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.     

Enhanced ethanol sensing properties based on α-Fe2O3/In2O3 hollow microspheres

α-Fe₂O₃ and In₂O₃ hollow microspheres were synthesized via a simple green hydrothermal route, and the α-Fe₂O₃/In₂O₃ composite sample was prepared by mixing two products above together in a molar ratio of 1:1. Traditional ceramic tube structure gas sensors were fabricated and their gas sensing characteristics were obtained. The results indicated that the α-Fe₂O₃/In₂O₃ sample showed an improved sensitivity and selectivity to ethanol, compared with either α-Fe₂O₃ or In₂O₃ sample. Moreover, the sensitivities of both In₂O₃ and α-Fe₂O₃/In₂O₃ sensors were good linear with gas concentrations (1–500?ppm) to ethanol, and the response was found to remain stable for 150?days. In addition, the gas sensing mechanism of ethanol detection has been discussed.     

Hydrothermal synthesis of monodisperse dodecahedron α-Fe2O3 nanocrystals with high photocatalytic activity

Novel α-Fe₂O₃ dodecahedron nanocrystals were prepared by a facile one-step hydrothermal method without using any templates. The samples were analyzed by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, respectively. The results revealed that the as-prepared nanocrystals with the average diameters of 200 nm are well-shaped symmetric hexagonal bipyramidal structure. The homogeneous dodecahedron nanoparticles were obtained by optimizing the experimental conditions including reaction temperatures and time. A possible formation mechanism was also proposed. To demonstrate potential applications, the photocatalytic activity of the as-prepared samples was evaluated by photo-degradation of rhodamine B from aqueous solution at room temperature. Results show that the α-Fe₂O₃ dodecahedron with exposed (012) plane exhibits significantly improved photocatalytic activities for degradation of rhodamine B in aqueous solution under visible light irradiation.     

Preparation and characterization of α-Fe2O3–CeO2 composite

In our previous study we attempted to see the effect of cerium doping (Ce/Fe ratio 0.015 to 0.074) on goethite matrix and conversion of doped goethite to hematite. In the present communication, nano-structured α-Fe₂O₃–CeO₂ composite with Fe/Ce weight ratio as 1.1 has been synthesized by calcination of goethite-cerium hydroxide precursor prepared by co-precipitation method. It was observed that co-precipitation of cerium along with iron in hydroxide medium resulted in hindering the formation of crystalline order as the precursor formed showed poorly crystallized goethite and almost no crystallinity in Ce(OH)₄. Calcination of the precursor at 400 °C showed the formation of hematite together with a broad peak corresponding to cerium oxide whereas at 800 °C, two distinct phases of α-Fe₂O₃ and CeO₂ were observed. The Mössbauer spectra showed the presence of a paramagnetic component both for the precursor as well as for the sample calcined at 400 °C but on raising the calcination temperature to 800 °C, the paramagnetic component disappeared and the spectrum corresponding to pure α-Fe₂O₃ phase was observed. The microstructure of the product obtained by calcining at 800 °C showed rod like structure (30 to 50 nm width and 300 to 500 nm length) of α-Fe₂O₃ having equi-dimensional CeO₂ particles on and around the surface. Besides the rods, equi-dimensional particles and agglomerates corresponding to CeO₂ were also observed. The results show that co-precipitation followed by calcinations gives nanorods hematite with CeO₂ particles bonded to its surface.     

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.     

