Photocatalytic degradation of non-steroidal anti-inflammatory drugs with ketoprofen as model compound. Intermediates and total reaction mechanism

Ketoprofen KET and other non-steroidal anti-inflammatory drugs NSAIDs are extensively used throughout the world to reduce pain, fever, and inflammation. As a result of this, they have been detected in environmental waters and represent a potential health risk. There are several reports about KET photocatalytic degradation but most of them deal with experimental conditions or catalytic materials to perform this process. In this study, the mechanisms and intermediates involved in KET photocatalysis with TiO₂ in aqueous media were investigated. First, the mineralization rate was assessed by TOC measurements. The formation and eventual degradation of intermediate organic compounds were investigated by HPLC, UV–Vis, IR, ¹H NMR and HPLC-MS studies. TOC analysis indicate that KET is quickly transformed into other compounds that eventually are degradated and 70 % mineralization was achieved after five hours of irradiation. UV–Vis and HPLC studies indicate that KET is transformed into some other aromatic compounds within minutes. IR studies demonstrate the conversion of KET into several aromatic compounds which in turn degradate into low molecular saturated and unsaturated acids. ¹H NMR studies indicate KET is transformed into several aromatic compounds such as 3-hydroxy-benzophenone, phenol, 1,4-hydroquinone, 1,2,4-benzenetriol, and catechol. HPLC-MS studies indicate KET is degradated by several photochemical and photocatalytic parallel mechanisms. Based on this and previous studies, a unified and complete mechanism for KET photocatalytic degradation is presented.