Photocatalytic Transformation of 2,4,5-Trichlorophenol on TiO2 under Sub-Band-Gap Illumination

Abstract

The adsorptive behavior of TiO2 under various illumination conditions was investigated. In the dark, Degussa P25, which contains both the anatase and rutile phases of TiO2, adsorbed significantly greater amounts of 2,4,5-trichlorophenol (TCP) than either pure anatase or pure rutile. Results in the literature and in our laboratory that appeared to indicate “photoenhanced adsorption” under ambient fluorescent lighting on P25 and anatase are in fact due to the photoreaction of TCP. On pure-phase anatase, all reactions are due to trace ultra-band-gap energy light present in the fluorescent lighting. On P25, however, reaction also occurs at sub-band-gap energies. TCP forms a charge-transfer complex with P25 that is activated by light wavelengths as long as 520 nm. The trichlorophenoxyl radicals resulting from charge-transfer couple with each other to form a suite of polyaromatic chlorinated products with detected masses as high as 1200 D. These products are not formed under UV irradiation and in fact are destr...