Photooxidation of dimethylsulfide in the gas phase:: A comparison between TiO2-silica and photo sensitizer-silica based materials

The photooxidation of dimethylsulfide (DMS) in the gas phase was studied with two different materials, under identical conditions. The first material (TiO2-QZ) is based on titanium dioxide (TiO2) deposited on quartz bars by the sol-gel method. The second one (DCA-SG) is based on the well known photosensitizer, 9,10-dicyanoanthracene (DCA) encapsulated in a sol-gel silica network. In spite of non-optimized conditions, both materials allow the oxidation of DMS in air under irradiation. However, the oxidation products are strikingly different: dimethyldisulfide is the main product detected in the gas phase with TiO2-QZ due to a too short residence time to achieve complete mineralization. With DCA-SG no gaseous product is detected in the treated gaseous flow for more than 100 h, due to the exclusive formation of polar dimethylsulfoxide and dimethylsulfone which are totally adsorbed on the highly polar silica gel. The efficiency of this latter reaction depends on the DMS concentration, gas flow and light intensity, but is not affected by the presence of small amounts of water. Singlet oxygen appears to be formed efficiently under these conditions. The saturation of DCA-SG by the oxidation products was demonstrated by several complementary methods, and some possible solutions to regenerate the material are proposed. The complementarities of both TiO2-QZ and DCA-SG could be used to achieve the oxidation of different classes of pollutants. (c) 2006 Elsevier B.V. All rights reserved.