DPV-assisted understanding of TiO2 photocatalytic decomposition of aspirin by identifying the role of produced reactive species

A TiO2/UV photocatalytic process generates various reactive species via different oxidation and reduction routes and thus the contribution of such reactive species to the decomposition of organic chemicals in water has been unclear. In this study, decomposition of acetylsalicylic acid (ASA) as a probe was performed to find the specific role of charge carriers (e(cb)(-) and h(vb)(+)) and primary active species (such as O-center dot(2)-, (OH)-O-center dot, (HO2)-H-center dot, and H2O2). Differential pulse voltammetry (DPV) was introduced as an in-situ fast electrochemical method to identify produced intermediates. The study revealed that hydroxyl radicals ((OH)-O-center dot) produced by reduction of oxygen with e(cb)(-) and subsequent primary reactions (reduction pathway) play the major role in the photocatalytic decomposition of ASA, in comparison to direct oxidation of OH- or ASA by h(vb)(+) (oxidation pathway). The in-situ DPV analysis probed that sequential (OH)-O-center dot addition to the ASA aromatic ring is the favorable oxidation mechanism.