Facile synthesis of ring-like α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> assembly composed of small hematite particles for highly efficient photocatalysis

A new-type of ring-like α-Fe₂O₃ assembly were prepared via facile top-down etching method from hematite saucer-like nanocrystals composed of small α-Fe₂O₃ particles. HRTEM and BET results demonstrated that the ring-like α-Fe₂O₃ assembly has zigzag edge and high specific surface area, which leads to higher efficient visible-light photocatalytic performance on the degradation of cationic dye Rhodamine B (RhB). UV–Vis diffuse reflectance spectra and photocurrent responses demonstrated a narrow bandgap and higher photocurrent response of ring-like α-Fe₂O₃ assembly, which were helpful for absorbing photons and restraint of recombination for photogenerated charges. These characters make them the promising candidates for photocatalysis.     

Synthesis of CaO–SiO<Subscript>2</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> mesoporous bioactive glasses with high P<Subscript>2</Subscript>O<Subscript>5</Subscript> content by evaporation induced self assembly process

Mesoporous bioactive glasses (MBGs) of the CaO–SiO₂–P₂O₅ system containing relatively high P₂O₅ contents (10–30 mol%) were prepared from a sol–gel. An evaporation-induced self-assembly (EISA) technique was used with poly(ethylene oxide)-block–poly(propylene oxide)-block–poly(ethylene oxide) (EO₂₀–PO₇₀–EO₂₀, P123) acting as a template. The structural, morphological and textural properties of MBGs were investigated by small-angle X-ray diffraction (SAXRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and a N₂ sorption/desorption technique. SAXRD and TEM results display the reduced long-range ordering of mesopores with increasing P₂O₅ content. N₂ sorption/desorption analysis shows that all three samples exhibit a type IV isotherm with type H1 hysteresis loops, characteristic of independent cylindrical slim pore channels and this material has a Barret–Joyner–Halenda (BJH) model pore size of ~4 nm and BET specific surface area ~430 m²/g. NMR results indicate a more condensed framework for samples with 30 mol% P₂O₅ than samples with 10 mol% P₂O₅. For in vitro bioactivity tests where samples were soaked in simulated body fluid (SBF), samples with 30 mol% P₂O₅ showed higher crystallinity than those with lower P₂O₅ contents Silicon concentration increased in SBF solution during the soaking period, which indicates MBGs can be degradable in SBF solution.     

BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> films produced from BaFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> heterostructures

BaFe₁₂O₁₉ hexaferrite films have been produced on thermally oxidized single-crystal silicon (SiO₂/Si) substrates by sequential ion-beam sputtering of BaFe₂O₄ and α-Fe₂O₃ targets in an argon-oxygen atmosphere. Their crystal structure has been studied, and the origin of the impurity phases forming during heat treatment has been identified. The results show that heat treatment may lead to the formation of eutectic melts. As a result, the hexaferrite films may contain spherulites.     

Facile synthesis of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/diatomite composite for visible light assisted degradation of Rhodamine 6G in aqueous solution

α-Fe₂O₃ particle supported on diatomite (α-Fe₂O₃/diatomite composite) was prepared at room temperature by the chemical precipitation method using ferrous sulphate as the raw material and diatomite as supporter. α-Fe₂O₃/diatomite composite was characterized by XRD, FE-SEM, FT-IR and DRS. The result showed that α-Fe₂O₃ was uniformly loaded on the diatomite. The photocatalytic activity was investigated under visible light toward degradation of Rhodamine 6G aqueous solution and the effects of various experimental factors on Rhodamine 6G degradation were investigated. Compared with the α-Fe₂O₃, α-Fe₂O₃/diatomite composite had significantly enhanced activity in the degradation of Rhodamine 6G under visible light irradiation. Besides, the photostability of catalysts was also investigated. The experimental results indicated that the prepared composite is a promising material for the wastewater treatment for its good catalytic performance property and long-term stability.     

