Iron Valence Research Articles

Green Synthesis of Nano-Zero Valence Iron with Green Tea and It's Implication in Lead Removal.

The nano-zero valence iron (nZVI) via green synthesis for heavy metal remediation has attracted many attentions due to its low-cost, environmental-safety, relative reproductivity, and high stability. However, influence of synthesis conditions on the physiochemical properties of nZVI via green tea extracts and the responding suspensibility, which is required for high reactivity, has not been fully elucidated. In this study, we investigated the zeta potentials, sedimentation and lead (Pb2+) removal capacity of various nZVIs synthesized using green tea extracts. The results showed that the tea extracts extracted at 80oC presented an excellent activity, which contributed to the outstanding suspensibility and reaction activity of nZVI synthesized in a volume ratio of 1:1 (tea extraction versus Fe2+ solution). Thus, the optimized nZVI was successfully prepared with a Pb2+ removal capacity (377.3mg/g), which was seven times stronger than 50.31mg/g of traditional chemical synthesized nZVI.

Enhanced catalytic activity of toluene oxidation over in-situ prepared Mn3O4-Fe2O3 with acid-etching treatment

Mn3O4-Fe2O3 composite catalysts are in-situ synthesized via advanced oxidation followed by modifying with hydrochloric acid to improve the catalytic toluene oxidation performance. Mn3O4-Fe2O3 modified with 1.0 M HCl (A-1.0) exhibited best activity of toluene oxidation. The temperature of 50% toluene conversion is 245 °C and the temperature of 90% conversion is 279 °C. There are much more abundant surface lattice oxygen species and higher amount of high valence manganese and iron ions on A-1.0 catalyst, which are beneficial for improving catalytic activity. In-situ DRIFTs indicated that benzaldehyde and benzoic acid are main intermediate products on A-1.0 catalyst during toluene oxidation.

Compressibilities along the magnetite–magnesioferrite solid solution

To calculate the thermodynamic properties of recently discovered high-pressure mixed valence iron oxides in the system Fe–Mg–O, information on the equation of state of precursor inverse spinel phases along the magnetite–magnesioferrite join is needed. The existing equation of state data, particularly for magnesioferrite, are in poor agreement and no data exist for intermediate compositions. In this study, the compressibility of nearly pure magnesioferrite as well as of an intermediate {{mathrm{Mg}}_{0.5}}^{vphantom{2+}}mathrm{Fe}_{0.5}^{2+}{mathrm{Fe}}_{2}^{3+}{mathrm{O}}_{4}^{vphantom{2+}} sample have been investigated for the first time up to approximately 19 and 13 GPa, respectively, using single-crystal X-ray diffraction in a diamond anvil cell. Samples were produced in high-pressure synthesis experiments to promote a high level of cation ordering, with the obtained inversion parameters larger than 0.83. The room pressure unit cell volumes, V0, and bulk moduli, KT0, could be adequately constrained using a second-order Birch–Murnaghan equation of state, which yields V0 = 588.97 (8) Å3 and KT0 = 178.4 (5) GPa for magnesioferrite and V0 = 590.21 (5) Å3 and KT0 = 188.0 (6) GPa for the intermediate composition. As magnetite has KT0 = 180 (1) GPa (Gatta et al. in Phys Chem Min 34:627–635, 2007. https://doi.org/10.1007/s00269-007-0177-3), this means the variation in KT0 across the magnetite–magnesioferrite solid solution is significantly non-linear, in contrast to several other Fe–Mg spinels. The larger incompressibility of the intermediate composition compared to the two end-members may be a peculiarity of the magnetite–magnesioferrite solid solution caused by an interruption of Fe2+–Fe3+ electron hopping by Mg cations substituting in the octahedral site.

