Développement d'un outil informatique opérationnel d'aide à la décision et de modélisation des pollutions en Méditerranée

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Etude du comportement photoélectrochimique d'oxydes semiconducteurs de quelques métaux de transition

Après avoir donné les bases théoriques du comportement des systèmes semiconducteur/solution électrolytique, soumis ou non à une illumination, nous étudions le cas de l'interface dioxyde de titane/solution électrolytique aqueuse. Nous donnons les différentes méthodes de préparation utilisées (oxydation anodique, thermique ; pulvérisation cathodique réactive) et décrivons les réactions qui se déroulent à cette interface dans l'obscurité ainsi que les effets d'une illumination d'énergie suffisante pour créer des paires électron-trou dans le semiconducteur (TiO2 de type n). La réaction d'oxydation photoinduite de l'eau en oxygène se produit par l'intermédiaire des trous générés par l'illumination dans la bande de valence. Cette réaction est accompagnée d'une réduction de l'oxygène en peroxyde d'hydrogène. D'autres réactions de réduction sont également possibles sur le semiconducteur à l'abandon, sous illumination, dans une solution électrolytique.LYON-Ecole Centrale (690812301) / SudocSudocFranceF

Etude des phénomènes d'adsorption par Résonance Magnétique Nucléaire in situ dans les systèmes silice/ solutions binaires eau-méthylpyridines (Relation avec la thermodynamique des systèmes)

Le comportement en adsorption sur une silice pyrogénique (Aerosil 200) de méthylpyridines à partir de leurs mélanges binaires avec l'eau a été étudié. Ces binaires présentent une lacune de miscibilité. Ils ont été étudiés non loin du point critique bas. Les isothermes d'adsorption sont du type "à marches" et font penser au phénomène de layering, empilement de couches de molécules adsorbées. Il est montré que ces couches sont structurées et présentent des transitions de phase de surface représentables sur un diagramme. Une étude RMN de la suspension de silice à l'équilibre d'adsorption a montré que, à l'opposé du cas de la pyridine, l'adsorption de ces molécules sur la silice s'opère par l'interaction de l'oxygène des ponts siloxane et du système p du cycle aromatique. Les aspects dynamiques de l'adsorption ont été mis en évidence. Les contributions complémentaires de la thermodynamique et de la RMN ainsi que des considérations théoriques montrent que l'idée d'un empilement en couches identiques doit être reconsidérée du fait de l'existence dans ces couches de transitions de phase de surface.Adsorption behaviour of pyridine methyl derivatives from their binary mixtures with water has been studied on pyrogenic silica (Aerosil 200). These mixtures exhibit a miscibility loop. The study was made near the louver critical point. Adsorption isotherme are stair-like, leading to the hypothesis of layering, i.e. stacking of adsorbed molecular layers. Experiments have shown that these layers are structured and exhibit surface phase transitions which could be depicted in a surface phase diagram built from a large number of isotherme. NMR experiments have been done on silica suspensions at equilibrium. pH influence on spectra has shown that, unlike the pyridine case, interaction between siloxane oxygen and p-system of the aromatic ring was responsible for adsorption. NMR has also evidenced the dynamic aspect of adsorption. Thermodynamic and NMR complementary contributions as well as theoretical results show that the idea of identical molecular layer stacking has to be revisited to take into account the experimental fact of surface phase transitions.BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF

Influence d’un rayonnement électromagnétique sur le comportement électrochimique de certains oxydes semi-conducteurs

Le comportement photocatalytique du dioxyde de titane a conduit les auteurs à étudier les propriétés photoélectrochimiques de celui-ci et à rechercher une corrélation entre ces deux effets.L’influence de différents paramètres (pH de la solution électrolytique, conditions d’illumination, température) sur l’électrode de TiO2 montre que l’effet photoélectrochimique permet d’oxyder l'eau en oxygène moléculaire à un potentiel inférieur de 1,05 volt à celui calculable par la thermodynamique

Operational Device and Procedure to Test the Initial Dissolution Rate of Chemicals After Ship Accidents: the Cedre Experimental Column