Synthesis,charge transport studies,and microwave shielding behavior of nanocomposites of polyaniline with Ti-doped γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

This article reports the synthesis, charge transport studies, and microwave shielding properties of polyaniline–Ti-doped γ-Fe₂O₃ nanocomposite. The composite has been prepared by the in situ chemical oxidative polymerization using dodecylbenzenzesulfonic acid as a dopant. These resulting polymer composites have been found thermally stability up to 260 °C with magnetization value of ~10 emu/g. The temperature dependence of electrical conductivity reveals the applicability of Mott’s 3D-VRH model. The composites has shown the shielding effectiveness of 35.64–45.20 dB (>99.99% attenuation) in 12.4–18 GHz (Ku-Band) frequency range. The enhancement of SE has been due to combination of dielectric and magnetic losses leading to decrease in skin depth increase in total (σ_T) conductivity and better matching of input impedance.     

α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> based nanomaterials as gas sensors

Interest in detecting and determining concentrations of toxic and flammable gases has constantly been on the increase in recent years due to increase of modernization, industrialization and high standards of life. Detection of such gases is very important in many different fields such as industrial emission control, household and social security, vehicle emission control and environmental monitoring. Metal oxide gas sensors are among most important devices to detect a large variety of gases. α-Fe₂O₃, an environmental friendly semiconductor (E _g = 2.1 eV), is the most stable iron oxide under ambient atmosphere and because of its low cost, high stability, high resistance to corrosion, and its environmentally friendly properties is one of the most important metal oxides for gas sensing applications. This is the first review about gas sensing properties of α-Fe₂O₃ nanostructures. In this paper gas sensing properties of α-Fe₂O₃ are extensively reviewed. After a brief explanation about metal oxide gas sensors and α-Fe₂O₃, sensors based on α-Fe₂O₃ nanomaterials have been reviewed. Gas sensing section is divided into five subsections: pure α-Fe₂O₃ gas sensors, metal/α-Fe₂O₃ gas sensors, metal oxide/α-Fe₂O₃ gas sensors, polymer/α-Fe₂O₃ gas sensors and graphene/α-Fe₂O₃ gas sensors.     

Study of the high-coercivity material based on ε-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in the silica gel matrix

We report the results of investigations of ε-Fe₂O₃ magnetic nanoparticles obtained by incipient wetness impregnation of silica gel. It was established that the obtained samples with an iron content of 12?16% mass % containing ε-Fe₂O₃ nanoparticles with an average size of 10 nm on the silica gel surface exhibit a room-temperature coercivity of about 10 kOe. Along with fabrication simplicity, this fact makes the prepared samples promising for application as a magnetically hard material.     

Spectroscopic characterisation of local structure in Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses doped with gadolinium

Gadolinium doped bismuth borate glasses containing up to 30 mol% Y₂O₃ were prepared by fast melt quenching method. The effect of yttrium on the local order in 3B₂O₃ · Bi₂O₃ and B₂O₃ · Bi₂O₃ glass matrices, particularly on the bismuth sites, was investigated by infrared (IR) spectroscopy and electron paramagnetic resonance (EPR) of Gd³⁺ ions. The IR results show that the local structure is more ordered in the glass system with higher bismuth content and the progressive addition of yttrium increases the local disorder in both bismuth–borate glass matrices. The EPR results indicate that Gd³⁺ ions occupy both bismuth and yttrium sites and reflect the same structural disorder like that suggested by IR results.     

Modification of the Magnetic Properties of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Powders by Ultrasonic Processing

Hematite (α-Fe₂O₃) powders after ultrasonic treatment (UST) in the regime of cavitation in aqueous suspension and in that with an organic component (albumin protein) have been studied by Mössbauer spectroscopy and ferromagnetic resonance techniques. It is established that the UST in aqueous hematite suspensions with albumin results in the formation of a new magnetic phase with parameters coinciding with those of the α-Fe metallic phase.     

Preparation of superparamagnetic and flexible γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowire arrays in an anodic aluminum oxide template

Superparamagnetic and flexible Fe₂O₃ nanowire arrays were fabricated by the controlled electrostatic assembly of iron oxide nanoparticles and poly(dimethyldiallylammonium chloride) (PDADMAC) in an anodic aluminum oxide (AAO) template. The micrograph of iron oxide nanowire arrays was characterized by field emission scanning electron microscopy. The magnetic hysteresis loops obtained by a vibrating sample magnetometer confirm that the nanowire arrays have superparamagnetic properties. The filling ratio of iron oxide nanoparticles and polymers in the AAO template was affected by four factors, including the concentration of iron oxide nanoparticles, the pore diameter of the AAO template, the charge ratio of iron oxide nanoparticles and PDADMAC, and the molecular weight of polyacrylic acid. The effect of the AAO template on the diameter and length of the nanowire arrays was also analyzed. In addition, the nanowire arrays were shown to be flexible because of the presence of polymers. These nanowire arrays with superparamagnetic and flexural properties have potential applications in sensor probes.     

