Degradation of Benzotriazole UV-stabilizers in the presence of organic photosensitizers and visible light: A time-resolved mechanistic study.

Benzotriazole UV-stabilizers (BUVSs) are commonly used in industry as solar filters, due to their strong UV light absorption. Because of their extended usage, environmental contamination of waters due to BUVSs constitutes a growing concern. Direct photodegradation of BUVSs is not efficient due to their intrinsic thermal pathways to release the absorbed light. Nevertheless, their abatement in natural environments could be assisted by chromophoric dissolved organic matter. Among the BUVSs, three representative candidates were selected, UV-326, UV-327 and UV-328, to demonstrate the potential of Riboflavin (RF) as a natural visible-light absorbing photocatalyst for the abatement of these recalcitrant pollutants under reductive conditions. The use of visible light and DABCO, as a model sacrificial electron donor, generates the radical anion RFTA. This key species reacts with the solar filters, achieving their reductive abatement from the medium. Moreover, the participation of every potential reactive species has been investigated by photophysical techniques, together with determination of the quenching rate constant for every reaction pathway. Consequently, evidence supported the main role of the reductive photodegradation pathway, being RFTA the key species in the abatement of BUVSs.