Gas-phase photocatalytic degradation and detoxification of o-toluidine: Degradation mechanism and Salmonella mutagenicity assessment of mixed gaseous intermediates

The photocatalytic degradation of toluidine over titanium oxide (TiO2) thin films under UV irradiation was investigated. The degradation efficiency of 98.7% was obtained for a toluidine concentration of about 4500 μg L−1 and illumination of 240 min. The degradation intermediates produced during photocatalytic oxidation were identified using Fourier transform-infrared spectrometry (FTIR) and gas chromatography–mass spectrometry (GC–MS). Only a small amount of intermediates, including phenol and toluene, were found in the gas phase. Many other trace amount intermediates, such as 2-hydroxybenzaldehyde, 2-nitrobenzaldehyde, 2-hydroxybenzenemethanol, 2-hydroxybenzoic acid, phenol etc., were detected on the TiO2 surface. An Ames assay of the Salmonella typhimurium strains TA98 and TA100 was employed to evaluate the mutagenicity of toluidine and its gaseous photocatalytic degradation intermediates. With or without rat liver microsomal fraction (S9 mix) activation, neither toluidine nor its gaseous intermediates presented mutagenic activity against strains TA98 (±S9) and TA100 (−S9) at all tested doses. Toluidine, however, can induce a weak positive response to the TA100 strain with an S9 mix at doses as high as 4000 μg plate−1. An increase of revertants per plate was obtained after 30 min photocatalysis in the TA100 strain with S9 mix. As reaction time further increased, photocatalytic technology exhibited the ability to completely and efficiently detoxify toluidine. Both our chemical analysis and toxic evaluation indicate that all mutagenic intermediates in the gas can be completely eliminated within 240 min, which further suggests that photocatalytic technology is an effective approach for degrading aromatic amines.

As for a mutagenic pollutant, toluidine, the mutagenicity to strains TA100 (+S9) increase firstly after 30 min photocatalytic oxidation and then decrease and totally detoxify with further increasing degradation time..Figure optionsDownload high-quality image (143 K)Download as PowerPoint slideResearch highlights▶ Two intermediates of toluene and phenol were found in the gas phase. ▶ Six trace amounts degradation intermediates were found on the surface of TiO2. ▶ o-Toluidine presented weak mutagenic activity against the TA100 strain with S9. ▶ Mutagenic toxicity of gaseous intermediates increased first and then decrease soon. ▶ Gaseous o-toluidine was successfully detoxified using photocatalytic technology.