Fe Increase Research Articles

Dielectric Properties of Nanocrystalline Yttrium Iron Manganites Synthesized by Sol–Gel Method

Hexagonal yttrium manganites, YMnO3, exhibit multiferroic behavior and doping suitable cations at the either Y-site or Mn-sites can significantly influence the structural and electrical properties. Nanocrystalline Fe3+-doped YMnO3 manganites substituting at the Y-sites having the general formula Y1-xFexMnO3 with x = 0, 0.1, 0.15, 0.20, 0.25 were synthesized by sol–gel method and were sintered at 1100 °C for 1 h. X-ray diffraction (XRD) studies confirmed the hexagonal phase of the samples and various structural parameters viz. lattice constant, crystallite size, X-ray density were evaluated from the XRD data. The crystallite size of the nanocrystalite manganites ranges from 39 to 63 nm. Investigation on the dielectric properties such as dielectric constant and dielectric loss of the samples was done using an impedance analyzer. The studies showed large increase in dielectric constant and dielectric loss for higher Fe3+-doped manganites i.e. for x ≥ 0.20. Temperature variation of dielectric properties revealed a ferroelectric phase transitions which shift to lower temperature with the increase of Fe3+ ion substitution.

Study on Defects in Fe-Doped SrTiO3 by Positron Annihilation Lifetime Spectroscopy

SrTi1−xFexO3−δ ceramics were prepared using a traditional solid-state reaction method. From X-ray diffraction (XRD) result, we found that the doped Fe3+ dissolved in the lattice, and no secondary phase was observed. Cation vacancies in perovskite oxides were identified via positron annihilation lifetime spectroscopy (PALS) measurements. Undoped and Fe-doped SrTiO3 ceramics and single-crystal SrTiO3 were measured by PALS at room temperature. The results show that the main defects in undoped SrTiO3 ceramics are Ti-related defects, and the isolated Ti vacancy lifetime is about 183.4 ps. With the increase of Fe3+, the concentration of the Ti vacancies decreases accompanied by the appearance of the V″Sr − nV o ∙∙ (defect association of Sr vacancies and multiple O vacancies) vacancy defect complexes.

Structural, optical properties and photocatalytic activity of Fe3+ doped TiO2 thin films deposited by sol-gel spin coating

Nanocrystalline TiO2: Fe3+ films were deposited using a simple spin coating technique. The effect of Fe3+ on spectroscopic features and photocatalytic activity of films were studied using X-ray diffractometer (XRD), scanning electron microscope (SEM), Energy dispersive X-ray (EDX), high-resolution transmission electron microscope (HR-TEM), Raman spectrometer, UV–Vis and fluorescence spectrophotometer. The XRD of all the TiO2: Fe3+ films exhibits a decrease in the crystallite size with an increase in Fe3+ concentration. The Fe3+ doped TiO2 nanocrystals exhibited a high specific surface area. The HR-TEM images of 1% and 7% Fe doped TiO2 thin films confirmed the average particle size is about 14 and 8 nm respectively. The Raman modes of vibrations present in the TiO2:Fe3+ films also confirms the formation of the anatase phase. The optical bandgap energy of titania decreases from 3.32 to 2.57 eV. The luminescent emission intensity of TiO2: Fe3+ films decreased compare to pure titania film. Moreover, the photocatalytic activity (PCA) of TiO2:x%Fe3+ (x = 0, 1, 3, 5, 7 and 10) catalysts were determined by the decomposition of methylene blue (MB) under irradiation of visible light. The observed results revealed that the optimized Fe3+ doped TiO2 film displayed high PCA. The enhancement of PCA of the films is due to the effect of Fe doping.

