Synthesis and characterization of maghemite iron oxide (γ-Fe2O3) nanofibers: novel semiconductor with magnetic feature

Among the reported nanostructural shapes, nanofibers have special interest due to the long axial ratio which has a distinct impact on many chemical and physical properties. In this study, synthesis of the desirable maghemite iron oxide (γ-Fe₂O₃) nanofibers is introduced. Calcination of electrospun mats composed of ferrous acetate and poly(vinyl alcohol) in argon atmosphere resulted in producing maghemite nanofibers. Detailed characterization affirmed that the obtained γ-Fe₂O₃ nanofibers are free of other iron oxides. Due to the axial ratio impact, the synthesized nanofibers which have an average diameter of ~70 nm do have magnetic properties resemble γ-Fe₂O₃ nanoparticles having an average diameter of ~5 nm. Accordingly, the produced nanofibers are considerable candidate for biomagnetic separation of the biomaterials. The prepared γ-Fe₂O₃ nanofibers can be easily handled as they were obtained in the form of strong mats. Electrical properties study indicated that the introduced nanofibers behave as a semiconducting material. Moreover, the synthesized γ-Fe₂O₃ nanofibers have band gap energy of ~4.2 eV. Based on the simplicity, effectiveness, high-yield, and low-cost features of the utilized preparation process and the studied physiochemical properties of the obtained product, the synthesized γ-Fe₂O₃ nanofibers might have considerable application fields.     

Fe(OH)2微波快速热解制备γ-Fe2O3

用硫酸亚铁为原料加NH3·H2O得到的Fe(OH)2作前驱物,在有CO32-存在下进行微波快速热解可直接得到γ-Fe2O3.与常规的热处理方式相比发现,微波热解产物的分散性较好且粒径减小.而在无CO32-存在时进行微波热解,产物为α-Fe2O3.另外用xRD、TEM等方法对产物进行了表征.     

Synthesis of maghemite (γ-Fe2O3) nanoparticles by wet chemical method at room temperature

In this research work an innovative one step method is described for the production of maghemite (γ-Fe₂O₃) nano-particles at room temperature. The nano-particles were characterized using X-ray diffraction (XRD), infrared spectrum (IR), transmission electron microscopy (TEM) and photon correlation spectroscopy (PCS), respectively. The average crystallite and particle size of the maghemite nano-particles were estimated to be 13 and 10 nm, by XRD and TEM, respectively. The TEM image showed that the γ-Fe₂O₃ nano-particles were of approximate spherical shape. Using the method presented here, maghemite nano-particles, 10 nm in size, could be produced without using organic solvent and oxidation.     

Microwave Synthesis of γ-Fe2O3

Fine-particle Fe₂O₃ is prepared via microwave processing of Fe(NO₃)₃ · nH₂O, followed by low-temperature annealing. The particle size of the resulting -Fe₂O₃ is 5–6 nm after microwave processing and 80–110 nm after subsequent low-temperature heat treatment.     

Synthesis and characterization of core∕shell Fe(3)O(4)∕ZnSe fluorescent magnetic nanoparticles

We report on the successful preparation and characterization of fluorescent magnetic core∕shell Fe(3)O(4)∕ZnSe nanoparticles (NPs) with a spherical shape by organometallic synthesis. The 7 nm core∕3 nm shell NPs show good magnetic and photoluminescence (PL) responses. The observed PL emission∕excitation spectra are shifted to shorter wavelengths, compared to a reference ZnSe NP sample. A dramatic reduction of PL quantum yield is also observed. The temperature dependence of the magnetization for the core∕shell NPs shows the characteristic features of two coexisting and interacting magnetic (Fe(3)O(4)) and nonmagnetic (ZnSe) phases. Compared to a reference Fe(3)O(4) NP sample, the room-temperature Néel relaxation time in core∕shell NPs is three times longer.     

