TPR/TPO characterization of cobalt–silicon mixed oxide nanocomposites prepared by sol–gel

Cobalt–silicon mixed oxides with Co/Si ratio of 10/90 (10Co), 20/80 (20Co) and 30/70 (30Co) were prepared by a modified sol–gel method. The materials treated in air at 400 and 600 °C were characterized by SEM and TPR/TPO techniques. TPR measurements showed that in all samples only a fraction of Co was present as Co₃O₄ and as amorphous silicate and was reducible by H₂ within 800 °C, while a part was not reducible under TPR conditions. The fraction of Co not reducible decreased with increasing Co content. A TPO/TPR cycle gave rise to an increase of the fraction of not reducible Co.     

Heat capacity measurements on uranium–cerium mixed oxides by differential scanning calorimetry

Uranium–cerium mixed oxides of three different compositions (U_0.2Ce_0.8)O₂, (U_0.5Ce_0.5)O₂ and (U_0.8Ce_0.2)O₂, were prepared by combustion synthesis and characterized by XRD. The compositional characterization was done by ICP-AES. Heat capacity measurements employed a heat flux type differential scanning calorimeter from 280 to 820 K. The heat capacity values of (U_0.2Ce_0.8)O₂, (U_0.5Ce_0.5)O₂ and (U_0.8Ce_0.2)O₂ at 298 K are 62.8, 64.2 and 70.1 J K⁻¹ mol⁻¹, respectively. Enthalpy increment, entropy and Gibbs energy function were computed from the heat capacity data.     

Hydrothermal synthesis and structure determination of the new vanadium molybdenum mixed oxide V1.1Mo0.9O5 from synchrotron X-ray powder diffraction data

A new vanadium molybdenum mixed oxide V_1.1Mo_0.9O₅ [V(V)_0.2V(IV)_0.9Mo(VI)_0.9O₅] has been synthesized, as a pure phase, via hydrothermal methods in the presence of molybdic acid and vanadyl sulfate. Its crystal structure has been solved ab initio from high-resolution powder diffraction data collected at the ESRF beamline ID31. This compound crystallizes in the monoclinic symmetry, space group C2/m, with cell dimensions , , , β=90.625(3)° and Z=2 per formula. The structure consists of double strings of VO₅ square pyramids sharing edges and corners along [100] and [010], and more weakly bound along [001]. In this latter direction, the bond (V,Mo)-O=2.377 Å, while remaining long, leads for the first time to the interpenetration of the apical oxygens of the [(V,Mo)₂O₅]_n layers, resulting in a three-dimensional (3D) structure closely related to R-Nb₂O₅. This structure will be compared to the pure layer structure of V₂O₅ where this bond reaches 2.793 Å.     

水相模拟体系中胆红素钙的合成与表征

以水溶液作为生物模拟体系,在不同反应摩尔比条件下,合成了一系列胆红素钙,利用中、远红外光谱,多晶X射线粉末衍射谱,电感耦合等离子体发射光谱等对合成的胆红素钙进行了表征.结果表明:胆红素钙的组成在Ca(C33H34N4O6)和Ca2.4(C33H32N4O6)(H2O)0.06之间变化,具有非化学计量性质,显示了与生物矿化产物相类似的特征.不同的胆红素钙其配位情况有所不同,并且钙含量较高时形成的胆红素钙有较好的结晶态.     

Structural and spectroscopic characterization of Mo1−xWxO3−δ mixed oxides

Mo_1−xW_xO₃ oxides with different cationic fraction (x=0.2, 0.5 and 0.8) and, for comparison purposes, pure MoO₃ and WO₃ were prepared. Along with textural and structural characterizations, absorbance FT-IR, diffuse reflectance UV-vis-NIR and EPR spectroscopies were employed to study the changes in the electronic properties of these materials passing from Mo_1−xW_xO₃ in oxidizing atmosphere to Mo_1−xW_xO_3−δ in reducing conditions. XRD analysis showed that the Mo-W mixed oxides are constituted by two or three crystalline phases, whose abundance and composition are well characterized by structural refinement with the Rietveld method. Only the sample with the highest Mo content (x=0.2) shows a predominant mixed phase and also a superior ability to lose oxygen with respect to the other mixed oxides. The oxygen loss in the reduced oxides induces the formation of defects with electronic levels in the band gap of the material, in particular, electrons trapped in oxygen vacancies and/or at cationic sites (polarons). While the nature of defect sites induced in the mixed and in the pure oxides is similar, the photo-ionization energies, the ratio between surface and bulk defects and the stability of the defects in oxygen at increasing temperature are peculiar of each mixed oxide.     

