Valence State Of Iron Research Articles

Study of the Structure of Iron-Containing Zinc Borate Glass

The results of the experimental study of glass of the xFe2O3–(100–x)[40ZnO. 60B2O3] composition in which the content of iron oxide varies from 0 to 10 mol % are presented. The regularities of the glass structure change in the short- and intermediate-range order structures are considered based on the data of infrared spectroscopy and Raman spectroscopy. The valence and coordination state of iron in a glass matrix is studied by Mossbauer spectroscopy.

Biolabile ferrous iron bearing nanoparticles in glacial sediments

Glaciers and ice sheets are a significant source of nanoparticulate Fe, which is potentially important in sustaining the high productivity observed in the near-coastal regions proximal to terrestrial ice cover. However, the bioavailability of particulate iron is poorly understood, despite its importance in the ocean Fe inventory. We combined high-resolution imaging and spectroscopy to investigate the abundance, morphology and valence state of particulate iron in glacial sediments. Our results document the widespread occurrence of amorphous and Fe(II)-rich and Fe(II)-bearing nanoparticles in Arctic glacial meltwaters and iceberg debris, compared to Fe(III)-rich dominated particulates in an aeolian dust sample. Fe(II) is thought to be highly biolabile in marine environments. Our work shows that glacially derived Fe is more labile than previously assumed, and consequently that glaciers and ice sheets are therefore able to export potentially bioavailable Fe(II)-containing nanoparticulate material to downstream ecosystems, including those in a marine setting. Our findings provide further evidence that Greenland Ice Sheet meltwaters may provide biolabile particulate Fe that may fuel the large summer phytoplankton bloom in the Labrador Sea, and that Fe(II)-rich particulates from a region of very high productivity downstream of a polar ice sheet may be glacial in origin.

Valence and spin states of iron are invisible in Earth\u2019s lower mantle

Heterogeneity in Earth’s mantle is a record of chemical and dynamic processes over Earth’s history. The geophysical signatures of heterogeneity can only be interpreted with quantitative constraints on effects of major elements such as iron on physical properties including density, compressibility, and electrical conductivity. However, deconvolution of the effects of multiple valence and spin states of iron in bridgmanite (Bdg), the most abundant mineral in the lower mantle, has been challenging. Here we show through a study of a ferric-iron-only (Mg0.46Fe3+0.53)(Si0.49Fe3+0.51)O3 Bdg that Fe3+ in the octahedral site undergoes a spin transition between 43 and 53 GPa at 300 K. The resolved effects of the spin transition on density, bulk sound velocity, and electrical conductivity are smaller than previous estimations, consistent with the smooth depth profiles from geophysical observations. For likely mantle compositions, the valence state of iron has minor effects on density and sound velocities relative to major cation composition.

Electrolysis of iron in a molten oxide electrolyte

Direct iron production at molten metal state from iron oxides by the sole application of electrical energy represents a possible route to decarbonize steel industry. Although chemically simple, this reaction is difficult to implement due to the problem of the multiple valence states of iron and to an operating temperature above 1811 K. Thermal, chemical, and electrical conditions have been identified based on thermodynamic considerations to carry out this reaction in a laboratory device. Experiments were undertaken to determine the contribution of the thermal level to the decomposition of iron oxide and to estimate the electronic current resulting from iron multiple valence states. The production of liquid iron was obtained resulting in recoverable samples produced at liquid state and from a faradaic process checked in real time by its accompanying anodic oxygen evolution.Graphical

Cation Distribution Assisted Tuning of Magnetization in Nanosized Magnesium Ferrite

The MgFe2O4 nanoparticles are synthesized by combustion method and annealed at different temperatures from 500 to 1000 °C. Magnetic properties, morphology, valence states of iron, crystal structure, and microstructure of the samples are investigated systematically by vibrating sample magnetometer, field emission scanning electron microscope, transmission electron microscopy, X‐ray absorption spectroscopy, and synchrotron X‐ray diffraction. Cation distribution is determined from synchrotron X‐ray diffraction data using Rietveld refinement combined with extended X‐ray absorption fine structure spectroscopy. The results indicates that all the samples are phase‐pure with crystallite size ranging from 11 to 41 nm. By adjusting the annealing temperature, cation distribution and particle size can be changed, and consequently leading to the change in structure and magnetic properties. The saturation magnetization of the samples are enhanced significantly compared to that of the bulk material. The variation of magnetic properties is discussed based on cation distribution, particle size, valence state, surface effect, and spin canting.

