Photocatalytic degradation of a ternary antibiotic mixture using UV/TiO₂ and UV/ZnO: Kinetics and mechanistic insights

Antibiotic resistance represents one of the most pressing global health challenges of the modern era. The widespread use of antibiotics leads to their dissemination into aquatic environments, posing a significant threat to both public health and ecosystem integrity. This study investigates the photocatalytic degradation of a ternary antibiotic mixture- Sulfamethoxazole (SMX), Trimethoprim (TRM), and Oxytetracycline (OTC)- using UV/TiO₂ and UV/ZnO processes. The experiments were conducted at an initial antibiotic concentration of 10 mg/L for each compound and a catalyst loading of 0.7 g/L for both TiO₂ and ZnO nanoparticles. The removal efficiency for all antibiotics increased with irradiation time, reaching a maximum after 1920 min, which corresponded to a decrease in their relative concentrations. The degradation kinetics were found to be dependent on the type of photocatalyst used for a given antibiotic. Among the three antibiotics, Oxytetracycline (OTC) exhibited the highest removal efficiency with both catalysts. Comparative analysis revealed that TiO₂ demonstrated superior photocatalytic activity for the degradation of Trimethoprim and Sulfamethoxazole, whereas ZnO was more effective for Oxytetracycline.