Reversed interfacial fractionation of carbonate and bicarbonate evidenced by X-ray photoemission spectroscopy

 · Invited

Abstract

The fractionation of ions at liquid interfaces and its effects on the interfacial structure are of vital importance in many scientific fields. Of particular interest is the aqueous carbonate system, which governs both the terrestrial carbon cycle and physiological respiration systems. We have investigated the relative fractionation of carbonate, bicarbonate, and carbonic acid at the liquid/vapor interface finding that both carbonate (CO32- ) and carbonic acid (H2CO3) are present in higher concentrations than bicarbonate (HCO3- ) in the interfacial region. While the interfacial enhancement of a neutral acid relative to a charged ion is expected, the enhancement of doubly charged, strongly hydrated carbonate anion over the singly charged, less strongly hydrated bicarbonate ion is surprising. As vibrational sum frequency generation experiments have concluded that both carbonate and bicarbonate anions are largely excluded from the air/water interface, the present results suggest that there exists a significant accumulation of carbonate below the depletion region outside of the area probed by sum frequency generation.
1 Royce K. Lam, Jacob W. Smith, Anthony M. Rizzuto, Osman Karsliog, Hendrik Bluhm, and Richard J. Saykally, J. Chem. Phys. 146, 094703 (2017).

** This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences and Materials Sciences Division of the U.S. Department of Energy at the Lawrence Berkeley National Laboratory under Contract No. DE-AC02- 05CH11231

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Presenters

  • Hendrik Bluhm

    • University of California at Berkeley, Lawrence Berkeley National Laboratory
    • Lawrence Berkeley National Laboratory

Authors

  • Hendrik Bluhm

    • University of California at Berkeley, Lawrence Berkeley National Laboratory
    • Lawrence Berkeley National Laboratory

  • Royce Lam

    • University of California at Berkeley, Lawrence Berkeley National Laboratory

  • Jacob Smith

    • University of California at Berkeley, Lawrence Berkeley National Laboratory

  • Anthony Rizzuto

    • University of California at Berkeley, Lawrence Berkeley National Laboratory

  • Osman Karsliog

    • University of California at Berkeley, Lawrence Berkeley National Laboratory

  • Richard Saykally

    • University of California at Berkeley, Lawrence Berkeley National Laboratory