Fe Cations Research Articles

Fabrication of Adsorbed Fe(III) and Structurally Doped Fe(III) in Montmorillonite/TiO2 Composite for Photocatalytic Degradation of Phenol

The Fe(III)-doped montmorillonite (Mt)/TiO2 composites were fabricated by adding Fe(III) during or after the aging of TiO2/Ti(OH)4 sol–gel in Mt, named as xFe-Mt/(1 − x)Fe-TiO2 and Fe/Mt/TiO2, respectively. In the xFe-Mt/(1 − x)Fe-TiO2, Fe(III) cations were expected to be located in the structure of TiO2, in the Mt, and in the interface between them, while Fe(III) ions are physically adsorbed on the surfaces of the composites in the Fe/Mt/TiO2. The narrower energy bandgap (Eg) lower photo-luminescence intensity were observed for the composites compared with TiO2. Better photocatalytic performance for phenol degradation was observed in the Fe/Mt/TiO2. The 94.6% phenol degradation was due to greater charge generation and migration capacity, which was confirmed by photocurrent measurements and electrochemical impedance spectroscopy (EIS). The results of the energy-resolved distribution of electron traps (ERDT) suggested that the Fe/Mt/TiO2 possessed a larger amorphous rutile phase content in direct contact with crystal anatase than that of the xFe-Mt/(1 − x)Fe-TiO2. This component is the fraction that is mainly responsible for the photocatalytic phenol degradation by the composites. As for the xFe-Mt/(1 − x)Fe-TiO2, the active rutile phase was followed by isolated amorphous phases which had larger (Eg) and which did not act as a photocatalyst. Thus, the physically adsorbed Fe(III) enhanced light adsorption and avoided charge recombination, resulting in improved photocatalytic performance. The mechanism of the photocatalytic reaction with the Fe(III)-doped Mt/TiO2 composite was proposed.

A Fast and Easy-To-Go Method for the Preparation of Au Nanocluster and Its Application for Fe(III) Cation Sensing.

In this article, we reported the synthesis and characterization of gold nanoclusters (AuNCs) with a diameter of ∼2 nm. A simple method of microwave-assisted reaction was applied here, with L-cysteine as both reducing agent and stabilizer. The resulting AuNCs were analyzed by means of TEM, XPS, DLS, and IR. Their photophysical performance was then analyzed in detail, including UV-vis absorption, emission, quantum yield, and lifetime. Efficient red emission was observed from these AuNCs, originating from ligand-to-metal nanoparticle core charge transfer (LMNCT). This red emission was found quenchable by Fe(III) cations. The corresponding quenching curve and sensing performance were discussed. An effective working region of 0–80 μM with an LOD of 3.9 μM was finally observed. Their quenching mechanism was revealed as Fe(III) energy competing for the LMNCT process. The novelty and advancement of this work is the simple synthesis and impressive sensing performance, including wide working region, good linearity, and selectivity.

Некоторые термодинамические и кинетические свойства системы H2SO4–H3PO4–H2O–Fe(III)

The values of the electrode potentials of the redox couple Fe(III) / Fe(II) and the half-wave potentials of the reactions Fe3+ + e– = Fe2+ и Fe2+ — e– = Fe3+ on the cyclic voltammogram of a platinum electrode in acid solutions containing Fe(III) salts have been measured to characterize the oxidizing ability of the H2SO4—H3PO4—H2O—Fe(III) system. The values of these experimentally obtained parameters are close. A decrease in the oxidizing ability of H2SO4 and H3PO4 mixtures containing Fe(III) with an increase in the molar fraction of H3PO4 in them occurs due to the formation of Fe(III) complexes with phosphate anions which are inferior to their hydrate and sulfate complexes in the oxidizing ability. The temperature coefficients of the electrode potential (dE / dt) of the redox couple Fe(III) / Fe(II) in the H2SO4—H2O, H2SO4—H3PO4—H2O and H3PO4–H2O systems were determined experimentally. The diffusion coefficients of Fe(III) in the studied solutions were calculated based on the Randles—Shevchik equation. The temperature dependence of the diffusion coefficients of Fe(III) cations is satisfactorily described by the Arrhenius equation. The parameters of this equation are calculated.

