in the coprecipitation reaction are not fully understood, despite the fact that the reaction path may be of significant importance in controlling the crystal structure, morphology, and particle size of magnetite nanoparticles.
Abstract: Magnetite nanoparticles for biomedical applications are typically prepared using the coprecipitation technique, which is the most convenient method. However, the reaction pathways leading to the production of the magnetite phase in the coprecipitation reaction are not fully understood, despite the fact that the reaction path may be of significant importance in controlling the crystal structure, morphology, and particle size of the magnetite nanoparticles. In the present study, we identified the reaction pathways in the coprecipitation of magnetite; when base was slowly added to an iron chloride solution, akaganeite nucleated and transformed through goethite to magnetite. At high addition rates, an additional pathway in which ferrous hydroxide nucleated and transformed through lepidocrocite to magnetite competed with the former pathway. This difference was due to the pH inhomogeneity in the reaction medium that was present before homogeneous mixing. In most coprecipitation reactions, these magnetite format...

245 citations


Journal ArticleDOI
TL;DR: In this paper, the trace element concentrations of Fe-oxides in massive sulfides that form Ni-Cu-PGE deposits at the base of the Sudbury Igneous Complex in Canada were determined.

243 citations


Journal ArticleDOI
TL;DR: Degradation experiments with various structurally distinct compounds were carried out, indicating a similar selectivity of the heterogeneous Fenton-like system to that known for oxidation with ·OH.

Journal ArticleDOI
TL;DR: In this paper, a study was conducted to evaluate hematite, magnetite, goethite, and iron rich laterite soil as arsenic adsorbents, and the results showed that arsenic adsorption occurred over the entire pH range tested (pH 4 − 11).

01 Jan 2012
TL;DR: In this article, the band gap parameters of magneto-nanopowders such as the direct, indirect-band gap energies, Fermi energy and Urbach energy are determined.
Abstract: Fe 3O4 nanoparticles and non aqueous stable magnetic fluid (MF) containing Fe 3O4 nanoparticles with mean diameters of 10 nm, which are in the range of super-paramagnetism, are prepared. Magnetite nanoparticles are synthesized via co-precipitation method from ferrous and ferric solutions. X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) are used to study the physical properties of the (MF) and powder. The band gap parameters of the magneto-nanopowders such as the direct, indirect-band gap energies, Fermi energy and Urbach energy are determined.

Journal ArticleDOI
TL;DR: Electrostatic attraction and oxidation-reduction between chromium and mixed maghemite-magnetite are postulated as mechanisms for the removal of Cr(VI) from aqueous solutions.

Journal ArticleDOI
TL;DR: In this article, the authors used electron microprobe analysis (EMPA), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis, and oxygen isotope analysis to test whether magnetite from the five following geologic settings in western Montana and northern Idaho has distinct geochemical signatures: (1) greenschist facies burial metamorphic rocks of the Middle Proterozoic Belt Supergroup, (2) sediment-hosted stratiform Cu-Ag deposits (Spar Lake and Rock Creek) in Belt Super
Abstract: Magnetite (Fe 3 O 4 ) is a common and widespread accessory mineral in many host rocks and mineral deposits. We used electron microprobe analysis (EMPA), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis, and oxygen isotope analysis to test whether magnetite from the five following geologic settings in western Montana and northern Idaho has distinct geochemical signatures: (1) greenschist facies burial metamorphic rocks of the Middle Proterozoic Belt Supergroup, (2) sediment-hosted stratiform Cu-Ag deposits (Spar Lake and Rock Creek) in Belt Supergroup metasedimentary rocks, (3) hydrothermal Ag-Pb-Zn veins of the Coeur d’Alene district, (4) extensively deformed and partially altered Belt Supergroup host rocks from the Coeur d’Alene district, and (5) two Cretaceous postmetamorphic igneous intrusions. EMPA results show that magnetite from each of these five settings is essentially pure Fe 3 O 4 , but LA-ICP-MS analyses results show that magnetite from these five settings has trace element concentrations that generally vary over less than one order of magnitude. These magnetite occurrences show subtle compositional differences that generally correlate with temperatures, as determined by oxygen isotope geothermometry. Burial metamorphic magnetite from the Coeur d’Alene host rocks has the smallest overall trace element contents. Chromium, Co, and Zn are depleted in both hydrothermal and host-rock magnetite from the Coeur d’Alene district. In contrast, magnetite from postmetamorphic igneous rocks in the Belt terrane has relatively large Mg, V, Co, and Mn values, consistent with its formation at relatively high temperatures and subsequent subsolidus reequilibration. Factor analysis was used to trace any underlying or latent relationships among elements that are likely to be incorporated into the magnetite structure. Factor analysis provides geochemical discrimination of at least three types of magnetite in the Belt terrane: (1) Mg-Mn, (2) Ga-Zn-Cr, and (3) Co-Ni-V magnetite. Hydrothermal magnetite from the Gold Hunter siderite vein shows characteristically high values for factor 1. Factor 2 is most pronounced in magnetite from the burial metamorphic host rocks and the sediment-hosted Cu-Ag deposits. Furthermore, factor 2 indicates that Ga, Zn, and Cr concentrations are lower on average in hydrothermal and host-rock magnetite from the Coeur d’Alene district. Factor 3 divides igneous magnetite from other magnetite occurrences. This factor also subdivides magnetite of an alkalic-ultramafic intrusive complex from that of the granitic stock. Hydrothermal magnetite from siderite and calcite veins in the Coeur d’Alene district has consistently low scores for factor 3. The geochemistry of magnetite can be a useful discriminator and pathfinder for hydrothermal deposits. The relatively low formation temperature and the metamorphic history of the Belt terrane led to low trace element concentrations and subtle differences between magnetite from different geologic settings. Nevertheless, by combining LA-ICP-MS analysis and factor analysis, compositional variations between groups of magnetite samples from different geologic settings can be recognized.

