Fe3O4 Fe2O3 Research Articles

Photocatalytic activity of Fe3O4–Fe2O3 particles supported on mordenite under visible light exposure for methylene blue degradation

Dyes pollution is a serious environmental problem and heterogeneous catalysis has been proposed as a remediation method. In this study, a set of catalysts of synthetic mordenite with iron oxides was synthesized by a simple chemical co-precipitation method assisted by subsequent thermal treatment with an oxidation process. Physicochemical characterization of prepared materials was performed by a variety of techniques, including XRD, SEM, EDS, SBET, UV–Vis DR, and XPS. Photocatalytic methylene blue (MB) degradation by the synthesized catalyst was evaluated with visible light excitation. From the studied set of catalysts, the sample prepared with a thermal treatment at 100 °C in air atmosphere for 3 h was capable of degrading ~ 90% of MB after 120 min with visible light of λ = 420 nm exposition and a small portion of H2O2 added. The catalyst used three processes to degrade MB: (1) adsorption of organic residues in the mordenite matrix support for electrostatic interactions, (2) photocatalysis heterogeneous reaction with visible light and (3) Fenton reaction catalyst with a small portion to H2O2 by Fe3O4–Fe2O3 presence. The catalytic efficiency to dye degradation was improved by a simple and economical thermal treatment without changing reaction conditions like pH, temperature, dose, or other. Studied mordenite iron oxide catalysts can be retrieved and reused at least five times without noticeable degradation, taking advantage of their magnetic properties. These catalysts could be proposed an economical, simple, and non-toxic alternative for eliminating organic dye pollution using visible light or solar irradiation in wastewater remediation related to textile, food, and pharmaceutical industries.

Features of the Interaction of Scheelite with HCl Solutions at 400 and 500°C, 100 MPa, and Various f(O2) (According to Experimental and Calculated Data)

Experimental studies were carried out on the solubility of scheelite in HCl solutions in the concentration range from 0.01 to 0.316 mol/kg H2O at 400 and 500°C, a pressure of 100 MPa and the fugacity of oxygen (hydrogen) specified by the buffers Cu2O–CuO, Fe3O4–Fe2O3, Ni–NiO, and Co–CoO. It was found that scheelite in HCl solutions at the specified parameters dissolves incongruently. In solutions containing from 0.01 to 0.0316 m HCl, minor amounts of WO3 and/or WO3 – x tungsten oxides are found in the run products, along with scheelite. In solutions containing from 0.1 to 0.316 m HCl, the formation of calcium tungsten bronzes CaxWO3 is observed, the average composition of which corresponds to the formula Ca0.07WO3. Based on the analysis of the experimental data obtained, the free energies of the formation of tungsten oxides WO3, WO2.9, scheelite, and calcium tungsten bronze were calculated. Using mutually agreed thermodynamic data, the solubility of Sch in solutions of HCl and (Na, K)Cl with the participation of aluminosilicates is calculated. It is shown that the scheelite has a wide area of congruent solubility in saline systems.

Synthesis of Fe3O4–Fe2O3@C Core-Shell Nanoparticles: Effect of Reactional Parameters on Structural and Magnetics Properties

The goal of this paper was to synthesize and characterize core–shell iron-carbon nanoparticles. For this purpose, nanoparticles were synthetized via a hydrothermal co-precipitation route, applying a 22 factorial experimental design with a central point, and varying both the concentration of the iron precursor (iron nitrate) and the reaction temperature. The nanoparticles were characterized via the following analysis: vibrating sample magnometry (VSM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX), high resolution field emission gun scanning electron microscopy (SEM/FEG) and transmission electron microscopy (TEM) analysis. The results showed that the hydrothermal co-precipitation synthesis route enabled the production of Fe3O4–Fe2O3@C core–shell nanoparticles with dimensions between 4 and 8 nm. An increase in iron nitrate concentration and temperature during synthesis entailed a decrease in the remnant field and the magnetization of the nanoparticles.

