Probing the interplay between factors determining reaction rates on silica gel using termolecular systems

This article was published in the journal, Photochemical and Photobiological Sciences [© Royal Society of Chemistry and Owner Societies]. The definitive version is available at: http://dx.doi.org/10.1039/c2pp25171jIn this study we have compared energy and electron transfer reactions in termolecular systems using a nanosecond diffuse reflectance laser flash photolysis technique. We have previously investigated these processes on silica gel surfaces for bimolecular systems and electron transfer in termolecular systems. The latter systems involved electron transfer between three arene molecules with azulene acting as a molecular shuttle. In this study we present an alternative electron transfer system using trans β-carotene as an electron donor in order to effectively immobilise all species except the shuttle, providing the first unambiguous evidence for radical ion mobility. In the energy transfer system we use naphthalene, a structural isomer of azulene, as the shuttle, facilitating energy transfer from a selectively excited benzophenone sensitiser to 9-cyanoanthracene. Bimolecular rate constants for all of these processes have been measured and new insights into the factors determining the rates of these reactions on silica gel have been obtained

Determination of the Exact Microporous Volume and BET Surface Area in Hierarchical ZSM-5

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Modeling of Copper Adsorption on Mesoporous Carbon CMK-3: Response Surface Design

CMK-3 mesoporous carbon was nanocast from SBA-15 silica. The obtained carbon was characterized by nitrogen sorption isotherms, X-ray diffraction and transmission electron microscopy (TEM). The batch adsorption tests were done at constant pH taking into account the initial metal ion concentration, adsorbent mass and temperature. A statistical study using a response surface design method was done to develop a mathematical model to predict copper adsorption on CMK-3 as a function of the mentioned experimental factors. It was found that all these parameters are significant, and copper concentration has the greatest effect on adsorption among them. Moreover, the obtained model proved to be adequate in predicting copper adsorption on CMK-3 and its performance under different experimental conditions

Adsorptive removal of α-endosulfan from water by hydrophobic zeolites. An isothermal study.

International audienceThis paper deals with the removal of α-endosulfan from water over HY and steamed HBEA zeolites. Experiments were performed to understand the adsorption mechanisms of α-endosulfan on zeolites and to determine the most efficient adsorbent for the purification of water contaminated by this pesticide. The experiments exhibit that α-endosulfan was adsorbed in the micropores. In the case of HY zeolites an adsorption of α-endosulfan molecules on BrØnsted sites was pointed out, due to a preferential water adsorption in mesopores. Moreover a physisorption of α-endosulfan occurred in micropores. For steamed HBEA zeolites physisorption in micropores was pointed out as the adsorption mode. For both types of zeolites a decrease of the adsorption capacities was noticed when the acidity of zeolites increased. There was also a linear relation between the adsorption capacities of α-endosulfan and the hydrophobicity (HI) of the samples and by determining the values of HI for a type of zeolite it was possible to deduce the uptake of α-endosulfan. The HY(40) sample was the most efficient for the removal of α-endosulfan from water because of preferential adsorption of water molecules in mesopores and lower acidity. For this sample the adsorption capacity for α-endosulfan was about 833.33 mg/g where for the most effective HBEA sample (St700(3)) the adsorption capacity was about 793.65 mg/g

Ajustement de l'hydrophobicité de silices mésoporeuses organisées pour l'adsorption sélective de polluants organiques en présence d'eau

