Photocatalytic Degradation Study of Paroxetine with g-C3N4 Prepared Using Different Precursors in Lab- and Pilot-Scale Conditions

The degradation of pharmaceuticals in wastewater treatment plants (WWTPs), particularly the antidepressant Paroxetine (PXT), is a growing concern because their insufficient removal leads to their release in the aquatic environment, causing toxic effects on aquatic organisms. This study investigates g-C3N4 materials synthesized from urea, melamine, and thiourea, including thermally exfoliated variants, as potential photocatalysts for removing PXT from water and secondary-treated hospital wastewater (HWW). Comparative photocatalytic experiments under simulated solar radiation indicated that g-C3N4 prepared by urea (CN-U) and its thermally exfoliated form [CN-U(exf.)] were highly effective (100% removal in 45 min) depending on the degradation rate constants (0.036 and 0.085 min−1 in U.P. water, respectively), with the latter achieving the fastest PXT degradation at 200 mg/L (k = 0.112 min−1). The study also analyzed mineralization and transformation products (TPs) using liquid chromatography–high-resolution mass spectrometry (LC–HR-MS-Orbitrap) and assessed their ecotoxicity with ECOSAR (Version 2.2) software. Additionally, toxicity decreased following the photocatalytic processes, as revealed by the Microtox bioassay. Overall, CN-U and especially CN-U(exf.) show promise as eco-friendly photocatalysts for pharmaceutical removal from wastewater (WW).