In Situ Studies on the Dissociation and Photocatalytic Reactions of CH3OH on TiO2 Thin Film by Sum Frequency Generation Vibrational Spectroscopy

Titanium dioxide (TiO2) has been widely used in the photodegradation of organic contaminants and wastewater treatment in recent years. However, the mechanism of photocatalytic reaction on TiO2 surfaces is still poorly understood, especially for the reactions under real environmental conditions. In the present study, the sum frequency generation vibrational spectroscopy, a surface-specific tool, has been employed to in situ study the dissociation and photooxidation reaction of CH3OH on TiO2 thin film, which served as a model system of photooxidizing organic compounds. The experimental results show that mixing O-2 with CH3OH promotes more CH3OH dissociation to produce CH3O, and UV light can not only induce CH3OH dissociation to CH3O but also generate large nonresonance. To mimic the photodegradation process of organics, removing methoxy on the TiO2 thin film has been investigated under both aerobic and anaerobic conditions. We have observed two types of methoxy, photocatalytically reactive under both conditions and photocatalytically less reactive aerobically and inert anaerobically. We propose to attribute the former to the monodentate methoxy, and the latter to the bidentate methoxy.