An XAFS Analysis of Strontium at the Hydrous Ferric Oxide Surface

Characterization of Sorbed Strontium on Monosodium Titanate

“…Some of the EXAFS studies that have characterized the environment of sorbed Sr 2+ on hydrous oxides of Fe and Mn observe a metal in the second coordination shell. 16,17 Because a metal was found in the second coordination environment, these studies refer to the nature of the sorption as being due to the ion exchange of hydrated Sr 2+ (Note: This conclusion is not consistent with the previous section that describes ion exchange in the strict sense. 16,17 These studies also report that they could fit Sr or Fe in the second shell over a range of surface Sr 2+ loadings and hence, these data present great confusion and about the quality of the XAFS data and the data analyses.…”

“…16,17 Because a metal was found in the second coordination environment, these studies refer to the nature of the sorption as being due to the ion exchange of hydrated Sr 2+ (Note: This conclusion is not consistent with the previous section that describes ion exchange in the strict sense. 16,17 These studies also report that they could fit Sr or Fe in the second shell over a range of surface Sr 2+ loadings and hence, these data present great confusion and about the quality of the XAFS data and the data analyses. 21 In contrast, other sorption studies with Sr 2+ sorbed on the FeOOH (goethite) do not observe a metal in the second coordination shell and conclude that outer sphere adsorption is operative.…”

“…10,11,12,13,14,15 Strontium K-edge XANES and XAFS techniques have been applied to study the bonding environment of sorbed, solution and solid phase Sr 2+ species. 16,17,18,19,20 Strontium-XANES studies have been performed with Sr 2+ -rich carbonates and Sr 2+ -containing silicates and the interpretations of spectra from sample treatments are generally qualitative. 20 This is because solution and solid phase Sr 2+ species are typically present in the +II oxidation state and large energy shifts for the XANES edge of Sr 2+ are usually not observed.…”

“…O'Day et al (2000) and others have included a third cumulant term (C3) in their fits for first shell Sr-O interactions to account for anharmonicity among light backscattering atoms Sr and O in aqueous environments. 16,17,18,19 For our studies, we will compare the results of our first shell Sr-O fits with and without the C3 term. It is our opinion that the reports that have excluded the C3 term during the data analyses are in error.…”

Inner-sphere complexation of cations at the rutile–water interface: A concise surface structural interpretation with the CD and MUSIC model

“…Molecular-scale surface structural information of the interaction of water and ion adsorption at metal-oxide surfaces, such as TiO 2 and various Fe(hydr)oxides, is available from in situ small-period X-ray standing wave measurements (Fenter et al, 2000(Fenter et al, , 2002, and references therein), grazing-incidence X-ray absorption (GI-XAF) spectroscopy (Towle et al, 1999a,b), and EXAFS (Axe et al, 1998;Ragnarsdottir et al, 1998;Brown et al, 1999;Sahai et al, 2000). Measurements with these techniques reveal precise structural information on the coordination geometry of specifically adsorbed ions.…”