Chemical State Of Sulfur Research Articles

Analytical Method for Rubber Materials Using Sulfur K-edge NEXAFS and Its Application

Here, we develop a technique for curve-fitting of the sulfur K-edge near-edge X-ray absorption fine structure (NEXAFS) to analyze the crosslinked structure of vulcanized rubber based on the chemical state of sulfur. The proposed analytical method provides the sulfur chain length (Sx), crosslink density, and sulfur oxide content simultaneously, and it is highly sensitive for the analysis of the depth direction. Furthermore, we verify the aging mechanism of the crosslinked structure using this analytical method. It is found that the sulfur chains, shortened and oxidized by heat aging at 120°C, can cause scission of the S—C bond, thereby decreasing the crosslink density. Long sulfur chains are more susceptible to oxidation, which rapidly decreases the sulfur chain length (Sx) and, in turn, the crosslink density compared with short sulfur chains. By comparing the heat-aging dependence between the S—C bond and S100, it is found that the styrene-butadiene rubber polymer surface can form the C—C crosslink. We present the aging mechanism of the crosslinked structure and establish NEXAFS as a useful analytical method for rubber materials.

Visualization of Sulfur Chemical State of Cathode Active Materials for Lithium–Sulfur Batteries by Tender X-ray Spectroscopic Ptychography

Visualization of Sulfur Chemical State of Cathode Active Materials for Lithium–Sulfur Batteries by Tender X-ray Spectroscopic Ptychography

High Purity Single Wall Carbon Nanotube by Oxygen-Containing Functional Group of Ferrocene-Derived Catalyst Precursor by Floating Catalyst Chemical Vapor Deposition.

Single wall carbon nanotubes (SWCNTs) were synthesized using oxygen-containing ferrocene derived catalysts. The mechanism of synthesizing carbon nanotubes was clarified by the catalyst’s exothermic or endothermic decomposition processes. By monitoring the decomposition process of ferrocene-derived catalyst precursors with and without sulfur, we found that the types of oxygen function groups closely influence catalyst formation and nanotube growth. The ferrocene-derived catalyst precursors have a different oxygen containing groups, which are hydroxyl (–OH, ferrocenenemethanol) and carbonyl (C=O, acetylferrocene, and 1,1′-diacetylferrocene). The sulfur chemical state (S 2p) on synthesized catalyst particles using acetylferrocene and 1,1′-diacetylferrocene has more sulfate () than others, and there also is a carbon state (C-S-C). The catalyst particle using ferrocenemethanol predominant formed metal–sulfur bonds (such as S2− and ). The hydroxyl group (–OH) of ferrocenemethanol enhanced the etching effect to remove amorphous carbon and prevented oxidation on the catalyst particle surfaces; however, the carbonyl group (C=O) of acetylferrocene reacted with the catalyst particles to cause partial oxidation and carbon dissociation on the surface of the catalyst particles. The partial oxidation and carbon contamination on catalyst particles controlled the activity of the catalyst. The DFT study revealed that the ferrocene-derived catalyst precursor was dissociated according to following process: the functional groups (such as CH3CO and COH) => first Cp ligands => second Cp ligands. The pyrolysis and release of Fe ions were delayed by the functional groups of ferrocene-derived precursors compared to ferrocene. The thermal-decomposition temperature of the catalyst precursor was high, the decomposition time was be delayed, affecting the formation of catalyst particles and thus making smaller catalyst particles. The size and composition of catalyst particles not only affect the nucleation of CNTs, but also affect physical properties. Therefore, the IG/ID ratio of the CNTs changed from 74 to 18 for acetylferrocene and ferrocene, respectively. The purity also increased from 79 to 90% using ferrocene-derived precursors.

