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.     

Behaviour of multiphase PVDF in (1−x)PVDF/(x)BaTiO<Subscript>3</Subscript> nanocomposite films: structural,optical, dielectric and ferroelectric properties

The present paper deals with the synthesis and characterization of (1?x)PVDF/(x)BaTiO₃ nanocomposite films with x?=?0.1, 0.2, 0.3, 0.4 and 0.5. The samples were synthesized by simple solution mixing method followed by tape casting process. FESEM images show the homogeneous dispersion of BaTiO₃ nanoparticles within the matrix of poly(vinylidene fluoride) (PVDF) with slight agglomeration. An improvement in the thermal stability of nanocomposite film is observed by TGA results. XRD as well as FTIR analysis indicate the α–β phase transition of PVDF in the nanocomposite films. The embedded BaTiO₃ forms an intermediate band among the PVDF structures and thus decreases the band gap of nanocomposite films by absorbing the wavelength of lower energies. The band gap of nanocomposite films for x?=?0.4 decreases to 2.4 eV as compared to 5.0 eV for pristine PVDF. The dielectric constant (?′) of pristine PVDF at 50 Hz is 8.9, which increases to 26.7 for (0.6)PVDF/(0.4)BaTiO₃ nanocomposite film. An increase in the charge storage ability is observed from PE loops, as (0.6)PVDF/(0.4)BaTiO₃ nanocomposite film has highest value of polarization (0.093 µC cm^?2) as compared to pristine PVDF (0.020 µC cm^?2). This shows an increase in the charge storage ability of (1?x)PVDF/(x)BaTiO₃ nanocomposite films as compared to pristine PVDF.     

Ammonium mediated hydrothermal synthesis of nanostructured hematite (α-Fe2O3) particles

Uniform α-Fe₂O₃ particles of different shapes have been synthesized through hydrothermal process. The additives, the type of Fe(III) salts and reaction conditions in hydrothermal process were thoroughly investigated. The crystalline structure and morphology of the as-synthesized powder have been characterized by using X-ray powder diffraction, scanning electron microscopy and field emission scanning electron microscopy. Rod and ellipsoidal-shaped α-Fe₂O₃ were obtained with ferric chloride as a precursor, while only irregular-shaped particles were synthesized by using ferric nitrate as precursors in the absence of NH₄OH. Direct transformation of micro-rod hematite to ellipsoidal particles with FeCl₃ as precursor was also observed by adding NH₄OH. It is shown that the nanorod was formed through presumed directional aggregation of rapidly formed nucleus, while the formation of ellipsoidal hematite particles may undergo a nucleation–aggregation–dissolution–recrystallization process in the presence of ammonium.     

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.     

The synthesis and selective gas sensing characteristics of SnO(2)/α-Fe(2)O(3) hierarchical nanostructures

SnO(2)/α-Fe(2)O(3) hierarchical nanostructures, in which the SnO(2) nanorods grow on the side surface of α-Fe(2)O(3) nanorods as multiple rows, were synthesized via a three-step process. The diameters and lengths of the SnO(2) nanorods are 6-15?nm and about 120?nm. The growth direction of SnO(2) nanorods is [001], significantly affected by that of α-Fe(2)O(3) nanorods. The hetero-nanostructures exhibit very good selectivity to ethanol. The sensing characteristics are related to the special heterojunction structures, confirmed by high-resolution transmission electron microscopy observation. Therefore, a heterojunction barrier controlled gas sensing mechanism is realized. Our results demonstrate that the hetero-nanostructures are promising materials for fabricating sensors and other complex devices.     

