Adsorption and thermal degradation of microplastics from aqueous solutions by Mg/Zn modified magnetic biochars

Microplastics (MPs) derived from plastic wastes have attracted wide attention throughout the world due to the wide distribution, easy transition, and potential threats to organisms. This study proposes efficient Mg/Zn modified magnetic biochar adsorbents for microplastic removal. For polystyrene (PS) microspheres (1 µm, 100 mg/mL) in aqueous solution, the removal efficiencies of magnetic biochar (MBC), Mg modified magnetic biochar (Mg-MBC), and Zn modified magnetic biochar (Zn-MBC) were 94.81%, 98.75%, and 99.46%, respectively. It is supposed that the adsorption process was a result of electrostatic interaction and chemical bonding interaction between microplastics and biochar. The coexisting H₂PO₄^- and organic matters in real water significantly affected the removal efficiency of Zn-MBC due to competitive adsorption effect. Microplastic degradation and adsorbent regeneration were accomplished by thermal treatment simultaneously. The degradation of adsorbed MPs was promoted by the catalytic active sites originated from Mg and Zn, releasing adsorption sites. Thermal regeneration maintained the adsorption capability. Even after five adsorption-pyrolysis cycles, MBC (95.02%), Mg-MBC (94.60%), and Zn-MBC (95.79%) showed high microplastic removal efficiency. Therefore, the low-cost, eco-friendly, and robust Mg/Zn-MBCs have promising potential for application in microplastic removal.