Jahn-Teller distortion effects on the transport properties of La0.7Ca0.3Mn1−xFexO3 perovskite NPs

This paper presents an examination of La0.7Ca0.3Mn1−xFexO3 (x = 0, 0.005, 0.01, 0.015 and 0.02) nanoparticles (NPs) with a single perovskite-type structure. Rietveld refinement confirms an orthorhombic structure with Pnma space group symmetry. An increase of the Fe3+ cation in lower concentrations provokes a reduction of the Jahn-Teller distortion, and consequently induces an increase in the tolerance factor, therefore, decreasing its unit-cell volume. The complex-plane impedance results indicated a semiconductor behavior thermally activated between 143 and 300 K. The activation energy () using a small polaron hopping model was found to increase proportionally to the increase in Fe3+-doped concentration. Above Tc, the behavior has been explained based on the VRH model, while in a temperature range below Tc using the SPH model. The findings reveal a strong influence of Fe concentration, which decreases the density of states at the Fermi level.

Effects upon Olive and Changes of its Physiological Status under the Compound Stresses of Ferrum and Zinc

Based on the high value of olive oil, this experiment was carried out in order to study its growth under heavy metal stress. In the experiment, Fe and Zn were used as heavy metal stress factors. Effects of Fe-Zn combined stress on physiological indexes of malondialdehyde (MDA), soluble sugar, SOD, POD, CAT and soluble protein in olive leaves. The results of the last experiment showed that with the increase of Fe2+ and Zn2+ concentration, the activity of POD and CAT showed a trend of increasing first and then decreasing, and the activity of SOD enzyme was always decreased. Malondialdehyde (MDA), soluble sugar content and accommodating protein the content is gradually increasing.

Role of iron in the enhanced reactivity of pulverized Red mud: Analysis by Mössbauer spectroscopy and FTIR spectroscopy

The present study is carried out to investigate the contribution of iron in the hematite phase in enhancing the reactivity of red mud. Compressive strength test was performed on the binder synthesized from both unpulverized and pulverized red mud. The results indicated an increase in strength of the pulverized red mud based binder. Test results of Mössbauer Spectroscopy showed transition of metastable ferrihydrite phase to hematite phase when the red mud was processed. An increase in line-width of the Moessbauer sextet and an increase in the area of doublet of pulverized red mud based binder hinted at the increase in Fe3+ ions which could have replaced Al3+ ions in the geopolymer network. Results of Fourier-Transform Infrared Spectroscopy (FTIR) test validated the Mössbauer Spectroscopy results. The participation of Fe3+ ions in geopolymerisation was confirmed from the reduction of hematite peak (wavenumber at 462 cm−1).

Facile synthesis of Fe3+ doped La2CuO4/LaFeO3 perovskite nanocomposites: Structural, optical, magnetic and catalytic properties

La2CuO4/LaFeO3 perovskite nanocomposites were prepared using a microwave combustion technique. The structural characterization by XRD and Rietveld refinements confirmed that Fe3+ substitution in La2CuO4 (LFC) induced the crystallization of secondary LaFeO3 phase. The orthorhombic/cubic nanostructured composites exhibited an average crystallite size in the range 37–47 nm and 14–39 nm, respectively. FTIR spectra revealed bands at 517, 683, and 561 cm−1, characteristics of perovskites orthorhombic and cubic stretching modes. With the increase in Fe3+ doping concentration, the optical band gap increased gradually. Surface morphology showed nanosized crystalline grains agglomerated with spherical and non-spherical shapes. The doping dependence of the magnetisation indicated magnetic transition from ferromagnetic to the paramagnetic state at room temperature. The bifunctional nanocomposites La2CuO4/LaFeO3 exhibited excellent catalytic performance and better conversion efficiency (conversion 100% and selectivity 98.6%) for glycerol.

Fe3+-doped SnO2 inverse opal with high structural color saturation

The structural color of inverse opal derived from the interaction between visible light and nanostructure is widely known for the extensive selection of materials, excellent light resistance stability, and environmental friendliness. In contrast to the opal structure, the light scattering in inverse opal is higher and results in milky appearance or even lack of color. In this work, we introduced Fe3+ into the structure of SnO2 inverse opal and successfully obtained an Fe3+-doped SnO2 inverse opal with high color saturation. The direct template method was applied, and the fcc arrangement of template spheres was well kept. Because of the charge transfer transition of Fe3+–O2−, Fe3+ absorbed most of the unwanted scattered light, thereby highlighting the band gap color. Meanwhile, the refractive index of inverse opal increased with the increase in Fe3+ content. It enabled the full spectral coverage in the visible region of the highly saturated structural color only by three particle size templates.

