Valence State Of Iron Research Articles

Overcoming the ultra-high C-rate limitation of LiFeBO3 with careful optimization of carbothermal synthesis conditions

Carbon coating with sucrose as the precursor under a moderate synthesis temperature of 500 °C results in a high-purity monoclinic LiFeBO3 phase. This material has a high specific discharge capacity of 200 mAh/g at 0.02 C, which is close to its theoretical capacity. However, its poor performance at high C-rates limits its utility in electric vehicles. Achieving ultra-high C-rate capability of more than 5 C for LiFeBO3 cathode for lithium-ion batteries is uncommon. To overcome this challenge, this study carefully optimizes the synthesis conditions, such as temperature and reducing atmosphere. In this work we utilize carbothermal synthesis method for modulating the reducing conditions. Usually, the carbothermal reaction is carried out using carbon at high temperatures which leads to the formation of CO and CO2 gases. In our work, we have utilized a mixture of sucrose and oxalic acid as the carbon source, that is intimately mixed with the other precursors to create moderate reducing conditions. Oxalic acid decomposes to generate CO which helps to attain the limited reducing atmosphere condition necessary to retain the low valence state of iron. This is important because the low valence state of iron is essential for a good rate-performance. However, if the amount of carbon source is too low, it can lead to poor rate-performance. On the other hand, if the amount of carbon source is too high, it can generate impurity phases, which can be detrimental to the material’s properties. The optimized sample can deliver electrochemical activity at ultra-high C-rates, even up to 30 C, which is achieved for the first time in this material. Comprehensive spectroscopic analyses reveal that multitude of factors, including improved particle crystallinity and better graphitization, favor the retention of the monoclinic phase during electrochemical cycling. A stable specific discharge capacity of 104 mAh/g at 10 C sets it as a benchmark for this material.

In-situ assemblage of Fe–V–P/graphene aerogel based on prussian blue analogue as a high-performance electrocatalyst for oxygen evolution reaction

The carbon scaffold with high conductivity is suitable to enhance the catalytic activity of prussian blue analogues (PBAs) in oxygen evolution reaction (OER) of water splitting. Herein, a two-step strategy is developed to synthesize Fe–V–P/graphene aerogel based on prussian blue analogue (Fe–V–P/GA) electrocatalysts, which possess dense arrangement of anomalous octahedron structure. In the vanadium-modified PBAs (FeV–PBAs), Fe/V with a series of different molar ratios has been investigated and when the molar ratio of Fe/V is 1:1, the catalyst achieves a fairly high specific surface area expressed by the double-layer capacitance of 5.29 mF cm−2 and requires overpotentials of only 234.0 and 314.3 mV to attain the benchmark current density of 10 and 50 mA cm−2 during OER process. Besides, the catalyst owns satisfactory stability and the current density remains almost constant during stability tests lasting up to 70 h. As revealed via electrochemical kinetics analysis and the spectroscopic measurement, embellished FeV–PBAs not only lead to larger tangible area, more accessible sites and higher durable stability, but also provide formation of high valence state of iron and vanadium species, strong modification of electronic state and faster kinetics. This study provides a novel mode of thinking to consummate the design of 3D construction so as to boost the catalytic effect of transition metal catalysts for efficient oxygen evolution.

The Interrelation between Iron Valence and Oxygen Vacancies in Substituted Orthoferrite La0.67Sr0.33FeO3– during Heat Treatment

In this paper, we studied substituted lanthanum orthoferrite La0.67Sr0.33FeO3– γ by Mössbauer spectroscopy using X-ray diffraction data. A series of vacuum annealings was performed in the temperature range of tann = 200–650°C, after which no significant changes in the structure of the samples were detected. The Mössbauer measurements at room temperature show that the Fe ions are in an average valence statebetween Fe3+ and Fe4+. Upon vacuum annealing, as the temperature tann increased, the average hyperfine magnetic field on the 57Fe nuclei and the isomer shift of the spectrum increased, which is associated with an increase in the number of vacancies and, accordingly, a decrease in the amount of Fe4+. Mössbauer measure-ments at 85 K showed that the average valence state of iron does not manifest itself. The hyperfine parameters of the low-temperature Mössbauer subspectra obtained from the model interpretation indicate that one of them belongs to Fe4+ ions, and the rest belong to Fe3+. The presence in the spectra of several sextets related to Fe3+ ions is due to the appearance of oxygen vacancies (breaking of the Fe3+–O2––Fe exchange bond) and Fe4+ ions (weakening of the Fe3+–O2––Fe exchange bond) in the nearest ionic neighborhood of Fe atoms. Both factors cause a decrease in the hyperfine magnetic field and a change in the isomer shift of the spectrum. As a result of model interpretation of the Mössbauer spectra, the numbers of oxygen vacancies and Fe4+ ions per formula unit depending on vacuum annealing temperature tann were determined for all samples. It wasshown that at tann above 450°C, the process of oxygen leaving the lattice ends and only Fe3+ ions are detected.

