Biochar and activated carbon for micro‐ and nanoplastic removal in aqueous systems: a systematic review on mechanisms, influencing factors, and performance

The increasing presence of micro‐ and nanoplastics (MNPs) in aquatic environments raises concerns for water quality, ecosystem integrity, and public health. This systematic review evaluated the adsorption mechanisms, influencing factors, and removal performance of biochar and granular activated carbon (GAC) for MNP remediation in aqueous systems, following PRISMA 2020 guidelines. Twelve eligible studies (2021–2026) were assessed using an adapted ROBINS‐I framework alongside SWiM and GRADE for narrative synthesis. The included studies showed substantial heterogeneity in feedstock origin, modification strategy, operational conditions, and aqueous matrices. Agricultural residues were the most frequently evaluated feedstock, and magnetic functionalization with Fe3O4/Fe2O3 was the predominant modification strategy. Magnetically functionalized biochars achieved the highest efficiencies, frequently exceeding 90%, and were the only materials for which regeneration was evaluated, retaining 72%–96% of capacity after four to six cycles. Electrostatic attraction, hydrogen bonding, π–π interactions, pore filling, and hydrophobic interactions were the dominant mechanisms, inferred mainly from kinetic and isotherm modeling. Performance depended more on surface chemistry than on surface area alone. Although the included studies demonstrated promising performance, most experiments used synthetic matrices and pristine microplastics under laboratory conditions, limiting extrapolation to environmentally representative systems, and a predominance of favorable results suggests possible publication bias. Nevertheless, engineered biochar, particularly magnetically functionalized biochar, emerges as a sustainable, cost‐effective candidate for MNP remediation. Future studies should prioritize environmentally relevant conditions, standardized methodologies, and long‐term performance evaluation.