Synergistic Effect of Neighboring Fe and Cu Cation Sites Boosts FenCum-BEA Activity for the Continuous Direct Oxidation of Methane to Methanol

Direct oxidation of methane to methanol (DMTM), constituting a major challenge for C1 chemistry, has aroused significant interest. The present work reports the synergistic effect of neighboring [Fe]--[Cu] cations, which can significantly boost the CH3OH productivity (100.9 and 41.9 → 259.1 μmol∙g−1cat∙h−1) and selectivity (0.28 and 17.6% → 71.7%) of the best performing Fe0.6%Cu0.68%-BEA (relative to monomeric Fe1.28%- and Cu1.28%-BEA) during the continuous H2O-mediated N2O DMTM. The combined experimental (in situ FTIR, D2O isotopic tracer technique) and theoretical (DFT, ab initio molecular dynamics (AIMD)) studies reveal deeper mechanistic insights that the synergistic effect of [Fe]--[Cu] can not only significantly favor active O production (ΔG = 0.18 eV), but also efficiently motivate the reaction following a H2O proton-transfer route (ΔG = 0.07 eV), eventually strikingly promoting CH3OH productivity/selectivity. Generally, the proposed strategy by employing the synergistic effect of bimetallic cations to modify DMTM activity would substantially favor other highly efficient catalyst designs.

Optical and magnetic properties of orthoferrite NdFeO3 nanomaterials synthesized by simple co-precipitation method

In this work, orthoferrite NdFeO3 nanomaterials with particle sizes 20-40 nm have been successfully synthesized via a simple co-precipitation method through the hydrolysis of Nd (III) and Fe (III) cations in hot water with 5% NaOH as a precipitating agent. Single-phase NdFeO3 was generated after calcination of the as-prepared powder at 700, 800, and 900 °C for 1 hour. The UV-Vis spectra at room temperature presented strong absorption in the UV-Vis regions (l = 200–400 nm and 400–600 nm) with small band gap energy (Eg = 2.2÷2.5 eV). The obtained NdFeO3 nanomaterials exhibited a hard ferromagnetic behavior with high coercivity (Hc = 600–1600 Oe).

Molecular orbital study of Fe(II) and Fe(III) complexation with salicylate and citrate ligands: Implications for soil biogeochemistry

AbstractThe formation of mineral‐associated organic matter (OM), typically with Fe oxy(hydr)oxide minerals, contributes to the long‐term storage of soil C. However, the changing climate is predicted to alter precipitation frequency and intensity patterns such that soils may experience greater periods of anoxic conditions leading to the reductive dissolution of the Fe oxy(hydr)oxide minerals. This would subject the released OM to microbial decomposition and the Fe cation to react with soil solution constituents. Using salicylate and citrate as model soil ligands, this study uses density functional theory to provide physical insights into the chemical bonds formed between Fe(II) and Fe(III) cations with the organic acids. The ΔG° for the complexation reactions of both salicylate and citrate were negative indicating that the complex formation is energetically favorable. Furthermore, the ΔG0 was more negative for the salicylate ligand as compared with the citrate ligand suggesting that the involvement of carboxyl‐O and phenoxyl‐O to form a complex is more thermodynamically favorable. We show from the molecular electron density data that the bonds involved in the complexation are more electrostatic than covalent in nature. Molecular orbital calculations show that the energies of the highest occupied orbitals of Fe(II)–salicylate and Fe(II)–citrate complexes are less negative than that of the uncomplexed Fe(II)–(H2O)6, suggesting that the complexed Fe(II)–organic species will be preferentially oxidized upon return of the soil to aerobic conditions. Our results provide a more fundamental chemical understanding of the reactions involved in the biogeochemical cycling of soil Fe and C. This knowledge may assist in evaluating the potential role of enhanced soil C sequestration as one approach to mitigate climate change.

