Oxidation of toluene on Bi-doped PbO<Subscript>2</Subscript> studied by electrochemical impedance spectroscopy and UV spectrophotometry

Oxidation of organics in the potential region of O₂ evolution is supposed to proceed through the oxidation of water to hydroxyl radicals, which then may either be further oxidized to give molecular oxygen or interact with organic molecules in an oxygen transfer reaction. Therefore, the electrode material must ensure (1) the preferential adsorption of the organic compound, (2) the production of adsorbed hydroxyl radicals able to react with this compound in a selective oxidation reaction (with as little as possible oxygen evolution), and (3) a long-term stability. In the present paper, the oxidative decomposition of toluene in sulfuric acid solution on PbO₂ coatings deposited on Ti substrate from acidic nitrate + fluoride baths containing Pb²⁺ and Bi³⁺ is investigated by voltammetry, electrochemical impedance spectroscopy, and UV spectrophotometry. The chemical composition and structure of the catalytic coatings is characterized with X-ray photoelectron spectroscopy and X-ray diffraction. The catalytic activity is estimated both from current density vs potential and polarization resistance vs potential plots using measurements on the same electrodes in sulfuric acid without toluene to eliminate the oxygen evolution reaction that proceeds in parallel to the oxidation of toluene. A skeletal reaction mechanism of the process is proposed to account for the steady-state and transient response of the catalytic electrodes during oxidation of toluene.     

Diffusion of particles over strongly anisotropic surface with traps

We investigate surface diffusion in a system of particles adsorbed on a two-dimensional strongly anisotropic lattice. There are two kinds of the lattice sites - ordinary sites and deep traps. Particles adsorbed in the ordinary sites can migrate over the surface, but particles adsorbed in traps are immobile. These particles do not move over the surface and they obstacle also the mobile particles migration (surface defects). Using kinetic Monte Carlo simulations we obtained coverage dependencies of the tracer, jump, and chemical diffusion coefficients. The coefficients are rather sensitive to the defect concentration. Even small admixture of the defects decreases drastically the fast diffusion. The effect is rather specific: strong dependence of the pre-exponential factor on the defect concentration and almost independent activation energy. The defect influence on the slow diffusion is weak. It results in strong decreasing of the surface diffusion anisotropy with the defect concentration. Such unusual behavior of the diffusion coefficients was observed in many experimental investigations of the surface diffusion of lithium, cesium, potassium, and strontium over strongly anisotropic W(1 1 2) and Mo(1 1 2) planes. It was shown that this specific behavior arises exclusively due to the surface anisotropy, and does not depend on the lateral interaction between the particles.     

ESR study of impurities in strontium titanate films

The paper reports on an ESR study of Cr-and Ca-codoped SrTiO₃ films, 1700 and 350 nm thick, before and after UV irradiation (λ=365 nm). The spectrum of the thick film (1700 nm) exhibits two ESR lines with g factors of 1.977 and 1.974, which belong to the Cr³⁺ centers. In the spectrum of the thin film (350 nm), one observes only one line, which is due to the chromium center with a g factor of 1.974. Calculations showed that the line with the smaller g factor belongs to the Cr³⁺ center located close to the film surface. The weak line observed in the spectrum after UV irradiation (g factor = 2.012) is most likely due to the O^? center. The regions of thermal stability of the observed centers were studied. A comparative analysis of the characteristics of impurities in bulk samples and films was carried out.     

Mixed Convection Flow Past a Horizontal Plate: The Trailing Edge

The mixed convection flow past a horizontal plate which is aligned under a small angle of attack to a uniform free stream will be considered in the limit of large Reynolds number and small Richardson number close to the trailing edge. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Raffinose Capped Silver Nanoparticles: A New Localized Surface Plasmon Resonance Based Sensor for Selective Quantification of Cr(VI) in Waste Waters

In this study, a new method for selective determination of Cr(VI) in water samples at pH 4 is presented using raffinose capped silver nanoparticles (Ag/Raff NPs) as an optical sensor. The method is based on the variation of LSPR absorption band intensity as a result of electrostatic interaction between the negatively charged Ag/Raff NPs and positive Cr(III) ions, in-situ produced by chemical reduction of Cr(VI) with ascorbic acid, combined with the fast kinetics of Cr(III) coordination to the –OH groups of the capping agent on the nanoparticle surface, further causing the nanoparticle aggregation. The calibration curve for Cr(VI) is linear in the range 2.5–7.5 μmol L⁻¹, the limit of quantification achieved is 1.9 μmol L⁻¹, and values of relative standard deviation vary from 3 to 5% for concentration level 1.9–7.5 μmol L⁻¹. The interference studies performed in the presence of various metal ions show very good selectivity of Ag/Raff NPs toward Cr(VI) species. The added–found method is used to confirm the accuracy and precision of developed analytical approach.     

Linear Conform Transformation: Errors in Both Coordinate Systems

Linear conform transformation in the case of non-negligible errors in both coordinate systems is investigated. Estimation of transformation parameters and their statistical properties are described. Confidence ellipses of transformed nonidentical points and cross covariance matrices among them and identical points are determined. Some simulation for a verification of theoretical results are presented.     

Tensile strain induced changes in the optical spectra of SrTiO3 epitaxial thin films

Effect of biaxial tensile strains on optical function and band edge transitions of ultra thin epitaxial films was studied using as an example a 13 nm thick SrTiO₃ films deposited on KTaO₃ (100) single-crystal substrates. Optical functions in the 200–1200 nm spectral range were determined by spectroscopic ellipsometry technique. It was found that tensile strains result in a shift of the low energy band gap optical transitions to higher energies and decrease the refractive index in the visible region. Comparison of the optical spectra for strained SrTiO₃ films and for homoepitaxial strain-free SrTiO₃: Cr (0.01 at %) films deposited on SrTiO₃ (100) single crystalline substrates showed that this “blue” shift of the band gap could not be related to technological imperfections or to reduced thickness. The observed effect is connected with changes in the lowest conduction and in the top valence bands that are due to increase of the in-plane lattice constant and/or onset of the polar phase in the tensile strain-induced ultra-thin epitaxial SrTiO₃ films.     

ChemInform Abstract: Redetermination of Na3TaF8.

The crystal structure of Na₃TaF₈ is redetermined at 153 K and well determined bond distances and angles are provided.     

Zur Theorie der Tribolumineszenz

Using simple theoretical conceptions the author has proved that all elastic, plastic, and damaging deformations can generate TBL radiations. On this occasion also mechano-electrons with high energies till to 10 keV can be observed. The strongest TBL radiation can be interpreted by the stimulated part of radiation (mechanical laser effect) in manganese doped zinc sulfide. The spectral-line displacement is interpreted by a conception other than that of MEYER , OBRIKAT and ROSSBERG (1970).