Insights into heteroaggregation of polystyrene nanoplastics with hematite nanoparticles and configuration-dependent adsorption for PFOA and PFOS

While the homoaggregation of nanoplastics (NPs) has received a great deal of attention, their heteroaggregation with natural colloids is not well understood. In this study, the heteroaggregation behavior and mechanism of polystyrene nanoplastics (PSNPs) with hematite nanoparticles (HemNPs) were comprehensively investigated. The increase in the PS/HemNP mass concentration ratio led to a corresponding increase in the heteroaggregation rate, with the optimal heteroaggregation occurring at a PS/HemNP ratio of 0.0372. The primary heteroaggregation via electrostatic attraction and secondary heteroaggregation via interactions between the PS-HemNP agglomerates were the predominant heteroaggregation mechanisms. Specifically, the aquatic environmental factors had a great impact on the heteroaggregation processes, whereby the presence of Suwannee River humic acid (SRHA) (selected as a representative example of natural organic matter (NOM)) induced a remarkable heteroaggregation inhibition effect due to charge neutralization and steric repulsion. An increasing in pH weakened the electrostatic attraction between the particles, and resulted in a disaggregation of the PS-HemNP agglomerates. Furthermore, the heteroaggregation of the PSNPs with HemNPs formed large PS-HemNP agglomerates and shielded a number of available adsorption sites for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), resulting in the reduction of their adsorption removal by the agglomerates. [Display omitted] •Heteroaggregation rate experienced a rise first then a decline as the PS/HemNP ratio increased.•Electrostatic attraction between the oppositely charged particles was the predominant heteroaggregation mechanism.•SRHA inhibited the heteroaggregation owing to surface charge neutralization and steric repulsion effect.•Increasing pH incurred disaggregation of the PS-HemNP agglomerates.•Heteroaggregation decreased the adsorption of PFOA and PFOS on the agglomerates.