Redox performance of Fe2O3/Al2O3 oxygen carrier calcined at different temperature in chemical looping process

Iron-based oxygen carriers often underwent severe phase segregation in the process of chemical looping, resulting in the reduction of the cyclic performance of oxygen carriers. The phase segregation characteristics of Fe2O3/Al2O3 calcined at different temperature (900 °C, 1100 °C, 1300 °C) were investigated in this study. The obtained samples were recorded as 900-FeAl, 1100-FeAl and 1300-FeAl, respectively. XPS results showed that the surface oxygen vacancies of Fe2O3/Al2O3 increased with the increase of calcination temperature. In the redox cycles, the deactivation rate of the three samples were 5.57% (900-FeAl), 6.99% (1100-FeAl) and 31.69% (1300-FeAl), respectively. After 20 cycles, the 1300-FeAl presented serious surface sintering and the largest enrichment degree of surface Fe (137.05%). It can be inferred that the severe enrichment of surface Fe leads to the serious sintering, which aggravates the deactivation of the 1300-FeAl in cyclic reactions. The low calcination temperature (900 °C, 1100 °C) makes the Fe2O3/Al2O3 exhibit rich pore structure, which generates space barrier for the outward migration of Fe cation and inhibits the phase segregation of Fe2O3/Al2O3. The results of this study are of great significance to understand the phase segregation of iron-based oxygen carriers, and provide guiding value for the synthesis of high-performance iron-based oxygen carriers.

Lab-made 3D-printed accessories for spectroscopy and spectroelectrochemistry: a proof of concept to investigate dynamic interfacial and surface phenomena.

3D printing is presentedas an auspicious additive manufacturing technique for diverse interesting applications coupling electrochemistry and spectroscopy techniques, proposing as utilities: a general-purpose module for specular spectroscopy and spectroelectrochemical (SEC) cells for in situ UV-VIS and Raman measures capable of acting in flux or a stationary regime. As a proof of concept, UV-VIS absorption and middle-infrared spectra of an azo dye thin film were collected with the specular module showing characteristic bands according to the literature data. SEC investigations related to the Prussian Blue (PB) film growth on the platinum electrode surface were also investigated. By applying appropriate potentials, the PB film growth was accompanied by a proportional increase in the absorption signal at 700 nm in the UV-VIS region. This signal was related to the intervalence charge transfer from the Fe(II)-C to Fe(III)-N. Moreover, the Raman SEC experiment presented scattering intensity at 2092 and 2156 cm-1, related to the (CN) mode associated with the Fe(II) and Fe(III) cations, which was observed during the thin film growth. In addition, the conversion to the Berlin Green (BG) and Prussian White (PB) forms was monitored while applying the suitable potential and in situ spectroscopic observations of structural changes during the redox processes were also detected as described in the literature. Thus, it is possible to state that the accessories successfully validated in situ spectroelectrochemical dynamic investigations unlocking many other applications in this research field.

Characterizing and Tuning the Properties of Polydiacetylene Films for Sensing Applications.

Self-assembled, polymerized diacetylene (DA) nanostructures and two-dimensional films have been studied over the past two decades for sensor applications because of their straightforward visual readout. DA monomers, when exposed to UV light, polymerize to produce a visibly blue polymer. Blue phase polydiacetylenes (PDAs) when exposed to an external stimuli, such as temperature or UV light, undergo a chromatic phase transition to a fluorescent, visibly red phase. The tunability of the monomer to blue to red chromatic phase transitions by choice of diacetylene monomer in the presence of metal cations is systematically and comprehensively investigated to determine their effects on the properties of PDA Langmuir films. The polymerization kinetics and domain morphology of the PDA films were characterized using polarized fluorescent microscopy, UV-vis-fluorescent spectroscopy, and Fourier transform infrared spectroscopy (FTIR). Increasing the monomer alkyl tail length was found to strongly increase the UV dose necessary to produce optimally blue films and fully red films. A decrease in the polymer domain size was also correlated with longer-tailed DA molecules. Metal cations have a diverse effect on the film behavior. Alkaline-earth metals such as Mg, Ca, and Ba have a negligible effect on the phase transition kinetics but can be used to tune PDA polymer domain sizes. The Ni and Fe cations increase the UV dose necessary to produce red phase PDA films and significantly decrease the polymer domain sizes. The Zn, Cd, and Cu ions exhibit strong directed interactions with the PDA carboxylic acid headgroups, resulting in quenched fluorescence and a unique film morphology. FTIR analysis provides insight into the metal-PDA binding mechanisms and demonstrates that the coordination between the PDA film headgroups and the metal cations can be correlated with changes in the film morphology and kinetics. The findings from these studies will have broad utility for tuning PDA-based sensors for different applications and sensitivity ranges.