Production of light aromatic hydrocarbons by catalytic cracking of coal pyrolysis vapors over natural iron ores

Four iron ores including limonite, siderite, hematite and magnetite are examined for their catalytic effects on coal pyrolytic products. Experiments were conducted at a pyrolyzer combined with gas chromatography/mass spectrometry (Py-GC/MS). The results show that limonite has the highest catalytic activity for light aromatic formation as a result of the conversion of aliphatic hydrocarbons and oxygenates. The total peak area of light aromatics such as benzene, toluene, ethylbenzene, xylene, and naphthalene (BTEXN) has increased by 52% after the catalysis of limonite. The good performance of limonite can be attributed to its large surface area. Multi-cycle tests were conducted over limonite to get the knowledge of its stability. The effect of valence state of iron is discussed by making comparison of the performances between the limonite and the reduced limonite. It is found that the reduced limonite has a more reactive catalytic activity for light aromatics production. Coal effect is also studied.

Nuclear inelastic scattering at the diiron center of ribonucleotide reductase from Escherichia coli

The enzyme ribonucleotide reductase R2 catalyzes an important step in the synthesis of the building blocks of DNA, and harbors a dinuclear iron center required for activity. Not only the iron valence states but also the protonation of the iron ligands govern the enzymatic activity of the enzyme. We have performed Nuclear Inelastic Scattering (NIS) experiments on the 57Fe reconstituted ribonucleotide reductase R2 subunit from Escherichia coli (Ec R2a). Accompanying Mossbauer spectroscopic investigations show that the partial density of vibrational states (pDOS) of the 57Fe reconstituted Ec R2a sample contained contributions from both 57Fe-Ec R2a protein as well as unspecifically bound 57Fe. Subtraction of a featureless pDOS as obtained from protein-coated iron oxide particles allowed modeling of the contribution of non-specifically bound iron and thus the pDOS of 57Fe-Ec R2a could be obtained. Quantum-mechanics/molecular-mechanics (QM/MM) calculations of the whole 57Fe-Ec R2a protein with variations of the cofactor protonation were performed in order to assign characteristic bands to their corresponding molecular vibrational modes.

Precipitation of Ru, Rh and Ir with iron ions from synthetic nickel sulphate leach solutions

The nickel sulphate leach solution produced in the first leaching stage of base metal refineries contains impurities such as iron as well as other precious metals (OPMs, i.e. ruthenium, rhodium and iridium). Precipitation of the dissolved iron in downstream unit operations leads to sludge formation. Some of the other precious metals have been reported to co-precipitate in the sludge; this could be used as a mechanism for OPM recovery. The objective of this study was to investigate the precipitation behaviour of OPMs during iron sludge formation from the nickel sulphate leach solution.Precipitation tests were performed on synthetic leach solutions to investigate the effect of solution pH, temperature, metal content, iron valence state and seeding on the iron and OPM precipitation behaviour. Typical iron precipitation via hydrolysis of ferric ions was observed. The primary mechanism of OPM precipitation also involved hydrolysis reactions. The solution pH had the most significant effect on OPM precipitation. Average ruthenium precipitation and rhodium precipitation of 98.1% and 92.2%, respectively, were achieved at pH4; the iron valence state and total metal concentration had no significant effect on the OPM precipitation. More basic conditions were required for thermodynamically stable iridium species to precipitate than for ruthenium and rhodium. Seeding did not enhance OPM scavenging from the leach solution.Tests performed on plant solution confirmed that OPM precipitation by neutralisation is possible. At high nickel concentrations, nickel sulphate crystallisation contributed to sludge formation and resulted in significant iridium co-precipitation due to entrainment.

