Effect of isomeric polysaccharides on heteroaggregation of nanoplastics in high ionic strength conditions: Synergies of morphology and molecular conformation.

Polysaccharides with various molecular structures and morphology may influence the aggregation kinetics of nanoplastics. This study used various characterization methods to elucidate the heteroaggregation mechanism of polystyrene nanoplastics (PSNPs) in the presence of polysaccharides (ionic strength (IS) 1-800 mM NaCl and 0.01-60 mM CaCl). The results showed that under high IS, cellulose (CL) accelerated the heteroaggregation of PSNPs, and the aggregation rate of PSNPs increased by approximately 62.05 %, while amylose (AM) had little effect (10.38 %). Compared with AM (43.2 nm), the morphology of the CL (78.4 nm) gully had improved surface roughness, leading to its decisive role in the heteroaggregation of PSNPs. Quantum chemistry calculations indicated that van der Waals forces of PSNPs-CL systems (-217.28 kJ mol) were stronger than those of PSNPs-AM systems (-184.62 kJ mol) based on the subtle molecular conformation differences between CL and AM (opposite and same sides of OH groups in CL and AM, respectively). The morphology and molecular conformation of polysaccharides collaboratively controlled the heteroaggregation of PSNPs. Because the morphology of polysaccharides was based on their molecular conformation, the latter is the most critical factor. These findings provide new insights into the effects of PSNPs stability in the environment.