A Bifunctional Lead–Iron Oxyfluoride, PbFeO2F, That Drives Photoelectrochemical and Electrochemical Water Oxidation

Introduction Photoelectrochemical water splitting has attracted attention as a method of generating solar fuel, such as hydrogen that is expected to be utilize as a renewable energy carrier and clean fuel of an internal‐combustion engine.1 In the photoanode materials reported so far, ordinary metal oxides require ultraviolet light for operation because of their wide bandgaps (>3 eV), and visible-light-responsive metal oxides need an additional electrochemical bias because their conduction-band minimum is a lower position than the H+/H2 reduction potential. Mixed-anion compounds fascinating recent photocatalyst researchers possess visible-light response because of a narrow bandgap with less electronegative anion species.1,2 However, they are not very stable for water oxidation, because photogenerated holes oxidize the anion species except for oxygen in the compounds. Recently, we have reported an oxyfluoride Pb2Ti2O5.4F1.2 as a stable photoanode material that absorbs visible light at wavelengths as long as ~500 nm.3 The VBM of Pb2Ti2O5.4F1.2 is mainly composed by the O 2p orbitals. As the result, the Pb2Ti2O5.4F1.2 photoanode is essentially stable toward self-oxidation by photogenerated holes. However, this is the sole example of a visible-light-responsive oxyfluoride photoanode. Development of a new oxyfluoride photoanode absorbing visible light is important for enabling the further design of visible-light-responsive photoanode materials. In the present work, a lead–iron oxyfluoride PbFeO2F is applied to a photoanode material and electrocatalyst for water-oxidation. PbFeO2F, which can be synthesized by a high-pressure method,4 has been reported to show a yellow colour. Thus, it is expected to function as a visible-light-responsive photoanode material. Moreover, PbFeO2F containing Fe cation is possible to provide catalytic performance for water oxidation, which means that this material may also function as an electrocatalyst. Results and Discussion According to the previously reported method,4 PbFeO2F powder was synthesized. It was deposited on a fluorine-doped tin oxide (FTO) glass substrate by electrophoresis. The PbFeO2F/FTO electrode was subjected to post-necking treatment by immersing in 0.1 M Ti{OCH(CH3)2}4 –isopropanol solution to deposit TiO2 layer (TiO2/PbFeO2F/FTO electrode), followed by electrodeposition of cobalt phosphate (Co-Pi) cocatalyst (Co-Pi/TiO2/PbFeO2F/FTO electrode). Linear-sweep voltammetry of the as-prepared electrodes in 0.1 M K3PO4 solution was conducted under intermittent visible-light irradiation (Figure 1A). The PbFeO2F/FTO electrode exhibited no photocurrent response. By contrast, a slight photocurrent response was observed for the TiO2/PbFeO2F/FTO electrode because of mainly improved interparticle conductivity in the electrode. Furthermore, a clear anodic photocurrent was observed for the Co-Pi/TiO2/PbFeO2F/FTO electrode. Loading the Co-Pi cocatalyst, known as a water-oxidation promoter, improved charge transfer at the electrode/water interface and charge separation from the surface to the bulk. Besides, the Co-Pi/TiO2/PbFeO2F/FTO electrode exhibited an anodic photocurrent under visible-light irradiation with wavelengths as long as ~600 nm. It indicates that PbFeO2F can function as a photoanode material under a wide range of visible-light wavelengths. Controlled-potential electrolysis with the as-prepared PbFeO2F/FTO electrode was operated at +1.7 V vs. RHE under dark conditions (Figure 1B). The evolved O2 was observed by GC analysis in the measurement. It was almost one-fourth the amount of electrons, which flowed during the electrolysis, giving a high Faradaic efficiency of 97%. This result means that the water oxidation was the major path at the PbFeO2F/FTO electrode. In addition, α-Fe2O3/FTO electrode does not work at this potential because of the larger overpotential than the PbFeO2F/FTO electrode for water oxidation. It reveals that PbFeO2F can also function as an electrocatalyst at a relatively low overpotential for water oxidation. References Seo, H. Nishiyama, T. Yamada and K. Domen, Visible-Light-Responsive Photoanodes for Highly Active, Stable Water Oxidation, Angew. Chem. Int. Ed., 57, 8396 (2018).Miyoshi and K. Maeda, Recent Progress in Mixed‐Anion Materials for Solar Fuel Production, Solar RRL, in press.Hirayama, H. Nakata, H. Wakayama, S. Nishioka, T. Kanazawa, R. Kamata, Y. Ebato, K. Kato, H. Kumagai, A. Yamakata, K. Oka and K. Maeda, Solar-Driven Photoelectrochemical Water Oxidation over an n-Type Lead-Titanium Oxyfluoride Anode, J. Am. Chem. Soc., 141, 17158 (2019).Inaguma, J.-M. Greneche, M.-P. Crosnier-Lopez, T. Katsumata, Y. Calage and J.-L. Fourquet, Structure and Mössbauer Studies of F−O Ordering in Antiferromagnetic Perovskite PbFeO2F, Chem. Mater., 17, 1386 (2005). Figure 1