Nonstoichiometric Strontium Ferromolybdate as an Electrode Material for Solid Oxide Fuel Cells

This review is devoted to the application of Sr2FeMoO6−δ (SFM) and Sr2F1.5Mo0.5O6−δ (SF1.5M) in La1−xSrxGa1−yMgyO3−δ (LSGM)-based SOFCs. We consider the most relevant physical properties (crystal structure, thermodynamic stability, iron and molybdenum valence states, oxygen vacancy formation and oxygen non-stoichiometry, electrical conductivity), A- and B-site ion substitution, and the performance of SF1+xM SOFCs (polarization resistance, operation with hydrogen, operation with hydrocarbons and methanol). Their properties can be tailored to a particular application by the substitution of different metal cations into their lattices. SF1+xM materials are excellent catalysts in hydrocarbon oxidation and can prevent carbon deposition due to the ability to exchange lattice oxygen with the gaseous phase. Moreover, they are sulfur tolerant. This opens the way to direct hydrocarbon-fueled SOFCs, eliminating the need for external fuel reforming and sulfur removal components. Such SOFCs can be greatly simplified and operate with much higher overall efficiency, thus contributing to the solution to the lack of energy problem in our modern world.

Phase Transitions and Physical Properties of the Mixed Valence Iron Phosphate Fe3(PO3OH)4(H2O)4.

Iron phosphate materials have attracted a lot of attention due to their potential as cathode materials for lithium-ion rechargeable batteries. It has been shown that lithium insertion or extraction depends on the Fe mixed valence and reduction or oxidation of the Fe ions' valences. In this paper, we report a new synthesis method for the Fe3(PO3OH)4(H2O)4 mixed valence iron phosphate. In addition, we perform temperature-dependent measurements of structural and physical properties in order to obtain an understanding of electronic-structural interplay in this compound. Scanning electron microscope images show needle-like single crystals of 50 μm to 200 μm length which are stable up to approximately 200 °C, as revealed by thermogravimetric analysis. The crystal structure of Fe3(PO3OH)4(H2O)4 single crystals has been determined in the temperature range of 90 K to 470 K. A monoclinic isostructural phase transition was found at ~213 K, with unit cell volume doubling in the low temperature phase. While the local environment of the Fe2+ ions does not change significantly across the structural phase transition, small antiphase rotations occur for the Fe3+ octahedra, implying some kind of electronic order. These results are corroborated by first principle calculations within density functional theory, which also point to ordering of the electronic degrees of freedom across the transition. The structural phase transition is confirmed by specific heat measurements. Moreover, hints of 3D antiferromagnetic ordering appear below ~11 K in the magnetic susceptibility measurements. Room temperature visible light absorption is consistent with the Fe2+/Fe3+ mixed valence.

The Valence and Spin State Tuning of Iron(II/III) Porphyrazines with Bulky Pyrrolyl Periphery in Solution and Solid State.

Iron(III) porphyrazines containing peripheral 2,5-dimethyl-, 2-methyl-5-phenyl-, and 2,3,5-triphenyl-1H-pyrrol-1-yl substituents were synthesized and subjected to physicochemical characterization. This was accomplished by high-resolution mass spectrometry, nuclear magnetic resonance (as diamagnetic Fe(II) derivatives), HPLC purity analysis, and UV-Vis spectroscopy, accompanied by the solvation study in dichloromethane and pyridine. X-ray structure analysis was performed for a single crystal of the previously obtained 2,5-diphenyl-substituted derivative of porphyrazine complex (5d). The octahedral geometries of iron cation, present in the porphyrazine core, influenced the packing mode of molecules in the crystals. Mössbauer studies, performed for solid samples of iron porphyrazines, indicated that low-spin reduced iron states might occupy low- or high-symmetry binding sites. It was found that the hyperfine parameters and the subsequent contribution of the iron cations depend on the number of phenyl groups surrounding the pyrrolyl moiety. For iron(II) porphyrazine 2,3,5-triphenylpyrrol-1-yl substituents (5b), a high-spin ferrous state fraction was observed. Temperature-dependent measurements showed that the freed rotation of the peripheral porphyrazine ligands and the increased flexibility of the macrocycle ring result in the Fe2+ ion being stabilized in a diamagnetic state at a binding site of high symmetry at room temperature in the solid state. This process is most probably stimulated by the range of collective motions of the polymeric ribbons consisting of iron(II) porphyrazines observed in the X-ray.

