Cu and Zr surface sites in the photocatalytic activity of TiO2 nanoparticles.

The rate of methylene blue and terephthalic acid degradation assisted with double metal-modified catalyst (0.1 mol% Cu and 1.0 mol% Zr) was enhanced as compared with single metal-modified catalysts (0.1, 0.5 mol% Cu and 1.0 mol% Zr). The wet impregnation method was used for copper and zirconium modification of the surface of Aeroxide P25 TiO2 particles. Simultaneous loading of both metals on the surface of P25 leads to an increased specific surface area of the obtained material despite negative Cu influence. The tendency of stabilization and agglomerate size rising with the time for Cu and Zr-modified catalysts were traced by dynamic light scattering (DLS) measurements. The observed optical characteristics suggest that Cu compensated the broadening of band gap caused by Zr loading. Crystal structure of obtained photocatalysts was explored by XRD; morphological data and particle size were obtained by SEM. EDX was used for Zr and Cu content determination. Cu K-edge extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) analytical techniques were used to investigate the local Cu neighbourhood in the samples and to identify copper coordination and valence state of copper species in the synthesized nanocomposites.

Strain-induced extrinsic high-temperature ferromagnetism in the Fe-doped hexagonal barium titanate.

Diluted magnetic semiconductors possessing intrinsic static magnetism at high temperatures represent a promising class of multifunctional materials with high application potential in spintronics and magneto-optics. In the hexagonal Fe-doped diluted magnetic oxide, 6H-BaTiO3-δ, room-temperature ferromagnetism has been previously reported. Ferromagnetism is broadly accepted as an intrinsic property of this material, despite its unusual dependence on doping concentration and processing conditions. However, the here reported combination of bulk magnetization and complementary in-depth local-probe electron spin resonance and muon spin relaxation measurements, challenges this conjecture. While a ferromagnetic transition occurs around 700 K, it does so only in additionally annealed samples and is accompanied by an extremely small average value of the ordered magnetic moment. Furthermore, several additional magnetic instabilities are detected at lower temperatures. These coincide with electronic instabilities of the Fe-doped 3C-BaTiO3-δ pseudocubic polymorph. Moreover, the distribution of iron dopants with frozen magnetic moments is found to be non-uniform. Our results demonstrate that the intricate static magnetism of the hexagonal phase is not intrinsic, but rather stems from sparse strain-induced pseudocubic regions. We point out the vital role of internal strain in establishing defect ferromagnetism in systems with competing structural phases.

Atomic background and EXAFS of gaseous hydrides of Ge, As, Se and Br.

K edge absorption spectra of elements from Ge to Br in gaseous hydrides were measured at the BM 29 station of ESRF with noise level as low as 2x10(-5), so far achievable only on noble gases. The dominant feature of the spectra is the atomic background similar to that of Kr and comparable to it in the quality of detail. Onto the background, a smooth weak EXAFS signal due to the hydrogen neighbors is superposed. For the very simple molecules such as these, its contribution can be calculated ab initio, with exact treatment of the effect of molecular vibrations, so that no best-fit adjustment to the experimental data is necessary. In comparison to the main constituent of the atomic background, i.e. the shake-up absorption edges, the EXAFS signal is of minor importance in HBr with a single H neighbor, but of the same order of magnitude in GeH4.

A study of transferability of atomic background on EXAFS spectra of simple gaseous compounds of As.

From EXAFS spectra of As and As2O3 vapors and arsine gas AsH3 the ab initio calculated structural signal is removed. The remainders comprise small absorption edges due to shake-up channels involving electrons from 3d or 3p subshell. With enhanced resolution, the edges reveal a fine splitting and a varying contribution of resonance channels, due to individual molecular energy-level structure of the samples. On the resolution level appropriate for routine EXAFS analysis the remainders coincide, representing a unique and transferable atomic absorption background for the range of As valence states spanned by the samples.

EXAFS study of NiAl in thin films.

Technologically important coatings of transition-metal aluminides call be produced by thermal or ion beam mixing of multilayer structures sputter deposited on substrates. The quantitative detection of constituents by depth profiling is sufficient to establish the efficiency of mixing methods. However, to decide whether a mixture of nanoparticles or a stoichiometric alloy is formed, EXAFS analysis of the local atomic neighborhood in the film is required. Ni K edge EXAFS spectra are measured on a series of samples of Ni/Al multilayer on Si(111) surface, after ion mixing at different substrate temperatures. The spectra show that with increasing temperature the nickel aluminide phase gradually substitutes the Ni fcc metal phase.

EXAFS determination of the size of Co clusters on silica.

The metallic Co catalyst for the Fischer-Tropsch reaction is prepared by reduction of Co salts impregnating microporous silica. The average size of the metallic Co clusters is determined from the average number of neighbours deduced from Co K-edge EXAFS of catalyst samples. A model EXAFS signal constructed from the scattering paths of Co metal fcc lattice with lengths up to 5 A is calibrated on a reference spectrum of Co metal foil. Catalyst spectra are interpreted with the same model expanded with variable neighbour fractions of the four nearest shells. Cluster size is obtained from comparison with the neighbour-fractions of consecutive fcc magic-number clusters.

Incorporation of Mn, Co and Zn cations into large-pore aluminophosphate molecular sieves MeAPO-50.

Large-pore metal modified aluminophosphate molecular sieves MeAPO-50 (Me=Co,Zn,Mn) were synthesised by hydrothermal crystallisation using di-n-propylamine as structure directing agent. EXAFS and XRD analysis show that cobalt(II), manganese(II) and zinc(II) are incorporated into the non-phosphorus tetrahedral framework sites of MeAPO-50 on the threefold-axis site, and on a site in a general position in the unit cell. Results of both methods on distribution of the metal over the two sites are compared.

Preparation and characterisation of copper(II) hyaluronate.

Amorphous copper complexes of the general composition Cu(C14H20O11N)2 x xH2O have been prepared with high- and low-molecular-weight hyaluronic acid (HA). Optimal conditions for preparation are obtained at pH values from 5.0 to 5.5, with a molar ratio of HA versus Cu2+ of 1:1, and at a mass concentration of 5 and 10 mg/mL for high- (Mw = 1.8 x 10(6) Da) and low-molecular-weight sodium hyaluronate (Mw = 2 x 10(5) Da), respectively. The coordination polyhedron of the copper ion has been elucidated by EXAFS and XANES spectroscopy. Copper atoms are octahedrally coordinated in both cases with four equatorial Cu-O bond lengths of 1.95 A, and two axial Cu-O bonds of 2.46 A. Visible spectra of acidic aqueous solution suggest that substitution of axial oxygens by NH groups occurs at pH 6.5 or higher. If the pH value of the copper(II) hyaluronate solution increases above 6.5, the coordination of copper(II) changes. It is very likely that the N atom coming from the acetamido group enters into the coordination sphere of the copper(II) ion.