A mechanistic study on the oxidative photodegradation of 2,6-dichlorodiphenylamine-derived drugs: Photo-Fenton versus photocatalysis with a triphenylpyrylium salt

Abstract

Emerging pollutants, such as drugs, are considered a potential hazard to the environment, and therefore advanced oxidation processes are being considered candidate tools for their elimination. Here, different oxidation processes have been investigated for the degradation of the non-steroidal antiinflammatories diclofenac and meclofenamic acid, derived from the model compound 2,6-dichlorodiphenylamine. They include oxidation under photo-Fenton conditions and treatment with organic photocatalysts such as rose Bengal (RB) and triphenylpyrylium (TPP+) salts. The role of the transient species involved in these processes (hydroxyl radical, singlet oxygen and radical cations, respectively) has been investigated by means of photophysical experiments. Based on the obtained results, participation of hydroxyl radical in photo-Fenton degradation appears feasible whereas singlet oxygen has been demonstrated to be unreactive for the degradation of the selected drugs. Finally the photocatalytic activity of triphenylpyrilium salts has been ascribed to electron transfer from the drugs to the triplet excited state of TPP+; ground state complexes have also been observed in this case, although their contribution to the photodegradation process is only marginal. (C) 2013 Elsevier B.V. All rights reserved.