Selective sulfuric acid cyclic leaching of vanadium from the calcification roasting pellets of vanadium titanomagnetite

Here, a new method of sulfuric acid cyclic leaching was proposed to selectively leach vanadium from the calcification roasting pellets of vanadium titanomagnetite. Cyclic leaching and conventional heap leaching were compared. The results showed that under the optimal conditions, the leaching rate of vanadium was higher and those of iron and titanium were lower than when using conventional heap leaching. Under the optimal cyclic leaching conditions (acid concentration 3.0 mol/L, liquid: solid ratio 4: 1, temperature 90 °C, and leaching time 100 h), the leaching rate of vanadium reached 80.28%, while the leaching rates of iron and titanium were 1.39% and 1.72%, respectively. After secondary roasting, the crushing strength of the leached pellets reached 2200 N, which meets the requirements for pellets used in blast furnace smelting. In addition, the valence states of vanadium and iron in the pellets before and after leaching and the main phases in the pellets were analyzed and characterized. Most V5+ and Fe2+ leached, while Fe3+ was hardly leached, and main phases in the pellet were unchanged. Furthermore, the leaching kinetics of vanadium during cyclic leaching showed that the reaction rate of vanadium was controlled by solid product diffusion during acid leaching. In this study, vanadium was selectively leached, and iron was obtained by secondary roasting of the pellets, followed by blast furnace ironmaking. This paper provides a new method for the comprehensive utilization of valuable metals in vanadium titanomagnetite.

Interaction between Iron Fluoride and Molten FLiBe

The equilibrium potentials of iron in a LiF-BeF2-FeF2 melt were measured using the EMF method and were dependent upon the temperature and iron fluoride concentrations. The empirical equations for the isotherms and equilibrium polytherms of the iron fluoride concentration were obtained. The cathode polarization of iron fluoride in the molten mixture of lithium and beryllium fluoride was measured using the current switch off method from the stationary state. It was found that in the studied temperature and concentration ranges of iron fluoride in the LiF-BeF2 electrolyte, the valence state of iron in the melt is mainly +2. According to the experimental values of the equilibrium potentials of the iron electrode in the LiF-BeF2-FeF2 melt, the conditional standard potentials of iron were calculated relative to the fluoride reference electrode in the molten mixture of lithium and beryllium fluoride. The conditional standard values of the Gibbs energy change were calculated at the formation of iron difluoride from the element in the form of dilute solutions, as were the thermodynamic values (enthalpy and entropy) when iron difluoride was mixed with LiF-BeF2.

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.

Inducing the SnO2-based electron transport layer into NiFe LDH/NF as efficient catalyst for OER and methanol oxidation reaction

• Introduce the electron transport layer SnO 2 between NiFe LDH and conductive substrate NF was first reported. • SnO 2 nanosheets are interwoven to form a sponge-like 3D structure, which promotes the formation of relatively smaller and thinner NiFe LDH nanosheets, thereby generating more active sites and reducing electron transmission resistance. • It was verified that the electronic structure of Ni and Fe was optimizing via the introduction of SnO 2 . • NiFe LDH@SnO 2 /NF possesses a low overpotential of 234 mV at 10 mA cm −2 for OER and 1.396 V at 10 mA cm −2 for methanol oxidation reaction. In an electrocatalyst with a heterointerface structure, the different interfaces can efficiently adjust the catalyst's conductivity and electron arrangement, thereby enhancing the activity of the electrocatalyst. Ultrathin and smaller NiFe LDH was successfully constructed on the surface of SnO 2 nanosheet supported NF by layer by layer assembly, and exhibits lower overpotential of 234 mV at a current density of 10 mA cm −2 , which only increases by 6.4% even at a high current density of 100 mA cm −2 . The excellent OER activity of catalyst is attributed to the contribution of the semiconductor SnO 2 electron transport layer. Through experiments and characterization, 3d structure SnO 2 nanosheets control the growth of ultra-thin nickel-iron, the hierarchical interface between SnO 2 and NiFe LDH can change the electron arrangement around the iron and nickel active centers at the interface, resulting the valence states of iron slightly increased and Ni 3+ content increased. The result will promote the oxidation of water. Meanwhile, the SnO 2 semiconductor as electron transport layer is conducive to trapping electrons generated in oxidation reaction, promoting electrons transferring from the NiFe LDH active center to the Ni substrate more quickly, and enhance the activity of NiFe LDH. It also shows excellent activity in an electrolyte solution containing 0.5 M methanol and 1 M KOH, and only 1.396 V (vs. RHE) is required to drive a current density of 10 mA cm −2 .

