Investigation of the photodecomposition of phenol in near-UV-irradiated aqueous TiO2 suspensions. II. Effect of charge-trapping species on product distribution

The photodegradation of phenol was investigated in the presence of TiO2 (an atase) as photocatalyst in near-UV-irradiated aqueous unbuffered suspension s. The distribution of degradation products and a reduction in total organi c carbon are reported, focusing on the influence of charge-trapping species (O-2, Ag+ and H2O2) In the presence of dissolved O-2, the degradation proc eeds predominantly via OH., where hydroxylated aromatics were detected: cat echol, hydroquinone and 1,2,4-trihydroxybenzene; in the presence of Ag+, th e direct hole oxidation dominates, with p-benzoquinone as the only identifi ed transient product; in the presence of H2O2, both OH. and direct oxidatio n by positive holes contribute to the degradation of phenol. Besides the id entified compounds, the formation of presumed ring-opening products occurs simultaneously. In contrast with the general view, it is pointed out that t he appearance of aliphatic products in the early stage of the oxidation pro cess is not unambiguous proof of the participation of direct hole oxidation in the degradation mechanism. (C) 1999 Elsevier Science B.V. All rights re served.