Anaerobic batch reactor treating acid mine drainage: Kinetic stability on sulfate and COD removal

The leaching of an acid solution containing metals and dissolved sulfate constitutes an environmental problem known as acid mine drainage (AMD). An anaerobic sequencing batch reactor designed for AMD treatment was evaluated regarding its capacity to accommodate an increase in metals concentrations. Time profiles were performed to verify chemical oxygen demand (COD) and sulfate removal kinetics. The resulting apparent kinetic constant values showed a decrease in the reaction rate at the same time that sulfate removal increased. An increase in Fe2+ concentration from 100 to 400 mg L−1 decreased the sulfate removal rate (KSap) from (0.20 ± 0.03) to (0.072 ± 0.004) h−1, and the COD removal rate (KCODap) from (0.057 ± 0.003) to (0.027 ± 0.002) h−1. Even with the reduction in the COD and sulfate removal rates, the system was stable for the cycle time of 48 h in all operation phases.

Catalytic effect of Fe@Fe2O3 nanowires and Fenton process on carbamazepine removal from aqueous solutions using response surface methodology

Carbamazepine is one of the hydrophilic compounds identified in aquatic environments. Due to toxicity and bio-stability of this psychotropic pharmaceutical in the environment and humans, its removal efficiency and mineralization are important. In this study, synthesized Fe@Fe2O3 nanowires were applied to improve Fenton oxidation process using FeCl3.6H2O and NaBH4. The effects of different parameters such as initial pH, H2O2, FeSO4.7H2O, carbamazepine concentrations, oxidation time, and nanowires dose were evaluated using response surface methodology. After scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffract meter analysis, Fe@Fe2O3 morphology was synthesized in the form of nanowires with diameters of about 40-80 nm. The optimum oxidation conditions for carbamazepine were established at pH= 4.3, reaction time of 45.9 min, nanowire dose of 179.4 mg/L as well as H2O2, FeSO4.7H2O and carbamazepine concentrations of 22, 52.2 and 7.7 mg/L, respectively. The oxidation efficiency (99.5%) achieved under the optimum condition, which was determined by the model, was consistent with the efficiency predicted by the model. The multi-parameter models showed good calibration and prediction abilities with R2= 0.922, R2adj= 0.907, R2pred= 0.868. According to the results, the carbamazepine degradation rate increased with the increase of Fe2+ due to the synergistic effect between Fe@Fe2O3 and Fe2+ on the catalytic decomposition of H2O2 and generation of OH•. It was concluded that the Fenton process based on the Fe@Fe2O3 nanowires can increase the carbamazepine oxidation rate in aqueous solutions. This method can also be used as an effective and pre-treatment process in the conventional treatment plants.

Multifunctional behavior of acceptor-cation substitution at higher doping concentration in PZT ceramics

Abstract The Fe-doped PZT, Pb (Zr, Ti)1-xFexO3, ceramics have gathered plenty of attention because of the interplay of ferroelectric and ferromagnetic properties. In the present study, we report the properties of Pb(Zr0.52Ti0.48)1-xFexO3 prepared by conventional solid-state reaction route with varying Fe3+ doping concentrations, x = 0, 0.05, 0.10, 0.15 and 0.20. Study of X-ray diffraction patterns confirmed the tetragonal crystal structure along with reduction in tetragonality and unit-cell size with doping. It also showed formation of secondary magneto-plumbite phase at higher doping concentrations. The SEM micrographs exhibited decrease in grain size with increase in doping concentration (for x > 0.05). The increase in oxygen vacancies and the formation of secondary magneto-plumbite phase and Fe3+–VO2−–Fe3+ defect dipole complexes introduced with the acceptor (Fe3+) doping, caused clamping of the domain walls and hence reduced the room temperature dielectric constant as the doping concentration was increased. The coexistence of electrical polarization and magnetic moment at room temperature in all PFZT compositions confirmed the multiferroic characteristic in the ceramic samples. Electric polarization (Pr) and coercive fields (Ec) decreased with increase in Fe3+ concentration in PFZT sample. However, magnetization (M) and magnetic coercive fields (Ec) increased with the increasing Fe3+ concentration due to the dominant effect of F-center exchange mechanism in Fe3+–VO2−–Fe3+ and formation of ferromagnetic secondary magneto-plumbite phase.

