Magnetic diphase nanostructure of ZnFe2O4/γ-Fe2O3

Magnetic diphase nanostructures of ZnFe₂O₄/γ-Fe₂O₃ were synthesized by a solvothermal method. The formation reactions were optimized by tuning the initial molar ratios of Fe/Zn. All samples were characterized by X-ray diffraction, thermogravimetric analysis, infrared spectroscopy, and Raman spectra. It is found that when the initial molar ratio of Fe/Zn is larger than 2, a diphase magnetic nanostructure of ZnFe₂O₄/γ-Fe₂O₃ was formed, in which the presence of ZnFe₂O₄ enhanced the thermal stability of γ-Fe₂O₃. Further increasing the initial molar ratio of Fe/Zn larger than 6 destabilized the diphase nanostructure and yielded traces of secondary phase α-Fe₂O₃. The grain surfaces of diphase nanostructure exhibited a spin-glass-like structure. At room temperature, all diphase nanostructures are superparamagnetic with saturation magnetization being increased with γ-Fe₂O₃ content.     

Electrochemically regenerative visible light-induced reactivity of α-Fe2O3 films with Ag(core)–AgCl(shell) microcrystal composites

Ag(core)–AgCl(shell) microcrystal composites (Ag@AgCl) have been formed on an α-Fe₂O₃ film-coated SnO₂ electrode by a 2 step method consisting of the electrochemical reduction of Ag⁺ ions and the subsequent electrochemical oxidation. The synergy of α-Fe₂O₃ and Ag@AgCl gave rise to a high visible light-induced reactivity (λ_ex > 420 nm) for the oxidation of 2-naphthol (2-NAP) used as a model water pollutant in the presence and absence of oxygen. These findings were attributable to the function of Ag@AgCl composites as an excellent charge-separation promoter and built-in acceptor.     

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.     

The Al2O3-Fe2O3 Mixed Oxidic System, I. Preparation and Characterization

A series of Al₂O₃-Fe₂O₃ mixed oxidic solids with composition ranging from 0 to 100% of Fe₂O₃ were prepared and examined for structural characteristics. XRD diagrams showed the presence of α-Al₂O₃ and hematite phases. The analysis of M?ssbauer spectra revealed the existence of two iron containing phases. The specific surface area of the mixture decreases by the addition of iron and depends on the crystal phases of the mixture. This revised version was published online in June 2006 with corrections to the Cover Date.     

Preparation of “pore-fill” type Pd–YSZ–γ-Al2O3 composite membrane supported on α-Al2O3 tube for hydrogen separation

Mesoporous YSZ–γ-Al₂O₃ membranes were coated on α-Al₂O₃ (Ø2 mm) tube by dipping the α-Al₂O₃ support tube into mixed sol consists of nano-size YSZ and bohemite particles followed by drying and calcination at 600 °C. Addition of bohemite in YSZ sol helped a good adhesion and uniform coating of the membrane film onto α-Al₂O₃ support. The quality of the mesoporous YSZ–γ-Al₂O₃ membranes was evaluated by the gas permeability experiments. The number of defects was minimized when the γ-Al₂O₃ content became more than 40%. Addition of γ-Al₂O₃ inhibited the crystal growth of YSZ, sintering shrinkage and distortion stress. Increase of calcination temperature and time results in the increase of pore size and N₂ permeance. A hydrogen perm-selective membrane was prepared by filling palladium into the nano-pores of YSZ–γ-Al₂O₃ layer by vacuum-assisted electroless plating. Crystal growth of palladium was observed by thermal annealing of the membrane at 600 °C for 40 h. The Pd–YSZ–γ-Al₂O₃ composite membrane revealed improved thermal stability allowing long-term operation at elevated temperature (>500 °C). This has been attributed to the improved fracture toughness of YSZ–γ-Al₂O₃ layer and matching of thermal expansion coefficient between palladium and YSZ. Although fracture of the membrane did not occur, decline of H₂ flux was observed when the membrane was exposed in 600 °C. This has been attributed to the agglomeration of palladium particles by crystal growth and dense packing into the pore networks of YSZ–γ-Al₂O₃ by elevation of temperature.     

α-Fe2O3/SiO2纳米颗粒混合体系表面的酸碱性质及其对重金属离子的吸附行为

以Fe(NO₃)₃·9H₂O和正硅酸乙酯(TEOS)为原料, 通过溶胶-凝胶法和辅助模板法分别制备了纳米α-Fe₂O₃和SiO₂, 并对所合成样品进行了粉末X射线衍射(XRD)和BET表征. 使用自动电位滴定仪测定了α-Fe₂O₃/SiO₂纳米颗粒混合体系的表面酸碱性质. 研究了在不同pH下α-Fe₂O₃/SiO₂混合体系对Cu²⁺、Pb²⁺、Zn²⁺离子的吸附行为. 基于上述实验数据, 用WinSGW软件计算了α-Fe₂O₃/SiO₂混合体系表面酸碱配位常数, 并得出结论: α-Fe₂O₃/SiO₂混合体系表面反应为单一脱质子反应≡XOH ⇔ ≡XO^-+ H⁺(lg K = -8.19±0.15), 明显区别于同时具有加质子和脱质子反应的α-Fe₂O₃/SiO₂/γ-Al₂O₃, α-Fe₂O₃/γ-Al₂O₃和SiO₂/γ-Al₂O₃等纳米颗粒混合体系. 在此基础上拟合得到α-Fe₂O₃/SiO₂混合体系吸附重金属离子Cu²⁺、Pb²⁺、Zn²⁺的表面络合反应平衡常数分别为:
≡XOH + M²⁺ ⇔ ≡XOM⁺+ H⁺ [lg K = -3.1, -3.6, -3.8 (M = Cu, Pb, Zn)].
≡XOH＋M²⁺＋H₂O ⇔≡XOMOH＋2H⁺[lg K = -8.8, -8.0, -10.5 (M = Cu, Pb, Zn)]     