Characterization of layered double hydroxide Mg-Al-CO<Subscript>3</Subscript> prepared by re-hydration of Mg-Al mixed oxide

Emanation thermal analysis, differential thermal analysis, thermogravimetry, X-ray diffraction, scanning electron microscopy (SEM) and surface area and porosity determination from nitrogen adsorption/desorption measurements were used to characterize the Mg-Al-CO₃ LDH compound with the Mg:Al ratio 3:1 prepared by re-hydration of the Mg-Al mixed oxide. The mixed oxide was obtained after heating of the intial Mg-Al-CO₃ LDH compound in air at 500°C for 2 h. The samples were re-hydrated by two ways namely in a distilled water at 20°C for 5 days or by moistening at 60°C in air with RH 80% during 10 days, respectively. The characteristics of the re-hydrated LDH samples were compared with the initial Mg-Al-CO₃ compound. The influence of the re-hydration conditions on the microstructure, surface morphology and thermal stability of the regenerated Mg-Al-CO₃ LDHs samples is discussed. It was demonstrated that the re-generation of the layered structure by the hydration of the mixed oxide in water or in air, respectively, took place via the dissolution-crystallization mechanism and that the layered double hydroxide with different surface area and thermal behavior were formed after re-hydration in water or humid air, respectively. The emanation thermal analysis revealed differences in the microstructure changes of the re-hydrated sample during heating. XRD patterns and results of the methods used supported the ETA results.     

Butane isomer transport properties of 6FDA–DAM and MFI–6FDA–DAM mixed matrix membranes

For the first time, we report the C4s’ transport properties: solubility, diffusivity, permeability in 6FDA–DAM polymer, one of most permeable glassy polymers with significant nC4 vs. iC4 selectivity. An nC4 permeability of 3.7 Barrer, and nC4/iC4 ideal selectivity of 21 was found in pure 6FDA–DAM polymer membrane. Mixed matrix films were successfully fabricated using a 6FDA–DAM as the matrix, with up to 35 wt% loading of MFI, modified by a two-step Grignard treatment (GT) that produced Mg(OH)₂ whiskers on the surface of the MFI particles. The permeability of nC4 more than doubled; however, the selectivity for the C4s remained the same. Permeation of mixed matrix films with impermeable GT-uncalcined-MFI agree with Maxwell modeling of films with an impermeable solid loading, thereby supporting the existence of a defect-free interface between MFI particles and the polymer matrix. This indicates that the MFI is too permeable to optimally match the properties of the 6FDA–DAM, which is one of the most permeable selective matrix polymers available. It appears unlikely that any currently known, adequately selective glassy polymer can match the high permeability of nC4 in MFI to enable development of promising composite membrane for the C4s separation based on MFI. Therefore a smaller pore size zeolite is required for a better match.     

Mixed metal oxide catalysts for the selective oxidation of ethylbenzene to acetophenone

MgAl and MgMAl oxides(M = Co,Ni and Cu) with a Mg:M:Al molar ratio = 4:1:1 were synthesized from the calcination of their corresponding layered double hydroxide(LDHs) precursors.Their catalytic activities were examined for the oxidation of ethylbenzene using tert-butylhydroperoxide(TBHP) as an oxidant.The oxidized product was mainly acetophenone.The catalytic activities were in the order of MgCuAl>MgNiAl～NiAl～MgCoAl～CoAl>CuAl>MgAl oxides.Reusability studies show that the catalysts are stable under the re...     

Cobalt–silicon mixed oxide nanocomposites by modified sol–gel method

Cobalt–silicon mixed oxide materials (Co/Si=0.111, 0.250 and 0.428) were synthesised starting from Co(NO₃)₂·6H₂O and Si(OC₂H₅)₄ using a modified sol–gel method. Structural, textural and surface chemical properties were investigated by thermogravimetric/differential thermal analyses (TG/DTA), XRD, UV–vis, FT-IR spectroscopy and N₂ adsorption at −196 °C. The nature of cobalt species and their interactions with the siloxane matrix were strongly depending on both the cobalt loading and the heat treatment. All dried gels were amorphous and contained Co²⁺ ions forming both tetrahedral and octahedral complexes with the siloxane matrix. After treatment at 400 °C, the sample with lowest Co content appeared amorphous and contained only Co²⁺ tetrahedral complexes, while at higher cobalt loading Co₃O₄ was present as the only crystalline phase, besides Co²⁺ ions strongly interacting with siloxane matrix. At 850 °C, in all samples crystalline Co₂SiO₄ was formed and was the only crystallising phase for the nanocomposite with the lowest cobalt content. All materials retained high surface areas also after treatments at 600 °C and exhibited surface Lewis acidity, due to cationic sites. The presence of cobalt affected the textural properties of the siloxane matrix decreasing microporosity and increasing mesoporosity.     

