Toward sustainable energy: photocatalysis of Cr-doped TiO<Subscript>2</Subscript>: 2. effect of defect disorder

The present chain of five papers considers the concept of solar-to-chemical energy conversion using TiO₂-based semiconductors. The series reports the effect of chromium on the key performance-related properties of polycrystalline TiO₂ (rutile), including electronic structure, photocatalytic activity, intrinsic defect disorder, electrochemical coupling and surface versus bulk properties. In this work, we show that the effect of chromium on photocatalytic performance of TiO₂ depends on its elemental content and the related defect disorder that is determined by oxygen activity in the oxide lattice. At high oxygen activity, chromium leads to enhanced photocatalytic performance only for dilute solid solutions (up to 0.04–0.043 at.% Cr). Higher chromium content results in a decrease of photocatalytic activity below that for pure TiO₂, despite the observed substantial decrease of the band gap. The photocatalytic performance of Cr-doped TiO₂ annealed in reducing conditions is low within the entire studied range of compositions. The obtained results led to derivation of a theoretical model representing the mechanism of the light-induced reactivity of TiO₂ with water and the related charge transfer. The photocatalytic performance is considered in terms of a competitive effect of several key performance-related properties. The performance is predominantly influenced by the concentration of titanium vacancies acting as reactive surface sites related to anodic charge transfer.

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q-Torsion freeness of symmetric powers

Letq be an integer ≥1, we study theq-torsion freeness of the symmetric powers of a module of projective dimension ≥2, by using the approximation complex of the module.     

Dynamics of ionization mechanisms in relativistic collisions involving heavy and highly-charged ions

The dynamics of mechanisms associated with the ionization of inner-shell electrons in relativistic collisions involving heavy and highly-charged ions is investigated within a nonperturbative approach formulated explicitly in the time domain. The theoretical treatment is based on the exact numerical solution of the time dependent Dirac equation for two Coulomb centers on a lattice in momentum space. We present results for ionization in encounters between 100 MeV/u Au⁷⁹⁺ projectile ions impinging on a hydrogen-like uranium target. By directly visualizing the collision dynamics we identify a new ionization mechanism in which electrons are emitted from the internuclear region preferentially in the transverse direction with respect to the projectile trajectory. A striking characteristic of this ionization mechanism is that the velocity of the electron is higher than the projectile velocity. Received 26 June 2001 and Received in final form 27 November 2001     

The time-varying discrete four block Nehari problem: A generalized Popov-Yakubovich type approach

The paper provides necessary and sufficient solvability conditions for the time-variant discrete four block Nehari problem in terms of the existence of the stabilizing solutions to two coupled Riccati equations. A parametrization of the class of all solutions is also given. The results are easily obtained from a signature condition — a generalized Popov Yakubovich type argument-imposed on an appropiate rational node. The present development may be seen as an alternative of the theory developed by Gohberg, Kaashoek and Woerdeman [15].     

Generalized KdV equation for fluid dynamics and quantum algebras

We generalize the nonlinear one-dimensional equation of a fluid layer for any depth and length as an infinite-order differential equation for the steady waves. This equation can be written as a q-differential one, with its general solution written as a power series expansion with coefficients satisfying a nonlinear recurrence relation. In the limit of long and shallow water (shallow channels) we reobtain the well-known KdV equation together with its single-soliton solution.This article is dedicated to Max Jammer on the occasion of his 80th birthday. He is a clear friend, who was a visiting professor at the Johann Wolfgang Goethe-University in 1985. His brilliant lectures on Philosophische Probleme der modernen Physik, delivered in perfect German language, will long be remembered. Above all, Max Jammer's contributions to the philosophy of science have enriched our understanding forever.     

Vibrational mode selectivity in hyperfine interactions: polarization quantum beat spectroscopy of HCF(A1A")

We report on the vibrational mode dependence of the 19F and 1H hyperfine interaction constants in the A1A" state of HCF, determined using polarization quantum beat spectroscopy. The nuclear spin/overall rotation coupling constants display a pronounced energy dependence and mode selectivity which can be traced to variations in both the A rotational constant and nuclear spin/electron orbital coupling constant a. In particular, modes containing C-F stretching excitation display significantly larger 19F spin-rotation constants, which is explained in terms of a decrease in back donation of electron density into the C 2p(pi) orbitals.     

Quantitative analysis of NO2 in the presence of CO using a single tungsten oxide semiconductor sensor and dynamic signal processing

We demonstrate that NO2 can be quantitatively analysed in the presence of CO using a single tungsten oxide based resistive gas sensor. The working temperature of the sensor was modulated between 190 and 380 degrees C and its dynamic response to different concentrations of CO, NO2, and CO + NO2 mixtures was monitored. Either the fast Fourier transform (FFT) or the discrete wavelet transform (DWT) was used to extract important features from the sensor response. These features were then input to different (statistical and neural) pattern recognition methods. The species considered can be discriminated with a success rate higher than 90% using a Fuzzy ARTMAP or a radial basis function neural network. The concentrations of the gases studied can be accurately predicted, by using the DWT coupled to partial least squares (PLS) models. The correlation coefficients of the predicted versus real concentrations were 0.923, 0.870 and 0.866 for CO, NO2, and NO2 in CO + NO2 mixtures, respectively.     

On manifolds swept out by high dimensional quadrics

We give a completely different, much shorter, proof of a substantial generalization of the main result from Kachi and Sato (Mem. Am. Math. Soc. 160:763, 2002). It states that embedded projective n-folds swept out by quadrics of dimension at least are either scrolls or hyperquadric fibrations, which are also Mori contractions. An erratum to this article can be found at     

Carbon Cavity Microelectrode for Electrical Wiring of Enzyme by Insoluble Electroactive Species in Aqueous Media

The carbon cavity microelectrode (CME), exhibiting a volume of 4×10^?6 cm³, offers a genuine alternative for immobilizing and connecting enzymes in aqueous electrolytes by powder of insoluble redox materials. In the present work, the electrochemical behavior of two redox species such as ferrocene (Fc) and tetrathiafulvalene (TTF) was investigated with CME to evaluate their potentialities in the electrical wiring of enzymes. For this purpose, powder of two enzymes, glucose oxidase (GOx) and horseradish peroxidase (HRP), was independently mixed with an insoluble redox material and forced to fill the single micro cavity of a carbon electrode covered by an inert insulator. The presence of the electroactive species, as well as the enzyme wiring was investigated by cyclic voltammetry. The amperometric detection of glucose was carried out by potentiostating the TTF/GOx and the Fc/GOx microelectrodes at 0.25 and 0.35 V respectively. The amperometric detection of H₂O₂ by the TTF/HRP microelectrode was performed at ?0.1 V vs. SCE.