Light-induced generation of radicals on semiconductor-free carbon photocatalysts

This work provides an experimental evidence of the photoinduced generation of radical species upon UV irradiation of aqueous suspensions of carbon materials with varied textural, structural and chemical composition. The use of a powerful spectroscopic tool as spin trapping electron spin resonance (ESR) has allowed to detect and identify these radicals (among which are hydroxyl, superoxide and other organic radicals), which are the basis of the so-called Advanced Oxidation Processes. Our results demonstrate the ability of carbon materials – including activated carbons – to interact with UV light, and also to generate highly reactive species capable of promoting the photooxidation of an aromatic pollutant. Moreover, for some of the carbons the concentration of radicals was higher than that detected for titania powders. Although the photogeneration of radicals upon irradiation is a well-known process for inorganic semiconductors such as titanium oxide or zinc oxide, our results demonstrate a similar behavior on carbon materials in the absence of semiconductor additives.

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► UV irradiation of free-semiconductor carbons from solution generates radicals.
► Hydroxyl and superoxide radicals have been detected by ESR.
► Photoinduced reactions occur at semiconductor free carbon materials.
► Higher amounts of radicals were detected for some carbons compared to TiO2.
► These radicals account for the photocatalytic activity of carbon materials.