γ-Fe2O3 Samples Research Articles

Nanostructured mesoporous g-Fe2O3: a novel photocatalyst for degradation of organic pollutants

The modified sol-gel synthesis technique was used to created of nanostructured maghemite (γ-Fe2O3). It has been shown that the molar concentration of the original precursors during synthesis affects on the average particle sizes, specific surface area, pore size distributions, optical and conductivity properties. The XPS metod allowed to establish features of electronic structure of the synthesized materials. Optimal conditions for the synthesis of nanostructured maghemite with mesoporous structure were selected. The mechanism of electrical conductivity formation for synthesized mesoporous materials was established. The width of the band gap is determined and its dependence on the molar concentration of precursors is established. The positive correlation between the specific surface area of γ-Fe2O3 samples and photocatalytic activity was installed - the photocatalytic activity of synthesized γ-Fe2O3 increase with growth of specific surface area of γ-Fe2O3 samples.

Bio-activity of superparamagnetic maghemite nanorods capped with dl-alanine

The present research work explores an economic way of synthesizing maghemite (ᵞ-Fe2O3) nanorods through chemical coprecipitation method in which, ferric chloride was used, as one of the precursors and Sodium hydroxide as fuel with the assistance of dl-alanine, an organic surfactant. The obtained ᵞ-Fe2O3 nanorods have been characterized by X-ray diffraction, Fourier Transform Infrared Spectroscopy, Scanning electron microscopy, Transmission Electron Microscopy and Vibrating sample magnetometer techniques. X-ray diffraction results show that the synthesized ᵞ-Fe2O3 nanorods are in cubic spinel phase with improved crystalanity. The morphology and the size of the nanoparticles were confirmed by SEM as well as TEM. High resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) of the sample have been performed. The FTIR spectra indicate the incorporation of dl-alanine on ᵞ-Fe2O3 nanorods. The saturation magnetization value of maghemite, measured by vibrating sample magnetometer corresponds to the typical superparamagnetic behavior. On examining the magnetic saturation (Ms) was found out to be 142emu/g, 57.7% higher than the bulk value, which is highly recommended for biomedical application. The antibacterial activity of ᵞ-Fe2O3 sample against gram-positive Streptococcus mutans, Staphylococus aures and gram-negative E.coli, Klebsiella pneumonia was investigated using Well diffusion method. The antifungal activity was tested by the same method against Aspergillus niger and Candida albicans. The MTT assay was employed to test the anticancerous activity of ᵞ-Fe2O3 against HT29 (coloncarcinoma) cell line. The sample shows positive control over antimicrobial species. The Lethal Dosage of the sample calculated to be 45.3149μg/ml, establishes its strong activity over HT29 cell line.

Porous Fe3O4 and gamma-Fe2O3 foams synthesized in air by sol-gel autocombustion

Porous magnetite (Fe3O4) and maghemite (γ-Fe2O3) foams were synthesized by a sol-gel autocombustion method in air atmosphere. Citric acid, ferric nitrate, and ammonia were used as the starting materials. The gels were ignited at a low temperature of 200 °C. Synthetic mechanism of Fe3O4 was studied by coupling mass spectrometry, thermogravimetry, and differential scanning calorimetry (MS-TG-DSC). The phase structures and the phase transformation of the samples were investigated by X-ray diffraction (XRD). Porous morphologies of the Fe3O4 and γ-Fe2O3 foams with micron-size pores were characterized by scanning electron microscopy (SEM). Magnetic properties of the Fe3O4 and γ-Fe2O3 samples were studied by vibration sample magnetometer (VSM) measurements at room temperature, which showed tunable saturation magnetization values and small coercivities. The highest saturation magnetization of the porous Fe3O4 sample is about 90% of its bulk value, implying that the purity of the products is quite good.