Les charbons actifs et les zéolithes microporeuses hydrophobes sont généralement utilisés pour l'élimination par adsorption des polluants organiques des effluents industriels. Grâce à leur très grande surface spécifique et à un volume poreux élevé, les silices mésoporeuses organisées ont des capacités de stockage plus importantes que leurs analogues microporeux. De plus, ces solides présentent une faible interaction eau-adsorbant aux faibles valeurs de P/P0 vis-à-vis de l eau ce qui leur confère un caractère hydrophobe. Cependant, la présence de groupements silanols dans les canaux limite fortement l'adsorption des molécules organiques en présence d'eau. Afin d'accroître fortement l'hydrophobicité des silices mésoporeuses, différentes modifications au cours de la synthèse (incorporation de groupements phényles) ou post-synthèse (greffage de groupements triméthylsilyles, aminopropyles et propyle sulfoniques) ont été envisagées. Le greffage de groupements triméthylsilyles et l'incorporation de groupements phényles permettent donc d'augmenter considérablement l'hydrophobicité des solides en réduisant le nombre de groupements silanols. Dans le cas de l'adsorption en phase gaz, l'hydrophobicité s'est révélée être un facteur clef positif. L'adsorption de polluants organiques apolaire en phase aqueuse nécessite également une silice hydrophobe. Pour des molécules polaires, le greffage de groupements polaires adaptés (amino ou sulfonique) à la forme chimique du polluant a un rôle déterminant sur son adsorption.Activated carbons and hydrophobic microporous zeolites are usually used for the removal of organic pollutants in wastewater. An extended BET surface and a relevant pore volume both confer high sorption capacities to organised silica materials. Moreover, these solids exhibite a low water-adsorbent interaction at low P/P0 giving them an hydrophobic character. However, the presence of silanol groups limits the adsorption of organic molecules in aqueous phase. In order to significantly increase the mesoporous silica hydrophobicity, various modifications during synthesis (phenyl groups incorporation) or post-synthesis (grafting of trimethylsilyl, aminopropyl and mecaptopropyl groups) were considered. The grafting of trimethylsilyl groups and phenyl groups incorporation can therefore considerably reduce the hydrophilicity of these solids by reducing the number of silanol groups. In the case of gas adsorption, hydrophobicity proved to be a positive key factor. In aqueous phase, the non-polar organic pollutants adsorption also requires hydrophobic silica. For polar molecules, the grafting of polar groups (amino or sulfonic) increases the pollutant adsorption capacities.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Hierarchical zeolites as adsorbents for mesosulfuron-methyl removal in aqueous phase

International audienceDesilication and soft acid leaching lead to hierarchical zeolites with low debris.•Hierarchical zeolites are promising adsorbents for bulky pesticides in water.•Mesosulfuron-methyl (MM) is chemisorbed on zeolite Brønsted acid sites.•The zeolite mesoporosity enhances significantly MM diffusion behavior and capacity.•MM abatement rate is up to 80% in water for hierarchical large pore H-MOR zeolite

Catalytic oxidation of VOCs on NaX zeolite: Mixture effect with isopropanol and o-xylene

International audienceCatalytic oxidation of isopropanol and o-xylene alone as well as in mixture was investigated over basic NaX zeolite. Experiments were carried out in wet air (11,000 ppm of water) and at a high gas hourly space velocity (GHSV) of 18,000 h(-1). Results show an inhibiting effect of the o-xylene on the isopropanol destruction whereas the isopropanol has no effect on the o-xylene destruction. Adsorption experiments as well as molecular modelling seem to demonstrate that this inhibiting effect of o-xylene is due to the adsorption of this aromatic VOCs near the apertures of the NaX supercages limiting the access of isopropanol to the basic active sites of this zeolite. Furthermore, the concentration of o-xylene influences the formation of secondary products (propene, coke) resulting from the isopropanol transformation. (C) 2010 Elsevier B.V. All rights reserve

Caractérisation et ajustement de l'hydrophobicité de divers solides poreux (application à l'élimination de polluants organiques)

Les solides poreux hydrophobes ont un vaste champ d'application potentiel dans les procédés de dépollution de l'air et des eaux résiduelles. Elles constituent donc une alternative intéressante aux charbons actifs pour l'élimination sélective des polluants organiques, car elles sont facilement régénérables à haute température. Leurs propriétés adsorbantes sont en grande partie liées à leurs indices d'hydrophobicité HI. Différents paramètres influent sur l'indice d'hydrophobicité. Dans le cas des zéolithes, ce sont la structure poreuse, l'acidité des échantillons (rapport Si/Al de charpente), la taille des cristallites, la présence de défauts (nids silanols) ou d'EFAl. Dans le cas des silices mésoporeuses, ce sont le volume poreux, le taux de greffage et la concentration en silanols. L'élimination du phénol est favorisée sur les zéolithes très hydrophobes, celle du chlorobenzène sur les zéolithes peu hydrophobes ; les silices mésoporeuses hydrophobes adsorbent bien le chlorobenzèneHydrophobic silica and zeolites found numerous applications in separation technologies. They are going to replace activated carbon because of their interesting regeneration properties. Their adsorptive properties are linked to their Hydrophobicity index defined by Weitkamp. Many parameters play a key role in the values of Hydrophobicity indexes. In the case of zeolites, parameters such as the partial pressure of sorbates, their acidity, their crystallite sizes, the presence of structural defects and EFAl species in the structure... determine the strength of the hydrophobic character. In the case of mesoporous silica, the silylation level is the main parameter determining the hydrophobic character. Phenol removal in aqueous solutions is efficient on hydrophobic zeolites and silylated silica. Chlorobenzene removal is efficient on the most acidic supports. This removal is improved on silylated mesoporous silicas.POITIERS-BU Sciences (861942102) / SudocSudocFranceF