Concerted Metal Cation Desorption and Proton Transfer on Deprotonated Silica Surfaces
| Autor: | Leung, Kevin, Criscenti, Louise J., Knight, Andrew W., Ilgen, Anastasia G., Ho, Tuan A., Greathouse, Jeffery A. |
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| Rok vydání: | 2018 |
| Předmět: | |
| Zdroj: | Journal of Physical Chemistry Letters 9(18), 5379-5385 (2018) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1021/acs.jpclett.8b02173 |
| Popis: | The adsorption equilibrium constants of monovalent and divalent cations to material surfaces in aqueous media are central to many technological, natural, and geochemical processes. Cation adsorption/desorption is often proposed to occur in concert with proton-transfer on hydroxyl-covered mineral surfaces, but so far this cooperative effect has been inferred indirectly. This work applies Density Functional Theory (DFT)-based molecular dynamics simulations of explicit liquid water/mineral interfaces to calculate metal ion desorption free energies. Monodentate adsorption of Na(+), Mg(2+), and Cu(2+) on partially deprotonated silica surfaces are considered. Na(+) is predicted to be unbound, while Cu(2+) exhibits larger binding free energies to surface SiO(-) groups than Mg(2+). The predicted trends agree with competitive adsorption measurements on fumed silica surfaces. As desorption proceeds, Cu(2+) dissociates one of the H2O molecules in its first solvation shell, turning into Cu(2+)O(-)(H2O)(3), while Mg remains Mg(2+)(H2O)(6). The protonation state of the SiO(-) group at the initial binding site does not vary monotonically with cation desorption. Comment: 4 figures |
| Databáze: | arXiv |
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