An anomalous anion transfer order in graphene oxide membranes induced by anion–π interactions†
Selective transport of anions across membranes has become an important goal in chemistry and biology. Here, we found an anomalous anion transfer order within the graphene oxide membrane: Cl− > Br− > F− > I−. This is at odds with the conventional ranking of the transfer order, which usually decreases as the radii of the anions increase, i.e., F− > Cl− > Br− > I−. The abnormal transportation of F− can be ascribed to the strong anion–π interactions between F− and graphene oxide sheets. Such unexpectedly strong anion–π interaction resulted in the lower movement of F− in the graphene oxide membrane and caused the anomalous anion transfer order. Our findings not only provide experimental evidence of anion–π interactions, but also improve our understanding of anion–π interactions in the selective transport of anions across a two-dimensional membrane.