XANES structure spectroscopy

XANES X-ray absorption near edge structure spectroscopy... 

Techniques of microscopic XRF ( j,-XRF) developed in the last 20 years provide 2D images and elemental maps of each element present in the target material. Portable/in situ p-XRF, j,-XRF spectrometers synchrotron-based ( -SRXRF) and micro-x-ray absorption spectroscopy/micro-x-ray absorption near-edge structure spectroscopy (XAS/ J,-XANES) have improved the mineralogical characterization, as well as the elemental and chemical imaging of samples at the submicrometer scale [61]. 

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)). 

XRF = X-ray fluorescence spectroscopy, XPS = X-ray photoelectron spectroscopy, AES = Auger electron spectroscopy, XANES = X-ray absorption near edge spectroscopy, RAIR = Reflectance-absorbance infrared spectroscopy, EXAFS = X-ray absorption fine-structure spectroscopy, ECR = Electric contact resistance, NMR = Nuclear magnetic resonance spectroscopy, IPS = Imaging photoelectron spectromicroscopy. 

The absorption edges in Fig. 10.10 are not perfectly sharp, but have a delicate fine structure ("Kossel35 lines") that was first explored in the 1930s. Since about 1970, this fine structure is now used in EXAFS (extended X-ray absorption edge fine structure spectroscopy) and in XANES (X-ray absorption near edge spectroscopy) the oscillations are due, again, to a chemical shift, which can be used to identify the local chemical environment of the emitting element in the sample. 

Solid-phase speciation has been measured both by wet chemical extraction and, for arsenic, by instrumental methods principally X-ray absorption near edge structure spectroscopy (XANES) (Brown et al., 1999). La Force et al. (2000) used XANES and selective extractions to determine the likely speciation of arsenic in a wetland affected by mine wastes. They identified seasonal effects with As(El) and As(V) thought to be associated with carbonates in the summer, iron oxides in the autumn and winter, and silicates in the spring. Extended X-ray absorption fine stmcture spectroscopy (EXAES) has been used to determine the oxidation state of arsenic in arsenic-rich Californian mine wastes (Eoster et al., 1998b). Typical concentrations of arsenic in sods and sediments (arsenic <20 mg kg ) are often too low for EXAFS measurements, but as more powerful photon beams become available, the use of such techniques should increase. 

The structure of the copolymer, poly(di-n-butylstannane-co-methylphenylsilane) with a Sn Si ratio of 1 3 was determined with X-ray absorption fine-structure spectroscopy (EXAES) and X-ray absorption near-edge spectroscopy (XANES). The bond distances of Sn-Sn (2.82 A), Sn-Si (2.58 A), and Sn-C (2.15 A) in the copolymer were comparable with the cyclooligostannylsilane, illustrated in Eigure 3.8.1. 

Chemical vapor deposition (CVD) has been used to prepare nanoparticle catalysts, although the technology is quite expensive. Dimethylgold acetylacetonate absorbs on supports such as MgO. Decomposition at > 100°C produces an efficient CO oxidation catalyst. X-ray absorption near edge (XANES) and extended X-ray absorption fine structure spectroscopies (EXAFS) showed that, under steady-state CO oxidation conditions, the catalyst contained Au(0) in the form of (on average) Aus clusters and also additional gold as... 

A veritable arsenal of techniques has been mobilized to provide information regarding the structure of redox molecular sieves [9-14], X-Ray powder diffraction (XRD) provides an immediate check for crystallinity and structural type. X-Ray absorption fine structure spectroscopy (EXAFS) and X-ray absorption near edge spectroscopy (XANES) give fiirther insights into coordination geometry and bond lengths. Infiared and Raman spectroscopy have been used to identify characteristic features, e.g. the 960 cm bond attributed to the Si-OTi stretching vibration in TS-1 [9]. 

Also XANES apparently indicates the presence of any Au-P bonds in a sample. EXAFS, extended X-ray absorption fine structure, spectroscopy has been used with curve fitting techniques to show that the gold atoms in solutions of sodium gold(I)thiomalate (GTM) are coordinated to two sulfur atoms at 2.29 R. Aurosomes, gold-containing lysosomal bodies formed in the kidneys of rats given chronic doses of GTM, have two sulfur atoms bound to gold(I) at 2.30... 

Farges F (2002) Improving data reduction methods in X-ray absorption fine structure spectroscopy. Part 1 pre-edge and XANES, resolution, convolution and component analyses. Phys Chem Minerals... 

Huffman GP, Mitra S, Huggins FE, Shah NS, Vaidya N, Lu F (1991) Quantitative analysis of all major forms of sulfur in coal by X-ray absorption fine structure spectroscopy. Energy Fuels 5 574-581 Huffman GP, Shah NS, Huggins FE, Stock LM, Chatterjee K, Kilbane JJ, Chou M, Buchanan DH (1995) Sulfur speciation of desulfurized coals by XANES spectroscopy. Fuel 74 549-555 Huggins FE, Huffman GP (1995) Chlorine in coal anEXAFS spectroscopic investigation. Fuel 74 556-569 Hundal LS, Carmo AM, Bleam WL, Thompson ML (2000) Sulfur in biosolids-derived fulvic acidic characterization by XANES spectroscopy and selective dissolution approaches. Environ Sci Technol 34 5184-5188... 

---