Fabrication and characterization of γ-Al2O3–clay composite ultrafiltration membrane for the separation of electrolytes from its aqueous solution

In this paper, we have reported the preparation of low cost γ-Al₂O₃ membrane on a macroporous clay support by dip-coating method. For the synthesis of γ-Al₂O₃ top layer on the support, a stable boehmite sol is prepared using aluminium chloride salt as a starting material by sol–gel route. The structural properties of the composite membrane as well as γ-Al₂O₃ powder is carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm data, Fourier transform infrared analysis (FTIR) and dynamic light scattering (DLS) analysis. The mean particle size of the boehmite sol used for coating is found to be 30.9 nm. The pore size distribution of the γ-Al₂O₃–clay composite membrane is found to be in the range of 5.4–13.6 nm. Separation performance of the membrane in terms of flux and rejection of single salts solution such as MgCl₂ and AlCl₃ as a function of pH, salt concentration and applied pressure is also studied. The rejection and flux behavior are found to be strongly dependent on electrostatic interaction between the charged molecules and γ-Al₂O₃–clay composite membrane. The intrinsic rejection has been determined by calculating the concentration at membrane surface (C_m) using Speigler–Kedem model. It is found that the observed rejection shows anomalous trend with increase in applied pressure and the intrinsic rejection increases with increase in applied pressure, a trend typical of the separation of electrolyte through charged membranes. At acidic pH, both the salt solution shows higher rejection. With increase in the salt concentration, observed rejection of salt decreases due to the enhanced concentration polarization. The maximum rejection of MgCl₂ and AlCl₃ is found to be 72% and 88%, respectively for salt concentration of 3000 ppm.     

Energetics of copper diphosphates – Cu2P2O7 and Cu3(P2O6OH)2

Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂. α-Cu₂P₂O₇ is reversibly transformed to β-Cu₂P₂O₇ at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol⁻¹. Enthalpies of formation from oxides of α-Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂ are −279.0 ± 1.4 kJ mol⁻¹ and −538.8 ± 2.7 kJ mol⁻¹, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol⁻¹ and −4302.7 ± 6.7 kJ mol⁻¹, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu₃(P₂O₆OH)₂, thus decreasing its thermodynamic stability.     

Chromium doped γ-Al2O3 powders. Features of the electrical double layer and state of the surface species

γ-Al₂O₃ samples, both pure and Cr doped, were prepared by heating at 470°C sol–gel precursors obtained by using aluminum tri-sec-butoxide [Al(OC₄H₉)₃] as the starting compound. The samples were characterised for phase composition (X-ray diffraction) and surface area (BET). Electrochemical determinations of the double layer reactivity of the pure and doped oxides were performed both by surface charge and by electrokinetic sonic amplitude (ESA) determinations. The interfacial electrostatic response is discussed and analysed also with reference to the sample surface state obtained by X-ray photoelectron spectroscopy (XPS).     

Formation of β- and β″-Al2O3 by the solid state reaction between NaAlO2 and γ-Al2O3

The solid state reaction of NaAlO₂ with γ-Al₂O₃ was investigated kinetically. Powdered compacts with various compositions (Al₂O₃/NaAlO₂ = 1–5) were fired at 700–1200°C for 1–768 hr. The amounts of the reaction product were determined by peak heights of X-ray diffraction patterns. β″-Al₂O₃ was formed predominantly from the sample with Al₂O₃/NaAlO₂ = 2. The firing time for the β″-Al₂O₃ formation was shortened as the firing temperature was raised, and the activation energy, E_a, for formation was about 130–135 kcal/mole. The sample of Al₂O₃/NaAlO₂ = 5 formed m-Al₂O₃ with the mullite structure and was observed to transform gradually to β-Al₂O₃. E_a for the m-Al₂O₃ formation and for the transition were about 55–60 and 40 kcal/mole, respectively, which resulted in E_a of about 95–100 kcal/mole for the β-Al₂O₃ formation. The mechanism of the m-Al₂O₃ formation is discussed briefly.     

Formation of α-Fe2O3/FeOOH nanostructures with various morphologies by a hydrothermal route and their photocatalytic properties

A series of α-Fe₂O₃/FeOOH nanostructures with different morphologies have successfully been synthesized based on K₄[Fe(CN)₆] at 140 °C by a novel hydrothermal method. The morphology and phase of α-Fe₂O₃/FeOOH can be controlled by adjusting the reaction time. UV–vis absorption spectrum, X-ray powder diffraction, and transmission electron microscopy analyses were used to characterize the resulting products. A detailed, rational mechanism is proposed for the formation of α-Fe₂O₃/FeOOH nanostructures. The potential applications of the as-synthesized α-Fe₂O₃/FeOOH nanoparticles with different morphologies on photocatalytic decomposition of salicylic acid were also investigated.     

