Anomalous temperature dependence of ion transport under osmotic pressure in graphene oxide membranes

Abstract

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.