Comparative study on the adsorption and desorption behaviors of quinolone pollutants on polystyrene microplastics of different particle sizes

The role of microplastics (MPs) as pollutant carriers in aquatic environments has gained considerable attention. However, the impact of MP particle size on pollutant adsorption and desorption behavior, as well as the underlying mechanisms, remains insufficiently explored. This study examines the adsorption and desorption differences in adsorption and desorption behavior of quinolone pollutants, ciprofloxacin (CIP) and gatifloxacin (GAT), onto polystyrene (PS) MPs of four different particle sizes. The adsorption process for different sizes of PS follows the Langmuir isotherm model and is a spontaneous, exothermic reaction. Smaller PS demonstrate higher adsorption capacity due to their larger specific surface area, higher surface negative charge, and increased oxygen-containing functional groups. Adsorption is primarily governed by electrostatic interactions and π-π interactions, with oxygen-containing functional groups on smaller PS further enhancing adsorption via hydrogen bonding. Comparative analysis of the acid dissociation constant (p K a ) and octanol-water partition coefficient ( K ow ), along with characterization results, indicate that GAT exhibits higher adsorption onto PS than CIP, primarily due to stronger electrostatic and hydrophobic interactions. Desorption experiments reveal these stronger interactions between smaller PS and pollutants result in more difficult pollutant desorption, enhancing the mobility of pollutant-loaded MPs in aquatic environments and elevating the risk of bioaccumulation. This study offers valuable insights into how MP particle size influences pollutant adsorption and desorption, contributing to a deeper understanding of the environmental interactions between MPs of varying sizes and pollutants. • Adsorption and desorption of quinolones on PS MPs of different sizes were compared. • Adsorption on smaller PS is controlled by intraparticle diffusion, unlike on larger PS. • Environmental factors influence adsorption of PS consistently across different sizes. • Differences in electrostatic and hydrophobic interaction affect pollutant adsorption. • Smaller PS MPs exhibit stronger pollutant retention, making desorption more difficult.