Extended X-ray adsorption fine structure EXAFS

Elder, R.C., Tepperman, K.G., Eidsness, M.K., Heeg, M.J., Shaw, C.F. Ill and Schaeffer, N. A. (1983) Gold-based antiarthritic drugs and metabolites. Extended x-ray adsorption fine structure (EXAFS) spectroscopy and x-ray absorption near edge spectroscopy (XANES). ACS Symposium Series, 209, 385-400. 

A number of different experimental methods are available to observe fine structure. In extended x-ray adsorption fine structure (EXAFS) experiments x-ray photons excite core levels and the cross section is determined by x-ray absorption... 

Direct in situ extended X-ray adsorption fine structure (EXAFS) measurements) from synchrotron radiation (14-18) permit the determination of species adsorbed to neighboring ions and to central ions on oxide surfaces in the presence of water. Such investigations showed, for example, that selenite is bound in an inner-sphere complex and selenate is bound in an outer-sphere complex to the central Fe(III) ions of a goethite surface. This technique also showed that Pb(II) is bound in an inner-sphere complex to 8-Al203 (19) and that Cr(III) is bound in an inner-sphere complex at the oxide-water interface of Mn(IV) oxides and ferric hydrous oxides (17, 18). 

Metallic sites Temperature-programmed reduction (TPR) X-ray adsorption near-edge spectroscopy (XANES) Extended X-ray adsorption fine structure (EXAFS) Mossbauer spectroscopy X-ray photoelectron spectroscopy (XPS) Electron paramagnetic spectroscopy (EPR)... 

NEXAFS is generally characterized by spectral features near to an X-ray absorption edge and contains information about the electronic and structural properties of the adsorbing atom. This is distinct from the extended X-ray adsorption fine structure (EXAFS), which is typically observed in the region 50-1000eV above an... 

Extended X-ray absorption fine structure (EXAFS) spectrum Part of an X-ray absorption spectrum that is used to identify the coordination of atoms, estimate bond lengths, and determine the adsorption complexes on the surfaces of adsorbents. EXAFS spectra may provide useful information on the speciation (valence state), surface complexes, and the coordination of arsenic on adsorbents (e.g. (Randall, Sherman and Ragnarsdottir, 2001 Ladeira, et al. (2001) Teixeira and Ciminelli (2005) Kober, et al. (2005)) (compare with X-ray absorption spectroscopy (XAS), X-ray absorption near edge structure (XANES) spectra, and X-ray absorption fine structure spectroscopy (XAFS)). 

X-ray absorption spectroscopy (XAS) Methods that use X-rays to investigate the physical and chemical properties of materials on an atomic scale. XAS includes X-ray adsorption fine structure (XAFS) spectroscopy and its X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra. 

The intent of this chapter is not to survey noninvasive surface spectroscopy but to illustrate briefly how it is applied to resolve the Stummian issue of whether inner-sphere surface complexes form. For this purpose, the application of electron spin resonance (ESR), electron nuclear double resonance (ENDOR), and electron spin echo envelope modulation (ESEEM) spectroscopies to elucidate metal cation speciation and the use of extended X-ray absorption fine structure (EXAFS) spectroscopy to detect surface anion species will be described. Emphasis will be on the interpretation of spectra. Sample preparation and instrumentation details were reviewed in recent volumes edited by Hawthorne (55) and Perry (27). Because the constant capacitance model was developed in the context of adsorption by hydrous oxides, these... 

According to the structure and composition of materials and analysis requirements of the researcher, the following analysis techniques can be selected for the characterization of mesoporous materials XRD, TEM, adsorption-desorption (N2 or other gas), solid MAS NMR (29Si, 27Al, 13C, etc.), scanning electron microscopy (SEM), catalysis test, Fourier Transform infra-red (FT-IR), thermal analysis, UV-visible, and chemical analysis. IR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge structure XANES, extended X-ray absorption fine structure EXAFS and other spectral methods are commonly used to analyse metal elements such as Ti in the mesoporous material frameworks. 

X-RAY ABSORPTION SPECTROSCOPY X-ray absorption spectroscopy (XAS) includes x-ray absorption near-edge (XANES) and extended x-ray absorption fine structure (EXAFS) spectroscopy. An advantage of XAS spectroscopy is that adsorption experiments can be carried out in aqueous systems (Fendorf et al., 1994). X-ray absorption spectroscopy has been used to examine the sorption of both cations and anions to oxide and silicate minerals found in soils, with an emphasis on ions that are potential contaminants in the environment. 

Chen, C.-C., Papelis, C., and Hayes, K. F. (1998). Extended x-ray absorption fine structure (EXAFS) analysis of aqueous Sr ion sorption at clay-water interfaces. In Adsorption of Metals by Geomedia Variables, Mechanisms, and Model Applications, Proc. American Chemical Society Symposium ed. Jenne, E. A., Academic Press, San Diego, CA, 333-348. 

Sparks CJ Jr (1980) X-ray fluorescence microprobe for chemical analysis. In Winick H, Doniach S (eds) Synchrotron Radiation Research, Plenum Press, New York, p 459-512 Spngberg D, Hermansson K, Lindqvist-Reis P, Jalilehvand F, Sandstroem M, Persson I (2000) Model extended X-ray absorption fine structure (EXAFS) spectra from molecular dynamics data for Ca2+ and Al3+ aqueous solutions. J Phys Chem 104 10467-10472 Sposito G. (1986) Distinguishing adsorption from surface precipitation. In Geochemical Processes at Mineral Surfaces, Davis JA, Hayes KF (eds) ACS Symposium Series 323, The American Chemical Society, Washington, DC, p 217-228... 

Extended X-ray absorption fine structure (EXAFS) is similar to NEXAFS but makes use of a wider energy region around the adsorption peak to determine information about the type of atoms surrounding the atom of interest and their distances from it. 

The most straightforward case of electrostatic adsorption occurs with the most stable metal complexes such as platinum or palladium tetraammines, [(NH3)4Pt]+ and [(NH3)4Pd]+ or PTA and PdTAs, respectively. Over the wide pH and concentration ranges that can be employed during syntheses from the lab to the industrial scale, the relatively strongly bound ammine ligands of these coordination complexes remain intact. This has been most directly confirmed in the case of Pt by extended X-ray absorption fine structure (EXAFS) analysis of PTA solutions and adsorbed species [23], and for PdTAs less directly by XPS [24]. 

The surface properties of supported Pt particles were examined by gas adsorption and X-ray photoelectron spectroscopy (XPS) with Shimadzu ESCA-750. The uptake of Hj and CO was measur by a static volumetric method at 292 K and an equilibrium pressure of about 25 kPa. In XPS, the catalysts were exposed to air on the introduction into the system, and the spectra for Pt and other species were collected after Ar sputtering. Tlie bulk structure of the particles was examined by extended X-ray absorption fine structure (EXAFS). Pt L -edge EXAFS spectra were measured at room temperature at the BL-lOB station of Photon Factory in the National Laboratory for High Energy Physics (Proposal No.93G147). In addition, the supported Pt was extracted by immersing the catalysts in a mixed acid of HCl and HNO3 at room temperature for 24 h and the amounts of Pt extracted were measured by AAS. 

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