Preparation and characterization of hollow α-Fe2O3 irregular microspheres

Hollow α-Fe₂O₃ irregular microspheres were prepared at 160 °C from a hydrolyzing Fe(ClO₄)₃ solution by adding sodium polyanethol sulphonate. The particles were characterized by ⁵⁷Fe Mössbauer, X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The walls of these hollow particles consisted of elongated subunits composed of elongated and thin α-Fe₂O₃ rods. The precipitation of hollow α-Fe₂O₃ irregular microspheres was governed by the preferential adsorption of sulphonate/sulphate groups. The lateral aggregation of elongated thin rods and subunits also played an important role in the formation of hollow α-Fe₂O₃ irregular microspheres.     

Preparation and characterization of single-phase α-Fe2O3 nano-powders by Pechini sol-gel method

In this work, single-phase α-Fe₂O₃ nano-particles were first synthesized via Pechini sol-gel method using citric acid and polyethylene glycol-6000 as chelating agents. The structural coordination of as-prepared polymeric intermediates was investigated by FTIR analysis. Thermal behavior of the polymeric intermediates was studied by TG-DTG-DSC thermograms. The structure of the powders calcined at different temperatures was characterized by XRD and FESEM. The single-phase α-Fe₂O₃ nano-powders with uniform size were prepared when the polymeric intermediate calcined at 600 °C, and the lowest particle size was found to be 30 nm.     

Preparation and characterization of γ-Fe2O3/ZnO composite particles

γ-Fe₂O₃/ZnO composite particles were prepared via a simple solution method using surface-modified γ-Fe₂O₃ nanoparticles as seeds. The phases and purity of the as-prepared γ-Fe₂O₃/ZnO composite particles were characterized by XRD analysis, and the morphology was studied by SEM, which showed that the γ-Fe₂O₃/ZnO composites are of typical sphere-like morphology with diameters in the range of 300-400 nm. The γ-Fe₂O₃/ZnO composites exhibit magnetic response to an external magnet field and efficient characteristic emissions of ZnO under UV excitation, respectively, indicating that these nontoxic, emissive and magnetic nanoparticles may find use as chemical/biological sensors especially in areas that directly impact human health.     

Template-free synthesis and characterization of snowflake-like α-Fe2O3 microstructures

Single-crystalline α-Fe₂O₃ with a micro-snowflake-like morphology has been synthesized though a hydrothermal reaction in a K₃[Fe(CN)₆] solution without the assistance of any template or surfactant. The morphology and structure of the synthesized hematite were characterized in detail by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. A possible growth process of α-Fe₂O₃ crystals has been proposed, and NaOH plays a crucial role in the formation of the snowflake-like structure. Additionally, magnetic investigations show that the α-Fe₂O₃ crystals exhibit a weakly ferromagnetic property at room temperature with a coercive force of 134 Oe and remnant magnetization of 0.67 emu g^− 1.     

Preparation and characterization of α-Fe2O3 nanorod-thin film by metal-organic chemical vapor deposition

Alpha iron oxide (α-Fe₂O₃) films were grown on catalyst-free silicon substrate using a vertical type metal-organic chemical vapor deposition process. X-ray powder diffraction and field-emission transmission electron microscopy measurements showed that these α-Fe₂O₃ films consisted of bundles of one dimensional (1D) nanorods and the nanorods in these α-Fe₂O₃ films were single crystalline with a well-ordered rhombohedral structure. The nanorods showed a preferred growth orientation in the [104] direction. Magnetic force microscopy image suggests that spin domains were formed in the α-Fe₂O₃ nanorods. Photo-catalytic property of these nanorod films was confirmed through the photo-degradation of Rhodamine B by UV irradiation. These α-Fe₂O₃ film/nanorod materials could be used as building blocks for nanodevice applications.     

Preparation and combustion properties of α-Fe2O3 coated Zr particles

Zirconium particles with irregular morphology and broad size distribution were uniformly coated by spherical α-Fe₂O₃ crystal grain via a facile route without polymer or surfactant as directing agents. The synthesized α-Fe₂O₃/Zr composite particles were characterized by X-ray diffraction, scanning electron microscopy, energy dispersion X-ray, UV-vis spectroscopy and Raman spectroscopy. The synthesis mechanism could be explained by cooperated heterogeneous nucleation and solid state transformation reaction. The combustion properties of α-Fe₂O₃/Zr composite particles were investigated. Compared with Zr particles, the combustion lasting time decreased from 16 s of Zr particles to 0.13 s of α-Fe₂O₃/Zr composite particles, and the top point of temperature reached in combustion increased from 2004 °C of Zr particles to 2378 °C of α-Fe₂O₃/Zr particles.     