Soft mechanochemical synthesis of MgFe2O4 nanoparticles from the mixture of α-Fe2O3 with Mg(OH)2 and Fe(OH)3 with Mg(OH)2

Abstract

The influence of long term soft milling of a mixture of (1) Mg(OH)₂ and α-Fe₂O₃ and (2) Mg(OH)₂ and Fe(OH)₃ powders in a planetary ball mill on the reaction synthesis of nanosized MgFe₂O₄ ferrites was studied. Soft mechanochemical reaction leading to formation of the MgFe₂O₄ spinel phase was followed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and magnetisation measurements. The spinel phase formation was first observed after 5 h of milling and its formation was completed after 15 h in case (2). The synthesised MgFe₂O₄ ferrite had a nanocrystalline structure with a crystallite size of about 10 and 15 nm respectively for cases (1) and (2). Measurements after 15 h of milling show magnetisation values of 15·23 and 10·14 J T^–1 kg^–1 respectively for cases (1) and (2).     

Synthesis of ferrite grade γ-Fe2O3

Iron(II) carboxylato-hydrazinates: Ferrous fumarato-hydrazinate (FFH), FeC₄H₂O₄·2N₂H₄; ferrous succinato-hydrazinate (FSH), FeC₄H₄O₄·2N₂H₄; ferrous maleato-hydrazinate (FEH), FeC₄H₂O₄·2N₂H₄; ferrous malato-hydrazinate (FLH), Fein4H₄O₅·2N₂H₄; ferrous malonato-hydrazinate (FMH), FeC₃H₂O₄·1.5N₂H₄·H₂O; and ferrous tartrato-hydrazinate (FTH), FeC₄H₄O₆·N₂H₄·H₂O are being synthesized for the first time. These decompose (autocatalytically) in an ordinary atmosphere to mainly γ-Fe₂O₃, while the unhydrazinated iron(II) carboxylates in air yield α-Fe₂O₃, but the controlled atmosphere of moisture requires for the oxalates to stabilize the metastable γ-Fe₂O₃. The hydrazine released during heating reacts with atmospheric oxygen liberating enormous energy, N₂H₄ + O₂ → N₂ + H₂O; ΔH₂O = −621 kJ/mol, which enables to oxidatively decompose the dehydrazinated complex to γ-Fe₂O₃. The reaction products N₂ + H₂O provide the necessary atmosphere of moisture needed for the stabilization of the metastable oxide. The synthesis, characterization and thermal decomposition (DTA/TG) of the iron(II) carboxylato-hydrazinates are discussed to explain the suitability of γ-Fe₂O₃ in the ferrite synthesis.     

One-step synthesis of hematite (α-Fe2O3) nano-particles by direct thermal-decomposition of maghemite

In this research work, α-Fe₂O₃ nano-particles were prepared by direct thermal-decomposition of γ-Fe₂O₃. Precursor powders (γ-Fe₂O₃) were synthesized by wet chemical method at room temperature and then, the precursors were subsequently calcined in air for 1 h at 500 °C. Samples were characterized by thermal gravimetric analysis (TGA), X-ray diffraction (XRD), energy dispersive spectra (EDS), infrared spectrum (IR) and transmission electron microscopy (TEM), respectively. The XRD, EDS, and IR results indicated that the synthesized α-Fe₂O₃ particles were pure. The TEM image showed that the α-Fe₂O₃ nano-particles were spherical and 18 ± 2 nm in size. Magnetic properties have been detected by a vibrating sample magnetometer (VSM) at room temperature. The γ-Fe₂O₃ and α-Fe₂O₃ nano-particles exhibited a super-paramagnetic and weak ferromagnetic behavior at room temperature, respectively. Using the present method, hematite nano-particles can be produced without expensive organic solvent and complicated equipment.     

Mössbauer Studies of the Structure of Core/Shell Fe3O4/γ-Fe2O3 Nanoparticles

Technical Physics Letters - The phase composition, the structure of cores and shells, and the dependences of the shell thickness on the fabrication technique were determined by Mössbauer...     