The valence state of iron-based nanomaterials determines the ferroptosis potential in a zebrafish model

Many nanomaterials containing different valences of iron have been designed for applications in biomedicine, energy, catalyzers, nanoenzymes, and so on. However, the toxic effects of the valence state of iron in iron-based nanomaterials are still unclear. Here, three different-valence iron-based nanomaterials (nFe@Fe3O4, nFe3O4 and nFe2O3) were synthesized and exposed to zebrafish embryos and mammalian cardiomyocytes. All of them induced ferroptosis along with an increase in valence through iron overload and the Fenton reaction. Specifically, we exposed Tg (cmlc2:EGFP) zebrafish to the three iron-based nanomaterials and found that nFe@Fe3O4 treatments led to enlarged ventricles, while nFe3O4 and nFe2O3 increased atrial size, which was consistent with the results from hematoxylin-eosin staining and in situ hybridization. Moreover, we used ferroptosis inhibitors (ferrostatin-1 or deferoxamine) to treat zebrafish along with nanoparticles exposure and found that the cardiac developmental defects caused by nFe3O4 and nFe2O3, but not nFe@Fe3O4, could be completely rescued by ferroptosis inhibitors. We further found that nFe@Fe3O4, rather than nFe3O4 and nFe2O3, reduced the dissolved oxygen in the medium, which resulted in hypoxia and acceleration of heart tube formation and ventricular enlargement, and both were fully rescued by oxygen donors combined with ferroptosis inhibitors. Consistently, these findings were also observed in mammalian cardiomyocytes. In summary, our study demonstrates that the valence state of iron-based nanomaterials determines the ferroptosis potential. Our study also clarifies that high-valence iron-based nanomaterials induce an enlarged atrium via ferroptosis, while low-valence ones increase the ventricular size through both hypoxia and ferroptosis, which is helpful to understand the potential adverse effects of different valences of iron-based nanomaterials on environmental health and assure the responsible and sustainable development of nanotechnology.

Iron valence state evolution and hydrochar properties under hydrothermal carbonization of dyeing sludge

Iron (Fe) migration mechanisms and hydrochar properties in dyeing sludge hydrothermal carbonization (HTC) are important topics in wastewater treatment. HTC treatment of sludge produces wastewater containing Fe so it is necessary to study the migration behavior of Fe during HTC treatment. This study investigated the basic properties and Fe migration behavior of hydrochar during HTC treatment supplemented with nitric acid (HNO3). The results showed that the carbonization degree and yield of hydrochar treated with the HNO3 solution (HHC) were much lower than those of hydrochar treated with ultrapure water (WHC). The variation of total Fe (TF) concentration indicated that the decomposition of organic material and dissolution of minerals in the aqueous release of Fe during the liquid phase, led to much lower TF concentrations compared to the original dyeing sludge. Fe release was further enhanced with the addition of HNO3 and increase of temperature, rendering a much lower TF concentration of the HHC compared to the WHC. The variations of Fe3+ and Fe2+ concentrations indicated that the HTC-treated hydrochar contained more Fe2+, caused by Fe3+ reduction with hydroxyl methyl-furfural and glucose in the liquid and subsequent Fe2+/Fe3+ transferral to the solid hydrochar phase. X-ray diffraction (XRD) showed that the main Fe content in WHC was FeO(OH), while HHC contained mainly Fe(SO4)(OH)•2H2O and Fe3O4. XPS and XRF showed that Fe could more easily enter the internal pores of the hydrochar instead of being deposited on the surface. This study provided more insights on Fe migration behavior during HTC treatment.

A novel complexation method for separation and recovery of low valence vanadium, iron and chromium from sulfuric acid solution

Traditional methods of vanadium recovery from vanadium slag suffer from serious environmental pollution due to the residue and wastewater containing highly toxic V(V) and Cr(VI). To avoid this, a complexation method based on sodium diethyldithiocarbamate (DDTC) complexing agent was proposed to separate and recover V(IV), Fe(II), Cr(III) in the leaching solution directly prepared from vanadium slag. Firstly, the recovery effect of DDTC on metal ions was studied in the imitated solution containing V (IV), Fe (II) and Cr (III), 97.67% vanadium, 99.51% iron and 98.99% chromium were recovered, respectively. In addition, DDTC was recycled in the complexation process. After four cycles, the regeneration rate of DDTC remained above 86%. Then, this method was applied to the leaching solution of vanadium slag, and 97.38% Cr, 97.69% V, 99.66% Fe and 97.64% Mn were recovered, respectively. Chromium was recovered as Cr2O3 with purity of 97.1%. Most iron was recovered as (NH4)2Fe(SO4)2·6H2O with purity of 99.23%. Manganese and a small amount of iron were enriched in the slag, which could be used to produce manganese alloy. Vanadium was recovered as calcium salt, which could be used to produce VOSO4 electrolyte with purity greater than 99.8%. Without waste water and residue containing highly toxic V(V) and Cr(VI) produced in this new method, which provides a new strategy for cleaner comprehensive utilization of vanadium slag.

