Influence of aging processes on PE microplastics with various oxidants: Morphology, chemical structure, and adsorption behavior toward tetracycline

Abstract

The presence of microplastics (MPs) in aquatic ecosystems and its capacity to load various environmental pollutants has garnered significant attention in recent years. Microplastics (MPs) are exposed to a variety of environmental aging processes, but the aging effect on fate of MPs in environment is poorly understood. In this study, the adsorption of tetracycline (TC) onto polyethylene (PE) MPs aged in different solutions, including H2O2, Na2S2O8, KMnO 4, and NaOCl was investigated. Aging processes were found to be responsible for surface oxidation of PE MPs, size reducibility, the production of new oxidation functional groups, and increased hydrophilicity. Based on the oxidation potential, the oxidizing agents were divided into a high-aging effect group (KMnO 4, NaOCl) and a low-aging effect group (H2O2, Na2S2O8). The adsorption capacities of MPs ranged from KMnO 4-PE (2.52 x 10−2 mmol g−1) > NaOCl-PE (2.07 x 10−2 mmol g−1)> PE (1.64 x 10−2 mmol g−1) >H2O2-PE (0.92 x 10−2 mmol g−1) > Na2S2O8-PE (0.28 x 10−2 mmol g−1). Chemical interactions, including such hydrogen bonding, and physical electrostatic attraction contributed to the adsorption of TC onto aged PE MPs. Also, parameters such as pH, temperature, and natural organic matter have a significant effect on the adsorption characteristics of aged PE MPs. This study reveals that aging microplastics may have a significant impact on the fate and mobility of pollutants, which calls for further research.