From iron(III) precursor to magnetite and vice versa

The syntheses of nanosize magnetite particles by wet-chemical oxidation of Fe²⁺ have been extensively investigated. In the present investigation the nanosize magnetite particles were synthesised without using the Fe(II) precursor. This was achieved by γ-irradiation of water-in-oil microemulsion containing only the Fe(III) precursor. The corresponding phase transformations were monitored. Microemulsions (pH  12.5) were γ-irradiated at a relatively high dose rate of 22 kGy/h. Upon 1 h of γ-irradiation the XRD pattern of the precipitate showed goethite and unidentified low-intensity peaks. Upon 6 h of γ-irradiation, reductive conditions were achieved and substoichiometric magnetite (Fe_2.71O₄) particles with insignificant amount of goethite particles found in the precipitate. Hydrated electrons , organic radicals and hydrogen gas as radiolytic products were responsible for the reductive dissolution of iron oxide in the microemulsion and the reduction Fe³⁺ → Fe²⁺. Upon 18 h of γ-irradiation the precipitate exhibited dual behaviour, it was a more oxidised product than the precipitate obtained after 6 h of γ-irradiation, but it contained magnetite particles in a more reduced form (Fe_2.93O₄). It was presumed that the reduction and oxidation processes existed as concurrent competitive processes in the microemulsion. After 18 h of γ-irradiation the pH of the medium shifted from the alkaline to the acidic range. The high dose rate of 22 kGy/h was directly responsible for this shift to the acidic range. At a slightly acidic pH a further reduction of Fe³⁺ → Fe²⁺ resulted in the formation of more stoichiometric magnetite particles, whereas the oxidation conditions in the acidic medium permitted the oxidation Fe²⁺ → Fe³⁺. The Fe³⁺ was much less soluble in the acidic medium and it hydrolysed and recrystallised as goethite. The γ-irradiation of the microemulsion for 25 h at a lower dose rate of 16 kGy/h produced pure substoichiometric nanosize magnetite particles of about 25 nm in size and with the stoichiometry of Fe_2.83O₄.     

Bulk and surface structures of iron doped zirconium oxide systems: Influence of preparation method

Three different Fe-Zr oxide systems were prepared using firstly classical impregnation of iron nitrates on calcined ZrO₂ (Fe_x/ZrO₂, x represents Fe/Zr ratio = 0.01 and 0.11), secondly impregnation of iron nitrates on dried zirconium hydroxide ZrO(OH)₂ (Fe_x/ZrO(OH)₂) and finally hydrolysis of aqueous suspension of iron and zirconium salts to coprecipitate iron and zirconium hydroxides (Fe_x-Zr). Thermal decomposition study of dried samples evidenced a delay in the temperature crystallization of zirconia for Fe_x-Zr and Fe_x/ZrO(OH)₂, the more the iron content in the sample, the more important the delay. For these samples, the formation and the stabilization of different phases were evidenced by several characterization techniques : X-Ray Diffraction (XRD), Raman spectroscopy and Electron Paramagnetic Resonance (EPR).The interaction of iron species with zirconia was different in accordance with different preparations. A bulk dispersion of the coprecipitated sample was observed and as a consequence Zr^{3 +} defects in the solid were not produced. In the case of Fe_x/ZrO₂ sample, production of surface Zr^{3 +} ions was established at low temperature of calcination (up to 600^∘C) and explained by the reaction of NO₃⁻ with Zr^{4 +} on the zirconia surface. However such interaction did not occur for Fe_x/ZrO(OH)₂ since a low dispersion of iron species was observed by X-ray Photoelectron Spectroscopy (XPS), deposited phase (Fe₂O₃) forming preferentially blocks. Temperature Programmed Reduction (TPR) showed that the reduction of small particles of Fe₂O₃ and bulk Fe₂O₃ present in the impregnated samples was easier than that of iron species well dispersed in the bulk of the coprecipitated solid.     

