Effect of Aged Microplastics on Photodegradation Behavior of Sulfamethoxazole

• • Aging PE microplastics for 600 h increased SMX photodegradation from 34% (virgin PE) to 77%, a 2.26-fold enhancement, demonstrating that aging-induced surface changes significantly boost indirect photolysis efficiency. • • The pseudo-first-order rate constant (kobs) for SMX photodegradation rose from 0.066 h−1 to 0.224 h−1 in the presence of aged PE, a 3.4-fold increase, indicating faster removal kinetics critical for water treatment design. • • Radical quenching and EPR confirmed that aged MPs generate ROS (·OH, 1O2, O2·−), which are the primary drivers of enhanced SMX photolysis, highlighting the role of surface reactive sites in pollutant degradation. • • DFT and LC-MS identified the benzene ring, five-membered heterocycle, and sulfonyl group as main attack sites, with p-aminobenzenesulfonamide as a key product, providing molecular-level understanding for predicting degradation pathways and toxicity.