Evaluation of metal-oxide semiconductors for the photocatalytic degradation of chloroquine phosphate in real-world water matrices

Abstract The persistence of pharmaceuticals in aquatic environments poses an increasing threat to aquatic ecosystems and human health, as conventional wastewater treatment plants often fail to remove contaminants of emerging concern (CECs) effectively. This work offers a systematic comparative assessment of the photocatalytic activity of TiO₂, ZnO, CeO₂, Bi₂O₃, and WO₃ nanoparticles for degrading chloroquine phosphate (CLQ), a widely used antiviral and anti-inflammatory drug, under ultraviolet irradiation in ultrapure water, drinking water, and synthetic seawater. The semiconductors were thoroughly characterised for morphology, crystalline structure, optical bandgap, and surface charge. Reactive oxygen species (ROS) generation, including hydroxyl radicals ( · OH) and singlet oxygen (¹O₂), was measured to clarify degradation efficiency in each matrix. TiO₂ demonstrated the highest photocatalytic efficiency, achieving up to 83% CLQ degradation in drinking water, consistent with its superior ROS production. ZnO and CeO₂ showed moderate activity, with performance significantly influenced by pH and ionic composition, while Bi₂O₃ and WO₃ remained suppressed, especially in complex water matrices. Overall, this study emphasises the importance of assessing photocatalysts under realistic environmental conditions and identifies TiO₂ as the most robust and adaptable semiconductor for removing CLQ, even in complex water matrices.