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.     

Synthesis of maghemite (γ-Fe2O3) nanoparticles by thermal-decomposition of magnetite (Fe3O4) nanoparticles

In this research work, we prepared γ-Fe₂O₃ nanoparticles by thermal-decomposition of Fe₃O₄. The Fe₃O₄ nanoparticles were synthesized via co-precipitation method at room temperature. This simple, soft and cheap method is suitable for preparation of iron oxide nanoparticles (γ-Fe₂O₃; Fe₃O₄). The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), vibrating sample magnetometer and differential scanning calorimeter (DSC). The XRD and FT-IR results indicated the formation of γ-Fe₂O₃ and Fe₃O₄ nanoparticles. The TEM images showed that the γ-Fe₂O₃ and Fe₃O₄ were spherical, and their size was 18 and 22 nm respectively. Magnetic properties have been measured by VSM at room temperature. Hysteresis loops showed that the γ-Fe₂O₃ and Fe₃O₄ nanoparticles were super-paramagnetic.     

Degradation of bisphenol A by combining ozone with UV and H<Subscript>2</Subscript>O<Subscript>2</Subscript> in aqueous solutions: mechanism and optimization

A laboratory-scale study on the abatement of bisphenol A (BPA) was performed by combining O₃ with H₂O₂ and UV (O₃/H₂O₂/UV), an ozone-based advanced oxidation processes technique (AOP). This work aimed to (1) evaluate the removal of BPA with O₃/H₂O₂/UV, and to compare the degradation efficiency with other ozone-based AOPs (such as O₃ alone, O₃/H₂O₂, and O₃/UV), (2) structurally optimize BPA abatement by using a central composite design (CCD) for experimental design purposes and/or a response surface methodology to find the optimum, and (3) identify the degradation pathways, and main intermediate products, formed during BPA abatement with O₃/H₂O₂/UV. The degradation pathways of BPA degradation were revealed by O₃/H₂O₂/UV on the basis of evidences of intermediate generation. The effect of initial pH, ozone, and H₂O₂ dose during BPA abatement was studied in detail. By increasing each of these three parameters, an enhancement of the BPA degradation efficiency is mostly observed. BPA can be degraded completely when a sufficiently high ozone dose is applied. However, excess H₂O₂, as a scavenger of HO·, has a negative effect on BPA abatement, resulting in a decrease in the BPA’s degradation efficiency. For example, the removal decreased from 64 to 58% by enhancing the H₂O₂ initial dose from 0.5 to 0.75 mmol/L (at an initial pH and ozone dose of, respectively, 7 and 0.1 mg/L). The results confirmed that combining ozone with H₂O₂ and UV was a more efficient method than the other three ozone-based AOPs on the removal of BPA. Therefore, this method could be further applied for the treatment of real wastewaters containing BPA and other micropollutants.     

Interfacial Engineering of Co3O4/Fe2O3 Nano-Heterostructure Toward Superior Li-O2 Batteries

A major issue with Li-O₂ batteries is their slow oxygen reduction and evolution kinetics, necessitating catalysts with high catalytic activity to improve reaction kinetics and cycle stability. Herein, a nano-heterostructured catalyst composed of Co₃O₄ and Fe₂O₃ (Co₃O₄/Fe₂O₃) with a porous rod morphology is achieved through an interfacial engineering strategy by constructing Fe₂O₃ on the Co₃O₄ surface, which can function as a high-performance cathode in order to efficiently encourage the oxygen reduction and evolution while also reduce the battery polarization during charging and discharging. The density functional theory (DFT) calculations show the differences in charge density at the interface of nano-heterostructures, demonstrating the occurrence of an electron transfer process in the interface region of Co₃O₄ and Fe₂O₃, implying a strong electronic coupling transfer, and in turn changing the electronic structure of the Co₃O₄. This significantly reduces the adsorption energy of LiO₂ intermediates, thereby effectively lowering the overpotential. The resultant Li-O₂ battery has larger discharge specific capacity, lower overpotential for the efficient oxygen evolution/reduction, as well as good cycling stability of 280 cycles. This work demonstrates an effective method to fabricate the nano-heterostrucutred materials with enhanced catalytic efficiency for advanced energy applications.     

