Fe2O3 System Research Articles

SODA LIME SILICATE GLASSES CONTAINING IRON OXIDE - IN VITRO EVALUATION

Three glasses with different iron oxide concentrations (between 5 and 8.1 mol %) were obtained in the CaO - Na2O - SiO2 - Fe2O3 system by using conventional melting-quenching technique. The amorphous nature of the synthesized materials is confirmed by X-ray diffraction analysis, XRD. The physico-chemical and structural characterization of the glasses was performed by measuring their density, refractive indices, as well as by calculating the molar volume, oxygen packing density and recording the infrared spectra by Fourier Transformed Infrared Spectroscopy, FT-IR, respectively. The glasses were evaluated in vitro by examining bone-like apatite formation on their surfaces in a simulated body fluid, SBF. The structural changes in the glasses during the in-vitro test were traced by means of FT-IR and Scanning Electron Microscopy, SEM. The solutions were examined by Inductively Coupled Plasma Optical Emission Spectroscopy, ICP-OES to determine the ion exchange between the glasses and the starting SBF and the corresponding effect on the pH was also recorded.

Development of binders based on the СаО–Fe2O3 system

The object of research is the processes of structure formation and modeling of the properties of a specialized binder. The development of new binding materials based on production waste with high early strength indicators could make it possible to speed up construction period and is one of the urgent tasks at present. This study focused on the creation of binders based on the СаО–Fe2O3 system. The developed binder of the СаО–Fe2O3 system has the following composition: limestone – 26 %; red slime – 74 %, which has a dense fine-porous structure and high early strength indicators – 22.5 MPa with a density of 1960 kg/m3. There is also an increase in the average density of samples annealed at a temperature of 1200 ℃ for 60 minutes, ground and mixed with water, in comparison with samples fired at 1100 ℃ for 60 minutes, by 500 kg/m3, due to new formations. The prospect of using modified composite binders with special functional properties has been substantiated. The use of production waste based on the СаО-Fe2O3 system could make it possible to obtain materials with high physical and mechanical properties, which makes them promising for application in various areas of the construction industry. The development of such binders will help reduce the environmental impact of the construction industry, owing to the use of affordable and effective components. This approach will not only contribute to the improvement of the quality of building materials but also help reduce the ecological burden on the environment by using alternative resources and industrial waste. The developed binder could be used for the development of solutions for 3d printing, as well as repair of concrete coatings

Composite catalysts based on the CaO‒Fe2O3 system for the oxidative conversion of methane

The catalysts of the CaO‒Fe2O3 system with Fe2O3 content in the range of 0‒100 wt.% were synthesized by the solid state method at 900 and 1000 °C. The catalysts were characterized by XRD and SEM‒EDX methods, and their activity in the oxidative conversion of methane at 750 °C was studied. The phase composition of the catalysts corresponds to the CaO‒Ca2Fe2O5, Ca2Fe2O5‒CaFe2O4 and CaFe2O4‒a-Fe2O3 regions of the phase diagram. The specific catalytic activity dependence on the Fe2O3 content has an extremum. The CaO‒Ca2Fe2O5 catalysts have the highest reactivity and the active centers in them are localized at the phase interface. The activity of Ca2Fe2O5–CaFe2O4 samples decreases with an increase in the CaFe2O4 content. The CaFe2O4‒a-Fe2O3 catalysts have a core-shell structure and exhibit the least activity, which is determined by the CaFe2O4 shell.

Preparation and application of SiO2–Fe2O3 and SiO2–Fe2O3–Fe for soot oxidation: A step toward decarbonization by reducing soot particle emissions

