Magneto Optical Properties of FeB<Subscript>x</Subscript>Fe<Subscript>2−x</Subscript>O<Subscript>4</Subscript> Nanoparticles

In this study, FeB_xFe_2?xO₄ nanoparticles (NPs) were synthesized by the polyol method. The M–H hysteresis curves exhibit superparamagnetic characteristics that are both coercivity and remanent magnetization values are negligible. The particle size dependent Langevin function was applied to calculate the magnetic particle dimensions around 9 nm. The measured magnetic moments of NPs are in range of (1.52–2.2) µ_B and almost half or less with respect to 4 µ_B of bulk Fe ferrite. Magnetic anisotropy was specified as uniaxial and calculated effective anisotropy constants (K _eff ) are between 43.3 × 10⁴ and 19.4 × 10⁴ emu/g. The UV–Vis diffuse reflectance spectroscopy and Kubelka–Munk theory were used to determine the optical properties. The estimated optical band gap values (2.15–2.48 eV) of FeB_xFe_2?xO₄ NPs are bigger with respect to reported values (1.88–2.12 eV) for Fe₃O₄ NPs in the literature. The bigger E _g values are mainly attributed to B concentration and partly to quantum confinement effect.     

Photon interaction parameters for some ZnO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Some photon interaction parameters such as mass attenuation coefficient, effective atomic number, half value layer, mean free path and electron density for 15ZnO–(17.5–x)Al₂O₃–xFe₂O₃–67.5P₂O₅ glass system (x = 0, 7.5, 12.5, 17.5) and 15ZnO–(25–x)Al₂O₃–xFe₂O₃–60P₂O₅ glass system (x = 0, 25) have been investigated in the photon energy range of 1 keV to 100 GeV. It has been observed that all the photon interaction parameters for the selected glass systems vary with the photon energy. Among the selected glass systems, the sample 15ZnO–25Fe₂O₃–60P₂O₅ glass system shows maximum values for mass attenuation coefficients, effective atomic numbers, electron densities and minimum values for mean free path and half value layer in the entire energy grid.     

Exploring the Redox Behavior of La<Subscript>0.6</Subscript>Sr<Subscript>0.4</Subscript>Mn<Subscript>1−x</Subscript>Al<Subscript>x</Subscript>O<Subscript>3</Subscript> Perovskites for CO<Subscript>2</Subscript>-Splitting in Thermochemical Cycles

Mixed oxides with perovskite structure have been proposed as promising alternative for the solar fuel production via thermochemical redox cycles. For this work, the system La_0.6Sr_0.4Mn_1?xAl_xO₃ (x?=?0 to 0.8) was selected according to its high thermal stability and rapid oxidation kinetics, and the influence of the Al/Mn ratio on the redox properties was investigated. The characterization of the five oxides samples with different Al content confirmed the high redox capacity and the favorable behavior of these materials in consecutive cycles, as analyzed thermogravimetrically. The results show that following reduction at 1300?°C in inert atmosphere up to 0.32 mmol g^?1 of O₂ are released, while a 10-cycle reaction test confirms the feasibility of long term operation with these perovskites. It was observed that the reduction extent was enhanced with increasing the Al-content, but the oxidation degree is maximum for compositions near x?=?0.5, corresponding to an O₂ release of 0.318 mmol g^?1 (δ?=?0.132). After selecting the compositions with more promising redox properties, additional reactions were performed in a lab-scale fixed bed reactor with injection of CO₂ in the oxidation step at 900?°C in order to generate CO. In these tests, the most interesting results were obtained for the perovskite La_0.6Sr_0.4Mn_0.6Al_0.4O_3, with reduction extent of 0.266 mmol?g^?1, but the production of CO is in comparison significantly lower (0.114 mmol?g^?1). Further studies are required to determine the best operation conditions for thermochemical cycles using those materials.     

Structural,Optical and Mössbauer Study of Ba<Subscript>1 − x</Subscript>Cu<Subscript>x</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript> (0.5 ≤ x) Nano Hexaferrites

In this study, a novel Ba_1?xCu_xFe₁₂O₁₉ (0.5?≤?x) nano-hexaferrites were prepared by a simple and cost-effective sol–gel auto-combustion method using barium nitrates, iron nitrate, copper (II) acetate monohydrate and citric acid, and its structural, optical properties and hyperfine interactions were reported. Structural properties were analyzed through XRD (X-ray diffraction), Scanning electron microscopy (SEM), and TEM (Transmission electron microscopy), while percent diffuse reflectance spectroscopy (DRS) and Mössbauer spectrometer were used for analyzing the optical and magnetic properties of the resultant products. The observed Mössbauer studies proved the ferromagnetic nature of nanoparticles (NPs) samples. The crystallite size (XRD) varies in a range of (23.30–35.12) nm. The direct optical energy band gap (E _g ) of all samples were calculated by Tauc plots where the E _g values are found in a small range of 1.97–2.15 eV. The experimental evidences signify the promising use of newly prepared nano-hexaferrites in the development of materials in various industrial devices and far better than the conventional available hexaferrites materials.     

