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Speciation analysis of Fe in single plagioclase crystals separated from two different gabbros was performed to understand the crystallization mechanisms of magnetite exsolution. Iron species in single crystals were measured using Fe K‐ and LIII‐edge X‐ray absorption fine structure (XAFS) analysis. The K‐edge pre‐edge analysis showed variation in the averaged valence state of Fe in plagioclase crystals even if they had been separated from the same gabbro that was further confirmed by the LIII‐edge analysis. The K‐edge pre‐dedge analysis also suggests the various degrees of contribution from tetrahedral Fe. The mixing of tetrahedral and octahedral Fe leads to an underestimation of the averaged valence state of Fe for the K‐edge pre‐edge analysis; thus, we adopted the LIII‐edge result for the valence state of Fe in plagioclase crystals. Iron K‐edge extended XAFS (EXAFS) analysis of two plagioclase crystals separated from the same gabbro clearly showed different coordination environments. A weakening of EXAFS oscillation was recognized in one sample, because two Fe–O bonds (Fe3+–O1 and Fe2+–O2) cancelled out the oscillations of each other. The EXAFS spectrum of the other plagioclase crystal suggested a homogeneous distribution of Fe. The content of exsolved magnetite in these crystals is nearly identical, indicating that the exsolution of magnetite in plagioclase crystal had been completed before the temperature decrease that stopped the ordering of Fe ions in tetrahedral sites. Key Points: Valence state of Fe in plagioclase varies among crystals separated from the same plutonic rockTwo different sites are confirmed as a host of Fe in plagioclase from the same rockLIII‐edge XANES is more suitable for speciation analysis because K‐edge XANES underestimate the contribution of tetrahedral Fe [ABSTRACT FROM AUTHOR]

In this research, a novel magnetic mesoporous adsorbent with mixed phase of Fe2O3/Mn3O4 nanocomposite was prepared by a facile precipitating method and characterized extensively. The prepared nanocomposite was used as adsorbent for toxic methyl orange (MO) dye removal from aqua matrix considering its high surface area (178.27 m2/g) with high saturation magnetization (23.07 emu/g). Maximum dye adsorption occurs at solution pH 2.0 and the electrostatic attraction between anionic form of MO dye molecules and the positively charged nanocomposite surface is the main driving force behind this adsorption. Response surface methodology (RSM) was used for optimizing the process variables and maximum MO removal of 97.67% is obtained at optimum experimental condition with contact time, adsorbent dose and initial MO dye concentration of 45 min, 0.87 g/l and 116 mg/l, respectively. Artificial neural network (ANN) model with optimum topology of 3–5–1 was developed for predicting the MO removal (%), which has shown higher predictive ability than RSM model. Maximum adsorption capacity of this nanocomposite was found to be 322.58 mg/g from Langmuir isotherm model. Kinetic studies reveal the applicability of second‐order kinetic model with contribution of intra‐particle diffusion in this process. [ABSTRACT FROM AUTHOR]

The open question of crystal symmetry for YBaCuFeO5, still under debate, is resolved by using diffraction anomalous fine structure and resonant multi-beam X-ray diffraction at the Fe and Cu K edges. The different asymmetric intensity distributions observed at 7, 7.1305 and 8.9945 keV give direct evidence that the space group of YBaCuFeO5 should be P4/ mmm with the distance between Cu and apical O atoms longer than that between Fe and O atoms. This approach provides a direct way to resolve detailed structural symmetry which is indeterminate in conventional Bragg diffraction. [ABSTRACT FROM AUTHOR]

The open question of crystal symmetry for YBaCuFeO5, still under debate, is resolved by using diffraction anomalous fine structure and resonant multi-beam X-ray diffraction at the Fe and Cu K edges. The different asymmetric intensity distributions observed at 7, 7.1305 and 8.9945 keV give direct evidence that the space group of YBaCuFeO5 should be P4/ mmm with the distance between Cu and apical O atoms longer than that between Fe and O atoms. This approach provides a direct way to resolve detailed structural symmetry which is indeterminate in conventional Bragg diffraction. [ABSTRACT FROM AUTHOR]

