Presence Of α-Fe2O3 Research Articles

Effect of lanthanum substitution and annealing temperature on the structural and morphological properties of M-type calcium hexaferrite

To investigate the influence of annealing temperature and lanthanum substitution on the structural properties of M-type calcium hexaferrite, we prepared unsubstituted and lanthanum-substituted Ca1-xLaxFe12O19 (x = 0.3, 0.4 and 0.5) powders by mean of sol–gel auto-combustion procedure, annealed between 800 °C and 1350 °C during 5 h in a rate of 180 °C per hour. XRD analysis showed that the M-type phase does not appear in the unsubstituted samples even with annealing at 1200 °C. The XRD patterns of the substituted samples contained peaks of the M-type phase with the presence of α-Fe2O3 as a secondary phase, the intensity of α-Fe2O3 decreased with increasing annealing temperature between 1200 °C and 1350 °C, and also as a function of lanthanum substitution concentration, which shows that the best lanthanum substitution concentration was x = 0.5. Lattice parameters of synthesized Ca0.5La0.5Fe12O19 align with literature results of various M-type hexaferrite. SEM micrographs of the Ca0.5La0.5Fe12O19 annealed at 1350 °C revealed that the mean and median crystallite size values were calculated to be 4.37 μm and 4.32 μm respectively.

Microscopic Mechanism of Fe2O3-Catalyzed NO Reduction during Sludge Combustion: A Density Functional Theory Study

Systematic studies on the mechanism underlying Fe2O3-catalyzed NO reduction in a reducing atmosphere during sludge combustion remain limited. In this study, density functional theory was employed to investigate the adsorption properties of NH3, CO, and NO on the α-Fe2O3(001) surface, and the mechanisms underlying the NH3 and CO reduction of NO during the adsorption process. The results demonstrated that NH3, CO, and NO chemically adsorbed on the surface Fe top site, thereby generating distinctly high adsorption energies. NO exhibited the highest adsorption energy. With regard to the catalytic mechanisms of NH3 and CO during NO reduction, the α-Fe2O3(001) surface exhibited different characteristics. NH3 reduction of NO tended to follow the Eley–Rideal (E-R) mechanism. The dissociation of -NH2NO is the rate-determining step for the NH3 reduction of NO. The presence of α-Fe2O3(001) reduced the dissociation energy barriers of NH3 and NH2NO, thereby catalyzing the reduction reaction. In contrast, NO dissociation was more challenging during the CO reduction of NO. The α-Fe2O3(001) surface reduced the dissociation barrier of the NO-NO dimer from 2.04 to 1.53 eV. Two adsorbed NO molecules first formed NO-NO dimers; these then dissociated into N2O and atomic oxygen, thereby catalyzing the reduction reaction.

Photocatalytic degradation of polyethylene and polystyrene microplastics by α-Fe2O3/g-C3N4.

This study investigated the photodegradation of microplastics (MPs) by α-Fe2O3/g-C3N4. The effects of α-Fe2O3/g-C3N4 on MPs' surface were investigated through various techniques. With the addition of α-Fe2O3/g-C3N4 and under visible light irradiation, cracks and folds were observed on the MP films and particles. Compared to the treatment without photocatalyst addition, the mass loss of MPs increased with irradiation time when α-Fe2O3/g-C3N4 was added. Specifically, polystyrene films and particles in water showed 9.94% and 7.81% increased mass loss, respectively. The degradation of MPs using α-Fe2O3/g-C3N4 demonstrated the behavior consistent with the pseudo-first-order kinetic model. The presence of α-Fe2O3/g-C3N4 led to an increase in surface oxygen-containing functional groups and crystallinity while decreasing the average molecular weight of MPs. After 30days of irradiation, the characteristic tensile bands of MPs with α-Fe2O3/g-C3N4 significantly increased, and the detection of carboxyl bands indicated the formation of carboxylic acid, ketones, and lactones as degradation products.

