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Enhanced polystyrene nanoplastic removal by CTAB-modified magnetic biochar: Adsorption performance and mechanisms
Summary
Researchers engineered a CTAB-modified magnetic biochar adsorbent that removes polystyrene nanoplastics with a maximum capacity of 234 mg/g — more than double unmodified biochar — through electrostatic attraction, hydrophobic interactions, and iron oxide surface complexation, while also being easily retrievable with a magnet.
Polystyrene (NPs) nanoplastics are emerging ubiquitous contaminants in aquatic environments, but their efficient removal remains challenging. Although conventional biochar offers cost-effective adsorption potential, its practical application is limited by inherent hydrophilicity and poor retrievability. To address these limitations, we engineered cetyltrimethylammonium bromide-modified magnetic biochar (CTAB/MBC) via chemical co-precipitation, synergistically enhancing both magnetism and CTAB-derived hydrophobicity. Remarkably, CTAB/MBC achieved a maximum NPs adsorption capacity of 234 mg g, representing a 2.1-fold increase over unmodified magnetic biochar (MBC) (113 mg g). Optimal performance occurred at environmentally relevant pH 7, attributed to its elevated point of zero charge. Coexisting anions (CO > SO) demonstrated greater inhibition than cations (Ca > Mg > Na), primarily through competitive electrostatic screening. Integrated characterization (SEM, FTIR, XPS) revealed the primary removal mechanisms involved electrostatic attraction facilitated by cationic quaternary ammonium groups, hydrophobic interactions between CTAB alkyl chains and NPs backbones, and surface complexation with FeO sites. This work establishes CTAB/MBC as a high-efficiency and magnetically retrievable adsorbent for nanoplastic remediation while providing a sustainable strategy for agricultural biomass valorization.