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Abstract Currently, 18-crown-6-like graphene nanopore has emerged and received much theoretical and experimental attention. Inspired by the multilayer oxygen-containing structure of the K+ channel (KcsA), we adopted molecular dynamics to investigate the selectivity of K+/Na+ for a series of multilayer 18-crown-6-like graphene nanopores. The results demonstrated that the nanopores of the multilayer graphene could facilitate the selectivity of K+/Na+ compared to the monolayer graphene. A proper combination of layer number and interlayer spacing could achieve a high selectivity. The spatial distribution of fluid molecules and ionic hydration microstructures indicated that the easier dehydration of K+ could lead to the more uniformity of K+ pathways in the central region of the nanopore and in turn be helpful in increasing the selectivity of K+. Meanwhile, the increased unsuitability for the pore wall oxygen atoms to compensate the partial dehydrated Na+ could enhance the resistance of Na+. These findings provide useful insights to the further design of 18-crown-6-like and other crown-ether-like graphene nanopore-based nanodevices as sensors and ion separators. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Residual Ca2+ decreases the efficiency and increases the power consumption of the chlor-alkali industry. However, Ca2+ and Na+ sieving is challenging due to the similar ionic radii of these cations. Inspired by the presence of carbonyl oxygens in key selective filters of biological Ca2+ and Na+ channels, we used molecular dynamics to investigate the effects of carbonyl oxygen atoms in modified graphene nanopores of various sizes (characteristic diameters: 0.57–1.50 nm) on Ca2+/Na+ sieving. The results demonstrated that selectivity is closely associated with the different roles of the carbonyl oxygen atoms. In small nanopores, Ca2+ sheds increased numbers of water molecules due to the predominant steric effect of carbonyl oxygen atoms. Thus, Ca2+ must overcome a higher energy barrier than Na+. This requirement prevents the passage of Ca2+. In large nanopores, carbonyl oxygen atoms do preferentially substitute water molecules outside the first hydration shell of Ca2+ compared with those outside the first hydration shell of Na+, thereby hindering Na+ departure from the nanopore. These findings provide useful guidance for the further development of Ca2+ separation materials as sensors and ion separators. Image 1 [ABSTRACT FROM AUTHOR]