Hydrothermal synthesis of Fe3O4 and α-Fe2O3 nanocrystals as anode electrode materials for rechargeable Li-ion batteries

This paper describes a facile, economical and environment-friendly hydrothermal method of fabricating Fe₃O₄ and α-Fe₂O₃ nanoparticles at 180 °C for 12 h, respectively. The as-obtained products were characterized in detail. X-ray powder diffraction and transmission electron microscopy were used to investigate the products’ properties of crystal form, size, and morphology. The results showed the Fe₃O₄ and α-Fe₂O₃ nanocrystals’ diameter were about 5 and 20 nm, respectively. Moreover, the electrochemical performances of the Fe₃O₄ and α-Fe₂O₃ nanoparticles as anode materials for Li-ion batteries were also evaluated. The first-discharge capacities of Fe₃O₄ and α-Fe₂O₃ nanocrystals were 1,380 and 1,280 mAh g^?1, and stabled about 96 and 75 mAh g^?1 after 20 cycles, respectively. These materials offer substantial promise for developing alternative, high capacity negative electrodes for safer lithium batteries as energy storage and conversion materials.     

Top-down synthesis of mesocrystalline α-Fe2O3 submillimeter-sized rhombohedrons

ABSTRACT

Here, we focus on the obtaining of mesocrystalline submillimeter-sized (150/50 µm) rhombohedral hematite (α-Fe₂O₃) by thermal treatment in air of single crystalline submillimeter-sized (150/50 µm) rhombohedrons of ferrous carbonate (FeCO₃). Mass spectrometer-coupled thermogravimetric analysis and TGA-MS revealed the chemical reactions occurring during the thermal treatment of ferrous carbonate sample. The X-ray Diffraction (XRD) data sustain that the final product is hematite. The XRD line-profile analysis indicates that the resulted hematite is built of individual ordered crystallites with 66 ± 5 nm average sizes, confirmed by scanning electron microscopy and transmission electron microscopy images. Small-angle x-ray scattering investigation of hematite sample was presented. The log-log plot of scattering intensity decay showed the same slope, α = ?3.76, corresponding to both high and low scattering vector regions; the fractal surface is D_s = 2.24. This fractality is extended over a range of sizes and can touch high molecular dimensionality. The internal morphology and the synthesis mechanism of the obtained hierarchical superstructure were described.     

Mechanochemical preparation and thermal stability of γ-Fe2O3 derived from γ-FeOOH

The dehydration process of lepidocrocite, γ-FeOOH, induced by wet grinding procedures has been studied. Microcrystals of maghemite, γ-Fe₂O₃, are found in the product of ball-milling in hexane and cyclohexane media. In contrast, grinding in air leads to hematite α-Fe₂O₃. This change is accompanied by the development of a characteristic texture in which a slit-shaped porous system is present. On the other hand, mechanochemically prepared maghemite increases in its thermal stability. This fact has been attributed to the higher crystallinity of ground microcrystals as revealed by the values of crystallite size and microstrains.     

Synthesis and characterization of hollow glass–ceramics microspheres

Hollow glass–ceramics microspheres (HGCMs), with the diameter from 10 to 60 μm and the shell thickness less than 2 μm, were successfully fabricated by a simple technique using polyacrylamide microspheres (PAMs) as template. The corresponding HGCM were obtained after a thermal treatment of the core–shell microspheres, which were synthesized with organic template method. The size, morphology and phase composition of synthesized products were determined via XRD, SEM, TGA. The effects of the amount of glass powder, the Hydrophile–Lipophile Balance (HLB) value, the sintering temperature, and the ratio of pre-adsorbed water to the water in the slurry on the morphologies of HGCM have been investigated. The results showed that the agglomeration of HGCM can be reduced by adjusting the HLB value. In addition, the amount of solid beads decreases obviously by reducing ratios and adjusting the HLB value. As the sintering temperature increases, the surface of the HGCM becomes smooth and compact. Meanwhile, computational investigations are carried out to better understand the strengthen effect of taking glass–ceramics materials in the system MgO–Al₂O₃–SiO₂ (MAS) as shell materials.     