Structural,optical, and opto-dielectric properties of W-doped Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films

A layer-by-layer deposition technique of Ga₂O₃ and WO₃ by vacuum evaporation method on glass and silicon substrates and subsequent annealing in oxygen atmosphere to form W-doped Ga₂O₃ (or Ga₂O₃:W) films was attempted here. The W doping level was measured by the energy dispersive X-ray fluorescence radiographic analysis. The crystalline structure of Ga₂O₃:W films was determined by the X-ray diffraction method. Experimental data indicate that W⁶⁺ ions doped in host Ga₂O₃ forming solid solutions (SS), in which the molar ratio (r) of W to Ga is 9.6, 13.4, 18.2, 22.7 and 30.4%. All the prepared SS have the known β-Ga₂O₃ crystalline structure. This doping controls the optical and electrical properties of the host Ga₂O₃. The optical properties of the prepared Ga₂O₃:W films were studied by UV–VIS–NIR absorption spectroscopy method from which the bandgap was determined. In general, it was found that the prepared Ga₂O₃:W films are wide-bandgap semiconductors with bandgap 4.69–4.47 eV and have dielectric properties. The optical sensitivity of the capacitance, dissipation factor and ac-conductance of the Ga₂O₃:W films grown on Si was studied as a function of W-doping level. It was observed that the prepared Ga₂O₃:W film of r = 22.7% has the highest photosensitivity amongst the other samples.     

Biomimetic fabrication of α-Fe2O3 with hierarchical structures as H2S Sensor

A facile sol–gel method is developed for the fabrication of α-Fe₂O₃ with quasi-honeycomb like structures inherited from Papilio paris butterfly wings. The exquisite hierarchical architecture is faithfully maintained in α-Fe₂O₃ from the skeleton of butterfly wings at the levels from macro to nano-scales. When used as a chemical sensor, the obtained α-Fe₂O₃ replica (P-α-Fe₂O₃) showed a much higher performance than that of the compared α-Fe₂O₃ nanoparticles synthesized under the same condition without biotemplate (S-α-Fe₂O₃). The P-α-Fe₂O₃-based sensor has a sensitivity of 19.2–50 ppm H₂S, which is four times more than that of S-α-Fe₂O₃, accompanied by a rapid response/recovery time within 1/10 s even at a relatively low working temperature of 180 °C. Compare to the S-α-Fe₂O₃, surface area of which cannot be detectable, the high sensing feature of P-α-Fe₂O₃ would be attributed to the relatively high-specific surface area 24.12 m²/g thus fabricated together with the unique 3D-network structures, which provide channel for the diffusion of H₂S. This strategy is expected to be used in fabrication of other kinds of metal oxide with unique structures for the potential application in gas sensor.     

New Method to Calculate the Sign and Relative Strength of Magnetic Interactions in Low-Dimensional Systems on the Basis of Structural Data

The connection of strength of magnetic interactions and type ordering the magnetic moments with crystal chemical characteristics in low-dimensional magnets is investigated. The new method to calculate the sign and relative strength of magnetic interactions in low-dimensional systems on the basis of the structural data is proposed. This method allows to estimate magnetic interactions not only inside low-dimensional fragments but also between them, and also to predict the possibility of the occurrence of magnetic phase transitions and anomalies of the magnetic interactions. Moreover, it can be used for search of low-dimensional magnets among the compounds whose crystal structures are known. The possibilities of the method are illustrated in an example of research of magnetic interactions in familiar low-dimensional magnets SrCu₂(BO₃)₂, CaCuGe₂O₆, CaV₄O₉, Cu₂Te₂O₅Cl₂, Cu₂Te₂O₅Br₂, BaCu₂Si₂O₇, BaCu₂Ge₂O₇, BaCuSi₂O₆, LiCu₂O₂, and NaCu₂O₂.     

Effect of gadolinia on phase structure and thermal conductivity of ZrO2-4.5 mol%Y2O3 ceramics

