Extended X-ray Absorption Fine Structure Techniques Research Articles

Sorption mechanism of cadmium on soils: A combination of batch experiment, path analysis, and EXAFS techniques

• The sorption mechanism of Cd(II) in 49 soils was fully explored. • Cd(II) sorption capacities were closely related to soil physicochemical properties. • Cd in soils was mainly bound to metal (hydro)oxides or existed as CdCO 3 . Soil cadmium (Cd) contamination has emerged as an alarming environmental issue worldwide. Chemical reactivity and bioavailability of Cd in soils are highly dependent on soil properties. However, the sorption mechanism of Cd(II) on soils is not yet fully explored. For this purpose, batch sorption experiments, statistical analysis, and extended X-ray absorption fine structure (EXAFS) spectroscopy were integrated to elucidate the Cd(II) sorption mechanism by investigating the Cd(II) sorption behaviors in 49 soils with contrasting physicochemical characteristics and to figure out the influence of soil properties on Cd(II) sorption in soils. The outcomes of this study revealed that the soils from different areas had large differences in their abilities to adsorb Cd(II), while the differences were closely related to the physicochemical properties of soils. Cd(II) sorption capacities were controlled together by pH, metal (hydro)oxides, organic matter, and cation exchange capacity. The soil pH was the most critical factor in connecting Q max with soil properties. EXAFS results indicated that Cd(II) adsorbed on soils was mainly bound with metal (hydro)oxides or existed as CdCO 3 precipitate. The findings of this study provide a theoretical basis for predicting the risk of soil Cd contamination.

Boosting Efficient Ammonia Synthesis over Atomically Dispersed Co-Based Catalyst via the Modulation of Geometric and Electronic Structures

Boosting Efficient Ammonia Synthesis over Atomically Dispersed Co-Based Catalyst via the Modulation of Geometric and Electronic Structures

Theoretical Study of the Thorium Structural in Solution by EXAFS Techniques

Thorium with symbol Th is radioactive metal which emits the alpha rays. This metal can be founded in different forms and can cause the negatives impacts on human health and environment. This is the reason which explains the importance to know the structure of this metal in different forms including the structure of hydrated Thorium. Structural information helps to understand and assess peculiarities this ion in different natural and technological processes taking place in aqueous solutions. The most and efficacy technique to know about distances between atoms and coordination numbers is EXAFS (extended X Ray Absorption Fine Structure) technique because it permits to know these above informations. My project research is was to determine the structure of hydrated, solvated Thorium ion in metal ions. For my research, I preferred to use the EXAFS method to study the structure of the hydrated Th ion and to determine the Th-O bond distance, and from that estimate the coordination number. Th-O distance in the case of hydrated Thorium appeared to be 2.44 Å which corresponds to 9-coordination, as also found in the solids. The Th-O bond distance in solvated plutonium is ca. 2.41 Å, which corresponds to eightcoordination. These informations have shown me that for Thorium ligand size and coordination number are correlated. In case of Thorium hydrated studies, I saw that shown don’t precipitate at the law concentration. As conclusion, when pH is in range, centrifugation is possible and thorium is in monomeric form, but for pH above 4 Thorium is restrained and centrifuging shown that Thorium is in non-ionic form.

Sorption mechanisms of diphenylarsinic acid on ferrihydrite, goethite and hematite using sequential extraction, FTIR measurement and XAFS spectroscopy

Diphenylarsinic acid (DPAA) is an organoarsenic compound derived from abandoned chemical weapons. DPAA sorption by iron (hydr)oxides is of considerable importance but remains largely unexplored. The current study aimed at investigating the sorption mechanisms of DPAA on ferrihydrite, goethite and hematite using both macroscopic sorption kinetics and sequential extraction procedure (SEP) as well as microscopic Fourier transformed infrared (FTIR) and extended X-ray absorption fine structure (EXAFS) spectroscopic techniques. Sorption kinetics studies show that >93% of added DPAA (4–100 mg L−1) was sorbed on ferrihydrite and hematite within 5 min, while only 84% of added DPAA (100 mg L−1) was sorbed on goethite after 24 h. The sequential extraction results and FTIR measurements reveal that DPAA formed simultaneously inner- and outer-sphere complexes on goethite and hematite, but predominantly inner-sphere complexes on ferrihydrite with limited formation of outer-sphere complexes (<15%). A combination of SEP, FTIR and EXAFS techniques further enables identification of the interfacial reactions between DPAA and solid surfaces of iron (hydr)oxides and the mechanisms involved. Results indicate that DPAA interacted with these iron (hydr)oxides via (1) electrostatic attraction or hydrogen bonding, (2) surface complexation and (3) complexation embedded inside the mineral particles. EXAFS studies further demonstrate that DPAA formed mainly bidentate binuclear corner-sharing (2C) complexes regardless of the iron substrate, with As-Fe distances at 3.19–3.32 Å. Comparison of these results with available data in the literature on inorganic, methyl and phenyl arsenics (As) suggests that it is the phenyl group substitution that finally determines the predominance of 2C complexes. Results from the present study will improve our knowledge of DPAA interaction with solid surfaces and may help in the prediction of the environmental fate and environmental risk management of DPAA in the soil-water system.