Simple and rapid synthesis of α-Fe2O3 nanowires under ambient conditions

We propose a simple method for the efficient and rapid synthesis of one-dimensional hematite (α-Fe₂O₃) nanostructures based on electrical resistive heating of iron wire under ambient conditions. Typically, 1–5 μm long α-Fe₂O₃ nanowires were synthesized on a time scale of seconds at temperatures of around 700 ° ⊂. The morphology, structure, and mechanism of formation of the nanowires were studied by scanning and transmission electron microscopies, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman techniques. A nanowire growth mechanism based on diffusion of iron ions to the surface through grain boundaries and to the growing wire tip through stacking fault defects and due to surface diffusion is proposed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Thermal decomposition synthesis of 3D urchin-like α-Fe2O3 superstructures

Urchin-like α-Fe₂O₃ superstructures have been deposited on Si substrate using thermal decomposition FeCl₃ solution at 200–600 °C in the oven. The morphologies and structures of the synthesized urchin-like superstructures have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results show that urchin-like α-Fe₂O₃ superstructures were a polycrystal with the rhombohedral structure and typical diameters of 16–20 nm and lengths up to 1.0 μm. The as-prepared α-Fe₂O₃ superstructures have a high Brunauer–Emmett–Teller (BET) surface area of about 60.24 m²/g. The photoluminescence spectrum of the urchin-like α-Fe₂O₃ superstructures consists of one weak emission peak at 548 nm (2.26 eV). A possible new mechanism for the formation of the urchin-like superstructures was also preliminarily discussed.     

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.     

Fabrication, growth mechanism, and characterization of α-Fe(2)O(3) nanorods

This work reports the facile synthesis of α-Fe(2)O(3) nanorods and nano-hexagons and its application as sunlight-driven photocatalysis. The obtained products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), diffused reflectance spectroscopy (DRUV-vis), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The phase and crystallinity were confirmed from the XRD study. Electron microscopy study clearly indicates the formation of different morphologies of nanocrystals. These hematite nanostructures were used as a model system for studying the shape-dependent photocatalytic degradation of phenol, methylene blue, and congo red. Amongst all the nanostructured semiconductors, Pt-doped hematite nanorod showed 55% efficiency towards the decolonization of methylene blue and 63% toward congo red under sun light illumination. The difference in photocatalytic activity is discussed in terms of their crystallize size and morphological ordering.     

Mechanochemical synthesis and characterization of xIn2O3��(1???x)��-Fe2O3 nanostructure system

Indium oxide-doped hematite xIn₂O₃·(1 ? x)??-Fe₂O₃ (x = 0.1?C0.7) nanostructure system was synthesized using mechanochemical activation by ball milling and characterized by XRD, simultaneous DSC?CTGA, and UV/Vis/NIR. The microstructure and thermal behavior of as obtained system were dependent on the starting In₂O₃ molar concentration x and ball milling time. XRD patterns yielded the dependence of lattice parameters and grain size as a function of ball milling time. After 12 h of ball milling, the completion of In³⁺ substitution of Fe³⁺ in hematite lattice occurs for x = 0.1, indicating that the solid solubility of In₂O₃ in hematite lattice is extended. For x = 0.3, 0.5, and 0.7, the substitutions between In³⁺ and Fe³⁺ into hematite and In₂O₃ lattice occur simultaneously. The lattice parameters a and c of hematite and lattice parameter a of indium oxide vary as a function of ball milling time. The changes of these parameters are due to ion substitutions between In³⁺ and Fe³⁺ and the decrease in the grain sizes. Ball milling has a strong effect on the thermal behavior and band gap energy of the as-obtained system. The hematite decomposition is enhanced due to the smaller hematite grain size. The crystallization of hematite and In₂O₃ was suppressed, with drops of enthalpy values due to the stronger solid?Csolid interactions after ball milling, which caused gradual In³⁺?CFe³⁺ substitution in hematite/In₂O₃ lattices. The band gap for hematite shifts to higher energy value, while that of indium oxide shifts to lower energy value after ball milling.     