Oxidation Removal of CO from Flue Gas Using Two Fenton-like Wet Scrubbing Systems

Advanced oxidation removal of carbon monoxide (CO) from flue gas using two Fenton-like wet scrubbing systems was studied in a bubbling scrubber for the first time. Influence of several technological parameters (e.g., H2O2 concentration, Fe3+/Cu2+ concentration, temperature, solution pH, CO inlet concentration, and gas flow rate) on the oxidation removal of CO was evaluated. Free radicals, products, and mechanism of CO oxidation removal were also studied. The results demonstrate that pH and temperature of the solution and concentration of H2O2 have double influence on the removal efficiency of CO. The increase of Fe3+/Cu2+ concentration elevates the removal efficiency of CO. The CO removal efficiency is reduced by raising the CO inlet concentration and the gas flow rate. Hydroxyl radical (•OH) oxidation is proved to be responsible for the oxidation removal of CO in the two studied Fenton-like wet scrubbing systems (H2O2/Cu2+ and H2O2/Fe3+). The main products of CO oxidation removal are bicarbonate, carbonate, and CO2 and can be effectively treated using a simple postprocessing strategy. The new removal process will not produce subsequent pollution, and may even provide a new option for green emission reduction of CO from exhaust gas.

Characteristics and inhibition of mercury re-emission from desulfurization slurry by Fenton reagent

In this paper, the mercury re-emission from desulfurization slurry and mercury distribution in gas-liquid-solid three-phase at different desulfurization slurry parameters were studied. Besides, the inhibition performance of Fenton reagent for mercury re-emission and distribution was also investigated. The results show that the Hg0 would re-emit from desulfurization slurry, and the proportions of mercury in gas-liquid-solid three-phase were about 12.17%, 77.72% and 12.08% at typical desulfurization slurry parameter. The S(IV) concentration (sulfite and/or bisulfite concentration), temperature and pH value of desulfurization slurry had great impacts on mercury re-emission and distribution. The increase of S(IV) concentration weakened the mercury re-emission, increased the proportions of mercury in solid phase and liquid phase. The increase of slurry temperature could intensify the mercury re-emission, increase the proportion of mercury in solid phase, but decrease the proportion of mercury in liquid phase. Higher pH value was favorable for the weakening of mercury re-emission, but would increase the proportion of mercury in solid phase and liquid phase. Moreover, the introduction of Fenton reagent into desulfurization slurry could inhibit the mercury re-emission and some mercury that should be re-emitted before would be restrained in solid phase, leading a slight increase of proportion of mercury in solid phase. The existing of oxygenated free radicals, which were generated from Fenton reagent, was the main reason for the inhibition of mercury re-emission. The increase of Fe2+ and H2O2 concentration was conducive to the promotion of inhibition performance, but the effect gradually to weaken. The appropriate value of Fe2+ concentration was 0.04 mM with the H2O2 concentration of 0.30 mM in experiments. In addition, the better inhibition performance (about 80%) of Fenton reagent for mercury re-emission would be realized at lower S(IV) concentration (1–5 mM), lower temperature (30–40 °C) and lower pH value (4.0–5.0) of slurry.

Tunable Magnetic Phases at Fe3O4/SrTiO3 Oxide Interfaces.

We demonstrate the emergence and control of magnetic phases between magnetite (Fe3O4), a ferrimagnetic halfmetal, and SrTiO3, a transparent nonmagnetic insulator considered the bedrock of oxide-based electronics. The Verwey transition ( TV) was detected to persist from bulk-like down to ultrathin Fe3O4 films, decreasing from 117 ± 4 K (38 nm) to 25 ± 4 K (2 nm), respectively. Element-selective electronic and magnetic properties of the ultrathin films and buried interfaces are studied by angle-dependent hard X-ray photoelectron spectroscopy and X-ray magnetic circular dichroism techniques. We observe a reduction of Fe2+ ions with decreasing film thickness, accompanied by an increase of Fe3+ ions in both tetrahedral and octahedral sites and conclude on the formation of a magnetically active ferrimagnetic 2 u.c. γ-Fe2O3 intralayer. To manipulate the interfacial magnetic phase, a postannealing process causes the controlled reduction of the γ-Fe2O3 that finally leads to stoichiometric and ferrimagnetic Fe3O4/SrTiO3(001) heterointerfaces.

