N-TiO2 Photocatalysts highly active under visible irradiation for NOX abatement and 2-propanol oxidation

N-doped TiO2 powders were prepared by two different sol–gel methods. Samples were characterised by X-ray diffraction (XRD), BET specific surface area measurements (SSA), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and Electron Paramagnetic Resonance (EPR). XPS measurements revealed a signal at 400 eV assignable to nitrogen in the form of Ti N O. EPR signals are attributed to molecular NO trapped with cavities/defects possibly interacting with oxygen vacancies. The photocatalytic activity under UV and visible light was determined following the abatement of NOx and the photodegradation of 2-propanol in gas–solid systems. N-doped TiO2 showed a higher activity compared with the pristine commercial and home prepared samples under visible light irradiation. A good photoactivity in the abatement of both NOx and 2-propanol is also observed for mechanical dispersions of N-TiO2 in CaCO3 serving as a model in view of perspective application in photocatalytically active construction and architectural materials

Photo-electro-chemical properties of TiO2 mediated by the enzyme glucose oxidase

Electrochemical measurements show that the enzyme Glucose oxidase (GO) is adsorbed on the surface of TiO2 without apparently changing the flat band potential of the semiconductor, indicating that it does not cause a change of the energy of conduction band electrons. On the other hand, it is observed that GO markedly increases the efficiency of the two electron reduction of O2 to H2O2 which is accumulated in the solution phase. ESR spin trapping investigations indicate that GO favors the formation of OH . radicals, due to either the inhibition of charge recombination processes or to H2O2 reduction by conduction band electrons. Accordingly, photo-oxidation of different alcohols to the corresponding radical species is also enhanced in the presence of GO. The photo-oxidation of 1,2-propandiol on TiO2/GO is regioselective in that i) partial oxidation to hydroxyacetone is observed and ii) no mineralization (full combustion to CO2) of the substrate occurs. These facts are of particular interest in the field of studies concerning the design of new photocatalytic systems with enhanced activity and controllable oxidative power

Medicamentos, consumos de performance e culturas terapêuticas em mudança

This work is licensed under a CC BY Creative Commons Attribution 3.0 License. Please visit http://creativecommons.org/licenses/by/3.0/"O uso de fármacos e produtos naturais para a gestão do desempenho pessoal, aqui designado consumos de performance, constitui o foco deste artigo e dá suporte a uma reflexão analítica sobre a mudança nas culturas terapêuticas. Tendo por referência a atual problemática da farmacologização, bem como o lugar do natural na expansão do uso do medicamento, demonstra-se que a farmacologização do quotidiano está a emergir noutros campos, que não exclusivamente o da saúde, dando lugar a novas lógicas de relação com estes recursos. A sustentação empírica desta abordagem tem por base os resultados de um estudo nacional sobre os consumos de performance na população jovem em Portugal.

Photoelectrocatalysis for water purification

A 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

Effect of the electrolyte cations on photoinduced charge transfer at TiO2

This work focuses on the effect of electrolyte cations on the behaviour of a probe photocatalytic system comprising 2-propanol and 4-nitrobenzaldehyde (O2NC6H4CHO) as the hole and electron scavenger, respectively. Photo-reductionofthe latter occurs via a stepwise pathway involving 4-aminobenzaldehyde (H2NC6H4CHO) as the stable intermediate and 4-aminobenzyl alcohol (H2NC6H4CH2OH) as the final product. 2-propanol photo-oxidation produces protons at the surface. The complete reduction of O2NC6H4CHO to H2NC6H4CH2OH needs photo-charging. Excess negative charge is compensated by cations adsorption and by lattice insertion. In the case of bulky K+ and TEA+ (tetraethylammonium ions) that apparently are not inserted, protons are inserted instead. In contrast, Li+ (and to a lesser degree Na+) ions favour selective reduction of O2NC6H4CHO to H2NC6H4CHO. Electrochemical measurements in the dark provide evidence of a strong interaction of 2-propanol with the surface and of the influence exerted by cations thereon. Additionally, electron paramagnetic resonance (EPR) spin trapping spectroscopy gives information about the formation of radicals intermediates from the alcohol photo-oxidation. Repeated illumination/dark runs showed that alkoxy (R-O•) radicals always formed when the electrolyte contains K+ or TEA+. Conversely, in prolonged experiments, Li+ favours the formation of hydroxyalkyl radicals (R-C•HOH), which indicates a non-dissociative interaction of 2-propanol with the surface. This weaker interaction can be reasonably ascribed to the know ability of TiO2 inserted Li+ to cause the formation of a new phase of the type LixTiO2

PHOTOCATALYSIS WITH ORGANIZED SYSTEMS FOR THE OXOFUNCTIONALIZATION OF HYDROCARBONS BY O2

none3Here, we attempt to summarize and classify the significant features of different organized systems able to induce photocatalytic hydrocarbon oxygenations.noneA.MALDOTTI; A. MOLINARI; R. AMADELLIMaldotti, Andrea; Molinari, Alessandra; R., Amadell

Inorganic membranes as redox- photo- and electro-catalysts

The development of the chemistry and microheterogeneous systems, particularly of inorganic membranes as redox catalysts, is a glamorous field of research and technological application. Photo- or electro-assisted catalytic redox membranes are efficient and versatil

Riduzione fotochimica di Fe(III) tetrafenilporfirina tetrasolfonata in solvente misto piridina-etanolo-acqua

--

EPR spin trapping Evidence of Radical Intermediates in the Photo-reduction of Bicarbonate/CO2 in TiO2 Aqueous Suspensions

Using 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