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.

Analysis of Raman, Mossbauer Spectra and Dielectric Behaviour of Sol-Gel Prepared Ni1-xCoxFe2O4 Spinel Ferrites

Single-phase spinel ferrites with formula of Ni1−xCoxFe2O4 where x values are varying from 0 to 1 with 0.25 steps were synthesized by sol-gel technique. Microstructure, cation distribution, valence state of iron and dielectric properties have been discussed. From the deconvoluted Raman spectra the positions of five Raman modes and intensity variation was calculated. Cationic arrangement in A and B sites was estimated from deconvoluted Raman peaks. The characteristic magnetic patterns of ferrites were given by room temperature Mossbauer spectra. Parameters like isomer shift, hyperfine magnetic field, quadrupole shift were estimated for all ferrites after fitting Mossbauer spectra. From XPS (X-ray Photoelectron Spectroscopy) analysis +3 ionic state for iron was found. Dielectric parameters were also studied for ferrites at room temperature. NiFe2O4 and Ni0.75Co0.25Fe2O4 had high values of dielectric permittivity, AC conductivity and loss tangent. The ferrite Ni0.5Co0.5Fe2O4 showed very less dielectric constant and conductivity values and dielectric loss resonance peak was around 1 kHz.

Fe3+ Distribution and Fe3+/ΣFe-Oxygen Fugacity Variations in Kimberlite-Borne Eclogite Xenoliths, with Comments on Clinopyroxene-Garnet Oxy-Thermobarometry

Abstract The valence state of iron in mantle-derived melts, such as mid-ocean ridge basalt, is a useful proxy for oxygen fugacity (ƒO2). On subduction, oceanic crust undergoes metamorphic reactions that alter its initial ƒO2, generating compositional and redox heterogeneity in the supra-subduction zone and in the convecting mantle source of oceanic basalts. Kimberlite-borne eclogite xenoliths with ancient oceanic crustal protoliths represent an important archive to trace these processes in deep time. We determined, by Mössbauer spectroscopy, Fe3+/ΣFe for garnet (0.03–0.15, average 0.08; n = 13) and clinopyroxene (0.05–0.37, average 0.23; n = 11) in bimineralic eclogite xenoliths from the Udachnaya kimberlite pipe (Siberian craton), combined the results with high-quality literature data to estimate bulk Fe3+/ΣFe and ƒO2, assessed associated uncertainties and discussed petrological implications. The incorporation of Fe3+ in, and distribution between, eclogite minerals is controlled by chemical composition (X), temperature (T), pressure (P) and ƒO2. Therefore, Fe3+/ΣFe in garnet alone is an imperfect proxy for bulk Fe3+/ΣFe. Values for the distribution of Fe3+/ΣFe between clinopyroxene and garnet (D(Fe3+/ΣFe)cpx-grt) range from 1.4 ± 0.1 to 20 ± 13 and correlate strongly with the abundance distribution of another polyvalent element, vanadium (r2 = 0.80, n = 28), probably because both vary as a function of X-T–P-ƒO2. This allows to estimate Fe3+/ΣFe in clinopyroxene and bulk rocks (0.01–0.32, average 0.06, n = 159) for the majority of literature data where only garnet Fe3+/ΣFe is known. Low Fe3+/ΣFe is retained in many high-Al2O3 eclogites with plagioclase-rich cumulate protoliths (Eu/Eu*> > 1), despite extended residence in the cratonic lithosphere. Bulk Fe3+/ΣFe increases during mantle metasomatism but is not particularly linked to enrichment in highly incompatible elements. Low grossular content in garnet ensuing from mantle metasomatism, especially at low temperature, limits uptake of Fe3+, which is accommodated in clinopyroxene instead, leading to very high D(Fe3+/ΣFe)cpx-grt. Eclogite oxybarometry requires that Fe3+/ΣFe of only garnet be known, whereby the input temperatures should be calculated with all Fe as Fe2+. For temperatures projected onto regional steady-state geothermal gradients, ƒO2 values relative to the fayalite-magnetite-quartz buffer (∆logƒO2(FMQ)) range from −5.9 to −0.2 (average − 3.1, n = 174), and are too low to stabilise oxidised sulphur in all and oxidised carbon in the vast majority of samples. Thus, ancient oceanic crust was a sink rather than a source of oxygen. In particular CaO-rich eclogite xenoliths occasionally are corundum-bearing and SiO2-undersaturated, typically with silica-deficient clinopyroxene with cations per formula unit <1.97 for 6 O anions, resulting in overestimated ƒO2. For the remaining samples, cryptic metasomatism, with enrichment in highly incompatible elements, is clearly focused in the ƒO2 interval of FMQ−4 to FMQ−3, indicating that mantle metasomatism can have both an oxidising and a reducing effect on eclogite. Unmetasomatised bimineralic eclogites have lower ƒO2 than coesite-bearing ones, reflecting reduction during metamorphism and silica-consuming partial melting of ancient subducted oceanic crust.

