Photoinduced halophenol formation in the presence of iron(III) species or cadmium sulfide

Phenol photo-induced decomposition has been investigated in the presence of iron(III) oxide or iron(III) ions at different pH, paying particular attention to the evolution of intermediates. The addition of halides causes a modest decrease in phenol degradation rate and starts additional transformation pathways. Chloride induces the formation of chlorinated compounds (2- and 4-chlorophenol), whose concentrations are strongly dependent on pH. Analogously, bromide ions lead to the formation of bromophenols. Similar investigations have been performed by adopting cadmium sulfide as a photocatalyst, whose valence band edge potential (E(VB)degrees) allows the oxidation of bromide but not chloride. The addition of chloride does not lead to chlorophenols, while bromide causes the fort-nation of bromophenols, thus confirming the possibility of obtaining selective abiotic halogenation of phenol. (C) 2004 Elsevier B.V. All rights reserved.