Atomistic insights into the K⁺/Na⁺ separation across amino modified graphene nanopore: The assisting role of Cl⁻

K⁺/Na⁺ separation has always been considered the most challenging. We adopted molecular dynamics to compare graphene nanopores modified with positively charged amino groups and their pristine counterparts to unravel the mechanism underlying the effect of positively charged amino groups on K⁺/Na⁺ separation and evaluate the assisting effect of Cl⁻. Two pore diameters of approximately 1 nm were selected. Results demonstrated that nanopore modification can effectively improve the K⁺/Na⁺ selectivity, and the spatial distribution and residence time of Cl⁻ near the nanopores indicated that modification with positively charged amino groups can induce the dynamical adsorption of Cl⁻ around the nanopores. In the studied nanopores, the prolongation of the residence time of Cl⁻ at the pore mouths can increase the difference between K⁺ and Na⁺ dehydration and thus can increase their transport resistance difference. The latter effect is conducive to improving the selectivity for K⁺. Our findings can provide useful insight for the further design of K⁺ separating two-dimensional materials as sensors and ion separators.