Investigation of gamma radiation induced changes in local structure of borosilicate glass by TDPAC and EXAFS

Gamma radiation induced changes in local structure around the probe atom (Hafnium) were investigated in sodium barium borosilicate (NBS) glass, used for immobilization of high level liquid waste generated from the reprocessing plant at Trombay, Mumbai. The (NBS) glass was doped with 181Hf as a probe for time differential perturbed angular correlation (TDPAC) spectroscopy studies, while for studies using extended X-ray absorption fine structure (EXAFS) spectroscopy, the same was doped with 0.5 and 2 % (mole %) hafnium oxide. The irradiated as well as un-irradiated glass samples were studied by TDPAC and EXAFS techniques to obtain information about the changes (if any) around the probe atom due to gamma irradiation. TDPAC spectra of unirradiated and irradiated glasses were similar and reminescent of amorphous materials, indicating negligible effect of gamma radiation on the microstructure around Hafnium probe atom, though the quaqdrupole interaction frequency (ω Q) and asymmetry parameter (η) did show a marginal decrease in the irradiated glass compared to that in the unirradiated glass. EXAFS measurements showed a slight decrease in the Hf-O bond distance upon gamma irradiation of Hf doped NBS glass indicating densification of the glass matrix, while the cordination number around hafnium remains unchanged.

Oxidative and non-oxidative steam reforming of crude bio-ethanol for hydrogen production over Rh promoted Ni/CeO2-ZrO2 catalyst

The catalytic oxidative and non-oxidative steam reforming of crude bio-ethanol for hydrogen production was studied in a tubular fixed bed reaction system over 30wt.%Ni/CeO2-ZrO2 and 1wt.%Rh-30wt.%Ni/CeO2-ZrO2 catalysts. The catalysts were prepared by impregnation-co-precipitation method and characterized by BET, XRD, TPR, TGA, XPS, XANES and EXAFS techniques. Characterization results revealed that the addition of Rh promotes reducibility of NiO at lower temperature for the bimetallic catalysts. Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) analysis depicted that NiO with 6-fold local co-ordination is present in all the samples. Ethanol conversion, hydrogen yield and product selectivity were investigated at 600°C and space time of 9.17kgcath/kgmol[EtOH]) at atmospheric pressure. In steam reforming of crude bio-ethanol, 81% ethanol conversion was achieved with 59% hydrogen selectivity on Ni/CeO2-ZrO2 catalyst, whereas, higher ethanol conversion (86%) with 73% hydrogen selectivity was achieved using Rh-Ni/CeO2-ZrO2 catalysts. In oxidative steam reforming of crude bio-ethanol, hydrogen yield and selectivity reduced due to the partial oxidation of oxygenate compounds present in the feed. The used catalysts were also analysed by BET, TGA/DTA, TPR, TPO, Raman spectroscopy, SEM, and TEM techniques to identify the cause of catalyst deactivation. The results indicate that the catalyst deactivation occurred mainly due to amorphous and filamentous carbon deposition on the catalysts surface, due to the presence of the impurities in the feed.

Application of X-ray Absorption Spectroscopy (XAS) in the Field of Stabilization of As and Heavy Metal Contaminated Soil

X-ray absorption fine structure (XAFS) analysis using X-ray absorption spectroscopy is being applied as a state-of-the- art method in a wide range of disciplines. This review article summarizes the overall procedure of XAFS analysis from the preparation of soil samples to the analysis of data in X-ray absorption near edge structure (XANES) region and extended X- ray absorption fine structure (EXAFS) region. The previous studies on application of XANES and EXAFS techniques in environmental soil science field are discussed and classified them according to metal(loid)s (As, Cd, Cu, Ni, Pb, and Zn). A significant number of previous studies of XAFS application in the environmental soil science field have focused on the identification of Pb chemical species in soil. Moreover, XANES and EXAFS techniques have been widely used to investigate the contamination source via identification of metal species. Similarly, these techniques were applied to identify the mechanisms of metal stabilization in soil after application of various amendments, phytoremediation, etc.

X-ray Absorption Study of the Solvation Structure of Cu2+ in Methanol and Dimethyl Sulfoxide

The solvation structure of Cu(2+) in methanol (MeOH) and dimethyl sulfoxide (DMSO) has been determined by studying both the extended X-ray absorption fine structure (EXAFS) and the X-ray absorption near-edge structure (XANES) regions of the K-edge absorption spectra. The EXAFS technique has been found to provide a very accurate determination of the next-neighbor coordination distances, but it is inconclusive in the determination of the coordination numbers and polyhedral environment. Conversely, quantitative analysis of the XANES spectra unambiguously shows the presence of an average 5-fold coordination in both the MeOH and DMSO solution, ruling out the usually proposed octahedral Jahn-Teller distorted geometry. The EXAFS and XANES techniques provide coherent values of the Cu-O first-shell distances that are coincident in the two solvents. This investigation shows that the combined analysis of the EXAFS and XANES data allows a reliable determination of the structural properties of electrolyte solutions, which is very difficult to achieve with other experimental techniques.

