1,721,028 research outputs found
Photo-(electro)-catalytic Oxidation of Alcohols on Visible Light-Absorbing Nitrogen-Doped TiO2
No full textDoping of TiO2 with nitrogen leads to catalysic activity upon visible light irradiatio
An electrochemical and radiotracer investigation on lead dioxide: Influence of the deposition current and temperature
No full textThe properties of electrodeposited PbO2 are sensibly influenced by the deposition current and temperature. In particular, tritium radiotracer measurements demonstrated that protons were incorporated into the bulk of an oxide film and on its surface. The degree of hydration increased with increasing current and decreased with temperature, and was related to the morphological characteristics of the oxide, such as roughness measured by changes in the double layer capacity. Conversely, the amount of hydrogen had negligible effects on the number of free carriers as evaluated from Mott-Schottky plots. The hydration degree of the surface seems to be an important factor influencing electrocatalytic processes at high potentials, such as O2 evolution and O3 formation. On less hydrated, more crystalline PbO2 surfaces, the first process was inhibited and accordingly, the second was favored. Copyright 2013 (CC) SCS
An electron spin resonance spin trapping investigation of azide oxidation on TiO2 powder suspensions.
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EPR spin trapping Evidence of Radical Intermediates in the Photo-reduction of Bicarbonate/CO2 in TiO2 Aqueous Suspensions
No full textUsing the EPR spin trapping technique, we prove that simultaneous reactions take place in illuminated suspensions of TiO2 in aqueous carbonate solutions (pH ≈ 7). Adsorbed HCO3- is reduced to formate as directly made evident by the detection of formate radicals (●CO2-). Additionally, the amount of OH● radicals from the photo-oxidation of water shows a linear dependence on the concentration of bicarbonate, indicating that electron scavenging by HCO3- increases the lifetime of holes. In a weakly alkaline medium, photo-oxidation of HCO3-/CO32- to ●CO3- interferes with the oxidation of water. A comparative analysis of different TiO2 samples shows that formation of (●CO2-) is influenced by factors related to the nature of the surface, once expected surface area effects are accounted for. Modification of TiO2 surface with noble metal nanoparticles does not have unequivocal benefits: the overall activity improves with Pd and Rh but not with Ru, which favours HCO3- photo-oxidation even at pH =7. In general, identification of radical intermediates of oxidation and reduction reactions can provide useful mechanistic information that may be used in the development of photocatalytic systems for the reduction of CO2 also stored in the form of carbonates
Heterogeneous photocatalytic systems for partial and selective oxidation of alcohols and polyols
No full textPhotocatalysis is becoming particularly important in the realization of partial and selective oxidations of organic substrates, including alcohols and polyols, and at the same time is an example of green catalysis since it moves towards a "sustainable chemistry" with a minimal environmental impact. Heterogeneous systems with well-defined textural characteristics represent a suitable means to tailor the selectivity of photocatalytic processes. Here, we describe the most significant features of photocatalytic systems and the achievements in the partial oxidation of various classes of alcohols, with a focus on titanium dioxide, other semiconducting oxides and polyoxotungstates, soluble models of semiconducting oxides. These compounds share similar primary photoreactions: light absorption causes a charge separation with formation of positive vacancies able to initiate the oxidation of many organic substrates. Works here discussed concern photooxidation reactions carried out in the presence of O2, whose role in not only that of scavenging the photogenerated electrons but also that of producing active oxygen species that take part to the overall oxidation process. We emphasize that the combination of the advances in the preparation of nanostructured materials with mechanistic knowledge, derived from surface science and molecular level investigations, is actually the goal in order to achieve optimal tailoring of photoactive materials for obtaining high selectivity. © 2013 Bentham Science Publishers
Photocatalysis with heterogenized W10O324- as Innovative tool for selective oxygenation of organic molecules
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A photo-(electro)-catalytic system illustrating the effect of lithium ions on titania surface energetics and charge transfer
No full textWe describe the effect of Li+ on photoinduced charge transfer at TiO2 in acetonitrile solutions at open circuit (photocatalytic conditions) or under potential control. Using 2-propanol and 4-nitrobenzaldehyde as probe scavengers of holes and electrons, respectively, we aim to demonstrate the importance of tuning the chemical role of electrons and holes through control of surface and interface properties
Riduzione fotochimica di Fe(III) tetrafenilporfirina tetrasolfonata in solvente misto piridina-etanolo-acqua
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