Experimental study on the mechanism of mercury removal with Fe2O3 in the presence of halogens: Role of HCl and HBr

Experiments were conducted in a bench-scale fixed bed reactor with α-Fe2O3 and γ-Fe2O3 samples to investigate the mechanism of Hg0 oxidation in the presence of HCl at 80–680°C respectively. HCl is one of the main impurities in coal-derived fuel gas and its contribution to Hg0 removal is complex and necessary to research. The experimental results showed that the Hg0 removal mechanism with HCl could probably be divided into three stages based on the reaction temperature. At low temperature, the Eley–Rideal mechanism with HCl pre-adsorption was the most probable Hg0 oxidation pathway. As the temperature increased more than 280°C, Hg0 removal efficiency differs significantly on α-Fe2O3 and γ-Fe2O3, and the most suitable mechanism was Langmuir–Hinshelwood. With the increasing temperature to 680°C, the homogeneous reaction between HCl and Hg0 as well as Langmuir–Hinshelwood are responsible for the transformation of Hg0. We also discovered that the reaction time played a significant impact on the Hg0 removal at low temperature, and caused the secondary mercury removal efficiency owing to the probable product of FeCl3. Additionally, HBr was adopted to compare with HCl, which obviously enhanced the Hg0 oxidation on α-Fe2O3.

Magnetic Properties of Ultrathin $\gamma \hbox{-}\hbox{Fe}_{2}\hbox{O}_{3}$ Films Grown on Silicon Substrate

The effect of thickness and annealing temperature on the room-temperature magnetic properties of ultrathin γ-Fe2O3 films grown on silicon substrate were investigated. Ultrathin γ-Fe2O3 films were grown on silicon substrates by ion beam sputtering. The saturation magnetization and coercive force of samples at room temperature increase with increasing of annealing temperature and decrease at annealing temperatures above 600 °C. The saturation magnetization of samples at room temperature decreases with increasing of γ-Fe2O3 thickness. The γ-Fe2O3 samples about 3 ~ 6 nm thick annealed at 600 °C show saturation magnetization of about 360 ~ 410 emu/cm3, which is close to the bulk value of about 390 emu/cm3 within the error range.

Porous Fluorine-Doped γ-Fe2O3 Hollow Spheres: Synthesis, Growth Mechanism, and Their Application in Photocatalysis

Porous fluorine-doped maghemite(γ-Fe2O3) hollow spheres have been prepared by facile route based on solvothermal reaction and sequential calcinations. The composition and morphology of the as-prepared samples were characterized by various techniques. The SEM and TEM results showed that the as-synthesized products exhibited a spherical morphology with porous hollow structures. Ultraviolet-visible (UV-vis) diffuse reflectance spectra display that the optical performance of γ-Fe2O3 products are related to their structure and the fluorine concentrations. The porous hollow structured fluorine-doped γ-Fe2O3 spheres exhibit ferromagnetic properties with relatively high saturation magnetization at room temperature. According to the experimental results, a formation mechanism of the fluorine-doped γ-Fe2O3 hollow spheres has been presented. Under UV light irradiation, the photocatalytic degradation activities of the as-synthesized fluorine-doped γ-Fe2O3 samples for RhB dye were 2-5 times higher than that of the undoped sample. The prepared fluorine-doped γ-Fe2O3 hollow spheres will also aroused great interest for their application in catalysis, separation technology, sensors, nanotechnology, and biomedical fields.

Maghemite and poly-dl-alanine based core–shell multifunctional nanohybrids for environmental protection and biomedicine applications

