Magnetic and EPR Studies of α-, β-, and γ-Fe2WO6 Phases at Low Temperatures

The polymorphic modifications α-, β-, and γ-Fe₂WO₆ of the iron tungstate system were studied by means of magnetic susceptibility and EPR measurements at low temperatures. Both methods revealed a significant paramagnetic contribution, probably resulting from local distortions of the antiferromagnetic bulk structure induced by a disturbed cation ordering or the presence of Fe²⁺ ions. The magnetic susceptibility revealed a peak at 260 K for all samples which can be related with an AF phase transition. The EPR spectra comprised the contribution of various isolated paramagnetic iron centers, one arising from high-spin Fe³⁺ ions in rhombic crystal field symmetry with E/D ≈ 1/3 and D ≈ 0.22 cm^-1, an anisotropic EPR signal consistent with an S= 3/2 ground state with large zero-field splitting, and a dominant component in the g ≈ 2 region presumably arising from an S = 1/2; spin state. The latter spectra were tentatively attributed to the formation of multi-iron clusters, one of them invoking the presence of Fe²⁺ ions as well. For the βFe₂WO₆ phase an additional EPR spectrum was observed, which probably results from high-spin Fe³⁺ ions in a weak crystal field.     

Mössbauer Study of the Structure of Fe - Zircon System

Iron-doped silicate (zircon), prepared by a ceramic method with the addition of LiF as mineralizer, was analyzed by X-ray powder diffraction (XRD) and ⁵⁷Fe Mössbauer spectroscopy to obtain information on the solid solution formation. The results of X-ray diffraction and Mössbauer spectroscopy have shown that only a small fraction of iron, about 1.5 mol%, is incorporated in the zircon structure as paramagnetic Fe³⁺ species while the remaining Fe³⁺ cations form magnetic -Fe₂O₃ particles which are trapped within the zircon matrix.     

A study on the reduction behavior of silica supported iron and platinum-iron catalysts

The reduction behavior of silica supported iron and platinum-iron catalysts were studied by combinedin situ temperature programmed reduction (TPR)-M?ssbauer Spectroscopy (MBS). The results indicated that the TPR profiles of the supported Fe catalysts were different from that of bulk α-Fe₂O₃. There existed an interaction between the Pt and Fe metals and the SiO₂ support for the Pt−Fe/SiO₂ catalyst. On the supported iron-containing catalysts, the Fe³⁺ species were highly dispersed on the SiO₂ supported before reduction. No Fe⁰ and Fe²⁺ in octahedral vacancy were found in the reduction of SiO₂ supported iron-containing catalysts. Addition of Pt to the Fe/SiO₂ catalyst could promote the reduction of the iron species.     

Influence of Sn and Sn/Mg doping on structural features and visible absorption properties of α-Fe2O3 hematite

Pure, Sn-doped and Mg/Sn co-doped α-Fe₂O₃ hematite samples were synthesized by precipitation process. Fe₂O₃ is the most popular red mineral pigment which is used largely in traditional ceramics, tar and concrete. The compounds were characterized by powder X-ray diffraction (XRD), scanning transmission electronic microscopy (energy dispersive X-ray cartography), Mössbauer spectroscopy, magnetic investigations versus temperature and visible-NIR spectroscopy. Both ⁵⁷Fe and ¹¹⁹Sn Mössbauer analyses combined with rietveld XRD refinements are the ideal techniques to characterize tin-iron oxides. Hence, thanks to these techniques it was shown how the synthesis temperature influences directly the grain size and the dopants concentration limit which can be incorporated into the host hematite matrix. The stabilization of these tetravalent and divalent dopants into the hematite framework leads to reduce the crystal growth and to limit the (AF) ordering due to the formation of cationic vacancies. The study of the Morin magnetic transition emphasizes this demonstration. In a second part, the influence of the dopants incorporation on the material color was investigated in order to show which key parameters allow improving the red color saturation of iron oxides. In order to improve the red color of the hematites, it was shown that the introduction of cationic vacancies—limiting the octahedral distortion thanks to the interruption of the dissymmetric metal-metal orbital coupling—is the key point. Vacancies are created by Sn⁴⁺, doping for an increase of the introduced Sn⁴⁺ concentration; it acts to the detriment of the color saturation.     