Effect of capping and particle size on Raman laser-induced degradation of γ-Fe2O3 nanoparticles

Diol capped γ-Fe₂O₃ nanoparticles are prepared from ferric nitrate by refluxing in 1,4-butanediol (9.5 nm) and 1,5-pentanediol (15 nm) and uncapped particles are prepared by refluxing in 1,2-propanediol followed by sintering the alkoxide formed. X-ray diffraction (XRD) shows that all the samples have the spinel phase. Raman spectroscopy shows that the samples prepared in 1,4-butanediol and 1,5-pentanediol and 1,2-propanediol (sintered at 573 and 673 K) are γ-Fe₂O₃ and the 773 K-sintered sample is Fe₃O₄. Raman laser studies carried out at various laser powers show that all the samples undergo laser-induced degradation to α-Fe₂O₃ at higher laser power. The capped samples are however, found more stable to degradation than the uncapped samples. The stability of γ-Fe₂O₃ sample with large particle size (15.4 nm) is more than the sample with small particle size (10.2 nm). Fe₃O₄ having a particle size of 48 nm is however less stable than the smaller γ-Fe₂O₃ nanoparticles.     

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.     

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.     

Synthesis and ac susceptibility of YCa2Cu3O7−δ

The bulk superconducting YCa₂Cu₃O_7−δ compounds are prepared at an ordinary pressure of oxygen by conventional solid-state reaction method. The formation of sample is tested by means of XRD and is studied for their ac susceptibility below room temperature up to 77.5 K. The samples are found single-phase orthorhombic structure and found superconducting at 83.5 K. It is shown that the analysis is consistent with published data on YBa₂Cu₃O_7−δ oxide superconductor.     

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.     

The Al2O3-Fe2O3 Mixed Oxidic System, II. Catalytic Decomposition of N2O

N₂O decomposition was examined over a series of Al₂O₃-Fe₂O₃ mixed oxidic solids with composition ranging from 0 to 100% of Fe₂O₃. The catalytic activity of the solids runs parallel to the number of atoms of iron in the Al_2−x Fe_xO₃ solid solution phase. Two compensation effects are present. The first corresponds to catalysts rich in alumina, and the second one to catalysts rich in hematite. This revised version was published online in June 2006 with corrections to the Cover Date.     

Characterization and evaluation of Fe2O3/Al2O3 oxygen carrier prepared by sol–gel combustion synthesis

The sol-gel combustion synthesis (SGCS) for oxygen carrier (OC) to be used in chemical looping combustion (CLC) was first designed and experimented in this work, which is a new method of OC synthesis by combining sol-gel technique and solution combustion synthesis. Cheap hydrated metal nitrates and urea were adopted as precursors to prepare Fe₂O₃/Al₂O₃ OC at the molar ratio to unity (Fe1Al1), which was characterized through various means, including Fourier transforms infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffractor (XRD), and N₂ isothermal adsorption/desorption method. FTIR analysis on the chemical structure of the dried gel of Fe1Al1 indicated that urea was partly hydrolyzed and the hydrated basic carbonate was formed by the combination of groups such as (Fe(_1−yAl_y)_1−xO_1−3x, CO₃²⁻ and -OH-. By analyzing the staged products during SGCS, calcination was found as a necessary step to produce Fe₂O₃/Al₂O₃ OC with separate phases of α-Fe₂O₃ and α-Al₂O₃. Through TGA-DTA, the decomposition of the dried gel was found to undergo five stages. The analysis of the evolved gases from the gel decomposition using FTIR partially confirmed the staged decomposition and assisted a better understanding of the mechanism of SGCS. XRD identification further substantiated the necessity of calcination to synthesize Fe₂O₃/Al₂O₃ OC with separate phases of α-Fe₂O₃ and α-Al₂O₃, though it was not necessary for the synthesis of single phase α-Fe₂O₃ and α-Al₂O₃. Structural characterization performed on N₂ adsorption analyzer displayed that the pore shape of Fe1Al1 particles was heterogeneous. Finally, H₂ temperature-programmed reduction (TPR) of Fe1Al1 products in TGA indicated that the reduction reaction of Fe1Al1 OC after calcination was a single step reaction from α-Fe₂O₃ to Fe, and calcination benefited to improve the transfer rate of the lattice oxygen from the OC to fuel H₂. Furthermore, four times of reduction and oxidization (redox) reaction by alternating with H₂ and air demonstrated the synthesized OC had good reactivity and sintering-resistance, much suitable to be used in the realistic CLC. Overall, the SGCS method was found superior to other existent methods to prepare Fe₂O₃/Al₂O₃ OC for CLC application.     

