Narrow Results

In this study, the $\alpha$-Fe₂O₃ nanowires were synthesized and decorated by ZnO nanoparticles using the hydrothermal method. The structural and morphological study of samples was carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrum (EDS), High resolution transmission electron microscopy (HRTEM), and Fourier transform infrared spectroscopy (FTIR) techniques. FTIR was employed for $\alpha$-Fe₂O₃ and $\alpha$-Fe₂O₃ decorated with ZnO nanoparticles composites to verify the presence of ZnO in the composite after decorating. Furthermore, the optical properties was carried out using UV-vis spectrophotometer and photoluminescence spectra (PL) techniques. XRD analysis showed $\alpha$-Fe₂O₃ nanowires had a rhombohedral structure with a preferred crystal plane (104). In the $\alpha$-Fe₂O₃ nanowires decorated by ZnO nanoparticles, ZnO nanoparticles showed a hexagonal structure. Due to SEM images, the nanowires had an average diameter of 41 nm, and ZnO nanoparticles had a spherical shape with a maximum diameter of 70 nm. A uniform distribution was observed for both the $\alpha$-Fe₂O₃ nanowires and the $\alpha$-Fe₂O₃ nanowires decorated with ZnO nanoparticles. Furthermore, the result of bandgap energy calculation was 2.12 eV for $\alpha$-Fe₂O₃, while for $\alpha$-Fe₂O₃ nanowires decorated with ZnO nanoparticles was 3.17 eV which is near to the bandgap energy of ZnO nanoparticles. PL spectra revealed a few transitions in which the origin of these emissions would be associated to oxygen vacancies, iron vacancies, defects and band-to-band transition. The PL emission peaks of $\alpha$-Fe₂O₃ nanowires decorated with ZnO nanoparticles are similar to $\alpha$-Fe₂O₃ nanowires, but notably quenched with the ZnO nanoparticles. Based on the result of this study, it is possible to tune bandgap energy for various applications. In addition, this composite is promising candidates for solar cell photo electrodes and gas sensor applications.

Structural and optical properties of F-center (two electrons trapped by an oxygen vacancy) defect in hematite have been studied using a quantum-chemical model. Calculated absorption energies, 0.9 eV and 3.6 eV, are discussed in terms of the available experimental data. An explanation for the origin of experimentally observed electron depletion in hematite is proposed.

Three-dimensional (3D) photocatalytic devices are economical and environmental, since they can be easily recycled and reused. In this paper, a kind of 3D photocatalytic device with a rod diameter of 250 μm was fabricated using the aqueous-based α-Fe₂O₃ ceramic inks by direct ink writing (DIW) method. The properties of the DIW woodpile samples were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and optical microscope. The result shows that the ink with solid content of 71.4 wt.% exhibits a shear thinning behavior and proper viscoelastic properties, which ensure a feasible extrusion in the whole shaping process. The sample sintered at 800°C in air causes photocatalytic degradation of methylene blue (MB) solution under the ultraviolet (UV) light. The photocatalytic properties of the α-Fe₂O₃ woodpile structure was characterized by the UV-visible light spectrophotometer, and it was found to be better than that of bulk sample with same weight for its higher specific surface. The DIW technique would offer a potential method for the design and fabrication of 3D photocatalytic devices.

A new technique for designing the crystal shape and orientation of single crystalline hematite (α-Fe₂O₃) nanoparticles was developed. By thermal decomposition of FeCO₃ single crystals, a novel micro-scale core–shell structured α-Fe₂O₃/Fe₃O₄ crystals were obtained. The shape of the crystal remained unchanged when single crystals of FeCO₃ phase changed into α-Fe₂O₃ at 450°C. The rhombohedral α-Fe₂O₃ unit cell had the same orientation with the parent rhombohedral FeCO₃. The α-Fe₂O₃ single crystal nanoparticles were formed continuous and intricate network in the core of Fe₃O₄ thin shell, and its temperature dependence of cell dimensions show non-linearity.

