Extended X-ray absorption fine structure

About: Extended X-ray absorption fine structure is a research topic. Over the lifetime, 10452 publications have been published within this topic receiving 276744 citations.

In Situ Grazing-Incidence Extended X-ray Absorption Fine Structure Study of Pb(II) Chemisorption on Hematite (0001) and (1-102) Surfaces

Abstract: The dominant mode of binding of aqueous Pb(II) to single-crystal (0001) (C-cut) and (1−102) (R-cut) surfaces of α-Fe2O3 has been determined by grazing-incidence X-ray absorption fine structure (GI-XAFS) spectroscopy. Oligomeric Pb(II) complexes were found to bind in inner-sphere modes on both surfaces, which is in contrast with the binding of aqueous Pb(II) on α-Al2O3 (0001) surfaces, where Pb(II) was found in past GI-XAFS studies to bind in a dominantly outer-sphere mode, indicating a significant difference in reactivity of these two surfaces to Pb(II). This difference in reactivity to Pb(II) is explained on the basis of recent crystal truncation rod diffraction studies of the α-Fe2O3 and α-Al2O3 C-cut surfaces in contact with bulk water, which found major structural differences between the surfaces of these two metal oxides.

Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water.

Abstract: X-ray transient absorption spectroscopy (X-TAS) has been used to study the light-induced hydrogen evolution reaction catalyzed by a tetradentate macrocyclic cobalt complex with the formula [LCoIIICl2]+ (L = macrocyclic ligand), [Ru(bpy)3]2+ photosensitizer, and an equimolar mixture of sodium ascorbate/ascorbic acid electron donor in pure water. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis of a binary mixture of the octahedral Co(III) precatalyst and [Ru(bpy)3]2+ after illumination revealed in situ formation of a Co(II) intermediate with significantly distorted geometry and electron-transfer kinetics of 51 ns. On the other hand, X-TAS experiments of the complete photocatalytic system in the presence of the electron donor showed the formation of a square planar Co(I) intermediate species within a few nanoseconds, followed by its decay in the microsecond time scale. The Co(I) structural assignment is supported by calculations based on density func...

Atomic structure relaxation in nanocrystalline NiO studied by EXAFS spectroscopy: Role of nickel vacancies

Abstract: Nanocrystalline NiO samples have been studied using the Ni K-edge extended x-ray absorption fine structure (EXAFS) spectroscopy and recently developed modeling technique, combining classical molecular dynamics with ab initio multiple-scattering EXAFS calculations (MD-EXAFS). Conventional analysis of the EXAFS signals from the first two coordination shells of nickel revealed that (i) the second shell average distance R(Ni–Ni2) expands in nanocrystalline NiO compared to microcrystalline NiO, in agreement with overall unit cell volume expansion observed by x-ray diffraction; (ii) on the contrary, the first shell average distance R(Ni–O1) in nanocrystalline NiO shrinks compared to microcrystalline NiO; (iii) the thermal contribution into the meansquare relative displacement σ 2 is close in both microcrystalline and nanocrystalline NiO and can be described by the Debye model; (iv) the static disorder is additionally present in nanocrystalline NiO in both the first Ni–O1 and second Ni–Ni2 shells due to nanocrystal structure relaxation. Within the MD-EXAFS method, the force-field potential models have been developed for nanosized NiO using as a criterion the agreement between the experimental and theoretical EXAFS spectra. The best solutions have been obtained for the 3D cubic-shaped nanoparticle models with nonzero Ni vacancy concentration Cvac: Cvac ≈ 0.4–1.2% for NiO nanoparticles having the cube size of L ≈ 3.6–4.2 nm and Cvac ≈ 1.6–2.0% for NiO thin film composed of cubic nanograins with a size of L ≈ 1.3–2.1 nm. Thus our results show that the Ni vacancies in nanosized NiO play important role in its atomic structure relaxation along with the size reduction effect.