This paper deals with the synthesis of two nanohybrid materials based on maghemite (γ-Fe2O3) and poly-dl-alanine using a two-step procedure consisting of maghemite nanoparticles synthesis by microemulsion method and nanohybrids obtaining by coating of maghemite nanoparticles with poly-dl-alanine biopolymer in two different molar ratios (H1:5 and H1:15). The maghemite and their corresponding nanohybrids were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoemission spectroscopy, Mössbauer spectroscopy, Transmission electron microscopy, High resolution transmission electron microscopy with selected area electron diffraction and Atomic absorption spectroscopy. The two nanohybrids under the investigation have the average particle sizes of 22nm and 23nm. The Fourier transform infrared spectroscopy spectra and X-ray photoemission spectroscopy data indicate the existence of some interactions between the maghemite nanoparticles and poly-dl-alanine shell. The saturation magnetization values for maghemite and the two nanohybrids determined by a Vibrating Sample Magnetometer correspond to a typical superparamagnetic behavior suitable for applying in biomedical field. Also, with respect of biomedical application the biological activity of maghemite and its corresponding nanohybrids was investigated on healthy human cells (PBMC) and cancerous cells (HeLa). Furthermore, in order to support the multifunctionality of the γ-Fe2O3 sample and nanohybrids we also investigated their wastewater treatment properties by measuring the removal efficiency of heavy metal Cd (II) ions.

Preparation and characteristics of core–shell F-doped γ-Fe2O3 hollow microspheres

Well-crystallized core–shell F-doped γ-Fe2O3 hollow microspheres have been fabricated by a simple approach consisting of solvothermal synthesis and post-synthesis calcination. The structure and morphology were investigated by XRD, XPS, SEM, TEM, UV, and EDS. XRD and XPS studies indicated that the as-prepared products were well-crystallized cubic spinel structure. TEM and SEM images showed that the F-doped γ-Fe2O3 samples were of hollow core–shell structures with an average diameter of about 450nm. The mean diameter of the cores of those spheres is about 200nm. UV–vis spectra reveal that the band gap energies of the γ-Fe2O3 microspheres can be tuned.

On the role of grain boundaries in nanocrystalline γ-Fe2O3 under high pressure

In situ impedance spectroscopy of nanophase and bulk γ-Fe2O3 were performed using a fabricated microcircuit on a diamond anvil cell. The results provide evidence for the existence of grain and grain boundary effects that are separated in the frequency region. The analysis establishes that the grain boundary conductance of nanocrystalline γ-Fe2O3 is higher than that of the bulk material. Both the grain and grain boundary resistances of γ-Fe2O3 smoothly decrease with pressure. A remarkable phenomenon of discontinuity appears at 7.4 GPa for the nanocrystals. This critical value is interpreted by the space charge model and changes in charge densities between the grain boundaries. The impedance analysis further reveals that the relaxation frequency gradually increased with the effect of pressure and the γ-Fe2O3 samples’ impedance imaginary part exhibits a typical capacitive characteristic. Within the given pressure range, the relaxation frequency of γ-Fe2O3 follows the Arrhenius behavior. This result was attributed to a dominant interfacial effect.

Effect of grain boundary on resistive magnetodielectric property of polycrystalline γ-Fe2O3

We have investigated the role of the grain boundary on the resistive magnetodielectric property of polycrystalline γ-Fe2O3 through impedance spectroscopy measurements. Depending on the sample preparation temperature, the dielectric constant of γ-Fe2O3 is significantly different especially at low frequencies ( 200 K). The value of the magnetodielectric effect at a specific frequency and the resonance frequency for the maximized magnetodielectric effect are different, although polycrystalline γ-Fe2O3 samples show a quite similar magnetoresistance. Through the experimentally obtained resistance ratio between the grain and the grain boundary, we can reproduce the magnetodielectric curves based on the Maxwell–Wagner model and the measured magnetoresistance.

Nanostructured Pure γ‐Fe2O3 via Forced Precipitation in an Organic Solvent.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Combustion Derived Ultrafine γ-Fe2O3 Structure, morphology and thermal studies

A novel combustion method of employing poly(ethylene glycol) with the precursor in a fixed ratio for the synthesis of ultrafine γ-Fe2O3 through a self-propagating combustion synthesis is reported. Four different precursors viz. ferrous hydroxide, ferrous oxalate dihydrate, ferric 8-hydroxyquinoline and ferric acetylacetonate are employed in this study for the conversion of these precursors to ultrafine g-Fe2O3 particles. The as synthesized γ-Fe2O3 samples are characterized by XRD, SEM and thermal techniques. A case study for the synthesis of γ-Fe2O3 employing ferric acetyl acetonate as precursor is reported. The importance of employing thermal analysis techniques in understanding the combustion synthesis is envisaged.