The mechanisms of fluorescence quenching of carbon dots upon interaction with heavy metal cations

The paper presents the results of a study of the interaction of heavy metal cations Fe3+, Cr3+, Cu2+, Pb2+, Zn2+, Ni2+, Ag+ with carbon dots synthesized by the hydrothermal method in water. It was found that all the studied cations quench the fluorescence of nanoparticles to one degree or another. The series of cations were determined according to the degree of their influence on the fluorescence of carbon dots. The mechanisms of quenching the fluorescence of carbon dots upon interaction with cations have been investigated. It is shown that the quenching of the luminescence of nanoparticles in the presence of the investigated cations of heavy metals has a complex character. The observed changes in the intensity of fluorescence of carbon dots are the result of a superposition of several factors—electrostatic interactions of metal cations with surface fluorophores of carbon dots, aggregation of nanoparticles, and the effect of an inner filter for iron ions.

Influence of polyethylene glycol on the physical properties of Co0.2Fe2.8O4 nanoparticles used as MRI contrast agent; synchrotron radiation Fe K-edge XAFS

We have synthesized and characterized the surface-modified nanoparticles (NPs) of Co0.2Fe2.8O4/x polyethylene glycol (PEG) (x = 0, 10, 20, 30, and 40%). The magnetic behavior was correlated with the electronic and structural properties by combining different techniques such as X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), High Resolution Transmission Electron Microscope (HRTEM), X-ray Absorption Fine structure (XAFS) (X-ray Absorption Near Edge Structure (XANES) & Extended X-ray Absorption Fine structure (EXAFS)), and Vibrating Sample Magnetometer (VSM). We have studied the effect of PEG capping with different percent on the structural, electronic, magnetic properties, and relaxivity r2 of the Co0.2Fe2.8O4 NPs. The value of r2 indicates the efficacy of the system as a Magnetic Resonance Imaging (MRI) contrast agent in vitro. XRD showed that the Co0.2Fe2.8O4 is a monophasic spinel structure. XAFS at Fe K-edge gave information about the oxidation state of Fe cations, their fractions, and site distribution, as well as the first and second neighbors' bond lengths. No pronounced changes appeared in XANES and EXAFS results as the main type, ratio, valence, and occupancy of metal ions were similar for all samples. The relationship between the chemical environment of Fe and Co cations and their influence on the physicochemical features of the target NPs, including magnetic performance and surface morphology, was investigated towards selecting the optimum samples for MRI contrast agent application. Although no significant changes in the magnetic properties or the average, morphological, and local/electronic structures, the compositions of 30% and 40% of PEG show promising results for MRI purposes reflecting the role of PEG as a capping agent.

