Eco-corona formation on aminated nanoplastics interacted with extracellular polymeric substances from bloom-forming cyanobacteria: Insightful mechanisms with DFT study

Abstract

Nanoplastics (NPs) with amino functional groups have wide distribution and high toxicity; however, their environmental behaviors remain inadequately understood. This study investigated the mechanisms of eco-corona formation on pristine polystyrene NPs (PSNPs) and aminated PSNPs (PSNPs-NH 2 ) by extracellular polymeric substances (EPS) from a bloom-forming cyanobacterium, Microcystis aeruginosa . Our results revealed that at the two tested concentrations of EPS (5.0 and 30.0 mg/L), the pristine PSNPs initially aggregated and subsequently repelled. In contrast, PSNPs-NH 2 showed a more pronounced aggregation at the elevated EPS concentration of 30 mg/L. In addition, the elemental compositions and functional groups on both types of PSNPs were markedly altered after eco-corona formation. Combining with density functional theory, our findings indicated that electrostatic interaction, hydrogen bonding , and Van der Waals force served as the main binding forces between model EPS (polysaccharide) and PSNPs units. Furthermore, the binding energies of pristine PSNPs-, and PSNPs-NH 2 -polysaccharide were calculated to be -63.25 and -179.43 kJ/mol, respectively, suggesting a greater affinity of PSNPs-NH 2 for polysaccharide. This outcome aligned with our experimental observation. Specifically, the xylose branch within polysaccharide was identified as an optimized binding site for interaction with PSNPs. Our research contributes to a deeper understanding of the environmental behaviors of aminated NPs in freshwater systems, particularly during periods of cyanobacterial blooms.