Fast decolorization of azo methyl orange via heterogeneous Fenton and Fenton-like reactions using alginate-Fe2+/Fe3+ films as catalysts

The efficiency of Fenton and Fenton-like processes can be seriously affected by the continuous loss of iron ions and by the formation of solid sludge. Here, alginate (Alg) films were synthesized to stabilize iron ions (Fe2+ and Fe3+) and to enhance their catalytic activities towards the decolorization of methyl orange via heterogeneous Fenton and Fenton-like processes. Iron ions were ionically bond to the Alg molecules resulting in a three-dimensional network with specific structural and morphological features according to the valence states of iron. Our results demonstrated that both Alg-Fe2+ and Alg-Fe3+ films show highlighted catalytic activity for the decolorization of MO and high decolorization rates. Reuse experiments demonstrated that both films could be employed in at least five consecutive decolorization processes without losing their catalytic efficiency or stability. Taken together, our findings reveal that the Alg-Fe2+ and Alg-Fe3+ films may be suitable low-cost catalysts in heterogeneous Fenton and Fenton-like processes.

Reduced lattice thermal conductivity of Fe‐bearing bridgmanite in Earth's deep mantle

AbstractComplex seismic, thermal, and chemical features have been reported in Earth's lowermost mantle. In particular, possible iron enrichments in the large low shear‐wave velocity provinces (LLSVPs) could influence thermal transport properties of the constituting minerals in this region, altering the lower mantle dynamics and heat flux across core‐mantle boundary (CMB). Thermal conductivity of bridgmanite is expected to partially control the thermal evolution and dynamics of Earth's lower mantle. Importantly, the pressure‐induced lattice distortion and iron spin and valence states in bridgmanite could affect its lattice thermal conductivity, but these effects remain largely unknown. Here we precisely measured the lattice thermal conductivity of Fe‐bearing bridgmanite to 120 GPa using optical pump‐probe spectroscopy. The conductivity of Fe‐bearing bridgmanite increases monotonically with pressure but drops significantly around 45 GPa due to pressure‐induced lattice distortion on iron sites. Our findings indicate that lattice thermal conductivity at lowermost mantle conditions is twice smaller than previously thought. The decrease in the thermal conductivity of bridgmanite in mid‐lower mantle and below would promote mantle flow against a potential viscosity barrier, facilitating slabs crossing over the 1000 km depth. Modeling of our results applied to LLSVPs shows that variations in iron and bridgmanite fractions induce a significant thermal conductivity decrease, which would enhance internal convective flow. Our CMB heat flux modeling indicates that while heat flux variations are dominated by thermal effects, variations in thermal conductivity also play a significant role. The CMB heat flux map we obtained is substantially different from those assumed so far, which may influence our understanding of the geodynamo.

Study on electrochemical performance of multi-wall carbon nanotubes coated by iron oxide nanoparticles as advanced electrode materials for supercapacitors

Iron oxide was deposited on surface of multi-walled carbon nanotubes (Fe2O3@MWNTs) by atomic layer deposition (ALD). By a following calcination process, the electrochemical performance of the Fe2O3@MWNTs nanocompisites was further improved. From the X-ray diffraction and Raman spectra analysis of nanocomposites, Fe2O3 nanocrystallites were found to be successfully formed after a simple calcination process. The transmission electron microscopy revealed that Fe2O3 nanoparticles with the size of less than 10 nm are uniformly anchored on the surface of MWNTs. The X-ray photoelectron spectroscopy further confirmed that the valence state of iron in the composites is +3 and no other impurities were detected. The Fe2O3@MWNTs nanocomposites were investigated as electrode materials for high-performance supercapacitor. Electrochemical test results exhibited a high specific capacitance with 787 F g−1 at a discharge current density of 1 A g−1 and an outstanding rate performance (72% capacitance retention at 30 A g−1), and even after 5000 cycles the capacity retention was still maintained at 91.6%.