Investigation of multiplet splitting of Fe 2p XPS spectra and bonding in iron compounds

Ferrous (Fe²⁺) and ferric (Fe³⁺) compounds were investigated by XPS to determine the usefulness of calculated multiplet peaks to fit high‐resolution iron 2p_3/2 spectra from high‐spin compounds. The multiplets were found to fit most spectra well, particularly when contributions attributed to surface peaks and shake‐up satellites were included. This information was useful for fitting of the complex Fe 2p_3/2 spectra for Fe₃O₄ where both Fe²⁺ and Fe³⁺ species are present. It was found that as the ionic bond character of the iron —ligand bond increased, the binding energy associated with either the ferrous or ferric 2p_3/2 photoelectron peak also increased. This was determined to be due to the decrease in shielding of the iron cation by the more increasingly electronegative ligands. It was also observed that the difference in energy between a high‐spin iron 2p_3/2 peak and its corresponding shake‐up satellite peak increased as the electronegativity of the ligand increased. The extrinsic loss spectra for ion oxides are also reported; these are as characteristic of each species as are the photoelectron peaks. Copyright © 2004 John Wiley & Sons, Ltd.     

A new analytical method for 32P: Liquid scintillation counting with solvent extraction

⁵⁷Fe Mössbauer spectroscopy has been applied to the ultramafic rocks collected from the Jinchuan nickel deposit in China to elucidate their mineralization process. Their Mössbauer spectra consisted of two sextets ascribable to magnetite, two doublets ascribable to Fe²⁺ and Fe³⁺ in chromite, and one doublet ascribable to olivine. The closest sample to the ore body did not contain chromite and contained a doublet ascribable to pyrite and a sextet ascribable to pyrrhotite. The valence and site distribution of iron species suggested low oxygen fugacity for the formation of the Jinchuan nickel deposit.     

UVA-Potentiated Damage to Calf Thymus DNA by Fenton Reaction System and Protection by para-Aminobenzoic Acid

Abstract— Calf thymus DNA was irradiated with low-intensity UVA (main output at 365 nm, 2 mW cm^?2 or 36 kj m ² for 30 min), and the role of metal ions, hydrogen peroxide and reactive oxygen species (ROS) was examined. DNA damage was measured as thiobarbituric acid-reactive substances (possibly from degradation of deoxyribose) and as changes in ethidium bromide-DNA fluorescence due to unwinding from strand breaks. Under the present experimental conditions, UVA alone or in the presence of H₂0₂ had no effect on DNA but slightly enhanced the damage by iron/EDTA. Ultraviolet A strongly enhanced DNA damage (ca four- to five-fold) by the Fenton reaction system (50 μM Fe²⁺/100 μM EDTA + 0.5 mM H₂0₂). The results suggest that the Fenton reaction system was “photosensitized” to damage DNA by low-intensity UVA radiation. The enhanced damage by UVA was attributed in part to the reduction of Fe³⁺ to Fe²⁺. Ultraviolet A had no effect when iron (ferric or ferrous) ions were replaced by Cu²⁺, Zn²⁺, Mn²⁺ or Cd²⁺. The ROS involved in the UVA-enhanced damage to DNA by the Fenton reagents were OH and, to a lesser extent, superoxide anions. The UVA-potentiated DNA damage by the Fenton reaction system was then used to examine the protective effect of para-aminobenzoate (PABA), a UVB-absorbing sunscreen that protects against photocarcinogenesis in hairless mice. The results show that PABA and mannitol dose-dependently inhibited the damage with concentrations required for 50% inhibition at 0.1 mM and 3 mM, respectively. The protection by PABA was attributed to its radical-scavenging ability because PABA does not absorb light in the UVA region. These findings may be relevant to the biological damage by UVA and suggest that PABA is useful in protection against photocarcinogenesis by wide-range UV radiation.     

三维介孔氨基三亚甲基膦酸锆的合成及其担载铁催化剂的甲醛催化氧化活性

以氧氯化锆和氨基三亚甲基膦酸(ATMP)为原料合成了一种新型介孔材料氨基三亚甲基膦酸锆(NTAZP)。使用XRD、FTIR、TG-DTA和SEM等手段对所合成的介孔材料进行了结构表征和形貌分析。然后以NTAZP为载体,用Fe(NO3)3水溶液处理,得到担载Fe3+的氨基三亚甲基膦酸锆。研究结果表明,Fe3+被吸附到载体孔道中后,NTAZP结构未被破坏,Fe3+离子与NTAZP孔壁骨架上的N发生了配位作用。铁担载NTAZP(NTAZP-Fe3+)对甲醛氧化具有良好的催化活性,催化反应条件温和,催化剂稳定性良好。以载体NTAZP担载铁还避免了Fe3+进入水体,催化剂得以回收利用,避免造成二次污染。NTAZP-Fe3+是一种高效绿色的新型小分子醛类化合物氧化催化剂。     