Synthesis,characterization and electrochemical properties of three-dimensionally ordered macroporous α-Fe2O3

Three-dimensionally ordered macroporous (3DOM) α-Fe₂O₃ electrode materials with large pore sizes and interconnected macroporous frameworks were successfully synthesized by a simply modified colloidal crystal templating strategy. The obtained samples were characterized by means of thermogravimetry, powder X-ray diffraction, nitrogen physisorption, scanning and transmission electron microscopy. The electrochemical properties of the 3DOM α-Fe₂O₃ were evaluated with cyclic voltammetry and discharge–charge experiments in an organic electrolyte containing a lithium salt. The results showed that the 3DOM α-Fe₂O₃ possessed a potential to be used as an anode material for lithium ion batteries with high initial discharge and charge capacities of 1883 and 1139 mAh g⁻¹, respectively. After 60th cycle, the reversible capacity could still be as high as 681 mAh g⁻¹ with a stable Coulombic efficiency of around 95%.     

Microwave-assisted synthesis and humidity sensing of nanostructured α-Fe2O3

Nanocrystalline α-Fe₂O₃ has been prepared on a large-scale by a facile microwave-assisted hydrothermal route from a solution of Fe(NO₃)₃·9H₂O and pentaerythritol. A systematic study of the morphology, crystallinity and oxidation state of Fe using different characterization techniques, such as transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy was performed. It reveals that nanostructured α-Fe₂O₃ comprises bundles of nanorods with a rhombohedral crystalline structure. The individual nanorod has 8-10 nm diameter and ∼50 nm length. The as-prepared nanostructured α-Fe₂O₃ (sensor) gives selective response towards humidity. The sensor shows high sensitivity, fast linear response to change in the humidity with almost 100% reproducibility. The sensor works at room temperature and rejuvenates without heat treatment. The as-prepared nanostructured α-Fe₂O₃ appears to be a promising humidity sensing material with the potential for commercialization.     

Characterization of structured α-Fe2O3 photoanodes prepared via electrodeposition and thermal oxidation of iron

In this paper we explore the feasibility of using electrodeposition as a low-cost, versatile and easily upscalable technique for preparing α-Fe₂O₃ (hematite) photoanodes for water splitting applications. The photoelectrodes are prepared on transparent conducting glass substrates by electrodeposition of Fe, using a non-aqueous precursor solution at room temperature, followed by thermal oxidation in air. Variations in deposition parameters yield films with diverse morphologies. The effects of the different morphologies on the structural, optical, and photoelectrochemical properties are investigated by photocurrent measurements under AM1.5 illumination. The photocurrent could be improved by growing the first part of the Fe film at low current densities, yielding a dense underlayer, followed by the deposition of a more structured, porous film at high current densities. X-ray diffraction reveals that high deposition currents result in smaller crystallites and a (110) preferred orientation. This orientation is favorable when using hematite as a photoanode, since the conductivity in the [110] direction is known to be up to four orders of magnitude higher than in directions perpendicular to this.     

Synthesis of monodisperse shuttle-like α-Fe2O3 nanorods via the EDA-assisted method

Monodisperse hematite shuttle-like nanorods were synthesized successfully by the ethylenediamine (EDA)-assisted method. The structure and morphology were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectrometer (EDS). XRD studies indicated that the as-prepared product was well-crystallized orthorhombic phase of α-Fe₂O₃. TEM and SEM images showed that the α-Fe₂O₃ nano-particles were of rod shape with an average length of 400 nm and diameter of about 80 nm in the middle part.     