Sequential photocatalytic degradation of organophosphorus pesticides and recovery of orthophosphate by biochar/α-Fe2O3/MgO composite: A new enhanced strategy for reducing the impacts of organophosphorus from wastewater

Photocatalysis is regarded as one of the most promising techniques for degrading organophosphorus pesticides (OPs) from wastewater given its low-cost and environmental benignity. Yet, photocatalytic degradation of OPs is an incomplete process, since PO43− is produced after photocatalysis. Here, biochar-supported α-Fe2O3/MgO composite (BC-α-Fe2O3/MgO) is developed for sequential photocatalytic degradation of OPs and recovery of the produced PO43−. The degradation efficiency of N-phosphonomethyl iminodiacetic acid (NPA) by BC-α-Fe2O3/MgO based photocatalysis reaches 90.1% within 80 min, and the recovery ratio of the produced PO43− by BC-α-Fe2O3/MgO is as high as 82.3%. Besides, the as-prepared BC-α-Fe2O3/MgO used in this integrated photocatalysis and adsorption process maintain a high stability towards NPA degradation and PO43− recovery during five cycling experiments. The mechanistic study reveals that holes, •OH, and •O2– radicals generated in the photocatalytic process are responsible for NPA degradation. UV light can activate persistent free radicals on BC-α-Fe2O3/MgO surface, which provide O2 withelectrons for the generation of •O2– and subsequent yield of •OH. Moreover, the presence of α-Fe2O3 and MgO on the surface of biochar leads to the excellent P adsorption performance of BC-α-Fe2O3/MgO. This study opens new possibilities for the recovery of P resource from organophosphorus polluted wastewater.

Effect of varying tartaric acid to metal nitrate ratio on the structure, morphology and magnetic properties of BaZn0.2Zr0.2Fe11.6O19 samples

Here in, we report synthesis of BaZn0.2Zr0.2Fe11.6O19 hexaferrite nanoparticles through the sol-gel auto-combustion route using tartaric acid as fuel. The nature of the fuel and fuel to metal nitrate ratio plays an important role in deciding the phase purity, grain size, shape, and magnetic properties of M-type hexaferrites. The optimization of the tartaric acid to metal nitrate (TA/MN) ratio was carried out by varying TA/MN ratios (0.00, 0.50, 0.75, 1.00, 1.25, and 1.50). XRD data revealed a single-phase M-type in samples synthesized using TA/MN ratio 0.50, 0.75, and 1.00 and the presence of α-Fe2O3 as an impurity phase beyond 1.00 TA/MN ratio and in a standard sample (TA/MN ratio is 0.00) both α-Fe₂O₃ and BaFe2O4 were found. FESEM micrographs revealed grain size continuously increases from 0.50 to 1.25 TA/MN ratio and decreases afterward for 1.50 TA/MN ratio. Magnetic measurements confirm that all the samples exhibit ferromagentic ordering. However, a kink along with wasp waist shape was observed in the samples synthesized using TA/MN ratio 0.00, 0.50, and 0.75 which may be due to presence of secondary phases/impurites and chemical inhomogeneity. The Hc was found to be minimum at 1.25 TA/MN ratio whereas Mr and Ms were found to be maximum at 1.00 TA/MN ratio. The optimum TA/MN ratio was found to be 1.00. These materials could be suitable for microwave absorber and magnetic recording applications due to their high Ms and low Hc values.