This paper deals with the effect of gadolinia on the phase structure and thermal conductivity of ZrO₂-4.5 mol%Y₂O₃ (YSZ) ceramics for thermal barrier coatings. The YSZ-Gd₂O₃ ceramics were synthesized by solid state reaction at 1500 °C for 2 h in air. The relative density, structure of different YSZ-Gd₂O₃ ceramics and thermal diffusivity in a temperature range of room temperature to 1200 °C were investigated by the Archimedes method, X-ray diffraction and laser-flash method. The ZrO₂-4.5 mol%Y₂O₃ (YSZ) ceramics consist of tetragonal, cubic and a small amount of monoclinic phase, and the YSZ-1.5 mol%Gd₂O₃ ceramics consist of both tetragonal and cubic phases. However, the YSZ-3.0 mol%Gd₂O₃, YSZ-4.5 mol%Gd₂O₃ and YSZ-6.0 mol%Gd₂O₃ ceramics only exhibit a cubic structure. The thermal conductivity of YSZ-Gd₂O₃ ceramics decreases with the increase of gadolinia content under identical temperature conditions. The thermal conductivities of the YSZ and YSZ-1.5 mol%Gd₂O₃ ceramics first decrease gradually with the increase of temperature below 800 °C and then increase slightly above 800 °C. The thermal conductivities of the YSZ-3.0 mol%Gd₂O₃, YSZ-4.5 mol%Gd₂O₃ and YSZ-6.0 mol%Gd₂O₃ ceramics are almost constants from room temperature to 1200 °C.     

A sensitive electrochemical detection of hydroquinone using newly synthesized α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-graphene oxide nanocomposite as an electrode material

This article presents the effect of hematite phase iron oxide (α-Fe₂O₃) on the electrocatalytic activity of graphene oxide (GO) for electrochemical detection of hydroquinone in aqueous solution. The different weight percentage (wt%) (1, 2 and 3%) of α-Fe₂O₃ added GO nanocomposites were synthesized by wet-impregnation method. The cyclic voltammetry studies using 2% α-Fe₂O₃-GO modified glassy carbon electrodes was found to exhibit an excellent electrocatalytic activity than α-Fe₂O₃ and GO electrodes that may be due to the synergistic effect of α-Fe₂O₃nanoparicles and GO sheet. In addition, the modified electrode exhibited a good reproducibility as well as long-term stability. Hence, the 2% α-Fe₂O₃-GO can be a promising catalytic material for electrochemical sensor applications.     

Mechanical properties and microstructure of Al2O3/TiAl in situ composites doped with Cr2O3

Al₂O₃/TiAl composites were successfully fabricated from powder mixtures of Ti, Al, TiO₂ and Cr₂O₃ by a hot-press-assisted exothermic dispersion method. The effect of the Cr₂O₃ addition on the microstructures and mechanical properties of Al₂O₃/TiAl composites was characterized, and the results showed that the Rockwell hardness, flexural strength and fracture toughness of the composites increased as the Cr₂O₃ content increased. When the Cr₂O₃ content was 2.5 wt%, the flexural strength and the fracture toughness attained peak values of 925 MPa and 8.55 MPa m^1/2, respectively. This improvement of mechanical properties was due to the more homogeneous and finer microstructure developed from the addition of Cr₂O₃ and an increase in the ratio of α₂-Ti₃Al to γ-TiAl matrix phases.     

Redox behavior and reduction mechanism of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–CeZrO<Subscript>2</Subscript> as oxygen storage material

Fe₂O₃–CeZrO₂ is a suitable oxygen storage material for the production of pure hydrogen by a cyclic water gas shift (CWGS) process which is based on the reduction of the material by syngas followed by the re-oxidation of the reduced material with water vapor. For identification of the reduction kinetics H₂-temperature programmed reduction experiments were performed. Several kinetic models were tested and the activation energy of reduction was calculated by the Kissinger method, by model-based curve fitting and by the isoconversional analysis method. The reduction of Fe₂O₃–CeZrO₂was found to occur in a four-step process including the reduction of Fe₂O₃,Fe₃O₄, and CeZrO₂. The overall process can be interpreted as phase-boundary controlled reduction of Fe₂O₃ to Fe₃O₄, and two-dimensional nucleation controlled reduction of Fe₃O₄ to Fe and of CeO₂ to Ce₂O₃. At higher oxygen conversion, the reduction of Fe₃O₄ and CeO₂ are significantly influenced by volume-diffusion in the solid bulk.     

Microstructural parameters of dispersion strengthened Cu–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> materials

The aim of the article was to evaluate the microstructural parameters of Cu–Al₂O₃ dispersion strengthened materials with different volume fraction of Al₂O₃ phase. For analyses of dispersoids Al₂O₃, the extraction carbon replica was used. The distribution of Al₂O₃ particles in the matrix was estimated by three methods (quadrant count method, polygonal method, and by interparticle distances), these methods showed that particle distribution in material with 1 vol.% of Al₂O₃ is very close to the Poisson point process (PPP), which is a model of randomly distributed points. Particle distributions in materials with 8 and 10 vol.% of Al₂O₃ achieve features of regularity proved mainly by the spherical contact distance.     