The effect of Fe3+ substitution on the negative magnetization and exchange bias in La0.5Pr0.5CrO3

Abstract The La0.5Pr0.5Cr1−xFexO3 (x = 0, 0.1, 0.3 and 0.5) ceramics are synthesized by a citric acid sol-gel method. The crystal structure, morphology, chemical composition and magnetic properties are studied. The X-ray diffraction patterns show that the ceramics crystalize in orthorhombic structure with space group Pnma. The Rietveld refinement results indicate that the lattice parameters get larger with the increase of Fe3+ doping. By means of magnetic measurements, negative magnetization in positive magnetic field is obtained with the decrease of temperature and positive exchange bias effect is observed after field cooling process in La0.5Pr0.5CrO3. When doping with Fe3+ at the Cr3+ sites, the negative magnetization disappears and the positive exchange bias effect transforms to negative. Meanwhile, the negative exchange bias field gradually decreases and vanishes when the doping value of x reaches 0.5. Based on the positive exchange bias effect, an abnormal magnetic switching phenomenon is obtained without changing the direction of the external field after field cooling process.

N-doped carbon dots/H2O2 chemiluminescence system for selective detection of Fe2+ ion in environmental samples

The nitrogen doped carbon dots (N-CDs) produces strong chemiluminescence (CL)-emission due to hydroxyl radical (•OH) induced electron-hole transition in N-CDs. The Fe2+ has the ability to generate •OH from available hydrogen peroxide (H2O2). Therefore, a pre-mixed N-CDs/H2O2 solution was utilized for selective quantification of Fe2+ in solution via CL-emission. A linear increase in the CL-emission intensity was observed within increase in Fe2+ concentration. The N-CDs/H2O2 system enabled the detection of Fe2+ up to lower concentration of 0.2 × 10−9 M with a linear dynamic range of 1.0 × 10−9–1.0 × 10−6 M. Significantly, no CL-emission was observed when other divalent cations, Al3+, Fe3+, or Cr3+ were injected to this system. Moreover, no interference was observed when a mixed solution of Fe2+ and other cations were introduced to N-CDs/H2O2. The practical evaluation of N-CDs/H2O2 system was demonstrated for detection of Fe2+ in tap, lotus pond, and canal water samples. The easy detection, high sensitivity, and selectivity make this method a significant tool for analysis of Fe2+ in solution.

Ferric/ferrous ratio in silicate melts: a new model for 1 atm data with special emphasis on the effects of melt composition

The effect of MgO and total FeO on ferric/ferrous ratio in model multicomponent silicate melts was investigated experimentally in the temperature range 1300–1500 °C at 1 atm total pressure in air. We demonstrate that the addition of these weak network modifier cations results in an increase of Fe3+/Fe2+ ratio in both mafic and silicic melts. Based on present and published experimental data, a new empirical equation is proposed to predict the ferric/ferrous ratio as a function of oxygen fugacity, temperature and melt composition. In contrast to previous equations, the compositional effect of melts on the Fe3+/Fe2+ ratio is not only modeled by the sum of the molar fraction of the individual oxide components. Additional interactions terms have also been incorporated. The main advantage of the proposed model is its applicability for a wide compositional range. However, its application to felsic melts (> 68 wt% SiO2) is not recommended. Other advantages of this equation and differences when compared with previous models are discussed.

