Kinetics and degradation pathways of photolytic and photocatalytic oxidation of the anthelmintic drug praziquantel

Abstract

In this study, an anthelmintic drug, praziquantel(PZQ), was degraded using the direct photolysis, photocatalysis, and oxidation processes including UV radiation, TiO₂ film, and hydrogen peroxide. The photolytic degradation with predominant wavelengths of 185/254nm (UV-C) proved to be more efficient with a half-life of 3.13min compared to the radiation of 365nm (UV-A) where the degradation did not occur. In order to enhance the rate of PZQ photolytic degradation, H₂O₂ was added, which resulted in two to three times higher degradation rates. In the photocatalytic degradation, TiO₂ film was used as catalyst. The degradation was ten times faster in the photocatalytic experiments where UV-C light (k=0.2390min^-1) was used than in those with UV-A (k=0.0201min^-1). Comparing the results from all performed experiments it can be concluded that the UV-C/TiO₂/H₂O₂ process yielded the highest degradation rate and complete degradation of PZQ was obtained in less than 7min. The degradation of PZQ followed the first order kinetics in all the experiments. The photo degradation was inhibited in the presence of methanol. The degradation pathways and the structural formulae of five degradation products (m/z 273, 269, 189, 147, 132) were proposed based on the liquid chromatography tandem mass spectrometry analysis.

Keywords: Pharmaceuticals; Photodegradation pathway; Photolysis and photocatalysis; Praziquantel; Titanium dioxide film.