Abstract: Photocatalytic oxidation (PCO) of toluene by TiO2 loaded on activated carbon fibers (ACF) in an environmental conditions-controlled chamber was investigated. The TiO2/ACF catalyst was characterized by N2 adsorption for pore structure and scanning electron microscopy for morphology. The remnant of toluene and the accumulation of intermediates on the TiO2/ACF catalyst under different relative humidity (RH) were determined by GC-MS and GC-FID. The results showed that the PCO conversion rate of toluene increased with the increase of RH in the chamber. The species of intermediates were the same at all RH levels. However, the accumulation amounts of side chain oxidation intermediates (benzyl alcohol, benzaldehyde, and benzoic acid) were much more than that of aromatic ring oxidation intermediates (cresol and p-toluquinone). Elevated RH increased the accumulation of all intermediates except benzaldehyde. These results suggested that environmental humidity plays an important role in the PCO of toluene, which affects both the PCO rate and the PCO process. Although methyl group oxidation is the major path, aromatic ring oxidation, which is not the expected path for the PCO of toluene, is enhanced when the RH increases. The roles of water in the PCO of toluene were discussed.

Key words: titanium dioxide, activated carbon fiber, toluene, photocatalytic oxidation, environmental humidity