Showing papers on "Magnetite published in 2011"

Size-dependent properties of magnetic iron oxide nanocrystals

Abstract: The fine control of iron oxide nanocrystal sizes within the nanometre scale (diameters range from 2.5 to 14 nm) allows us to investigate accurately the size-dependence of their structural and magnetic properties. A study of the growth conditions of these nanocrystals obtained by thermal decomposition of an iron oleate precursor in high-boiling point solvents has been carried out. Both the type of solvent used and the ligand/precursor ratio have been systematically varied, and were found to be the key parameters to control the growth process. The lattice parameters of all the nanocrystals deduced from X-ray diffraction measurements are consistent with a structure of the type Fe3−xO4, i.e. intermediate between magnetite and maghemite, which evolves toward the maghemite structure for the smallest sizes (x = 1/3). The evolution of the magnetic behavior with nanoparticle sizes emphasizes clearly the influence of the surface, especially on the saturation magnetization Ms and the magneto-crystalline anisotropy K. Dipolar interactions and thermal dependence have been also taken into account in the study on the nanoscale size-effect of magnetic properties.

Discriminant diagrams for iron oxide trace element fingerprinting of mineral deposit types

Abstract: Magnetite and hematite are common minerals in a range of mineral deposit types. These minerals form partial to complete solid solutions with magnetite, chromite, and spinel series, and ulvospinel as a result of divalent, trivalent, and tetravalent cation substitutions. Electron microprobe analyses of minor and trace elements in magnetite and hematite from a range of mineral deposit types (iron oxide-copper-gold (IOCG), Kiruna apatite–magnetite, banded iron formation (BIF), porphyry Cu, Fe-Cu skarn, Fe-Ti, V, Cr, Ni-Cu-PGE, Cu-Zn-Pb volcanogenic massive sulfide (VMS) and Archean Au-Cu porphyry and Opemiska Cu veins) show compositional differences that can be related to deposit types, and are used to construct discriminant diagrams that separate different styles of mineralization. The Ni + Cr vs. Si + Mg diagram can be used to isolate Ni-Cu-PGE, and Cr deposits from other deposit types. Similarly, the Al/(Zn + Ca) vs. Cu/(Si + Ca) diagram can be used to separate Cu-Zn-Pb VMS deposits from other deposit types. Samples plotting outside the Ni-Cu-PGE and Cu-Zn-Pb VMS fields are discriminated using the Ni/(Cr + Mn) vs. Ti + V or Ca + Al + Mn vs. Ti + V diagrams that discriminate for IOCG, Kiruna, porphyry Cu, BIF, skarn, Fe-Ti, and V deposits.

Synthesis of Magnetite/Graphene Oxide Composite and Application for Cobalt(II) Removal

Abstract: A magnetite/graphene oxide (M/GO) composite was synthesized via a chemical reaction with a magnetite particle size of 10–15 nm and was developed for the removal of heavy metal ions from aqueous solutions. The composite was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The sorption of Co(II) on the M/GO composite was carried out under various conditions, that is, contact time, sorbent content, pH, ionic strength, foreign ions, and temperature. The sorption isotherms of Co(II) on the M/GO composite could be described well by the Langmuir model. The thermodynamic parameters (ΔH0, ΔS0, and ΔG0) calculated from the temperature-dependent isotherms indicated that the sorption reaction of Co(II) on the M/GO composite was an endothermic and spontaneous process. M/GO can be separated and recovered by magnetic separation. Results show that the magnetic M/GO composite is a promising sorbent material for the preconcentration an...