Fabrication and structure characterization of MnCO3/α-Fe2O3 nanocrystal heterostructures

Novel MnCO₃/α-Fe₂O₃ nanocrystal heterostructures, with MnCO₃ nanorods 5-10 nm in diameter and 15-50 nm in length, grown onto the surfaces of the α-Fe₂O₃ nanohexahedrons sized around 30-50 nm, were fabricated via a two-step solvothermal route. The coalescent planes of the heterostructure for the MnCO₃ nanorod and the α-Fe₂O₃ nanohexahedron were determined to be (01?4) and (110), respectively. The formation of the MnCO₃ nanorods from the Mn contained amorphous flakes was tracked by transmission electron microscopy observations at various reaction stages, which suggested a rolling-broken-growth process. Evidenced by the comparative experimental result, the α-Fe₂O₃ nanohexahedrons played an important role in inducing the nucleation and growth of the hexagonal MnCO₃ nanorods on their surfaces.     

Facile synthesis and characterization of ZnFe2O4/α-Fe2O3 composite hollow nanospheres

ZnFe₂O₄/α-Fe₂O₃ composite hollow nanospheres were successfully fabricated via a facile one-pot solvothermal method, utilizing polyethylene glycol as soft template. X-ray diffraction and scanning electron microscopy analysis revealed that the prepared nanospheres with cubic spinel and rhombohedra composite structure had a uniform diameter of about 370 nm, and the hollow structure could be further confirmed by transmission electron microscopy. Energy dispersive X-ray, X-ray photoelectron spectroscopy and Fourier transform infrared techniques were also applied to characterize the elemental composition and chemical bonds in the hollow nanospheres. The ZnFe₂O₄/α-Fe₂O₃ composite hollow nanospheres show attractive light absorption property for potential applications in electronics, optics, and catalysis.     

Preparation and characterization of Y2O3–Sm2O3 co-doped ceria electrolyte for IT-SOFCs

Y₂O₃–Sm₂O₃ co-doped ceria (YSDC) powder was synthesized by a gel-casting method using Ce(NO₃)₃·6H₂O, Sm₂O₃ and Y₂O₃ as raw materials. Phase structure of the synthesized powders was characterized by X-Ray diffraction analysis. Sinterability of the powders was investigated by testing the relative density and observing the microstructure of the sintered YSDC samples. Electrical conductivity of the sintered YSDC samples was measured using impedance spectra method. Single solid oxide fuel cells based on the YSDC electrolyte were also assembled and tested. The results showed that YSDC powders with single-phase fluorite structure can be obtained by calcining the dried gelcasts at temperature above 800 °C. Average particle size of the YSDC powder is 50–100 nm. Relative density of more than 95% of the theoretical can be achieved by sintering the YSDC compacts at temperature above 1400 °C. The sintered YSDC sample has an ionic conductivity of 4.74 × 10⁻² S cm⁻¹ at 800 °C in air. Single fuel cells based on the YSDC electrolyte with 50 μm in thickness were tested using humidified hydrogen as fuel and air as oxidant, and maximum power densities of about 190 and 112 mW cm⁻² were achieved at 700 and 600 °C, respectively.     

Morphological and magnetic properties of the hydrothermally prepared α-Fe2O3 nanorods

α-Fe₂O₃ nanorods were synthesized via hydrothermal method. X-ray powder diffraction revealed the formation of rhombohedral α-Fe₂O₃ single crystal phase with fiber texture. Scanning and transmission electron micrographs analyses showed that the rhombohedral α-Fe₂O₃ has nanorods in shape with diameters of 40–85 nm and lengths of 150–45,000 nm. Isothermal magnetization vs. applied magnetic field curves measured at room and liquid nitrogen temperatures displayed a variation on magnetic ordering: from weak ferromagnetism at room temperature to not hysteretic behavior at liquid nitrogen temperature that is well described by a Langevin function. Moreover, the zero field cooling-field cooling curves under applied magnetic field of 100 Oe confirms the decreasing of Morin temperature transition due to nanometric size of the samples.     

Structural and magnetization studies on nanoparticles of Nd doped α-Fe2O3

It has been observed that, compared to bulk form, the nanocrystalline α-Fe₂O₃ is finding application in various areas. Magnetic properties of α-Fe₂O₃ are found to be influenced by the size of particles and are also sensitive to synthesis method employed for sample preparation. In the present work we have prepared a series of Nd doped α-Fe_2−xO₃ samples (x = 0.0–0.5) by combustion method, without using any fuel. The analysis of room temperature neutron diffraction patterns shows that all the compounds of the series form in the hematite (α-Fe₂O₃) structure, space group R−3c. Magnetization measurements show that there is a broad distribution of particle size in the samples. We find that the increase in the Nd content results in the dilution of magnetism of α-Fe₂O₃. From results we believe that inclusion of Nd in α-Fe₂O₃ drastically modifies the magnetic properties.     

