Original Paper

Analytical and Bioanalytical Chemistry

, 383:12

First online:

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

  • G. WaychunasAffiliated withLawrence Berkeley National Laboratory Email author 
  • , T. TrainorAffiliated withUniversity of Alaska Fairbanks
  • , P. EngAffiliated withCARS, Argonne National Laboratory
  • , J. CatalanoAffiliated withEnvironmental Chemistry Division, Argonne National Laboratory
  • , G. BrownAffiliated withStanford University
  • , J. DavisAffiliated withUS Geological Survey
  • , J. RogersAffiliated withStanford Synchrotron Radiation Laboratory
  • , J. BargarAffiliated withStanford Synchrotron Radiation Laboratory

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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.


Crystal truncation rod GIXAFS EXAFS Surface structure Hematite Arsenate