Photocatalytic degradation of tetrachloroethylene (PCE) over TiO2 investigated by synchrotron radiation photoionization mass spectrometry

Online SR-PIMS enables real-time detection of gaseous photocatalytic products. • Gas-phase products formed during PCE photocatalysis over TiO 2 were identified. • Oxygen promotes oxidative dechlorination and mineralization of PCE. • Water redirects chlorine chemistry toward HCl and HOCl formation. • A photocatalytic degradation pathway is proposed based on identified products. Tetrachloroethylene (PCE) is a fully chlorinated ethene whose photocatalytic transformation involves coupled carbon oxidation and chlorine-release processes. Although gas-phase PCE photocatalysis over TiO 2 has been investigated using conventional analytical techniques, the evolution of gaseous products and the effects of reaction atmosphere remain incompletely resolved. In this study, online synchrotron radiation photoionization mass spectrometry (SR-PIMS) was employed to investigate the photocatalytic degradation of gaseous PCE over TiO 2 under 360 nm LED irradiation. Photoionization efficiency (PIE) analysis enabled the identification of CO, CO 2 , Cl 2 , COCl 2 , HCl, and HOCl as major gaseous products. Signals tentatively assigned to C 2 OCl 3 and C 2 Cl 5 were also observed, although their neutral precursors could not be unambiguously established. Systematic variation of the reaction atmosphere revealed distinct effects of O 2 and H 2 O on the observed product chemistry. Increasing O 2 availability was accompanied by a decrease in the PCE signal and increased formation of CO 2 , COCl 2 , and Cl 2 , consistent with enhanced oxidative transformation and dechlorination under the investigated conditions. In contrast, the introduction of water vapor resulted in the appearance of HCl and HOCl, while no obvious change in PCE signal intensity was observed between the dry and humid aerobic experiments. These observations indicate that O 2 and H 2 O influence different aspects of PCE photocatalytic transformation, with O 2 affecting the observed conversion and oxidation/dechlorination products and H 2 O primarily affecting chlorine-product speciation. The results provide experimentally based constraints on possible PCE degradation pathways under the investigated low-pressure conditions. Download: Download high-res image (98KB) Download: Download full-size image