Micro-goethite in percolated water from Fushui Reservoir in Hubei Province,China

The sediments in the percolated water from Fushui Reservoir have been studied. The cause for formation of a special-shaped micro-goethite in the modern depositional environment (reservoir) as well as the action and the significance of microorganism in the biomineralization of iron are discussed in this paper. Tests show that the main cations in the percolated water include Ca²⁺, Mg²⁺, K⁺ and Na⁺, with minor Fe²⁺ and Fe³⁺, whereas the main anion is HCO₃⁻. The sediments from the percolated water are mainly oxidized products of iron. The mineral phase and the form of the particles from percolated water in Fushui Reservoir are studied by such means as powder X-ray diffraction (XRD), differential thermal analysis (DTA), infrared spectroscopic analysis (IR), Mössbauer spectrum, transmission electron microscope (TEM) and scanning electron microscope (SEM). The main mineral phases include goethite, quartz, illite, montmorillonite and small amounts of calcite, only slightly crystallized. The Mössbauer spectral characteristics and the special form of goethite imply that goethite originated from ferric bacteria. The following results can be reached: the sediments in Fushui Reservoir are mainly composed of amorphous ferric hydroxide colloid and weakly crystalline goethite; the genesis of goethite is related with ferric bacteria.     

Gum kondagogu modified magnetic nano-adsorbent: An efficient protocol for removal of various toxic metal ions

Gum kondagogu (GK) modified magnetic iron oxide nanoparticles (MNP) have been prepared by co-precipitating Fe^2 + and Fe^3 + ions using ammonia solution in presence of GK biomacromolecules. The TEM analysis revealed the presence of nearly spherical size iron oxide particles with diameters in the range of 8−15 nm; while the XRD results confirmed the crystallinity of iron oxide nanoparticles. The magnetic measurements demonstrated the ferromagnetic behavior of GK − MNP with a magnetic saturation value of ~ 60 emu/g. The removal efficiencies for a variety of metal cations by the GK − MNP were determined quantitatively in the order: Cd^2 + > Cu^2 + > Pb^2 + > Ni^2 + > Zn^2 + > Hg^2 + at a pH of 5.0 ± 0.1 and at a temperature of 30.0 ± 1.0 °C. A maximum of 106.8 mg/g and a minimum of 35.07 mg/g adsorption capacities were observed for the Cd^2 + and Hg^2 + ions, respectively using the Langmuir isotherm model.     

Immobilization of Acidithiobacillus ferrooxidans on sulfonated microporous poly(styrene–divinylbenzene) copolymer with granulated activated carbon and its use in bio-oxidation of ferrous iron

The immobilization efficiencies of Acidithiobacillus ferrooxidans cells on different immobilization matrices were investigated for biooxidation of ferrous iron (Fe^2 +) to ferric iron (Fe^3 +). Six different matrices were used such as the polyurethane foam (PUF), granular activated carbon (GAC), raw poly(styrene–divinylbenzene) copolymer (rawSDVB), raw poly(styrene–divinylbenzene) copolymer with granular activated carbon (rawSDVB-GAC), sulfonated poly(styrene–divinylbenzene) copolymer (sulfSDVB) and sulfonated poly(styrene–divinylbenzene) copolymer with granular activated carbon (sulfSDVB-GAC). The sulfSDVB-GAC polymer showed the best performance for Fe^2 + biooxidation. It was used at packed-bed bioreactor and the kinetic parameters were obtained. The highest Fe^2 + biooxidation rate (R) was found to be 4.02 g/L h at the true dilution rate (D_t) of 2.47 1/h and hydraulic retention time (τ) of 0.4 h. The sulfSDVB-GAC polymer was used for the first time as immobilization material for A. ferrooxidans for Fe^2 + biooxidation.     

