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Transport of nanoplastics in saturated porous media: Synergy of particle size, surface functional groups, and low molecular weight organic acids
Summary
Researchers systematically tested how particle size and surface functional groups interact with low-molecular-weight organic acids to control nanoplastic mobility through saturated sand columns, finding that carboxyl-coated particles became less mobile as size increased while amine-coated particles became more mobile, with citric acid providing stronger steric hindrance than lactic acid.
The structural heterogeneity of nanoplastics (NPs) significantly affects their transport behavior and ecological risks. However, there is still a lack of systematic research on the synergistic influence of different structural features on the transport behavior of NPs. In this paper, the transport behaviors of polystyrene nanoparticles (PSNPs) with different particle sizes and surface functional groups under environmental factors were systematically investigated. With the particle size increased, the transport of PS-COOH was inhibited while PS-NH₂ mobility increased. This difference is due to the increase in particle size, which enhances the electrostatic repulsion between the medium and -COOH and reduces the electrostatic attraction between the medium and -NH₂. With the increase of IS and decrease of pH, the transport of PSNPs was reduced by the combined effects of double-layer compression and protonation. LMWOAs inhibited PSNPs transport via hydrogen bonding, and the inhibition degree depended on their types. The mobility of PSNPs under citric acid (CA) conditions was significantly higher than that under lactic acid (LA), which was related to the fact that CA contained more -COOH groups and had a stronger steric hindrance effect. DFT calculations further verified that CA had a stronger binding energy compared to LA. The above findings revealed the regulatory role of structural heterogeneity in the transport of PSNPs, clarified the colloid chemical-interface mechanism of PSNPs under different environmental conditions, and provided new scientific insights for a deeper understanding of the environmental risks of NPs.