9 Identification of reaction intermediates/products from the photocatalytic degradation of trichloroethylene on illuminated titanium dioxide surfaces

摘要

The objective of this study was to identify reaction intermediates/proceducts from the gas-phase photocatelytic degradation of trichloroethylene (TCE) on anatase titanium doixide (TiO_2) surfaces illuminated with near-ultraviolet light (360 nm wavelength). A Pyrex glass annular photocataltic reactor fabricated with tubulence promoters was used for this purpose. The inne surface of the otside tube forming the annular reactor was coated with TiO_2 prepared by vapor phase hydrolysis of t itanum isopropoxide. Reaction intermediates/products were concentrated gy passing the photocatalytic reactor off-gas through a stainless steel tube immersed in lquid nitrogen. Compounds deposited were allowed to revolatilze or were washed with deionized water and analyzed by gas chromatography with a mass spectrum selective detector (GC/MS), or by ion chromatograhy (IC), respectively. Preliminary results revealed the presence of many halogenated organic compounds, including phosgene, 1, 2-dichloroethylene, chloroform, carbon terachloride, dichloroacetyl chloride, 1, 1, 2-trichloroethane, tetrachloroetylene, 1, 1, 2, 2-tetrachloroethane, pentichloroethane, and hexachloroethane, as well as hydrochloric acid. The abundance of most of these compounds except phosgene and hydrochloric acid was observed to diminish with increasing oxygen concentrations. Possible reaction mechanisms and pathways for the photocoatalytic degradation of TCE will be presented