Synthesis and characterization of Fe2O3/SiO2 nanocomposites

Fe₂O₃/SiO₂ nanocomposites based on fumed silica A-300 (S_BET = 337 m²/g) with iron oxide deposits at different content were synthesized using Fe(III) acetylacetonate (Fe(acac)₃) dissolved in isopropyl alcohol or carbon tetrachloride for impregnation of the nanosilica powder at different amounts of Fe(acac)₃ then oxidized in air at 400–900 °C. Samples with Fe(acac)₃ adsorbed onto nanosilica and samples with Fe₂O₃/SiO₂ including 6–17 wt% of Fe₂O₃ were investigated using XRD, XPS, TG/DTA, TPD MS, FTIR, AFM, nitrogen adsorption, Mössbauer spectroscopy, and quantum chemistry methods. The structural characteristics and phase composition of Fe₂O₃ deposits depend on reaction conditions, solvent type, content of grafted iron oxide, and post-reaction treatments. The iron oxide deposits on A-300 (impregnated by the Fe(acac)₃ solution in isopropanol) treated at 500–600 °C include several phases characterized by different nanoparticle size distributions; however, in the case of impregnation of A-300 by the Fe(acac)₃ solution in carbon tetrachloride only α-Fe₂O₃ phase is formed in addition to amorphous Fe₂O₃. The Fe₂O₃/SiO₂ materials remain loose (similar to the A-300 matrix) at the bulk density of 0.12–0.15 g/cm³ and S_BET = 265–310 m²/g.     

Environment-friendly synthesis of N-phenylpiperidine from aniline and 1,5-pentanediol over γ-Al2O3 catalyst

An efficient environment-friendly synthesis of N-phenylpiperidine was developed from aniline and 1,5-pentanediol over γ-Al2O3 catalyst under atmospheric pressure. The conversion of 1,5-pentanediol reached 97% and the selectivity for N-phenylpiperidine attained 94%. The structure of the catalyst was characterized by NH3-TPD and BET. The influences of calcination temperature of the catalyst and reaction temperature on activity and selectivity of the catalyst were investigated.     

Macroscopic and spectroscopic characterization of selenate, selenite, and chromate adsorption at the solid–water interface of γ-Al2O3

The interaction of selenate, selenite, and chromate with the hydrated surface of γ-Al₂O₃ was studied using a combination of macroscopic pH edge data, electrophoretic mobility measurements, and X-ray absorption spectroscopic analyses. The pH edge data show generally increased oxyanion adsorption with decreasing pH, and indicate ionic strength-(in)dependent adsorption of chromate and selenate across the pH range 4–9, and ionic strength-(in)dependent adsorption of selenite in this pH range. The adsorption of chromate peaks at pH 5.0, whereas for selenate and selenite no pH adsorption maxima are observed. Electrophoretic mobility measurements show that all three oxyanions decrease the zeta potential of γ-Al₂O₃ upon adsorption; however, only selenite decreased the pH_PZC of the γ-Al₂O₃ sorbent. EXAFS data indicate that selenite ions are coordinated in a bridging bidentate fashion to surface AlO₆ octahedra, whereas no second-neighbor Al scattering was observed for adsorbed selenate ions. Combined, the results presented here show that pH is a major factor in determining the extent of adsorption of selenate, selenite, and chromate on hydrated γ-Al₂O₃. The results point to substantial differences between these anions as to the mode of adsorption at the hydrated γ-Al₂O₃ surface, with selenate adsorbing as nonprotonated outer-sphere complexes, chromate forming a mixture of monoprotonated and nonprotonated outer-sphere adsorption complexes, and selenite coordinating as inner-sphere surface complexes in bridging configuration.     

