Surface-engineered anisotropic Fe₃O₄ nanoplates for highly efficient magnetic field-assisted micro/nanoplastics...

Micro- and nanoplastics (MNPs) are emerging contaminants of global concern, but their efficient removal from aqueous environments poses a critical challenge. This paper reports the development of anisotropic magnetite nanoplates (MNPLs) coated uniformly with SiO₂ to yield MNPL@SiO₂ as highly efficient magnetic nanoharvesters for MNPs. Engineering the SiO₂ surface with aminopropyl (NH₂-), octadecyl (C₁₈-), and phenylethyl (Ph-) groups to tune the electrostatic, hydrophobic, and π-π interactions enabled optimally functionalized MNPL@SiO₂ to show rapid and highly efficient MNPs remediation, with 93.4 %, 92.1 %, and 94.3 % removal efficiencies (REs) for 100 nm, 500 nm, and 1 μm polystyrene (PS) MNPs, within 10 min under magnetic field-assisted conditions. The mechanistic insights were obtained through a systematic evaluation of the MNPs removal kinetics and isotherms. The kinetic data followed a pseudo-second order model, indicating chemisorption driven by electrostatic interactions, while equilibrium adsorption isotherms conformed to the Langmuir model with high sorption capacity (∼3630.2 mg/g), outperforming many reported nanostructured adsorbents. In addition to classical adsorption, a secondary mechanism-dynamic trapping-was uncovered when plate-like MNPL@SiO₂ aggregated into hierarchical architectures under a magnetic field that physically entrap unadsorbed MNPs within the void spaces. Dynamic trapping contributed significantly to RE enhancement, where an additional 18.2 % removal was shown. Reusability assessments confirmed that NH₂-MNPL@SiO₂ retained promising activity across multiple cycles after solvent cleaning. These findings highlight the synergistic contributions of shape anisotropy, surface engineering, and magnetic field-assisted dynamic trapping in MNPs removal, providing new mechanistic insights and offering a scalable approach for rapid, efficient, and sustainable water remediation applications.