Investigation of the Adsorption of Sulfamethoxazole by Degradable Microplastics Artificially Aged by Chemical Oxidation.

In this study, three different types of microplastics were aged by the thermal activation K2S2O8 method to investigate the adsorption behavior for sulfamethoxazole (SMX) in aqueous solution. The effects of pH, salinity and humic acid (HA) on adsorption behavior were also investigated. At the same time, the morphology and functional groups of microplastics before and after adsorption were characterized. As the aging time increased, the adsorption capacity of the microplastics also increased significantly. Whether it was pristine or aged, polylactic acid (PLA) had the highest adsorption capacity. The adsorption capacity of microplastics was the largest under acidic conditions, and its adsorption capacity decreased significantly in alkaline solutions. The presence of salinity inhibited the adsorption of SMX on polyethylene terephthalate (PET) and PP, but the adsorption capacity of PLA increases when salinity was above 10‰. The adsorption of SMX on microplastics was promoted by HA. When the concentration of HA was 20 mg/L, the adsorption capacity of PLA and PET decreased. Kinetic and isotherm fits were applied to the adsorption process. The increase in sorption capacity was related to the development of holes and cracks and the enhanced number of surface oxygen-containing functional groups. The adsorption kinetics to pristine microplastics conformed to a pseudo-first-order kinetic model, while the kinetics of the aged microplastics conformed to a pseudo-second-order kinetic model. It implies that the adsorption of SMX by aging microplastics involves multiple processes. The adsorption isothermal adsorption process of SMX by microplastics accorded with Freundlich model, belonging to multi-layer adsorption.