Gamma coloration of mixed crystals of KCl–KBr doped with Pb

The amount of the first stage coloration in KCl_1−xBr_x doped with Pb²⁺ has been investigated as a function of the dose rate and impurity concentration. For a dose rate of 12.88 kGy/h, the F color center production was independent of the quantity of Pb²⁺, and varied according to the ratio KCl/KBr. At a proportion of 50% of each halogen the typical stages were observed. However, if the dose rate is less than 3.22 kGy/h, the coloration production depends on the quantity of Pb²⁺.     

Effect of the synthesis conditions on the magnetic and electrical properties of the BaFeO3−x oxide: A metamagnetic behavior

The BaFeO_2.95 oxide has been obtained from thermal decomposition of the [BaFe(C₃H₂O₄)₂(H₂O)₄] metallo-organic precursor at 800 °C under atmospheric oxygen pressure as small and homogeneous particles. From electronic paramagnetic resonance data, a metallic behavior in the 230-130 K temperature range has been observed. Magnetic measurements confirm the existence of a ferro-antiferromagnetic transition at 178 K. The magnetic properties of the BaFeO_2.95 oxide are strongly dependent on both temperature and magnetic field with a metamagnetic behavior. The synthesis conditions play an important role on the morphology and the electrical and magnetic properties. The syntherization of the sample produces a dramatic change in the transport properties and the existence of conductivity disappears.     

Processing and structure of gallium nitride—gallium oxide platelet nanostructures

Gallium nitride-gallium oxide structures were formed by heat-treating gallium nitride (GaN) powders in several gas environments at temperatures from 400°C to 900°C. The platelet nanostructured particles were examined at several stages of oxidation by microscopic, structural, chemical and optical spectroscopic techniques. Particle morphology, nanophase characterization and photoluminescence data showed that the oxide layers passivate the GaN platelets surfaces and significantly reduce the yellow emission while enhancing near band-edge emission.     

A new method of direct synthesis of bimetallic phases: Silica supported Pd---Cu catalysts from mixed acetylacetonates

The direct synthesis on a silica support of well defined, crystalline, mixed Pd---Cu bis-acetylacetonates has been achieved and the structure of these new compounds was determined by powder X-ray diffraction. These clusters have been deposited on a silica support and their thermal decomposition under helium was followed by in situ X-ray diffraction, thermo-gravimetry and mass spectroscopy. Microcrystalline metallic alloys with a narrow distribution of composition and particle size in the 2–4 nm range are obtained. Infrared experiments of CO chemisorption confirm the homogeneity of composition of the particles but conclude to a partial coverage of palladium by copper.     

Baeyer–Villiger oxidation of cyclohexanone by molecular oxygen with Fe–Sn–O mixed oxides as catalysts

Fe–Sn–O mixed oxides were synthesized and used as catalysts for Baeyer–Villiger oxidation of cyclohexanone, which showed both high catalytic activity and selectivity. X‐ray powder diffraction and scanning electron microscopy suggested that the Fe–Sn–O catalysts had a tetragonal structure with a grain size of 29.3 nm. An ε‐caprolactone yield as high as 98.8% was obtained in a small‐scale experiment (5 mmol of cyclohexanone). In a scale‐up test (20 mmol of cyclohexanone), the cyclohexanone conversion and ε‐caprolactone yield were 96.7 and 96.5%, respectively. In addition, the catalysts can be reused five times without any major decline in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Surface and catalytic properties of Cu/Zn mixed oxide catalysts

Copper catalysts supported on zinc oxide, with different loading (1–20 wt.% CuO), were prepared by impregnation of the basic zinc carbonate with a water solution of copper nitrate. The impregnated samples were dried at 120°C and calcined at 400–700°C. The surface and catalytic properties of CuO loaded on ZnO were determined by N₂ adsorption measurements conducted at −196°C and CO oxidation by O₂ at 150–300°C, respectively. The results obtained revealed that the surface and catalytic properties of different solids were dependent upon CuO content and calcination temperature. The specific surface areas of various adsorbents decreased monotonically as a function of both calcination temperature and extent of loading. However, the activation energy of sintering, ΔE_S, was found to increase by increasing the amount of CuO present. On the other hand, the CO oxidation activity on various catalysts was found to increase progressively by increasing the calcination temperature from 400 to 500°C, then decreased by increasing the temperature from 500 to 700°C. The augmentation of CuO content from 1 to 5 wt.% resulted in an increase in the CO oxidation activity, which decreased by increasing the extent of loading above this limit.     

