Selective transport of water molecules through interlayer spaces in graphite

Here the authors expanded interlayer spaces in graphite by intercalating aqueous KCl ions utilizing an electric field. It exhibited salt rejection efficiencies >99% and high water permeation rates, a property very useful for desalination. Interlayer space in graphite is impermeable to ions and molecules, including protons. Its controlled expansion would find several applications in desalination, gas purification, high-density batteries, etc. In the past, metal intercalation has been used to modify graphitic interlayer spaces; however, resultant intercalation compounds are unstable in water. Here, we successfully expanded graphite interlayer spaces by intercalating aqueous KCl ions electrochemically. Our spectroscopy studies provide clear evidence for cation-pi interactions explaining the stability of the devices, though weak anion-pi interactions were also detectable. The water conductivity shows several orders of enhancement when compared to unintercalated graphite. Water evaporation experiments further confirm the high permeation rate. There is weak ion permeation through interlayer spaces, up to the highest chloride concentration of 1 M, an indication of sterically limited transport. In these very few transported ions, we observe hydration energy-dependent selectivity between salt ions. These strongly suggest a soft ball model of steric exclusion, which is rarely reported. These findings improve our understanding of molecular and ionic transport at the atomic scale.

Automated summary

In this study, the authors successfully expanded the interlayer spaces in graphite by intercalating aqueous KCl ions using an electric field. This method exhibited high salt rejection efficiencies and water permeation rates, making it highly promising for desalination applications. The expansion of the interlayer spaces in graphite opens up possibilities for various areas such as desalination, gas purification, and high-density batteries. The authors also discovered the interactions between ions and graphite through spectroscopy studies.