Influence of UV wavelength variations on tetracycline adsorption by polyethylene microplastics in aquatic environments

The effect of ultraviolet (UV) light on structural changes is a significant concern, particularly regarding the weathering and aging effects on microplastics (MPs). This research focused on examining how various UV light wavelengths (UVC, UVB, and UVA) influence the adsorption behavior of aged polyethylene (PE) MPs toward tetracycline (TC). To explore the adsorption mechanism in detail, adsorption kinetics were studied under different UV light wavelengths. PE MPs exposed to UV light exhibited a slower adsorption rate in the following order: virgin PE > PE MPs/UVA > PE MPs/UVB > PE MPs/UVC. The study also evaluated changes in the adsorption mechanism with prolonged UVC irradiation. The Langmuir model was used to determine the adsorption capacity of virgin PE MPs, which was found to be 1.497 × 10 mmol·g. Notably, the adsorption capacity decreased to 0.260 × 10 mmol·g after 1 day, 0.326 × 10 mmol·g after 3 days, and 0.514 × 10 mmol·g after 7 days. Surface characterization analysis revealed that UV irradiation led to the formation of new oxygenated functional groups (OFGs), such as carbonyl and hydroxyl groups, on the PE MPs surface due to the generation of OH radicals. Additionally, surface melting caused by irradiation increased hydrophobicity, resulting in reduced TC adsorption capacity, as TC is hydrophilic. Overall, this study provides a fundamental comparison of the effects of different UV light wavelengths on PE MPs.