Effect of Aged Microplastics on Photodegradation Behavior of Sulfamethoxazole
Sulfamethoxazole (SMX) and microplastics (MPs) are ubiquitous co-existing pollutants in aquatic environments. This study investigated the effects of polyethylene (PE), polypropylene (PP), and polystyrene (PS) MPs with varying aging degrees on the photodegradation of SMX. In the absence of MPs, SMX photodegradation was only 28%, while the presence of virgin PE increased it to 34%. Aging PE for 200, 400, and 600 h further enhanced degradation to 46%, 56%, and 77%, respectively. Pseudo-first-order kinetics showed that the rate constant (kobs) increased from 0.066 h−1 to 0.224 h−1 with aged PE. Aged MPs generated more reactive oxygen species (ROS) under irradiation, including hydroxyl radicals (·OH), singlet oxygen (1O2), and superoxide anions (O2·−), as confirmed by radical quenching and EPR analysis. Density functional theory identified the benzene ring, five-membered heterocycle, and sulfonyl group as primary ·OH attack sites. LC-MS analysis revealed degradation products such as p-aminobenzenesulfonamide, indicating both direct and indirect photolysis pathways. This work provides mechanistic insights into antibiotic-MP interactions and informs strategies for managing co-existing pollutants.