XANES

About: XANES is a research topic. Over the lifetime, 7737 publications have been published within this topic receiving 188032 citations.

A structural basis for the corrosion resistance of lead-iron-phosphate glasses: an X-ray absorption spectroscopy study

Abstract: Lead metaphosphate glass is characteristically prone to aqueous attack but becomes chemically resistant on the addition of iron oxide. We have measured the K-edge extended X-ray absorption fine structure (EXAFS) of Fe and the LIII-edge EXAFS of Pb and find the atomic environments of the two sites to be very different. Whereas Fe is octahedrally coordinated with an oxygen distancce of 1•9(5) A, the coordination of Pb is 8 (±1) and the sites display considerable disorder with an average lead—oxygen distance of 2•4(7) A. X-ray absorption near-edge structure (XANES) measurements of the P K-edge confirm the presence of phosphate as (PO4)n, chains. These results suggest that, by pinning the structure, Fe sites not only shorten the average polyphosphate chain length but also block the percolation of Pb ions. Both effects increase the chemical resistance of the structure to aqueous attack and also reduce the tendency of these glasses to crystallize.

Design of spectroelectrochemical cell for in situ X-ray absorption fine structure measurements of bulk solution species

Abstract: A purpose-built spectroelectrochemical cell for in situ fluorescence XAFS (X-ray absorption fine structure) measurements of bulk solution species is described. The cell performance was demonstrated by the collection of europium L3-edge XANES (X-ray absorption near edge structure) during constant-potential electrolysis of 14.2mmEuCl3.6H2Oin1mH2SO4 aqueous electrolyte. Additionally discussed in this report are the probabilities of 2p3/2→5d electronic transitions pertaining to Euiii and Euii ions. Implications for the use of XANES in studying intermediate-valence materials, and some potential applications of the presently reported spectroelectrochemical cell are described.

Surface Structure and Chemical Switching of Thioctic Acid Adsorbed on Au(111) As Observed Using Near-Edge X-ray Absorption Fine Structure

Abstract: Thioctic acid (alpha-lipoic acid) is a molecule with a large disulfide-containing base, a short alkyl-chain with four CH{sub 2} units, and a carboxyl termination. Self-assembled monolayer (SAM) films of thioctic acid adsorbed on Au(111) have been investigated with near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and x-ray photoelectron spectroscopy (XPS) to determine film quality, bonding and morphology. Using standard preparation protocols for SAMs, that is, dissolving thioctic acid in ethanol and exposing gold to the solution, results in poor films. These films are highly disordered, contain a mixture of carboxyl and carboxylate terminations, have more than monolayer coverage, and exhibit unbound disulfide. Conversely, forming films by dissolving 1 mmol thioctic acid into 5% acetic acid in ethanol (as previously reported with carboxyl-terminated alkyl-thiols) forms ordered monolayers with small amounts of unbound sulfur. NEXAFS indicates tilted over endgroups with the carboxyl group normal on average 38{sup o} from the surface normal. Slight dichroism in other features indicates alkyl chains statistically more upright than prostrate on the surface. Reflection-absorption Fourier transform infrared (RA-FTIR) spectra indicate hydrogen bonding between neighboring molecules. In such well-formed monolayers, a stark reorientation occurs upon deprotonation of the endgroup by rinsing in a KOH solution. The carboxylate planemore » normal is now about 66{sup o} from sample normal, a much more upright orientation. Data indicate this reorientation may also cause a more upright orientation to the alkyl portion of the molecules.« less

Surface complexation of copper(II) on soil particles: EPR and XAFS studies.

Abstract: The interactions of transition metals with natural systems play an important role in the mobility and the bioavailability of these metals in soils. In this study, the adsorption of copper(II) onto natural soil particles was studied as a function of pH and metal concentration. The retention capacity of soil particles was determined at pH 6.2 to be equal to 6.7 mg of copper/g of solid. The Langmuir and Freundlich isotherm equations were then used to describe the partitioning behavior of the system at different pH values. A combination of EPR, extended X-ray absorption fine structure (EXAFS), and X-ray absorption near-edge structure (XANES) spectroscopies was used to probe the Cu atomic environment at the soil particles/aqueous interface. The spectroscopic study revealed that copper(II) ions are held in inner-sphere surface complexes. It also revealed that Cu was in an octahedral coordination with first-shell oxygen atoms. A weak tetragonal distortion was pointed out due to the Jahn−Teller effect, with a mea...