Synthesis and vibrational properties of hematite (α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>) nanoparticles

α- Fe₂O₃ nanoparticles have been synthesized by gel evaporation method in air at 300°C. The average size of as synthesized α-Fe₂O₃ nanoparticle was estimated to be 30 nm and the particles were of good crystalline nature. Shape of the nanoparticles were slightly deviated from spherical which is attributed to the asymmetric growth of primary nuclei. MicroRaman and X-ray diffraction results have shown mixed phases of α-Fe₂O₃ and γ-Fe₂O₃. However, the α-Fe₂O₃ phase is more predominant than γ-Fe₂O₃ due to the incomplete nucleation of α-Fe₂O₃ particles at the size of 30 nm. The vibrating sample magnetometer measurement shows that the nanoparticles possess ferromagnetic property.     

Synthesis of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> powder via PVA assisted sol–gel process

CoFe₂O₄ ferrites were synthesized by sol–gel method, having metal nitrates as precursors and PVA as surfactant, followed by a heat treatment at 960 °C for 2 h. The ultrafine ferrite powders obtained have been characterized by X-ray diffraction, thermal gravimetry, differential scanning calorimetry and room temperature magnetic measurement studies. The morphology of the powder was identified by high resolution-scanning electron microscopy. X-ray diffraction results indicate that the resultant CoFe₂O₄ crystallites consist of spinel phase. Significant differences in magnetic properties of CoFe₂O₄ samples synthesized with various concentrations of PVA were observed. The magnetisation measurements show that when the PVA concentration increased, coercivity initially decreased and then increased where as retentivity and magnetisation decreased. The optimum concentration of PVA for the synthesis of CoFe₂O₄ ferrites is obtained from this investigation. Obviously this material can be used as an efficient candidate for practical recording purpose.     

Mechanochemical synthesis of fine-particle γ-LiAlO<Subscript>2</Subscript>

Using thermogravimetry, in situ X-ray diffraction, room-temperature X-ray diffraction, specific surface area measurements, and particle size analysis, we have studied how preliminary mechanical activation of a mixture of aluminum hydroxide and lithium carbonate in an AGO-2 planetary mill and subsequent heat treatment of the mixture influence the synthesis of fine-particle nanostructured gamma-lithium monoaluminate. We have proposed a scheme of the structural changes accompanying the synthesis of gamma-lithium monoaluminate.     

Effect of sintering temperatures on properties of BaO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass/silica composites for CBGA package

BaO–B₂O₃–SiO₂–Al₂O₃ (BBSA) glass/silica composites synthesized by solid-state reaction method were developed for CBGA packages, and the effects of sintering temperature (900–950 °C) on the phase transformation, microstructure, thermal, mechanical and electrical properties were investigated. XRD results show that the major phases quartz and cristobalite, and the minor phase BaSi₂O₅ are detected in BBSA composites. Furthermore, it was found that the quartz phase transforms to cristobalite phase at 930–940 °C. The formation of cristobalite phase with higher coefficient of thermal expansion (CTE) led to the increase of CTE value of BBSA composites. However, excessive cristobalite phase content would degrade the mechanical properties and the linearity of thermal expansion of the ceramics. BBSA composites sintered at 920 °C exhibited excellent properties: low dielectric constant and loss (ε_r = 6.2, tanδ = 10^?4 at 1 MHz), high bending strength (179 MPa), high CTE (12.19 ppm/°C) as well as superior linearity of the thermal expansion.     

Synthesis and evolution of α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanorods for enhanced visible-light-driven photocatalysis

Single-crystalline α-Fe₂O₃ nanorods were prepared by a simple and direct hydrothermal method in large quantities. The 1, 2-propanediamine played the role of shape-control agent for the formation of α-Fe₂O₃ nanorods. The characteristics and the evolution mechanism of α-Fe₂O₃ nanorods were investigated in detail. As reaction time prolonged, the hydrogen ions generated by the hydrolysis of Fe³⁺ could etch the surface of α-Fe₂O₃ nanorods and resulted in the eroded α-Fe₂O₃ nanorods formation. HRTEM results demonstrated that the eroded α-Fe₂O₃ nanorods have rough edges and corners which leading to higher photodegradation ability. Absorption spectra and photocurrent responses indicated that the eroded α-Fe₂O₃ nanorods have a narrow bandgap and higher photocurrent response, which were benefit for absorbing photons and inhibiting the recombination of photogenerated charges. It is expected that the etching of semiconductor materials is an effective way to design the photocatalysts with a high performance, and the α-Fe₂O₃ nanorods with high visible-light photocatalytic activity could find potential applications in the field of environmental management.     