On the ensemble requirement of fully selective chemical looping methane partial oxidation over La-Fe-based perovskites

The dynamic nature of active sites on La-Fe-based perovskites in chemical looping methane oxidation has been studied. According to experimental observations, the reduction of the oxygen carrier is divided into three stages occurring at different active ensembles where the Fe cations are in different coordination environments. The Mars van Krevelen mechanism formulated by microkinetic analysis describes well the effect of oxygen vacancy on the catalytic performance of LaFeO3. CO2 is not produced by CO oxidation but rather is a primary product of methane oxidation, and the presence of surface oxygen vacancies would dramatically increase the overall energy barrier for total combustion, thus decreasing the selectivity toward CO2. Hence, the Fe coordination environment (and hence the oxygen vacancy concentration) is the key parameter governing the catalyst selectivity, in the sense that methane oxidation can vary from total combustion on the O-rich surface to fully selective partial oxidation on the O-deficient surface.

A Study of CexFe1−xO2 as a Reducible Oxide for the Thermal Hydrogen Production from Water

Thermal water splitting over 1550 °C‐reduced CeO2 and Ce0.95Fe0.05O2−δ is studied. Hydrogen production over Ce0.95Fe0.05O2−δ was found to be equal to which is higher than that observed on CeO2. The reaction kinetics for Ce0.95Fe0.05O2−δ is also found to be faster. The oxides are studied by X‐ray diffraction, temperature programmed reduction, and scanning transmission electron microscopy (STEM). XRD results show that Fe is substituted for Ce4+ in the as prepared oxides. Fe3+ cations substitution also decreases the CeO2 crystallites size. Heating to 1100 °C increases their size, although the Fe‐containing oxide still shows smaller crystallites when compared with CeO2 alone. The activation energy for surface reduction of CeO2, extracted from TPR, is found to be slightly higher (1.58 eV) than that of bulk reduction (1.43 eV). While high resolution TEM and electron energy loss spectroscopy before reaction show that Fe cations are homogenously distributed, those after reaction show in addition to the growth of the crystallites size, Fe segregation to the edges of the crystals, although no detachment of Fe oxide particles is seen. The mechanism of water dissociative adsorption and hydrogen re‐combinative desorption is discussed in which the role of Ce–O–Fe sites is considered.

Enhancing the electrocatalytic activity of Fe phthalocyanines for the oxygen reduction reaction by the presence of axial ligands: Pyridine-functionalized single-walled carbon nanotubes

We have examined the electrocatalytic activity of iron phthalocyanine (FePc) and perchlorinated iron phthalocyanine 16(Cl)FePc for the oxygen reduction reaction (ORR) in alkaline medium with the two molecules either adsorbed on the external surface of single-wall carbon nanotubes (SWCNT) or covalently anchored via an axial pyridine ligand on pyridine-functionalized single-wall carbon nanotubes (py-SWCNT). Regardless of the particular phthalocyanine type, the ORR activity is higher when the substrate is py-SWCNT rather than SWCNT. The Tafel slopes for ORR are very similar for the two Fe macrocyclic complexes attached to SWCNTs in the two different configurations, suggesting a common rate-determining step for the ORR for all four catalysts. It is also observed that, for both the SWCNT and py-SWCNT supports, the ORR activity is higher for 16(Cl)FePc than for FePc. This is attributed to the electron-withdrawing effect of the peripheral and non-peripheral chlorine atoms in the macrocyclic ligand. While FeN4 macrocycles are known to be located on the strong binding side of a volcano correlation including several MN4 species, the chlorine substituents decrease the binding energy of O2 on the central Fe cation, thereby moving up the macrocycle catalyst towards the apex of the volcano correlation. Both the carbon surface and macrocyclic ligand effects were optimized with 16(Cl)FePc attached to py-SWCNT, which is more active than both FePc on SWCNT and FePc on py-SWCNT. Here we show that both the axial ligand and the electron withdrawing groups (-Cl) have a combined collaborative effect in increasing the catalytic activity for ORR of Fe-phthalocyanines confined on the external walls of single-wall carbon nanotubes.