The article presents a method for obtaining catalytic systems: SiO2–Fe2O3, SiO2–Fe2O3–Fe and verification of their catalytic properties in the oxidation process of technical soot N550. The process of immobilization of Fe3+ ions on microsilica-SiO2 was investigated in the batch system (equilibrium, kinetics, thermodynamics). The process was aimed at obtaining a system with a developed surface and using less iron while maintaining the same catalysis active surface. In the next stages, the SiO2–Fe3+ systems were modified to obtain SiO2–Fe2O3 and SiO2–Fe2O3–Fe materials, which exhibited catalytic properties. To obtain catalytic systems, the processes of Fe3+ ions sorption, iron oxide precipitation - Fe2O3 and Fe reduction using a plant extract were used. Catalytic systems were applied in the N550 technical soot oxidation process to reduce the conversion temperature and increase its efficiency. The soot oxidation process was carried out in a muffle furnace using variable process parameters, i.e. temperature (450, 475, 500, 525 and 550oC), time (1, 2 and 3h), type of catalytic system (SiO2–Fe2O3, SiO2–Fe2O3–Fe) and its % content relative to the constant mass of soot (0, 10, 20 and 30%). The greatest increase in the conversion efficiency of soot particles was obtained using the SiO2–Fe2O3 system with a content of 20% at a temperature of 550oC and for 3 h.

Understanding and optimizing the sensitization of anatase titanium dioxide surface with hematite clusters

The presence of hematite (Fe2O3) clusters at low coverage on titanium dioxide (TiO2) surface has been observed to enhance photocatalytic activity, while excess loading of hematite is detrimental. We conduct a comprehensive density functional theory study of Fe2O3 clusters adsorbed on the anatase TiO2 (101) surface to investigate the effect of Fe2O3 on TiO2. Our study shows that TiO2 exhibits improved photocatalytic properties with hematite clusters at low coverage, as evidenced by a systematic study conducted by increasing the number of cluster adsorbates. The adsorption of the clusters generates impurity states in the band gap improving light absorption and consequently affecting the charge transfer dynamics. Furthermore, the presence of hematite clusters enhances the activity of TiO2 in the hydrogen evolution reaction. The Fe valence mixing present in some clusters leads to a significant increase in H2 evolution rate compared with the fixed +3 valence of Fe in hematite. We also investigate the effect of oxygen defects and find extensive modifications in the electronic properties and local magnetism of the TiO2 -Fe2O3 system, demonstrating the wide-ranging effect of oxygen defects in the combined system.

Ginger extract loaded Fe2O3/MgO-doped hydroxyapatite: Evaluation of biological properties for bone-tissue engineering.

Since antiquity, the medicinal properties of naturally sourced biomolecules such as ginger (Zingiber officinale) extract are documented in the traditional Indian and Chinese medical systems. However, limited work is performed to assess the potential of ginger extracts for bone-tissue engineering. Our work demonstrates the direct incorporation of ginger extract on iron oxide-magnesium oxide (Fe2O3 and MgO) co-doped hydroxyapatite (HA) for enhancement in the biological properties. The addition of Fe2O3 and MgO co-doping system and ginger extract with HA increases the osteoblast viability up to ~ 1.4 times at day 11. The presence of ginger extract leads to up to ~ 9 times MG-63 cell viability reduction. The co-doping does not adversely affect the release of ginger extract from the graft surface in the biological medium at pH 7.4 for up to 28 days. Assessment of antibacterial efficacy according to the modified ISO 22196: 2011 standard method indicates that the combined effects of Fe2O3, MgO, and ginger extract lead to ~ 82 % more bacterial cell reduction, compared to the control HA against S. aureus. These ginger extract-loaded artificial bone grafts with enhanced biological properties may be utilized as a localized site-specific delivery vehicle for various bone tissue engineering applications.

Doping of large amount tetravalent Ge ions into Fe2O3 structure and experimental results on modified structural, optical and electronic properties

We report the doping of high concentration of tetravalent Ge4+ ions (5 mol % for x = 0.05–30 mol % for x = 0.30) at the Fe3+ sites of Fe2-xGexO3 system by chemical coprecipitation route. The charge state of Fe and Ge ions has been modified into lower values, in addition to their normal +3 and + 4 states, to stabilize the rhombohedral phase of hematite (α-Fe2O3) structure. X-ray photoelectron spectra and optical band gap measurements indicated a combination of ionic and covalence character of metal-oxygen bonds as an effect of Ge doping in the hematite structure. The Ge doped hematite samples have exhibited semiconductor properties with band gap of 1.50–4.70 eV and remarkably enhanced electrical conductivity (σ ∼ 10−4 S/m) in comparison to α-Fe2O3 (10−11 S/m). The results confirmed the strategy of enhancing electrical conductivity in hematite structure by doping of tetravalent cations. The thermo-conductivity measurements using warming and cooling modes showed highly irreversible feature at higher temperatures. Some of the samples indicated metal-like state at lower temperature, in addition to semiconductor state at higher temperatures. It has been understood that combination of ionic and covalence character of the metal-oxygen bonds has played an important role in modifying the semiconductor properties in Ge doped Fe2O3 system.

