Tunable Anion Selective Transport through Mono-Layer Graphene and Hexagonal Boron Nitride

Membranes that filter selectively for both anions and cations are central to technological applications from clean energy generation to desalination devices. 2D materials have immense potential as these ion selective membranes, due to their thinness, mechanical strength and tunable surface chemistry. However, currently only cation selective membranes have been reported. Here, we demonstrate controllable cation and anion selectivity of both mono-layer graphene and hexagonal boron nitride. In particular, we measure the ionic current through membranes grown by chemical vapour deposition containing well-known intrinsic defects, native to wet-transferred 2D materials. We observe a striking change from cation selectivity with monovalent ions to anion selectivity by controlling the concentration of multivalent ions and inducing charge inversion on the 2D membrane. Furthermore, we find good agreement between our experimental data and theoretical predictions from the Goldman-Hodgkin-Katz equation and use this mode...