Magnetic Iron Oxide Nanoparticles in 10−40 nm Range: Composition in Terms of Magnetite/Maghemite Ratio and Effect on the Magnetic Properties

Abstract: Magnetic iron oxide nanoparticles in the 10−40 nm size range and with a reduced distribution in size have been synthesized under argon by using ammonium bases R4NOH (R = CH3, C2H5, C3H7) and a hydrothermal treatment. The size is tuned owing to the base to iron ratio and to the length of the alkyl chain R. We precipitate first ferric hydroxides at pH 1.5−2, then ferrous hydroxide at pH 5.5−6. The rapid increase of pH up to basic pH leads to the formation of magnetic iron oxide particles of 12 nm. For [base] to [Fe] ratio above 3.5, a homogeneous growth occurs during further hydrothermal treatment at 250 °C. The higher the quantity of base added and the longer the alkyl chain used, the smaller the particle size produced. For sizes above 20 nm, the Verwey transition at 120 K, characteristic of magnetite, is observed on the field cooling−zero field cooling magnetization curve. The nanoparticles can be described by a core−shell model, that is, a magnetite core surrounded by an oxidized layer close to maghemite...

Synthesis and applications of nano-structured iron oxides/hydroxides - a review

Abstract: The nano iron oxides have been synthesized by almost all the known wet chemical methods which include precipitation at ambient/elevated temperatures, surfactant mediation, emulsion/micro-emulsion, electro-deposition etc. Iron oxides in nano-scale have exhibited great potential for their applications as catalytic materials, wastewater treatment adsorbents, pigments, flocculants, coatings, gas sensors, ion exchangers, magnetic recording devices, magnetic data storage devices, toners and inks for xerography, magnetic resonance imaging, bioseparation and medicine. Nano sized magnetite Fe3O4, and maghemite γ-Fe2O3 exhibiting excellent magnetic properties find applications for biomedical purposes and as soft ferrites. Iron hydroxides and oxyhydroxides such as ferrihydrite, goethite, akaganeite, lepidocrocite are being evaluated for their applications in water purification for the removal of toxic ions. Hematite, α-Fe2O3 in the nano range has been used to obtain transparent paints. In catalysis both iron oxides and hydroxides find application in numerous synthesis processes. This review outlines the work being carried out on synthesis of iron oxides in nano form and their various applications.

Tuning the Size, the Shape, and the Magnetic Properties of Iron Oxide Nanoparticles

Abstract: The influence of a variety of parameters on the synthesis of iron oxide nanoparticles (magnetite/maghemite Fe3O4/γ-Fe2O3) by thermal decomposition of a metal−organic iron precursor in an organic medium is reported. We study the role of both the surfactant and the reducing agent on the shape, the size distribution, and the magnetic properties. We aim at synthesizing magnetic nanoparticles with high crystal quality and good magnetic response. A narrow size distribution of pseudospherical and faceted particles (4−20 nm) with a high saturation magnetization (Ms ≈ 80−85 emu/g at 5 K) is obtained when using oleic acid as a surfactant. In contrast, decanoic acid yields much larger pseudocubic particles (45 nm) with a wider size distribution and a larger saturation magnetization (Ms = 92 emu/g at 5 K), close to the expected value for bulk magnetite. Besides, the use of a variety of reducing agents monitors the magnetic behavior. In the case of 1,2-hexadecanediol, magnetic characterization suggests that the nanopa...

Water-dispersible magnetite-graphene-LDH composites for efficient arsenate removal

Abstract: A composite material, containing magnetite particles, graphene and layered double hydroxides (LDHs) was fabricated through a simple two-step reaction. Graphene was used as the matrix for supporting magnetite particles and LDH nanoplates. The synthesized magnetite-graphene-LDH (MGL) composites were characterized by field emission scanning electron microscopic (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transformed infrared (FTIR) spectroscopy, N2adsorption-desorption, and X-ray photoelectron spectroscopy (XPS). The MGL composites were applied to remove arsenate from aqueous solutions and could be easily separated by magnetic separation process. The results showed enhanced adsorption capacity of arsenate on the MGL as compared to that of pure Mg/Al LDHs. The surface area of MGL is greatly enhanced through the incorporation of magnetite particles and graphene, which provides more active sites for arsenate uptake. Moreover, LDHs were hybridized with mechanically and chemically stable graphene materials, providing an accessible diffusion pathway in the macropore domain, and therefore their adsorption capacity was enhanced. The fast and efficient adsorption of arsenate from solution to MGL suggests that the MGL composites are potential and suitable materials in the preconcentration of arsenate from large volumes of aqueous solutions in wastewater treatment.