Magnetic Enhancement of γ-Fe2O3 Nanoparticles by Sonochemical Coating

We show that sonochemistry is an efficient and facile route for quantitative coating of γ-Fe2O3 nanoparticles with octadecyltrihydrosilane (OTHS, CH3(CH2)17SiH3). The presence of C−H stretching (2950−2850 cm-1) and bending (1475−1375 cm-1) bands, and the absence of peaks at 2150 and 925 cm-1 (Si−H stretching and bending respectively) confirm the presence of grafted hydrocarbon chains in the irradiated sample, hence the reaction of OTHS with γ-Fe2O3 nanoparticles. The coated nanoparticles show increased magnetization compared to the uncoated ones. X-ray diffraction, magnetization studies, Mossbauer spectra, and electron paramagnetic resonance spectra reveal that the magnetic ordering is more prominent in the OTHS-coated γ-Fe2O3 sample because of improved crystallinity.

Structural phase transition in nanostructured γ-Fe2O3

We have found that there is an exothermal peak on the DTA curve of nanostructured γ-Fe2O3 sample and that this peak is not repeatable. The XRD microstructure analysis confirms for the first time that this exothermal peak corresponds to the structural phase transition from γ-Fe2O3 to α-Fe2O3. After this transition, the nanostructured Fe2O3 crystalline grains grow continuously with increasing temperature.

Mössbauer study of the thermal decomposition of lepidocrocite and characterization of the decomposition products

The lepidocrocite (γ-FeOOH) to maghemite (γ-Fe2O3), and the maghemite to hematite (α-Fe2O3) transition temperatures have been monitored by TGA and DSC measurements for four initial γ-FeOOH samples with different particle sizes. The transition temperature of γ-FeOOH to γ-Fe2O3 and the size of the resulting particles were not affected by the particle size of the parent lepidocrocite. In contrast, the γ-Fe2O3 to γ-Fe2O3 transition temperature seems to depend on the amount of excess water molecules present in the parent lepidocrocite. Thirteen products obtained by heating for one hour at selected temperatures, were considered. Powder X-ray diffraction was used to qualify their composition and to determine their mean crystallite diameters. Transmission electron micrographs revealed the particle morphology. The Mossbauer spectra at 80 K and room temperature of the mixed and pure decomposition products generally had to be analyzed with a distribution of hyperfine fields and, where appropriate, with an additional quadrupole-splitting distribution. The Mossbauer spectra at variable temperature between 4.2 and 400 K of two single-phase γ-Fe2O3 samples with extremely small particles show the effect of superparamagnetism over a very broad temperature range. Only at the lowest temperatures (T⩽55 K), two distributed components were resolved from the magnetically split spectra. In the external-field spectra the ΔmI=0 transitions have not vanished. This effect is an intrinsic property of the maghemite particles, indicating a strong spin canting with respect to the applied-field direction. The spectra are successfully reproduced using a bidimensional-distribution approach in which both the canting angle and the magnetic hyperfine field vary within certain intervals. The observed distributions are ascribed to the defect structure of the maghemites (unordered vacancy distribution on B-sites, large surface-to-bulk ratio, presence of OH- groups). An important new finding is the correlation between the magnitude of the hyperfine field and the average canting angle for A-site ferric ions, whereas the B-site spins show a more uniform canting. The Mossbauer parameters of the two hematite samples with MCD104 values of respectively 61.0 and 26.5 nm display a temperature variation which is very similar to that of small-particle hematites obtained from thermal decomposition of goethite. However, for a given MCD the Morin transition temperature for the latter samples is about 30 K lower. This has tentatively been ascribed to the different mechanisms of formation, presumably resulting in slightly larger lattice parameters for the hematite particles formed from goethite, thus shifting the Morin transition to lower temperatures.

