Photoinduced halophenol formation in the persence 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 (EVB°) allows the oxidation of bromide but not chloride. The addition of chloride does not lead to chlorophenols, while bromide causes the formation of bromophenols, thus confirming the possibility of obtaining selective abiotic halogenation of phenol.