Arsenic removal from water by photocatalytic functional Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> porous ceramic

Fe₂O₃–TiO₂ porous ceramic (Fe/TiPC) beads with photo-catalytic performances and high adsorption capacities were prepared by a simple high temperature solid reaction and were applied for arsenic removal from drinking water. The microstructure and morphology of Fe/TiPC were characterized by X-ray diffraction and scanning electron microscopy. More than 90% removal ratio for As (III) and As (V) were respectively achieved by Fe/TiPC within 2 h under UV irradiation. The Langmuir capacity values of Fe/TiPC for As (III) and As (V) were 13.86 and 15.73 mg/g, respectively. In addition, Fe/TiPC could be reused for up to five times without significant reduction in the photocatalytic sensitivity and adsorption capacity aspects. Good catalytic oxidation performances and high adsorption capacities as well as a sample preparation for Fe/TiPC suggest that the composites may have practical prospects for the As (III) and As (V) removal from contaminated water.     

Synthesis of the study of solid solutions based on the ZrO<Subscript>2</Subscript>–HfO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript>(CeO<Subscript>2</Subscript>) system

The results of the studies of the conditions of the liquid-phase synthesis of highly dispersed xerogels with a low degree of agglomeration and precursor nanopowders (~10–12 nm) based on zirconium dioxide in the ZrO₂–HfO₂–Y₂O₃(CeO₂) system are presented. The thermal decomposition of xerogels and formation of crystalline solid solutions with the structure of fluorite are investigated. The optimal conditions for the solidification of nanodispersed powders for fabricating compact ceramics based on solid solutions of ZrO₂ and the physical–chemical properties of these ceramics are studied.     

Spatial localization of holes in La<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CuO<Subscript>4</Subscript>

The parameters of the tensor of the electric field gradient (EFG) in cation sites of the La_{2 ? x} Sr _x CuO₄ lattice have been determined by the method of emission Mössbauer spectroscopy on ⁵⁷Co(^57m Fe), ⁶⁷Cu(⁶⁷Zn), ⁶⁷Ga(⁶⁷Zn), and ¹⁵⁵Eu(¹⁵⁵Gd) isotopes. There is no quantitative agreement between the calculated (the pointcharge model) and experimental values of the main component of the tensor EFG V _zz , which is explained by the absence of the reliable data on the Sternheimer coefficients for Fe³⁺, Zn²⁺, and Gd³⁺ ions. Based on the comparison of the calculated and experimental dependences of V _zz on x it was shown that the holes appearing during the substitution of La³⁺ for Sr²⁺ are localized preferably on the oxygen atoms that are in the same plane as the copper atoms, which is in agreement with the model discussed in the literature and assumes that the mechanism responsible for the high-temperature superconductivity of solid solutions La_{2 ? x} Sr _x CuO₄ is the interaction between the conductivity electrons and two-atomic two-electron centers with negative correlation energy.     

Structural heterogeneity of SiO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass

It is shown that the phase heterogeneity of SiO₂–Na₂O–Al₂O₃ glass has a liquation and crystallization nature, the balance between which is determined by the conditions of their synthesis. An increase in the aluminum oxide content decreases the number of liquation and crystallization sites, and also the linear sizes of the crystalline formations without eliminating the phase separation due to the liquation. The area of metastable immiscibility in the SiO₂–Na₂O–Al₂O₃ system, which is determined by scanning electron microscopy, is probably wider than the area detected by the optical methods.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–Au and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–Au Hybrid Nanorods: Layer-by-Layer Assembly Synthesis and Their Magnetic and Optical Properties

A layer-by-layer technique has been developed to synthesize FeOOH–Au hybrid nanorods that can be transformed into Fe₂O₃–Au and Fe₃O₄–Au hybrid nanorods via controllable annealing process. The homogenous deposition of Au nanoparticles onto the surface of FeOOH nanorods can be attributed to the strong electrostatic attraction between metal ions and polyelectrolyte-modified FeOOH nanorods. The annealing atmosphere controls the phase transformation from FeOOH–Au to Fe₃O₄–Au and α-Fe₂O₃–Au. Moreover, the magnetic and optical properties of as-synthesized Fe₂O₃–Au and Fe₃O₄–Au hybrid nanorods have been investigated.     