Preparation of pH-sensitive chitosan/polyvinylpyrrolidone/α-Fe2O3 nanocomposite for drug delivery application: Emphasis on ameliorating restrictions

Chitosan (CS)/polyvinylpyrrolidone (PVP)/hematite (α-Fe2O3) nanocomposites loaded with Doxorubicin (drug model) were synthesized via an oil-in-water emulsification method to develop a biocompatible and pH-sensitive drug nanocarrier for the first time. A hydrogel, including CS, PVP, and α-Fe2O3, was fabricated successfully with glutaraldehyde (GA) as the cross-linker. Incorporating α-Fe2O3 into CS/PVP hydrogel improved the pH-sensitivity and developed beneficial hydrogel. FTIR and XRD analysis illustrated physical interactions between polymer-polymer, polymer-drug, and crystalline behavior of prepared nanocomposite. These analyses also confirmed chemical bonding in nanocomposite's structure. The FE-SEM analysis showed successful impregnation of α-Fe2O3 into CS/PVP matrix and spherical structure. To clarify the size distribution and surface charge of the drug-loaded nanocomposite (CS/PVP/α-Fe2O3/Dox), DLS and zeta analyses were conducted. They showed the mean size of nanocomposites at about 247 nm. Drug-loaded CS/PVP/α-Fe2O3 nanocomposite and CS/PVP/Dox were studied for their release behavior and kinetics. Furthermore, the effect of α-Fe2O3 on release from CS/PVP/α-Fe2O3/Dox nanocomposite was investigated. That showed an increase in encapsulation of Doxorubicin and beneficial release behavior such as slow-release and retention effect. The release from this drug-loaded nanocomposite revealed excellent pH-sensitive and controlled release of the drug. Besides, the in vitro cytotoxicity and cell apoptosis were studied to recognize biological properties. These analyses revealed that drug-loaded nanocomposite caused high inhibition to MCF-7 cells in presence of α-Fe2O3 and proved the hematite's anti-cancer effect. By and large, this study confirmed CS/PVP/α-Fe2O3 nanocomposites as a potential candidate for the controlled pH-sensitive release of the drug.

Hierarchical porous nanorod@core-shell α-Fe2O3/TiO2 microspheres: Synthesis, characterization, and gas-sensing applications

Hierarchical porous α-Fe2O3/TiO2 nanorod@core-shell microspheres were synthesized by a facile one-step hydrothermal approach without templates or surfactants. The as-obtained α-Fe2O3/TiO2 nanorod@core-shell microspheres had an average diameter of 3.5 μm. Porous nanorods, with an average length of 1.5 μm, were randomly grown on the core-shell microsphere surfaces. The morphology, microstructure, and composition of the α-Fe2O3/TiO2 heterostructures were characterized by various analytical techniques. Changes in the morphology and composition of the microspheres had an effect on the final gas sensing performance. Gas sensors based on the porous nanorod@core-shell α-Fe2O3/TiO2 microspheres exhibited an excellent gas-sensing performance, with markedly enhanced responses in comparison with the pristine α-Fe2O3 sensor. The response of the porous nanorod@core-shell α-Fe2O3/TiO2 microspheres to 20 ppm acetone was approximately 34, which was 2.7 times higher than that of pure α-Fe2O3 at 220 °C. Furthermore, the sensor could be easily recovered to its initial state following a short exposure to fresh air. The remarkably enhanced acetone-sensing performance was attributed to the unique porous nanorod@core-shell microsphere morphology, the strong interfacial interaction between TiO2 and α-Fe2O3, and the presence of α-Fe2O3/TiO2 heterojunctions. Thus, the prepared porous nanorod@core-shell α-Fe2O3/TiO2 microspheres sensors showed an outstanding performance in acetone detection.

Preparation and application of α-Fe2O3@MIL-101(Cr)@TiO2 based on metal-organic framework for photocatalytic degradation of paraquat.