Preparation and tribological properties of polyurethane/α-aluminum oxide hybrid films

This study focused on the preparation and tribological properties of polyurethane/α-aluminum oxide (PU/α-Al₂O₃) hybrid films. PU/α-Al₂O₃ hybrid films containing various nanoscaled α-Al₂O₃ contents were prepared by an effectively mechanical stirring method. The tribological properties of PU/α-Al₂O₃ hybrid films were investigated by a TABER type abrasion tester after 2000 cycles. The results of abrasion tests showed the abrasion resistance of the PU/α-Al₂O₃ hybrid film was increased as the α-Al₂O₃ content was increased. The abrasion resistance of the PU/α-Al₂O₃ hybrid film was significantly improved up to 27.4% by adding 2 wt.% nanoscaled α-Al₂O₃ particles. The surface morphologies of PU/α-Al₂O₃ hybrid films, before and after abrasion tests, were examined by scanning electron microscopy (SEM). For the loading of 2 wt.% α-Al₂O₃ particles, the SEM image of the worn surface of the PU/α-Al₂O₃ hybrid film showed much smoother than those of pure PU film and other PU/α-Al₂O₃ hybrid films.     

Effect of highly dispersed yttria addition on thermal stability of hydroxyapatite

The capability of the colloidal method to produce yttria (Y₂O₃) dispersed hydroxyapatite (HA) has been investigated as an alternative method to the conventional method of mechanical mixing and sintering for developing HA-based materials that could exhibit controllable and enhanced functional properties. A water based colloidal route to produce HA materials with highly dispersed Y₂O₃ has been applied, and the effect of 10 wt.% Y₂O₃ addition to HA investigated by thermal analysis, X-ray diffraction and Fourier transform infrared spectroscopy. These measurements evidence a remarkable effect of this Y₂O₃ addition on decomposition mechanisms of synthetic HA. Results show that incorporation of Y₂O₃ as dispersed second phase is beneficial because it hinders the decomposition mechanisms of HA into calcium phosphates. This retardation will allow the control of the sintering conditions for developing HA implants with improved properties. Besides, substitution of Ca^2 + with Y^3 + ions appears to promote the formation of OH^? vacancies, which could improve the conductive properties of HA favorable to osseointegration.     

Large-scale synthesis of single-crystal alpha manganese sesquioxide nanowires via solid-state reaction

Smooth single-crystal α-Mn₂O₃ nanowires have been fabricated using a one-step solid-state reaction method. X-ray diffraction patterns show that the nanowires have pure phase of α-Mn₂O₃. Transmission electron microscopy was employed to investigate the size and morphology of the products. The α-Mn₂O₃ nanowires exhibit mean diameter of 50 nm and length of 10 μm. Selected-area electron diffraction pattern demonstrates the single-crystal structure of the α-Mn₂O₃ nanowires, which are in good agreement with the X-ray diffraction results. The processes of the reactions and the phase transitions were also studied by using a simultaneous thermal gravimetric/differential thermal analyzer. It is found that the concentration of the precursor MnCO₃ is a crucial factor in the formation of the nanowires. This work provides the probability of the industrialization of fabricating smooth single-crystal α-Mn₂O₃ nanowires.     

Synthesis of Y2O2S:Eu3+ luminescent nanobelts via electrospinning combined with sulfurization technique

Y₂O₂S:Eu³⁺ nanobelts were successfully prepared via electrospinning method and sulfurization process using the as-prepared Y₂O₃:Eu³⁺ nanobelts and sulfur powders as sulfur source by a double-crucible method for the first time. X-ray diffraction analysis indicated that the Y₂O₂S:Eu³⁺ nanobelts were pure hexagonal in structure with space group P $ \bar{3} $ m1. Scanning electron microscope images showed that the width and thickness of the Y₂O₂S:Eu³⁺ nanobelts were ca. 6.7 μm and 125 nm, respectively. Under the excitation of 325-nm ultraviolet light, Y₂O₂S:Eu³⁺ nanobelts exhibited red emissions of predominant peaks at 628 and 618 nm, which are attributed to the ⁵D₀ → ⁷F₂ transition of the Eu³⁺ ions. It was found that the optimum doping concentration of Eu³⁺ ions in the Y₂O₂S: Eu³⁺ nanobelts was 3 %. Compared with bulk particle, Eu³⁺–O^2?/S^2? charge transfer bands (260 and 325 nm) of the Y₂O₂S:Eu³⁺ nanobelts showed a blue-shift significantly. The formation mechanism of the Y₂O₂S: Eu³⁺ nanobelts was also proposed. This new sulfurization technique is of great importance, not only to inherit the morphology of rare earth oxides but also to fabricate pure-phase rare earth oxysulfides at low temperature compared with conventional sulfurization method.     