A structural study of praseodymium gallate glasses by combined neutron diffraction, molecular dynamics and EXAFS techniques

Neutron diffraction and Extended X-ray Absorption Fine Structure (EXAFS) studies have been carried out on a range of praseodymium gallate glasses (Pr2O3-Ga2O3) prepared by aerodynamic levitation and laser heating. The short and intermediate range ordering around the rare-earth have been obtained by a multi-technique method. The results show that simple molecular dynamics simulations give a good representation of the coordination structure around the rare-earth in these glasses.

Sorption of Eu(III) on Attapulgite Studied by Batch, XPS, and EXAFS Techniques

The effects of pH, ionic strength, and temperature on sorption of Eu(III) on attapulgite were investigated in the presence and absence of fulvic acid (FA) and humic acid (HA). The results indicated that the sorption of Eu(III) on attapulgite was strongly dependent on pH and ionic strength, and independent of temperature. In the presence of FA/HA, Eu(III) sorption was enhanced at pH < 4, decreased at pH range of 4-6, and then increased again at pH > 7. The X-ray photoelectron spectroscopy (XPS) analysis suggested that the sorption of Eu(III) might be expressed as is identical to X3Eu0, is identical to S(w)OHEu3+, and is identical to SOEu-OOC-/HA in the ternary Eu/HN/attapulgite system. The extended X-ray absorption fine structure (EXAFS) analysis of Eu-HA complexes indicated that the distances of d(Eu-O) decreased from 2.415 to 2.360 angstroms with increasing pH from 1.76 to 9.50, whereas the coordination number (N) decreased from approximately 9.94 to approximately 8.56. Different complexation species were also found for the different addition sequences of HA and Eu(III) to attapulgite suspension. The results are important to understand the influence of humic substances on Eu(III) behavior in the natural environment.

Spectroscopic Characterization of Ni-Mo/γ-Al2O3-B2O3 Catalysts for Hydrodesulfurization of Dibenzothiophene

The effects of boron on the dispersion of active metal species and hydrodesulfurization (HDS) activity of dibenzothiophene (DBT) over Ni-Mo/γ-Al2O3 containing boron were studied by means of BET surface area measurement, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Mo K-edge extended X-ray absorption fine structure (EXAFS), and B K-edge X-ray absorption near-edge structure. The HDS activity of DBT over Ni-Mo/γ-Al2O3-B2O3 reaches a maximum at the B2O3 loading of about 1 mol%, in agreement with the basal dispersion and thus with the hydrogenation ability of the catalysts. It has been proven that the combination of XRD, XPS, and EXAFS techniques gives a complete description of the dispersion of active metal species in heterogeneous environmental catalysts.

Strain and relaxation in InAs and InGaAs films grown on GaAs(001)

The strain and relaxation of InAs and InGaAs films grown on GaAs(001) have been examined by the x-ray standing wave and extended x-ray absorption fine-structure techniques. While 1 monolayer (ML) films of both InAs and InGaAs are found to be tetragonally distorted in accordance with the prediction of macroscopic-elastic theory, thicker InAs films are found to collapse to their natural-lattice constant past a critical thickness Tc, of ∼2 ML’s. By 8 ML’s, bond-length strain is no longer evident, and a large degree of structural disorder is observed.

EXAFS and XRD analyses of the structural evolutions involved during drying of SnO 2 hydrogels

In order to determine structural changes during drying of inorganic gels, the local and long-range order structure of SnO 2- x (OH) 2 x xerogels resulting from drying hydrogels with different concentrations of electrolyte (Cl − and NH + 4) have been measured by extended X-ray absorption fine structure (EXAFS), X-ray diffraction (XRD) and N 2 adsorption techniques. EXAFS measurements performed at the Sn K edge on the hydrogels and xerogels show the existence of microcrystallites with the cassiterite structure. Two drying modes have been used: freeze drying and drying by evaporation at 45°C. It is shown that the microcrystallite size determined by XRD and EXAFS techniques on the drying mode and on the electrolyte concentrations. The microcrystallite size measured on the freeze dried xerogels is similar to that of their parent hydrogels, whatever the concentration of electrolyte; however, during drying by evaporation, a preferential growth of microcrystallites along the c-axis of the cassiterite structure is observed. The size of these crystallites is enhanced with a decrease of the electrolyte concentration. Specific surface areas calculated by the Brunauer-Emmett-Teller method indicate that this preferential growth is related to the improvement of the network connectivity. The comparison of both drying processes indicates that crystallization and polycondensation are independent phenomena.

XAFS study of molybdenum oxide catalysts on various supports

In the present study, X-ray absorption fine structure (XAFS) analyses (extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES)) have been used to obtain a better understanding of the support effects on the structure of the calcined catalysts. In particular, the focus of the discussion is on the coordination symmetry around Mo, since the EXAFS techniques gives direct information on the local structure aroud specific atoms.