The band structures and optical properties of α-Fe₂O_3-xSe_x alloys are studied by means of first-principles methods, considering different Se contents x. Numerical results show that Se content has an obvious influence on band structures and optical properties of α-Fe₂O_3-xSe_x alloys. The band gap values of α-Fe₂O_3-xSe_x alloys decrease monotonically when Se concentrations increase, resulting in an obvious increase of the optical absorption edge in the visible range. In particular, our results show that α-Fe₂O_3-xSe_x alloys have the direct band gap properties with band gap values when Se content x ≈ 0.17, which is beneficial to solar cell applications.

This paper presents the study of forming mechanism of $\alpha$-Fe₂O₃ in oxide films on electrolytic in-process dressing (ELID) grinding wheel surface. To investigate the component content and the microtopography of oxide films, XRD, XPS, IR spectrum analysis, SEM, and TEM measurements are performed on ELID grinding wheels. In XRD test results, the characteristic absorption band of $\alpha$-Fe₂O₃ is found in the oxide film. XPS tests show that there is full of ferrous iron and oxygen element in the oxide film. Also, the characteristic spectral line of XPS is identical to the standard spectrum of $\alpha$-Fe₂O₃. Several vibration peaks (471, 1029, 1384, 1630, 3430) are observed by IR spectrum analysis. It can be easily seen by contrast with the standard photographs that the vibration peak of 1029 is of Fe-O vibration band in IR spectrum of $\alpha$-Fe₂O₃ powder. Therefore, these measurement results confirm the existence of $\alpha$-Fe₂O₃ in the oxide films, and explain the polishing effect of oxide films during ELID grinding. The fresh oxide film is porous and moisture rich. However, the oxide film after squeezing to dry is investigated by SEM imaging to present tortoiseshell cracks. Geometrically, $\alpha$-Fe₂O₃ appears to be nearly spherical with particle size around 5–50 nm. This indicates fine polishing improvement by oxide films, and is identified as the mechanism responsible for excellent surface quality by ELID grinding.

The hematite surface will affect the field emission of the iron materials. This work is to investigate the work functions of (001) and (00−1) surfaces of $\alpha$-Fe₂O₃ by using the density functional theory. In order to avoid the polarization effect, a symmetric slab model is constructed in the calculation. Their work functions are 6.10 eV and 5.49 eV, respectively.

α-Fe₂O₃@ATO (antimony doped tin oxide) nanocomposite particles with core–shell structure were prepared by homogeneous precipitation method using monodispersed α-Fe₂O₃ (hematite) nanoparticles as cores, SnCl₄ · 5H₂O and SbCl₃ as the precursor of the shell. The morphology and structure of the nanocomposite particles were studied with transmission electron microscopy and X-ray diffraction, respectively. The electricity properties of the nanocomposite were also investigated in terms of coating amount, molar ratio of element Sb to Sn, and heat treatment conditions. The results showed that the conditions of ATO/α-Fe₂O₃ (weight ratio) = 70%, n(Sb)/n(Sn) = 10%, calcined at 700°C for 1 h were optimal for the conductivity of the nanocomposite.

Nanoparticles of alpha ferric oxide ($\alpha$-Fe₂O₃) were prepared by the hydrothermal method. Structural properties of $\alpha$-Fe₂O₃ were determined by XRD, SEM and AFM measurements. The particles had a good matching with standard pattern. Average particle size was about 90nm and the distribution extended from about 20nm to 120nm. Biocompatibility study of ferric oxide nanoparticles against bacteria, parasites, tumor cell line and normal cells was determined. No antibacterial activity was observed for the concentration, of ferric oxide nanoparticles in distilled water, up to 1.5mg/ml vs. E. coli and S. aureus. Moreover, MTT assay was used to determine the cytotoxicity against parasites and cells. Intermediate cytotoxicity (53.30%) of 1.5mg/ml of prepared nanoparticles was noted against L. tropica, while weak cytotoxicity of 5.20% was observed against L. donovani at the same concentration of ferric oxide nanoparticles. On the other hand, the prepared nanoparticles revealed low cytotoxicity (47.28%) against SR tumor cell line, while no cytotoxicity was shown against lymphocytes, as a model of normal cells.

In this paper, a new simple approach has been developed for the preparation of α-Fe₂O₃ microspheres by a facile hydrothermal method using PVP as a surfactant. Uniform α-Fe₂O₃ microspheres could be routinely synthesized through solvothermal approach by controlling the PVP/FeCl₃⋅6H₂O ratio. The as-obtained α-Fe₂O₃ microspheres exhibit high efficiency on the decolorization of RhB aqueous solution in the presence of H₂O₂ at room temperature.

