Insight into the characteristics and sorption behaviors of aged polystyrene microplastics through three type of accelerated oxidation processes

Ageing process can significantly alter the structural properties, environmental behaviors and potential ecotoxicity of microplastics (MPs) in water. In this study, the structural properties of aged polystyrene (PS) MPs being exposed to UV/H₂O, UV/H₂O₂ and UV/Cl₂ artificially accelerated oxidation processes and related sorption behaviors of bisphenol A (BPA) on those virgin/aged PS were investigated. The surface oxidation and hydrophilicity of aged PS were significantly increased according to infrared spectroscopy (IR) and water contact angle (CA) measurements. The differential scanning calorimetric (DSC) and gel permeation chromatography (GPC) revealed apparent degradation of aged PS especially in their amorphous domain. Obviously deteriorative BPA sorption capacity on aged PS was observed compared with that of virgin PS. The sorption rates of BPA on aged PS were accelerated and sorption of BPA shifted from partition dominant mechanism on virgin PS to the adsorption dominant mechanism through being fitted with the dual-mode sorption model. Besides, ageing in UV/Cl₂ system introduces C–Cl groups on the surface of PS which strengthen the combination with BPA through halogen bonding interaction. Salt and dissolved organic matters (DOM) in marine water may increase the BPA sorption on aged MPs due to enhanced polar interaction.