Preparation of high tap-density LiFePO4/C composite cathode materials by carbothermal reduction method using two kinds of Fe precursors

LiFePO₄ belongs to a new generation cathode material for lithium ion batteries. The improvement of the material's tap density is considered as an important research direction. LiFePO₄/C composite was synthesized by a solid-state carbothermal reduction (CTR) method. The iron resource was obtained by the addition of (i) Fe₂O₃ and citrate ferric or (ii) single Fe₂O₃ as the Fe³⁺ precursors during synthesis. The LiFePO₄/C composite synthesized with two kinds of Fe³⁺ precursors exhibited trimodal distribution and consisted of nanometer-sized and micrometer-sized particles, whereas the LiFePO₄/C composite prepared with single Fe³⁺ precursor demonstrated unimodal distribution and was composed mainly of micrometer-sized particles. Because of the nanometer-sized particles filling in the space between the micrometer-sized particles, the composite synthesized with two kinds of Fe³⁺ precursors exhibited less vacancy than that prepared with single Fe³⁺ precursor and led to high tap density. The composite synthesized with two kinds of Fe³⁺ precursors had smaller grain size and resulted in superior discharge capacities at the rates of 0.1–1.0 C to that prepared with single Fe³⁺ precursor. The two kinds Fe³⁺ precursors method provides a simple and effective route to rapidly prepare high tap-density LiFePO₄ product with excellent electrochemical performance, so it will achieve a wide-range of applications to the production of LiFePO₄.     

Röntgenographische und mössbauer-spektroskopische untersuchungen am system Fe1+xYb2−xS4

Polycristalline samples of the system Fe_1+xYb_2?xS₄ have been investigated in the range 0,0 ≤ x ≤ 0,4 in both the low temperature structure and the spinel-type high temperature structure. The lattice constants of the spinels decrease linearly with increasing x; the tetrahedral sites are occupied by iron only. The valence distribution Fe⁺² Fe⁺³_xYb⁺³_2?x S^?2₄ and a slight distortion of the spinel lattice are concluded from the Mößbauer parameters at room temperature.     

Spectroscopic investigation of iron ions in a novel ferrisilicate pentasil zeolite

Synthetic H-ferrisilicate of the pentasil family was studied by means of diffuse reflectance i.r., e.s.r. and luminescence spectroscopies. In this paper it is shown that only a part of the Fe³⁺ ions (< 30%) enter the lattice isomorphically replacing silicon ions. The rest of the iron ions are in an extralattice state, perhaps in the form of a Fe₂O₃ microphase in zeolite pores. Extralattice iron ions can be easily reduced to Fe²⁺ species. Structural hydroxyl groups connected with Fe³⁺ ions in the framework are shown to have bridging structure and to possess strong acidic properties.     

Study of iron-ion implantation in rutile single crystals

TiO₂ crystals implanted with 100 keV ⁵⁷Fe⁺ ions at doses ranging from 10¹⁶ to 10¹⁷ ions.cm^?2 have been investigated with the conversion electron Mössbauer spectroscopy (CEMS), Rutherford backscattering (RBS) and transmission electron microscopy (TEM). Implanted samples of iron ions are mostly in a Fe²⁺ state and small precipitates of FeTi₂O₅ are observed using TEM. The migration of iron ions in a Fe³⁺ state occurs at about 600°C. Such a low temperature diffusion is thought to go along extended defects.     

Desorption of 90Sr and 137Cs from Flood Plain Deposits of the Sozh River and Rocks of the Adjacent Catchment Areas