Preparation of magnetite core–shell nanoparticles of Fe3O4 and carbon with aryl sulfonyl acetic acid

High quality Fe₃O₄/carbon core–shells and shell–core nanoparticles have been successfully synthesized by depositing an epitaxial growth of Fe₃O₄ or carbon shell onto carbon or Fe₃O₄ nanocore. By employing the agents such as aryl sulfonyl acetic acid and glucose, Fe₃O₄ and carbon in a nanoscale was prepared from iron aryl sulfonyl acetate and then by the solvothermal reaction of glucose in a reverse microemulsion. The advantages of present approach rely not only on its simplicity, rapidity, and efficiency of the procedure, but also the formation of the controlled core–shell structures as well. It is highly suitable for further applications. Different core–shell structure controls could be attained by careful adjustment of the procedure sequences of decarboxylation and solvothermal reaction. The magnetic studies show that Fe₃O₄/carbon core–shell and shell–core nanoparticles found to be superparamagnetic. The characteristic differences in the core–shell structures would lead to the change of magnetization behaviors of Fe₃O₄ nanoparticles.     

Synthesis of α-Fe2O3 via oxidative hydrolysis of iron(II) sulphate

The influence of the main reaction parameters (temperature, pH and concentration) in the oxidative hydrolysis of iron (II) sulphate in an acid medium on the properties of the obtained -Fe₂O₃ and its applicability in ferrite production has been studied. The addition of manganese(II) ions catalyses the process in the homogeneous phase, probably by activation of oxygen. The obtained results are discussed within the framework of the assumed reaction mechanism, which includes an homogeneous reaction and a heterogeneous one with the participation of the oxidative hydrolysis product -FeOOH.     

Synthesis, characterization and magnetic properties of polyaniline/γ-Fe2O3 composites

Conducting polyaniline/γ-Fe₂O₃ (PANI/FE) composites have been synthesized using an in situ deposition technique by placing fine-graded γ-Fe₂O₃ in a polymerization mixture of aniline. The composites are characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and infrared (IR) spectroscopy. The electrical properties such as d.c. and a.c. conductivities are studied by sandwitching the pellets of these composites between the silver electrodes. It is observed that the conductivity increases up to a composition of 20 wt.% of γ-Fe₂O₃ in polyaniline and decreases thereafter. The initial increase in conductivity is attributed to the extended chain length of polyaniline, where polarons possess sufficient energy to hop between favourable sites. Beyond 20 wt.% of γ-Fe₂O₃ in polyaniline, the blocking of charge carrier hop occurs, reducing conductivity values. The magnetic properties such as hysteresis characteristics and normalized a.c. susceptibility are also measured, which show a strong dependence on content of γ-Fe₂O₃ in polyaniline. Because of superparamagnetic behaviour of these composites, they may find extensive technological applications, especially for absorbing and shielding applications in microwave frequencies.     

Synthesis and gas sensing properties of α-Fe(2)O(3)@ZnO core-shell nanospindles

α-Fe(2)O(3)@ZnO core-shell nanospindles were synthesized via a two-step hydrothermal approach, and characterized by means of SEM/TEM/XRD/XPS. The ZnO shell coated on the nanospindles has a thickness of 10-15 nm. Considering that both α-Fe(2)O(3) and ZnO are good sensing materials, we have investigated the gas sensing performances of the core-shell nanocomposite using ethanol as the main probe gas. It is interesting to find that the gas sensor properties of the core-shell nanospindles are significantly enhanced compared with pristine α-Fe(2)O(3). The enhanced sensor properties are attributed to the unique core-shell nanostructure. The detailed sensing mechanism is discussed with respect to the energy band structure and the electron depletion theory. The core-shell nanostructure reported in this work provides a new path to fabricate highly sensitive materials for gas sensing applications.     

