Photocatalytic Oxidation of Gaseous Formaldehyde on TiO2: An In Situ DRIFTS Study

Abstract The adsorption and photocatalytic oxidation of formaldehyde on the pure TiO2 under dry and humid conditions were studied by in situ diffuse reflectance Fourier transform infrared spectroscopy. It was found that the formaldehyde molecules can be adsorbed on the hydroxyl groups on the TiO2 surface via hydrogen bonding. With UV irradiation, the adsorbed formaldehyde rapidly converts to the formate species even on the pure TiO2 at room temperature and atmospheric pressure. In the dry environment, the superoxide radical anion O2-•, formed by adsorbed oxygen reacting with electrons, is suggested to play an important role in the formaldehyde oxidation. The introduction of water vapor provides a large amount of water and hydroxyl groups on the catalyst surface. Oxi-dation of water and hydroxyl groups by the photogenerated holes produces very active OH • radicals, which take part in the redox reactions and improve significantly the mineral-ization rate of formaldehyde on the TiO2 due to its high redox potential