The spin state of Fe3+in lower mantle bridgmanite

Iron- and aluminum-bearing MgSiO 3 bridgmanite is the most abundant mineral in the Earth’s interior; hence its crystal chemistry is fundamental to expanding our knowledge of the deep Earth and its evolution. In this study, the valence and spin state of iron in well-characterized Al-free Fe 3+ -rich bridgmanite were investigated by means of Mossbauer spectroscopy to understand the effect of ferric iron on the spin state. We found that a minor amount of Fe 3+ is in the low-spin state above 36 GPa and that its proportion does not increase substantially with pressure up to 83 GPa. This observation is consistent with recent experimental studies that used Mossbauer and X-ray emission spectroscopy. In the Earth’s deep lower mantle, Fe 3+ spin crossover may take place at depths below 900 and 1200 km in pyrolite and MORB, respectively. However, the effect of spin crossover on physical properties may be small due to the limited amount of Fe 3+ in the low-spin state.

Structure and Electrical Properties of Iron Borosilicate Glasses

Glassesofnominal composition 25SiO2- 30Na2O-2Al2O3-x Fe2O3-(43- x)B2O3 (x = 1 to 6 mol%) were prepared by the ordinary melt quenching technique. The influence of Fe2O3 substitution at the expense of B2O3 on structure and electrical conductivity of sodium borosilicate glasses was investigated. The conductivity was found to increase with increasing Fe2O3 content. A double channel conduction mechanism was introduced to explain the electrical conductivity measurements. Moreover, the activation energy decreases considerably in the temperature range from 473 to 773 °K. The activation energies of conduction in various temperature regions were calculated. The conduction was best described by sodium ion migration and hopping between the two valence states of iron. FTIR absorption spectra in the spectral range 1600-400 cm−1 were measured and a deconvolution analysis technique (DAT) using Gaussian peaks was introduced to analyze the studied glasses. Different characteristic bands were observed and attributed to different types of borate besides silicate vibrational groups.

Optical signatures of low spin Fe3+ in NAL at high pressure

AbstractThe iron spin transition directly affects properties of lower mantle minerals and can thus alter geophysical and geochemical characteristics of the deep Earth. While the spin transition in ferropericlase has been documented at P ~60 GPa and 300 K, experimental evidence for spin transitions in other rock‐forming minerals, such as bridgmanite and post‐perovskite, remains controversial. Multiple valence, spin, and coordination states of iron in bridgmanite and post‐perovskite are difficult to resolve with conventional spin probing techniques. Optical spectroscopy, on the other hand, can discriminate between high and low spin and between ferrous and ferric iron at different sites. Here we establish the optical signature of low spin Fe3+O6, a plausible low spin unit in bridgmanite and post‐perovskite, by optical absorption experiments in diamond anvil cells. We show that the optical absorption of Fe3+O6 in new aluminous phase (NAL) is very sensitive to the iron spin state and may represent a model behavior of bridgmanite and post‐perovskite across the spin transition. Specifically, an absorption band centered at ~19,000 cm−1 is characteristic of the 2T2g → 2T1g (2A2g) transition in low spin Fe3+ in NAL at 40 GPa, constraining the crystal field splitting energy of low spin Fe3+ to ~22,200 cm−1, which we independently confirm by first‐principles calculations. Together with available information on the electronic structure of Fe3+O6 compounds, we show that the spin‐pairing energy of Fe3+ in an octahedral field is ~20,000–23,000 cm−1. This implies that octahedrally coordinated Fe3+ in bridgmanite is low spin at P > ~40 GPa.

ChemInform Abstract: Iron‐Catalyzed C—H Activation

AbstractReview: 83 refs.

