On the high structural heterogeneity of Fe impregnated graphite-carbon catalysts from Fe nitrate precursor

Wet impregnation is broadly applied for the synthesis of carbon supported metal/metal oxide nanostructures because of its high flexibility, simplicity and low cost. By contrast, impregnated catalysts are typified by a usually undesired nanostructural and morphological heterogeneity of the supported phase resulting from a poor stabilization at the support surface. This study on graphite-supported Fe based materials from Fe nitrate precursor is concerned with the understanding of the chemistry that dictates during the multi-step synthesis, which is key to designing structurally homogeneous catalysts. By means of core level X-ray photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy and atomic resolution electron microscopy, we not only found a large variety of particles sizes and morphologies but also chemical phases. Herein, thermally stable single atoms and few atoms clusters are identified together with large agglomerates of an oxy-hydroxide ferrihydrite-like phase. Moreover, the thermally induced phase transformation of the initially poorly ordered oxy-hydroxide phase into several oxide phases is revealed, together with the existence of thermally stable N impurities retained in the structure as Fe-N-O bonds. The nature of the interactions with the support and the structural dynamics induced by the thermal treatment rationalize the high heterogeneity observed in these catalysts

New high-pressure phase of HfTiO4 and ZrTiO4 ceramics

We studied the high-pressure effects on the crystalline structure of monoclinic HfTiO4 and ZrTiO4. We found that the compressibility of these ceramics is highly non-isotropic, being the b-axis the most compressible one. In addition, the a-axis is found to have a small and negative compressibility. At 2.7 GPa (10.7 GPa) we discovered the onset of an structural phase transition in HfTiO4 (ZrTiO4), coexisting the low- and high-pressure phases in a broad pressure range. The new high-pressure phase has a monoclinic structure which involves an increase in the Ti-O coordination and a collapse of the cell volume. The equation of state for the low-pressure phase is also determined.Comment: 16 pages, 5 figures, 26 references, Article in Pres

Some Thermoelectrical Properties of Thiospinels Cu2B II Ti3 S 8 (B II –Cr, Mn, Fe, Co, Ni)

У роботі досліджено окремі електричні та термоелектричні властивості маловивчених складних шпінелей Cu2B II Ti3 S 8 (B II –Cr, Mn, Fe, Co, Ni). Встановлено особливості їх електропровідностей і значення коефіцієнта об’ємної термо-е.р.с. Згідно знаку термо-е.р.с., всі сполуки належать до напівпровідників n-типу провідності. ; Some electrical and thermoelectrical properties of poorly investigated complex thiospinels Cu2B II Ti3 S 8 (B II –Cr, Mn, Fe, Co, Ni), such as peculiarities of their electroconductivity at 295 K, thermoE.M.P. factor, were determined. The sign of termo-E.M.P. indicates, that all compounds belong to the n-type semiconductors

Characterization of Ti-B-C-N Nanocomposite Coatings

Nanocomposite Ti-B-N-C coatings were deposited by magnetron sputtering of TiN and B4C targets in the argon-nitrogen atmosphere at different nitrogen flow rates (FN2). The structure, chemical bonding and mechanical properties were investigated. The results of the investigations of the nanocomposite, TiN and BCN coatings show that the Ti-B-C-N coatings consist of the TiNC nanocrystals (3.4 – 6.5 nm) embedded into the amorphous matrix that consists of amorphous boron nitrogen (a-BN) and amorphous carbon (a-C). The coatings contain a small admixture of titanium oxides that are aggregated at the grain boundaries. The coatings deposited at high nitrogen flow rates were textured. An introduction of nitrogen prompts the formation of the nanocrystallites of the TiN-TiC solid solutions and the a-BN amorphous tissue, which, in turn, causes the improvement of the mechanical properties of the Ti-B-C-N coatings. The best samples ex-hibited nanohardnes above 39 GPa. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3505

X-ray spectroscopy studies of the electronic structure and band-structure calculations of cubic TaCxN1-x carbonitrides

The electronic structure of almost stoichiometric cubic (NaCl structure) tantalum carbonitrides TaCxN₁₋x synthesized under high pressure-high temperature conditions (7-10 GPa and 2100-2400°C) was studied employing X-ray photoelectron spectroscopy (XPS), Xray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS). The XPS valence-band and core-level spectra, the XES Ta Lβ ₅, C Kα and N Kα bands (reflecting energy distributions of mainly the Ta 5d-, C 2p- and N 2p-like states, respectively), as well as the XAS Ta LIII edges (unoccupied Ta d-like states) were derived and compared on a common energy scale for the compounds TaC₀.₉₈, TaC₀.₅₂N₀.₄₉ and TaN₀.₉₇ obtained under the mentioned high pressure-high temperature conditions. To investigate the influence of substitution of carbon atoms by nitrogen in the cubic TaCxN₁₋x system, the cluster self-consistent calculations of the electron density of states for cubic TaC, TaC₀.₅N₀.₅ and TaN compounds were carried out with the FEFF8 code. In the present work a rather good agreement of the experimental and theoretical results for the electronic structure of the TaCxN₁₋x system under consideration was obtained

