graphene
; ion
; water
; adsorption
; air
; Article
; computer simulation
; molecular dynamics
; priority journal
; spectroscopy
; ultraviolet radiation
英文摘要:
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.
McCaffrey, D.L., Department of Chemistry, University of California, Berkeley, CA 94720, United States, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States; Nguyen, S.C., Department of Chemistry, University of California, Berkeley, CA 94720, United States, Hamburg Centre for Ultrafast Imaging, University of Hamburg, Hamburg, 22761, Germany; Cox, S.J., Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States; Weller, H., Hamburg Centre for Ultrafast Imaging, University of Hamburg, Hamburg, 22761, Germany, Institute of Physical Chemistry, University of Hamburg, Hamburg, 20146, Germany; Alivisatos, A.P., Department of Chemistry, University of California, Berkeley, CA 94720, United States, Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, United States, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States, Kavli Energy Nanoscience Institute, University of California, Berkeley, CA 94720, United States; Geissler, P.L., Department of Chemistry, University of California, Berkeley, CA 94720, United States, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States; Saykally, R.J., Department of Chemistry, University of California, Berkeley, CA 94720, United States, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States
Recommended Citation:
McCaffrey D.L.,Nguyen S.C.,Cox S.J.,et al. Mechanism of ion adsorption to aqueous interfaces: Graphene/water vs. air/water[J]. Proceedings of the National Academy of Sciences of the United States of America,2017-01-01,114(51)