Journal ArticleDOI
TL;DR: In this article, uniform iron oxide magnetic nanoparticles, with sizes in the range 9-22 nm, have been synthesized by thermal decomposition of an iron oleate complex in 1-octadecene, controlling reaction parameters related to the nucleation and growth processes.
Abstract: Uniform iron oxide magnetic nanoparticles, with sizes in the range 9–22 nm, have been synthesized by thermal decomposition of an iron oleate complex in 1-octadecene, controlling reaction parameters related to the nucleation and growth processes. After transferring to water through a ligand substitution process, nanoparticles display very good magnetic and magneto-thermal properties. The relationship between these properties and the size and size distribution of the particles is discussed. The colloidal stability of the nanoparticles dispersed in common biological buffers has also been studied.

Journal ArticleDOI
TL;DR: It is demonstrated that the stoichiometry (the bulk Fe(2+)/Fe(3+) ratio, x) of magnetite can, in part, explain the observed discrepancies in the extent of U(VI) reduction by magnetite.
Abstract: Hexavalent uranium (UVI) can be reduced enzymatically by various microbes and abiotically by Fe2+-bearing minerals, including magnetite, of interest because of its formation from Fe3+ (oxy)hydroxides via dissimilatory iron reduction. Magnetite is also a corrosion product of iron metal in suboxic and anoxic conditions and is likely to form during corrosion of steel waste containers holding uranium-containing spent nuclear fuel. Previous work indicated discrepancies in the extent of UVI reduction by magnetite. Here, we demonstrate that the stoichiometry (the bulk Fe2+/Fe3+ ratio, x) of magnetite can, in part, explain the observed discrepancies. In our studies, magnetite stoichiometry significantly influenced the extent of UVI reduction by magnetite. Stoichiometric and partially oxidized magnetites with x ≥ 0.38 reduced UVI to UIV in UO2 (uraninite) nanoparticles, whereas with more oxidized magnetites (x < 0.38) and maghemite (x = 0), sorbed UVI was the dominant phase observed. Furthermore, as with our chemi...