Accumulation of Intracellular Ferrous Iron in Inflammatory-Activated Macrophages.

Macrophages are important innate immune cells which can be polarized into heterogeneous populations. The inflammatory-activated M1 cells are known to be involved in all kinds of inflammatory diseases, which were also found to be associated with dysregulation of iron metabolism. While iron overload is known to induce M1 polarization, the valence states of iron and its intracellular dynamics during macrophage inflammatory activation have not been identified. In this study, THP-1-derived macrophages were polarized into M1, M2a, M2b, M2c, and M2d cells, and intracellular ferrous iron (Fe(II)) was measured by our previously developed ultrasensitive Fe(II) fluorescent probe. Significant accumulation of Fe(II) was only observed in M1 cells, which was different from the alterations of total iron. Time-dependent change of intracellular Fe(II) during the inflammatory activation was also consistent with the expression shifts of transferrin receptor CD71, ferrireductase Steap3, and Fe(II) exporter Slc40a1. In addition, accumulation of Fe(II) was also found in the colon macrophages of mice with ulcerative colitis, which was positively correlated to inflammatory phenotypes, including the productions of NO, IL-1β, TNF-α, and IL-6. Collectively, these results demonstrated the specific accumulation of Fe(II) in inflammatory-activated macrophages, which not only enriched our understanding of iron homeostasis in macrophages, but also indicated that Fe(II) could be further developed as a potential biomarker for inflammatory-activated macrophages.

Front Cover: Crystal Structures of Iron‐Based Oxides and Their Catalytic Efficiencies for the Oxygen Evolution Reaction: A Trend in Alkaline Media (ChemElectroChem 9/2022)

The Front Cover illustrates that artificial intelligence facilitates the understanding of science in electrocatalysis on heterogeneous crystalline compounds. Machine learning method demonstrates that alkaline oxygen evolution reaction on iron-based multimetal oxides is uniquely controlled by a structural descriptor, Fe–O bond length, and the trend is generally applicable regardless of chemical compositions, valence states of iron and structural categories of the crystals. More information can be found in the Research Article by Y. Sugawara et al.

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.

Synthesis of ferrian and ferro-saponites: Implications for the structure of (Fe,Mg)-smectites formed under reduced conditions

