Singlet oxygen in microporous silica xerogel: Quantum yield and oxidation at the gas-solid interface

The quantum yields of singlet oxygen (O-1(2)) production (Phi(Delta)) and O-1(2), lifetimes (tau(Delta)) 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-dicyanoanthrocene (DCA), 9, 10-anthroquinone (ANT), and a benzophenone derivative, 4-benzoyl benzoic acid (4BB). These experiments are mainly based on time-resolved O-1(2), phosphorescence detection, and the obtained Phi(Delta) and tau(Delta) values are compared with those of a reference sensitizer for O-1(2), production, 1H-phenalen-1-one (PN), included in the some xerogel. The trend between their lambda ficiency for O-1(2) production is investigated through photooxidation experiments of a test pollutant dimethylsulfide (DMS). The Phi(Delta) value is high for DCA-SG relative to the PN reference, whereas it is slightly lower for 4BB-SG and for ANT-SG. Phi(Delta) 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 cleoveage, appear to mainly occur for the less efficient singlet oxygen sensitizers 4BB-SG and ANT-SG.