Coarse-grained Molecular Dynamics Simulations of Nanoplastics Interacting with a Hydrophobic Environment in Aqueous Solution

Nanoplastics (NPs) are emerging threats for marine and terrestrial ecosystems, but little is known about their fate in the environment at the molecular scale. In this work, coarse-grained molecular dynamics simulations were performed to investigate nature and strength of the interaction between NPs and hydrophobic environments. Specifically, NPs were simulated with different hydrophobic and hydrophilic polymers while carbon nanotubes (CNTs) were used to mimic surface and confinement effects of hydrophobic building blocks occurring in a soil environment. The hydrophobicity of CNTs was modified by introducing different hydrophobic and hydrophilic functional groups at their inner surfaces. The results show that hydrophobic polymers have a strong affinity to adsorb at the outer surface and to be captured inside the CNT. The accumulation within the CNT is even increased in presence of hydrophobic functional groups. This contribution is a first step towards a mechanistic understanding of a variety of processes connected to interaction of nanoscale material with environmental systems. Regarding the fate of NPs in soil, the results point to the critical role of the hydrophobicity of NPs and soil organic matter (SOM) as well as of the chemical nature of functionalized SOM cavities/voids in controlling the accumulation of NPs in soil. Moreover, the results can be related to water treatment technologies as it is shown that the hydrophobicity of CNTs and functionalization of their surfaces may play a crucial role in enhancing the adsorption capacity of CNTs with respect to organic compounds and thus their removal efficiency from wastewater.