Journal ArticleDOI
TL;DR: The extent of Fe atom exchange between magnetite and aqueous Fe(2+) was significant, and went well beyond the amount of Fe atoms found at the near surface, suggesting that for magnetite, unlike goethite, Fe atom diffusion is a plausible mechanism to explain the rapid rates ofFe atom exchange in magnetite.
Abstract: The reaction between magnetite and aqueous Fe(2+) has been extensively studied due to its role in contaminant reduction, trace-metal sequestration, and microbial respiration. Previous work has demonstrated that the reaction of Fe(2+) with magnetite (Fe(3)O(4)) results in the structural incorporation of Fe(2+) and an increase in the bulk Fe(2+) content of magnetite. It is unclear, however, whether significant Fe atom exchange occurs between magnetite and aqueous Fe(2+), as has been observed for other Fe oxides. Here, we measured the extent of Fe atom exchange between aqueous Fe(2+) and magnetite by reacting isotopically "normal" magnetite with (57)Fe-enriched aqueous Fe(2+). The extent of Fe atom exchange between magnetite and aqueous Fe(2+) was significant (54-71%), and went well beyond the amount of Fe atoms found at the near surface. Mossbauer spectroscopy of magnetite reacted with (56)Fe(2+) indicate that no preferential exchange of octahedral or tetrahedral sites occurred. Exchange experiments conducted with Co-ferrite (Co(2+)Fe(2)(3+)O(4)) showed little impact of Co substitution on the rate or extent of atom exchange. Bulk electron conduction, as previously invoked to explain Fe atom exchange in goethite, is a possible mechanism, but if it is occurring, conduction does not appear to be the rate-limiting step. The lack of significant impact of Co substitution on the kinetics of Fe atom exchange, and the relatively high diffusion coefficients reported for magnetite suggest that for magnetite, unlike goethite, Fe atom diffusion is a plausible mechanism to explain the rapid rates of Fe atom exchange in magnetite.

Journal ArticleDOI
01 Jun 2012-Fuel
TL;DR: In this article, the chemical oxidative degradation of oil hydrocarbons was investigated by magnetite catalyzed Fenton-like (FL) and activated persulfate (AP) oxidation.

Journal ArticleDOI
TL;DR: In this article, the inner Fe-Cr spinel layer grows according to a mechanism involving void formation at the oxide/metal interface and the driving force for pore formation is the outward magnetite growth.
Abstract: Under CO2 exposure at an intermediate temperature, typically 550 °C, 9Cr–1Mo steel forms a duplex oxide scale made of an outer magnetite layer and an almost-as-thick inner Fe–Cr rich spinel oxide layer It is proposed that the inner Fe–Cr spinel layer grows according to a mechanism involving void formation at the oxide/metal interface The driving force for pore formation is the outward magnetite growth: iron vacancies are injected at the oxide/metal interface then condense into voids The fresh metallic surface made available is then oxidized by CO2, which diffuses fast through the scale The physical aspects, the integrity and the nature of the scale are shown to be very dependent on the oxygen potential existing in the environment

Journal ArticleDOI
TL;DR: In this article, a two-dimensional model of a slice through the center of a spherical particle in a fluid is proposed, and only the magnetic force and the drag force are taken into consideration.
Abstract: Magnetic iron oxide nanoparticles are attracting increased attention due to their interesting properties that can be applied in a large number of applications such as catalysis and biomedicine. This paper focuses on the synthesis, characteristics, and biomedical applications of iron oxide nanoparticles. The two most common iron oxides, including magnetite and maghemite, are discussed in this study. For most of their applications, the magnetic behavior of iron oxide nanoparticles in a fluid is very important – especially, the high-gradient magnetic separation of the particles from a non-magnetic liquid medium such as blood in the human body. A two-dimensional model, which represents a slice through the center of a spherical particle in a fluid, is proposed in this study, and only the magnetic force and the drag force are taken into consideration. The magnetization of the particles is calculated by using the Langevin function, and the fluid drag force is calculated by using the Navier–Stokes equation. The t...

Journal ArticleDOI
TL;DR: In this paper, the authors showed that using sodium carbonate as a co-precipitating agent for the synthesis of uncoated iron oxide nanoparticles, the reaction proceeds sufficiently slowly to enable a detailed study of both the reaction pathway and products.
Abstract: Ferrimagnetic iron oxides are the common choice for many current technologies, especially those with application in biology and medicine. Despite the comprehensive knowledge accumulated about their chemistry in the bulk state, the sequence of changes taking place during the precipitation of iron oxide nanoparticles in aqueous media is much less extensive. We show that using sodium carbonate as a co-precipitating agent for the synthesis of uncoated iron oxide nanoparticles, the reaction proceeds sufficiently slowly to enable a detailed study of both the reaction pathway and products. The effect of pH, temperature and reaction time on particle size, morphology, crystalline phase and its magnetic properties was investigated. The obtained nanoparticles showed an increase in average particle size of about 10 nm per pH unit for the magnetite phase leading to 6.9 ± 0.4 nm, 18 ± 3 nm and 28 ± 5 nm for pH 8, 9 and 10 respectively. Goethite was initially formed by an olation mechanism at room temperature, followed by a slow transformation into magnetite over a 24 h period, as tracked by X-ray diffraction. In another set of experiments where the reaction temperatures were varied, magnetite was obtained directly by the oxolation mechanism at temperatures above 45 °C. The optimization of the experimental parameters led to superparamagnetic nanoparticles with a high saturation magnetization of 82 A m2 kg−1 at 300 K when synthesized at pH 9.

