Studies of Cu(II) in soil by X-ray absorption spectroscopy

Abstract

Frenkel, A. I. and Korshin, G. V. 2001. Studies of Cu(II) in soil by X-ray absorption spectroscopy. Can. J. Soil Sci. 81: 271-276. Based on original data for copper, this paper evaluates the use and advantages of X-ray absorption fine structure (XAFS) in studies of heavy metals in soils. The structural parameters of the Cu 2+ target were quantified for soil exposed to copper and the same soil eluted with 0.1 M HCl. Experimental data were obtained using synchrotron sources of second and third generations. X-ray absorption near edge structure (XANES) indicated that the copper in both samples is likely to be predominantly bound by oxygen-containing functional groups. Extended X-ray absorption fine structure (EXAFS) analysis showed that the equatorial Cu-O distances were similar to those seen for Cu 2+ -humic complexes in aqueous solutions, but the axial distances for both samples were longer than in water. In the axial direction, this may indicate a type of ligation dissimilar to that in solutions. The magnitude of the mean square deviation of the axial Cu-O distance in the 0.1 M HCl eluted sample indicated a stronger bond compared with that in the sample containing both extractable and tightly bound copper. The results indicate that careful examination of structural data for sequentially eluted soils in combination with the development of new radiation sources to improve the sensitivity and quality of the data are likely to improve insight into the nature of interactions between heavy metals and soil.Key words: Soil, copper, humic, speciation, extended X-ray absorption fine structure, X-ray absorption near edge structure Mots clés: Sol, cuivre, humique, espèces chimiques, EXAFS, XANES X-Ray Absorption Fine Structure spectroscopy is an advanced structural technique based on the use of high intensity synchrotron radiation to measure the X-ray absorption coefficient of a material as a function of the X-ray energy. The interpretation of XAFS spectra provides quantitative information regarding the short-range atomic structure around the target element in the sample.The fine structure in the XAFS spectrum originates from the oscillatory nature of the wave function of the photoelectron ejected from the target atom in the photoabsorption process. The fine structure in the absorption coefficient starts at ca. 40 eV and extends ca. 1000 eV past the absorption edge. For these energies, single and multiple scatterings of the photoelectron by its nearest neighbors define the behavior of the X-ray absorption coefficient, which, due to its nature, contains the information about the identity and coordination numbers of the surrounding atoms, as well as about relevant distances and their disorders. The method of XAFS, which studies the absorption coefficient in the discussed range of energies, is called Extended X-Ray Absorption Fine Structure (EXAFS). The X-ray absorption near edge structure (XANES) spectroscopy is an allied but independent method that examines the data in the energy region from the Fermi level up to 40 eV past t...

Relationship between iron and trace metal fractionation in soils

“…This is in accordance with the results of X-ray absorption analyses by other studies (e.g. Frenkel and Korshin, 2001;Lewis et al, 2011), which showed that both Pb and Cu are bound predominantly by oxygen-containing functional groups in soils, which may be associated both with organic (humic-like) and inorganic metal-oxide (e.g. Pb-and Cu-oxides) or even silicate phases.…”

Characterization of a Poly‐4‐Vinylpyridine‐Supported CuPd Bimetallic Catalyst for Sonogashira Coupling Reactions

“…The EXAFS data analysis of the CuPd/PVPy sample revealed the presence of two Cu–O coordination shells consistent with Cu 2+ ions coordinated with O atoms at short (1.94 Å) and longer (2.52 Å) distances and a Cu–Pd contribution exhibiting a distance and coordination number compatible with the results obtained at the Pd K‐edge . The two different Cu–O distances found were also confirmed by the presence of the two peaks (labelled C and D) between 8981 eV and 8993 eV in the first derivative of the XANES spectrum of the CuPd sample (Figure ) that are normally associated to a tetragonal distortion of the CuO 6 octahedron that gives shorter equatorial and longer axial Cu−O bonds. In the absence of a tetragonal distortion, the splitting observed in Figure disappears.…”

Copper sorption by the edge surfaces of synthetic birnessite nanoparticles

“…5b) indicates that the axial ligand(s) are located at about 1.9 + 0.4 Å or 2.3 Å (Frenkel et al, 2000). We cannot confirm whether Cu has one or two axial ligands but, in principle, both outcomes are reasonable because Cu in aqueous solution prefers a 5-fold elongated square pyramidal coordination that is likely to be competitive with a 6-fold distorted octahedral coordination (Frenkel and Korshin, 2001;Bryantsev et al, 2008).…”