Photochemical Reaction of VOC Gases on the Visible Light Photocatalyst Surfaces

Abstract

We report the photochemical reaction of volatile organic compounds (VOC's), such as acetaldehyde and toluene, over nitrogen doped TiO2(TiO-N) under visible light irradiation, using liquid chromatography (LC), gas chromatography (GC) and gas chromatograph mass spectrometer (GC-MS) for gases analysis, and diffuse reflectance fourier transform infrared spectroscopy (DRIFTS) and ion chromatography (IC) for adsorbed organics. We evaluated the photo degradation rates and intermediates for the above gases. As a result, the degradation rates of acetaldehyde gas on TiO-N were 1.2-3 times greater than those on TiO2, and those of toluene gas on TiO-N were 4-49 times greater than those on TiO2. Low concentrations of acetone and acetic acid were produced during the photo degradation of acetaldehyde by the TiO-N. From toluene, very low concentrations of formaldehyde, acetaldehyde, acetone and benzaldehyde gases were produced. We also revealed the decomposition processes of toluene. Results obtained indicate that toluene, weakly adsorbed on the photocatalyst surface, is initially photooxidized to benzaldehyde which adsorbs onto the TiO-N surface more strongly, leading to the formation of ring-opening products such as carboxylic acids and aldehydes. These intermediate products were gradually photodegraded to CO2 and H2O under visible light irradiation.