Governing mechanism of ion transport in lithium-iron-phosphate glasses

We show a fundamental relationship between network structural attributes and ionic transport of lithium iron phosphate glasses xLi2O–2Fe2O3–3 P2O5 (xLFPO; x = 0.375, 0.75, 1.5, 3.0) used for a cathode in lithium-ion batteries. The glass samples have been synthesized using a solid-state reaction method. We have investigated the electrical characteristics of the glass by combinational measurements of electrical impedance in the frequency 100 Hz – 30 MHz and temperature from ambient to 240 °C, differential thermal analysis, X-ray diffraction pattern, and Raman spectroscopy. The ionic hopping and relaxation processes in xLFPO glasses are analyzed by using Cole-Cole, power law, and modulus representations. We reveal that the exponential increase in dc conductivity with increasing Li2O in xLFPO glasses is caused by the combination of an increase in non-bridging oxygen sites and a change in the bonding forces of iron valence surrounding the iron phosphate clusters inside the network. The power law conductivity, which is driven by the fractional Rayleigh equation, exhibits that the rate of increase in dc ionic conductivity is the same as the rate of increasing numbers of the ionic charge carriers. Raman spectra show that the increase of depolymerization of the iron phosphate network with the addition of Li2O content is due to the conversion of Q2 to Q1 and Q0 species.

Orbital memory from individual Fe atoms on black phosphorus

Bistable valency in individual atoms presents an approach toward single-atom memory, as well as a building block to create tunable and stochastic multiwell energy landscapes. Yet, this concept of orbital memory has thus far only been observed for cobalt atoms on the surface of black phosphorus, which are switched using tip-induced ionization. Here, we show that individual iron atoms on the surface of black phosphorus exhibit orbital memory using a combination of scanning tunneling microscopy and spectroscopy with ab initio calculations based on density functional theory. Unlike cobalt, the iron orbital memory can be switched in its nonionized ground state. Based on calculations, we confirm that each iron valency has a distinct magnetic moment that is characterized by a distinguishable charge distribution due to the different orbital population. By studying the stochastic switching of the valency with varying tunneling conditions, we propose that the switching mechanism is based on a two-electron tunneling process.

Estimating the Iron Valence Distribution of Synthetic Coal Ash Slags through Thermophysical Modeling

Estimating the Iron Valence Distribution of Synthetic Coal Ash Slags through Thermophysical Modeling

Investigation of Valence Mixing in Sodium-Ion Battery Cathode Material Prussian White by Mössbauer Spectroscopy

Prussian white (PW), Na2Fe [Fe(CN)6], is a highly attractive cathode material for sustainable sodium-ion batteries due to its high theoretical capacity of ∼170 mAhg−1 and low-cost synthesis. However, there exists significant variability in the reported electrochemical performance. This variability originates from compositional flexibility possible for all Prussian blue analogs (PBAs) and is exasperated by the difficulty of accurately quantifying the specific composition of PW. This work presents a means of accurately quantifying the vacancy content, valence distribution, and, consequently, the overall composition of PW via Mössbauer spectroscopy. PW cathode material with three different sodium contents was investigated at 295 and 90 K. The observation of only two iron environments for the fully sodiated compound indicated the absence of [Fe(CN)6]4- vacancies. Due to intervalence charge transfer between iron centers at 295 K, accurate determination of valences was not possible. However, by observing the trend of spectral intensities and center shift for the nitrogen-bound and carbon-bound iron, respectively, at 90 K, valence mixing between the iron sites could be quantified. By accounting for valence mixing, the sum of iron valences agreed with the sodium content determined from elemental analysis. Without an agreement between the total valence sum and the determined composition, there exists uncertainty around the accuracy of the elemental analysis and vacancy content determination. Thus, this study offers one more stepping stone toward a more rigorous characterization of composition in PW, which will enable further optimization of properties for battery applications. More broadly, the approach is valuable for characterizing iron-based PBAs in applications where precise composition, valence determination, and control are desired.

