Photodegradation of gaseous volatile organic compounds (VOCs) using TiO2 photoirradiated by an ozone-producing UV lamp: decomposition characteristics, identification of by-products and water-soluble organic intermediates

The photodegradation of the toluene and benzene with TiO2 (P25) and UV254+185 nm radiation from an ozone-producing UV lamp was studied. The VOCs were decomposed and mineralized efficiently owing to the synergistic effect of photochemical oxidation in the gas phase and photocatalytic oxidation on the TiO2 surface. The conversion levels obtained with UV254+185 nm photoirradiated TiO2 were much higher than those with conventional UV sources (UV365 nm and UV254 nm), which suffer from both catalyst deactivation and the generation of harmful intermediates. The products from the photodegradation of VOCs with the UV254+185 nm photoirradiated TiO2 were mainly mineralized CO2 and CO, but some water-soluble organic intermediates were also formed under more severe reaction conditions. The water-soluble aldehydes and carboxylic intermediates disappeared from the effluent gas stream and were detected in the water impingers. These findings suggest that the intermediates can be washed out by conventional gas washing technique, such as wet scrubber. Excess ozone could be easily removed by means of an MnO2 ozone-decomposition catalyst.