Linear reciprocating wear behaviour of plasma-sprayed Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> coatings at different loading and sliding conditions

Linear reciprocating wear test is carried out on atmospheric plasma-sprayed Al₂O₃–Cr₂O₃ coatings applied on steel substrates. Linear bi-directional sliding wear test of the coatings is performed at different loading and sliding conditions such as load (10, 20 and 30 N), reciprocating amplitude (1.5, 3 and 6 mm) and frequency (5, 10, 15 and 20 Hz) using ball on flat linear reciprocating tribometer. The patterns of tribological behaviour of the coatings, as manifested at the tribo-contact surface, are judged. Results have shown that the wear rate increases with increasing applied load and frequency and that decreases with increasing reciprocating amplitude. Plastic deformation, detachments of unmelted core, reattachments, delamination and adhesive wear dominate the main failure mechanism of coating.     

Facile Synthesis of Magnetically Recyclable Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–MFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Photocatalyst from Saprolite-Limonite Laterite Leach Liquors

Photocatalyst degradation is an effective and environment-friendly method for dye pollution. Magnetically recyclable Fe₂O₃–MFe₂O₄ composites were successfully synthesized from laterite leach liquors by a simple coprecipitation-calcination method. The as-prepared samples were characterized by x-ray diffraction (XRD), physical property measurement system (PPMS), and UV-Vis. The results show that the Fe₂O₃–MFe₂O₄ composites can be easily recycled from the solution due to the magnetic properties. Photodegradation experiments results indicated that the degradation rate of rhodamine B (RhB) solution were found to be about 90.0% for the composites, and the degradation rate were still more than 80.0% after being reused for five times. The heterostructure between the Fe₂O₃ and MFe₂O₄ effectively enhanced the separation of electron hole pairs, facilitating the photocatalysis process. This paper provided a facile pathway for comprehensive utilization of laterite leach liquor to synthesize magnetically recyclable Fe₂O₃–MFe₂O₄ with enhanced photocatalyst performance.     

Atomistic structure and energetics of interface between Mn-doped γ-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript>

The interface between an Mn-doped γ-gallium oxide (Ga₂O₃) thin film and an MgAl₂O₄ (001) substrate has been investigated using high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and first-principles calculations. A high-quality Mn-doped γ-Ga₂O₃ film with a defective spinel structure has been epitaxially grown by pulsed laser deposition. The γ-Ga₂O₃ crystal shows an uniform tetragonal distortion with a tetragonality of 1.05 throughout the film thickness of 75 nm. HRTEM and HAADF-STEM observations reveal that the γ-Ga₂O₃ and MgAl₂O₄ crystals form a coherent interface without any interfacial layers or precipitates. The atomistic structure and energies are theoretically evaluated for the interfaces with two types of termination plane, i.e., Mg- and Al₂O₄-termination of MgAl₂O₄. The cation sublattice is found to be continuous for both interfaces despite the defective spinel structure of Mn-doped γ-Ga₂O₃ with some vacant cation sites. The Al₂O₄-termination shows a lower interfacial energy than the Mg-termination under most conditions of the chemical potentials. This behavior is attributed to the energetic preference of the Mn–Al₂O₄ local configuration at the interface.     

System ZnO ⋅ B<Subscript>2</Subscript>O<Subscript>3</Subscript>-CuO ⋅ B<Subscript>2</Subscript>O<Subscript>3</Subscript>

Differential thermal analysis and x-ray diffraction data indicate that the ZnO B₂O₃-CuO B₂O₃ join of the ternary system CuO-B₂O₃-ZnO is pseudobinary, with eutectic phase relations and a liquid-liquid miscibility gap in the composition range 25–35 mol % CuO.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 339–340.Original Russian Text Copyright © 2005 by Kasumova, Bananyarly.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.