Synthesis and characterization of nanocomposites Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>–SiO<Subscript>2</Subscript>–chitosan based on lbl technology

In this paper, the apparent chain-like core-shell structure Fe₃O₄–SiO₂–chitosan nanoparticles was synthesized by two-step method with cross-linking action of glutaraldehyde based on layer-by-layer technology, the composite particles were characterized by IR, XRD, TEM, SEM, EDS and VSM analytical methods, and the synthesis conditions of the product were studied. The results indicated that the diameter of the composite particles is about 106.5 nm, the parietal layer of chitosan is 20 nm, and after crosslinking action of glutaraldehyde, chitosan uniformaly coated the outer surface of Fe₃O₄–SiO₂.     

Vitreous region and properties of glasses of the Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>–GeS<Subscript>2</Subscript>–PbF<Subscript>2</Subscript> system

Vitrification in the Ga₂S₃–GeS₂–PbF₂ system is considered. The physicochemical properties of glasses, such as density, microhardness, electroconductivity, refraction index, and transmission percentage of specimens in visible and IR ranges of spectrum are studied; differential thermal analysis is carried out; and Raman and electron paramagnetic resonance spectra are investigated.     

Role of CeO<Subscript>2</Subscript> in Rh/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts for CO<Subscript>2</Subscript> Reforming of Methane

Abstract  

The Rh/α-Al₂O₃ catalyst was modified by CeO₂ in order to improve the thermal stability and the carbon deposition resistance during the CO₂ reforming of methane The carbon formation was determined by TPO, TEM and Raman spectroscopy. Characterization results showed that the incorporation of Ce in the support inhibits the carbon deposition, increasing the useful life and the stability of the Rh base catalysts.     

Study on flame structures and emissions of CO and NO in Various CH<Subscript>4</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript>–O<Subscript>2</Subscript>/N<Subscript>2</Subscript> counterflow premixed flames

An oxygen-diluted partially premixed/oxygen-enriched supplemental combustion (ODPP/OESC) counterflow flame is studied in this paper. Flame images are obtained through experiments and numerical simulations with the GRI-Mech 3.0 chemistry. The oxygen dilution effects are revealed by comparing the flame structures and emissions with those of a premixed flame and partially premixed flame (PPF) at the same equivalence ratio (?_Σ = 0.95 and ? _f = 1.4). The results show that both PPF and ODPP/OESC flames have distinct double flame structures; however, the location of the premixed combustion zone and the distance between premixed/nonpremixed combustion zone are significantly different for these two cases. For the ODPP/OESC flame, the temperature in the premixed combustion zone is lower and the premixed zone itself is located farther downstream from the fuel nozzle, which leads to reduction of NO and CO emissions, as compared to those of the PPF. Therefore, by adjusting the distribution of the oxygen concentration in the premixed and nonpremixed combustion zones, the ODPP/OESC can effectively balance the chemical reaction rate in the entire combustion zone and, consequently, reduce emissions.     

Effects of the geometry and operating temperature on the stability of Ti/IrO<Subscript>2</Subscript>–SnO<Subscript>2</Subscript>–Sb<Subscript>2</Subscript>O<Subscript>5</Subscript> electrodes for O<Subscript>2</Subscript> evolution

Ternary IrO₂–Sb₂O₅–SnO₂ anode has shown its superiorities over IrO₂ and many other electrocatalysts for O₂ evolution, in terms of electrochemical stability, activity and cost. The performance of IrO₂–Sb₂O₅–SnO₂ anodes is affected by its electrochemical properties and operating conditions. In this paper, the electrochemical stability and activity of the Ti/IrO₂–Sb₂O₅–SnO₂ anodes prepared with three different geometries were investigated under different operating conditions. It was found that anodes with large mean curvature have high electrochemical stability. Although increasing temperature results in a decrease in the stability of Ti/IrO₂–Sb₂O₅–SnO₂, the anode with a mean curvature of 200 m⁻¹ still shows acceptable service life even at 70 °C. This tolerance of high temperature was attributed to the thermal expansion difference between the substrate and the coating layer, the redox window for Ir(V)/Ir(IV) conversion, and the redox reversibility of Sb and Sn species in the coating layer.     