Journal ArticleDOI
TL;DR: This study investigated the methylene blue (MB) decolorization through heterogeneous UV-Fenton reaction catalyzed by V-Ti co-doped magnetites, with emphasis on comparing the contribution of V and Ti cations on improving the adsorption and catalytic activity of magnetite.

Journal ArticleDOI
24 Aug 2012-Langmuir
TL;DR: The difference between the concentration results from VSM and the Tiron test confirmed the reduction of magnetic phase of magnetic core in the presence of coatings and different suspension media, and the corresponding effective thickness of the nonmagnetic layer between magnetic core and surface coating was calculated.
Abstract: Magnetic iron oxide nanoparticles have numerous applications in the biomedical field, some more mature, such as contrast agents in magnetic resonance imaging (MRI), and some emerging, such as heating agents in hyperthermia for cancer therapy. In all of these applications, the magnetic particles are coated with surfactants and polymers to enhance biocompatibility, prevent agglomeration, and add functionality. However, the coatings may interact with the surface atoms of the magnetic core and form a magnetically disordered layer, reducing the total amount of the magnetic phase, which is the key parameter in many applications. In the current study, amine and carboxyl functionalized and bare iron oxide nanoparticles, all suspended in water, were purchased and characterized. The presence of the coatings in commercial samples was verified with X-ray photoelectron spectroscopy (XPS). The class of iron oxide (magnetite) was verified via Raman spectroscopy and X-ray diffraction. In addition to these, in-house prepared iron oxide nanoparticles coated with oleic acid and suspended in heptane and hexane were also investigated. The saturation magnetization obtained from vibrating sample magnetometry (VSM) measurements was used to determine the effective concentration of magnetic phase in all samples. The Tiron chelation test was then utilized to check the real concentration of the iron oxide in the suspension. The difference between the concentration results from VSM and the Tiron test confirmed the reduction of magnetic phase of magnetic core in the presence of coatings and different suspension media. For the biocompatible coatings, the largest reduction was experienced by amine particles, where the ratio of the effective weight of magnetic phase reported to the real weight was 0.5. Carboxyl-coated samples experienced smaller reduction with a ratio of 0.64. Uncoated sample also exhibits a reduction with a ratio of 0.6. Oleic acid covered samples show a solvent-depended reduction with a ratio of 0.5 in heptane and 0.4 in hexane. The corresponding effective thickness of the nonmagnetic layer between magnetic core and surface coating was calculated by fitting experimentally measured magnetization to the modified Langevin equation.

Journal ArticleDOI
TL;DR: In this paper, the main focus was on the fabrication of deaggregated spherical nanoparticles with a narrow size distribution, and further separation of air-dry EEW nanoparticles was performed in aqueous suspensions.
Abstract: Nanoparticles of iron oxides (MNPs) were prepared using the electric explosion of wire technique (EEW). The main focus was on the fabrication of de-aggregated spherical nanoparticles with a narrow size distribution. According to XRD the major crystalline phase was magnetite with an average diameter of MNPs, depending on the fraction. Further separation of air-dry EEW nanoparticles was performed in aqueous suspensions. In order to provide the stability of magnetite suspension in water, we found the optimum concentration of the electrostatic stabilizer (sodium citrate and optimum pH level) based on zeta-potential measurements. The stable suspensions still contained a substantial fraction of aggregates which were disintegrated by the excessive ultrasound treatment. The separation of the large particles out of the suspension was performed by centrifuging. The structural features, magnetic properties and microwave absorption of MNPs and their aqueous solutions confirm that we were able to obtain an ensemble in...