Magnetic Nanoparticles of Iron Carbide, Iron Oxide, Iron@Iron Oxide, and Metal Iron Synthesized by Laser Ablation in Organic Solvents

Abstract: Iron-based nanoparticles can have useful magnetic and catalytic properties. We investigated the synthesis of iron-based nanostructures by laser ablation of bulk iron with 1064 nm nanosecond pulses in the following organic solvents: tetrahydrofuran, acetonitrile, dimethylformamide, dimethylsulfoxide, toluene, and ethanol. Structural analysis carried out by transmission electron microscopy and X-ray diffraction revealed that the solvent has a dramatic influence on both the composition and the nanostructure of nanoparticles. Various magnetic nanoparticles like iron carbide (Fe3C), magnetic iron oxide (magnetite/maghemite), metal iron (α-Fe), and iron@iron oxide are obtained by varying the solvent and keeping unchanged all the other experimental conditions. These results are the consequences of the different reactivity of solvent molecules exposed to the plasma plume generated during the ablation process.

Template free synthesis and electromagnetic wave absorption properties of monodispersed hollow magnetite nano-spheres

Abstract: Monodispersed hollow magnetite spheres with diameter of about 500 nm and a shell thickness of approximately 150 nm were synthesized through a simple solvothermal process in ethylene glycol (EG) in the presence of polyvinyl-pyrrolidone and urea for electromagnetic absorption applications. The electron microscopy images showed that the obtained magnetite spheres are composed of small particles with the size 50–100 nm and are hollow in nature. A possible formation mechanism for the hollow magnetite spheres was proposed and it was confirmed by the control experiments. The hollow magnetite spheres exhibited a high saturation magnetization value of 90.6 emu g−1 and coercivity of 300 Oe at room temperature. The epoxy resin composites with 68 wt% hollow magnetite spheres provided good electromagnetic wave absorption performance (RL < −20 dB) in the range of 1.6–3.0 GHz over the absorber thickness of 5–9 mm. A minimum RL value of −42.7 dB was observed at 2.0 GHz with a thickness of 6.9 mm.

Magnetite Colloidal Nanocrystals: A Facile Pathway To Prepare Mesoporous Hematite Thin Films for Photoelectrochemical Water Splitting

Abstract: In this study, we demonstrate an alternative and promising way to produce hematite photoanodes with high performance and without the addition of doping or catalytic coating. In this approach, we pr...

Arsenic removal from aqueous solutions by mixed magnetite–maghemite nanoparticles

Abstract: In this study, magnetite–maghemite nanoparticles were used to treat arsenic-contaminated water. X-ray photoelectron spectroscopy (XPS) studies showed the presence of arsenic on the surface of magnetite–maghemite nanoparticles. Theoretical multiplet analysis of the magnetite–maghemite mixture (Fe3O4-γFe2O3) reported 30.8% of maghemite and 69.2% of magnetite. The results show that redox reaction occurred on magnetite–maghemite mixture surface when arsenic was introduced. The study showed that, apart from pH, the removal of arsenic from contaminated water also depends on contact time and initial concentration of arsenic. Equilibrium was achieved in 3 h in the case of 2 mg/L of As(V) and As(III) concentrations at pH 6.5. The results further suggest that arsenic adsorption involved the formation of weak arsenic-iron oxide complexes at the magnetite–maghemite surface. In groundwater, arsenic adsorption capacity of magnetite–maghemite nanoparticles at room temperature, calculated from the Langmuir isotherm, was 80 μmol/g and Gibbs free energy (∆G0, kJ/mol) for arsenic removal was −35 kJ/mol, indicating the spontaneous nature of adsorption on magnetite–maghemite nanoparticles.

