Visible-Light-Induced Photocatalytic Degradation of Naproxen Using 5% Cu/TiO₂, Transformation Products, and Mechanistic Studies

The presence of drugs in wastewater effluent is of concern due to their effects on the aquatic fauna and flora and there are growing efforts for their removal from the environment. In this paper, we study the photocatalytic visible-light degradation of naproxen, an over-the-counter anti-inflammatory drug, using 5% copper-doped TiO₂. The photocatalyst was characterized by XRD and BET surface area measurements. The optimal conditions for the degradation of 1 × 10⁻³ M of naproxen were found to be 3 h, with a catalyst loading of 50 mg/100 mL of the drug solution, and an acidic pH of 4.55. The degradation followed pseudo-first order kinetics and achieved a photodegradation efficiency of 44.8%. HPLC was used to separate the degradation products and their structures were determined using MS/MS data. A pathway for the degradation of naproxen is proposed along with degradation mechanisms. The major degradation events involve the formation of hydroxyl radicals, hydroxylation, keto-enol tautomerism, and decarboxylation.