Adsorption behavior and mechanism of tetracycline on microplastics subjected to peroxymonosulfate and alkaline aging

Microplastics (MPs) served as potential vectors for antibiotics in aquatic environments. The adsorption between MPs and antibiotics may be potentially affected by the aging processes for MPs. This study aimed to investigate the adsorption of tetracycline (TC) on polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET) and polylactic acid (PLA) aged by ferrous ion/peroxymonosulfate (Fe2+/PMS) and alkaline treatments. The results showed that both the physical and chemical properties of MPs experienced significant changes after aging. The surfaces of all four types of MPs became rougher, resulting in an increased specific surface area and a slight decrease in particle size. The O/C ratio was significantly increased after aging for PS and PP, which was changed slightly for PET and PLA. For PLA, the changes in crystallinity and hydrophobicity were different from the other three non-biodegradable MPs, with hydrophobicity enhancing after aging. The adsorption capacity of all four types of MPs for TC significantly increased after aging from the adsorption experiments. Particularly, after aging with Fe2+/PMS, the adsorption capacity of PET for TC increased to its highest value of 1.34 mg center dot g- 1. Mechanism analysis indicated that the chemical adsorption of TC on MPs was mainly influenced by it-it interactions and hydrogen bonds.