The response of sulfur chemical state to different leaching conditions in chloride leaching of chalcocite

Heap chloride leaching of low-grade copper sulfides with the use of seawater has been proposed as a feasible alternative to address challenges associated with water scarcity and depletion of oxides. Our previous study of leaching kinetics showed that the leaching reaction slowed down in the second stage and the maximum copper extraction achieved at ambient temperature was around 70–80%. To uncover the reasons for the slowed-down leaching, we investigated the evolution of solid surface properties during leaching, particularly morphology and sulfur chemical state, and the responses of mineral surface properties to different leaching conditions using SEM-EDX and XPS techniques. The results showed that sulfur sequentially transformed from monosulfide S2− to disulfide S22−, and then to polysulfide Sn2− and elemental sulfur S0. Less elemental sulfur was present on the solid particle surfaces at high solution potentials, the removal of which by CS2 washing did not improve copper extraction. In contrast, at low solution potentials, a slight increase in copper extraction was associated with sulfur removal from the solid surfaces. These results led to the conclusion that the slow decomposition of polysulfide formed during leaching was responsible for the slow reaction at high solution potentials, whereas at low solution potentials, a combination of polysulfide decomposition and diffusion barrier by elemental sulfur layer was the reason for the slow dissolution. The effect of chloride was concluded to be important only at low solution potentials where the level of elemental sulfur crystallinity was lower.

Structural and optical properties of penicillamine-protected gold nanocluster fractions separated by sequential size-selective fractionation

Polydisperse water-soluble gold nanoclusters (AuNCs) protected by penicillamine have been synthesized in this work. The sequential size-selective precipitation (SSSP) technique has been applied for the size fractionation and purification of the monolayer-protected AuNCs. Through continuously adding acetone to a crude AuNC aqueous solution and controlling the volume percentage of acetone, we successfully separated the polydisperse AuNCs with diameters ranging from 0.5 to 5.4 nm into four different fractions sequentially. High-resolution transmission electron microscopy (HRTEM) shows that the four fractions are well-dispersed spherical particles of diameter 3.0 ± 0.6, 2.3 ± 0.5, 1.7 ± 0.4, and 1.2 ± 0.4 nm. Proton nuclear magnetic resonance spectroscopy suggests that disulfide, excess ligands and gold(I) complexes were removed from the AuNCs fractions. These results demonstrate the considerable potential of the SSSP technique for size-based separation and purification of AuNCs, achieving not only the isolation of larger nanoclusters (NCs) from small NCs in a continuous fashion, but also for the removal of small-molecule impurities. Based on the results from the mass spectrometry and thermogravimetric analysis, the average composition of the four fractions can be represented by Au38(SR)18, Au28(SR)15, Au18(SR)12, and Au11(SR)8, respectively. This indicates that the SSSP separation is mainly dependent on the core size and the ratio of Au atoms to ligands of AuNCs. X-ray photoelectron spectroscopy (XPS) has also been applied to observe the molecular dependence on the gold and sulfur chemical state of organosulfur monolayers of the fractions. The photoluminescence spectra of these AuNCs in the range of 900–790 nm was investigated at room temperature. The results show that the peak emission energy of the size-selected AuNCs undergoes a blue shift when the size is decreased, which can be attributed to the quantum confinement effect.

Hard X-ray photoelectron spectroscopy study of thermal effect on chemical state of sulfur in rubber compound

Hard X-ray photoelectron spectroscopy study of thermal effect on chemical state of sulfur in rubber compound

Sulfur Chemical State and Chemical Composition of Insoluble Substance in Soft Rime, Hard Rime, and Snow Collected in Remote and Rural Areas in Japan Using Wavelength-dispersive X-ray Fluorescence.

Using a commercially available wavelength-dispersive X-ray fluorescence (WDXRF) spectrometer, the chemical composition and S-Kα spectrum of rime and snow samples collected in remote and rural areas of Japan were measured with a membrane filter sample technique to investigate the long-range transport of aerosol from the East Asian continent. Insoluble substances are derived into three categories: 1) conventional mineral origin (crustal substance), 2) urban dust origin (Fe-Zn-Ca) and 3) coal origin (S-As). Assuming that (i) S(VI) was found as a plaster-like substance in hard rime, depending on [Ca], and that (ii) S(-II) was found as non-crustal sulfur compounds, fractions of S(VI) and S(-II) in rime could be calculated as 35 ± 6 and 66 ± 7% by [Ca], which is in agreement with 32 ± 8 and 68 ± 8%, respectively, by the chemical shift of the S-Kα line. During a one-day meteorological event that included the accumulation of both rime and snow, differences to the snow-like content corresponded to characteristics typical of rime since the chemical compositions of rime also includes the composition of the snow. The fractions of 22 ± 12% of S(VI) and 76 ± 12% of S(-II), respectively, were found in rime. The fraction of S(-II) decreased from the Chugoku district towards the Shikoku district. Along the coast of the Japan Sea, the fraction of S(-II) decreased from Chugoku district toward the Northeast Japan. It can be proposed that other analytical techniques of S, Al, and Ca in that are favorable to this fractionation.