Actual chemical composition of 123-phase and revised phase diagram for the Y2O3 – BaO – Fe2O3 system

A systematic study of phase equilibria of the Y2O3 – BaO – Fe2O3 system in the vicinity of YBa2Fe3O8+δ reveals that the actual composition of the 123-type oxide differs from the ideal one. It is shown that a single-phase oxide with a 123-type structure can be obtained at 1373 ​K in air only with a slight deficit of Ba and an excess of both Y and Fe components. The overall formula of the single-phase 123-type oxide is written as Y1.05Ba1.92Fe3.03O8+δ. The composition of one more complex oxide, which is absent in the reported earlier phase diagram, is also found to be Ba-deficient; it can be presented as Y1.04Ba0.96FeO4. As a result, the revised version of phase diagram for the Y2O3 – BaO – Fe2O3 system is constructed at 1373 ​K in air.

Application of Mössbauer spectroscopy and FT-IR to describe coordination of amphoteric ions in structure of glasses from the SiO2–Na2O–MgO–CaO–Al2O3–Fe2O3 system

Glasses from the SiO2-Na2O-MgO-CaO-Al2O3-Fe2O3 system include, among others, amorphous materials obtained by the vitrification of industrial slags, ashes, dusts, but also various hazardous wastes (e.g. asbestos) containing a high proportion of Al2O3 and Fe2O3 oxides in their basic composition. The main goal of the work was to evaluate the method of incorporation into the glass structure of amphoteric ions (Fe2+, Fe3+ and Al3+) incorporation into the glass structure and its effect on the glass viscosity. A mixture of 10 wt% and 12 wt% pure Fe2O3 powder and float glass cullet was melted in an electric furnace at 1450°C for 4 hours and then poured onto a steel plate. X-ray results confirmed the amorphous structure of all molten glasses. The viscosity of glasses was examined using linear dilatometry and high-temperature microscopy. Fourier transform infrared (FT-IR) and Mössbauer spectroscopy were used to study the coordination number of amphoteric ions and how they were incorporated into the glass lattice. The research confirmed that the increase in the share of amphoteric metal ions in the coordination number 4 causes the incorporation of these ions into the glass network. Metal ions Fe2+, Fe3+ and Al3+ occurring in tetrahedral coordination, depositing in the glass network next to Si4+ ions, strengthen the network and, as a result, can increase its viscosity in the range of forming temperatures.

Bisthiourea immobilized UiO-66-NH2 supported Fe2O3 nanoparticles to accelerate dual centers Fenton-like reaction

In this paper, an efficient catalyst UiO-66-BTU/Fe2O3 was synthesized by using bisthiourea modified zirconium-based metal organic framework (Zr-MOF). The UiO-66-BTU/Fe2O3 system features outstanding Fenton-like activity that is 22.84 times and 12.91 times larger than Fe2O3 and conventional UiO-66-NH2/Fe2O3 system. It also exhibits good stability, broad pH range and recycle ability. Through comprehensive mechanistic investigations, we have ascribed the excellent catalytic performance of the UiO-66-BTU/Fe2O3 system to 1O2 and HO as the reactive intermediates, cause Zr centers can make complexation with Fe to form dual centers. Meanwhile, the CS on the bisthiourea can form Fe-S-C bonds with Fe2O3, reducing the redox potential of Fe(III)/Fe(II) and influencing the decomposing of H2O2, which indirectly regulate the interaction between Fe and Zr to accelerate electron transfer during the reaction. This work exhibits the design and understanding of the iron oxides incorporated in modified MOFs with excellent Fenton-like catalytic performance to remove phenoxy acid herbicides.

