Aging Mechanism of Microplastics in UV/Persulfate System and Its Effect on Norfloxacin Adsorption Behavior
This study investigates the aging mechanism of polystyrene microplastics (PS MPs) induced by ultraviolet (UV)-activated potassium persulfate (KPS) and its influence on the adsorption of norfloxacin (NOR). Results show that aged PS exhibited yellowing, increased surface roughness and specific surface area, enhanced oxygen-containing functional groups, and elevated negative surface charge, along with the generation of environmentally persistent free radicals (EPFRs). Compared with UV alone, UV+KPS induced more pronounced aging due to the generation of reactive oxygen species (ROS) including hydroxyl radicals (·OH) and superoxide radicals (O2·−). Adsorption kinetics and isotherm data revealed that UV+KPS-aged PS significantly enhanced NOR adsorption, with a maximum adsorption capacity of (2.539±0.032) mg·g−1, which was 4.20 times higher than that of pristine PS. The adsorption mechanism was governed by hydrogen bonding, electrostatic interactions, and pore filling. Solution pH modulated the electrostatic interactions by affecting NOR speciation and PS surface charge, thereby influencing NOR adsorption. This study systematically reveals the accelerated aging of coexisting MPs and EPFRs generation during UV+KPS treatment, contributing to a comprehensive understanding of MPs environmental behavior and potential ecological risks.