Effect field controlled magnetization in NiFe2O4/SrRuO3/PMN-PT heterostructures for nonvolatile memory applications: XMCD study

Electric-field controlled magnetism is a potential way to realize strong magneto-electric (ME) coupling for nonvolatile memory applications. The electric field induced nonvolatile modulated magnetization was obtained in NiFe2O4/SrRuO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) thin film heterostructures. The collective effect of charge and strain significantly modified the magnetization of the NiFe2O4 layer in NiFe2O4/SrRuO3/PMN-PT heterostructures. The analysis of XMCD data establishes that the cation (Fe3+/Ni2+) redistribution occurs on tetrahedral and octahedral sites in the electric field poled NiFe2O4 films, confirming the coupling between magnetism and ferroelectric properties. The films demonstrate repeatable switching of sign of ME output voltage α (α = dP/dH) in response to the applied positive and negative electric pulse, which can be used to store binary information in the nonvolatile manner. The electric-field-controlled switching of α in thin films offers an energy-efficient approach for low-power-consumption nonvolatile memory devices.

Determining the Role of Fe-Doping on Promoting the Thermochemical Energy Storage Performance of (Mn1- x Fex )3 O4 Spinels.

Mn oxides are promising materials for thermochemical heat store, but slow reoxidation of Mn3 O4 to Mn2 O3 limits efficiency. In contrast, (Mn1- x Fex )3 O4 oxides show an enhanced transformation rate, but fundamental understanding of the role played by Fe cations is lacking. Here, nanoscale characterization of Fe-doped Mn oxides is performed to elucidate how Fe incorporation influences solid-state transformations. X-ray diffraction reveals the presence of two distinct spinel phases, cubic jacobsite and tetragonal hausmannite for samples with more than 10% of Fe. Chemical mapping exposes wide variation of Fe content between grains, but an even distribution within crystallites. Due to the similarities of spinels structures, high-resolution scanning transmission electron microscopy cannot discriminate unambiguously between them, but Fe-enriched crystallites likely correspond to jacobsite. In situ X-ray absorption spectroscopy confirms that increasing Fe content up to 20% boosts the reoxidation rate, leading to the transformation of Mn2+ in the spinel phase to Mn3+ in bixbyite. Extended X-ray absorption fine structure shows that FeO length is larger than MnO,but both electron energy loss spectroscopy and X-ray absorption near edge structure indicate that iron is always present as Fe3+ in octahedral sites. These structural modifications mayfacilitate ionic diffusion during bixbyite formation.

Cu2XSnS4 (X = Mn, Fe, Co) semiconductors: Boltzmann theory and DFT investigations

Cu2XSnS4 (X = Mn, Fe, Co) semiconductor represent one of the most promising quaternary family for the photovoltaic devices. For this purpose, a comparative study of structural, electronic, linear/non-linear optical and thermoelectrical properties of Cu2XSnS4 based on the first-principles calculations and Boltzmann theory was done, using the generalized gradient approximation GGA with applying the Hubbard on-site coulombic correction to Mn, Fe and Co cations. The computation of the lattice constants shows a good agreement with the experimental results, also the simulation of X-ray diffraction (XRD) spectra shows that the compounds have crystallized in the polycrystalline kesterite form with a preferential orientation along (112) plane. The GGA + U method offering that CMTS, CFTS and CCTS materials exhibit a duality ferromagnetic semiconductor behavior. The optical properties showed good optical absorption in order of 20 and 30 (104 cm−1) for the three compounds, and a high optical conductivity in the visible range. Thus, the non-linear optical properties as well as suitable optical band gaps of about 1.44–1.56 eV confirms the applicability of CMTS, CFTS and CCTS materials as absorbent layers in photovoltaic solar cells. In addition, the thermoelectric properties such as electrical conductivity (σ/τ), Seebeck coefficient (S) and power factor (S2σ/τ) as a function of temperature were investigated using Boltztrap package, we have found that CMTS, CFTS and CCTS kesterite materials exhibit p-type behavior and good thermoelectric transport properties in the temperature range of 300 - 800K, therefore, we expect these materials to be potential candidates for clean energy applications.