Structure, crystal chemistry and thermal evolution of the δ-Bi2O3-related phase Bi9ReO17

The thermal evolution and structural properties of fluorite-related δ-Bi₂O₃-type Bi₉ReO₁₇ were studied with variable temperature neutron powder diffraction, synchrotron X-ray powder diffraction and electron diffraction. The thermodynamically stable room-temperature crystal structure is monoclinic P2₁/c, a=9.89917(5), b=19.70356(10), c=11.61597(6) Å, β=125.302(2)° (R_p=3.51%, wR_p=3.60%) and features clusters of ReO₄ tetrahedra embedded in a distorted Bi–O fluorite-like network. This phase is stable up to 725 °C whereupon it transforms to a disordered δ-Bi₂O₃-like phase, which was modeled with δ-Bi₂O₃ in cubic Fm3¯m with a=5.7809(1) Å (R_p=2.49%, wR_p=2.44%) at 750 °C. Quenching from above 725 °C leads to a different phase, the structure of which has not been solved but appears on the basis of spectroscopic evidence to contain both ReO₄ tetrahedra and ReO₆ octahedra.     

Study of CO2 Hydrogenation to Methanol over Cu-V/γ-Al2O3 Catalyst

The effect of vanadium addition to CU/γ-Al2O3 catalyst used in the hydrogenation of CO2 to produce methanol was studied. It was found that the catalytic performance of the Cu-based catalyst improved after V addition. The influence of reaction temperature, space velocity and the molar ratio of H2 to CO2 on the performance of 12%Cu-6%V/γ-Al2O3 catalyst were also studied. The results indicated that the best conditions for reaction were as follows: 240℃, 3600 h-1 and a molar ratio of H2 to CO2 of 3:1. The results of XRD and TPR characterization demonstrated that the addition of V enhanced the dispersion of the supported CuO species, which resulted in the enhanced catalytic performance of CU-V/γ-Al2O3 binary catalyst.     

Preparation and hydrogen permeation of SrCe0.95Y0.05O3−δ asymmetrical membranes

Asymmetrical thin membranes of SrCe_0.95Y_0.05O_3−δ (SCY) were prepared by a conventional and cost-effective dry pressing method. The substrate consisted of SCY, NiO and soluble starch (SS), and the top layer was the SCY. NiO was used as a pore former and soluble starch was used to control the shrinkage of the substrate to match that of the top layer. Crack-free asymmetrical thin membranes with thicknesses of about 50 μm and grain sizes of 5–10 μm were successfully pressed on to the substrates. Hydrogen permeation fluxes (J_H2) of these thin membranes were measured under different operating conditions. At 950 °C, J_H2 of the 50 μm SCY asymmetrical membrane towards a mixture of 80% H₂/He was as high as 7.6 × 10⁻⁸ mol/cm² s, which was about 7 times higher than that of the symmetrical membranes with a thickness of about 620 μm. The hydrogen permeation properties of SCY asymmetrical membranes were investigated and activation energies for hydrogen permeation fluxes were calculated. The slope of the relationship between the hydrogen permeation fluxes and the thickness of the membranes was −0.72, indicating that permeation in SCY asymmetric membranes was controlled by both bulk diffusion and surface reaction in the range investigated.     

Ce改性的Pt/γ-AlO3催化剂用于富氢气氛下CO选择氧化

研究了Ce改性的Pt/γ-AlO3对于富氢气氛下CO选择氧化反应的催化行为考察了制备条件（共沉积沉淀法、分步沉积沉淀法以及沉积沉淀温度）对催化活性的影响．结果表明，在80℃时用共沉积沉淀方法制备的催化剂Pt/γ-AlO3-CP-80对CO氧化反应表现出良好的活性和选择性，CO转化率在120℃时可以达到85％．利用氢气程序升温还原和原位漫反射红外光谱对不同条件下制备的催化剂进行了表征，分析了Cc的促进作用．     

Ternary [Al2O3–electrolyte–Cu] species: EPR spectroscopy and surface complexation modeling

Cu²⁺ binding on γ-Al₂O₃ is modulated by common electrolyte ions such as Mg²⁺, , and in a complex manner: (a) At high concentrations of electrolyte ions, Cu²⁺ uptake by γ-Al₂O₃ is inhibited. This is partially due to bulk ionic strength effects and, mostly, due to direct competition between Mg²⁺ and Cu²⁺ ions for the SO⁻ surface sites of γ-Al₂O₃. (b) At low concentrations of electrolyte ions, Cu²⁺ uptake by γ-Al₂O₃ can be enhanced. This is due to synergistic coadsorption of Cu²⁺ and electrolyte anions, and _. This results in the formation of ternary surface species (SOH₂SO₄Cu)⁺, (SOH₂PO₄Cu), and (SOH₂HPO₄Cu)⁺ which enhance Cu²⁺ uptake at pH < 6. The effect of phosphate ions may be particularly strong resulting in a 100% Cu uptake by the oxide surface. (c) EPR spectroscopy shows that at pH  pH_PZC, Cu²⁺ coordinates to one SO⁻ group. Phosphate anions form stronger, binary or ternary, surface species than sulfate anions. At pH  pH_PZC Cu²⁺ may coordinate to two SO⁻ groups. At pH  pH_PZC electrolyte ions and are bridging one O-atom from the γ-Al₂O₃ surface and one Cu²⁺ ion forming ternary [γ-Al₂O₃/elecrolyte/Cu²⁺] species.     