Desorption of ⁹⁰Sr and ¹³⁷Cs from flood plain warps, meadow sod, humus-containing sandy loam, peat, clays, limonite, meadow marl, and friable rocks of the adjacent catchment areas (moraine clay, loam, sandy loam) was studied. ¹³⁷Cs is sorbed the most strongly on clays by the mechanism of isomorphic ion-exchange incorporation into the crystal lattice of montmorillonite-type minerals. ¹³⁷Cs is also tightly fixed on buried and peaty soils due to association with the poorly mobile species of humic acids and humin. The strong fixation of ⁹⁰Sr on amorphous iron hydroxides is caused by its association with poorly soluble ferrite-type minerals. Sorption of ⁹⁰Sr on peaty soils can be attributed to their association with aluminum and iron-containing organomineral complexes. ¹³⁷Cs sorbed on flood plain warps, sandy loams, and loams exhibits increased mobility and is leached with all the tested desorbing solutions. These deposits apparently contribute maximally to the redistribution of radiocesium over flood plain and the adjacent catchment areas. The desorption efficiency of cations of the desorbing solutions decreases in the order Cs⁺ > K⁺ > Fe^{3 +} > NH₄ ⁺ > Ca^{2 +} > H⁺ for radiocesium and Fe^{3 +} > Sr^{2 +} > K⁺ > H⁺ > Ca^{2 +} > NH₄ ⁺ for radiostrontium.     

Synthesis of cubic type hollow silica particles

Cubic-type hollow silica particles were prepared from Fe₂O₃-SiO₂ core-shell composite particles by selectively leaching the iron oxide core materials using acidic solution. The cubic Fe₂O₃ core particles were obtained by the hydrolysis reaction of iron salts. The Fe₂O₃-SiO₂ core-shell type particles were prepared by the deposition of a SiO₂ layer onto the surface of Fe₂O₃ particles using a two-step coating process. The first step involved primary coating with sodium silicate solution followed by subsequent coating by controlled hydrolysis of tetraethoxysilicate (TEOS). The core Fe₂O₃ was removed by dissolution in an acidic solution which gave rise to the hollow type silica particles. Scanning electron microscopic observation clearly revealed that the morphology is closely related to those of core the Fe₂O₃ particles. The cross sectional view determined by transmission electron microscopy revealed a silica shell with a thickness of about 50 nm. The porous texture of the hollow type silica particles is further characterized by nitrogen adsorption-desorption isotherm measurements.     

Influence of catalyst particles on multi-walled carbon nanotubes morphology and structure

Multi-walled carbon nanotubes (MWCNTs) have been successfully grown by Chemical Vapor Deposition (CVD) method. Elucidating the key characteristics of catalyst sources that affect carbon nanotubes growth is of great importance for improving and control MWCNTs morphology and structure. In this work we present a systematically study of CVD parameters, such as catalyst source, substrate morphology and temperature and how it affects carbon nanotubes synthesis. The novelty of this work lies on the catalyst composition. Two specific catalyst sources were analyzed: (i) Fe₂Co and (ii) Fe₂Co with ferrocene. Cyclic Voltammetry results confirmed the presence of Fe²⁺ in the Fe₂Co with ferrocene solution. X-Ray Diffraction analysis confirmed the presence of iron particles on the substrate surface after its submission to growth conditions. Raman results suggested an improvement in carbon nanotubes crystalline quality catalyzed by Fe₂Co with ferrocene. For tridimensional substrates such as fibers, the Fe₂Co with ferrocene provided aligned CNTs with lower defects density noticed in Raman spectra and SEM micrographs. Finally, we corroborated the Fe²⁺ encapsulation relation with the growth mechanism and MWCNTs formation.     

Kinetics of neptunium(V) reduction with iron(II) sulfamate in nitric acid solutions

The kinetics of chemical reduction of Np(V) with iron(II) sulfamate in HNO₃ solutions was studied by spectrophotometry. The reduction process can be described by the equation NpO ₂ ⁺ + Fe²⁺ + 4H⁺ ? Np⁴⁺ + Fe³⁺ + 2H₂O and follows the first- and zero-order rate law with respect to the Np(V) concentration. The reaction rate constants were determined in relation to the HNO₃ concentration (1–3 M), iron(II) sulfamate concentration [(0.59–2.94) × 10^?3 M], and temperature (298.2–319.2 K). The activation energy (E _a) and the thermodynamic functions of formation of the activated complex (activation free energy ΔG ^≠, enthalpy ΔH ^≠, entropy ΔS ^≠) were calculated.     

