Triclosan photolysis: operating condition study and photo-oxidation pathway

In this paper, Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol; TCS) photodegradation is studied by using a lab-scale experimental apparatus with a parametric variation study. Experiments were performed by using a lab view experimental set-up, consisting in a batch reactor (Petri dish) irradiated by UV-light at a wavelength of 254 nm and an UV dose of 400 mJ m−2. The effect of Triclosan initial concentration (TCS0), irradiated solution volume (V), solution initial pH (pH), nitrate anions (NO3−) and humic acids (HA) as a function of the irradiation time (0–60 min) is investigated, in order to study both direct photolysis and the combination of direct and indirect photolysis. Furthermore, TCS heterogeneous catalytic photolysis is studied when titanium dioxide (TiO2) is added to the experimental solution. The main obtained results have shown that TCS removal seems not to be significantly affected by TCS0 and V, while pH, NO3−, HA and TiO2 appear to be effective for TCS degradation; in particular, TCS photodegradation is enhanced by titanium dioxide. Finally, photo-oxidation by-product identification was performed, by determining 2,8-DCDD and 2,4-DCP as TCS photolysis reaction products, and a photoreaction pathway has been proposed, which allowed to assess TCS photolysis degradation rate constants, 2,8-DCDD and 2,4-DCP generation rate constants.