Fe-assisted formation of α-Al2O3, starting from sol-gel precursors

The role of Fe³⁺ ions in the transformations from boehmites and pseudoboehmite xerogels via transition aluminas to corundum was studied here. Especially, the active iron species responsible for the decrease of the temperature of transformation to corundum were looked for. To enable the formation of various Fe³⁺ and Fe²⁺ species, samples were subjected to thermal treatments in different atmospheres as well as mechanically activated. Thermal analysis and ESR spectroscopy served to follow the processes and to characterise the resulting products. It was found that (i) isolated Fe³⁺ ions can indicate local structural changes but have (almost) no influence on the temperature of corundum formation, (ii) the temperature of corundum formation decreases in the result of action of small α-Fe₂O₃ particles and (iii) during thermal treatments Fe³⁺ ions are distributed between different phases or precursors thereof: transition aluminas, corundum, Fe₂O₃, and a Fe³⁺ pool.     

Nano particles of iron oxides in SiO<Subscript>2</Subscript> glass prepared by ion implantation

Quartz (SiO₂) glass was implanted with 5 × 10^{16 57}Fe ions/cm² at a substrate temperature of 500 °C, and annealed at temperatures between 700 and 950 °C. The implanted and annealed plates were characterized by conversion electron Mössbauer spectroscopy (CEMS), and measured by a Kerr effect magnetometer or a vibration sample magnetometer. Kerr effect measurement of as-implanted SiO₂ glass showed ferromagnetism at room temperature. CEM spectrum of the as-implanted glass consisted of magnetic relaxation peaks of finely dispersed metallic Fe species, and paramagnetic doublets of Fe³⁺ and Fe²⁺ species. The sample heated at 700 °C contained large grains of metallic Fe and a lot of oxidation products of Fe²⁺ species. After oxidation at temperatures higher than 800 °C, the samples showed also ferromagnetism, which was attributed mainly to ferromagnetic ε-Fe₂O₃ precipitated in SiO₂ matrix. Small amounts of α-Fe₂O₃ were produced at 950 °C. The results suggest that ion implantation and oxidation make a transparent ferromagnetic glass possible.     

Investigating the oxidation state of Fe from LiFePO4-based lithium ion battery cathodes via capillary electrophoresis

A capillary electrophoresis (CE) method with ultraviolet/visible (UV–Vis) spectroscopy for iron speciation in lithium ion battery (LIB) electrolytes was developed. The complexation of Fe²⁺ with 1,10-phenantroline (o-phen) and of Fe³⁺ with ethylenediamine tetraacetic acid (EDTA) revealed effective stabilization of both iron species during sample preparation and CE measurements. For the investigation of small electrolyte volumes from LIB cells, a sample buffer with optimal sample pH was developed to inhibit precipitation of Fe³⁺ during complexation of Fe²⁺ with o-phen. However, the presence of the conducting salt lithium hexafluorophosphate (LiPF₆) in the electrolyte led to the precipitation of the complex [Fe(o-phen)₃](PF₆)₂. Addition of acetonitrile (ACN) to the sample successfully re-dissolved this Fe²⁺-complex to retain the quantification of both species. Further optimization of the method successfully prevented the oxidation of dissolved Fe²⁺ with ambient oxygen during sample preparation, by previously stabilizing the sample with HCl or by working under counterflow of argon. Following dissolution experiments with the positive electrode material LiFePO₄ (LFP) in LIB electrolytes under dry room conditions at 20°C and 60°C mainly revealed iron dissolution at elevated temperatures due to the formation of acidic electrolyte decomposition products. Despite the primary oxidation state of iron in LFP of +2, both iron species were detected in the electrolytes that derive from oxidation of dissolved Fe²⁺ by remaining molecular oxygen in the sample vials during the dissolution experiments.     

