Matrix influence on antibiotics photocatalytic removal from water by magnetic TiO₂–Carbon Quantum Dots composites

Over the years, global consumption of antibiotics has increased, as has their presence in the environment, mainly due to the discharge of ineffectively treated wastewater. Until 2045, Urban Wastewater Treatment Plants (UWWTP) with a population equivalent load of 150,000 or more must implement quaternary treatments to promote the removal of micropollutants, such as antibiotics. For such a purpose, solar-driven photocatalysis is considered promising. In this study, a novel photocatalyst composed of TiO₂, Carbon Quantum Dots (CQD), and magnetic nanoparticles was produced using co-precipitation. The produced magnetic TiO₂/CQD composite was tested for the removal of 3 antibiotics (amoxicillin (AMX), sulfamethoxazole (SMX) and trimethoprim (TMP)) under simulated solar irradiation and different operation conditions: pH (6, 7, 8 and 9), dissolved organic matter (10, 20 and 40 mg/L), and water matrices with distinct complexity (phosphate-buffered ultrapure water at pH 8 and secondary UWWTP effluent (sUWWTPe)). Tests at different pH levels revealed no significant effect of pH for most antibiotics. Conversely, 10 mg/L of dissolved organic matter enhanced the photodegradation of the tested antibiotics, whereas higher concentrations slowed the removal of all antibiotics and decreased photocatalyst efficiency. In PBS, the magnetic TiO₂/CQD photocatalyst resulted in a 154-fold increase in the photodegradation kinetic rate compared to photolysis. Meanwhile, in sWWTPe, the photodegradation kinetic rate increased by 2 times for both TMP and SMX, whereas external factors hindered precise quantification of the kinetic rate enhancement for AMX. Furthermore, the magnetic TiO₂/CQD photocatalyst improved antibiotics mineralisation, reaching 80% after 15 h of irradiation for AMX and TMP and 30 h for SMX, compared with only 20% without the photocatalyst. Therefore, the applied photocatalyst is a promising option for solar-driven quaternary wastewater treatments in UWWTP, enabling the sustainable removal of antibiotics.