A novel anode supported BaCe0.4Zr0.3Sn0.1Y0.2O3−δ electrolyte membrane for proton conducting solid oxide fuel cells

A novel BaCe_0.4Zr_0.3 Sn_0.1Y_0.2O_3−δ (BSY) electrolyte membrane with thickness of 20 μm was fabricated on NiO-based anode substrate via a one-step all-solid-state method followed by a co-sintering at 1450 °C for 5 h. Chemical stability test demonstrated that BSY electrolyte showed adequate chemical stability against CO₂ and H₂O at intermediate temperature. Besides, the doping of Sn also enhanced the conductivity in humidified hydrogen. With Nd_0.7Sr_0.3MnO_3−σ cathode and hydrogen fuel, the fuel cell generated maximum output of 320, 185 and 105 mW cm⁻² at 700, 650 and 600 °C, respectively. The interfacial resistance of the fuel cell was studied under open circuit conditions and the short-term cell performance also confirmed the stability of BSY electrolyte membrane.     

High-pressure preparation, crystal structure, and properties of the new rare-earth oxoborate β-Dy2B4O9

In this work we report about a new rare-earth oxoborate β-Dy₂B₄O₉ synthesized under high-pressure/high-temperature conditions from Dy₂O₃ and boron oxide B₂O₃ in a B₂O₃/Na₂O₂ flux with a walker-type multianvil apparatus at 8 GPa and 1000°C. Single crystal X-ray structure determination of β-Dy₂B₄O₉ revealed: , a=616.2(1) pm, b=642.8(1) pm, c=748.5(1) pm, α=102.54(1)°, β=97.08(1)°, γ=102.45(1)°, Z=2, R1=0.0151, wR₂=0.0475 (all data). The compound exhibits a new structure type which is built up from bands of linked BO₃- (Δ) and tetrahedral BO₄-groups (□). The Dy³⁺-cations are positioned in the voids between the bands. According to the conception of fundamental building blocks β-Dy₂B₄O₉ can be classified with the notation 2Δ6□:Δ3□=4□=3□Δ. Furthermore we report about temperature-resolved in situ powder diffraction measurements and IR-spectroscopic investigations on β-Dy₂B₄O₉.     

Preparation of Nano-Sized γ-Al2O3 Supported Iron Catalyst for Fischer-Tropsch Synthesis by Solvated Metal Atom Impregnation Methods

Two types of small iron clusters supported onγ-Al2O3-RT(dehydroxylated at room temperature) andγ-Al2O3-800 (dehydroxylated at 800℃) were prepared by solvated metal atom impregnation (SMAI) techniques. The iron atom precursor complex, bis(toluene)iron(0) formed in the metal atom reactor, was impregnated intoγ-Al2O3 having different concentrations of surface hydroxyl groups to study the effect of surface hydroxylation on the crucial stage of iron cluster formation. Catalysts prepared in this way were characterized by TEM, Mossbauer, and chemisorption measurements, and the results show that higher concentration of surface hydroxyl groups ofγ-Al2O3-RT favors the formation of more positively charged supported iron cluster Fen/γ-Al2O3-RT, and the lower concentration of surface hydroxyl groups ofγ-Al2O3-800 favors the formation of basically neutral supported iron cluster Fen/γ-Al2O3-800. The measured results also indicate that the higher concentration of surface hydroxyl groups causes the rapid decomposition of precursor complex, bis(toluene)iron(0), and favors the formation of relatively large iron cluster. Consequently, these two types of catalysts show different catalytic properties in Fischer-Tropsch reaction. The catalytic pattern of Fen/γ-Al2O3-RT in F-T reaction is similar to that of the unreducedα-Fe2O3 and that of Fen/γ-Al2O3-800 is similar to that of the reducedα-Fe2O3.     