P25-inspired α/γ-Fe2O3 isoelement heterostructures for visible-light photocatalysis: Optimization of crystalline ratios and mechanism investigation

Heterojunction with same elements but different types of semiconductors is a special material which is convenient for fabrication and industrialization. In this work, a series of α/γ-Fe2O3 isoelement heterostructures with different crystal contents (γ-Fe2O3, 10 % α-Fe2O3/90 % γ-Fe2O3, 33 % α-Fe2O3/67 % γ-Fe2O3, 55 % α-Fe2O3/45 % γ-Fe2O3, 78 % α-Fe2O3/22 % γ-Fe2O3 and α-Fe2O3) were constructed by hydrothermal method combined with controlled partial annealing process. Physicochemical analyses including XRD, TEM, XPS, BET, UV-Vis, PL spectra and ESR analyses were applied to investigate the advantages of isoelement α/γ-Fe2O3 compared with the pure single-crystalline Fe2O3. Benefiting from the enlarged specific surface area and staggered band structure, the fabricated heterostructure with 78 wt% α-Fe2O3 content exhibited more efficient separation of charge carriers and thus superior photodegradation efficiency than pure Fe2O3 under visible-light irradiation. Different from TiO2-based P25 heterostructures, Fe2O3 system possesses narrower bandgap and cannot efficiently consumed the excited holes. As a result, the accumulated h+ would inhibit the further separation of excitons with photocatalysis proceeding and thus induce insufficient driving force for the increment of photocatalytic ability like P25. The results presented in this work would be conducive to the rational design of staggered heterostructures.

CeFeO3-CeO2-Fe2O3 Systems: Synthesis by Solution Combustion Method and Catalytic Performance in CO2 Hydrogenation.

Rare-earth orthoferrites have found wide application in thermocatalytic reduction-oxidation processes. Much less attention has been paid, however, to the production of CeFeO3, as well as to the study of its physicochemical and catalytic properties, in particular, in the promising process of CO2 utilization by hydrogenation to CO and hydrocarbons. This study presents the results of a study on the synthesis of CeFeO3 by solution combustion synthesis (SCS) using various fuels, fuel-to-oxidizer ratios, and additives. The SCS products were characterized by XRD, FTIR, N2-physisorption, SEM, DTA-TGA, and H2-TPR. It has been established that glycine provides the best yield of CeFeO3, while the addition of NH4NO3 promotes an increase in the amount of CeFeO3 by 7-12 wt%. In addition, the synthesis of CeFeO3 with the participation of NH4NO3 makes it possible to surpass the activity of the CeO2-Fe2O3 system at low temperatures (300-400 °C), as well as to increase selectivity to hydrocarbons. The observed effects are due to the increased gas evolution and ejection of reactive FeOx nanoparticles on the surface of crystallites, and an increase in the surface defects. CeFeO3 obtained in this study allows for achieving higher CO2 conversion compared to LaFeO3 at 600 °C.

Development and validation of a real-time and non-destructive method for direct measurement of solid mixture based on reflection spectra

The Belt and Road countries are facing low resource exploitation efficiency and environmental pollution problems in the field of industrialization and production. Real-time and accurate determination of solid composition is urgently required. Herein, a new quantitative model and method were developed based on the mass conservation law, the elementary reaction and interaction between light and substance. Charge-coupled Device receiver was used to directly measure the solids and quickly obtain the spectral reflectance. According to the difference of spectral reflectance, partial least squares mathematical iterative fitting is utilized to optimize the model parameters based on the relationship between concentration and reflectance at 380–740 nm. It is applied to three typical mineral systems: I. Fe2O3 and Fe3O4 system with different metal valence states; II. ZnO and ZnS system with different anions; and III. Fe2O3 and ZnS system with different element compositions. The best characteristic wavelengths are 560 nm, 720 nm and 680 nm. The goodness of fit is 0.97–0.99 with root mean square less than 0.04, standard recoveries 98%–108%, and relative error of blind sample less than 5%. Compared with some conventional solid analysis methods, this method has the advantages of real-time, non-destructive, no pretreatment and no secondary pollution.

