Micro- and nano-plastics (MNPs) exhibit a wide-ranging chemical composition. This manifests in a variety of surface properties (e.g., charged, hydrophobic) when dispersed in the aquatic environment. What role do these aqueous/MNP interfacial environment play in the adsorption proclivity of organic contaminants (OCs) is the focus of this study.  Using <i>in situ</i> second harmonic generation (SHG) technique, we have tested the effect of MNP charge and surface hydrophobicity on the adsorption of charged and neutral organic dyes, representing small OCs. Adsorption isotherm and kinetic results show that for microplastics with different compositions, such as styrene, carboxylate, aliphatic amine, amidine, have different degrees of affinity for positively and negatively charged SHG dyes. We have also characterized the surface compositions of pristine MNPs using IR spectroscopy, dynamic size scattering for their size and zeta-potential, and surface tension for hydrophobicity. By mapping out the thermodynamic adsorption parameters as a function of zeta-potential and MNP hydrophobicity, it appears that Coulombic interaction dictates the favorability of adsorption. However, hydrophobic interactions cannot be ignored. A potential to deduce a structure-functional correlation for the binding interactions exist. This will be presented in the context of fate and transport of OCs where MNPs play a significant role as a vector. The effect of MNP aging on the adsorption will also be discussed.

Role of microplastic composition and surface properties on molecular adsorption

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