Xanes Spectroscopy of Sulfur in Earth Materials

Abstract

X-ray absorption near-edge structure (XANES) spectroscopy is the ideal non-destructive technique for characterizing and quantifying S species in compositionally complex natural materials such as silicate glasses and minerals, coals, asphalts and asphaltenes, kerogens and humic substances. Sulfur absorption edges represent the transition of S 1s and 2p core electrons to unoccupied antibonding orbitals at the bottom of the conduction band. Shifts in the position of the absorption-edge feature of S K-and L-edge XANES spectra constitute a chemical ruler for oxidation state of both inorganic and organic species of S; the S K edge shifts from 2469.5 eV for chalcopyrite (2-oxidation state) to 2482 eV for gypsum (6+). However, chemical state of S in Earth materials is most readily assigned by comparing the overall XANES profi le with spectra for reference compounds. Sulfur XANES spectra are reviewed for pyrite, troilite, pyrrhotite and NiAs-type Co 0.923 S and Ni 0.923 S, niningerite (MgS), oldhamite (CaS), alabandite (MnS) and cubic FeS, and sphalerite and related phases, as well as for selected solid-solutions of the monosulfi des. Sulfur XANES spectra for FeS, CoS, NiS, MgS, CaS, MnS and ZnS have been simulated by multiple scattering calculations. The S K-edge XANES of transition-metal-bearing monosulfi des generally show anomalous absorption consistent with hybridization of the fi nal S 3p * antibonding states with empty 3d orbitals on the metal atoms. Various applications of S K-and L-edge XANES fi ngerprinting are discussed, including speciation of inorganic S in basaltic glasses, lazurite and haüyne, identifi cation of organic functional groups of S in coals, kerogens and humic substances extracted from subtropical soils and marine sediments, and the association of sulfated sugars with calcifi cation of coral aragonite skeletons.Keywords: XANES spectroscopy, chemical state of S, electronic structure and bonding, sulfi des, sulfates, magma, organic geochemistry. SOMMAIRELa spectroscopie d'absorption des rayons X dans la région pré-seuil (XANES) s'avère la technique non-destructive par excellence pour caractériser et quantifi er les espèces de soufre dans les matériaux naturels de composition complexe, par exemple les verres silicatés et minéraux, charbons, asphaltes et asphaltènes, kérogènes et substances humiques. Les seuils d'absorption du soufre résultent de la transition des électrons 1s et 2p du noyau à des orbites non occupés anti-liaisons à la base de la bande de conduction. Les décalages dans la position des seuils K et L du soufre des spectres XANES constituent un barème chimique important dans l'évaluation du niveau d'oxydation du soufre, à la fois pour les espèces inorganiques et organiques; le seuil K est déplacé de 2469.5 eV dans la chalcopyrite (valence 2-) à 2482 eV dans le gypse (6+). Toutefois, l'état du soufre des matériaux terrestres est plus facilement attribué en comparant le profi l XANES entier d'un échantillon aux spectres des composés de réfé-rence. Les spectres XANES du soufre so...

Operando Characterization of Intermediates Produced in a Lithium-Sulfur Battery

“…Although Li 2 S is in a more reduced state than S 8 and polysulfides, the presence of its main features in the 2473-2475.5 eV region can be explained by the ionic character of the Li 2 S bond. 49 In our qualitative analysis we will identify formation of polysulfides by the appearance of the 2470 eV feature and the formation of Li 2 S by the appearance of a convex feature at 2475.5 eV ( Figure 5). The slightly dampened shape of all the peaks indicates the presence of self-absorption, which can be explained by the use of manual grinding procedure and the resulting micrometer-sized and not the needed sub-micrometer-sized particles and/or slightly too high amount of the sulfur compound used.…”

Hard X-ray photoelectron and X-ray absorption spectroscopy characterization of oxidized surfaces of iron sulfides

“…The XAS spectra of NiAs-structured pyrrhotite and stoichiometric troilite FeS have been measured, calculated and analyzed in a number of studies; the spectroscopic features are largely similar to those in pyrite, despite different electronic structures, and their detailed description can be found in the literature [43][44][45][46][47][48][49][50][51][52][53][54][55][56]. The main differences observed in the S K-edge XANES (Fig.…”

“…A number of XANES studies on iron sulfides have been reported previously [33,[43][44][45][46][47][48][49][50][51][52][53][54][55][56], but the difference between TEY and PFY Kedge spectra of air-oxidized and chemically etched materials has not been analyzed yet. Here, samples of each mineral (i.e., pyrite and pyrrhotite) polished in air were compared with those treated with an acidic ferric chloride solution to probe the effect of exposure to the leaching (etching) medium in hydrometallurgy and natural environments, and in materials science.…”

Exploring tarnished daguerreotypes with synchrotron light: XRF and μ-XANES analysis

“…6), which arises from a 1s→ 3p transition. The location of this first transition doublet suggests that the S pπ * orbital is directly involved in the covalent Ag-S interaction [38]. This metal-sulfur bond is seen as the double feature of the first peak [39].…”