High performance protonic ceramic membrane fuel cells (PCMFCs) with Ba0.5Sr0.5Zn0.2Fe0.8O3−δ perovskite cathode

Protonic ceramic membrane fuel cells (PCMFCs) based on proton-conducting electrolytes have attracted much attention because of many advantages, such as low activation energy and high energy efficiency. BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7) electrolyte based PCMFCs with stable Ba_0.5Sr_0.5Zn_0.2Fe_0.8O_3−δ (BSZF) perovskite cathode were investigated. Using thin membrane BZCY7 electrolyte (about 15 μm in thickness) synthesized by a modified Pechini method on NiO-BZCY7 anode support, PCMFCs were assembled and tested by selecting stable BSZF perovskite cathode. An open-circuit potential of 1.015 V, a maximum power density of 486 mW cm⁻², and a low polarization resistance of the electrodes of 0.08 Ω cm² was achieved at 700 °C. The results have indicated that BZCY7 proton-conducting electrolyte with BSZF cathode is a promising material system for the next generation solid oxide fuel cells.     

The Phase Relations in the System In2O3–TiO2–MgO at 1100 and 1350°C

The phase relations in the system In₂O₃–TiO₂–MgO at 1100 and 1350°C are determined by a classical quenching method. In this system, there are four pseudobinary compounds, In₂TiO₅, MgTi₂O₅ (pseudobrookite type), MgTiO₃ (ilmenite type), and Mg₂TiO₄ (spinel type) at 1100°C. At 1350°C, in addition to these compounds there exist a spinel-type solid solution Mg_2−xIn_2xTi_1−xO₄ (0≤x≤1) and a compound In₆Ti₆MgO₂₂ with lattice constants a=5.9236(7) Å, b=3.3862(4) Å, c=6.3609(7) Å, β=108.15(1)°, and q=0.369, which is isostructural with the monoclinic In₃Ti₂FeO₁₀ in the system In₂O₃–TiO₂–MgO. The relation between the lattice constants of the spinel phase and the composition nearly satisfies Vegard's law. In₆Ti₆MgO₂₂ extends a solid solution range to In₂₀Ti₁₇Mg₃O₆₇ with lattice constants of a=5.9230(5) Å, b=3.3823(3) Å, c=6.3698(6) Å, β=108.10(5)°, and q=0.360. The distributions of constituent cations in the solid solutions are discussed in terms of their ionic radius and site preference effect.     

Investigation on double perovskite Ba4Ca2Ta2O11

The structure, conductivity and water uptake of the oxygen-deficient perovskite-type compound Ba₄Ca₂Ta₂O₁₁ have been investigated. Ba₄Ca₂Ta₂O₁₁ crystallizes in the cryolite structure (cubic, Fm3m SG) with a = 8.4508(2) Å, under dry air. The compound can be partially hydrated up to a maximum water content of approximately 0.52 mol H₂O per mol Ba₄Ca₂Ta₂O₁₁. In moist air, the structure symmetry becomes monoclinic (C2/m) and the temperature dependence of total conductivity shows a different behavior because of changes in transport mechanism. Three regions can be observed as a function of temperature. For the low temperature range 200–400 °C, the protonic conduction is prevailing with an activation energy E_A = 0.85 eV. In the intermediate temperature range (400–600 °C), O²⁻ anionic and protonic conductions are mixed with an activation energy E_A = 0.45 eV and in the third region, for temperatures above 600 °C, O²⁻conduction is prevailing with an activation energy E_A = 0.85 eV.     

Reinvestigation of the Fe-rich part of the pseudo-binary system SrO–Fe2O3

The phase relations in the Fe-rich part of the pseudo-binary system SrO–Fe₂O₃ (>33 mol% Fe₂O₃) were reinvestigated between 800 and 1500 °C in air. A combination of microscopy, electron probe micro-analysis, powder X-ray diffraction and thermal analysis was used to determine phase relations, crystal structure parameters and phase transition temperatures. M-type hexagonal ferrite SrFe₁₂O₁₉ (85.71 mol% Fe₂O₃) is stable up to 1410 °C. No indication of a significant phase width was found; Sr₄Fe₆O_13±δ appears as a second phase in compositions with <85.71±0.2 mol% Fe₂O₃. Sr₄Fe₆O_13±δ itself is stable between 800 and 1250 °C. Two other hexagonal ferrites were found to exist at high temperatures only: W-type SrFe²⁺₂Fe³⁺₁₆O₂₇ is stable between 1350 and 1440 °C and X-type ferrite Sr₂Fe²⁺₂Fe³⁺₂₈O₄₆ between 1350 and 1420 °C, respectively, which is shown here for the first time. These findings in combination with previously published data were used to derive a corrected phase diagram of the Fe-rich part of the pseudo-binary system SrO–Fe₂O₃.