Available acid consumption capacity of sediments in six water bodies in the Yangtze River Basin in China

Acid-base reactivity is a fundamental property of sediments and is responsible for sediments’ multiple roles in aquatic ecosystems. However, little information currently exists about the composition, magnitude, and change of the available acid consumption capacity (AACC) of sediments. To optimize reaction conditions, we developed operational procedures to determine AACC using base titration to recover surplus acid in suspensions. We characterized the sediment AACC of Dianchi Lake (DL), Daduhe River (DR), Tuojiang River (TR), Honghu Lake (HL), Wuhan Donghu Lake (DhL), and Taihu Lake (TL) in the Yangtze River Basin, China. The procedure demonstrated that reacting 40 mL 0.1 M HCl with fresh sediments equivalent to 1.0 g dry weight for 4 h and recovering surplus acid in the suspension by NaOH titration to an endpoint pH of 3.0 could determine sediment AACC. Sediment AACC in the Yangtze River Basin had high regional variability. The mean magnitude of AACC among sites was ranked DL > DR > DhL > TR > HL > TL, which is extremely similar to their geographical location from the upper to lower reaches of the Yangtze River Basin. Qualitative results from acid titration curves showed that more components contributed to AACC in DL, DR, TR, and DhL sediments than to those in HL and TL sediments. The correlation between AACC and the total amount of multivalent cations released indicated that AACC depended significantly on labile acid-soluble minerals that contain multivalent cations (Fe3+, Fe2+, Ca2+, Al3+, Mg2+, and Mn2+) (p < 0.01). Based on the contribution percentages of multivalent cations to AACC, sediment AACC of six water bodies were divided into two types: Ca-Mg dominated (DL, DR, and TR) and Fe-Al dominated (HL, DhL, and TL). We suggest that sediment AACC complexing with pH can contribute to a better description of the acid-base characteristics of sediments.

Совместное влияние катионов Fe(II) и Fe(III) на коррозию низкоуглеродистой стали в смеси серной и фосфорной кислот, содержащих композиционные ингибиторы на основе ИФХАН-92

Corrosion of 08PS low-carbon steel was studied in a wide temperature range t = 25—100 °C in 1 M H2SO4 + 1 M H3PO4, 2 M H2SO4 и 2 M H3PO4, inhibited by the binary mixture IFKhAN-92 + KNCS (a molar ratio of components 9:1) and a three-component mixture IFKhAN-92 + KNCS + urotropine (9:1:400), in the presence of high concentrations of Fe(III) and Fe(II) salts, as well as in their joint presence. It is shown that under experimental conditions the corrosion inhibitors under study provide effective protection of steel in 1 M H2SO4 + 1 M H3PO4 even in the presence of Fe(III), Fe(II) salts or their mixtures. The highest protective effects are provided by a three-component inhibitor mixture. Under similar conditions in individual 2 M H3PO4 and, especially, 2 M H2SO4, the protective effects of inhibitors are lower. A stronger deceleration of steel corrosion by composite inhibitors based on IFKhAN-92 in H2SO4 + H3PO4 solutions containing Fe(III) salts in comparison with similar solutions of individual H2SO4, is largely due to the binding of Fe(III) cations by phosphate anions into complexes, that significantly reduces their chemical activity and, as a result the corrosion rate of steel.