Preparation and mechanical properties of high-purity Al2O3 fibre/Al2O3 matrix composite

Al₂O₃ matrix composites with unidirectionally oriented high-purity Al₂O₃ fibre with and without carbon coating, were fabricated by the filament-winding method, followed by hot-pressing at 1573–1773 K. The composite with non-coated Al₂O₃ fibre exhibited a bending strength (594 MPa) comparable to that of monolithic Al₂O₃ (589 MPa). While the composite with a carbon-coated fibre had lower strength (477 MPa), it showed improved fracture toughness (6.5 MPa m^1/2) compared to the composite with an uncoated fibre (4.5 MPa m^1/2) and monolithic Al₂O₃ (5.5 MPa m^1/2). This toughness enhancement was explained based on the increased crack extension resistance caused by the fibre pull-out observed by SEM at the notch tip. This revised version was published online in November 2006 with corrections to the Cover Date.     

Phase equilibria and ordering in the erbia-zirconia system

The phase diagram for the system ZrO₂-Er₂O₃ was redetermined. At high temperatures, the system is dominated by wide regions of solid solution based on ZrO₂ and Er₂O₃ separated by a two-phase field which appears to extend to the solidus. The range of existence of these solid solution fields was determined using the precision lattice parameter method. A low-temperature (<1800° C) long-range ordering occurred between 20 and 90 mol % Er₂O₃, and three ordered phases were found: the first compound was present at 40 mol % Er₂O₃ and corresponds to the ideal formula Er₄Zr₃O₁₂ with rhombohedral symmetry (space group R¯3), is isostructural with UY₆O₁₂, and decomposes at about 1500° C into fluorite solid solution by an order-disorder process; the second ordered phase is formed at about 55 mol % Er₂O₃, its formula is close to Er₅Zr₂O_11.5, and it decomposes at about 1650° C into cubic solid solutions of the fluorite and C-type; the third compound is formed at 75 mol % Er₂O₃, its formula is Er₆ZrO₁₁, it has a wide homogeneity range, and it decomposes above 1700° C into a cubic solid solution of the C-type. Liquidus determination indicated the existence of a peritectic at 62 mol % Er₂O₃.This work is based on the Ph.D. thesis of C. Pascual, Madrid University, 1980.     

Enhanced Charge Separation through ALD‐Modified Fe2O3/Fe2TiO5 Nanorod Heterojunction for Photoelectrochemical Water Oxidation

Hematite suffers from poor charge transport and separation properties for solar water splitting. This paper describes the design and fabrication of a 3D Fe₂O₃/Fe₂TiO₅ heterojunction photoanode with improved charge separation, via a facile hydrothermal method followed by atomic layer deposition and air annealing. A highly crystallized Fe₂TiO₅ phase forms with a distinct interface with the underlying Fe₂O₃ core, where a 4 nm Fe₂TiO₅ overlayer leads to the best photoelectrochemical performance. The favorable band offset between Fe₂O₃ and Fe₂TiO₅ establishes a type‐II heterojunction at the Fe₂O₃/Fe₂TiO₅ interface, which drives electron–hole separation effectively. The Fe₂O₃/Fe₂TiO₅ composite electrode exhibits a dramatically improved photocurrent of 1.63 mA cm^?2 at 1.23 V versus reversible hydrogen electrode (RHE) under simulated 1 sun illumination (100 mW cm^?2), which is 3.5 times that of the bare Fe₂O₃ electrode. Decorating the Fe₂O₃/Fe₂TiO₅ heterojunction photoanode with earth‐abundant FeNiO_x cocatalyst further expedites surface reaction kinetics, leading to an onset potential of 0.8 V versus RHE with a photocurrent of 2.7 mA cm^?2 at 1.23 V and 4.6 mA cm^?2 at 1.6 V versus RHE. This sandwich photoanode shows an excellent stability for 5 h and achieves an overall Faradaic efficiency of 95% for O₂ generation. This is the best performance ever reported for Fe₂O₃/Fe₂TiO₅ photoanodes.