Aging Differences of Colored Microplastics and Their Adsorption Behavior towards Acesulfame

This study investigated the aging behavior differences of MPs of different colors under UV light aging and thermal activation of K2S2O8 chemical oxidation, as well as their adsorption characteristics towards the artificial sweetener acesulfame. By simulating photoaging and chemical oxidation in the laboratory, and combining surface morphology, chemical structure, and adsorption kinetics/isotherm models, the impact of color on the aging process and the adsorption behavior of aged MPs were systematically assessed. The results showed that the aging effect of thermal activation of K2S2O8 was significantly better than that of UV light aging, with the CI of red PE increasing the most (photoaging: 0.0765; chemical oxidation: 0.1081), and the surface wrinkles and cracks increased, providing more adsorption sites. Color had a significant impact on photoaging, with red PE aging and fading more easily due to its light absorption characteristics, while black MPs had a lower degree of aging due to the shading effect and the action of antioxidants. Aging significantly enhanced the adsorption capacity of PE for acesulfame, with the highest adsorption amount of PE treated by thermal activation of K2S2O8 (2.478 mg/g), which was 33.8% higher than that of the original PE. Adsorption kinetics indicated that the adsorption process of the original and photoaged PE conformed to the pseudo-first-order model (dominated by physical adsorption), while the PE treated by chemical oxidation conformed more to the pseudo-second-order model (synergistic effect of physical and chemical actions). Isotherm adsorption followed the Freundlich model, indicating a multilayer heterogeneous adsorption mechanism. This study revealed the regulatory effect of color on the aging behavior of MPs and clarified the mechanism by which the aging process enhanced the adsorption capacity for pollutants by changing surface physicochemical properties. It provides a theoretical basis for assessing the environmental risk of colored MPs and the migration and transformation of artificial sweeteners.