Development of Degradation Process for VOC Gases Using Mist Containing Titania Particles

Abstract

The present work studied the photocatalytic degradation of VOC gas by a mist formed by ultrasonic nebulization of TiO₂ suspension with various wave lengths of UV rays. With UV₃₆₅ irradiation, toluene was decomposed by photocatalytic reaction either on the mist surface or inside it. The toluene removal efficiency increased with the TiO₂ concentration of the suspension. Water-soluble intermediates formed by the decomposition of VOC gases were completely trapped in the mist and were not detected at the reactor exit. Under UV_254+185 irradiation, the complete decomposition efficiency to CO₂ and H₂O was higher than that with UV₃₆₅ or UV₂₅₄ irradiation. With UV_254+185 irradiation, it was found that VOC gases were immediately degraded and converted to water-soluble intermediates by not only direct photolysis but also oxidation by OH radicals, because the removal rate of several organic gases depended on the reaction rate with OH radicals. On the other hand, ozone mainly contributed to complete decomposition of intermediates, because the complete decomposition efficiency of intermediates was decreased without ozone generation under UV_254+185 irradiation in N₂. Finally, we proposed the degradation mechanisms of organic gaseous pollutants on the mist surface.