From Au-Thiolate Chains to Thioether Sierpiński Triangles: The Versatile Surface Chemistry of 1,3,5-Tris(4-mercaptophenyl)benzene on Au(111).

Self-assembly of 1,3,5-tris(4-mercaptophenyl)benzene (TMB), a 3-fold symmetric, thiol-functionalized aromatic molecule, was studied on Au(111) with the aim of realizing extended Au-thiolate-linked molecular architectures. The focus lay on resolving thermally activated structural and chemical changes by a combination of microscopy and spectroscopy. Thus, scanning tunneling microscopy (STM) provided submolecularly resolved structural information, while the chemical state of sulfur was assessed by X-ray photoelectron spectroscopy (XPS). Directly after room-temperature deposition, only less well ordered structures were observed. Mild annealing promoted the first structural transition into ordered molecular chains, partly organized in homochiral molecular braids. Further annealing led to self-similar Sierpiński triangles, while annealing at even higher temperatures again resulted in mostly disordered structures. Both the irregular aggregates observed at room temperature and the chains were identified as metal-organic assemblies, whereby two out of the three intermolecular binding motifs are energetically equivalent according to density functional theory (DFT) simulations. The emergence of Sierpiński triangles is driven by a chemical transformation, i.e., the conversion of coordinative Au-thiolate to covalent thioether linkages, and can be further understood by Monte Carlo simulations. The great structural variance of TMB on Au(111) can on one hand be explained by the energetic equivalence of two binding motifs. On the other hand, the unexpected chemical transition even enhances the structural variance and results in thiol-derived covalent molecular architectures.

X‐ray fluorescence determination of sulfur chemical state in sulfide ores

This paper describes the X‐ray fluorescence technique for estimation of the ratio between sulfide and total sulfur in sulfide ores using the influence of sulfur chemical state on positions and intensities of lines (SKα1,2, SKβ1,3) and satellites (SKβ′, SKα3,4) of the sulfur X‐ray emission spectra measured by the wavelength‐dispersive X‐ray fluorescence spectrometer. The samples to be analyzed were prepared as pressed powder pellets on boric acid substrate. The SKα1,2 line chemical shift is the most appropriate parameter for sulfur chemical state estimation because spectral lines in this field are intensive and are almost not affected by spectral overlap of lead spectrum lines. The ratios of line intensities SKβ′/SKβ1,3, SKα3,4/SKα1,2 and SKβ1,3/SKα1,2 were also used as analytical parameters. Forty‐one samples of sulfide ores collected in the Russian Far East and Southern Ural deposits have been analyzed. The results of estimation of sulfur chemical state by gravimetric and proposed X‐ray fluorescence techniques agree fairly well. Copyright © 2016 John Wiley & Sons, Ltd.

Nature of chemical states of sulfur embedded in atomic-layer-deposited HfO2film on Ge substrate for interface passivation

Sulfur was embedded in atomic-layer-deposited (ALD) HfO2 films grown on Ge substrate by annealing under H2S gas before and after HfO2 ALD. The chemical states of sulfur in the film were examined by S K-edge X-ray absorption spectroscopy. It was revealed that the valences of S-ions were mostly –2 at Ge/HfO2 interface (GeSx or HfO2–ySy to passivate the interface), while they were mostly +6 in HfO2 layers (sulfates; HfO2–z(SO4)z). The leakage current density in post-deposi-tion-treated film was lower than that in pre-deposition-treated one. This suggests that the passivation of defects in oxide layer by sulfate ions is more effective to lower the leakage current rather than the interface defect passivation by S2– ions. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Changes in the surface phase composition of sulfide minerals upon irradiation by high-power nanosecond pulses

The effect of high-power (high-voltage) nanosecond pulses on the phase composition and chemical state of atoms of surface layers of sulfide minerals with different semiconductor properties (galenite, molybdenite, and sphalerite) is investigated by means of XPES. Common patterns and characteristic features of the structural phase transformations of sulfide surfaces under the pulsed energetic effect are the formation and growth of a surface layer by the nonstoichiometric sulfur-enriched sulfide phase and Zn and Mo oxides and hydroxides; the staged character of the transformation of sulfur atoms in the composition of galenite and sphalerite surface layers; and the stability of the chemical state of sulfur in the molybdenite composition and lead atoms in the galenite composition.

