A floatable TiO2–Ag photocatalyst enables effective antibiotic degradation and pathogen growth control†

This study explores the powerful capabilities of a floatable photocatalyst, TiO₂–Ag immobilized on expanded clay (EC), for photocatalytic antibiotic degradation and pathogen inhibition in aquaculture systems. The porous and floatable nature of EC makes it an ideal carrier for enhancing photocatalytic activity, enabling the easy recovery and reusability of TiO₂–Ag. The synthesis of TiO₂–Ag/EC is optimized by adjusting TiO₂–Ag concentration, integration time, and stirring speed, with a peak Ti content of 2584.51 ± 49.52 ppm achieved under specific conditions (35 000 ppm TiO₂–Ag, 12 hours integration, 100 rpm stirring). Remarkably, within 2 hours of sunlight exposure, TiO₂–Ag/EC (10% w/v) reduced the pathogenic density of Vibrio harveyi, Vibrio parahaemolyticus, and Escherichia coli from 10⁶ CFU mL⁻¹ to under 100 CFU mL⁻¹, maintaining antibacterial efficacy even after seven cycles. Beyond pathogen control, TiO₂–Ag/EC degraded over 92% of tetracycline and oxytetracycline at pH 7–9 and achieved up to 95.7% rifampicin removal at pH 5, within 4 hours of sunlight exposure. The degraded antibiotic solution lost its bactericidal activity, suggesting the safety of the formed byproducts for the environment. Notably, at the TiO₂–Ag/EC addition ratio of 2.5% w/v, equivalent to a Ti concentration of approximately 62.5 ppm, the material reached a maximum COD removal efficiency of 82.7 ± 2.0% after 40 hours of illumination. These results highlight the potential of TiO₂–Ag/EC as a sustainable solution for eliminating antibiotic residues, organic matter, and controlling disease spread in aquaculture environments.