Aging Characteristics of PET Microplastics under Interaction of Environmental Factors and Their Adsorption Behavior toward Ciprofloxacin

The environmental risks of microplastics as pollutant vectors have garnered extensive attention. This study investigates the interactive effects of illumination, temperature, and oxidation on the surface morphology, functional groups, and adsorption behavior of conventional non-biodegradable polyethylene terephthalate (PET) using a Box-Behnken design. SEM and FTIR characterized the physicochemical properties, while kinetic and isotherm models evaluated ciprofloxacin (CIP) adsorption onto pristine and weathered PET. Results reveal that PET, inherently possessing an aromatic backbone, exhibits pronounced thermo-driven and chemical oxidative degradation. Optimal weathering occurred under UV irradiation, 60 °C, and Fenton oxidation. Post-weathering, PET displayed edge erosion, increased specific surface area, and an enrichment of secondary oxygen-containing polar sites at the solid-liquid interface triggered by polymer backbone cleavage. CIP adsorption followed pseudo-second-order kinetics, shifting from the Langmuir to the Freundlich model post-weathering. Consequently, the weathered PET achieved a 50.7% increase in adsorption capacity. This study provides critical data support for evaluating the long-term combined ecological risks of conventional microplastics and co-contaminants.