Novel co-polymerization of polypyrrole/polyaniline on ferrate modified biochar composites for the efficient adsorption of hexavalent chromium in water

It is still a huge challenge to prepare cheap and effective composite materials for removing hexavalent chromium (Cr(VI)) in sewage treatment. In this study, a noval co-polymerization of polypyrrole/polyaniline on ferrate modified biochar (Ppy/PANI/FBC) was fabricated via ferrate-promoted pyrolysis and in-situ oxidative polymerization of pyrrole and aniline molecules to effectively remove Cr(VI) from polluted water. The Ppy/PANI/FBC quickly decreased Cr(VI) concentration from 38.92 to 3.92 mg/L within 400 min, with an efficient removal efficiency (89.92%), which was significantly higher than that of FBC (4.75%), Ppy/FBC (72.30%), and PANI/FBC (42.43%). These results are mainly caused by its conjugated connection and well-dispersion of Ppy and PANI on the surface of a carbon-based material. Meanwhile, the experimental results were in line with the pseudo-second-order kinetic and Freundlich models. The Ppy/PANI/FBC is featured by a high capacity of Cr(VI) adsorption (up to 203.71 mg/g). In addition, it could be adopted for efficiently removing Cr(VI) over a wide pH range (4–9) because of the positively charged nitrogen (–NH.+– and = N+–). The sorption mechanisms of Cr(VI) were identified, including electrostatic interaction with surface protonated nitrogen (N+), ion exchange between the doped Cl− ions and Cr(VI), chemical decrease of the Cr(VI) to Cr(III) by the iron valence cycle and efficient electron transfer of Ppy/PANI/FBC, as well as surface complexation by amine and oxygen-containing groups. More importantly, 97.98% Cr(VI) was efficiently removed in 20 min by coupling a photocatalytic reaction, also providing a novel idea for the practical use of adsorbents in wastewater treatment.

Enhancing catalytic activity of NdFeO3 perovskite by tuning A-site cation deficiency for oxygen evolution reaction

Electrochemical water splitting got much attention because of its great promising electrochemical technology to generate sustainable and renewable energy resources. In this aim, we have prepared a novel series of electrocatalysts Nd1-xFeO3 (x = 0.0, 0.05, 0.1, 0.15) by sol-gel method. The effect of the deficiency in the A-site on the structure, morphology, surface and electrocatalytic activity of these perovskites were studied by means of XRD, XPS, MEB, LSV, EIS and chronopotentiometric measurements. Among all the samples, Nd0.9FeO3 (denoted NF10) exhibits the higher catalytic activity with a low overpotential of 370 mV at a current density of 10 mA cm−2, a small Tafel slope of 79 mV dec−1 and a good electrochemical stability in 1 M KOH solution. The OER performance of NF10 can be effectively enhanced by optimizing iron valence and highly oxidative oxygen species (O22−/O−) based on the surface of catalyst. The results of this study indicate that the NF10 electrocatalyst can be considered as a good candidate for the OER in alkaline media.

One-step corrosion method for preparing Ni–Fe layered double hydroxide on nickel foam: Importance of the iron valence state

A facile chloride corrosion method was adopted to synthesize Ni−Fe layered double hydroxide (LDH) materials on Ni foam. Ni–Fe LDH catalysts with varying oxygen evolution reaction (OER) performance were obtained by using different iron salts. The reasons for differences in the OER activity were investigated through experiments and characterizations. Structural characterization results showed that Fe3+ salts generated Ni–Fe LDH on nickel foam (NF), and FeOOH was additionally obtained by Fe2+ salts. Compared with NiFe/NF prepared with ferrous salts precursors, NiFe/NF catalysts produced using ferric salts exhibited markedly enhanced OER performance, presenting lower overpotentials of approximately 290 mV to deliver a current density of 100 mA cm−2 and lower Tafel slopes of approximately 96 mV dec−1 in 1.0 M KOH.