X-ray emission and photoelectron spectroscopy studies of interaction of nanocrystalline TiN and TiB₂ after highpressure sintering

A few samples of nanocrystalline TiN–TiB₂ ceramics were synthesized by high-pressure (3.0 GPa) and high-temperature (t = 1300–1500°C) sintering a mixture of TiN and TiB₂ nanopowders (80 wt.% TiN and 20 wt.% TiB₂) and the microhardness of the samples was determined. Peculiarities of the chemical bonding of the TiN–TiB₂ ceramics possessing the highest microhardness among the samples under consideration, mainly 29.65 ± 0.90 GPa, were studied in the present work using the X-ray emission and photoelectron spectroscopy methods. The X-ray emission spectra reflecting the energy distribution of the valence electronic states of the constituents (the N Kα (N 2p-like states), B Kα (В 2p-like states), Ti Lα (valence Ti s,d-like states) and Ti Kβ₅ (Ti 4p-like states) bands) were measured for the mentioned ceramics and for the initial mixture of TiN and TiB₂ nanopowders. For the above substances the X-ray photoelectron core-level binding energies were evaluated as well. It has been established that, when synthesizing the nanocrystalline TiN–TiB₂ ceramics from the initial mixture of TiN and TiB₂ nanopowders, the half-widths of the X-ray emission Ti Lα and Ti Kβ₅ bands decrease by (0.5–0.6) ± 0.2 eV

Controlled Growth of WO3Nanostructures with Three Different Morphologies and Their Structural, Optical, and Photodecomposition Studies

Tungsten trioxide (WO3) nanostructures were synthesized by hydrothermal method using sodium tungstate (Na2WO4·2H2O) alone as starting material, and sodium tungstate in presence of ferrous ammonium sulfate [(NH4)2Fe(SO4)2·6H2O] or cobalt chloride (CoCl2·6H2O) as structure-directing agents. Orthorhombic WO3having a rectangular slab-like morphology was obtained when Na2WO4·2H2O was used alone. When ferrous ammonium sulfate and cobalt chloride were added to sodium tungstate, hexagonal WO3nanowire clusters and hexagonal WO3nanorods were obtained, respectively. The crystal structure and orientation of the synthesized products were studied by X-ray diffraction (XRD), micro-Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM), and their chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS). The optical properties of the synthesized products were verified by UV–Vis and photoluminescence studies. A photodegradation study on Procion Red MX 5B was also carried out, showing that the hexagonal WO3nanowire clusters had the highest photodegradation efficiency

Optical and structural studies of phase transformations and composition fluctuations at annealing of Zn₁₋xCdxO films grown by dc magnetron sputtering

Ternary Zn₁₋xCdxO (x < 0.12) alloy crystalline films with highly preferred orientation (002) have been successfully deposited on sapphire c-Al₂O₃ substrates using the direct current (dc) reactive magnetron sputtering technique and annealed at temperature 600 °C in air. The structural and optical properties of Zn₁₋xCdxO thin films were systematically studied using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), micro-Raman and photoluminescent (PL) spectroscopy. XPS measurements clearly confirmed Cd incorporation into ZnO lattice. XRD data revealed that the growth of wurtzite Zn₁₋xCdxO films occurs preferentially in the (002) direction. Also, when the Cd content is increased, the XRD peaks shift towards smaller angles and the full width at half-maximum of the lines increases. When the Cd content increases, LO A1 ( Zn₁₋CdxO )-like Raman modes show composition dependent frequency decrease and asymmetrical broadening. The near band-edge PL emission at room temperature shifts gradually to lower energies as the Cd content increases and reaches 2.68 eV for the highest Cd content (x = 0.12). The analysis of NBE band emission and Raman LO A1 ( Zn₁₋xCdxO ) mode shows that at a higher Cd content the coexistence of Zn₁₋xCdxO areas with different concentrations of Cd inside the same film occurs. The presence of CdO in annealed Zn₁₋xCdxO films with the higher Cd content was confirmed by Raman spectra of cubic CdO nanoinclusions. The XRD data also revealed phase segregation of cubic CdO in annealed Zn₁₋xCdxO films (Tann = 600 °C) for x ≥ 0.013

Hollow Sodium Tungsten Bronze (Na0.15WO3) Nanospheres: Preparation, Characterization, and Their Adsorption Properties

We report herein a facile method for the preparation of sodium tungsten bronzes hollow nanospheres using hydrogen gas bubbles as reactant for chemical reduction of tungstate to tungsten and as template for the formation of hollow nanospheres at the same time. The chemical composition and the crystalline state of the as-prepared hollow Na0.15WO3nanospheres were characterized complementarily, and the hollow structure formation mechanism was proposed. The hollow Na0.15WO3nanospheres showed large Brunauer–Emment–Teller specific area (33.8 m2 g−1), strong resistance to acids, and excellent ability to remove organic molecules such as dye and proteins from aqueous solutions. These illustrate that the hollow nanospheres of Na0.15WO3should be a useful adsorbent