Understanding Cation Selectivity in Carbon Nanopores with Hybrid First-Principles/Continuum Simulations: Implications for Water Desalination and Separation Technologies

Understanding
ion adsorption in porous carbons is critical for
a wide range of technologies, including water desalination and energy
storage. In this work, we combined density functional theory with
a continuum solvation model to investigate thermodynamics and kinetics
of the adsorption process of alkali metal ions from aqueous solutions
into carbon nanopores with different sizes and geometries. We found
that cations with a larger ionic radius are more favorable to enter
the nanopores because of a lower energy penalty of dehydration. In
addition, the pore size and geometry were found to have a significant
impact on the ion–pore interaction under confinement and cation
selectivity. Our study highlights a complex interplay among nanopore
geometry, ion size, and hydration on the cation adsorption selectivity,
suggesting that tuning the porosity could represent a general strategy
for improving ion separations.