Structural analyses of RuO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti and IrO<Subscript>2</Subscript>–RuO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>/Ti anodes used in industrial chlor-alkali membrane processes

The morphology and composition of RuO₂–TiO₂/Ti and IrO₂–RuO₂–TiO₂/Ti anodes, which have been used for the production of chlorine for more than 10 years, were analyzed by various methods; such as high-resolution scanning electron microscopy, high-resolution Auger electron spectroscopy, electron probe X-ray emission microanalysis and X-ray diffraction analysis. Drastic changes in the surface morphology, including partial exfoliation of a small amount of the oxide layer and a reduction in the content of ruthenium species through dissolution, were observed for the RuO₂–TiO₂/Ti anode. For the IrO₂–RuO₂–TiO₂/Ti anode, on the other hand, there were moderate changes in the surface morphology and moderate dissolution of iridium and ruthenium species.     

Effect of iron oxide (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>) on the structural,optical, electrical,and dielectric properties of SrO–V<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

The oxide glass system of the composition (10 – x)SrO–xFe₂O₃–90V₂O₅, (x = 0, 2, 4, 6 and 8 mol %) were prepared by a standard melt quenching technique. The amorphous nature of the prepared glass was confirmed using X-ray diffraction technique. The infrared spectra of these glasses were recorded over a continuous spectral range (850–1500 cm^–1). The density of prepared sample was obtained by the Archimedes principle. The physical parameters of the glasses were also determined with respect to the composition. Density increases from 3.10 to 3.20 g/cm³, whereas the molar volume decreases with the increase in Fe₂O₃ concentration. In order to study optical properties, absorption spectra were measured at room temperature. Indirect optical energy band gap, optical dielectric constant, refractive index were calculated from optical energy band gap. The refractive index decreases gradually with the increase in Fe₂O₃ content due to increase of bridging oxygen’s. For temperatures from 300 to 500 K, the dc conductivity increased with the increasing Fe₂O₃ content. The dielectric properties like dielectric constant, dielectric loss factor and dielectric loss tangent investigated at the room temperature in the frequency range of 10 kHz to 1 MHz decreases with frequency. The dielectric behavior shows strong frequency as well as composition dependence.     

Correlation of thermal properties and electrical conductivity of La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>Cu<Subscript>0.2</Subscript>Fe<Subscript>0.8</Subscript>O<Subscript>3−δ</Subscript> material for solid oxide fuel cells

A copper-doped ferrite with the chemical composition La_0.7Sr_0.3Cu_0.2Fe_0.8O_3−δ (LaSrCuFe) was prepared using the classical ceramics method starting from the oxides. The linear thermal expansion coefficient in air was measured in the temperature range between 550 and 1,250 K to be between 10 × 10⁻⁶ and 15 × 10⁻⁶ K⁻¹. The electrical conductivity in air was found to be higher than 100 S cm⁻¹ for temperatures lower than 1,100 K. A change of oxygen stoichiometry was found above 650 K in an atmosphere of 20 vol% oxygen with argon. This change can be correlated with the electrical conductivity.     

Phase relationships in the Na<Subscript>2</Subscript>ZnP<Subscript>2</Subscript>O<Subscript>7</Subscript>–LiKZnP<Subscript>2</Subscript>O<Subscript>7</Subscript> system

The phase relationships in the Na₂ZnP₂O₇–LiKZnP₂O₇ system are studied. They are represented by a mixture of the starting components in the subsolidus region. The eutectic was found at a temperature of 640°C and composition of 0.5LiKZnP₂O₇. The phase formation of this system is compared with the previously studied NaKZnP₂O₇–LiKZnP₂O₇ system. It is shown that a structural factor affects the geometry of the state diagrams.     

Biodiesel Preparation from Soybean Oil by Using a Heterogeneous Ca<Subscript>x</Subscript>Mg<Subscript>2−x</Subscript>O<Subscript>2</Subscript> Catalyst

Abstract  

An effective heterogeneous catalyst, Ca_xMg_2−xO₂, was prepared and tested for soybean oil transesterification with methanol. The catalysts were characterized by using X-ray diffraction , Fourier transform infrared spectra, thermo gravimetric and differential thermal analysis , and Hammett indicator method. The catalyst with Ca/Mg ratio of 1.0 and calcined at 800 °C exhibited high catalytic activities. Under the suitable transesterification conditions (methanol/oil ratio 12:1, catalyst loading 6 wt%, reaction time 5 h, at reflux of methanol), the oil conversion of 91.3% could be achieved. The catalyst can be easily recovered and reused without significant deactivation.