Heterovalent Al/Mn bimetallic MIL-53(Al) with engineered defects for effective removal of nanoplastic from water

Nanoplastics (NPs) pose severe risks to aquatic environments, and adsorption technology provides a promising strategy for their removal. Metal-organic frameworks (MOFs) are promising adsorbents, but their practical application is limited by insufficient water stability and restricted pore accessibility. To bridge this gap, defect-engineered Al/Mn bimetallic MOFs were synthesized via mild post-synthetic ion exchange. n-Octanoic acid (OA) was employed to modulate the crystallization process of MIL-53(Al), inducing missing linker defects, suppressing excessive crystal growth, and generating mesoporous structure. Subsequently, the partial substitution of terephthalic acid linkers with manganese clusters could introduce additional active sites, alter the surface properties while maintain the overall crystallinity of MOFs. The optimized Mn-0.2-OA maintained high PS removal efficiency under acidic to neutral conditions, with removal efficiencies above 92% over pH 1–7. It also showed good tolerance to representative interference factors, retaining removal efficiencies above 97.5% in the presence of common cations and 89.37% at 40 mg/L humic acid. The adsorption of 500 nm polystyrene microspheres was mainly driven by the synergistic effects of electrostatic attraction, π-π interactions, enhanced hydrophobic affinity, and hierarchical pore structure. Meanwhile, Mn-0.2-OA achieved a Langmuir-fitted maximum adsorption capacity of 849.17 mg/g and exhibited rapid adsorption kinetics, removing 96.4% of PS within 10 min at an initial concentration of 25 mg/L. Regeneration tests further confirmed its acceptable reusability for repeated PS adsorption. This strategy provides a feasible approach for designing efficient and reusable adsorbents for nanoplastic removal from aquatic environments.