Photocatalytic degradation of toluene in the gas phase: relationship between surface species and catalyst features.

Photocatalytic activity of both commercial and homemade samples was tested for the degradation of toluene in the gas phase by using two different irradiation sources, UV and solar. The role played by humidity in affecting the final toluene degradation was discussed. Catalyst deactivation (due to the high toluene level, 1000 ppm) and subsequent regeneration, by washing with water, were analyzed. Highest degradations and corresponding kinetic constants were achieved in the case of the anatase/brookite composite samples, while the commercial ones (including P25 Degussa) showed lower efficiency. Various adsorbed aromatic species (benzoic acid, the major surface product hydroquinone, benzylic alcohol, benzaldehyde, and cresols) obtained by washing the exhaust catalysts were analyzed by HPLC. Parallel results were achieved by Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy. The presence of different photodegradation surface species for the various photocatalysts suggests the occurrence of different reaction pathways, depending on the fine physicochemical features of the specific TiO2 adopted in the reaction.