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Unexpected Behavior of Chloride and Sulfate Ions upon Surface Solvation of Martian Salt Analogue

journal contribution
submitted on 2024-08-25, 09:23 and posted on 2024-08-25, 09:24 authored by Nicolas Fauré, Jie Chen, Luca Artiglia, Markus Ammann, Thorsten Bartels-Rausch, Jun Li, Wanyu Liu, Sen Wang, Zamin A. Kanji, Jan B. C. Pettersson, Ivan Gladich, Erik S. Thomson, Xiangrui Kong

Gas-phase interactions with aerosol particle surfaces are involved in the physicochemical evolution of our atmosphere as well as those of other planets (e.g., Mars). However, our understanding of interfacial properties remains limited, especially in natural systems with complex structures and chemical compositions. In this study, a surface-sensitive technique, ambient pressure X-ray photoelectron spectroscopy, combined with molecular dynamics simulations, were employed to investigate a Martian salt analogue sampled on Earth, including a comparison with a typical sulfate salt (MgSO4) commonly found on both Earth and Mars. For MgSO4, elemental depth profiles show that there always exists residual water on the salt surface, even at very low relative humidity (RH). When RH rises, water is well mixed with the salt within the probed depth of a few nanometers. The Cl- and SO42–-bearing Martian salt analogue surface is extremely sensitive to water vapor, and the surface layer is already fully solvated at very low RH. Unexpected ion-selective surface behavior are observed as RH rises, where the chloride is depleted, while another major anion, sulfate, is relatively enhanced when the surface becomes solvated. Molecular dynamics simulations suggest that, upon solvation with the formation of an ion-concentrated water layer adsorbed on the crystal substrate, monovalent ions experience a higher degree of dehydration than the divalent ions. Thus, to complete their first solvation shell, monovalent ions are driven away from the surface and move toward the water accumulated at the hydrophilic crystal structure.

Other Information

Published in: ACS Earth and Space Chemistry
License: https://creativecommons.org/licenses/by/4.0/
See article on publisher's website: https://dx.doi.org/10.1021/acsearthspacechem.2c00204

History

Language

  • English

Publisher

American Chemical Society

Publication Year

  • 2023

License statement

This Item is licensed under the Creative Commons Attribution 4.0 International License.

Institution affiliated with

  • Hamad Bin Khalifa University
  • Qatar Environment and Energy Research Institute - HBKU

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