Abstract Clay minerals are widely distributed on the surface of Earth, Mars, and Ceres in the solar systems. Among numerous clay minerals, smectites can record the history of the environment through the exchange of interlayer cations with those in water or through redox reactions with the atmosphere. Therefore, characterization of chemical compositions and crystal structures of smectites is crucial for revealing the paleoenvironment. For instance, the crystal structure within octahedral sheets of iron-bearing smectites changes to trioctahedral sheets under reduced or dioctahedral sheets under oxidizing conditions. Orbital infrared and X-ray diffraction (XRD) analyses by Mars orbiters/rovers revealed the presence of (Fe,Mg)-smectites on the surface of Mars; however, it has been difficult to characterize the properties of these (Fe,Mg)-smectites, which are rare on the surface of Earth. In this study, we synthesized ferrian (ferric ion-rich) and ferrous (ferrous ion-rich) (Fe,Mg)-saponite and revealed the effect of valence states and iron contents on the crystal structures. These saponites were synthesized using a hydrothermal method under reduced conditions. The crystal structures and valence states of iron were analyzed by XRD, Fourier-transform infrared spectroscopy, transmission electron microscopy, Mössbauer spectroscopy, and X-ray absorption near edge measurements. The synthesized clays were trioctahedral swelling clays and were identified as saponites. The valence state of iron in these synthesized saponites is altered by oxygen and a reducing agent in water; however, the trioctahedral structures are maintained under both oxidizing and reduced conditions, following a reversible reaction. This mechanism can be interpreted by the desorption and adsorption of hydrogen in the hydroxyls of the octahedral sheets of the smectite layers. The maximum basal spacing of the (02l) lattice plane in the octahedral sheets was defined by compiling various smectite data. When the basal spacing of (02l) is larger than the maximum in dioctahedral smectites, smectite can be identified as trioctahedral smectite. The redox state of iron in the octahedral sheet cannot be determined from the basal spacing of (02l). We revealed that the iron content in the trioctahedral sheet has a linear relationship with lattice parameter b. This provides a method to estimate the iron content in saponite from XRD data. The XRD profiles of smectites found at the Yellowknife Bay on Mars can be explained only by trioctahedral smectites, and the iron content in the octahedral sheet is roughly estimated to be 0.5–1.7 in a half-unit cell. These results indicate that the presence of (Fe,Mg)-saponite implies a reduced environment during the formation and that this iron-bearing saponite has both oxidation and reduction capabilities depending on the environment.

Carbothermal reduction synthesis of zero-valent iron and its application as a persulfate activator for ciprofloxacin degradation

• Novel Fe@BC was synthesized by carbothermal reduction method. • Corn straw based-biochar was used as a carbon source to prepare ZVI. • The synthesis process of ZVI was the conversion of Fe 2 O 3 into Fe 3 O 4 , and then into Fe 0 . • Ciprofloxacin was effectively removed by Fe@BC/PS. In the present research, zero-valent iron (ZVI) was synthesized by carbothermal reduction method and its formation mechanism was studied. The obtained material (Fe@BC) was applied as a persulfate (PS) catalyst for ciprofloxacin degradation. Further, Scanning Electron Microscopy (SEM) of Fe@BC has shown that the crystal shape of Fe 2 O 3 changed with the increase in temperature, and also revealed the spherical morphology of ZVI. X-ray Diffraction (XRD) further verified the process of conversion of Fe 2 O 3 to Fe 3 O 4 and then to ZVI. X-ray Photoelectron Spectroscopy (XPS) revealed that the change of iron valence state during the conversion process and the peak area of Fe 2+ increased with sintering temperature. The effect of experimental parameters including pH, Fe@BC dosage, PS concentration and temperature on ciprofloxacin degradation, were thoroughly investigated. The results illustrated that the Fe@BC has excellent catalytic performance and can remove 90.78% of ciprofloxacin within 120 min. Free radical quenching experiments confirmed that the reaction of ciprofloxacin with ∙ OH and SO 4 ∙ - mainly occurs on the Fe@BC surface. Based on the different experiments, it was proposed that degradation mechanism of ciprofloxacin via Fe@BC includes three aspects. Thus, it was found that carbothermal synthesis of Fe@BC is cost effective and potential technology for ciprofloxacin remediation.

