Almond-shell-derived Fe-La biochar enables magnetic capture and pyrolysis-assisted conversion of nanoplastics

Nanoplastics (NPs) are emerging aquatic contaminants with high mobility, colloidal stability, and potential biological accessibility. However, many existing treatment methods mainly transfer captured NPs into a secondary solid phase, leaving NP-bearing residues that still require further handling. To address this issue, Fe-La-modified magnetic almond-shell biochar was prepared as a regenerable adsorbent that integrates nanoplastics capture, magnetic recovery, and pyrolysis-assisted regeneration. Among the prepared materials, Fe/La@MBC-1:1 exhibited the best overall adsorption performance toward polystyrene nanoplastics (PSNPs), with a Langmuir maximum capacity of 555 mg/g. Stable removal behavior was maintained under varying water chemistry conditions and in real-water matrices. Additional tests further showed effective removal at lower PSNPs concentrations and across different particle sizes, surface functionalities, and selected nanoplastic types. The adsorption behavior was associated with enhanced interfacial interactions between Fe/La@MBC-1:1 and nanoplastics, including electrostatic attraction and van der Waals forces. After five adsorption-pyrolysis regeneration cycles, the removal efficiency remained at 85% in batch adsorption and above 70% after the fifth regeneration cycle in flow-through column operation. These results indicate that Fe/La@MBC-1:1 provides a feasible biochar-based route for integrated nanoplastics capture, magnetic recovery, and pyrolysis-assisted regeneration.