室温离子液体介质中尺寸、结构可控Ni纳米微粒的制备及结构表征

分别以室温离子液体1-丁基-3-甲基-咪唑四氟硼酸盐和1-己基-3-甲基．咪唑四氟硼酸盐为介质,采用有机化合物热分解的方法制备了尺寸和结构均可控的金属Ni纳米微粒．采用X射线衍射仪、透射电子显微镜和傅立叶红外光谱仪对所制备的样品进行了结构表征．X射线衍射结果表明：以1-丁基-3-甲基-咪唑四氟硼酸盐为介质制备的Ni纳米微粒具有立方相结构,而以1-己基-3-甲基-咪唑四氟硼酸盐为介质制备的Ni纳米微粒具有六方相结构．透射电子显微镜结果表明：随着反应原料浓度的不同所制备的纳米微粒具有不同的粒径．傅立叶红外光谱表明：离子液体不但作为反应的介质而且作为修饰剂修饰在了Ni纳米微粒的表面,从而有效地阻止了Ni纳米微粒的团聚和氧化。     

Evidence of lanthanum–chromium mixed oxides formed in CrOx/La2O3 model catalysts

CrO_x/La₂O₃ mixed oxides, prepared by impregnating La₂O₃ with appropriate aqueous solutions of (NH₄)₂CrO₄ and calcining at 600 °C for 4 h, have been investigated by means of XRD, TPR, XPS, DRIFTS, and Raman spectroscopy (RS). The formation of the compounds La₂CrO₆, La(OH)CrO₄ and LaCrO₄ under these conditions was evidenced. Strong peaks at 864, 884, 913, and 921 cm⁻¹, as well as weak peaks at 136, 180, 354, 370, and 388 cm⁻¹ in the RS spectrum of CrO_x/La₂O₃ have been assigned to La₂CrO₆.     

Sol–gel synthesis, characterization, and catalytic activity of Fe(III) titanates

Nanostructured iron–titanium mixed oxides with different Fe/Ti ratios were prepared by sol–gel methods under different preparative conditions. When equal molar amounts of Fe and Ti ions were employed, the product calcined at 500 °C showed an X-ray diffraction pattern that resembles Fe₂Ti₃O₉. On the other hand, lower Fe/Ti ratios favored the formation of Fe₂TiO₅ while higher ratios resulted in free α-Fe₂O₃ and TiO₂. Besides the effect of the Fe/Ti ratio, the composition of the final product was dependent on the preparative conditions and the calcination temperature. Enhancing the gelation process by heating or by employing an acid catalyst favored the formation of Fe₂TiO₅ at relatively low temperatures. Compared with the corresponding pure oxides, the prepared iron–titanium mixed oxides showed modified textural characteristics which were also dependent on the composition and the calcination temperature. The mixed oxides showed higher catalytic activity in the oxidation of methanol than their corresponding pure oxides with a noticeable enhanced oxidation potential forming methyl formate and carbon dioxide.     

Green biosynthesis of silver nanoparticles using Torreya nucifera and their antibacterial activity

Silver nanoparticles were biosynthesized with the aid of a novel and eco-friendly biological material Torreya nucifera. Temperature and extract concentration were found to influence the size and shape of the biosynthesized silver nanoparticles. Morphological images of biosynthesized nanomaterials revealed that the particles are in spherical shape and size ranging between 10 and 125 nm. Crystalline nature of nanoparticles in face centered cubic (fcc) structure was ensured by diffraction pattern peaks corresponding to (1 1 1), (2 0 0), (2 2 0) and (3 1 1) planes. Characterization of the biosynthesized nanoparticles was performed by the X-ray diffraction and Fourier Transform Infrared spectroscopy analyses. FT-IR analysis indicates that nanoparticles are bound to proteins through amine groups of the aminoacid. Furthermore the biosynthesized nanoparticles were found to be highly effective against Salmonella typhimurium bacterium, which validates its potential applications as antibacterial agents in drinking water treatment and in food packagings.