Structure and magnetic properties of the nanocomposites γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript>

The structural features and magnetic properties of composite materials Fe₂O₃-SiO₂ consisting of γ-Fe₂O₃ nanoparticles in an amorphous porous matrix of SiO₂ were considered. The studied samples were synthesized by the sol-gel method. The structure of γ-Fe₂O₃-SiO₂ depending on the heating temperature was studied by electron microscopy, X-ray diffraction analysis, ESR and IR spectroscopy. Magnetic measurements were performed on a SQUID magnetometer in the range 2–350 K.     

Preparation,characterization and catalytic studies of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> xerogel composite

In this work, we report the synthesis, characterization and catalytic properties of a vanadium oxide–silicon oxide composite xerogel prepared by a soft chemistry approach. In order to obtain such material, we submitted a vanadium pentoxide gel previously synthesized via protonation of metavanadate species to an “in situ” progressive polycondensation into silica gel. The material has been characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. Further, the catalytic activity of this material was evaluated for the epoxidation of styrene and cyclooctene using iodosylbenzene, hydrogen peroxide and m-chloroperbenzoic acid as the oxidizing agent.     

The characterization and property of polystyrene compounding of α-Fe<Subscript>2</Subscript>O<Subscript>3 </Subscript>in the nano-scale

-Fe₂O₃/polystyrene composite nanoparticles were synthesized in an oil/water microemulsion. Their structure was characterized by transmission electron microscopy, X-ray diffraction and Fourier transform-infrared spectrometry. An Ubbelonde viscometer, a Gouy balance and a model 283 potentiostat/galvanostat measured the molecular weight of the composite nanoparticles and their magnetic and electrical characteristics respectively.     

Thermal and Magnetic Properties of Maghemite γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Synthesized by a Precursor Method

Low-dimension ferromagnetic maghemite γ-Fe₂O₃ was synthesized through a precursor route, using basic iron formate Fe(OH)(HCOO)₂ as a precursor. Conditions of formation of γ-Fe₂O₃ and the temperature range of its existence on heating in air were determined. The saturation magnetization of γ-Fe₂O₃ produced through heating the precursor at 350°C 57.5 (T = 4.2 K) and 43.8 emu/g (T = 300 K).     

Synthesis and properties of γ-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> solid solutions

The textural and structural properties of mixed oxides Ga₂O₃–Al₂O₃, obtained via impregnating γ-Al₂O₃ with a solution of Ga(NO₃)₃ and subsequent heat treatment, are studied. According to the results from X-ray powder diffraction, gallium ions are incorporated into the structure of aluminum oxide to form a solid solution of spinel-type γ-Ga₂O₃–Al₂O₃ up to a Ga₂O₃ content of 50 wt % of the total weight of the sample, accompanied by a reduction in the specific surface area, volume, and average pore diameter. It is concluded that when the Ga₂O₃ content exceeds 50 wt %, the β-Ga₂O₃ phase is observed along with γ-Ga₂O₃–Al₂O₃ solid solution. ⁷¹Ga and ²⁷Al NMR spectroscopy shows that gallium replaces aluminum atoms from the tetrahedral position to the octahedral coordination in the structure of γ-Ga₂O₃–Al₂O₃.     

Characterization of gold supported on Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–CuO–Mn<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts obtained by thermal decomposition of aerosols

The purpose of this work was to employ the differential thermal analysis (DTA) technique to compare variations in the collapse energy of the zeolite Y crystalline structure in a fresh catalyst and in the same catalyst impregnated with nickel and vanadium. A small exothermic signal in the DTA curve at 950–1150 °C indicated the collapse of the crystalline structure. The areas of the exothermic signals in the DTA curves of the two samples indicated a reduction in the curve of the metal impregnated catalyst. These results were compared with X-ray data, leading to the conclusion that metal impregnation affects the zeolite Y crystalline structure and that the DTA technique is a potentially useful tool for measuring the integrity of zeolite Y in catalysts.     

Preparation of ceramic γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> nanofiltration membranes for desalination

As one of the most recently developed membrane separation processes, nanofiltration (NF) has found a number of industrial applications. Ceramic NF membranes are also regarded as the appropriate choice in many applications, due to their higher chemical and physical stability. In this study, the rejection of the chloride ion is investigated using bi-layered γ-Al₂O₃-TiO₂ NF membranes based on α-alumina supports. Compression is used in preparation of the supports and sol-gel dip-coating for the top-layer formation. SEM micrographs, XRD, and nitrogen adsorption/desorption isotherms are used for membrane characterisation. The results show that the calcination temperature (600°C) results in different crystal structures including the brookite phase of TiO₂, the γ phase of Al₂O₃, and a combined phase of aluminium-titanium oxides. The average pore size of the membrane was identified as 1.6 nm using an adsorption/desorption isotherm. The rejection was also studied for the chloride ion, using a cross-flow filtration module. Filtration tests were carried out under different pressures, pH values, and salt concentrations; these showed a smoother behaviour particularly around the isoelectric points (IEPs) due to the dual-layer structure, with the best rejection at pH of approximately 5.     