Sulfur and nitrogen in the high-sulfur coals of the Late Paleozoic from China

Abstract The chemical states of sulfur and nitrogen in high-sulfur coals were investigated via X-ray photoelectron spectroscopy (XPS). Twenty-five high-organic-sulfur coal samples of the Late Paleozoic from China were reported, fourteen of which were superhigh organic sulfur (SHOS) coals collected from southern China with organic sulfur contents >8% (on dry and ash-free basis). The aromatic fraction of organic sulfur increased with the increasing carbon content and was inversely proportional to aliphatic sulfur, indicating that the relative abundance of thiophenic and thiol sulfur compounds were probably related to the coal rank. The nitrogen contents of the SHOS coals from southern China were much lower than expected. In an uncommon manner, inorganic oxidized nitrogen, instead of pyrrolic and pyridinic nitrogen, was the predominant nitrogen form in the SHOS coals with only bituminous rank. Some signs pointed to ammonium illite as the probable form of inorganic nitrogen, which may provide another piece of evidence for the new viewpoint of the volcanic and/or hydrothermal origin of SHOS coals. The presence of the amine N peak in coals requires further study, which is selectively lost during thermal maturation and should not appear in normal coal.

Forensic analysis of tire rubbers based on their sulfur chemical states

The chemical states of sulfur in 11 tires were analyzed using X-ray absorption near-edge structure (XANES) in order to discriminate between various tire rubbers. All tires had peaks around 2471.5 and 2480.5eV, and the shapes and heights of these peaks differed among tires, suggesting that the sulfur chemical state could be used for discrimination between tire rubbers. Based on t-tests on the results of XANES, 43 of 55 combinations were different at a significance level of 5%.

Sulfur-Metal Orbital Hybridization in Sulfur-Bearing Compounds Studied by X-ray Emission Spectroscopy

The electronic structure and ligand environment of sulfur was investigated in various sulfur-containing compounds with different structures and chemical states by using X-ray emission spectroscopy (XES). Calculations were performed using density functional theory (DFT) as implemented in the StoBe code. The sulfur chemical state and atomic environment is discussed in terms of the molecular orbitals and partial charges that are obtained from the calculations. The main spectral features can be modeled using our calculational approach. The sensitivity of the Kbeta emission to the cation and the local symmetry is discussed.

Phase separation of borosilicate glass containing sulfur

A 10Na(2)S·30B(2)O(3)·60SiO(2) (mol %) glass was prepared, and the changes in glass structure and chemical state of sulfur caused by phase separation were investigated. In the as-prepared and heat-treated glasses, sulfur was present as S(2)− anion and polysulfide S(2)− and S(3)− anions, and Si–S and B–S bonds were not confirmed. A phase separation by spinodal decomposition was observed after heat-treatment, where sulfur was preferentially distributed to borate-rich phase. Even after the phase separation, formation of non-bridging oxygen was not recognized. The preferential distribution of sulfur anions in the present glass was explainable on the basis of the change in population of sodium ions, which compensated the negatively-charged sulfur anions.

Sulfur K-edge XANES spectroscopy as a tool for understanding sulfur chemical state in anaerobic granular sludge

Sulfur is an essential biological element, yet its biochemistry in anaerobic biofilm is poorly understood because there are few tools for studying this element in biological systems. X-ray absorption spectroscopy provides a unique approach to determining the chemical speciation of sulfur in intact biological samples. When treating sulfate containing wastewaters in full scale up-flow anaerobic sludge bed bioreactors, microbial activity forms biofilms, consisting of a complex mixture of cells and associated extracellular substances as well as undefined inorganic precipitates. In addition to the anaerobic sludges, a large variety of model compounds of S (esp. sulfides) were investigated to find consistencies in the XANES that were used to model each "valence state" of S. The results confirmed that attributing a specific valence to most sulfides is impossible as we measured a continuum of edge shifts from sulfur "-2" to "-1", depending on the electronic structure of S in the probed sulfides. In the sludges, various sulfur hot spots were probed for speciation, despite photo-reduction was sometimes a problem. First, we index the main features of complex K-edge XANES spectra for S2--type units and sulfate units. Organic sulfur compounds were also shown to contribute significantly to the sulfur species present in some anaerobic granular sludge.

