Electrically-switchable, permselective membranes prepared from nano-structured N-doped DLC

In this study, we report a fabrication of a conductive DLC through-hole membrane with highly ordered nanopore arrays by template synthesis using an anodic porous alumina and effects of intrinsic properties of DLC (a wide working potential range and low ion adsorption) on ion permselectivity when the membrane is applied to separate ions.We have successfully fabricated the conductive DLC membranes that have pore diameters ranging from 14 nm to 105 nm and show electrically tunable charge selectivity. With these membranes, fluxes of cations across the membrane can be reduced by applying positive potentials and can be increased by applying negative potentials. In the case of anions, a selectivity pattern opposite to cations was observed. Inside pore surfaces of the conductive DLC membrane could have excess charge by potentiostatically charging. This excess charge regulates ion transport across the membranes. The membranes reject ions of the same sign as excess charge and transport ions of the opposite sign. The permselectivity of the membrane can be reversibly switched from cation-permselective to anion-permselective by changing potentials applied to the membrane (because the signs of excess charge can be controllable by applied potentials).DLC membrane exhibited ion permselectivity even in an electrolyte solution including ions strongly adsorb to electrode surfaces such as Na2SO4 and HCl solutions. By using DLC membrane, ion permselectivity can be controlled in real samples commonly including adsorbing ions (that cannot be controlled with Au nanotubule membrane due to a specific adsorption to electrode surfaces).We could also demonstrate the permselectivity of target ions by controlling the potential applied to the membrane even in the mixed solution, which contains both cations and anions and is close to actual samples including ions aimed to be separated.

► We fabricated conductive DLC membranes with highly ordered nanopore arrays.
► The conductive DLC membranes show electrically tunable charge selectivity.
► The permselectivity can be reversibly switched by changing potentials.
► Ion permselectivity can be observed in the presence of strong adsorbing anions Cl−.
► Fluxes of target ions can be controlled in the mixed solution of cations and anions.