Oxide Transformation During Preparation of Black Pottery in Hungary

Traditional black pottery produced in Nádudvar, E-Hungary, was studied by ⁵⁷Fe Mössbauer spectroscopy, X-ray diffractometry and microscopy. Quartz, feldspar, clay minerals (kaolinite, smeetite, illite) and calcite were identified in the basic clay material by X-ray diffractometry (XRD). Mössbauer spectroscopy (MS) of the original clay revealed that about 35% of iron compounds were present in goethite while the rest in clay minerals (illite and smectite). After firing the clay in air using an electric furnace (red pottery is prepared in the same way), the Mössbauer spectra showed hematite as the only iron oxide or hydroxide phase, being in good agreement with X-ray diffractometry. In the black product itself, fired in the traditional open-flame furnace, the Mössbauer spectra reflected the presence of iron in magnetite and in sheet silicates with approximately the same relative ratio of oxides and silicates as in the starting material. This can be interpreted as a result of the transformation of goethite to hematite in the first step of firing (in air), and as a reduction of hematite to magnetite in the second step of firing (closed from air). A significant difference was found in the distribution of iron at the Fe²⁺ and Fe³⁺ cation sites in the black surface (more Fe²⁺) and at the dark gray bulk of the fired pottery (less Fe²⁺), showing that the reduction of Fe³⁺ occurs in the silicates instead of further reduction of the magnetite (e.g., to wüstite).     

Structural and Electrical Properties of Iron-Containing Aluminosilicate Gel-Derived Pellets

Aluminosilicate pellets containing 10 mol% of Fe₂O₃, prepared by the sol-gel method, have been investigated. Electrical conductivity, dielectric constant, X-ray diffraction, scanning electron microscopy and electron paramagnetic resonance have been used to characterize the evolution of the samples with the heat-treatment temperature and atmospheric conditions. Results show that iron is present in the air heat-treated samples as Fe³⁺, goethite and hematite particles. Metallic iron and magnetite were identified in the samples heat-treated under reducing conditions. The d.c. conductivity decreases with increasing heat-treatment temperature of the samples indicating a variation, with the temperature, of the electrical free charges. However, in the case of the dielectric constant the samples heat-treated in air and under reducing conditions do not present the same behaviour. This variation was related with the microstructural evolution of the samples.     

In Situ Identification of Carbonate-Containing Green Rust on Iron Electrodes in Solutions Simulating Groundwater

Open-circuit potential-time and spectral measurements were performed on ironelectrodes in aqueous solutions containing calcium carbonate to simulateground-water, to which an amount of carbon tetrachloride was added. In the case of apreoxidized iron electrode, the injection of the chlorinated aliphatic hydrocarbonresulted in the formation of carbonate-containing green rust. In situ identification,performed by Raman spectroscopy, was based on bands at ca. 433, 509, and1053 cm^–1, which were assigned, respectively, to the Fe²⁺—OH stretching modeof green rust, the Fe³⁺—OH stretching mode of green rust, and the stretchingvibrations of carbonate ions in the interlayer regions of the green rust. Theassignment of the Fe²⁺—OH and Fe³⁺–OH stretching mode bands was confirmedby parallel experiments using D₂O solution. The results of the open-circuitpotential-time experiments are in good agreement with literature thermodynamic datafor iron in carbonate-containing aqueous solutions.     

Aggregation process of fine hematite particles suspension using xanthan gum in the presence of Fe(III)

Aggregation is an economical and widely existing method to in hematite mineral processing. In order to achieve the aggregation of hematite particles, high-efficiency agents are required. In this work, the xanthan gum (XG) and Fe³⁺ were used to explore its aggregation effect on the fine hematite particles. The settling and adsorption experiments were conducted on hematite with XG in the absence and presence of Fe³⁺. The results show that it is difficult to settle hematite with XG alone, and XG exhibits excellent performance with the mass ratio of 2/1 (XG/ FeCl₃) at pH 2–10 in the presence of Fe³⁺. Zeta potential measurements, Fourier transform infrared (FTIR), Microscope and X-ray photoelectron spectroscopy (XPS) analyses were performed to detect the underlying mechanism. The zeta potential, solution chemistry and FTIR analyses results show that the co-adsorption of XG, Fe(OH)₂⁺, Fe(OH)²⁺ and Fe³⁺ is found on hematite surface through specific and electrostatic adsorption, respectively, and the hematite surface is also covered by Fe(OH)_3(s) precipitation turned by Fe³⁺. XPS spectral investigations and microscope observations provide evidence in support of coordination interaction between ferric ions active sites and XG. In addition, the aggregation model of fine hematite particles suspension using XG in the presence of Fe³⁺ was drawn.     