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.     

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.     

不同磷含量对NiMoP/Al2O3加氢处理催化剂的影响

采用NiMoP浸渍液浸渍载体γ Al₂O₃制备了不同磷含量的NiMoP/Al₂O₃加氢处理催化剂。为了研究磷对该系列催化剂活性相结构的影响,用二苯并噻吩（DBT）和喹啉为模型化合物,考察了催化剂的加氢脱硫（HDS）和加氢脱氮（HDN）性能。结果表明,添加适当的磷能够提高催化剂的HDS和HDN活性,但是高含量的磷能显著的降低催化剂的催化性能。通过对催化剂进行XRD和HRTEM表征发现,添加磷能够增加MoS2的堆积层数以及Ⅱ型“Ni-Mo-S”相的相对含量,这是因为在制备过程中添加磷降低了活性组分与载体之间的相互作用。     

Partial Oxidation of Methane to Synthesis Gas over Hexaaluminates LaMAl11O19-δ Catalysts

A series of M-substituted hexaaluminates LaMAl11O19-δ （M=Fe, Co, Ni, Mn, and Cu） were prepared and characterized by XRD, XPS, TPR and TGA techniques, respectively. They exhibited different reducibility and catalytic activity for partial oxidation of methane （POM） to synthesis gas. Among the LaMAl11019-δ samples, LaNiAl11O19-δ showed the best catalytic activity for the topic reaction and selectivity for synthesis gas at 780 ℃ for 2 h. The conversion of CH4 was over 99.2%, and the product selectivity for both CO and H2 was above 90.3%.     

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.     

Phase formation, crystal chemistry, and properties in the system Bi2O3-Fe2O3-Nb2O5

Subsolidus phase relations have been determined for the Bi₂O₃-Fe₂O₃-Nb₂O₅ system in air (900-1075 °C). Three new ternary phases were observed—Bi₃Fe_0.5Nb_1.5O₉ with an Aurivillius-type structure, and two phases with approximate stoichiometries Bi₁₇Fe₂Nb₃₁O₁₀₆ and Bi₁₇Fe₃Nb₃₀O₁₀₅ that appear to be structurally related to Bi₈Nb₁₈O₅₇. The fourth ternary phase found in this system is pyrochlore (A₂B₂O₆O′), which forms an extensive solid solution region at Bi-deficient stoichiometries (relative to Bi₂FeNbO₇) suggesting that ≈4-15% of the A-sites are occupied by Fe³⁺. X-ray powder diffraction data confirmed that all Bi-Fe-Nb-O pyrochlores form with positional displacements, as found for analogous pyrochlores with Zn, Mn, or Co instead of Fe. A structural refinement of the pyrochlore 0.4400:0.2700:0.2900 Bi₂O₃:Fe₂O₃:Nb₂O₅ using neutron powder diffraction data is reported with the A cations displaced (0.43 Å) to 96g sites and O′ displaced (0.29 Å) to 32e sites (Bi_1.721Fe_0.190(Fe_0.866Nb_1.134)O₇, Fd3¯m (#227), ). This displacive model is somewhat different from that reported for Bi_1.5Zn_0.92Nb_1.5O_6.92, which exhibits twice the concentration of small B-type cations on the A-sites as the Fe system. Bi-Fe-Nb-O pyrochlores exhibited overall paramagnetic behavior with large negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. The single-phase pyrochlore with composition Bi_1.657Fe_1.092Nb_1.150O₇ exhibited low-temperature dielectric relaxation similar to that observed for Bi_1.5Zn_0.92Nb_1.5O_6.92; at 1 MHz and 200 K the relative permittivity was 125, and above 350 K conductive effects were observed.     

Self-powdering and nonlinear optical domain structures in ferroelastic β′-Gd2(MoO4)3 crystals formed in glass

Ferroelastic β′-Gd₂(MoO₄)₃, (GMO), crystals are formed through the crystallization of 21.25Gd₂O₃–63.75MoO₃–15B₂O₃ glass (mol%), and two scientific curious phenomena are observed. (1) GMO crystals formed in the crystallization break into small pieces with a triangular prism or pyramid shape having a length of 50–500 μm spontaneously during the crystallizations in the inside of an electric furnace, not during the cooling in air after the crystallization. This phenomenon is called “self-powdering phenomenon during crystallization” in this paper. (2) Each self-powdered GMO crystal grain shows a periodic domain structure with different refractive indices, and a spatially periodic second harmonic generation (SHG) depending on the domain structure is observed. It is proposed from polarized micro-Raman scattering spectra and the azimuthal dependence of second harmonic intensities that GMO crystals are oriented in each crystal grain and the orientation of (MoO₄)²⁻ tetrahedra in GMO crystals changes periodically due to spontaneous strains in ferroelastic GMO crystals.