The design and controllable synthesis of semiconductors at the nanoscale level is a critical strategy for adjusting the performance of catalysts. In this work, size-controlled $\alpha$-Fe₂O₃ with nanocubic structure is fabricated through a simple solvothermal method. The growth process of cubic $\alpha$-Fe₂O₃ nanocrystals is investigated by time-dependent solvothermal reaction experiments, which displays a typical Oswald ripening mechanism: flower-like nucleation, followed by growing and ripening of nuclei into different morphologies and sizes during the solvothermal process. The UV–vis absorption results revealed that $\alpha$-Fe₂O₃ nanocubes present a size-dependent optical property. The $\alpha$-Fe₂O₃-10h with an average particle size of 37nm exhibits good crystallinity, large specific surface area and high UV–vis light absorption, subsequently resulting in the highest photocatalytic efficiency together with excellent stability.

Hematite is currently considered one of the most promising photoanode materials for light-driven water splitting. The photoelectrochemical performance of hematite is limited by its low conductivity. In this work, we demonstrate that the conductivity of hematite films can be tuned by controlling the orientation of hematite crystals. By applying a high magnetic field (up to 10 T) during the drop-casting preparation, hematite films composed of single crystal particles show featured texture by promoting those particles alignment with (001) normal to the substrate. By enhancing the photocurrent densities with tuned hematite orientation, the current method provides an effective way for increasing the number of carriers that can reach the surface.

Barium hexaferrite was synthesized by combining citric acid sol–gel process with self-propagating at high temperature, relationship between the forming temperature of barium ferrite, and crystal phase was investigated in the experiment. The thermo-gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used in the analysis to discuss the influence of different amounts of citric acid additives on the calcination product crystal phase, and relationship of transformation of $\gamma$-Fe₂O₃ to $\alpha$-Fe₂O₃ between W-type and M-type of the crystal phase of barium hexaferrite. The results revealed that the crystal phase of barium hexaferrite was W-type when the value of CA/MN $\le 1.2$, and if CA/MN $=2$, the crystal phase became M-type. With the increase in the amount of citric acid, the crystallization temperature of product rose. The excessive citric acid additive changed the existing form of Fe, which contributed to the transformation of $\gamma$-Fe₂O₃ to $\alpha$-Fe₂O₃. The latter had greater thermal stability, resulting in an increase in the formation temperature of the W-type barium hexaferrite, and finally obtaining the M-type.

Herein, $\alpha$-Fe₂O₃ hollow cage-like nanostructures were prepared via a simple in situ template-assisted hydrothermal route. The results showed that the shell and the size of the $\alpha$-Fe₂O₃ hollow nanostructures could be easily controlled by adjusting the amount of Fe source (FeCl${}_3)$. By increasing the amount of Fe source, the size increases, and the shells are built up from the dense single nanoparticle aggregations to crosslinked nanoparticle aggregations with large cavities gradually. It is found that the surface morphology has great impact on charge separation and transport of the $\alpha$-Fe₂O₃ cage-like nanostructures, too dense particle aggregations and too many large cavities are unfavorable for electron transport, only the product with an optimal primary particles and channels could exhibit good catalytic performance in photo-Fenton degradation of rhodamine B (RhB) with visible light.

As a novel strategy for improving the photocatalytic activity through hybrid with small molecule photosensitizer, $\alpha$-Fe₂O₃ has been successfully functionalized with protoporphyrin IX (PPIX) in order to enhance sunlight-driven photocatalytic degradation of dyes and antimicrobial activity due to the staggered energy band structures which promote a charge transfer between $\alpha$-Fe₂O₃ and PPIX and generate free holes and electrons. The results show that $\alpha$-Fe₂O₃ could absorb more sunlight and generate more free electrons and holes after being decorated with PPIX. As a result, PPIX-functionalized $\alpha$-Fe₂O₃ has an enhanced photocatalytic degradation of dyes ability against rhodamine B and methyl orange and antimicrobial activity against Escherichia coli. The present strategy gives a promising way to prepare photocatalytic agent hybrid with small molecule photosensitizer.