Green synthesis of α-Fe2O3 nanoparticles for photocatalytic application

In this study, the preparation of α-Fe₂O₃ nanoparticles using curcuma and tea leaves extract are reported. The curcuma and tea leaves are acted as a reductant and stabilizer. The crystal structure and particle size of the as-synthesized materials were measured through X-ray diffraction. X-ray diffraction patterns revealed that the as-prepared samples were α-Fe₂O₃ nanoparticles with well-crystallized rhombohedral structure and the crystallite sizes of the α-Fe₂O₃ nanoparticles are 4 and 5 nm. Scanning electron microscopy images showed that the prepared samples have spherical shape. The purity and properties of the as-synthesized α-Fe₂O₃ nanoparticles were measured by Raman spectroscopy. The chemical compositions of the as-prepared α-Fe₂O₃ nanoparticles have been analyzed by Fourier transform infrared spectroscopy. The absorption edge of the α-Fe₂O₃ nanoparticles are 561 and 551 nm. The photocatalytic activity of the α-Fe₂O₃ nanoparticles was measured by degradation of methylene orange and the α-Fe₂O₃ nanoparticles showed the excellent photocatalytic performance.     

Sonochemical fabrication and catalytic properties of α-Fe2O3 nanoparticles

In this study, α-Fe₂O₃ (hematite) nanoparticles were synthesised by a sonochemical method. The influence of different factors such as chemical composition of the precursors, atmosphere of the reactions and type of the sonicator on the chemical formula, crystallinity, morphology and size of the obtained products were investigated. Powder X-ray diffraction, scanning electron microscopy and IR spectroscopy, were used to characterise the nanostructures. The catalytic tests were performed in the reaction of methyl phenyl sulphide oxidation. The results exhibit the good catalytic performance of the as-prepared α-Fe₂O₃ nanoparticles.     

Solvothermal synthesis and characterization of acicular α-Fe2O3 nanoparticles

Nanometer-sized α-Fe₂O₃ particles have been prepared by a simple solvothermal method using ferric acetylacetonate as a precursor. The products were characterized by X-ray diffraction (XRD), energy dispersive X-ray microanalysis (EDAX), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transition electron microscopy (TEM), infrared spectroscopy (IR) and thermal analysis (TG-DTA). XRD indicates that the product is single-phase α-Fe₂O₃ with rhombohedral structure. Bundles of acicular shaped nanoparticles are seen in TEM images with an aspect ratio ～ 12; typically 8–12 nm wide and over 150 nm long. The α-Fe₂O₃ nanoparticles posses a high thermal stability, as observed on thermal analysis traces.     

Green synthesis of mesoporous hematite (α-Fe2O3) nanoparticles and their photocatalytic activity

A green synthesis method for the preparation of mesoporous α-Fe₂O₃ nanoparticles has been developed using the extract of green tea (camellia sinensis) leaves. This simple and one-step method can suitably be scaled up for large-scale synthesis. The as-prepared mesoporous nanoparticles were characterized by SEM, TEM, XRD, XPS, Raman, UV–visible spectroscopy and N₂ adsorption analysis. The nanoparticles were highly pure and well crystallized with an average particle size of 60 nm. The photocatalytic activity of nanoparticles was evaluated by the amount of hydroxyl radical formation under visible light irradiation detected by fluorescence spectroscopy. The as-prepared α-Fe₂O₃ showed two times higher activity than commercial α-Fe₂O₃ in term of hydroxyl radical formation and enhanced performance in a photoelectrochemical cell. Also, a plausible mechanism for the formation of mesoporous α-Fe₂O₃ has been suggested.     

Synthesis and Mossbauer studies of mesoporous γ-Fe2O3

A method of synthesis of mesoporous γ-Fe₂O₃ by thermal decomposition of iron citrate has been proposed. Investigations of the crystalline and magnetic structure of obtained materials were done. Nanodispersed maghemite (γ-Fe₂O₃) with the sizes of coherent scattering regions of about 4–7 nm consisted of one phase only after gel sintering at 200, 250 and 300 °C. The particles of synthesized materials were both in magnetically ordered, and superparamagnetic states, and they formed a grid-like mesoporous structure. The influence of magnetic dipole interparticle interaction on the parameters of Mossbauer spectra was observed. A phenomenological model of the differences between nanodispersed γ-Fe₂O₃ magnetic microstructures obtained after annealing at different temperatures was presented.