Removal of polystyrene nanoplastics from aqueous solutions using a novel magnetic material: Adsorbability, mechanism, and reusability

Nano/microplastics (NPs/MPs) in aquatic systems have become a special source of concern to the global environment and have attracted widespread attention over the years. However, there is no effective method to remove MPs from sewage. In this study, fly ash, as a raw material, is modified with Fe ions, thereby synthesizing a new magnetic material (NMA) to remove polystyrene nanoplastics (PNPs) from aqueous solutions. The various characterization analyses show the strong interaction between NMA adsorbents and PNPs, and they show that the PNPs are successfully attached to the surface and pores of the material. Additionally, the pH range between weak acidity and neutrality is favorable to the adsorption of PNPs, and the adsorption amounts of PNPs are 82.8–89.9 mg g−1 at pH 5–7. The existence of competitive ions can significantly affect the removal of PNPs. Kinetic, isothermal, and thermodynamic models are employed to analyze the potential adsorption mechanism, which reveals that electrostatic attraction, complexation, and π–π interactions are involved in the adsorption process. Further, the adsorption–desorption experiments show that the NMA adsorbents have excellent reusability for PNPs; they can be used 4 times. Therefore, the inexpensive and reusable NMA adsorbents can control the NPs/MPs contamination.