In this study, a new magnetic α-Fe2O3@MIL-101(Cr)@TiO2 photocatalyst was successfully synthesized. The material synthesized had been fully characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, vibrating sample magnetometry, transmission electron microscopy, and Brunauer-Emmett-Teller isotherm methods. The X-ray diffraction analysis corroborates that nanoparticles are polycrystalline with rhombohedral and tetragonal crystal structures for Fe2O3 and TiO2, respectively. In addition, the photocatalytic degradation of the herbicide paraquat in the presence of α-Fe2O3@MIL-101(Cr)@TiO2 under ultraviolet (UV) irradiation was studied. The effect of experimental parameters such as the initial concentration of catalyst, the pH, and the initial paraquat was investigated. The optimal conditions were achieved for concentration of catalyst 0.2 g L-1, pH 7, and concentration of paraquat 20 mg L-1. The photocatalytic degradation efficiency was 88.39% after 15 min with α-Fe2O3@MIL-101(Cr)@TiO2 under UV irradiation. The pseudo-second-order kinetic model for photocatalytic degradation of paraquat was obtained. The catalysts could be recovered and reused without any loss of efficiency for five times in the consequent reactions. To the best of our knowledge, this is the first report on the photocatalytic degradation of paraquat using new α-Fe2O3@MIL-101(Cr)@TiO2 photocatalyst under UV irradiation condition.

Synthesis, characterization and in vitro analysis of α-Fe2O3-GdFeO3 biphasic materials as therapeutic agent for magnetic hyperthermia applications

The use of gadolinium orthoferrite for biomedical application like as contrast agents for magnetic resonance imaging (MRI) has been found to be very promising due to its fascinating properties. The present study focuses on the determination of the effect of the gadolinium concentration in the formation biphasic α-Fe2O3-GdFeO3 for hyperthermia applications. An in-situ sol-gel technique was adopted for the synthesis of biphasic orthoferrites with four different gadolinium concentrations. The XRD analysis confirmed the formation of gadolinium orthoferrites after heat treatment at 1000 °C, 1100 °C, and 1200 °C. The presence of α-Fe2O3 in trace amounts was observed in the materials with low gadolinium concentrations. VSM (Vibrating-sample magnetometer) analysis was performed to ensure the magnetic properties of the materials, which were found to be weakly ferromagnetic. The biocompatibility of the materials was investigated through MTT assay and no cytotoxic effect was observed. The assessment of heating ability of the materials was performed under an alternating magnetic field using an induction heating instrument and all the samples showed temperature rise in the range of hyperthermia temperature with a maximum temperature of 55.71 °C in 6 min. The heating experiments at 44 °C in the absence of samples established the vulnerability of cancer cells as compared to normal cells.

Effect of Excess Iron on Oxidative Dehydrogenation of 1-Butene over a Series of Zinc Ferrite Catalysts

The influence of excess Fe3+ in ZnFe2O4 for the catalytic oxidative dehydrogenation of 1-butene to 1, 3-butadiene was investigated to try to clarify inconsistencies in the existing literature. A series of nanoscale zinc ferrite powders were produced with increasing Fe: Zn ratios. The materials were characterized by a range of techniques, which showed the presence of α-Fe2O3 as a distinct phase with an increasing excess of Fe3+ and SEM highlighted the increased presence of surface structures on the ferrites at higher Fe: Zn ratios. Reaction testing showed α-Fe2O3to be virtually inactive for the oxidative dehydrogenation of 1-butene. Results for the ferrite catalysts showed a significant decrease in both conversion and yield with an increasing excess of Fe3+. Therefore an excess of Fe3+ has a negative effect on catalytic activity and selectivity of zinc ferrite for the oxidative dehydrogenation of 1-butene, but acts as a promoter for competing hydrogenation and combustion side reactions.

