Thermally and chemically stable Fe/Mg-layered double oxides-biochar for enhanced polystyrene nanoplastic adsorption and sustainable recycling

Nanoplastics, characterized by their small size, high diffusion, and stability, have emerged as the new class of pollutants posing a global threat. For achieving both chemical and thermal stability of adsorbents, this study synthesized FeMg-LDO@BC, a novel adsorbent prepared through the in-situ growth and calcination of FeMg-layered double hydroxide (FeMg-LDH) on pre-treated biochar. FeMg-LDO@BC demonstrated an excellent adsorption rates and removal efficiencies for polystyrene nanoplastics (PSNPs) as determined by pseudo-first-order kinetic model and Sips isotherm model, reaching a 99.8 % adsorption efficiency and the maximum capacity of 97.93 mg/g. The removal mechanism was primarily attributed to π-π EDA interactions, surface complexation, and hydrogen bonding. Furthermore, the composite exhibited excellent chemical and thermal stability, demonstrating robust environmental adaptability and regenerative performance. After five cycles of adsorption-thermal degradation, FeMg-LDO@BC maintained 80 % of its initial adsorption capacity. The thermal regeneration products were primarily composed of styrene, with the presence of alkenes and aromatic hydrocarbons, confirming the simultaneously degradation of nanoplastics and the regeneration of the biochar adsorbent.