Density, viscosity and surface tension of high-silicate CaO–SiO2 and CaO–SiO2–Fe2O3 slags derived by aerodynamic levitation. The behavior of Fe3+ in high-silicate melts

Thermophysical data for liquid slag are required for the optimization and control of metallurgical processes. The density, surface tension and viscosity were measured by employing aerodynamic levitation under contactless conditions. The high-silicate slag (44 and 63 mass-% of SiO2) of the CaO–SiO2 and CaO–SiO2–Fe2O3 systems (with 5 and 10 mass-% Fe2O3) was investigated under (80% Ar + 20% O2) gas atmosphere. The temperature ranges were between 800 °C and 2000 °C for the density and 1500 °C–2000 °C for surface tension and viscosity measurements. The influence of the CaO/SiO2 ratio on the investigated properties and the behavior of Fe3+ ions in high-silicate melts were examined. The density of the CaO–SiO2 melt was lower than that of the CaO–SiO2–Fe2O3 systems. The surface tension of all compositions tested decreased with temperature and showed compositional dependence. The viscosity measured was higher in the Fe2O3-containing slag. The Raman spectroscopy analyses confirmed the increase in the degree of polymerization with the addition of Fe2O3 for the silicate-rich slag. The formation of a complex anion of a ferric ion and contribution to the silicate network were assumed. The trends observed were related to the structural properties and different interionic bonding. Urbain's viscosity model and FactSage™ 7.3 were applied for the assessment of the experimental data.

Synthesis and Investigation of Physical and Chemical Properties of Nanopowders and Ceramics in the La2O3–SrO–Ni(Co,Fe)2O3 System

Synthesis and Investigation of Physical and Chemical Properties of Nanopowders and Ceramics in the La2O3–SrO–Ni(Co,Fe)2O3 System

Facile microwave-assisted synthesis of magnetic ferrite: Rapid interfacial reaction underlying intensifying mechanism

Microwave-assisted (MW-assisted) heating is clean and intensively used to synthesize materials owing to the high-efficiency volumetric and selective heating modes. In the current paper, a design and facile synthesis of magnetic ferrite ceramics by microwave-assisted heating of MnO2 and Fe2O3 was conducted to reduce the synthetic temperature of conventional heating. The microwave absorptivity and temperature rise characteristics of the MnO2–Fe2O3 system were first assessed for the material design of MnFe2O4, and then the phase transformation, microstructure evolution, and magnetism change of the MnO2–Fe2O3 system heated under conventional and MW-assisted heating were compared. Investigations on electromagnetic properties and heating behaviors of MnO2–Fe2O3 mixture suggested that a suitable cylinder sample size for microwave heating was designed to be 10 mm in diameter and 10 mm in length based on the dielectric loss and magnetic hysteresis loss of microwave penetration at different depths. The intensifying mechanism for microwave heating was associated with the rapid interfacial reaction between MnO2 and Fe2O3. Under microwave irradiation at 935 °C, some perfectly crystallized MnFe2O4 was preferentially formed at the interface of MnO2 and Fe2O3, and these MnFe2O4 were evenly distributed in the cylinder samples. Similar to the “self-propagating” effect, the in-situ generation of MnFe2O4 with good energy conversion ability evenly distributed everywhere of the cylinder would facilitate the reaction of MnO2 and Fe2O3 under microwave irradiation based on the distinctive selective and volumetric heating. Compared with conventional heating at 1200–1250 °C, ferrite synthetic temperatures via MW-assisted heating decreased to 900–1000 °C, and the low-temperature synthesis of ferrite also had a good electromagnetic performance. Eventually, the clean and value-added utilization of low-grade ferruginous manganese ores via MW-assisted heating was validated for the preparation of manganese ferrite from minerals under reduced roasting temperatures.

Coexistence of MnO2 impedes the degradation of BPA in iron oxide/ascorbic acid systems: Disclosing the molecular mechanism