Improvement of supercooling and thermal conductivity of the sodium acetate trihydrate for thermal energy storage with α-Fe2O3 as addictive

In this study, iron oxide nanoparticles (α-Fe2O3) have been firstly used as a nucleating agent, which simultaneously reduces the supercooling degree of sodium acetate trihydrate (SAT) and improves its thermal conductivity. A series of SAT composite phase change materials (PCMs) for potential latent heat thermal energy storage applications were prepared by a ball milling method using carboxymethyl cellulose as a thickening agent and sodium dodecyl sulfonate as a dispersant. In order to investigate the effect of the mass ratio of α-Fe2O3 nanoparticles on the supercooling degree of SAT, various α-Fe2O3 contents (0.2, 0.4, 0.6, 0.8, and 1.0 mass%) were added into the SAT matrix. It was found that the supercooling degree of the SAT composite PCM was reduced to 0 °C at a α-Fe2O3 content of 0.8 mass%. Furthermore, no chemical reaction between SAT and α-Fe2O3 occurred, and the presence of α-Fe2O3 had no effect on the energy storage capability of SAT. The thermal conductivity of the SAT composite PCM was improved by 22.5% due to the addition of 0.8 mass% α-Fe2O3. After 60 melting–freezing cycles, the composite PCMs retained excellent stability with a small reduction in the phase change temperature (0.33 °C) and low latent heat loss rate (0.796%).

Influence of Ca–La and Cr-addition on the structure and magnetic characteristics of nanocrystalline Sr-hexaferrite powder

Sr–Ca hexaferrite nanopowders with a nominal chemical composition of Sr1−xCaxFe12O19, Sr1−xCaxFe11.5Cr0.5O19 and Sr0.85−xCaxLa0.15Fe11.5Cr0.5O19, with x = 0, 0.1, 0.3, and 0.5, were synthesized via sol–gel auto combustion method. Structural and phase formation of the samples were evaluated through X-ray diffraction (XRD). The XRD results indicated the Sr–Ca hexaferrites formation with the presence of α-Fe2O3 as second phase, after subsequent heat treatment of the synthesized samples at 1030 °C for 2.5 h. By increasing the amount of Ca from x = 0 to x = 0.5, the intensity of second phase (α-Fe2O3) increased. Furthermore, the hexaferrite lattice constant “c” decreased while the “a” remained almost constant. Field emission scanning electron microscopy results indicated that the grains shape becomes more needle and spherical like with increasing the X content. By doping Cr3+ at x = 0.5, the grains would vary from needle-like shape to platelet hexagonal. The magnetic behavior of the Sr–Ca hexaferrite samples with and without adding La3+ and Cr3+ ions were studied. The best result was achieved for the nanopowders with a chemical composition of Sr0.35Ca0.5La0.15Fe11.5Cr0.5O19 with coercivity (HcJ) = 5474.28 Oe, saturation magnetization (Ms) = 61.16 emu/g and remnant magnetization (Mr) = 42.57 emu/g.

One-step synthesis of single phase micro-sized BaFe12O19 hexaplates via a modified hydrothermal approach

Single phase BaFe12O19 ferrite identified by X-ray diffraction and Raman spectroscopy has been successfully synthesized using Fe(NO3)3·9H2O and Ba(NO3)2 as starting materials and NaOH as a precipitant via a modified one-step hydrothermal approach which involves the elimination of carbonate radicals from reaction system based on the stoichiometric ratio of [Ba2+]/[Fe3+]. Hydrothermal products under various synthetic conditions were studied, including different addition amounts of Ba(NO3)2 in the modified operation, reaction temperatures and times, and hydroxyl concentrations. The BaFe12O19 particles featuring an excellent hexagonal plates shape can be hydrothermally synthesized with the aid of polyethylene glycol. It has been found that the presence of α-Fe2O3 in a traditional hydrothermal process is motivated by the deviation from the desired [Ba2+]/[Fe3+] ratio caused by the negligent precipitation of Ba2+ ions to BaCO3. An investigation on the preferred hydrothermal product through thermodynamic calculation shows that the reduction in Gibbs free energy for the exclusive formation of BaFe12O19 with 1 mol of Fe3+ ions at 220 °C is approximately 32 kJ higher than that for the complete transformation to α-Fe2O3 with an equal consumption quantity of Fe3+ ions.

