Use of scavenger agents in heterogeneous photocatalysis: truths, half-truths, and misinterpretations

/UVA reactions. Electron paramagnetic resonance spectroscopy (EPR) was applied to investigate radicals formed in the presence of each interfering/scavenger species. Some scavengers and interfering species were studied during phenol degradation, chosen as a model substrate. All species, except bromate, hindered the degradation. para-Benzoquinone showed an increased hydroxyl radical production, attributed to the photo-reduction of quinones. Radicals other than hydroxyl radicals, such as carbon dioxide, hydroxymethyl, azide, and semiquinone, were identified in the presence of oxalate, methanol, azide, and para-benzoquinone, respectively. Some of these radicals can possibly interact with organic substrates due to their reduction potential; as a result, a critical interpretation must be done when these species are added to a heterogeneous photocatalysis process.