Improvement of supercooling and thermal conductivity of the sodium acetate trihydrate for thermal energy storage with α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> as addictive

In situ calorimetric technology was firstly employed to study the effects of surfactants on the materials formation. In the present study, different kinds of surfactants were selected as additives during cluster-shaped Ni-doped Fe₃O₄ synthesis. Experimental results indicate that the surfactants reduced the particle size and changed the cationic distribution, compositions and magnetic properties of the as-synthesized materials. The microcalorimetric results demonstrate that the sample formation was endothermal and divided into five processes based on the heat-flow versus time curves. No significant effects of the surfactants on these processes were found. However, the surfactants addition affected the heat flow and the temperatures for peaks in these curves. The surfactant adsorption on the crystal facet and nuclei of the sample, and the interactions among surfactants and ions contained in the system may be mainly the reason for these effects. These results demonstrate different actions of surfactants and ligands on materials formation.     

A Green,Low-Cost and Efficient Photocatalyst: Atomic-Hydrogenated α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The environmental-friendly hematite iron oxide (α-Fe₂O₃) has important application prospects in the photocatalysis field owing to its narrow indirect band gap. Here, we report a band gap engineering of α-Fe₂O₃ by incorporation of electrochemically-generated atomic hydrogen at moderate conditions. The ultraviolet–visible spectra show the reduction of the α-Fe₂O₃ band gap after hydrogenation and the absorption region from 200–800 nm is enhanced, especially in the visible light region. First principles calculation reveals the mixing of the new hybrid energy level with the valence band top resulting in a decrease in the band gap of α-Fe₂O₃. Further photocatalytic degradation experiments of dyes demonstrate that the photocatalytic efficiency of α-Fe₂O₃ can be greatly enhanced by the atomic hydrogen incorporation. The hydrogenated α-Fe₂O₃ can be easily recycled by magnets and has good photocatalytic stability. These findings offer possibilities for utilizing this inexpensive and earth-abundant oxide materials in the pollution controlling areas.     

Preparation and characterization of rapid magnetic recyclable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript>@TiO<Subscript>2</Subscript>–Sn photocatalyst

Effective procedure to synthesize Fe₃O₄@SiO₂@TiO₂–Sn magnetically separable photocatalyst by a combination of co-precipitation, sol–gel and photodeposition methods was introduced. Products were characterized by XRD, SEM, VSM, EDS, DRS, TEM, ICP-OES and IR techniques. The dimensions of catalyst particle size were evaluated by scanning electron microscopy, and results approved nanoscale size for product. In addition, studying the magnetic nature by VSM analysis showed superparamagnetic properties for all samples. XRD pattern indicates that TiO₂ coated on Fe₃O₄@SiO₂ core well crystallized at 400 °C in anatase phase. Synthesized photocatalyst shows good photocatalytic performance in decolorization of rhodamine B aqueous solution. The composite nanoparticles showed high recycling efficiency and stability over five separation cycles.     

Adsorption of Cl<Superscript>−</Superscript> ions on γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> oxide from nitrate solutions

The adsorption of chloride ions on γ-Fe₂O₃ oxide (maggemite) from nitrate solution is studied using the method of potentiometric titration and an ion-selective electrode. The specific character of adsorption is determined. It is shown that the maggemite surface coverage with Cl^? ions increases with increasing concentration of ions in the solution, decreasing pH value, and increasing potential. The adsorbability of ions changes drastically in the pH range about pH₀ (γ-Fe₂O₃)6.2. It is found that the adsorption of chloride ions from neutral nitrate solution exponentially increases in the potential range from 0.1 to 1.0 V. The type of adsorption isotherm and the adsorption parameters are determined. It is found that, in the absence of external polarization, the concentration dependences of adsorption of Cl^? ions are complex-shaped, and their initial portions are described by the Langmuir isotherm. Further increase of adsorption is explained by the penetration of Cl^? ions inwards the oxide.     

