Ca

2+

/Na

+

separation is a common problem in industrial applications

biological and medical fields. However

Ca

2+

and Na

+

have similar ionic radii and hydration radii

thus Ca

2+

/Na

+

separation is challenging. Inspired by biological channels

group modification is one of the effective methods to improve the separation performance. In this work

molecular dynamics simulations were performed to investigate the effects of different functional groups (COO

-

NH

3

+

) on the separation performance of Ca

2+

and Na

+

through graphene nanopores under an electric field. The pristine graphene nanopore was used for comparison. Results showed that three types of nanopores preferred Ca

2+

to Na

+

and Ca

2+

/Na

+

selectivity followed the order of GE-COO

-

(4.06) GE (1.85) GE-NH

3

+

(1.63). Detailed analysis of ionic hydration microstructure shows that different nanopores result in different hydration factors for the second hydration layer of Ca

2+

and th

e first layer of Na

+

. Such different hydration factors corresponding to the dehydration ability can effectively evaluate the separation performance. In addition

the breaking of hydrogen bonds between water molecules due to electrostatic effects can directly affect the dehydration ability. Therefore

the electrostatic effect generated by group modification will affect the ionic hydration microstructure

thus reflecting the differences in dehydration ability. This in turn affects the permeable and separation performance of cations. The results of this work provide perceptive guidelines for the application of graphene-based membranes in ion separation.