The iron selenidoantimonate(III) [Fe(phen)3]Sb6Se10 ( 1) (phen = 1, 10-phenanthroline) was prepared by reaction of Fe, Sb, Se, phen, and 1, 4-diazabicyclo[2.2.2]octane in MeOH and H2O mixed solvent under solvothermal conditions. 1 consists of a [Fe(phen)3]2+ cation and a two dimensional [Sb6Se10]2- anion. The [Sb6Se10]2- anion is constructed by SbSe3, SbSe4, and SbSe6 primary building blocks by corner- and edge-sharing, resulting Sb4Se4, Sb5Se5, and Sb6Se6 heterorings and a semi-cubic Sb4Se6 motif, which act as secondary building units. The octahedral SbSe6 primary unit and semi-cubic Sb4Se6 motif make compound 1 quite different from the thioantimonates(III). Compound 1 exhibits steep bandgap ( Eg) of 1.56 eV, indicating potential semiconducting property. The thermal stability of 1 was also investigated. [ABSTRACT FROM AUTHOR]

The iron selenidoantimonate(III) [Fe(phen)3]Sb6Se10 ( 1) (phen = 1, 10-phenanthroline) was prepared by reaction of Fe, Sb, Se, phen, and 1, 4-diazabicyclo[2.2.2]octane in MeOH and H2O mixed solvent under solvothermal conditions. 1 consists of a [Fe(phen)3]2+ cation and a two dimensional [Sb6Se10]2- anion. The [Sb6Se10]2- anion is constructed by SbSe3, SbSe4, and SbSe6 primary building blocks by corner- and edge-sharing, resulting Sb4Se4, Sb5Se5, and Sb6Se6 heterorings and a semi-cubic Sb4Se6 motif, which act as secondary building units. The octahedral SbSe6 primary unit and semi-cubic Sb4Se6 motif make compound 1 quite different from the thioantimonates(III). Compound 1 exhibits steep bandgap ( Eg) of 1.56 eV, indicating potential semiconducting property. The thermal stability of 1 was also investigated. [ABSTRACT FROM AUTHOR]

In this work, a non-covalent interaction of iron and metal-free meso-tetra (4-sulfonatophenyl) porphines (FeTPPS and TPPS, respectively) with high-quality single-layer graphene is studied by Raman spectroscopy. Such a kind of graphene functionalization is promising for a development of novel optoelectronic devices and sensors. Our results show that the central metal atom of porphyrin macrocycle, iron particularly, plays an important role in the integrity of FeTPPS on graphene surface; however, the predicted Raman enhancement is not significant. The interaction of metal-free TPPS with graphene leads to the deprotonation of TPPS molecules and higher Raman enhancement values. Moreover, initially deprotonated TPPS solutions after the adsorption onto the graphene surface demonstrate the appearance of new Raman bands and significantly enhanced Raman signals. We propose that a strong interaction between deprotonated TPPS and graphene is realized through pyrrole and desulfonated phenyl rings of closely located planar TPPS molecules on the graphene surface. The results show that both the protonation of porphyrin macrocycle and the existence of central metal atom are crucial for a formation of nanocomposites with defined electronic properties. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The cathode materials LiNi0.5Mn1.5O4 and LiNi0.4Fe0.2Mn1.4O4 were synthesized using a citric acid-assisted sol-gel method with a final calcination temperature of 1000 °C. An impurity phase exists in LiNi0.5Mn1.5O4 powders, which can be eliminated by substituting some of the Ni2+ and Mn4+ ions with Fe3+. The substitution of Fe into the spinel structure was confirmed by NMR and Mössbauer spectroscopy. The initial capacity of LiNi0.4Fe0.2Mn1.4O4 powder synthesized at 1000 °C (LNFMO) is slightly higher than that of LiNi0.5Mn1.5O4 powder synthesized at 1000 °C (LNMO). Additionally, its capacity retention of 92 % at room temperature after 300 cycles at C/2 charging-discharging rate between 3.5-5.0 V is higher than that of the Fe-free sample (79.5 %) under same conditions which could arise from the difference in their cycling mechanisms. In order to understand the structural evolution of these materials during electrochemical cycling, in situ studies under real operating conditions were performed. Measurements of initial powders in capillaries and in situ experiments during the first galvanostatic cycle were carried out by high resolution powder diffraction using synchrotron radiation. [ABSTRACT FROM AUTHOR]

