Skip to main content
eScholarship
Open Access Publications from the University of California

Mechanism of ion adsorption to aqueous interfaces: Graphene/water vs. air/water

  • Author(s): McCaffrey, DL
  • Nguyen, SC
  • Cox, SJ
  • Weller, H
  • Alivisatos, AP
  • Geissler, PL
  • Saykally, RJ
  • et al.

Published Web Location

https://doi.org/10.1073/pnas.1702760114
No data is associated with this publication.
Abstract

The adsorption of ions to aqueous interfaces is a phenomenon that profoundly influences vital processes in many areas of science, including biology, atmospheric chemistry, electrical energy storage, and water process engineering. Although classical electrostatics theory predicts that ions are repelled from water/hydrophobe (e.g., air/water) interfaces, both computer simulations and experiments have shown that chaotropic ions actually exhibit enhanced concentrations at the air/water interface. Although mechanistic pictures have been developed to explain this counterintuitive observation, their general applicability, particularly in the presence of material substrates, remains unclear. Here we investigate ion adsorption to the model interface formed by water and graphene. Deep UV second harmonic generation measurements of the SCN-ion, a prototypical chaotrope, determined a free energy of adsorption within error of that for air/water. Unlike for the air/water interface, wherein repartitioning of the solvent energy drives ion adsorption, our computer simulations reveal that direct ion/graphene interactions dominate the favorable enthalpy change. Moreover, the graphene sheets dampen capillary waves such that rotational anisotropy of the solute, if present, is the dominant entropy contribution, in contrast to the air/water interface.

Many UC-authored scholarly publications are freely available on this site because of the UC Academic Senate's Open Access Policy. Let us know how this access is important for you.

Main Content

13369.full.pdf.webarchive

Download