Adsorption of Polystyrene (PS) Microplastic from Aqueous Solution by Black Tea Magnetic Nanoparticles (BTMNPs): Adsorbability, Mechanism, and Reusability

Microplastics (MPs) derived from plastic waste are a major environmental concern due to their wide distribution and potential threats to organisms. The removal of MPs is essential, especially when they carry pollutants. In this study, we explored the magnetic adsorption efficiency of multiple Polystyrene (PS) MP sizes by Black Tea Magnetic Nanoparticles (BTMNPs). BTMNPs were synthesized by green method with various promising capabilities i.e., fast adsorption (15 min for 900 µm, 18 min for 500 µm and 200 µm PS MPs), high capacity (745.94 mg/g for 900 µm, 581.33 mg/g for 500 µm, and 579.09 mg/g for 200 µm), strong magnetization (37 emu/g), complete separation by magnet, excellent interference-tolerance and reusability. Our results indicate that multiple mechanisms including π-π interaction, hydrogen bonding, and electrostatic interaction, effectively can compensate for the adsorption of PS MPs on BTMNPs. The FTIR and SEM images confirmed the adsorption of PS MPs on BTMNPs. The adsorption process is likely a monolayer and occurs on a homogeneous surface, as indicated by a superior fit of the Langmuir isotherm model. The adsorption kinetics followed a pseudo-second-order model, suggesting a quick and strong interaction between PS MPs and BTMNPs. Given the relative size difference, PS MPs are significantly larger than the BTMNPs and are attached to the surface of the PS MPs via strong surface interaction. This study shows that BTMNPs are efficient in PS MP removal and highlights their potential use as a sustainable method to address environmental pollution caused by plastic waste.