Fenton-based aging of low-density polyethylene microplastics and their adsorptive interactions with ofloxacin: kinetics and isotherm studies

Microplastics (MPs) are emerging as dynamic pollutants, whose surface properties evolve through aging and influencing their interactions with coexisting contaminants. This study investigated the oxidative aging of low-density polyethylene (LDPE) MPs via the Fenton process and their adsorption behavior toward the antibiotic ofloxacin (OFL). Optimized aging conditions significantly enhanced LDPE surface functionality, reflected by an increase in the carbonyl index from 0.221 to 0.932. Functional characteristics have confirmed the formation of oxygenated groups and morphological analysis revealed increment in roughness and crystallinity. Compared to pristine MPs, aged MPs demonstrated higher adsorption capacity for OFL, reaching equilibrium within 24 h. Maximum adsorption was found at neutral pH, due to the balance of hydrogen bonding and electrostatic interactions. Kinetic modeling followed the pseudo-second-order model. Freundlich and Dubinin–Radushkevich isotherm models better described the process, indicating heterogeneous multilayer physisorption with enhanced capacity upon aging. These results suggest that advanced oxidation processes, though effective for treatment, may unintentionally enhance MP reactivity and their role in contaminant transport. Overall, this work contributes to a deeper understanding of the evolving role of microplastics in aquatic pollution dynamics and highlights the need for integrated approaches to mitigate their environmental impact.