Efficient solar-driven degradation of diclofenac in aquatic environments using Cu-TiO2/Kaolin thin films: insights from different water matrices

Photocatalysis has gained considerable attention for the degradation of hazardous pollutants. In this study, the photocatalytic efficiency of Cu(0.50%)/TiO₂/Kaolin thin films was evaluated for the removal of diclofenac (DCF), a widely used non-steroidal anti-inflammatory drug, from aquatic environments. The photocatalytic activity of the thin films was assessed in three different water matrices: distilled water (DW), tap water (TW), and river water (RW), using pollutant concentrations reflective of environmental levels. The catalyst’s effect was more pronounced in RW. Under solar irradiation, the films achieved high DCF removal rates, demonstrating their low energy requirements. The degradation rate constants were 0.496 h⁻¹, 1.097 h⁻¹, and 2.560 h⁻¹ for DW, TW, and RW, respectively, at an initial DCF concentration of 25 mg/L. These findings indicate that Cu(0.50%)/TiO₂/Kaolin thin films exhibit robust photocatalytic activity under direct sunlight across different water matrices without significant activity suppression. Degradation mechanisms were proposed based on the transformation products identified. Additionally, toxicity assays employing Vibrio fischeri revealed that while DCF increases toxicity in aquatic systems, photocatalysis with Cu(0.5%)/TiO₂/Kaolin under solar irradiation significantly reduced it, though the final solutions remained “toxic”. In contrast, photocatalysis under UV irradiation, despite achieving faster DCF degradation, did not reduce toxicity, which remained close to 100%. This work provides evidence of advanced DCF degradation under direct sunlight, highlighting the potential of Cu(0.50%)/TiO₂/Kaolin thin films for sustainable water treatment applications.