Abstract

Interactions between pharmaceuticals and nano(micro)plastics in aqueous environments have been widely reported; nevertheless, the molecular-level factors governing adsorption stability at these nanostructured interfaces remain poorly quantified. Here, we study the adsorption of representative pharmaceutical and personal care products (PPCPs) on nanoplastics models in water to provide a quantitative interfacial description of the driving forces controlling stability. Five non-biodegradable polymeric matrices (PA, PE, PET, PP, and PVC) and seven PPCPs with distinct acid-base speciation were studied using density functional theory calculations. Adsorption energies in water span from-7.2 to-33.3 kcal/mol, with the highest affinities obtained for polar adsorbent surfaces such as those of PA, PET, and PVC. Avobenzone and diclofenac consistently exhibit the most stable adsorption across the nanoplastics, despite their different speciation, indicating that adsorption is governed by the energetic compensation between stabilizing contributions (dispersion and electrostatics) and destabilizing terms (Pauli repulsion and solvation), rather than by charge or polarity properties of the adsorbates. Thermo-chemical analysis reveals an enthalpy-dominated adsorption regime, where entropy opposes stabilization within the implicit solvent description, leading to progressively weaker adsorption at higher temperatures. These results contribute to the knowledge and molecular-level characterization of the adsorption processes occurring at polymeric nanostructured surfaces and interfaces in aqueous environments.