Core-shell structural magnetic nanocatalysts, involving carbon-coated magnetic Fe3O4 nanoparticles supported on graphene oxide sheets (mildly reduced graphene oxide (MRGO)/Fe3O4@C) and carbonaceous coatings on magnetic Fe3O4 nanoparticles (Fe3O4@C), for immobilizing metal (CuII, CoII, FeIII or VOIV)-salen complexes were prepared by a facile, green, and efficient chemical approach and first applied in the aerobic epoxidation of styrene with air as the oxidizing agent. The prepared catalysts were characterized by different techniques, such as XRD, TEM, FTIR spectroscopy, inductively coupled plasma atomic emission spectroscopy, TEM, thermogravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. The magnetic nanocatalysts MRGO/Fe3O4@C-salen-M (M=Cu, Co, Fe, or V) exhibited higher catalytic reactivity than that of the corresponding Fe3O4@C-salen-M (M=Cu, Co, Fe, or V) species possibly owing to site isolation, good dispersion of magnetic Fe3O4 nanoparticles, and an efficiently synergistic effect between the metal complexes and the supports. Furthermore, MRGO/Fe3O4@C-salen-Co exhibited up to 92.3 % conversion of styrene and 59.2 % selectivity to the styrene oxide upon using air as the oxidizing agent and showed good recoverability with negligible loss in activity and selectivity within successive runs owing to superparamagnetism. Most importantly, these materials can be easily recovered by simple magnetic separation. [ABSTRACT FROM AUTHOR]

[FeFe]-hydrogenases are the best natural hydrogen-producing enzymes but their biotechnological exploitation is hampered by their extreme oxygen sensitivity. The free energy profile for the chemical attachment of O2 to the enzyme active site was investigated by using a range-separated density functional re-parametrized to reproduce high-level ab initio data. An activation free-energy barrier of 13 kcal mol−1 was obtained for chemical bond formation between the di-iron active site and O2, a value in good agreement with experimental inactivation rates. The oxygen binding can be viewed as an inner-sphere electron-transfer process that is strongly influenced by Coulombic interactions with the proximal cubane cluster and the protein environment. The implications of these results for future mutation studies with the aim of increasing the oxygen tolerance of this enzyme are discussed. [ABSTRACT FROM AUTHOR]

[FeFe]-hydrogenases are the best natural hydrogen-producing enzymes but their biotechnological exploitation is hampered by their extreme oxygen sensitivity. The free energy profile for the chemical attachment of O2 to the enzyme active site was investigated by using a range-separated density functional re-parametrized to reproduce high-level ab initio data. An activation free-energy barrier of 13 kcal mol−1 was obtained for chemical bond formation between the di-iron active site and O2, a value in good agreement with experimental inactivation rates. The oxygen binding can be viewed as an inner-sphere electron-transfer process that is strongly influenced by Coulombic interactions with the proximal cubane cluster and the protein environment. The implications of these results for future mutation studies with the aim of increasing the oxygen tolerance of this enzyme are discussed. [ABSTRACT FROM AUTHOR]

