Study on the Photocatalytic Reaction of Trichloroethylene (TCE) over TiO2 Using Synchrotron Radiation Photoionization Mass Spectrometry.

Trichloroethylene (TCE) is a widely used solvent in industrial processes, which is harmful to human health and the environment. Photocatalysis is a promising method for the degradation of TCE. In this work, the photocatalytic reaction of TCE over TiO₂ was studied using synchrotron radiation photoionization mass spectrometry (SR-PIMS) under 360 nm UV light irradiation. First, more than 12 kinds of gas phase degradation intermediates and products were detected, including newly identified products such as formaldehyde (HCHO), formic acid (HCOOH) and hypochlorous acid (HOCl) and tetrachloroethane (C₂H₂Cl₄). Second, the effects of water and oxygen on the photocatalysis of TCE over TiO₂ were investigated. It was found that water vapor showed a negligible effect on the photocatalytic degradation efficiency TCE, but could enhance the generation of oxygen-containing species, like hypochlorous acid (HOCl), Phosgene (COCl₂), and dichloroacetyl chloride (C₂HOCl₃). The presence of oxygen in the gas phase significantly enhanced the photocatalytic degradation of TCE, due to its role as an electron acceptor, preventing the recombination of photogenerated electron-hole pairs on the TiO₂ surface, thereby enhancing the generation of reactive species like superoxide radicals (O₂^•-), which are essential for the effective degradation of TCE. Finally, the photocatalytic degradation network of TCE over TiO₂ was proposed.