Oxidation of microplastics by O3 and O3/H2O2: Surface modification and adsorption capacity

Abstract When Microplastics (MPs) pass through wastewater treatment plants equipped with advanced oxidation systems, they might be oxidized, thus changing their surface characteristics and adsorption behavior. This work evaluated if ozone (O3) and the association of O3 and hydrogen peroxide (H2O2) are capable of changing the adsorption potential of three plastics present in water. Polyethylene (PE), polypropylene (PP) and polystyrene (PS) MPs were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR) analyses. To perform this study, the sorption of two pesticides, chlorpyrifos (CPF) and dichlorvos (DDVP), onto PE, PP and PS was analyzed using different kinetic and isotherm models. The sorption capacity follows the trend of PE > PP > PS. The second-order kinetic model described the sorption kinetics of DDVP and CPF, with an R2 higher than 0.99 for CPF in all plastics and ranging from 0.96 to 0.98 for DDVP in all plastics. Freundlich and Henry isotherm models described the adsorption mechanism of DDVP and CPF, respectively. O3 and O3/H2O2 oxidation were able to modify the adsorption behavior by the formation of carbonyl and hydroxyl groups in MPs, thus, changing chemical interactions between adsorbate-adsorbent. This study demonstrated that MPs might have their adsorption characteristics changed if submitted to oxidation processes used in wastewater treatment plants, thus, changing their interaction with micropollutants when released into the environment.