Preparation, Characterization, and Acidity Evaluation of Perfluorosulfonic Acid-Functionalized Silica Catalysts

Three different hybrid organic/inorganic solid acid catalysts were prepared by grafting perfluorosulfonic acid onto amorphous silica gel by covalently anchoring β-sultone onto the hydroxyl groups on the silica surface. The anchored sulfonic groups have been characterized by thermal analysis, infrared spectroscopy, and photoelectron spectroscopy (XPS). Particularly, the XPS technique has proven to be an extremely powerful tool to determine the nature and chemical state of sulfur and carbon, as well as the surface density of the acid groups. The hybrid organic/inorganic systems functionalized with sulfonic acid groups were tested in the esterification reaction of acetic acid with methanol in liquid phase. Activity results obtained at 333 K and using an initial molar ratio AcOOH:MeOH = 1:1 revealed that the acid-functionalized, nonsilylated catalyst reaches acetic acid conversion of ∼50%, which contrasts with the much lower level (∼30%) reached by a commercial Nafion silica composite sample. Treatment of the catalysts in methanol at 333 K under stirring for 48 h emphasized that only the acid-functionalized and silylated sample retains some of the sulfonic groups.

High-resolution photoelectron spectroscopy of self-assembled mercaptohexanol monolayers on gold surfaces

Mercaptohexanol (MCH) monolayers assembled on gold surfaces were investigated by means of high-resolution X-ray photoemission spectroscopy (XPS). The presence of three chemical states of sulfur was detected which exhibit different strength of interaction with the gold surface. Comparing the relative intensities of the corresponding subspectra allowed to estimate which fraction of the deposited MCH molecules is not bound to the metal surface via the thiol group, and thus, the characterization of the quality of the self-assembled monolayer (SAM). The number of sulfur atoms bound to the gold surface decreased when part of the the hydroxyl endgroup of the assembled MCH molecules is substituted by DNA duplexes. Long-term irradiation experiments on MCH layers revealed that soft X-ray radiation induces damage of the SAMs, accompanied with a preferential cleavage of both hydroxyl groups and hydrogen atoms from the alkane chains, leading in turn to a rearrangement of those MCH molecules which were not bound to the gold surface during the SAM preparation. The fraction of molecules which are bound to the metal via the thiol group, however, is practically not affected by the irradiation with soft X-rays.

Comparative XPS Study of Silver and Copper Surfaces Exposed to Flowing Air Containing Low Concentration of Sulfur Dioxide

Sulfur dioxide (SO2) is a typical gas affecting the atmospheric corrosion of metals, particularly outdoors. Although many studies have investigated the effect of SO2 on the atmospheric corrosion of silver and copper, little is known about the early stage of their corrosion behavior. In this study we analyzed the chemical state of sulfur on silver and copper plates exposed to flowing air containing low concentrations (18 and 148 ppb) of SO2 using X-ray photoelectron spectroscopy (XPS). The shapes of the spectra were the same for both concentrations, indicating that the chemical state of the analyzed elements did not depend on the SO2 concentration. There was a difference in the chemical state of the sulfur between the silver and copper. Three peaks were observed in the S 2p XPS spectra for the silver originating from bisulfite, S2O52-, S2O32-, and S2-. The bisulfite resulted from SO2 dissolution into the surface electrolyte, and the others resulted from the reduction of sulfurous acid. In contrast, only bisulfite was observed in the S 2p XPS spectra for the copper. It also originated from the dissolution of SO2 into the surface electrolyte. The difference in the chemical state of the sulfur between the silver and copper is attributed to the presence of native oxides on the surface, which may have impeded the reduction of bisulfite.

Sulfur chemical state analysis of diesel emissions of vehicles using X-ray absorption

Soft X-ray absorption spectra of sulfur K edge were measured for diesel exhaust particles from three different vehicles. The X-ray spectra were measured using a synchrotron radiation beamline. The spectra were measured by surface sensitive total electron yield method and bulk sensitive X-ray fluorescence yield method. One vehicle concentrated the S 2− on the surface of the emission particles; the others did not concentrate S 2−. This type of chemical state analysis method is useful for the process analysis such as diesel emissions.