Discovery of the recoverable high-pressure iron oxide Fe4O5

Abstract: Phases of the iron–oxygen binary system are significant to most scientific disciplines, directly affecting planetary evolution, life, and technology. Iron oxides have unique electronic properties and strongly interact with the environment, particularly through redox reactions. The iron–oxygen phase diagram therefore has been among the most thoroughly investigated, yet it still holds striking findings. Here, we report the discovery of an iron oxide with formula Fe4O5, synthesized at high pressure and temperature. The previously undescribed phase, stable from 5 to at least 30 GPa, is recoverable to ambient conditions. First-principles calculations confirm that the iron oxide here described is energetically more stable than FeO + Fe3O4 at pressure greater than 10 GPa. The calculated lattice constants, equation of states, and atomic coordinates are in excellent agreement with experimental data, confirming the synthesis of Fe4O5. Given the conditions of stability and its composition, Fe4O5 is a plausible accessory mineral of the Earth’s upper mantle. The phase has strong ferrimagnetic character comparable to magnetite. The ability to synthesize the material at accessible conditions and recover it at ambient conditions, along with its physical properties, suggests a potential interest in Fe4O5 for technological applications.

Nano magnetite decorated multiwalled carbon nanotubes: a robust nanomaterial for enhanced carbon dioxide adsorption

Abstract: It has long been seen as a demanding task to counteract the raised levels of greenhouse gases including carbon dioxide (CO2). Current worldwide research is focused on the investigation of materials which can capture large amounts of CO2 through physical or chemical adsorption. The present work focuses on a high pressure CO2 adsorption study of functionalized MWNTs (f-MWNTs) and a magnetite decorated MWNT nanocomposite. Multiwalled carbon nanotubes (MWNTs) were prepared by a catalytic chemical vapor deposition method followed by purification and functionalization. Magnetite (Fe3O4) nanoparticles were decorated over the f-MWNT surface by a chemical method. The functionalized MWNTs and magnetite decorated MWNTs were characterized by electron microscopy, X-ray powder diffraction, Raman spectroscopy and FTIR spectroscopy. The CO2 adsorption capacity was measured using high pressure Sieverts' apparatus. A large enhancement in the CO2 adsorption capacity was achieved by decorating magnetite nanoparticles over the MWNT surface.

The growth of the passive film on iron in 0.05 M NaOH studied in situ by Raman micro‐spectroscopy and electrochemical polarisation. Part I: near‐resonance enhancement of the Raman spectra of iron oxide and oxyhydroxide compounds

Abstract: Raman spectroscopy, in principle, is an excellent technique for the study of molecular species developed on metal surfaces during electrochemical investigations. However, the use of the more common laser wavelengths such as the 514.5-nm line results in spectra of less than optimal intensity, particularly for iron oxide compounds. In the present work, near-resonance enhancement of the Raman spectra was investigated for the iron oxide and iron oxyhydroxide compounds previously reported to be present in the passive film on iron, using a tuneable dye laser producing excitation wavelengths between 560 and 637 nm. These compounds were hematite (α-Fe2O3), maghemite (γ-Fe2O3), magnetite (Fe3O4), goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH) and feroxyhyte (δ-FeOOH). Optimum enhancement, when compared to that with the 514.5-nm line, was obtained for all the iron oxide and oxyhydroxide standard samples in the low wavenumber region (<1000 cm−1) using an excitation wavelength of 636.4 nm. Particularly significant enhancement was obtained for lepidocrocite, hematite and goethite. Copyright © 2010 John Wiley & Sons, Ltd.