The interaction between iron oxides and ascorbic acid (AA) normally leads to the degradation of organic pollutants by inducing the generation of hydroxyl radical (OH). However, the influence of different iron oxides on such processes is poorly understood. Moreover, a more complex but very common scenario in real environment is the coexistence of iron oxides with other reactive minerals (e.g., MnO2), while the underlying mechanism of the interplay of different reactive minerals is still unclear, and knowledge of how the participation of MnO2 impacts OH generation and pollutant transformation in iron oxides/AA system is an unsolved problem. This study quantified the yields of OH in three iron oxide/AA systems and the transformation of bisphenol A (BPA). We found that AA greatly promoted electron-transfer and OH production on iron oxides, and the OH concentrations were 0.42 mM, 0.24 mM, and 0.08 mM in FeOOH, Fe2O3, and Fe3O4 systems, respectively. In addition, coexistence of β-MnO2 inhibited BPA transformation by decreasing OH concentration to 0.19 mM in FeOOH/AA system. This is because β-MnO2 strongly competed for AA species against FeOOH. In β-MnO2 system the generated H2O2 was very limited in spite of the greater reaction rate, and consequently almost no OH was detected. Interestingly, AA enhanced O2− production while interacting with MnO2. Accordingly, the reaction mechanism for the interaction between β-MnO2 and AA involving reactive oxygen species (ROS) generation was achieved at the molecular level. This study elucidates the effect of environmental factors on the ROS formation by Fe/Mn oxides, and provides a theoretical basis for understanding realistic environmental processes.

Chemical looping reaction of methane with oxygen from La0.8Sr0.2FeO3-\u03b4 and La0.8Sr0.2FeO3-\u03b4 -Fe2O3 systems to syngas

The reaction of methane with oxygen from La0.8Sr0.2FeO3-δ (LSF) and several LSF-Fe2O3 configurations was studied in chemical looping mode. Shell (LSF) and core (Fe2O3) (four catalysts called CS-3, CS-4, CS-5 and CS-6, over a range of coverage), LSF mixed uniformly with Fe2O3 (UM) and Fe2O3 (front) followed by LSF (PIS) were packed in a tubular reactor. The reaction was conducted at 900 °C and weight hourly space velocity (g methane/g catalyst/h) of 3 h−1 in 20 min reduction (10 mol% methane in nitrogen) and 20 min oxidation (10 mol% oxygen in nitrogen) cycles. LSF, CS, UM and PIS configurations yielded a significantly different performance (methane conversion, CO, CO2 and H2 selectivity and coke formation) measured in 10 reproducible cycles. The reaction and XRD data indicate that CO2 and steam formed by combustion of methane on Fe2O3 modify the phase composition of LSF, inhibits the initial LSF activity and improves the performance. Feeding a mixture containing 0.4 mol% CO2, 10 mol% methane in nitrogen to LSF confirms the positive effect of CO2 on the performance of LSF.

Phase equilibria in the Nd2O3–BaO–Fe2O3 system: Crystal structure, oxygen content, and properties of intermediate oxides

AbstractThe phase equilibria in the ½Nd2O3–BaO–½Fe2O3 system were systematically studied at 1373 K in air and presented in the form of a phase diagram. By X‐ray diffraction (XRD) analysis of quenched samples, the homogeneity ranges and crystal structure were determined for the following intermediate oxides: Nd1‐xBaxFeO3‐δ with 0.0 ≤ x ≤ 0.05 (space group (SG) Pnma) and with 0.6 ≤ x ≤ 0.7 (SG Pm‐3m), Ba6+yNd2‐yFe4O15‐δ with 0.0 ≤ y ≤ 0.4 (SG P63mc), and Ba1.1Nd1.9Fe2O7‐δ (SG P42/mnm). The structural parameters of single‐phase oxides were refined by the Rietveld method. The changes in oxygen content for Nd1‐xBaxFeO3‐δ (0.6 ≤ x ≤ 0.7), Ba6Nd2Fe4O15‐δ, and Ba1.1Nd1.9Fe2O7‐δ versus temperature in air were determined by thermogravimetric analysis. Gradual substitution of neodymium by barium in the Nd1‐xBaxFeO3‐δ (0.6 ≤ x ≤ 0.7) oxides leads to a decrease of oxygen content. Partial ordering via formation of separate domains with ap × ap × 5ap superstructure in Nd0.4Ba0.6FeO3‐δ, which cannot be detected by XRD, noticeably influence its thermal expansion and electrical conductivity.

Synthesis and Photocatalytic and Electrophysical Properties of Ceramic Materials in the PbO–Bi2O3–Fe2O3 System

Synthesis and Photocatalytic and Electrophysical Properties of Ceramic Materials in the PbO–Bi2O3–Fe2O3 System