Explicit Modeling of Electronic Polarization Reveals Water-Mediated Screening of Ion Adsorption at Hexagonal Boron Nitride Interfaces.

Abstract

Understanding ion adsorption at hexagonal boron nitride (hBN)/water interfaces is essential for applications in nanofluidics, membrane separations, and electrochemical sensing. Water, being polar, and salt ions, being charged, can generate electric fields that strongly polarize a contacting hBN surface. Further, with hBN being heteropolar, there is a possibility of a coupling between the permanent and induced charge distributions, whose implications on the ion adsorption phenomenon remain unclear. In this study, we develop all-atomistic polarizable force fields by incorporating electronic polarization effects via the classical Drude oscillator model to accurately model hBN-water and hBN-ion interactions. By carrying out classical molecular dynamics (MD) simulations, we compute free energy profiles for the adsorption of various ions comprising the well-known Hofmeister series at the hBN/water interface. Our explicit modeling of the electronic polarization of hBN accurately predicts ion-specific effects, which agree well with ab initio MD simulation results. In contrast, implicit modeling of hBN-ion and hBN-water polarization energies using traditional nonpolarizable force fields overestimates adsorption free energies, leading to incorrect predictions of ion adsorption. Furthermore, our findings indicate that interfacial water molecules significantly attenuate hBN-ion polarization interactions, a screening effect that modulates the ion adsorption behavior. Our study demonstrates the need to explicitly model many-body polarization effects to accurately describe ion adsorption thermodynamics at hBN and other 2D material interfaces, offering insights for the design of 2D-material nanodevices.