1,721,006 research outputs found
TETRALKYLAMMONIUM AND SODIUM DECATUNGSTATE HETEROGENIZED ON SILICA: EFFECTS OF THE NATURE OF CATIONS ON THE PHOTOCATALYTIC OXIDATION OF ORGANIC SUBSTRATES
No full textTetralkylammonium and sodium decatungstates have been heterogenized on silica. The so-obtained materials have been characterized by UV-vis and Fourier transform infrared spectroscopies, N2 adsorption experiments, and measurements of surface polarity. Both the anion W10O324- and the countercations are anchored on the surface of the support without undergoing any appreciable modification. The size of the cations plays a key role in determining the degree of coverage and, consequently, the surface polarity of silica. The heterogenized systems are characterized by different and tunable photoreactivities depending on the nature of the countercation. In particular, tetralkylammonium cations enhance the efficiency of cyclohexane photooxidation both to radical species and to the stable oxygenation products cyclohexanol and cyclohexanone. The cation makes the environment where the photoactive anion is localized more or less hydrophobic; this influences the possibility of the approach of the substrate and, consequently, the photocatalytic efficiency of the process. The stability of these photocatalysts is demonstrated by the fact that they can be used at least three times without any loss of activity. Some alcohols with increasing dielectric constants, like cyclohexanol, ethanol, and methanol, have been used in an electron paramagnetic resonance spin trapping investigation in order to gain more information about the action of the different cations. With bulky and organic cations, alcohols were oxidized in the order from the less polar to the more polar, in terms of dielectric constants. On the contrary, the order is reversed with inorganic cations, such as Na+
Progettazione e caratterizzazione di sistemi fotocatalitici inorganici per la sintesi selettiva di molecole di interesse in chimica fine ed industriale
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CYCLOHEXANE OXYGENATION WITH INORGANIC PHOTOCATALYSTS
No full textThis chapter is a presentation of the results of the research for new catalysts able to perform oxidations of alkanes in mild temperature and pressure conditions. In particular, the oxidation of cyclohexane is considered, bacause it is a simple and representative molecule and because its oxidation to cyclohexanone is of general interest
Photocatalysis with organized systems for the oxofunctionalization of hydrocarbons by O2
No full textA report on the photocatalysis with organized systems for the oxofunctionalization of hydrocarbons by oxygen was presented. The activation processes of both the substrate and the oxygen was examined. The nonemissive platinum (II) quaterpyridine complex showed strong photoluminescence at room temperature. The results demonstrated unique aspects of host-guest photocatalysis in the solid state as well as solution phase
INFLUENCE OF THE ELECTRODE HISTORY AND EFFECTS OF THE ELECTROLYTE COMPOSITION AND TEMPERATURE ON O2 EVOLUTION AT BETA-PbO2 ANODES IN ACID MEDIA
No full textAn investigation is reported on O2 electrogeneration at b-PbO2 electrodes in HClO4, H2SO4 and CF3SO3H (TFMSA) using steady-state and impedance measurements. It is established that desorption of reaction intermediates is rate limiting in all the cases examined, and it is proposed that elementary reactions leading to oxygen evolution take place at a surface consisting of crystal line (PbO2) and hydrous zones. ...Different important factors are found to affect the electrochemical process: (i) pre-treatment of the electrode....; (ii) the temperature at which electrodeposition of PbO2 is carried out....; (iii) electrolite anions are adsorbed and inhibit desorption of reaction intermediates....; (iv) fluoride added to the electrolyte is strognly adsorbed and suppresses or modifies the structure of the hydrous layer .....; (v) a low electrolite temperature also inhibits O2 evolution ...
Photo-electro catalytic oxidation of aromatic alcohols on visible light-absorbing nitrogen-doped TiO2
No full textVisible light illumination of nitrogen-doped TiO(2) brings about the selective oxidation of benzyl and cinnamyl alcohol to the corresponding aldehydes. The photocatalyst was prepared by a sol-gel method and characterised mainly by XRD, UV-vis diffuse reflectance and Raman spectroscopy. The conditions limiting the observation of visible light photoactivity are the use of dry nitriles as nonaqueous solvents and aromatic alcohols as the substrates. No visible light oxidation takes place in an aqueous medium. The efficiency of benzyl and cinnamyl alcohol photo-oxidation in nitrile solvents follows the order: CH(3)CN > CH(3)CH(2)CN > CH(3)(CH(2))(2)CN. Conversely, since alcohol photo-oxidation occurs with 100% selectivity on electrodes in O(2) saturated solutions at potentials close to Eft, or under open-circuit conditions, suspensions of the photocatalyst can be advantageously employed. The process involves a relatively weak adsorption of the alcohol substrates which, however, do not readily capture the photogenerated holes. On the basis of the electrochemical and photoluminescence data, it appears that the solvent (e.g. acetonitrile), in addition to O(2) has an active role in the reaction mechanism. (C) 2010 Elsevier Ltd. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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