Ion-Specific Nanoconfinement Effect in Multilayered Graphene Membranes: A Combined Nuclear Magnetic Resonance and Computational Study

Diyan Liu, Zhiyuan Xiong, Peiyao Wang, Qinghua Liang, Haijin Zhu*, Jefferson Zhe Liu, Maria Forsyth, Dan Li*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Ion adsorption within nanopores is involved in numerous applications. However, a comprehensive understanding of the fundamental relationship between in-pore ion concentration and pore size, particularly in the sub-2 nm range, is scarce. This study investigates the ion-species-dependent concentration in multilayered graphene membranes (MGMs) with tunable nanoslit sizes (0.5–1.6 nm) using nuclear magnetic resonance and computational simulations. For Na+-based electrolytes in MGMs, the concentration of anions in graphene nanoslits increases in correlation with their chaotropic properties. As the nanoslit size decreases, the concentration of chaotropic ion (BF4–) increases, whereas the concentration of kosmotropic ions (Cit3–, PO43–) and other ions (Ac–, F–) decreases or changes slightly. Notably, anions remain more concentrated than counter Na+ ions, leading to electroneutrality breakdown and unipolar anion packing in MGMs. A continuum modeling approach, integrating molecular dynamic simulation with the Poisson–Boltzmann model, elucidates these observations by considering water-mediated ion–graphene non-electrostatic interactions and charge screening from graphene walls.
Original languageEnglish
JournalNano Letters
DOIs
StatePublished - 14 Jun 2023

Keywords

  • nanoconfinement
  • ion-specific effect
  • electroneutrality breakdown
  • graphene membrane
  • nuclear magnetic resonance

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