Coating ligand-mediated dynamic formation of natural organic matter (NOM) corona on engineered nanoparticles in natural environments

Abstract

Natural organic matter (NOM) can adsorb onto engineered nanoparticles (ENPs) and form NOM-corona on the ENP–solution interface, thus affecting the performance and ecotoxicity of ENPs in natural environments. Nevertheless, the formation dynamics of the NOM-corona on ENP surfaces as well as the role of coating ligands during the dynamic adsorption process are largely unknown. In this study, with silver nanoparticles (AgNPs) as the representative ENPs, the interaction between NOM and ENPs and the dynamic formation of NOM-corona were systematically investigated. NOM showed high adsorption affinity toward AgNPs with a large adsorption equilibrium constant (0.18 ± 0.01 L per mg C), thus leading to the fast formation of NOM-corona in several minutes and the enhanced nanoparticle stability under high salinity. As the important intermediary on the ENP–solution interface, coating ligands, such as citrate and polyvinylpyrrolidone, can substantially affect the dynamics and the equilibrium constant of NOM-corona formation. Moreover, NOM-corona formation was also reshaped by the coating ligands through adsorption, ligand exchange, and overcoating mechanisms. These mechanisms were illuminated by spectral investigations and theoretical calculations that NOM and polyvinylpyrrolidone have high binding abilities toward AgNP surfaces while citrate is more susceptible to replacement. This work provides a deeper understanding of the formation dynamics of the NOM-corona and the important role of coating ligands, which will facilitate the rational design of the surface chemistry of ENPs for nano-based environmental applications and the accurate prediction of the ENP fates in natural environments.