Dégradation photocatalytique de microorganismes (inactivation) par une montmorillonit, pontée au titane et des photosensibilisateurs - comparaison avec Ti02

La photocatalyse a été utilisée pour éliminer des microorganismes (Escherichia-Coli) qui constituent une pollution biologique de l'eau. Le procédé photocatalytique associe un semi-conducteur (le dioxyde de titane) à des rayonnements UVA pour générer des espèces réactives de l'oxygène (EROs), qui vont à leur tour inactiver E-coli grâce au stress oxydant que les EROs provoquent. Plusieurs matériaux ont été impliqués dans cette étude: le Ti02, les photosensiblisateurs et une argile pontée avec le titane. Cette dernière s'est montrée totalement inefficace à éliminer les microorganismes par photocatalyse. Le Ti02 a été le plus efficace des matériaux testés, l'inactivation bactérienne a été totale après 180 minutes d'irradiation en UVA et en présence de seulement 0,25 gIL. Le traitement photocatalytique des bactéries semble être durable puisqu'aucune recultivabilité des microorganismes n'est observée 48 heures après les irradiations. Les photosensibilisateurs ont été moins efficaces que le Ti02 mais ils présentent l'avantage, non négligeable, d'être activable dans le visible. Ce résultat ouvre la voie pour une application solaire du procédé de désinfection photocatalytiquePhotocatalysis has been used to eliminate microorganisms (Escherichia-Coli) which act as a biological pollutant in water. The photocatalytic process associates a semiconductor (the titania dioxyde) with UV radiations to generate the Reactive Species of the Oxygen (ROSs), which, in tum, inactivates E-coli thanks to the oxydative stress that the ROSs engenders. Several materials have been inc1uded in this study: Ti02, photosensitizers and titania pillared clay. The latter proved completely inefficient in eliminating microorganisms by photocatalysis. The Ti02 was the most efficient among the materials tested. Bacterial inactivation was total after 180 minutes of radiation with UVA and with a presence of only 0,25 gIL. The photocatalytic treatment ofbacteria seems to be durable since no sign of re-emergence of microorganisms has been noticed 48 hours after radiation. Photosensitizers proved less efficient than the Ti02, yet their role is, to a certain extent, quite significant as they can be activated with visible light. The result of this study paves the way for the solar application of the process of photocatalytic disinfectionLYON1-BU.Sciences (692662101) / SudocSudocFranceF

Visible-light photosensitized oxidation of alpha-terpinene using novel silica-supported sensitizers: photooxygenation vs. photodehydrogenation

Three silica-immobilized organic photocatalysts, based on rose bengal (RB), antraquinone-2-carboxylic acid (ANT-COOH) and a new cyanoanthracene derivative (DBTP-COOH), were prepared and characterized. Their efficiency for the photooxidation of alpha-terpinene was compared to that of their soluble counterparts. In solution, the three sensitizers showed high quantum yield of singlet oxygen production. Significant autooxidation to p-cymene occurred in the absence of catalyst while the mechanism of the sensitized reaction strongly depended on sensitizer structure. With DBTP and RB materials, ascaridole was rapidly produced by singlet oxygen addition. In contrast, ANT-based sensitizers favored photodehydrogenation to p-cymene through an electron-transfer step inducing a radical chain reaction, followed by further p-cymene oxidation upon prolonged irradiation. The highest efficiency and selectivity were obtained for photooxygenation with DBTP-based materials, and for photodehydrogenation with ANT-based materials, these properties make them attractive for future applications as immobilized photocatalyst in solar synthesis, waste treatment, and microflow reactors