Mineral Morphology-Mediated Interaction of Boehmite with Polystyrene Nanoplastics (PSNPs) and Validation in an Aqueous Environment

In an aqueous environment, the aggregation between minerals and polystyrene nanoplastics (PSNPs) is a crucial process affecting the geochemical behavior of PSNPs. Mineral morphology is an important factor determining their properties, further influencing the heteroaggregation of PSNP-minerals. In this study, the aggregation between PSNPs and three morphologies of boehmite (γ-AlOOH) was investigated, and the effects of pH, electrolytes, and hydrogen bonds were discussed to further explore the mechanism. The results showed that boehmite played an important role in the aggregation. The heteroaggregation behavior was inhibited with the decrease of pH or the increase of electrolyte concentration, which followed the DLVO theory. The heteroaggregation extent of PSNPs among boehmites was rod-shaped boehmite (Rod-boe) > flake-shaped boehmite (Flake-boe) > fiber-shaped boehmite (Fiber-boe), which could be explained by the different contents of hydroxyl groups of boehmites and the formation of hydrogen bonds. Furthermore, natural samples from the Pearl River with a salinity gradient were collected for aggregation experiments. The results showed that electrolyte is an important factor in the aggregation of PSNPs in natural water. Our study reflected the important role of mineral morphology in the aggregation of PSNPs and provided new insights into the potential fate of PSNPs in an aqueous environment.