New insights into the facilitated dissolution and sulfidation of silver nanoparticles under simulated sunlight irradiation in aquatic environments by extracellular polymeric substances

Abstract

Due to their widespread application and consequent release into aquatic environments, silver nanoparticles (AgNPs) are widely present in aquatic environments. Extracellular polymeric substances (EPS) originating from aquatic organisms are naturally biogenic polymers and may interact with nanomaterials in the environment. In this study, the impacts of EPS harvested from Chlorella vulgaris on the oxidative dissolution and sulfidation of AgNPs were explored through a combination of spectral analyses and kinetic estimations. At various concentrations, algal EPS facilitated both the dissolution and sulfidation of AgNPs. The abundant aromatic groups and nitrogen containing groups were conducive to the adsorption of the algal EPS onto the surface of AgNPs. In addition, several kinds of reactive oxygen species (ROS) were generated from the EPS under light irradiation, and might actively react with AgNPs. Moreover, the abundant surface functional groups of EPS might complex with Ag⁺ ions. These could synergistically facilitate the dissolution of AgNPs. Besides, the adsorption of EPS on AgNPs reduced the electrostatic repulsion and favored the access of sulfide to react with AgNPs, and therefore promoted the sulfidation of AgNPs to a great extent. This study provides important insights into the interaction mechanisms between EPS and AgNPs and the results are helpful to predict the fate and risk of AgNPs in complicated natural aquatic environments.