Singlet oxygen in microporous silica xerogel: Quantum yield and oxidation at the gas-solid interface
Résumé
The quantum yields of singlet oxygen (1O2) production (ΦΔ) and 1O2 lifetimes (τΔ) at the gas-solid interface in silica gel material are determined. Different photosensitizers (PS) are encapsulated in parallelepipedic xerogel monoliths (PS-SG). PS were chosen according to their known photooxidation properties: 9,10-dicyanoanthracene (DCA), 9,10-anthraquinone (ANT), and a benzophenone derivative, 4-benzoyl benzoic acid (4BB). These experiments are mainly based on time-resolved 1O2 phosphorescence detection, and the obtained ΦΔ and τΔ values are compared with those of a reference sensitizer for 1O2 production, 1H-phenalen-1-one (PN), included in the same xerogel. The trend between their ability to oxidize organic pollutants in the gas phase and their efficiency for 1O2 production is investigated through photooxidation experiments of a test pollutant dimethylsulfide (DMS). The ΦΔ value is high for DCA-SG relative to the PN reference, whereas it is slightly lower for 4BB-SG and for ANT-SG. ΦΔ is related to the production of sulfoxide and sulfone as the main oxidation products for DMS photosensitized oxidation. Additional mechanisms, leading to C-S bond cleaveage, appear to mainly occur for the less efficient singlet oxygen sensitizers 4BB-SG and ANT-SG. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.