Reduction of Oxide Mixtures of (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + CuO) and (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> + Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) by Low-Temperature Hydrogen Plasma

The paper presents experimental results pertaining to the reduction of oxide mixtures namely (Fe₂O₃ + CuO) and (Fe₂O₃ + Co₃O₄), by low-temperature hydrogen plasma in a microwave hydrogen plasma set-up, at microwave power 750 W and hydrogen flow rate 2.5 × 10^?6 m³ s^?1. The objective was to examine the effect of addition of CuO or Co₃O₄, on the reduction of Fe₂O₃. In the case of the Fe₂O₃ and CuO mixture, oxides were reduced to form Fe and Cu metals. Enhancement of reduction of iron oxide was marginal. However, in the case of the Fe₂O₃ and Co₃O₄ mixture, FeCo alloy was formed within compositions of Fe₇₀Co₃₀, to Fe₃₀Co₇₀. Since the temperature was below 841 K, no FeO formed during reduction and the sequence of Fe₂O₃ reduction was found to be Fe₂O₃ → Fe₃O₄ → Fe. Reduction of Co₃O₄ preceded that of Fe₂O₃. In the beginning, the reduction of oxides led to the formation of Fe–Co alloy that was rich in Co. Later Fe continued to enter into the alloy phase through diffusion and homogenization. The lattice strain of the alloy as a function of its composition was measured. In the oxide mixture in which excessive amount of Co₃O₄ was present, all the Co formed after reduction could not form the alloy and part of it appeared as FCC Co metal. The crystallite size of the alloy was in the range of 22–30 nm. The crystal size of the Fe–Co alloy reduced with an increase in Co concentration.     

Preparation and characterization of CeO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> aerogels supported ruthenium for catalytic wet air oxidation of p-hydroxybenzoic acid

Catalytic wet air oxidation of an aqueous solution of p-hydroxybenzoic acid was conducted over ruthenium catalysts (1 wt%) supported on CeO₂–Al₂O₃ aerogels mixed oxides at 140 °C and 50 bars of air. We study the effect of the amount of CeO₂ in the catalyst. We found that the optimal cerium content in the Al₂O₃ support was 20 wt%. The activity of the Ru/Al₂O₃ and Ru/CeO₂ was also tested for comparison. It was found that the addition of CeO₂ on the alumina support improves the activity of Ru catalysts. The activity of the samples decreases in the following order: Ru/Ce–Al (20) > Ru/Ce–Al (10) > Ru/Ce–Al (5) ≈ Ru/Al₂O₃ > Ru/CeO₂. Samples characterization was performed by means of N₂ adsorption–desorption, XRD, UV–Vis, TPR, SEM and TEM.     

Preparation of Mesoporous γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> from Aluminum Hydroxide Peptized with Organic Acids

The relationships of the formation of aluminum oxide from aluminum hydroxide peptized with organic acids (propionic, maleic, malonic, tartaric) were studied. The pore structure parameters of the hydroxide samples and of aluminum oxide samples obtained from them are strongly influenced by acid peptization. The nature of the acid influences the extent of defectiveness of the γ-Al₂O₃ structure, manifested in the density of aluminum oxide, measured by helium pycnometry. The possibility and conditions for preparing mesoporous γ-Al₂O₃ suitable for use in chemical and petrochemical processes were determined.     

The state of dispersed niobia species on γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and their catalytic performance for condensation of isobutylene and isobutyraldehyde

Catalysts of Nb₂O₅/γ-Al₂O₃ were prepared by aqueous solution impregnation. The state of niobia species on surface of γ-Al₂O₃ is characterized by using the technology of X-ray power diffraction (XRD) and analyzed using the “incorporation model”. The acidity and the nature of acid sites of the catalysts were evaluated by means of Fourier transform infrared (FTIR) spectroscopy of adsorbed pyridine. The catalytic activity of Nb₂O₅/γ-Al₂O₃ catalysts was evaluated by a condensation reaction from isobutene and isobutyraldehyde to 2,5-dimethyl-2,4-hexadiene. The results of XRD indicate that the dispersion capacity of niobia on γ-Al₂O₃ is about 0.76 mmol Nb per 100m² γ-Al₂O₃, which is almost identical to the theoretical value (0.75 mmol Nb per 100m² γ-Al₂O₃) calculated by the “incorporation model”. The results of Py-IR and catalytic activity evaluation indicate that the acidity feature is related to the state of dispersed niobia species as well as the loading of niobia onto the surface of γ-Al₂O₃ support.     

