Graphene is an ideal candidate for the development of solid state nanopores due to its thickness at the atomic scale and its high chemical and mechanical stabilities. A facile method was adopted to prepare single graphene nanopore supported by PET membrane (G/PET nanopore) within the three steps assisted by the swift heavy ion irradiation and asymmetric etching technology. The inversion of the ion rectification effect was confirmed in G/PET nanopore while comparing with bare PET nanopore in KCl electrolyte solution. By modifying the wall charge state of PET conical nanopore with hydrochloric acid from negative to positive, the ion rectification effect of G/PET nanopore was found to be greatly enhanced and the large rectification ratio up to 190 was obtained during this work. Moreover, the high ionic flux and high ion separation efficiency was also observed in the G/PET nanopore system. By comparing the "on" and "off" state conductance of G/PET nanopore while immersed in the solution with pH value lower than the isoelectric point of the etched PET (IEP, pH = 3.8), the voltage dependence of the off conductance was established and it was confirmed that the large rectification effect was strongly dependent on the particularly low off conductance at higher applied voltage.

Bioinspired nanoporous membranes show great potential in ionic separation and water filtration by offering high selectivity with less permeation resistance. However, complex processes always limit their applications. Here, we report a convenient approach to introduce ionic selective channels in a micron-thick polycarbonate membrane through swift heavy ion irradiation accompanied by UV sensitization and pulsed-electrical etching. The characteristic dimension of channels was tuned through regulating energy loss of the incident ion and UV sensitization time of the membrane, resulting in the subnanoporous membranes with mean channel diameter ranging from <2.4 to 9.7 Å. These membranes showed the voltage-activated ionic transport properties associated with the dehydration effect, and the corresponding I−V characteristics were related to ionic strength, solution pH, ionic type, and channel diameter. It was found that the transmembrane conduction of multivalent ions was severely suppressed compared to monovalent ions, until the size of the membrane channel was comparable to the hydrated diameter of multivalent ions. Ionic sieving experiments also demonstrated the excellent ionic valence selectivity of the membrane. Even for the membrane with a channel diameter close to 1 nm, the Li + /Mg 2+ separation ratio was still as high as 40, and an even higher separation ratio was found for Li + /La 3+ (>3000).