Photocatalytic degradation of antibiotics: The case of sulfamethoxazole and trimethoprim

The aim of this study is the evaluation of photocatalysis to degrade two antibiotics widely used in both human and veterinary medicine: sulfamethoxazole (SMX) and trimethoprim (TMP), in aqueous medium. The degradation of SMX and TMP, and the TOC reduction, were improved when TiO2 concentration was increased, up to 0.5 and 0.2–0.5 g TiO2 L−1 in the case of SMX and TMP, respectively, where the scattering phenomena start being noticeable. The comparison between photocatalysis and photolysis shows that the SMX degradation is improved when the catalyst is present in the solution. In the case of TMP, the final degradation achieved by the two processes is similar, but the evolution during time can be clearly differentiated, indicative of different reaction pathways. Surprisingly, when monitoring the aromatic content during TMP photocatalysis, this increases to a large extent during the first 3 h. On the contrary, the photocatalytic degradation of SMX results in a gradual cleavage of the molecule, because the aromatic content decreases gradually during the photocatalytic reaction (72%). Finally, the experimental data of both antibiotics were fitted to a simple model, taking into account the effect of the radiation on the kinetic constants.