High-temperature low-friction behaviors of γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>@SiO<Subscript>2</Subscript> nanocomposite coatings obtained through sol–gel method

In the present paper, the γ-Fe₂O₃@SiO₂ nanocomposite is prepared by sol–gel method and the γ-Fe₂O₃@SiO₂ nanocomposite coatings are deposited on the steel substrate. The microstructure, surface topography, and tribological properties of the γ-Fe₂O₃@SiO₂ nanocomposite were measured and investigated by X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR), transmission electron microcopy (TEM), and high-temperature tribometer, respectively. The tribotest were performed by high-temperature tribometer in the temperature ranges from 400 to 600?°C to investigate the tribological properties of the nanocomposites under high temperature. The experimental results show that there is the core-shell structure in the γ-Fe₂O₃@SiO₂ nanocomposite. It is also found that the γ-Fe₂O₃@SiO₂ nanocomposite coatings exhibit low friction (0.05) from 500 to 600?°C. XRD measurements show that low-friction behavior of the friction pair under high temperature is involved in the transformation between α-Fe₂O₃ and γ-Fe₂O₃ and the oxidations of the steel substrate during sliding. The core-shell structure of the nanocomposites inhibits γ-Fe₂O₃ of the soft phase changing into α-Fe₂O₃ phase and the thermal energy of the friction heat activates the oxidation of the steel substrate in ambient air, which are beneficial to form low shear interface and achieve high temperature low friction.

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The γ-Fe₂O₃@SiO₂ nanocomposite coatings by sol–gel method with amorphous and multi-core SiO₂ wrapping nano crystalline γ-Fe₂O₃ exhibit low coefficient of friction (CoF) from 500 to 600?°C.

     

Effect of MoO<Subscript>3</Subscript> additions on the thermal stability and crystallization kinetics of PbO–Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>–As<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

The present paper reports on the effect of MoO₃ on the glass transition, thermal stability and crystallization kinetics for (40PbO–20Sb₂O₃–40As₂O₃)_100−x –(MoO₃) _x (x = 0, 0.25, 0.5, 0.75 and 1 mol%) glasses. Differential scanning calorimetry (DSC) results under non-isothermal conditions for the studied glasses were reported and discussed. The values of the glass transition temperature (T _g) and the peak temperature of crystallization (T _p) are found to be dependent on heating rate and MoO₃ content. From the compositional dependence and the heating rate dependence of T _g and T _p, the values of the activation energy for glass transition (E _g) and the activation energy for crystallization (E _c) were evaluated and discussed. Thermal stability for (40PbO–20Sb₂O₃–40As₂O₃)_100−x –(MoO₃) _x glasses has been evaluated using various thermal stability criteria such as ΔT, H _r , H _g and S. Moreover, in the present work, the K _r(T) criterion has been considered for the evaluation of glass stability from DSC data. The stability criteria increases with increasing MoO₃ content up to x = 0.5 mol%, and decreases beyond this limit.     

Structural and Temperature Dependent Electrical Conductivity Properties of Dy<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> CO-Doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>

In the present work, Dy₂O₃ and Sm₂O₃ double-doped Bi₂O₃-based materials are synthesized by exploiting the solid-state synthesis method. The structural and temperature dependent electrical properties of these ternary ceramic samples, which are candidate materials for solid oxide fuel cell (SOFCs) electrolyte, are determined by means of a powder X-ray diffractometer (XRD), the four point-probe method (FPPM), and the thermal-gravimetry/differential thermal analysis (TG/DTA). As a result of the XRD measurements, the fluorite-type fcc δ-phase with a stable structure is obtained for higher values of the dopant oxide material, which are the samples with the maximum content of fixed 20% Dy₂O₃ and 15% and 20% Sm₂O₃. The samples with the stable δ-phase structure have higher conductivities. The highest electrical conductivity is found for the (Bi₂O₃)0.6(Dy₂O₃)_0.2(Sm₂O₃)_0.2 sample, which was 2.5×10^–2 (Ohm cm)^–1 at 750 °C. The activation energies are also calculated from the Arrhenius charts, which were determined from the FPPM measurements. The lowest activation energy is found as 0.85 eV for the sample with the highest electrical conductivity.     

Thermal studies of ZnO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–TeO<Subscript>2</Subscript> glasses

The effect of TeO₂ additions on the thermal behaviour of zinc borophosphate glasses were studied in the compositional series (100 − x)[0.5ZnO–0.1B₂O₃–0.4P₂O₅]–xTeO₂ by differential scanning calorimetry, thermodilatometry and heating microscopy thermal analysis. The addition of TeO₂ to the starting borophosphate glass resulted in a linear increase of glass transition temperature and dilatometric softening temperature, whereas the thermal expansion coefficient decreased. Most of glasses crystallize under heating within the temperature range of 440–640 °C. The crystallization temperature steeply decreases with increasing TeO₂ content. The lowest tendency towards crystallization was observed for the glasses containing 50 and 60 mol% TeO₂. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were Zn₂P₂O₇, BPO₄ and α-TeO₂. Annealing of the powdered 50ZnO–10B₂O₃–40P₂O₅ glass leads at first to the formation of an unknown crystalline phase, which is gradually transformed to Zn₂P₂O₇ and BPO₄ during subsequent heating.