Phase composition and magnetic properties of niobium-iron codoped TiO2 nanoparticles synthesized in Ar/O2 radio-frequency thermal plasma

Nanoparticles of Nb⁵⁺-Fe³⁺ codoped TiO₂ with various Nb⁵⁺ concentrations (Nb/(Ti+Fe+Nb)=0-10.0 at%) and Fe³⁺ (Fe/(Ti+Fe+Nb)=0-2.0 at%) were synthesized using Ar/O₂ thermal plasma. Dopant content, chemical valence, phase identification, morphology and magnetic properties were determined using several characterization techniques, including inductively coupled plasma-optical emission spectrometer, X-ray photoelectron spectroscopy, X-ray diffraction, UV-vis diffuse reflectance spectrometer, field-emission scanning electron microscopy, transmission electron microscopy and SQUID commercial instrument. The XRD revealed that all the plasma-synthesized powders were exclusively composed of anatase as major phase and rutile. The rutile weight fraction was increased by the substitution of Fe³⁺ for Ti⁴⁺ whereas it was reduced by the Nb⁵⁺ doping. The plasma-synthesized Nb⁵⁺-Fe³⁺ codoped TiO₂ powders had intrinsic magnetic properties of strongly paramagnetic and feebly ferromagnetic at room temperature. The ferromagnetic properties gradually deteriorated as the Fe³⁺ concentration was decreased, suggesting that the ferromagnetism was predominated by the phase composition as a carrier-mediated exchange.     

A 2-D bimetallic assembly with bridging cyanide ions

A novel cyanide-bridged bimetallic assembly, [Cu(1,3-Pn)₂]₂[Fe^III(CN)₆]ClO₄ · 2H₂O (1,3-Pn = 1,3-diaminopropane), derived from [Fe(CN)₆]^3– building blocks and four-coordinated bisdiamine metal(II) ions [Cu(1,3-Pn)₂]²⁺ is described and characterized by X-ray crystal analysis. The compound contains a two-dimensional network structure extended through Fe^III—CN—Cu linkages. Mössbauer experimental results indicate that the iron is ferric (Fe³⁺) in the complex. Cryomagnetic measurements reveal an antiferromagnetic exchange interaction between the nearest paramagnetic metal ions in the compound. The exchange mechanism was also discussed.     

Structural Characterization of Divalent Magnesium-Dopedα-Fe2O3

The defect structure of divalent magnesium-dopedα-Fe₂O₃has been examined by Rietveld structure refinement of the X-ray powder diffraction data. The results show that the Mg²⁺ions occupy the vacant interstitial octahedral sites as well as substituting on the two adjacent octahedral Fe³⁺sites in the corundum-relatedα-Fe₂O₃structure. The structure therefore involves a linear cluster of three Mg²⁺ions replacing two Fe³⁺ions. Interatomic potential calculations indicate that this is the most energetically favorable defect cluster for the system.     

Mössbauer study of the FeV2O4---Fe3O4 system

Mössbauer spectra of the Fe_1+xV_2−xO₄ spinel solid solutions are taken to investigate the cation distribution. Room temperature spectra can be interpreted by assuming that the cation distribution is represented approximately as Fe²⁺[Fe³⁺_xV³⁺_2−x]O₄ for 0 x 0.35 and Fe³⁺[Fe²⁺Fe³⁺_x−1V³⁺_2−x]O₄ for 1 x 2 and the ionic valence arrangement changes from the 2-3-3 type (Fe²⁺[Fe³⁺_xV³⁺_2−x]O₄) to the 3-2-3 one (Fe³⁺[Fe²⁺V³⁺]O₄) in the range 0.35 x 1. Fe₂VO₄ is found to be 3-2-3 spinel, Fe³⁺[Fe²⁺V³⁺]O₄. Its paramagnetic spectrum at 473°K is, however, composed of a broad single line with isomer shift value of 0.61 mm/sec relative to stainless steel, in which the line splitting due to the ferric and ferrous ions is rendered indistinguishable.     

聚乙烯醇在强碱性水溶液中与Fe(Ⅲ)离子间的配位-交联反应

在不断搅拌1×10~(-4)m~3 pH>13的5％ PVA碱性水溶液中,缓慢地添加1×10~(-4)kgFeCl_36H_2O,溶液中即析出红棕色树胶状物.以XPS、ESR和IR等研究该析出物的组分及其形成过程.推定PVA部分羟基在上述条件下发生脱质子反应而提供L~-配位体,Fe(Ⅲ)盐水解生成初生Fe(OH)_3的Fe~(3+),它既有空轨道,又有较强的正电场,故能吸引PVA高分子配位体L~-上的氧而形成O→Fe配位键,从而发生L~-与Fe~(3+)离子间的交联反应,生成多核Fe(Ⅲ)-PVA配位聚合物而析出红棕色树胶状物。