Identification of Defects of Stainless Steel Sold with Brand Names, by Studying their Surface Thin Films with Scanning Electron Microscope (SEM)

In the present paper, we have studied the thin films formed on the commercial stainless steel sold under different brand names in Pakistan with the help of SEM, EDX and XRD and have further investigated that how such stainless steels lose their brightness and become dull. A sample of recycled stainless steel melted in induction furnace was taken for study. The analysis of the layer formed is as follows: wt. %, C = 6.55, O = 6.20, Na = 0.47, Mg = 0.31, Al = 2.28, Si = 1.23, Cr = 15.42, Mn = 1.06, Fe = 59.58, Ni = 6.91 Total = 100, Atomic %, C = 21.02 O = 14.93, Na = 0.79, Mg = 0.49, Al = 3.26, Si = 1.68, Cr = 11.43, Mn = 0.74, Fe = 41.12, Ni = 4.53. Stainless steel has austenite structure, is non magnetic and forms fine passive film of Cr (III) oxide, (Cr2O3) which prevents surface corrosion and avoids further corrosion from spreading in metal’s internal structure. Mn and Ni stabilize austenite structure. XRD spectra show presence of αFe2O3 and Cr2O3 and spinal oxides in the film formed on the sample taken for study. SEM images show how this thin film tears. In a sound stainless steel, the film formed is too thin to be visible and metal remains lustrous. The film quickly reforms when surface is scratched (passivation). Mostly stainless steel is recycled and average stainless steel objects manufactured and marketed are composed of above 60% recycled material. Oxide spinals of Mn, Ni, Cr with iron oxide are not very resistive to the corrosion. Recently Duplex stainless steel has been manufactured which contains 50:50 austenite and ferrite and have twice the strength compared to austenite stainless steel. Keywords Recycle stainless steel, composition of thin film with EDX, SEM images, investigation on αFe2O3 and Cr2O3 spinals. In the present paper, we have studied the thin films formed on the commercial stainless steel sold under different brand names in Pakistan* with the help of SEM, EDX and XRD and have further investigated that how such stainless steels lose their brightness and become dull. The sample is austenitic stainless steel.

The role of fuel concentration on particle size and dielectric properties of manganese substituted zinc ferrite nanoparticles

Mn substituted ZnFe2O4 nanoparticles were prepared by the auto-combustion method using different fuel ratios of 50%, 75% and 100%.The powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectrum (EDX). Also, the dielectric behaviors of the samples were investigated for different annealing temperatures. The X-ray diffraction patterns indicated that the annealed samples resulted in the formation of crystalline powder and the presence of α-Fe2O3 as a secondary phase. The average crystallite sizes of the samples are from ~12 to 60nm. The external morphology and microstructure of the samples are tested by SEM and TEM. The effect of annealing temperature and particle size on dielectric properties such as dielectric constant (έ) and dielectric loss (D) of the spinel MnxZn1−xFe2O4 nanoparticles was measured using impedance analyzer in the frequency range 100kHz–5MHz.

Ultrasonic assisted-Fenton-like degradation of nitrobenzene at neutral pH using nanosized oxides of Fe and Cu

Ultrasonic-assisted heterogeneous Fenton reaction was used for degradation of nitrobenzene (NB) at neutral pH conditions. Nano-sized oxides of α-Fe2O3 and CuO were prepared, characterized and tested in degradation of NB (10mgL−1) under sonication of 20kHz at 25°C. Complete degradation of NB was effected at pH 7 in presence of 10mM H2O2 after 10min of sonication in presence of α-Fe2O3 (1.0gL−1), (k=0.58min−1) and after 25min in case of CuO (k=0.126min−1). α-Fe2O3 showed also effective degradation under the conditions of 0.1gL−1 oxide and 5.0mM of H2O2, even though with a lower rate constant (0.346min−1). Sonication plays a major role in enhancing the production of hydroxyl radicals in presence of solid oxides. Hydroxyl radicals-degradation pathway is suggested and adopted to explain the differences noted in rate constants recorded on using different oxides.