: This paper describes an experimental procedure recently developed to simulate and study the behaviour of various chemicals in seawater during their transfer in a 5 m deep water column. Since chemical pollution can be harmful to the environment, anticipating the evolution of a chemical spill is important for authorities, so that they can act rapidly and efficiently after a spill. In the case of a sunken wreck containing chemicals with a lower density than seawater in its leaking tanks, it could be useful to estimate the quantity of chemicals that should be found at the sea surface. On the other hand, in the case of a spill occurring at the sea surface, the mass of chemicals liable to sink and accumulate on the seabed without being dissolved during sinking is an important piece of information required to choose the most suitable response strategy. The solubility of a particular chemical is not always available from the literature. In particular, the solubility in seawater is seldom documented and, whenever it is, it is usually in the form of solubility limits. As important as this parameter may be, it is not the most significant one in situations in which the interface between the (sea) water and the chemical involved undergoes permanent renewal. A more operational parameter would be the initial dissolution rate. The Cedre Experimental Column (C.E.C.) was designed for this purpose and a method was defined. The volume and dimensions of droplets of chemicals were studied in order to characterize the dissolution of different products throughout their journey through the water column. The dissolution rate can be expressed as a volume loss during a flow time or between two given depths. Experiments were performed on eight chemicals with different water solubility limits (8.7 to 290 g L-1) using video imagery to analyze the chemicals' behaviour. If the initial dissolution rate is dependent on solubility, it appears clearly that other physical parameters are also relevant to predict the behaviour of a product, for instance its density and viscosity. In addition to these intrinsic parameters, the dissolution kinetics of a product are also linked to its injection flow in the water column, determined, for example, by the size of the hole in the ship which will define the droplet speed. The C.E.C is therefore an operational tool which can be used to study the behaviour of specific chemicals, either as part of a particular study or in the event of a spill, taking into account all the relevant factors involved. It provides accurate and detailed information on the product's dissolution kinetics, enabling it to be used to assist in decision-making for emergency response

Enhanced metal adsorption on solid suspensions by organic molecules

International audienceThis laboratory study mimicked the pollution of a suspension of silica beads, used as a crude model of sand, by naphthalene in mixture with carbofuran at first, and then by this mixture in association with a metal salt, Pb(NO(3))(2). The silica properties and the working conditions were such that they allowed us to only observe physisorption, which is the first and essential step of any adsorption mechanism. Naphthalene and carbofuran were, respectively, chosen as hydrocarbon and pesticide. Naphthalene adsorption from simple solutions is rather large compared to other organic adsorptions, and carbofuran seems to adsorb on a layer of naphthalene when the latter is mixed in solution with carbofuran. Like other organics, naphthalene favours the adsorption of lead ions, but ionic adsorption is considerably increased by the combination of naphthalene and carbofuran. The Wagner-Onsager-Samaras theory shows that the result implies a special organization of organic molecules at the interface. Conclusions about some environmental mechanisms of fixation, or release, of ions on sands in the case of simple physisorption are drawn from the study

Experimental evidence of pure layering at the solid/liquid binary mixture interface. Silica/water-2,5-dimethylpyridine system

International audienceExperimental evidence is brought for layering transitions at solid (silica) surfaces in contact with liquid mixtures, i.e., first-order transitions whereby the coverage of the surface jumps by an amount equivalent to one extra monolayer of 2,5-dimethylpyridine (2,5-DMP) adsorbed from a liquid mixture with water. These jumps are similar to surface phase changes whose aspects are all shown on the adsorption isotherms: coexistence of two values of adsorption for the same bulk equilibrium composition, adsorption plateaus, persistent metastability lines, characteristic evolution of the plateau's length with temperature, and the proximity of bulk demixing. Known for gas adsorption on a solid both experimentally and theoretically, this behavior is seen for the first time at a solid-liquid interface

Experimental evidence of pure layering at the solid/liquid binary mixture interface. Silica/water-2,5-dimethylpyridine system

International audienceExperimental evidence is brought for layering transitions at solid (silica) surfaces in contact with liquid mixtures, i.e., first-order transitions whereby the coverage of the surface jumps by an amount equivalent to one extra monolayer of 2,5-dimethylpyridine (2,5-DMP) adsorbed from a liquid mixture with water. These jumps are similar to surface phase changes whose aspects are all shown on the adsorption isotherms: coexistence of two values of adsorption for the same bulk equilibrium composition, adsorption plateaus, persistent metastability lines, characteristic evolution of the plateau's length with temperature, and the proximity of bulk demixing. Known for gas adsorption on a solid both experimentally and theoretically, this behavior is seen for the first time at a solid-liquid interface

Polyethylene Glycol adsorption on silica: from bulk phase behavior to surface phase diagram

International audienc

Coadsorption of carbofuran and lead at the air/water interface. Possible occurrence of non-volatile pollutant co-transfer to the atmosphere.

International audienceThe weak solubility of carbofuran allows adsorption at the air/water interface. Carbofuran-rich layers can then induce the coadsorption of metallic salts such as lead nitrate; on the other hand, when carbofuran is missing, no adsorption of this salt takes place. This phenomenon was quantitatively studied through surface tension measurements under concentration conditions close to the environmental ones. Heavy metal salt adsorbed about ten times more than carbofuran. Evidence was then provided that the simultaneous presence of both pollutants in water favours their adsorption and passing from water to the atmosphere through mechanisms such as bubbling