Field response of surface spins on Co-adsorbed γ-Fe2O3 (abstract)

The Mössbauer spectrum of a small particle (250 Å diameter), partially reduced γ-Fe2O3 sample coated sequentially with 57Fe and Co was obtained in a 1.8-kOe field transverse to the γ-ray propagation direction at room temperature. The adsorbed 57Fe, less than a monolayer thick, provided half the Mössbauer signal. The data were fit with a distribution in hyperfine fields. The relative areas of the Mössbauer lines of each subspectrum are in the ratio 3:2p:1:1:2p:3, with p the common polarization; large p implies small HK.1 For several possibilities of B-site to A-site population ratios and variations in core isomer shifts, the resultant spectrum least-squares fit values of p were found to be about 1.4. Theoretical calculations1 of composite Mössbauer line intensities based on a model2 of a rigid random-spin shell and a core with its p determined by the anisotropy field obtained1 from magnetization vs applied field measurements yield a composite p≊1.2. Since this value is substantially smaller than experimentally observed, the outer shell spins are not rigidly pinned even in this weak applied field. A simple theoretical free-energy minimization calculation of a linear chain of ferrimagnetically coupled atoms in an external field applied along the hard axis shows that a high anisotropy ‘‘shell’’ will cause a parabolic dependence of sublattice spin angle vs position along the chain, with the maximum deviation from collinearity of a few degrees.<ks>

Some magnetic properties of ?-Fe2O3 synthesized from ferrous fumarate half-hydrate

γ-Fe2O3 synthesized from ferrous fumarate half-hydrate was studied by measurements of D.c. electrical conductivity, Seebeck coefficient, initial magnetization and magnetic hysteresis, and by Mossbauer spectroscopy and scanning electron microscopy. The phase transformation observed by electrical conductivity measurements matched well with the phase transformation observed by the variation with temperature of initial magnetization measurements of γ-Fe2O3; this magnetic study also established the single-domain character of γ-Fe2O3. The magnetic hysteresis values of the γ-Fe2O3 synthesized indicated improved values over that of a γ-Fe2O3 sample synthesized by established procedures. The scanning electron micrographs showed that the γ-Fe2O3 particles were acicular in shape and the Mossbauer spectrum showed a well-resolved six-band spectrum. The presence of a hydrogen ferrite phase was also confirmed by the electrical and magnetic measurements.

Stress-induced playback loss and switching field reduction in recording materials

When a magnetized tape in an oppositely directed field is rubbed, the stress σ reduces the switching field by an amount ΔHσ so as to produce a partial reversal of the magnetization ΔMH,σ. This inverse magnetostrictive effect leads to the playback loss ΔL that is observed in a recorded tape. The loss depends on ΔHσ, the coercive force Hc, the demagnetizing field and the shape of the hysteresis loop. The parameter ΔHσ is proportional to σ and is related to the magnetostriction constants. It can exceed 300 Oe or greater than one half the coercive force in a 3.5% Co-doped γ-Fe2O3 sample when σ=500 kg/cm2. When Co is adsorbed on the surface of γ-Fe2O3 particles the saturation magnetostriction ‖γs‖, ΔHσ and ΔL are all smaller than for a Co-doped tape with an equivalent Hc. The small ΔL for CrO2 is due to its low λs whereas low stress related losses in Fe are due primarily to a high Hc.

Shape Distribution of Magnetic Powders

In work reported earlier, the average length-to-diameter ratios determined magnetically did not agree with those observed under the electron microscope; this was thought due to magnetic interactions. This paper describes further shape determination measurements on γ-Fe2O3 samples of increasing dilution by the original method and by two analogous methods described by Wohlfarth. The results show a slight increase of mean length-to-diameter ratio with dilution and a considerable broadening of the distribution toward large length-to-diameter ratios. The different methods of measurement described do not yield the expected congruent curves at very low concentration. This indicates a deviation from Stoner-Wohlfarth rotation in these particles. The details of the mathematical methods are also described.