▎ 摘　　要

Ion sieving is of great importance in a variety of applications, including water purification, bio-medical engineering, resource utilization and environment protection. Despite previous efforts, the separation efficiency for mono-/multi valent ions is still far from satisfactory. Here, we use high concentration of KCl solution to control the interlayer spacings of graphene oxide (GO) membranes. Then, these KCl-controlled GO membranes can precisely sieve mono-/multi-valentions, especially for Na+/Mg2+ separation. The excellent performance of the membranes can be attributed to the narrower interlayer spacings of KCl-controlled GO membranes.