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Anions Enhance Rare Earth Adsorption at Negatively Charged Surfaces

preprint
submitted on 05.04.2020 and posted on 07.04.2020 by Srikanth Nayak, Kaitlin Lovering, Wei Bu, Ahmet Uysal
Anions are expected to be repelled from negatively charged surfaces. At aqueous interfaces, however, ion-specific effects can dominate over direct electrostatic interactions. Using multiple in situ surface sensitive experimental techniques, we show that surface affinity of SCN- ions are so strong that they can adsorb at a negatively charged floating monolayer at the air/aqueous interface. This extreme example of ion-specific effects may be very important for understanding complex processes at aqueous interfaces, such as chemical separations of rare earth metals. Adsorbed SCN- ions at the floating monolayer increase the overall negative charge density, leading to enhanced trivalent rare earth adsorption. Surface sensitive X-ray fluorescence measurements show that the surface coverage of Lu3+ ions can be triple of the apparent surface charge of the floating monolayer in the presence of SCN-. Comparison to NO3- samples show that the effects are strongly dependent to the character of the anion, providing further evidence to ion-specific effects dominating over electrostatics.

Funding

U.S. Department of Energy, Office of Basic Energy Science, Division of Chemical Sciences, Geosciences, and Biosciences, under contract DE-AC02-06CH11357.

History

Email Address of Submitting Author

ahmet@anl.gov

Institution

Argonne National Laboratory

Country

United States

ORCID For Submitting Author

0000-0003-3278-5570

Declaration of Conflict of Interest

Authors declare no competing financial interest.

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