The selective transport of ions in nanopores attracts broad interest due to their potential applications in chemical separation, ion filtration, seawater desalination, and energy conversion. The ion selectivity based on the ion dehydration and steric hindrance is still limited by the very similar diameter between different hydrated ions. The selectivity can only separate specific ion species, lacking a general separation effect. Herein, we report the highly ionic selective transport in charged nanopore through the combination of hydraulic pressure and electric field. Based on the coupled Poisson–Nernst–Planck (PNP) and Navier–Stokes (NS) equations, the calculation results suggest that the coupling of hydraulic pressure and electric field can significantly enhance the ion selectivity compared to the results under the single driven force of hydraulic pressure or electric field. Different from the material-property-based ion selective transport, this method endows the general separation effect between different kinds of ions. Through the appropriate combination of hydraulic pressure and electric field, an extremely high selectivity ratio can be achieved. Further in-depth analysis reveals the influence of nanopore diameter, surface charge density and ionic strength on the selectivity ratio. These findings provide a potential route for high-performance ionic selective transport and separation in nanofluidic systems.
Graphene oxide (GO) membranes have attracted broad interest because of their unique mass transport properties. Towards the controllable ionic transport in GO membranes, physical fields or external driving forces are induced to control the behavior of ionic migration in situ. However, the adjustable ionic transport regulated by temperature and osmotic pressure in GO materials is still absent. Herein, we report the anomalous temperature dependence of ion transport under osmotic pressure in GO membranes. The ions can diffuse spontaneously along the concentration gradient or the temperature gradient. Intriguingly, it is found that the reverse temperature difference can promote ion transport driven by osmotic pressure. Theoretical analysis reveals that the anomalous temperature dependence of ion transport stems from the thermal-diffusion-assisted ion concentration polarization (ICP). The high temperature in the low-concentration side largely enhances the ionic thermal diffusion and suppresses the ICP, which eventually strengthens the ion current along the concentration gradient. The finding can be developed into the temperature sensor for aqueous solutions and bring inspiration to the application involving ion transport under thermodynamic and osmotic driven forces.
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