Decomposition of gas-phase octamethyltrisiloxane on TiO2 thin film photocatalysts—catalytic activity, deactivation, and regeneration

The photocatalyzed decomposition reaction of gas-phase octamethyltrisiloxane (OMTS) on TiO2 thin films was investigated in a batch-type photocatalytic reactor. The effectiveness of TiO2 photocatalyst for decomposing OMTS was demonstrated by the decrease of OMTS concentration and increase of carbon dioxide concentration with illumination time as monitored using a gas chromatography. However, the photocatalytic activity was found to decrease with increasing reaction time, and catalyst deactivation was finally observed on the TiO2 film that suffered from a long-time reaction. Formation and accumulation of hydroxylated SiOx (x=3 ∼ 4) on the irradiated TiO2 surface were detected by X-ray photoelectron spectroscopic (XPS) measurements. An equivalent amount of ∼7 monolayers of OMTS was estimated to be decomposed on the fully deactivated TiO2 photocatalyst as calculated from the saturated adsorption value and the total decomposed amount of OMTS. It was found that thus formed SiOx can be easily removed by treatment in an alkaline solution for a short period of time without influencing the underlying TiO2 film. Regeneration of the photocatalytic activity of the SiOx-removed TiO2 thin film was confirmed by the re-decomposition of OMTS under the same experimental conditions.