Surface Charge Regulation of Nanoplastics in Aquatic Environments

Nanoplastics (NPs) pose significant environmental and health hazards, with their aquatic transport and aggregation being critically governed by surface charge properties. However, the factors controlling NPs' surface charge remain incompletely understood. This study develops a coupled model that integrates the Poisson-Nernst-Planck (PNP) equation (encompassing electrostatic field and diffusive transport) with a surface adsorption reaction model. Employing polystyrene NPs adsorbing sulfate ions as a model system, we systematically analyze the effects of particle size, shape, and ionic exclusion on surface charge across varying pH. Interparticle interaction energies are quantified via Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. This work provides quantitative insights into the mechanisms governing the variability of NPs' surface charge. The findings offer a theoretical basis for developing strategies to control the aggregation and removal of NPs in aqueous environments.