Denecke, M.

Eng, P.

Geckeis, H.

Heberling, F.

Lützenkirchen, J.

English

KITopen

KIT – University of the State of Baden-Wuerttemberg and  National Research Center of the Helmholtz Association www.kit.edu Rb+ at the  calcite(104)–water– interface  F. Heberling, P. Eng, M. Denecke, J. Lützenkirchen, H. Geckeis Ions at solid electrolyte interfaces – Lorentz Discussion 2014  – Leiden Institute for Nuclear Waste Disposal, KIT 2 Outline  Introduction  Surface diffraction: non-resonant crystal truncation rod (CTR) measurements and resonant interface diffraction (RIDS)   Rb+ at the calcite(104)-water-interface Institute for Nuclear Waste Disposal, KIT 3 Introduction Influx of groundwater into a waste repository in a deep geological formation Containers and waste may corrode  radionuclides may be released into the groundwater Radionuclides migrate through an aqifer and interact with mineral surfaces: outer-sphere adsorption inner-sphere adsorption inclusion structural incorporation Calcite Institute for Nuclear Waste Disposal, KIT 4 X-ray Surface Diffraction Kin Kout Kout Pilatus Pixel array Detector Incident beam 2Θ Q Crystal Truncation Rods (CTRs) I(Q) ≈ |F(Q)|2 C(Q) I0 Institute for Nuclear Waste Disposal, KIT 5 Surface diffraction data for Rb+ at the calcite(104)–water–interface  c2 = 1.64  data model |F| |F| Modeled using python interface structure refinement, (https://github.com/xraypy/tdl) 25 resonant datasets: energy scans around Rb K-edge at 15200 eV at fixed points in reciprocal space 0.01M RbCl, pH 8.2,  eq. calcite-solution-air Institute for Nuclear Waste Disposal, KIT 6 Specular and off-specular resonant surface diffraction data Institute for Nuclear Waste Disposal, KIT 7 Rb+ at calcite(104), specular resonant amplitude and phase    z Determination of resonant amplitudes and phases allows straight forward Fourier synthesis of the electron density distribution related to Rb+.  Institute for Nuclear Waste Disposal, KIT 8 Capabilities of the method Advantages  Surfaces can be studies in-situ with molecular scale resolution Element specific information is obtained Multiple species can be structurally characterized and quantified simultaneously. Compared to XSW the method is sensitive to a larger sample volume; usually 1 UC in X and Y and several UCs in z  Disadvantages  Flat and large (at least some mm2) good quality crystals are required Measurements and data analysis are time consuming / beam time is restricted Average structures are obtained that do not necessarily correctly reflect the local structural environment of adsorbed ions.  Institute for Nuclear Waste Disposal, KIT 9 Rb+ at calcite(104), simple model Inner-sphere adsorption  Agrees nicely with recent AFM results by M. Ricci et al. (2013) Langmuir Institute for Nuclear Waste Disposal, KIT 10 Rb+ at calcite(104), full model Three distinct adsorption species (confirmed by off-specular data)  Intense layering of the electrolyte (Rb+)  Cl-?  might be a similar effect as proposed by Shchukarev et al. (2007) for NaCl on hematite (001) based on cryo XPS Institute for Nuclear Waste Disposal, KIT 11 Rb+ at calcite(104) Institute for Nuclear Waste Disposal, KIT 12 Calcite Surface Complexation Model? Basic Stern Model (Heberling et al. (2011) JCIS):  0-plane:  between surface and first water layer, highly negative harged due to deprotonation  of surface hydration water  b-plane:  0-plane charge screened by outer-sphere adsorbed cations beyond second water  layer  Diffuse layer beyond the b-plane z ψ Slip plane ζ 0 b C Institute for Nuclear Waste Disposal, KIT 13 Acknowledgement  thanks to Tom Trainor (UAF), Matt Newville, Joanne Stubbs, Craig Biwer (GSECARS) for the xraypy/tdl project thanks to Paul Fenter and his group for helpful discussions thanks for financial support through the projects: RECAWA (Geotechnologien, BMBF/DFG), VESPA (BMWi), and SKIN (Euratom7, EU) thanks to the APS / GSECARS for providing beam time, funded by NSF and DoE   and thanks for your attention… 

Rb⁺ at the calcite(104)-water-interface

https://publikationen.bibliothek.kit.edu/230098278/3816718

Rb⁺ at the calcite(104)-water-interface

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