Journal ArticleDOI
TL;DR: In this article, the reaction between lepidocrocite (γ-FeOOH, 21 −42 mmol L−1) and dissolved S(-II) (3 −9 mmol L −1) in batch experiments at pH 7 in a glove box using TEM, XRD, Mossbauer spectroscopy, and wet chemistry extraction was studied.

Journal ArticleDOI
TL;DR: A magnetite-loaded mesocellular carbonaceous material, Fe(3)O(4)/MSU-F-C, exhibited superior activity as both a Fenton catalyst and an adsorbent for removal of phenol and arsenic, and strong magnetic property rendering it separable by simply applying magnetic field.

Journal ArticleDOI
TL;DR: In this paper, the Cs+ sorption ability of the Prussian-blue-modified magnetite (PB-Fe3O4) was evaluated by batch magnetic separation.
Abstract: Prussian-blue-modified magnetite (PB-Fe3O4) was prepared by a simple method. The Cs+ sorption ability of PB-Fe3O4 was evaluated by batch magnetic separation. As a result, the maximum sorption amoun...

Journal ArticleDOI
Haiyan Sun1, Bo Chen1, Xiuling Jiao1, Zhen Jiang1, Zhenhua Qin1, Dairong Chen1 
TL;DR: A solvothermal process was designed to synthesize magnetite (Fe3O4) nanorods using iron pentacarbonyl (Fe(CO)5), oleic acid, and hexadecylamine as raw materials as discussed by the authors.
Abstract: A solvothermal process was designed to synthesize magnetite (Fe3O4) nanorods using iron pentacarbonyl (Fe(CO)5), oleic acid, and hexadecylamine as raw materials. In the preparation process, Fe(CO)5 was first decomposed and oxidized to form FeO. Meanwhile, Fe(CO)5 reacted with oleic acid to form iron oleate. In the system water derived from the reaction between oleic acid and hexadecylamine resulted in the hydrolysis of iron oleate to form the initial Fe3O4 nanorods. In the following process, the dissolution of FeO and decomposition of residual Fe(CO)5 as well as the hydrolysis of iron oleate provided the source for the growth of Fe3O4 nanorods, which led to the enlargement of the particles with time. By adjusting the reaction time or the amount of the added hexadecylamine, the length of uniform nanorods could be tuned from 63 to 140 nm. Furthermore, the as-prepared Fe3O4 nanorods showed excellent performance in electrochemical property and exhibited different magnetic property from spherical nanoparticles...

Journal ArticleDOI
TL;DR: Malvoisin et al. as discussed by the authors developed a new method using the magnetic properties of magnetite, Fe 3 O 4, to monitor experimental serpentinization, where the saturation remanent magnetization signal (Jrs) was measured during the course of experiments designed to react San Carlos olivine, (Mg 0.91, Fe 0.09) 2 SiO 4, with water at 250 to 350°C and 500 bars.
Abstract: [1] A new method using the magnetic properties of magnetite, Fe 3 O 4 , was developed to monitor experimental serpentinization. The saturation remanent magnetization signal (Jrs) was measured during the course of experiments designed to react San Carlos olivine, (Mg 0.91 , Fe 0.09) 2 SiO 4 , with water at 250 to 350°C and 500 bars. At the end of the experiments, the ratio with saturation magnetization (Jrs/Js ratio) allowed to convert each successive Jrs measurement into an in situ amount of magnetite produced by the serpentinization reaction. Water weight loss was also measured on the end product to determine the final degree of serpentinization. The application of this procedure to a series of experiments performed at 300°C/500 bars for various run duration (9 to 514 days) and starting olivine grain size (1 to 150 mm) shows a linear relationship between magnetite production and reaction progress. This relationship can be safely transposed to other experimental conditions using thermochemical modeling and/or the Fe content of the product phases. We show that this high-sensitivity magnetic method is a powerful tool to precisely monitor serpentinization kinetics in Fe-bearing systems. It represents, in addition, a new indirect mean for monitoring the production of hydrogen which is bound to magnetite production rate. Citation: Malvoisin, B., J. Carlut, and F. Brunet (2012), Serpentinization of oceanic peridotites: 1. A high-sensitivity method to monitor magnetite production in hydrothermal experiments,