Study on photocatalytic degradation of several volatile organic compounds.

The gas-phase photolytic and photocatalytic reactions of several aromatics and chlorohydrocarbons were investigated. The experimental results revealed that chlorohydrocarbons like trichloroethylene, dichloromethane and chloroform could be degraded through either photolysis or photocatalysis under irradiation of germicidal lamp, and the elimination rate of chlorohydrocarbons through photolysis was quicker than that through photocatalysis. UV light from a germicidal lamp could directly lead to degradation of toluene but could hardly act on benzene. The photodegradation rate for these volatile organic compounds (VOCs) through photolysis followed an order: trichloroethylene>chloroform>dichloromethane>toluene>benzene>carbon tetrachloride, and through photocatalysis followed: trichloroethylene>chloroform>toluene>dichloromethane>benzene>carbon tetrachloride. Besides, a series of modified TiO2 photocatalysts were prepared by depositing noble metal, doping with transition metal ion, recombining with metal oxides and modifying with super strong acid. Activity of these catalysts was examined upon photocatalytic degradation of benzene as a typical compound that was hard to be degraded. It indicated that these modification methods could promote the activity of TiO2 catalyst to different extent. The apparent zero-order reaction rate constant for degrading benzene over SnO2/TiO2 catalyst had the highest value, which was nearly three times as that over P25 TiO2. But it simultaneously had the lowest rate for mineralizing the objective compound. In spite that Fe3+/TiO2 catalyst behaved slightly less active than SnO2/TiO2 for degradation of benzene, the mineralization rate over Fe3+/TiO2 was the highest one among the prepared catalysts.