GI-EXAFS

The GI-EXAFS study of Bargar et al. [155] found that Pb(II)aq forms dominantly outer-sphere complexes at the a-Al203(0001)/aqueous solution interface after reaction of the substrate for a minimum of 90 min with a 0.25 mM Pb(N03)2 solution... 

Indicates single crystal substrates and GI-EXAFS or UHV XAFS experiments. All other samples are high surface area powdered solids or bacterial, fungal, or organic substances. 

Figure 21. Fe3+ sorption on natural single quartz surfaces ( Herkimer diamonds )- GI-EXAFS Fourier transform functions. Parallel and perpendicular symbols refer to X-ray electric vector in the plan of the sample surface and normal to it, respectively.

Figure 22. GI-EXAFS model Fourier transform functions for Fe3+ sorption on quartz as small precipitates. Top 47 atom hematite-like cluster with [0001] direction normal to surface plane. Middle analogous 21 atom cluster. Bottom weighted 21 atom cluster, where the EXAFS for each Fe ion has been individually calculated and added as a weighted average. This gives best agreement with observations indicating oriented clusters of average 0.9 nm diameter.

Figure 23. Fc sorption on synthetic single quartz epi quality surfaces. GI-EXAFS Fourier transform functions. Bottom two functions show effect of sorption from silica-saturated solution, hor 90 refers to electric vector in the plane of the quartz surface at right angles to the mirror plane, vert is e-vector perpendicular to the surface. Middle two functions contrast analogous experiment done without silica saturation. Top two functions show the effect of diying (i.e., ex situ experiment) on the unsaturated sorption sample. The diy and washed ex situ sample has been cleaned with a high pressure jet of DI water to remove surface precipitates. It s function is consistent with soibed complexes with little precipitate signature.

Figure 24. Possible stable Co2+ surface complexes on the (A) (001) and (B) (110) surfaces of rutile indicated by the GI-EXAFS data of Towle et al. (1999). In (A), site (1) is a bidentate polynuclear complex, while site (2) is a bidentate mononuclear complex. In (B), site (1) is a monodentate complex, while site (2) is a bidentate binuclear complex.

Figure 34. FT GI-EXAFS for Fe in the four aquifer samples from Figure 33. (Waychunas et al., in prep.)...

XAS. In order to better understand the catal)4ic processes, we investigated Co nanoparticle catalysts in SAN and SiNW with grazing incidence X-ray absorption spectroscopy (GI-XAS). Figure 10.16 shows the results of EXAFS measurements. FT of the EXAFS of both SAN and SiNW samples are shown. 

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