| AVS 61st International Symposium & Exhibition | |
| In-Situ Spectroscopy and Microscopy Focus Topic | Tuesday Sessions |
| Session IS+AS+MC+SS-TuA |
| Session: | Environmental Electron Microscopies |
| Presenter: | Kathryn Perrine, University of California Irvine |
| Authors: | K.A. Perrine, University of California Irvine M.H.C. Van Spyk, University of California Irvine M.J. Makowski, University of California Irvine A.C. Stern, University of California Irvine K. Parry, University of California Irvine D.J. Tobias, University of California Irvine A. Shavorskiy, Lawrence Berkeley National Laboratory H. Bluhm, Lawrence Berkeley National Laboratory B. Winter, Helmholtz-Zentrum Berlin für Materialien und Energie/Elektronenspeicherring BESSY II, Germany J.C. Hemminger, University of California Irvine |
| Correspondent: | Click to Email |
Ions impact chemistry at the aqueous liquid/vapor interface in environmental chemistry, electrochemistry and biomolecular chemistry. Ions are characterized as structure makers or breakers for protein mixtures, and the trend is known as the Hofmeister series.1 The Born electrostatic model of ions at interfaces has shown that ions should be repelled from the liquid/vapor interface due to a decrease in free energy when solvation by water occurs.2 Molecular dynamic (MD) simulations and recent experimental studies have shown that anions tend to adsorb to the liquid interface in an inverse Hofmeister trend.3, 4 Our synchrotron based XPS studies carried out over the last five years have provided experimental evidence that most cations follow classical ionic solution behavior and are repelled from the liquid/vapor interface, whereas some anions exhibit significant propensity for the surface. In this talk we present our recent experiments on Li salt solutions. Our experiments indicate that unlike larger cations, Li+ is not repelled from the interface and has a significant surface propensity.
Liquid jet-X-ray photoelectron spectroscopy (LJ-XPS) is used to explore the relative ion concentrations at different depths in aqueous salt solutions. Low photoelectron kinetic energies are used to probe the surface of solutions yielding relative ionic concentrations that are present at the liquid/vapor interface. Higher photoelectron kinetic energies probe deeper into the bulk of aqueous solutions. The relative ionic concentrations of solutions prepared from lithium halide salts are compared to potassium halide solutions at different depths. MD simulations support our studies and suggest that Li+ cations have interfacial propensity due to factors such as the tight water solvation shell on the Li+ ions. Density profiles reveal anion and Li+ ion adsorption to the liquid/vapor interface. In addition, we also compare various concentrations of KI and LiI aqueous solutions to determine ion adsorption at the aqueous interface.
1. K. D. Collins and M. W. Washabaugh, Quarterly Reviews of Biophysics, 1985, 18, 323-422.
2. M. Born, Zeitschrift Fur Physik, 1920, 1, 45-48.
3. P. Jungwirth and D. J. Tobias, Journal of Physical Chemistry B, 2002, 106, 6361-6373.
4. D. J. Tobias, A. C. Stern, M. D. Baer, Y. Levin and C. J. Mundy, Annual Review of Physical Chemistry, Vol 64, 2013, 64, 339-359.