Iron carbide inclusions in lower-mantle diamond from juina, brazil

Abstract: Iron carbides in association with native iron, graphite, and magnetite were identified in a crystal of diamond from the Juina area, Brazil, that contains a series of other, deep-mantle mineral inclusions Among the iron carbides, Fe 3 C, Fe 2 C (“chalypite”), and Fe 23 C 6 (haxonite) are present; the two latter phases are identified in the terrestrial environment for the first time Some of the analyzed iron carbide grains contain 73–91 at% N and are, in fact, nitrocarbide We suggest, on the basis of the high-pressure mineral parageneses previously observed in the diamond and experimental data on the system Fe–C, that “chalypite” crystallized within a pressure interval of 50–130 GPa from an iron–carbon melt rich in nitrogen Following crystallization, iron carbides and native iron were partially oxidized to magnetite, and encapsulated in diamond along with other high-pressure minerals The finds of various iron carbides, some of which are rich in nitrogen, in lower-mantle diamond confirm a significant role of carbides and nitrogen in the Earth’s interior

Hamaker constants of iron oxide nanoparticles.

Abstract: The Hamaker constants for iron oxide nanoparticles in various media have been calculated using Lifshitz theory. Expressions for the dielectric responses of three iron oxide phases (magnetite, maghe...

Oxidation state and local structure of plutonium reacted with magnetite, mackinawite, and chukanovite.

Abstract: Due to their redox reactivity, surface sorption characteristics, and ubiquity as corrosion products or as minerals in natural sediments, iron(II)-bearing minerals control to a large extent the environmental fate of actinides. Pu-LIII-edge XANES and EXAFS spectra were used to investigate reaction products of aqueous 242Pu(III) and 242Pu(V) reacted with magnetite, mackinawite, and chukanovite under anoxic conditions. As Pu concentrations in the liquid phase were rapidly below detection limit, oxidation state and local structure of Pu were determined for Pu associated with the solid mineral phase. Pu(V) was reduced in the presence of all three minerals. A newly identified, highly specific Pu(III)-sorption complex formed with magnetite. Solid PuO2 phases formed in the presence of mackinawite and chukanovite; in the case of chukanovite, up to one-third of plutonium was also present as Pu(III). This highlights the necessity to consider, under reducing anoxic conditions, Pu(III) species in addition to tetravalen...

Study of iron oxide nanoparticles in soil for remediation of arsenic

Abstract: There is a growing interest in the use of nanoparticles for environmental applications due to their unique physical and chemical properties. One possible application is the removal of contaminants from water. In this study, the use of iron oxide nanoparticles (19.3 nm magnetite and 37.0 nm hematite) were examined to remove arsenate and arsenite through column studies. The columns contained 1.5 or 15 wt% iron oxide nanoparticles and soil. Arsenic experiments were conducted with 1.5 wt% iron oxides at 1.5 and 6 mL/h with initial arsenate and arsenite concentrations of 100 μg/L. Arsenic release occurred after 400 PV, and 100% release was reached. A long-term study was conducted with 15 wt% magnetite nanoparticles in soil at 0.3 mL/h with an initial arsenate concentration of 100 μg/L. A negligible arsenate concentration occurred for 3559.6 pore volumes (PVs) (132.1 d). Eventually, the arsenate concentration reached about 20% after 9884.1 PV (207.9 d). A retardation factor of about 6742 was calculated indicating strong adsorption of arsenic to the magnetite nanoparticles in the column. Also, increased adsorption was observed after flow interruption. Other experiments showed that arsenic and 12 other metals (V, Cr, Co, Mn, Se, Mo, Cd, Pb, Sb, Tl, Th, U) could be simultaneously removed by the iron oxide nanoparticles in soil. Effluent concentrations were less than 10% for six out of the 12 metals. Desorption experiment showed partial irreversible sorption of arsenic to the iron oxide nanoparticle surface. Strong adsorption, large retardation factor, and resistant desorption suggest that magnetite and hematite nanoparticles have the potential to be used to remove arsenic in sandy soil possibly through in situ techniques.