HP-PdF2-type FeCl2 as a potential Cl-carrier in the deep Earth

Abstract We report for the first time the formation of a HP-PdF2-type FeCl2 phase (space group Pa3), through high pressure-temperature (P-T) reactions in the hydrous systems (Mg0.6Fe0.4)SiO3–H2O–NaCl and FeO2H–NaCl in a laser-heated diamond-anvil cell up to 108 GPa and 2000 K. Applying single-crystal X-ray diffraction (XRD) analysis to individual submicrometer-sized grains, we have successfully determined the crystal structure of the as-synthesized FeCl2 phase, in agreement with our theoretical structure search results. In situ high P-T XRD data revealed the substitution of Cl for OH(O) in such a cubic Pa3 structure, demonstrating that this topology is a potential host for both H and Cl in the deep Earth. The chemical analysis of the recovered sample showed that the post-perovskite phase contains considerable amounts of Na2O and Fe2O3. The coexistence of the cubic FeCl2 phase and post-perovskite suggests that the lowermost mantle could be a potential reservoir of Cl. The possible presence of volatiles such as H and Cl in the deep lower mantle would impact the composition and iron valence state of the post-perovskite phase.

Improving the reliability of Fe- and S-XANES measurements in silicate glasses: Correcting beam damage and identifying Fe-oxide nanolites in hydrous and anhydrous melt inclusions

The redox state of silicate melts influences crystallization, element partitioning, and degassing behavior. Synchrotron-based micro-X-ray absorption near edge structure (μXANES) spectroscopy has emerged as a powerful tool for determining redox conditions through the direct measurement of speciation of multivalent elements such as iron and sulfur in silicate glasses. In particular, the high spatial resolution afforded by synchrotron μXANES makes it one of the few techniques available for determining redox conditions in melt inclusions, which can provide insights into pre-eruptive melt properties. However, the small size of melt inclusions, the deep penetration of X-rays, and irradiation-induced beam damage make μXANES measurements in melt inclusions challenging. Here we present data showing the rapid occurrence of Fe- and S-μXANES beam damage in experimental glasses, mid-ocean ridge basalt glasses, and olivine-hosted melt inclusions from the southern Cascade arc and Kīlauea Volcano and develop approaches to recognize and correct for beam damage through repeated rapid analyses. By applying a time-dependent correction to a series of rapid measurements (~82 s/scan) of Fe-μXANES pre-edge centroid positions, irradiation-induced photo-oxidation (Fe2+ to Fe3+) can be corrected back to undamaged initial Fe3+/ΣFe even in damage-susceptible hydrous glasses. Using this beam damage correction technique, hydrous basaltic melt inclusions from the southern Cascades have Fe3+/ΣFe values that are ~0.036 lower (corresponding to -0.5 log units lower oxygen fugacity) than would have been indicated by standard Fe-μXANES measurements. Repeated, rapid analyses (150–300 s/scan) were also used to identify S-μXANES beam damage (photo-reduction of S6+ to S4+), which was corrected with a peak fitting method to restore initial S6+/ΣS. We observe that S-μXANES beam damage can occur rapidly even in low-H2O mid-ocean ridge basaltic glasses and melt inclusions from Kīlauea Volcano, which are otherwise stable during even prolonged Fe-μXANES analyses. By mitigating and correcting for sulfur photo-reduction, we conclude that some mid-ocean ridge basaltic glasses contain 0.08–0.09 S6+/ΣS, which is more sulfate than might be expected based on the reduced oxidation state of these glasses (near the fayalite-magnetite-quartz oxygen buffer). Using beam damage identification and correction techniques, the valence states of iron and sulfur can be accurately measured even in beam damage-susceptible glasses and melt inclusions. Finally, using Fe-μXANES, we demonstrate the presence of Fe-oxide nanolites within otherwise glassy, naturally quenched melt inclusions, which can complicate determination of iron valence state in affected glasses.

Valence control of charge and orbital frustrated system YbFe2O4 with electrochemical Li+ intercalation

We report an attempt valence control of the mixed valence iron triangular oxide YbFe2O4 to develop an effective technique controling the frustration of charges in strongly correlated electron systems. The electrochemical doping of Li + into YbFe2O4 was examined on a cell-type sample similar to the Li-ion secondary battery cell. Systematic changes in the lattice constant and Fe – Fe and Fe–Yb distance were observed with Li doping. Maximum value of the doping was over 300 mAh/g. An EXAFS experiment indicated that Li positioned between Yb octahedron layer (U-layer) and Fe-bipyramidal layer (W-layer). However, detailed change of iron valence state of YbFe2O4was not clearly observed because of the superimpose of the signal from iron metal nano particles in XANES observation. We discuss that the uncertainty might arise from the inhomogeneous distribution of the sample particle size, which might prevent the homogeneous doping of Li because the doping occurs on the surface of each nano-particles.

