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Title: Rb+ adsorption at the quartz(101)-aqueous interface: comparison of resonant anomalous x-ray reflectivity with ab initio calculations

We study adsorption of Rb+ to the quartz(101)–aqueous interface at room temperature with specular X-ray reflectivity, resonant anomalous X-ray reflectivity, and density functional theory. The interfacial water structures observed in deionized water and 10 mM RbCl solution at pH 9.8 were similar, having a first water layer at height of 1.7 ± 0.1 Å above the quartz surface and a second layer at 4.8 ± 0.1 Å and 3.9 ± 0.8 Å for the water and RbCl solutions, respectively. The adsorbed Rb+ distribution is broad and consists of presumed inner-sphere (IS) and outer-sphere (OS) complexes at heights of 1.8 ± 0.1 and 6.4 ± 1.0 Å, respectively. Projector-augmented planewave density functional theory (DFT) calculations of potential configurations for neutral and negatively charged quartz(101) surfaces at pH 7 and 12, respectively, reveal a water structure in agreement with experimental results. These DFT calculations also show differences in adsorbed speciation of Rb+ between these two conditions. At pH 7, the lowest energy structure shows that Rb+ adsorbs dominantly as an IS complex, whereas at pH 12 IS and OS complexes have equivalent energies. The DFT results at pH 12 are generally consistent with the two site Rb distribution observed from the X-raymore » data at pH 9.8, albeit with some differences that are discussed. In conclusion, surface charge estimated on the basis of the measured total Rb+ coverage was -0.11 C/m2, in good agreement with the range of the surface charge magnitudes reported in the literature.« less
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [1]
  1. Argonne National Lab. (ANL), Argonne, IL (United States). Chemical Sciences and Engineering Division
  2. Pennsylvania State Univ., University Park, PA (United States). Department of Geosciences
  3. St. Petersburg State University, St. Petersburg (Russia). Department of Quantum Chemistry
  4. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
Publication Date:
OSTI Identifier:
1265355
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 119; Journal Issue: 9; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 36 MATERIALS SCIENCE; 47 OTHER INSTRUMENTATION