Controlled synthesis of mesoporous α-Fe2O3 nanorods and visible light photocatalytic property

Porous α-Fe₂O₃ nanorods with typical pore size of 2–4 nm were controlled prepared by a facile hydrothermal process of Fe(NO₃)₃·9H₂O aqueous solution in the presence of NaOH, followed by a calcination treatment. Contrast experiments indicate that the morphology and crystalline structure of the hydrothermal products depend greatly on the quantity of NaOH. Hematite nanoparticles and microplates were respectively obtained under conditions without or with excess NaOH. The porous α-Fe₂O₃ nanorods exhibit a high BET surface area of 105.1 m² g^?1 and a pore volume of 0.13 m³ g^?1. UV–vis measurement shows wide absorption to visible light and an obvious blue-shift of the adsorption edge due to the quantum size effect. The visible-light photocatalytic performances of the as-prepared samples were evaluated by photocatalytic decolorization of methylene blue at ambient temperature. The results indicate that the photocatalytic activity of the porous α-Fe₂O₃ nanorods is superior to hematite nanoparticles and platelets and exhibit good reusable feature. The photocatalytic process of porous structure is determined to be pseudo-first-order reaction with apparent reaction rate constant of 1.04 × 10^?2 min^?1. And the optimum photocatalyst dosage is 20 mg per 100 mL of dye solution. The porous α-Fe₂O₃ nanorods are considered potential photocatalyst for practical application due to the excellent photocatalytic behavior and good reusability.     

Novel process for synthesis of α-Fe2O3: microstructural and optoelectronic investigations

Novel chemical synthesis method has been successfully employed for the preparation of n type α-Fe₂O₃ nanoparticles. Thin films of annealed Fe₂O₃ powders processed on glass substrates using spin coating technique. The effects of process temperature on the structural, morphological, electrical transport and optical properties were studied. X-ray diffraction study revealed formation of single phase nanocrystalline hexagonal α-Fe₂O₃. Microstructural analysis confirms nanostructured morphology. Dc electrical conductivity measurement reveled the semiconducting nature with room temperature electrical conductivity increased from 10^?4 to 10^?3 (Ω cm)^?1 as process temperature of Fe₂O₃ increased from 400 to 700 °C respectively. The n-type electrical conductivity is confirmed from thermo-emf measurement with no appreciable change in thermoelectric power after increasing processing temperature. The decrease in the band gap energy from 3.88 to 2.62 eV was observed after increasing process temperature.     

Chemical synthesis of faceted α-Fe2O3 single-crystalline nanoparticles and their photocatalytic activity

Faceted hematite nanocrystals have been synthesized via a hydrothermal route and their different morphologies can be tuned by appropriate stabilizer molecules. Detailed observation by high-resolution transmission electron microscopy and atomic force microscopy has revealed many terraces, steps, and kinks on the faceted surface of hematite nanoparticles, and thus, one growth mechanism of the terrace-step-kink model has been suggested to play a major role in determining the equilibrium morphology, together with effect of surface chemistry via the interaction between outer surfaces of iron and oxygen ions and functional groups. The photocatalytic activities were evaluated by decomposing rhodamine B dye. It has been shown that polyhedron hematite particles enclosed by high-index surface planes exhibited higher photoactivity. Density functional theory calculations revealed that the higher photoactivity originates from the more flat band edge in directions normal to the surface planes.     

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.     

Effect of mechanical activation on the synthesis of α-Fe2O3-Cr2O3 solid solutions

Continuous -Fe₂O₃-Cr₂O₃ solid solution series have been synthesized by two methods: (i) direct heating of coprecipitated hydroxides, and (ii) mechanical pre-treatment followed by heating. It is shown that mechanical treatment leads to a decrease in the preparation temperature of the solid solutions to 623 K. The formation of a continuous solid solution series by direct heating begins only at 773 K. The formation of the solid solutions was established by X-ray diffraction analysis, infrared and Mössbauer spectroscopy. The decrease in synthesis temperature of the -Fe₂O₃-Cr₂O₃ solid solutions is attributed to activation of the samples during their mechanical treatment. The samples obtained have large specific surface areas (up to 130 m² g^–1).