Monoatomic nanosheets can form 2-dimensional channels with tunable chemical properties, for ion storage and filtering applications. Here, we demonstrate transport of K+, Na+, Li+ cations and F-, Cl- anions on the centimeters scale in graphene oxide membranes (GOM), triggered by an electric bias. Besides ion transport, the GOM channels foster also the aggregation of the selected ions in salt crystals, whose composition is not the same of the pristine salt present in solution, highlighting the difference between chemical environment in the 2D channels and in bulk solutions.