Assessing the environmental transport and fate of manufactured nanoparticles (NPs) and potential exposure risks requires models for predicting attachment of NPs coated with organic macromolecules in porous media. The objective of this study was to determine the properties of coated nanoparticles that control their attachment behavior. Deposition data for a variety of nanoparticles with different types of anionic organic coatings, including natural organic matter (NOM)-coated latex and hematite nanoparticles, and poly(styrenesulfonate)-, carboxymethylcellulose-, and polyaspartate-coated hematite and titanium dioxide nanoparticles (80 data points), were used to develop an empirical correlation between measurable NP properties and their sticking coefficient (alpha) under a variety of electrolyte conditions and flow velocities. Available semiempirical correlations used to predict the attachment efficiency of electrostatically stabilized (uncoated) NPs overestimate the attachment efficiency of nanoparticles coated with NOM or synthetic polyelectrolytes because the correlations neglect electrosteric repulsions and the decreased friction afforded by such coatings that can inhibit attachment to surfaces. Adding a dimensionless parameter (N(LEK)) representing steric repulsions and the decreased friction force afforded by adsorbed NOM or anionic polyelectrolytes in the correlation significantly improves the correlation. This establishes the importance of including the adsorbed NOM- or polyelectrolyte layer properties for estimating the attachment efficiency of NPs in the environment. The form of N(LEK) suggests that limiting unintended transport and exposure to NPs could be achieved by using coatings with the smallest adsorbed mass and polymer density, shortest extended layer thickness, and largest molecular weight that would still afford the desired functionality of the coating.

A fundamental understanding of attachment of surface-coated nanoparticles (NPs) is essential to predict the distribution and potential risks of NPs in the environment. Column deposition studies were used to examine the effect of surface-coating hydrophobicity on NP attachment to collector surfaces in mixtures with varying ratios of octadecylichlorosilane (OTS)-coated (hydrophobic) glass beads and clean silica (hydrophilic) glass beads. Silver nanoparticles (AgNPs) coated with organic coatings of varying hydrophobicity, including citrate, polyvinylpyrrolidone (PVP), and gum arabic (GA), were used. The attachment efficiencies of GA and PVP AgNPs increased by 2- and 4-fold, respectively, for OTS-coated glass beads compared to clean glass beads. Citrate AgNPs showed no substantial change in attachment efficiency for hydrophobic compared to hydrophilic surfaces. The attachment efficiency of PVP-, GA-, and citrate-coated AgNPs to hydrophobic collector surfaces correlated with the relative hydrophobicity of the coatings. The differences in the observed attachment efficiencies among AgNPs could not be explained by classical DLVO, suggesting that hydrophobic interactions between AgNPs and OTS-coated glass beads were responsible for the increase in attachment of surface-coated AgNPs with greater hydrophobicity. This study indicates that the overall attachment efficiency of AgNPs will be influenced by the hydrophobicity of the NP coating and the fraction of hydrophobic surfaces in the environment.