Photodegradation of toluene over TiO2–xNx under visible light irradiation

Abstract

We report the photooxidation of toluene over nitrogen doped TiO₂ (TiO_2−xN_x) under visible light irradiation. The photocatalytic oxidation of toluene in air over TiO_2−xN_x powders was studied using diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), gas chromatography (GC), ion chromatography (IC), and gas chromatography mass spectrometry (GC-MS), focusing on the photocatalytic decomposition processes of toluene. Results obtained indicate that toluene, weakly adsorbed on the catalyst surface, is initially photooxidized to benzaldehyde which adsorbs onto the TiO_2−xN_x surface more strongly, leading to the formation of ring-opening products such as carboxylic acids and aldehydes. No gaseous intermediates were detected during the photooxidation. Major intermediates adsorbed at the catalyst surface were oxalic acid, (COOH)₂, acetic acid, CH₃COOH, formic acid, HCOOH, and pyruvic acid, CH₃COCOOH, whereas more complicated carboxylic species, including propionic acid, CH₃CH₂COOH, isovaleric acid, (CH₃)₂CHCH₂COOH, and succinic acid, (CH₂COOH)₂, were also found in the early stage of the photooxidation. These intermediate products were gradually photodegraded to CO₂ and H₂O under visible light irradiation.