Fabrication and magnetic property of α-Fe2O3 nanoparticles/TiO2 nanowires hybrid structure

α-Fe₂O₃ nanoparticles/TiO₂ nanowires hybrid structure is fabricated by two-step hydrothermal treatment. TiO₂ nanowires are prepared by heating of titanate nanowires, which are obtained by hydrothermal treatment of TiO₂ powder and further repeated HCl treatment. α-Fe₂O₃ nanoparticles are deposited on the surface of TiO₂ nanowires by hydrothermal treatment in Fe(NO₃)₃ solution. The HRTEM images confirm the junctions between α-Fe₂O₃ nanoparticles and TiO₂ nanowires. The formation of hybrid structures has significant influence on the magnetic properties of α-Fe₂O₃. The Morin transition temperature of α-Fe₂O₃ nanoparticles/TiO₂ nanowires hybrid structure is 190 K, which is determined by the sharp peak in the differential ZFC curve. Whereas there is no observable Morin transition for the corresponding isolated α-Fe₂O₃ nanoparticles with similar average particles size of ca. 20 nm.     

Low-temperature mechanochemical–thermal synthesis of α-Al2O3 nanocrystals

The great capability of high-energy ball milled basic polyaluminium chloride gel (PACl) which consisted of the monomeric Al³⁺ ions and polymerized Al³⁺ species such as [Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺ with a Keggin like structure to enhance the phase transformation into α-Al₂O₃ nanocrystals at low temperature was verified. PACl gel 10 min milled and annealed at 400 °C, partially transformed to nanocrystalline α-Al₂O₃ with the mean XRD crystallite size in the range of 15–17 nm, embedded in an amorphous or transition alumina matrix. Further crystal growth up to ∼50 nm and phase pure α-Al₂O₃ powder was obtained when heat-treated at 1000 °C. In contrast to this, the non-milled PACl gel transforms to the transition θ-Al₂O₃ phase at 1000 °C. The evolution of α-Al₂O₃ nanocrystals was studied by XRD, TEM, selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) methods.     

Novel rose-type magnetic (Fe3O4, γ-Fe2O3 and α-Fe2O3) nanoplates synthesized by simple hydrothermal decomposition

Rose-type magnetic nanoplates (RTMNPs) were synthesized by a simple hydrothermal decomposition method where FeCl₂·4H₂O was solely used as a precursor. The synthesized nanoplates were characterized using XRD, FE-SEM, UV-vis absorption (reflectance) spectra and magnetic hysteresis loops. The resulting nanoplates were in the ranges of size 350-500 nm and width 60-70 nm with high crystallinity, purity (shown by XRD) and reproducibility. These iron oxide nanoplates have a great potential in magnetic nanodevices and biomagnetic applications.     

Preparation,magnetization, and microstructure of ionic ferrofluids based on γ-Fe2O3/Ni2O3 composite nanoparticles

Ionic ferrofluids based on γ-Fe₂O₃/Ni₂O₃ composite nanoparticles are a polydispersed system prepared by the Massart method. The magnetization and optical relaxation behaviors of these ferrofluids show that, in addition to the ring-free micelle aggregates, there are also chainlike aggregates in the ferrofluids. The chainlike aggregation is attributed to so-called “depletion force” in the polydispersed ferrofluids because magnetic interaction between the ferrofluid particles is so weak that these particles cannot form the aggregates just by the magnetic interaction. For the γ-Fe₂O₃/Ni₂O₃ ionic ferrofluids, the “depletion force” stimulates the larger ferrofluid particles, forming short chains in the absence of a magnetic field and their macroscopic properties, e.g., magnetization and optical relaxation, all result from the short chains. Ferrofluids having chainlike aggregates alone could have excellent magneto-optical effects.     

Uniform α-Fe2O3 nanotubes fabricated for adsorption and photocatalytic oxidation of naphthalene

Uniform α-Fe₂O₃ nanotubes with small aspect ratio were successfully fabricated by a hydrothermal method. In situ Fourier-transform infrared spectroscopy was used to study the mechanistic details of adsorption and photocatalytic oxidation of naphthalene over theα-Fe₂O₃ nanotubes. A possible degradation mechanism of naphthalene was proposed.