Physical synthesis of iron oxide nanoparticles and their biological activity in vivo

The physical synthesis of iron oxide nanoparticles obtained from the vapor phase using the electron beam physical vapor deposition method is considered. The results of studying the structure of porous condensates of iron—sodium chloride compound, chemical and phase compositions, as well as nanoparticles size are presented. With a rapid removal from vacuum, iron nanoparticles are oxidized in the air to magnetite. In the initial state, they have significant sorption capacity with respect to oxygen and moisture, therefore, with further heating in the air, the porous condensate mass decreases up to the temperature 650 °C, primarily due to the desorption of physically sorbed moisture. Physically adsorbed oxygen participates in oxidation of Fe3O4–Fe2O3 in the range of 380–650 °C. An increase in condensation temperature is accompanied by an increase of nanoparticle size, as a result of which the total surface area of nanoparticles is significantly reduced, and, consequently, their sorption capacity is decreased. Even without stabilization, such nanoparticles studied as ex tempore prepared aqueous dispersion have characteristic anti-anemic effect in the laboratory animals that can be used in medicine.

A sensitive nonenzymatic hydrogen peroxide sensor based on Fe3O4–Fe2O3 nanocomposites

The Fe3O4–Fe2O3 nanocomposites were prepared by the co-precipitation method and followed by calcination process. The products were synthesized and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray analysis. The obtained Fe3O4–Fe2O3 nanocomposites were then applied to study the electrocatalytic reduction of hydrogen peroxide (H2O2) in 0.01 M pH 7.0 phosphate buffer medium. Then the Fe3O4–Fe2O3 nanocomposites were used as active electrode material of electrochemical sensors for H2O2 detection The detection sensitivity of the sensor was 20.325 μA mM −1 , and the detection limit was estimated to be about 0.2 mM.

Experiments on liquid immiscibility in silicate melts with H2O, P, S, F and Cl: implications for natural magmas

Isobaric (200 MPa) experiments have been performed to investigate the effects of H2O alone or in combination with P, S, F or Cl on liquid-phase separation in melts in the systems Fe2SiO4–Fe3O4–KAlSi2O6–SiO2, Fe3O4–KAlSi2O6–SiO2 and Fe3O4–Fe2O3–KAlSi2O6–SiO2 with or without plagioclase (An50). Experiments were heated in a rapid-quench internally heated pressure vessel at 1,075, 1,150 or 1,200 °C for 2 h. Experimental fO2 was maintained at QFM, NNO or MH oxygen buffers. H2O alone or in combination with P, S or F increases the temperature and composition range of two-liquid fields at fO2 = NNO and MH buffers. P, S, F and Cl partition preferentially into the Fe-rich immiscible liquid. Two-liquid partition coefficients for Fe, Si, P and S correlate well with the degree of polymerization of the SiO2-rich liquid and plot on similar but distinct power-law curves compared with equivalent anhydrous or basaltic melts. The addition of 2 wt% S to the system Fe3O4–Fe2O3–KAlSi2O6–SiO2 stabilizes three immiscible melts with Fe-, FeS- and Si-rich compositions. H2O-induced suppression of liquidus temperatures in the experimental systems, considered with the effects of pressure on the temperature and composition ranges of two-liquid fields in silicate melts, suggests that liquid-phase separation may be stable in some H2O-rich silicate magmas at pressures in excess of 200 MPa.