Effect of annealing temperature on structural and magnetic properties of manganese substituted NiFe2O4 nanoparticles

The structural and magnetic properties of manganese substituted nickel ferrite nanoparticles were synthesized by auto-combustion and evaporation methods. The effects of annealing treatment on structural and magnetic behavior of the samples have been studied for 600°C and 900°C. The ferrite powders were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The X-ray diffraction patterns indicated that the annealed samples resulted in the formation of Mn–Ni ferrite and the presence of α-Fe2O3 as a secondary phase. The average crystallite sizes of the annealed samples are in the range from ~25 to 65nm for auto combustion method and ~45 to 98nm for evaporation method. The morphology and particle size of the annealed samples are examined by SEM and TEM. The annealing effect on the magnetic properties of Mn–Ni ferrites were analyzed by using a Vibrating Sample Magnetometer (VSM). The impact of particle size, the saturation magnetization of Mn–Ni ferrite nanoparticles increase with increasing annealing temperature.

Synthesis and Characterization of Nanocomposites of Mixed Oxides of Iron and Cerium in a Polymer Matrix

The structure and magnetic behavior of nanostructured cerium ferrite nanoparticles have been investigated by both conventional and synchrotron-based FTIR, X-ray diffraction, Mössbauer spectroscopy, SEM, TEM, and VSM studies. Far infrared absorption bands, first around 575 cm−1 and second around 425 cm−1 are respectively attributed to tetrahedral (A) and octahedral (B) sites. The powder X-ray diffraction patterns reveal both the presence of α-Fe2O3 and cerium ferrite spinel phase. The Mössbauer spectra show the presence of sextets corresponding to magnetically ordered phase and a doublet corresponding to ferromagnetic cerium ferrite phase.

Factors Affect on the Reaction Performance of the Oxidative Dehydrogenation of n-Butene to 1,3-Butadiene Over Zn-Ferrite Catalysts

Two types of zinc ferrite catalysts have been prepared by physical mixing or coprecipitation and applied to the oxidative dehydrogenation of n-butene to 1,3-butadiene. It is observed that the catalytic activity is significantly dependent upon not only the crystallinity but also the composition of a ferrite catalyst. If crystallinity of a catalyst is too high, the oxygen spillover through the lattice is severely suppressed and results in low catalytic activity. On the other hand, the presence of α-Fe2O3 in ferrite structure may lead to decrease of the reaction performance. Coprecipitation with strong base such as NaOH is found to be one of the efficient methods to form a catalytically active ferrite structure in that it is advantageous to obtain pure ferrite composition with appropriate crystallinity. During catalyst preparation, complete removal of sodium is essential because the residual sodium in catalyst considerably reduces the reaction performance. Although the use of mild base such as NH4OH is advantageous to prevent the exhaustive washing, the formation of mixed phase both α-Fe2O3 and ZnFe2O4 may reduce n-butene conversion as well as 1,3-butadiene selectivity.

Iron-containing atmospheric aerosols in the Chernobyl fallout

Mossbauer spectroscopy was applied to determine the composition and the iron concentration in the atmospheric aerosols contaminated in Sofia, Bulgaria after the Chernobyl accident. The results confirm the major conclusion of the Kopcewiczs for Poland, i.e. that in the initial filters, collected during the contaminating fallout (30.04–05.05.1986), the iron concentration was highest, 3.69 μg/m3 and that magnetite Fe3O4 was present. For the following days a change in the chemical composition including the presence of α-Fe2O3, α-FeOOH and γ-FeOOH as well as the absence of magnetite, was detected. Input of industrial iron contamination was negligible since the nearby steel plant had worked at minimum power due to official holidays. Unfortunately, Mossbauer spectroscopy studies only, do not allow a definite conclusion about an increase of the isotope abundance of 57Fe in the Chernobyl fallout.