Boronic acid functionalized superparamagnetic iron oxide nanoparticle as a novel tool for adsorption of sugar

Synthesis of boronic acid functionalized superparamagnetic iron oxide nanoparticles has been reported. Magnetite nanoparticles were prepared by simple co-precipitation from Fe²⁺ and Fe³⁺ solution. m-Aminophenyl boronic acid was attached to iron oxide particles through 3,4-dihydroxy benzaldehyde through CN bond. X-ray diffraction and selected area electron diffraction have shown the formation of inverse spinel phase magnetite of both as prepared and functionalized magnetite particles. FTIR shows attachment of boronic acid-imine onto iron oxide surface through enediol group. Transmission electron microscopy shows well dispersion of boronic acid functionalized particles of size 8 ± 2 nm. Vibration sample magnetometry shows both the particles are superparamagnetic at room temperature having saturation magnetization (Ms) 52 emu/g. In this work the affinity of these boronic acid functionalized particles towards sugar binding was studied taking dextrose sugar as a model. The influence of pH and sugar concentration has been extensively investigated. The results show that such boronic acid modified superparamagnetic particles are efficient support for sugar separation having maximum sugar loading capacity (60 µg/50 µl) at pH 8.     

Characterizing the discoloration of methylene blue in Fe/H2O systems

Methylene blue (MB) was used as a model molecule to characterize the aqueous reactivity of metallic iron in Fe⁰/H₂O systems. Likely discoloration mechanisms under used experimental conditions are: (i) adsorption onto Fe⁰ and Fe⁰ corrosion products (CP), (ii) co-precipitation with in situ generated iron CP, (iii) reduction to colorless leukomethylene blue (LMB). MB mineralization (oxidation to CO₂) is not expected. The kinetics of MB discoloration by Fe⁰, Fe₂O₃, Fe₃O₄, MnO₂, and granular activated carbon were investigated in assay tubes under mechanically non-disturbed conditions. The evolution of MB discoloration was monitored spectrophotometrically. The effect of availability of CP, Fe⁰ source, shaking rate, initial pH value, and chemical properties of the solution were studied. The results present evidence supporting co-precipitation of MB with in situ generated iron CP as main discoloration mechanism. Under high shaking intensities (>150 min⁻¹), increased CP generation yields a brownish solution which disturbed MB determination, showing that a too high shear stress induced the suspension of in situ generated corrosion products. The present study clearly demonstrates that comparing results from various sources is difficult even when the results are achieved under seemingly similar conditions. The appeal for an unified experimental procedure for the investigation of processes in Fe⁰/H₂O systems is reiterated.     

Iron species in fusion-cast,glassy-phase-containing corundum materials; EPR and susceptibility analyses

By means of EPR, susceptibility, EMP, light-microscopic, thermal and chemical methods the influence of production conditions and subsequent treatments on glassy-phase-containing corundum materials were studied. Melting of the system (Al₂O₃, SiO₂, Na₂O, Fe₃O₄) under reductive conditions leads to a reduction of Fe³⁺ species contained to Fe²⁺ and even to Fe⁰ clusters with ferromagnetic behaviour. Both species markedly influence the mechanical properties of the material by increase of their volumes in consequence of oxidation in subsequent thermal processes. The following model with regard to the localization of the iron species in the system ensues: Fe(III) in corundum, Fe₂O₃, Fe₃O₄ and (scarcely) in the glassy phase; Fe(II) in the glassy phase, FeAl₂O₄ (hercynite) as a solid solution in corundum, and Fe₃O₄; (Fe⁰) clusters in corundum. It is therefore not surprising that grinding of the compact material considerably alters the magnetic properties of the samples.     