Another iron in the fire: X‐ray anomalous diffraction studies on the nitrogenase MoFe protein show the presence of a mononuclear iron site, designated as Fe16, which was previously identified as either Ca2+ or Mg2+. The position of the absorption edge indicates that this site is in the oxidation state +2. The high sequence conservation of the residues coordinated to Fe16 emphasizes the potential importance of the site in nitrogenase. [ABSTRACT FROM AUTHOR]

Selected minerals from oval inclusions (nodules) in the Morasko IAB iron meteorite have been investigated by electron microprobe (EMP) and micro-Raman spectroscopy. Collected spectra of quartz, forsterite-rich olivine, chromite, kosmochlor (Na-Cr-rich clinopyroxene) and Na-feldspar (albite) were compared with corresponding measurements of earth minerals and used for fast identification of meteorite fragments not EMP characterized. Some structural conclusions concerning particular minerals, like solid-state form or average crystallite size, were also drawn from the measured spectra. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Tube-shaped beads excavated from grave pits at the prehistoric Gerzeh cemetery, approximately 3300 BCE, represent the earliest known use of iron in Egypt. Using a combination of scanning electron microscopy and micro X-ray microcomputer tomography, we show that microstructural and chemical analysis of a Gerzeh iron bead is consistent with a cold-worked iron meteorite. Thin fragments of parallel bands of taenite within a meteoritic Widmanstätten pattern are present, with structural distortion caused by cold-working. The metal fragments retain their original chemistry of approximately 30 wt% nickel. The bulk of the bead is highly oxidized, with only approximately 2.4% of the total bead volume remaining as metal. Our results show that the first known example of the use of iron in Egypt was produced from a meteorite, its celestial origin having implications for both the perception of meteorite iron by ancient Egyptians and the development of metallurgical knowledge in the Nile Valley. [ABSTRACT FROM AUTHOR]

Ferrous and ferric phosphate crystalline compounds and glasses were studied using Raman spectroscopy. A comparison of the spectra from crystalline and glassy ortho-, pyro-, and metaphosphates indicates that similar phosphate anions constitute the structures of the respective materials, and some information about the compositional dependence of the phosphate-site distributions in the glasses can be gleaned from relative peak intensities. A correlation exists between the average P-O bond distance and the Raman peak frequencies in the crystalline compounds, and this correlation is used to provide information about the structures of the iron phosphate glasses. For example, the average P-O bond distance is estimated to decrease from about 1.57 Å for iron metaphosphate glasses (O/P∼3.0) to 1.54 Å for iron orthophosphate glasses (O/P∼4.0). These bond distances are in good agreement with those reported from diffraction studies of similar glasses. [ABSTRACT FROM AUTHOR]

Magnetite crystals precipitated as a consequence of Fe(III) reduction by Shewanella algae BrY after 265 h incubation and 5-year anaerobic storage were investigated with transmission electron microscopy, Mössbauer spectroscopy and X-ray diffraction. The magnetite crystals were typically superparamagnetic with an approximate size of 13 nm. The lattice constants of the 265 h and 5-year crystals are 8.4164Å and 8.3774Å, respectively. The Mössbauer spectra indicated that the 265 h magnetite had excess Fe(II) in its crystal-chemistry (Fe3+1.990Fe2+1.015O4) but the 5-year magnetite was Fe(II)-deficient in stoichiometry (Fe3+2.388Fe2+0.419O4). Such crystal-chemical changes may be indicative of the degeneration of superparamagnetic magnetite through the aqueous oxidization of Fe(II) anaerobically, and the concomitant oxidation of the organic phases (fatty acid methyl esters) that were present during the initial formation of the magnetite. The observation of a corona structure on the aged magnetite corroborates the anaerobic oxidation of Fe(II) on the outer layers of magnetite crystals. These results suggest that there may be a possible link between the enzymatic activity of the bacteria and the stability of Fe(II)-excess magnetite, which may help explain why stable nano-magnetite grains are seldom preserved in natural environments. [ABSTRACT FROM AUTHOR]