Removal of gaseous hydrogen sulfide using Fenton reagent in a spraying reactor

Removal of gaseous hydrogen sulfide using Fenton solution in a spraying tower was studied systematically. The effects of several key running parameters such as H2O2 concentration, Fe2+ concentration, reaction temperature, solution pH value, hydrogen sulfide concentration and liquid-gas ratio on hydrogen sulfide removal were investigated. Products, free radicals and mechanism of hydrogen sulfide removal were also studied. The results show that an increase in Fe2+ concentration, liquid-gas ratio or solution pH value can increase removal efficiency of hydrogen sulfide. Increasing hydrogen sulfide concentration can reduce removal efficiency of hydrogen sulfide. H2O2 concentration and reaction temperature have double influence on hydrogen sulfide removal removal efficiency. Hydrogen sulfide removal by oxidation of hydroxyl radical (OH) is the main removal pathways. Hydrogen sulfide removal by oxidation of H2O2 and hydrolysis reaction are the secondary removal pathways. The main oxidation products of hydrogen sulfide removal are sulphuric acid and elemental sulfur in solutions.

How Does Fault-Related Alteration of Basalt Affect the Potential for Geological Carbon Sequestration in Basalt Formations?

Basalt is an increasingly attractive target for CO2 storage via mineral trapping, due to its abundance of reactive divalent cations such as Ca2+, Mg2+ and Fe2+. The majority of previous studies into the potential for CO2 storage in basalts have used fresh basalt samples. However, it has generally been beyond of the scope of existing studies to look at the effects of faulted and altered basalt at depth, which might have an effect on CO2 storage estimates, especially in geologically older basalt volumes. In this study, two mugearite basalt samples were collected to assess potential for CO2 reactions: a fresh basalt, and its faulted equivalent (altered by fault-related fluids). The faulted equivalent contains less olivine and clinopyroxene compared with its fresh counterpart, due to fluids altering them to clay minerals during and after faulting. Two batch experiments were conducted in synthetic aquifer water (brine) at 50C and PCO2= 130 bar with the aim of investigating potential change in basalt composition and/or concentration of the brine caused by chemical reactions between the basalt rocks and CO2-saturated brine. After 30 days of reaction, Fe2+, Ca2+, Si4- , Al3+ and Mg2+ were leached from the fresh basalt sample showing a potential dissolution of reactive minerals such as olivine and clinopyroxene minerals from the original sample. In contrast, no changes of Fe2+ concentration were observed in experiments performed for faulted basalt. The increase of Fe2+, Ca2+, Si4- , Al3+ and Mg2+ concentration was higher in the fresh basalt experiment compared with the faulted basalt sample. This is most likely due to less reactive minerals available within the faulted sample, such as olivine and pyroxene, having been partially or completely replaced by clay minerals following faulting. Our study therefore finds that faulted and altered basalt is in general less reactive to CO2 than fresh basalt, and this may have implications for the storage of CO2 via mineral trapping in basalts in geologically old and faulted basalt volumes. If basalt volumes targeted for CO2 storage in the future contain geological faults, bulk estimates for mineral trapping of CO2 should take into account the possibility of a difference in reaction rates across the rock volume, and complete additional lab studies to quantify any difference.

The oxidation of Fe(II) with Cu(II) in acidic sulfate solutions with air at elevated pressures

The oxidation of ferrous ions in acidic sulfate solutions in the presence of cupric ions at elevated air pressures was investigated in a high-intensity gas–liquid contactor. The study was required for the design of the regeneration steps of the novel Vitrisol® desulphurization process. The effects of the Fe2+ concentration, Cu2+ concentration, Fe3+ concentration, initial H2SO4 concentration, and partial oxygen pressure on the reaction rate were determined at three different temperatures, i.e., T = 50 °C, 70 °C, and 90 °C. Most of the experiments were determined to be affected by the mass transfer of oxygen, and therefore true intrinsic kinetics could not be fully determined. An increase in Fe2+ and Cu2+ concentrations, as well as the partial pressure of oxygen and temperature, increased the Fe2+ oxidation rate. H2SO4 did not influence the Fe2+ oxidation rate. An increase in Fe3+ concentration decreased the Fe2+ oxidation rate. Although determined from experiments partially affected by mass transfer, a first order of reaction in Fe2+ was observed, fractional orders in both Cu2+ and O2 were measured, a zero order in H2SO4 was determined, and a negative, fractional order in Fe3+ was obtained. The activation energy was estimated to be 31.3 kJ/mol.