A Novelty Analytical Approach to Determine Oxidation States in Complex Refractory Oxides Containing Iron, Uranium, Cerium and other Mixed Valence Cations

Titrimetry technique has been used for the first time to determine the oxidation state in complex refractory oxides containing iron, uranium, cerium, and other mixed valence cations. In particular, sodium molybdate (3Na2O-4MoO3), used as an oxidative solvent for metal oxides. Cerium (IV) sulfate solution which prepared with sulfuric acid was used as a titrant. The excess Ce (IV) is back titrated with Fe (II) standard solution with indicator ferroin. The mechanism and the results have been interpreted.

Железодефицитные состояния в практике акушера-гинеколога

Deficiency or excess of microelements and vitamins significantly affects the vital activity at each step of human life. This is particularly significant during pregnancy because of immediate and long-term effects on the fetus and newborn. Iron is one of the essential microelements and plays an important role in the mechanisms of biological oxidation. Iron metabolism in the human body is quite complex and impossible without synergy with other metals and vitamins. Iron is most closely related to folic acid and is critical for many vital processes, including embryogenesis. Considering that iron and folic acid deficiencies (leading to anemias in extreme cases) negatively affect pregnancy course, its favorable outcome, and prognosis for a newborn, these conditions are to be addressed. Medications are diverse, they should be selected based on the specificity of iron and folic acid metabolism. Among preparations currently available in Russia, combined ones best meet the requirements (iron valence, iron compounds, association with synergid components, dosage form). KEYWORDS: iron, folic acid, iron-deficiency anemia, folate-deficiency anemia, therapy, combined preparations. FOR CITATION: Mikhelson Ar.A., Lebedenko E.Yu., Gayda O.V. et al. Iron deficiencies in obstetric-gynecologic practice. Russian Journal of Woman and Child Health. 2022;5(2):129–137 (in Russ.). DOI: 10.32364/2618-8430-2022-5-2-129-137.

Statistical analysis of PN clusters in Mo/VFe protein crystals using a bond valence method toward their electronic structures.

Nowadays, large numbers of MoFe proteins have been reported and their crystal data obtained by X-ray crystallography and uploaded to the Protein Data Bank (PDB). By big data analysis using a bond valence method, we make conclusions based on 79 selected PN in all 119 P-clusters of 53 MoFe proteins and 10 P-clusters of 5 VFe proteins from all deposited crystallographic data of the PDB. In the condition of MoFe protein crystals, the resting state PN clusters are proposed to have the formal oxidation state of 2Fe(iii)6Fe(ii), hiding two oxidized electron holes with high electron delocalization. The calculations show that Fe1, Fe2, Fe5, Fe6 and Fe7 perform unequivocally as Fe2+, and Fe3 is remarkably prone to Fe(iii), while Fe4 and Fe8 have different degrees of mixed valences. For PN clusters in VFe protein crystals, Fe1, Fe2, Fe4, Fe5 and Fe6 tend to be Fe2+, but the electron distributions rearrange with Fe7 and Fe8 being more oxidized mixed valences, and Fe3 presenting a little more reductive mixed valence than that in MoFe proteins. In terms of spatial location, Fe3 and Fe6 in P-clusters of MoFe proteins are calculated as the most oxidized and reduced irons, which have the shortest distances from homocitrate in the FeMo-cofactor and [Fe4S4] cluster, respectively, and thus could function as potential electron transport sites. This work shows different electron distributions of PN clusters in Mo/VFe protein crystals, from those obtained from previous data from solution with excess reducing agent from which it was concluded that PN clusters are all ferrous according to Mössbauer and electron paramagnetic resonance spectra.

Study on ultrasonic / hydraulic cavitation field for enhanced degradation of ceflor masonry in water

Based on ultrasonic cavitation, with low concentration of levofloxacin hydrochloride solution and cavitation product analysis, the degradation rules of levofloxacin hydrochloride were studied by ultrasonic, zero valent iron and zero valence iron (US / Fe0). The results showed that zero-valent iron promotes the degradation of levofloxacin hydrochloride solution by ultrasonic cavitation, and the degradation reaction fits the first-order reaction kinetic model, with a degradation rate constant of 6.3710-3min-1. Under the reaction conditions, the biodegradability of levofloxacin hydrochloride solution was significantly improved, and after 270min minutes of the reaction, the solution BOD5 / CODcr was increased from 0 to 0.421.