Oxygen isotope partitioning between immiscible silicate melts with H2O, P and S

Differences between the δ18O values of immiscible Si- and Fe-rich melts in the systems Fe2SiO4–Fe3O4–KAlSi2O6–SiO2, Fe3O4–KAlSi2O6–SiO2, and Fe3O4–Fe2O3–KAlSi2O6–SiO2, with H2O, H2O+P or H2O+S have been determined in isothermal, isobaric experiments at 1100 and 1200°C and 200MPa. The Δ18O values for conjugate Fe2SiO4–Fe3O4–KAlSi2O6–SiO2+H2O and, Fe3O4–KAlSi2O6–SiO2·KAlSi2O6–SiO2+H2O melts are only 0.4–0.6‰ and do not differ significantly from those for anhydrous melts of similar composition. The Δ18O values for melts with added H2O+P or S are more variable, ranging from 0.0 to 0.8‰. Partitioning of 18O between the immiscible melts is 0.6–1‰ less than the partitioning reported for melt–mineral and mineral–mineral pairs. The partitioning of 18O in the network modifier-bearing immiscible melts is not controlled by the relative degree of polymerization in the melts or fO2. The upper limit of the range of Δ18O values (<1‰), and the variation in the δ18O values of conjugate melts that occurs with the inclusion of network modifying constituents, suggest that in some cases, oxygen isotope ratios might be useful to distinguish lithologies evolved from coexisting immiscible silicate melts, from lithologies that have evolved by crystal fractionation only.

Corrosion of Iron in a Carbonate-Bicarbonate Solution. Part 1. Crystallographic Analysis of Passive Films

Visible passive films are formed on the surface of 1010 steel at 325 K in a solution of 1 N NaHCO3 + 1 N Na2CO3 at anodic potentials up to −320 mVNHE inclusively. For potentials below −400 mV, they are dull and contain FeCO3. For −(390–320) mV, the films are thin blackish bright. Most probably, the diffraction peaks are caused by Fe3O4–Fe2O3. For −(430–400) mV, the films are dull blackish. Probably, this color is caused by a composite of magnetite and siderite.

Bulk and surface phases of iron oxides in an oxygen and water atmosphere at low pressure

Thermodynamic stability ranges of different iron oxides were calculated as a function of the ambient oxygen or water gas phase pressure (p⩽1 bar) and temperature by use of the computer program EquiTherm. The phase diagram for Fe–H2O is almost completely determined by the O2 pressure due to the H2O dissociation equilibrium. The formation of epitaxially grown iron oxide films on platinum and ruthenium substrates agrees very well with the calculated phase diagrams. Thin films exhibit the advantage over single crystals that bulk diffusion has only limited influence on the establishment of equilibrium phases. Near the phase boundary Fe3O4–Fe2O3, surface structures are observed consisting of biphase ordered domains of FeO(111) on both oxides. They are formed due to kinetic effects in the course of the oxidation to hematite or reduction to magnetite, respectively. Annealing a Fe3O4(111) film in 5 × 10−5 mbar oxygen at 920–1000 K results in a new γ-Fe2O3(111)-like intermediate surface phase during the oxidation to α-Fe2O3(0001). A model is suggested for the growth of iron oxides and for redox processes involving iron oxides. The formation of several equilibrium surface phases is discussed.

Damage tolerance and supportability aspects of ARALL laminate aircraft structures: Gunnink J.W. Compos. Struct. 1988, 10, (1), 83–104

Slow strain rate stress corrosion tests have been performed on a nuclear reactor pressure vessel steel in pure water at temperatures from 150 to 288°C and at various oxygen contents. The variation of cracking susceptibility correlates with the electrochemical potential, and cracking occurs for this temperature range if the rest potential is greater than about −0.2 V(SHE). It was confirmed that the oxygen in the water acts as a chemical potentiostat, which drives the steel into or out of the cracking range, by showing that cracking could be prevented in 45 ppm O2 water at 288°C by applying cathodic polarization. Cracking could also be induced in < 5 ppb O2 content water by applying anodic potentials. Large IR drops occurred in the potentiostatically controlled tests and it is probable that the potential need only be moved slightly from the cracking potential to induce a significant reduction in the susceptibility to cracking. The cracking potential correlates well with the Fe3O4Fe2O3 boundary for high temperature potential-pH data. It is probable that the mechanism of stress corrosion cracking requires that both Fe2O3 and Fe3O4 can form in the crack enclave. By replotting the potential-pH data in the form of the required oxygen for a given potential against temperature, it is shown that the oxygen content for inducing cracking agrees closely with the Fe3O4-Fe2O3 boundary at temperatures from 150°C to 288°C and that in this temperature range cracking is more likely to be associated with an anodic dissolution mechanism than by hydrogen-assisted cracking.