Mechanistic study and mutagenicity assessment of intermediates in photocatalytic degradation of gaseous toluene

Photocatalytic oxidation is a promising technique for the degradation of volatile organic compounds. However, it is necessary to clarify the genotoxicity mutagenic potential of intermediates formed during photocatalytic degradation. A gas–solid TiO2 thin film reactor was fabricated to degrade toluene under UV irradiation. The results showed that the degradation efficiencies of toluene at a concentration of about 1500 μg L−1 reached almost 100% within 120 min of illumination. The intermediates produced during the photocatalytic degradation were identified by using gas chromatography–mass spectroscopy. Benzene was the only by-product identified in the gas phase, while small amounts of benzaldehyde and benzoic acid were detected at the TiO2 surface. Species such as benzene and CO2 should derive from the photo-decarboxylation of benzoic acid, produced by further oxidation of benzaldehyde. Neither the original toluene nor the gaseous intermediates produced at different times presented mutagenic activity to strains TA98 and TA100 in the presence or absence of the S9 mixture at the tested doses by using Ames assay. All of the results indicated that the effluent gas of toluene treated by photocatalysis will not cause mutagenic toxicity to humans or other organisms.