Photocatalytic Oxidation of Toluene by Activated Carbon Fibers Coated nano-TiO2: Intermediates and Mechanism

摘要

Photocatalytic oxidation (PCO) tests have been carried out for toluene adsorbed on the activated carbon fibers (ACFs) coated nano-TiO2 in an environmental condition controlled chamber. Elimination of toluene and accumulation of the intermediates were studied under different UV illumination intensity, relative humidity (RH), and temperature levels in order to explore the influence of reaction conditions on the accumulation of intermediares during the PCO process. Three kinds of index (photocatalytic conversion ratio, photocatalytic mineralization ratio, and photocatalytic degradation efficiency) were used to evaluate the PCO efficiency. Results showed that: Five intermediate products, benzyl alcohol, benzaldehyde, benzoic acid, p-toluquinone and cresol, were detected on the TiO2/ACF. The accumulation amounts of these intermediates increased with the increase of the illumination intensity and the weight ratio of them didn't change, which indicated the increase of illumination intensity accelerated all reactions involved in the PCO process to the same extent. With the increase of the RH, intermediates accumulated on the TiO2/ACF increased except benzaldehyde; meanwhile, the photocatalytic degradation efficiency increased when RH rose, which suggested the increase of RH gave more positive effect on the photocatalytic mineralization process of intermediates than on the conversion process of toluene. Accumulation amounts of intermediates were much higher under high temperature than low temperature. Besides toluene, the transfer events of intermediates between TiO2 and ACFs was observed in the experiments and diffusion is the key foundation of the matter transfer.