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Introduction to Heterogeneous Catalysis in Organic Transformation
Published in Varun Rawat, Anirban Das, Chandra Mohan Srivastava, Heterogeneous Catalysis in Organic Transformations, 2022
Garima Sachdeva, Gyandshwar Kumar Rao, Varun Rawat, Ved Prakash Verma, Kaur Navjeet
X-ray absorption spectroscopy (XAS) is frequently utilized for determining the local geometric and electrical structure of materials. Typically, the experiment is conducted using synchrotron radiation, which generates powerful and tunable X-ray beams. Samples can be in gas, solution, or solid form. This technique can be utilized for the structural and compositional analysis of solid catalysts. The main advantage of using this technique is that it does not require long-range order in the samples and can work efficiently under non-vacuum conditions [25].
Biodistribution and Toxicity of Gold Nanoparticles
Published in Lev Dykman, Nikolai Khlebtsov, Gold Nanoparticles in Biomedical Applications, 2017
For identification and localization of GNPs in tissues, the histology, autometallography, SEM, and TEM techniques are in common use [56]. SEM or TEM analysis can be combined with energy dispersive x-ray spectroscopy (EDX) to obtain elemental data. Additionally, x-ray absorption spectroscopy (XAS and its variants X-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS)) [59] can be used to obtain structural information on sulfur and gold atoms in samples under examination.
Vanadium Speciation in Soil Aqueous and Solid Phases
Published in Jörg Rinklebe, Vanadium in Soils and Plants, 2023
Worachart Wisawapipat, Yohey Hashimoto, Shan-Li Wang
X-ray absorption spectroscopy (XAS) is a powerful technique for identifying and quantifying chemical speciation (e.g., oxidation state, coordination geometry, and bond distance) of elements, including V in soil and environmental samples. The chemical species are of great importance for deliberating information about elemental (bio)availability, mobility, and solubility in terrestrial and aquatic systems.
A deep neural network for valence-to-core X-ray emission spectroscopy
Published in Molecular Physics, 2023
X-ray absorption spectroscopy (XAS) in the extended X-ray absorption fine structure (EXAFS) and the X-ray absorption near-edge structure (XANES) spectral domains has been widely used across the natural sciences to provide insight into the immediate (typically <6 Å) geometric structure around the absorbing atom and, through the information encoded in the pre-edge region of the XAS spectrum, the unoccupied valence electronic structure [1,2]. However, although XAS contains a large quantity of valuable structural information such as first-coordination-shell bond lengths and coordination numbers, it cannot directly deliver insight into the nature of bonding, often referred to as covalency [3], neither does it have sufficient sensitivity to distinguish between ligands binding through atoms with similar atomic numbers, e.g. C, N, and O. Instead, this information is best ascertained by probing the electronic structure of the occupied states which are directly involved in bonding.
Probing local electronic and geometric changes of hydrated calcium vanadium oxide (CaxV2O5·yH2O) upon Zn ion intercalation
Published in Journal of Coordination Chemistry, 2019
X-ray absorption spectroscopy (XAS) is an element-specific probe, wherein the experiment measures the absorption coefficient (μ(E)) as a function of energy. An X-ray is absorbed to eject a core electron when the X-ray energy exceeds the binding energy of the core electron. This absorption event causes a sharp increase in the linear μ(E) called the “absorption edge”. This process is governed by the electric-dipole selection rules for available electronic transitions (Δl = ±1) [36]. The lifetime of the core-hole is extremely short and therefore information is limited to ∼0.5 nm around the absorber and allows study of amorphous materials. The μ(E) is also highly sensitive to the environment or “molecular cage” of the photoabsorber. The formal oxidation state, coordination number, and the coordinating species that surround the absorber modulates the signal generating unique features for comparison. The allowed core electron (K shell) transitions for the first row transition metals (V and Zn) are 1s → 4p [37]. The oxidation of transition metals causes a stronger electrostatic attraction of core shell electrons and therefore the absorption edge will monotonically shift to higher energy with increased oxidation of the absorber [38, 39]. EXAFS is a similar process, however, well past the absorption edge, the X-ray has excess energy above the binding energy and results in the production of a photoelectron that is scattered by the local structure and Fourier transform approximates the radial distribution function [40].
Remediation of Clay Soils Contaminated with Potentially Toxic Elements: The Santo Amaro Lead Smelter, Brazil, Case
Published in Soil and Sediment Contamination: An International Journal, 2018
L. R. P. de Andrade Lima, L. A. Bernardez, M. G. dos Santos, R. C. Souza
The X-ray absorption spectroscopy (XAS) includes the X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions. In the present case, soil samples were used to perform EXAFS at the Brazilian Synchrotron Light Laboratory (LNLS) on the XAFS2 beam line. The energy calibration was done using a Pb foil and the transmission was measured at the Pb-LIII edge (Manceau et al., 1996). The measurements were replicated two or three times. Seven pure Pb compounds were used as standards: Pb, PbS, PbSO4, PbCO3, PbO, PbO2, and Pb2O3. Samples of the contaminated soil were used to evaluate the Pb pollutants, and soil samples were used to perform a dynamic EXAFS. A tubular furnace with a controlled atmosphere, using injection of synthetic air or argon, was used. The X-ray absorption spectra were repeatedly collected after temperature stabilization at 25, 400, 600, 800, 900, and 1000 °C. The EXAFS data analysis was performed using the Athena XAS data processing program v.0.9.22 (Ravel and Newville, 2005). The pre-edge background was removed and the post edge continuum was modeled using fit procedures. The normalized EXAFS data (c) were converted into wave vector (k) and k2 weighted data (Ravel and Newville, 2005).