PHOTOCATALYTIC DEGRADATION OF PENTACHLOROPHENOL ON TIO2 PARTICLES - IDENTIFICATION OF INTERMEDIATES AND MECHANISM OF REACTION

The photoassisted oxidation of pentachlorophenol (PCP) in TiO2 particle suspensions was investigated. Complete dechlorination of 47 muM PCP was achieved after 3 h of illumination at high intensity with apparent quantum efficiencies (PHI(PCP), PHI(Cl-), PHI(H+), PHI(H2O2)) ranging from 1 to 3 %. p-Chloranil, tetrachlorohydroquinone, H2O2, and o-chloranil were formed as the principal intermediates. Formate and acetate were formed as products during the latter stages of photooxidation. The mechanism for photooxidation of PCP proceeds via hydroxyl radical attack on the para position of the PCP ring to form a semiquinone radical which in turn disproportionates to yield p-chloranil and tetrachlorohydroquinone. Under high-intensity illumination, the reaction intermediates are attacked further by .OH to yield HCO2-, CH3CO2-, CO2, H+, and Cl-.