Journal
JOURNAL OF PHYSICS-CONDENSED MATTER
Volume 29, Issue 36, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1361-648X/aa7e4f
Keywords
density functional theory molecular dynamics; water-material interface; ion Adsorption; deprotonation
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Funding
- US Department of Energy's National Nuclear Security Administration [DE-NA0003525]
- US DOE Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences
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The complexation of toxic and/or radioactive ions on to mineral surfaces is an important topic in geochemistry. We apply periodic-boundary-conditions density functional theory (DFT) molecular dynamics simulations to examine the coordination of Pb(II), SeO32-, and their contact ion pairs to goethite (101) and (210) surfaces. The multitude of Pb(II) adsorption sites and possibility of Pb(II)-induced FeOH deprotonation make this a complex problem. At surface sites where Pb(II) is coordinated to three FeO and/or FeOH groups, and with judicious choices of FeOH surface group protonation states, the predicted Fe-Pb distances are in good agreement with EXAFS measurements. Trajectories where Pb(II) is in part coordinated to only two surface Fe-O groups exhibit larger fluctuations in Pb-O distances. Pb(II)/SeO32- contact ion pairs are at least metastable on goethite (2 1 0) surfaces if the SeO32- has a monodentate Se-O-Fe bond. Our DFT-based molecular dynamics calculations are a prerequisite for calculations of finite temperature equilibrium binding constants of Pb(II) and Pb(II)/SeO32- ion pairs to goethite adsorption sites.
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