Adsorption characteristics of three microplastics for thiamethoxam in water

This study investigated the adsorption behavior of the neonicotinoid pesticide thiamethoxam (THM) on three common microplastics, polyethylene (PE), polypropylene (PP), and polystyrene (PS). Batch experiments were conducted and analyzed using adsorption isotherm, kinetic and thermodynamic models, complemented by SEM and FTIR characterization. The adsorption isotherms were better described by the Langmuir model, and the kinetic data were best fitted by the pseudo-second-order model. Thermodynamic parameters indicated a spontaneous and endothermic adsorption process, with both equilibrium capacity and adsorption rate following the order PS > PP > PE. FTIR spectra showed almost unchanged characteristic bands of the microplastics before and after adsorption, and together with the relatively low enthalpy changes, confirmed that THM adsorption was dominated by physisorption. Overall, differences in chemical structure and surface properties among the three microplastics are key factors governing their distinct adsorption capacities for THM. These findings provide fundamental data and scientific support for assessing the environmental behavior and risks of microplastic–pesticide co-contamination.