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

The photodegradation of phenol was investigated in the presence of TiO2 (anatase) as photocatalyst in near-UV-irradiated aqueous unbuffered suspensions. The distribution of degradation products and a reduction in total organic carbon are reported, focusing on the influence of charge-trapping species (O2, Ag+ and H2O2). In the presence of dissolved O2, the degradation proceeds predominantly via OH⋅, where hydroxylated aromatics were detected: catechol, hydroquinone and 1,2,4-trihydroxybenzene; in the presence of Ag+, the direct hole oxidation dominates, with p-benzoquinone as the only identified transient product; in the presence of H2O2, both OH⋅ and direct oxidation by positive holes contribute to the degradation of phenol. Besides the identified compounds, the formation of presumed ring-opening products occurs simultaneously. In contrast with the general view, it is pointed out that the appearance of aliphatic products in the early stage of the oxidation process is not unambiguous proof of the participation of direct hole oxidation in the degradation mechanism.