Hydrothermal synthesis,characterization and thermal stability studies of α-Fe2O3 hollow microspheres

A simple, cost-effective hydrothermal technique was used in this study to successfully fabricate hollow α-Fe₂O₃ microspheres, using only fructose and anhydrous ferric chloride without any organic solvent or additive. The synthesized α-Fe₂O₃ hollow microspheres were characterized by X-ray diffraction spectroscopy (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). Based on the results, the shell was composed of aggregated α-Fe₂O₃ nanoparticles, while the fructose-derived carbon core was decomposed during calcination, leaving a hollow interior. XRD analysis confirmed the presence of the α-phase and the absence of γ-phase Fe₂O_3. A mean diameter of 595 nm was estimated for the microspheres by the Gaussian fit of the histogram constructed from the diameters measured over the SEM images. EDX spectrum of the sample showed signals attributed to Fe and O, and a homogenous distribution of these elements was confirmed by elemental mapping studies. ATR-FTIR analysis confirmed the bending and stretching vibration modes of the Fe-O bond. TGA-DTA data depicted that thermal stability of α-Fe₂O₃ hollow microsphere was achieved at 480 °C and no weight loss was observed up to 1000 °C. High-temperature calcination results showed that the material can maintain its hollow morphology up to 700 °C. This material has potential applications in drug delivery, gas sensing, and lithium storage.     

Synthesis and properties of dielectric (HfO2)1 − x (Sc2O3) x films

(HfO₂)_{1 ? x} (Sc₂O₃) _x films have been grown by chemical vapor deposition (CVD) using the volatile complexes hafnium 2,2,6,6-tetramethyl-3,5-heptanedionate (Hf(thd)₄) and scandium 2,2,6,6-tetramethyl-3,5-heptanedionate (Sc(thd)₃) as precursors. The composition and crystal structure of the films containing 1 to 36 at % Sc have been determined. The results demonstrate that, in the composition range 9 to 14 at % scandium, the films are nanocrystalline and consist of an orthorhombic three-component phase, which has not been reported previously. Using Al/(HfO₂)_{1 ? x} (Sc₂O₃) _x /Si test structures, we have determined the dielectric permittivity of the films and the leakage current through the insulator as functions of scandium concentration. The permittivity of the films with the orthorhombic structure reaches k = 42–44, with a leakage current density no higher than ～10^?8 A/cm².     

纳米α-Fe2O3制备的研究进展

综述了近期常用的几种纳米α-Fe2O3制备方法的进展,分类评述了各种方法的优势及存在的问题,指出了发展可控产物粒径和形貌的新途径,揭示了反应的实质,便于其指导并实现大规模工业生产。     

Three-dimensional hierarchical flowerlike α-Fe2O3 nanostructures: synthesis and ethanol-sensing properties

The α-Fe(2)O(3) hierarchical nanostructures have been successfully synthesized via a simple solvothermal method. The as-prepared samples are loose and porous with flowerlike structure, and the subunits are irregularly shaped nanosheets. The morphology of the α-Fe(2)O(3) structures was observed to be tunable as a function of reaction time. To demonstrate the potential applications, we have fabricated a gas sensor from the as-synthesized hierarchical α-Fe(2)O(3) and investigated it for ethanol detection. Results show that the hierarchical α-Fe(2)O(3) sensor exhibits significantly improved sensor performances in comparison with the compact α-Fe(2)O(3) structures. The enhancement of sensing properties is attributed to the unique porous and well-aligned nanostructure.     

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.     

Interface interaction and wetting in the Er2O3/(Cu–Al) and Er2O3/(Cu–Ti) systems

The wetting behavior and metal-oxide interface interactions in the Er₂O₃/(Cu–Al) and Er₂O₃/(Cu–Ti) systems were investigated at 1,423 K in order to evaluate the compatibility of ceramic crucibles with liquid metals, containing active elements. Pure Cu does not wet Er₂O₃ (Θ ≈ 140°) but the wettability is significantly improved by the addition of Al or Ti. It was established that Er₂O₃ reacts with Ti and Al dissolved in liquid Cu and the wettable spinel ErAlO₃ and ErTiO₃ is formed at the interface. The amount of the released Er from the substrate as a result of the reaction and the depth of the reaction zone beneath the drop are controlled by the thermodynamic properties of liquid solutions.     

