Ion Enrichment on the Hydrophobic Carbon-based Surface in Aqueous Salt Solutions due to Cation-π Interactions

摘要

By incorporating cation-π interactions to classic all-atoms force fields, we show that there is a clear enrichment of Na⁺ on a carbon-based π electron-rich surface in NaCl solutions using molecular dynamics simulations. Interestingly, Cl⁻ is also enriched to some extend on the surface due to the electrostatic interaction between Na⁺ and Cl⁻, although the hydrated Cl⁻-π interaction is weak. The difference of the numbers of Na⁺ and Cl⁻ accumulated at the interface leads to a significant negatively charged behavior in the solution, especially in nanoscale systems. Moreover, we find that the accumulation of the cations at the interfaces is universal since other cations (Li⁺, K⁺, Mg²⁺, Ca²⁺, Fe²⁺, Co²⁺, Cu²⁺, Cd²⁺, Cr²⁺, and Pb²⁺) have similar adsorption behaviors. For comparison, as in usual force field without the proper consideration of cation-π interactions, the ions near the surfaces have a similar density of ions in the solution.