Combined Experimental and Computational Analyses on the Electronic Structure of Alluaudite-Type Sodium Iron Sulfate

Alluaudite-type sodium iron sulfate, Na2.56Fe1.72(SO4)3, has the highest redox potential in any Fe3+/Fe2+ environment; here, its electronic structure is investigated by combining X-ray absorption spectroscopy (XAS), semiempirical ligand field multiplet (LFM) simulations, and ab initio calculations. The LFM simulations for the Fe L2,3-edge XAS reveals the exceedingly ionic character of the Fe–O bond due to the strong inductive effect of the sulfate group; this is one of the main factors which enhance the electrode potential of Na2.56Fe1.72(SO4)3. Both experimental XAS measurements and ab initio calculations indicate electrochemical charging (desodiation) gives more hybridized iron 3d and oxygen 2p states. The degree of covalency between iron and oxygen changes reversibly along with the change of the iron valence state.

The right mud: Studies in the mud-coating technique of Gambiered Guangdong silk

Gambiered Guangdong silk is a traditional cloth with two-tone colors, deeply rooted in China. Its coating technique has been included in the National Intangible Cultural Heritage List. In the unique coating process of the silk, river mud plays an important role but there has been very little research involving it. To gain insight into the characterization of the special mud, the usable mud with the unusable mud were compared with SEM-EDS and XRD. The results showed that Fe(II) was the main valence state of iron in the usable clay mud (nearly 90%). Although the iron mineral particles constituted of akaganeite coated on the coated silk surface, akaganeite was not used as the original pigment because of its poor availability. The significant correlation between the Fe(II) content and textile lightness (L*1) (r=−0.82, p<0.05), and sterilization test confirmed the role of Fe(II) in the coating process. Meanwhile, given the penetration of FeSO4 into the back side, it suggested that the solid and organic-binding phases of Fe(II) were the main forms of Fe. Moreover, there were no bacteria participating in the 1-h coating process but they importantly maintained the coating availability of the mud. In short, the right mud for coating Gambiered Guangdong silk need enough precipitated Fe(II) which could obtain from bacteria reducing Fe(III). This paper provided the scientific basis for the inheritance of the mud-coating technique of Gambiered Guangdong silk.

Iron‐catalyzed C−H Activation

Transition‐metal‐catalyzed C–H activation and C–C formation have been receiving considerable attention because of their high atom economy and synthesis efficiency. Iron is widely used in catalytic reactions because it has the advantages of abundance, low cost, accessibility, and environmental friendliness. In recent years, research on the Fe‐catalyzed C–H activation of C–C formation has made considerable progress. This paper summarizes latest studies on iron‐catalyzed C–H activation, classifies the catalysts according to the different valence states of iron, and expounds the catalytic mechanism.

Role of iron in synthetic tetrahedrites revisited

The valence state of iron in Cu12−xFexSb4S13 tetrahedrites have been revisited by the combination of the crystallographic results, Mössbauer spectroscopy, and magnetization measurements. The crystal structure solution for Cu11.0Fe1.0Sb4S13 (space group I4¯3m, a=10.3253(12), z=2, R=0.011) proved that iron substitutes for copper only in the Cu1 position. At the iron content of x=0.8, 1.0, and 1.2, the presence of two nonequivalent and non-interacting Fe3+ cations was inferred from Mössbauer spectra. At higher levels of substitution (x=1.5 and 2.0), room-temperature Mössbauer spectra indicate the electron hopping between part of Fe3+ and Fe2+ centers, whereas the rest of iron atoms exists as valence-localized Fe3+ and Fe2+ cations. Electron transfer is frozen out at 77K, where a combination of two Fe3+ sites and one high-spin Fe2+ site is observed. Paramagnetic effective moments extracted from the magnetic susceptibility data point at the Fe3+ state of iron at x=0.8, while a mixture of Fe2+ and Fe3+ is presumed in the samples with higher Fe content.

Investigation of alumino-silicic reagent interaction with iron in water by Mössbauer spectroscopy

Mössbauer spectroscopy is a required analytical technique in the investigations of water treatment process mechanism for purification from iron. In this paper the new-made alumosilicic reagent for purification of water was described. This reagent was used for water purification from iron dissolved complexes. The precipitated sediment is obtained and investigated. The iron valence state and relative concentrations of these states were detected in sediment. The presence of superparamagnetic particles is established.