Exploring the molecular mechanisms of herbicide adsorption on microplastics: A quantum chemical approach

The widespread presence of microplastics in the environment has raised significant concerns, particularly regarding their potential interactions with herbicides and the combined pollution effects on ecosystems. In this study, quantum chemical calculations were employed to investigate the interaction mechanisms between polyethylene (PE) and polyvinyl chloride (PVC) microplastics and phenoxyacetic herbicides. The results revealed that PVC exhibits a stronger adsorption capacity compared to PE, and that low ionic strength conditions weaken the interactions between microplastics and herbicides. The energy decomposition analysis indicates that dispersion and electrostatic interactions are the predominant components contributing to the interaction energy, thus positioning the herbicide adsorption sites on microplastics near the minima of van der Waals and electrostatic potentials. The presence of hydrogen bond acceptors in microplastics influences the formation of intramolecular or intermolecular hydrogen bonds with the carboxylic groups of herbicides, resulting in significant changes in vibrational modes and infrared spectral absorption peaks, which offers a potential method for in situ monitoring of herbicide adsorption on microplastics. Additionally, different charge transfer phenomena are observed during the adsorption process, with PVC tending to lose electrons and PE to gain electrons. These insights provide a theoretical foundation for a deeper understanding of the adsorption behavior of phenoxyacetic herbicides on microplastics and hold significant implications for the optimization of environmental remediation strategies.