PPy/α-Fe2O3 hybrid nanocomposites: effect of CSA doping on structural, morphological, optical and electrical transport properties

Hybrid nanocomposites of camphor sulfonic acid (CSA) doped organic polypyrrole and inorganic alpha-ferric oxide (PPy/α-Fe₂O₃) have been successfully prepared using different weight percentages of CSA (10–50 %) dispersed in PPy/α-Fe₂O₃ hybrid nanocomposite by solid state synthesis method. These hybrid nanocomposites are characterized by using various techniques such as X-ray diffraction (XRD), fourier transform infra red (FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–visible spectroscopy and two probe techniques respectively. The XRD spectra revealed that the addition of CSA has no effect on crystallinity of PPy/α-Fe₂O₃ hybrid nanocomposite. The FTIR results show that, the characteristic peaks of PPy/α-Fe₂O₃ hybrid nanocomposite shift to higher wave number after addition of CSA in the PPy/α-Fe₂O₃ nanocomposites indicates some chemical interactions and better conjugation between CSA and PPy/α-Fe₂O₃ hybrid nanocomposites. SEM studies revealed that strong effect on morphology of PPy/α-Fe₂O₃ nanocomposite. The AFM analysis show uniform nano porous granular morphology. UV–visible spectroscopy studies have provided insight into the electronic interaction between the PPy, α-Fe₂O₃ and CSA. DC electrical conductivity showed a steeply increase in electrical conductivity of PPy/α-Fe₂O₃ nanocomposites with increase in amount of CSA from 10 to 50 %.     

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 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.     

A new combustion route to γ-Fe2O3 synthesis

A new combustion route for the synthesis of γ-Fe ₂ O ₃ is reported by employing purified a-Fe ₂ O ₃ as a precursor in the present investigation. This synthesis which is similar to a self propagation combustion reaction, involves fewer steps, a shorter overall processing time, is a low energy reaction without the need of any explosives, and also the reaction is completed in a single step yielding magnetic iron oxide i.e. γ-Fe ₂ O ₃ .The as synthesized γ-Fe ₂ O ₃ is characterized employing thermal, XRD, SEM, magnetic hysteresis, and density measurements. The effect of ball-milling on magnetic properties is also presented.     

Magnetic properties,phase evolution,hollow structure and biomedical application of hematite (α-Fe2O3) and QUAIPH

We investigate synthesis, phase evolution, hollow and porous structure and magnetic properties of quasi-amorphous intermediate phase (QUAIPH) and hematite (α-Fe₂O₃) nanostructure synthesized by annealing of akaganeite (β-FeOOH) nanorods. It is found that the annealing temperature determines the phase composition of the products, the crystal structure/size dictates the magnetic properties whereas the final nanorod morphology is determined by the starting material. Annealing of β-FeOOH at ～300 °C resulted in the formation of hollow QUAIPH nanorods. The synthesized material shows low-cytotoxicity, superparamagnetism and good transverse relaxivity, which is rarely reported for QUAIPH. The QUAIPH nanorods started to transform to porous hematite nanostructures at ～350 °C and phase transformation was completed at 600 °C. During the annealing, the crystal structure changed from monoclinic (akaganeite) to quasi-amorphous and rhombohedral (hematite). Unusually, the crystallite size first decreased (akaganeite → QUAIPH) and then increased (QUAIPH → hematite) during annealing whereas the nanorods retained particle shape. The magnetic properties of the samples changed from antiferromagnetic (akaganeite) to superparamagnetic with blocking temperature T_B = 84 K (QUAIPH) and finally to weak-ferromagnetic with the Morin transition at T_M = 244 K and high coercivity H_C = 1652 Oe (hematite). The low-cytotoxicity and MRI relaxivity (r₂ = 5.80 mM^?1 s^?1 (akaganeite), r₂ = 4.31 mM^?1 s^?1 (QUAIPH) and r₂ = 5.17 mM^?1 s^?1 (hematite)) reveal potential for biomedical applications.     

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.     

Studies on densification ofα-Fe2O3 ceramics

The densification of ceramics of -Fe₂O₃ depends on the processing parameters. The separate influences of milling, sieving, isostatic pressure and sintering atmosphere were investigated. The maximum density, with a value around 96%, was obtained in a sintering atmosphere of nitrogen.