Characterizing the effects of shaking intensity on the kinetics of metallic iron dissolution in EDTA

Despite two decades of intensive laboratory investigations, several aspects of contaminant removal from aqueous solutions by elemental iron materials (e.g., in Fe⁰/H₂O systems) are not really understood. One of the main reasons for this is the lack of a unified procedure for conducting batch removal experiments. This study gives a qualitative and semi-quantitative characterization of the effect of the mixing intensity on the oxidative dissolution of iron from two Fe⁰-materials (materials A and B) in a diluted aqueous ethylenediaminetetraacetic solution (2 mM EDTA). Material A (fillings) was a scrap iron and material B (spherical) a commercial material. The Fe⁰/H₂O/EDTA systems were shaken on a rotational shaker at shaking intensities between 0 and 250 min⁻¹ and the time dependence evolution of the iron concentration was recorded. The systems were characterized by the initial iron dissolution rate (k_EDTA). The results showed an increased rate of iron dissolution with increasing shaking intensity for both materials. The increased corrosion through shaking was also evidenced through the characterization of the effects of pre-shaking time on k_EDTA from material A. Altogether, the results disprove the popular assumption that mixing batch experiments is a tool to limit or eliminate diffusion as dominant transport process of contaminant to the Fe⁰ surface.     

Chemical synthesis of α-iron in aqueous FeCl3

Iron-aluminium composite and α-iron powder have been prepared by chemical reduction of aqueous FeCl₃ with aluminium at different conditions. Experiments showed that the concentration of FeCl₃ and aluminium particle size are the main factors to influence the reaction. XRD, SEM and potentiometric titration were employed to characterize the products. SEM showed that as iron particles grow they tend to form spherical seed on the surface of aluminium. XRD revealed that the α-iron was single phase after deposit treatment by NaOH solution. The purity of as-prepared α-iron was 99.5%, as determined from the X-ray fluorescence spectroscopy. The possible formation mechanism is a two-stage red-ox-process: Fe³⁺→Fe²⁺→α-Fe.     

Preparation of mullite-based iron magnetic nanocomposite powders by reduction of solid solution

In this article, the preparation of mullite-based iron magnetic nanocomposite powders by hydrogen reduction of Fe-doped mullite solid solution with a nominal composition of Al_5.4Fe_0.6Si₂O₁₃ is reported. The formation process of Al_5.4Fe_0.6Si₂O₁₃ solid solution was analyzed using X-ray diffraction analysis (XRD), Fourier Transform Infrared Spectrum (FT-IR), thermogravimetric, and differential thermal analysis (TG-DTA). It is found that doping with Fe³⁺ cation affects the crystallization temperature of mullite. During the hydrogen reduction process, more than 89% Fe³⁺ cation in solid solution were transformed into α-Fe phase when reduction temperature reached 1200 °C. Microstructure characterization of nanocomposite powders reduced at 1300 °C reveals that there are two types of α-Fe particles in mullite matrix. Fe nanoparticles with a size of approximately 10 nm were precipitated within the mullite grains, while Fe particles larger than hundreds of nanometers were located at the surfaces of the mullite grains. The measurement of the magnetic properties of nanocomposite powders indicates that large particles and nanoparticles of α-iron have the ferromagnetic and superparamagnetic behavior at room temperature, respectively.     

Synthesis of barium hexaferrite by the co-precipitation method using acetate precursor

Fine particles of barium hexaferrite were synthesised by a chemical co-precipitation method using acetate-nitrate (barium acetate + iron nitrate) precursors. The thermal properties, phase composition and morphology of hexaferrite powders were studied. Simultaneous DTA/TG results confirmed by those obtained from XRD and VSM, indicated that the formation of barium hexaferrite occurs at a relatively low temperature of 710°C. This temperature is affected by the Fe³⁺/Ba²⁺ molar ratio. The SEM investigations revealed that the mean particle size of barium hexaferrite increases with increasing calcination temperature. In this system the Fe³⁺/Ba²⁺ molar ratio of 12 (stoichiometric ratio) is favourable.