Towards in Operando XAS Investigation of CO2 Electrolysis in Solid Oxide Cells: Synchrotron Studies of La0.3Ca0.7Fe0.7Cr0.3O3-δ Perovskites

Solid oxide cells (SOCs) are poised to provide a significant contribution to the emerging field of green technology. SOCs could form the basis for a closed loop, sustainable energy system in which fuel cells generate power efficiently and any waste products are converted back into fuel or useful products.Early solid oxide fuel cell (SOFC) systems utilized ceramic-metal composites, such as Ni-YSZ, as the fuel electrodes. Ni metal provides electronic conduction while YSZ plays the role of oxygen anion conductor. This requires the catalyst target (e.g., H2) to come into contact with both Ni and YSZ, forming a so-called triple phase boundary.Cermet systems perform well but are typically unstable under oxidizing conditions and are susceptible to passivating phenomena, such as sulfur poisoning. Since then, mixed ionic and electronic conductors (MIECs) have been developed, where a single material such as a perovskite replaces both cermet components. The gas-MIEC interface acts as a double phase boundary, theoretically providing electrochemical reaction sites on the entire surface of the electrode. This makes them less susceptible to poisoning by impurities, and the oxide composition can be tailored to improve stability in reducing or oxidizing environments. SOFCs based on mixed-conducting catalysts have shown marked performance increases over room-temperature fuel cells in ORR catalysis, often with an order of magnitude advantage in current response. Further work led to MIEC compositions being used at SOFC fuel electrodes, and more recently, as active catalysts for the carbon dioxide reduction (CO2RR) reaction in electrolysis cells (SOECs).Our research group recently demonstrated that the perovskite material, La0.3Ca0.7Fe0.7Cr0.3O3-δ (LCFCr), shows excellent stability and activity during the OER and ORR. This single composition is also highly active for the CO2RR, opening the door for reversible and symmetrical SOC devices (RSOFCs) that promise to greatly reduce device complexity. This should ease the difficulty of scaling up these technologies for industrial applications. While we have observed performance gains in both SOC modes of operation using LCFCr, we sought to better understand the underlying mechanism of catalysis in CO2 electrolysis. This has led us to begin a thorough investigation of LCFCr-based reversible SOFCs using synchrotron x-ray absorption spectroscopy (XAS), culminating with in operando studies, where CO2 electrolysis can be tracked as it happens in fully operational electrolysis cells. Harsh operating conditions have made in situ or in operando SOC studies more challenging than those for RT cells, which also share the barriers of access to electrode surfaces and the attenuation effect of feedstocks on incident energy used for spectroscopy.This presentation will introduce our initial efforts in synchrotron XAS studies of the as-synthesized LCFCr material, which was prepared by combustion synthesis of precursor metal nitrates. Synchrotron energy provided by the Canadian Light Source (CLS) was used to study powder samples of this composition; experiments were carried out at both hard (SXRMB) and soft (SGM) x-ray sources at the CLS. Preliminary experiments consisted of ex situ XAS testing of samples heat treated using conditions similar to those encountered in operation (800 °C in air or CO2). When compared to spectra of as-synthesized compositions, this provides a conventional “before and after” comparison and has demonstrated that overall changes in oxidation state and coordination environment could be observed. In situ testing was also carried out at SXRMB on La0.3Ca0.7Fe0.7Cr0.3O3-δ powder samples. Samples were placed in a “six-shot” apparatus that provided a versatile test bed for semi-realistic conditions. In these studies, materials were heated in air to 800 °C, while XANES spectra (Fe K-edge) were collected simultaneously. This process was repeated as the gas was changed to CO2, and then upon cooling. These transitionary XAS measurements allowed us to observe both structure and valence state of the material responding in real time. The results showed changes in the pre-edge feature and edge intensity that we have attributed to a change in local vacancy concentration around Fe metal centers. At each stable set of conditions, full EXAFS spectra were collected for all four metals; initial analysis suggests that chromium undergoes redox changes while the iron valence state remains largely unchanged. Together, this set of experiments is allowing us to assemble a dynamic picture of the chemical and structural state of the catalyst during operation.This study underscores the value of in situ and in operando investigation of SOC catalysts compared to traditional ex situ analysis. Insights into efficient SOC electrolysis of CO2 could give us the ability to reduce carbon emissions. It is both urgent and vital that the underlying mechanisms are understood more completely.