Surface complexation studied via combined grazing-incidence EXAFS and surface diffraction: arsenate on hematite (0001) and (10–12)

  • G. Waychunas
  • T. Trainor
  • P. Eng
  • J. Catalano
  • G. Brown
  • J. Davis
  • J. Rogers
  • J. Bargar
Original Paper

Abstract

X-ray diffraction [crystal-truncation-rod (CTR)] studies of the surface structure of moisture-equilibrated hematite reveal sites for complexation not present on the bulk oxygen-terminated surface, and impose constraints on the types of inner-sphere sorption topologies. We have used this improved model of the hematite surface to analyze grazing-incidence EXAFS results for arsenate sorption on the c (0001) and r (10–12) surfaces measured in two electric vector polarizations. This work shows that the reconfiguration of the surface under moist conditions is responsible for an increased adsorption density of arsenate complexes on the (0001) surface relative to predicted ideal termination, and an abundance of “edge-sharing” bidentate complexes on both studied surfaces. We consider possible limitations on combining the methods due to differing surface sensitivities, and discuss further analysis possibilities using both methods.

Keywords

Crystal truncation rod GIXAFS EXAFS Surface structure Hematite Arsenate 

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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • G. Waychunas
    • 1
  • T. Trainor
    • 2
  • P. Eng
    • 3
  • J. Catalano
    • 4
  • G. Brown
    • 5
  • J. Davis
    • 6
  • J. Rogers
    • 7
  • J. Bargar
    • 7
  1. 1.Lawrence Berkeley National LaboratoryBerkeleyUSA
  2. 2.University of Alaska FairbanksFairbanksUSA
  3. 3.CARS, Argonne National LaboratoryArgonneUSA
  4. 4.Environmental Chemistry DivisionArgonne National LaboratoryArgonneUSA
  5. 5.Stanford UniversityStanfordUSA
  6. 6.US Geological SurveyMenlo ParkUSA
  7. 7.Stanford Synchrotron Radiation LaboratoryStanfordUSA

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