1,720,971 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
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
Some Aspects of Photocatalysis at Doped and Surface Modified TiO2
No full textWe show that photo-oxidation on N-TiO2 with visible light leads to selective formation of aldehydes
While for UV light irradiation the same reaction is not selective.
Reactions occur in nitrile medium only.
not in water or in other polar solvents such propylene carbonate
Rather,.small amounts of these species inhibit photo-oxidation in acetonitril
Photoelectrocatalysis for Water Purification
No full textA review. This paper gives an account of photoelectrocatalysis (PEC) for water purifn. Anal. of results show's that the electrode material, the morphol., the applied potential, the pH, the electrolyte compn., and the presence of oxygen strongly influence PEC performance
Method for the preparation of a titanium dioxide having photocatalytic activity by irradiation with visible light
No full textThe invention relates to a method of preparation of a titanium dioxide doped with nitrogen that involves the hydrolysis of precursor of the titanium dioxide with a first aq. ammonia solution until reaching an appreciably neutral pH, the recovery of the solid hydrolysis product, then its pretreatment by drying and calcination after at least a washing carried out with a second aq. ammonia solution. The N-containing TiO2 photocatalyst is highly reproducible with regard to its photocatalytic properties by irradiation with visible ligh
Electro-oxidation of Some Phenolic Compounds by Electrogenerated O<sub>3</sub> and by Direct Electrolysis at PbO<sub>2</sub> Anodes
No full textThe oxidative degradation of phenolic compounds (4-chlorophenol and 4-nitrophenol) was studied using different electrochemical systems involving ozone formation at PbO2 anodes: (i) direct electrolysis at constant current; (ii) ex-situ use of O3 and (iii) combined use of anodically generated stream of O3/O2 fed into the cathode where H2O2 is electrogenerated by O2 reduction. We show that the latter advanced oxidation method gives the best results: it is a Fenton-type degradation of the target pollutants taking place in the cathodic compartment by reason of the highly oxidizing environment brought about by radicals that are formed mainly in the reactions of O3 with OH− and HO2
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Composite PbO2-TiO2 materials deposited from colloidal electrolyte: electrosynthesis and physicochemical properties
No full textElectrodeposition of PbO2 from nitrate solutions in the presence of TiO2 nanoparticles leads to composite PbO2-TiO2 films. The content of the dispersed oxide which is finally occluded into the composite PbO2 film depends on electrodeposition conditions such as pH, the value of the electrodeposition constant current or potential, the amount of added TiO2 and on temperature. It also depends strongly on the presence of anionic additives such as sodium dodecyl sulfate (SDS) whose adsorption decreases the positive charge on the surface of the TiO2 particles. The photo-electrocatalytic activity of the prepared materials has been tested in the oxidation of oxalic acid and benzyl alcohol. Electrodes showed a photoresponse to illumination at λ > 320 nm confirming literature reports on synergistic effects of illumination in electro-oxidation processes at PbO2-based anodes. We also established that the life service of these electrodes increases by a factor of about 3 with respect to traditional P..
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
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