Development of micro‐XANES mapping in the diamond anvil cell

Energy‐dispersive X‐ray absorption spectroscopy is now a well established method that has been applied to a broad range of applications. At the energy‐dispersive EXAFS beamline of the ESRF, ID24, the recently achieved 5 × 5 µm focal spot combined with fast acquisition has allowed complex and non‐uniform samples to be mapped and images to be obtained where each pixel contains full XAS information. This method has been applied to a study under extreme conditions of pressure and temperature in a diamond anvil cell in transmission mode. The case study was the investigation of the Fe K‐edge XANES of (Mg,Fe)SiO₃‐perovskite and (Mg,Fe)O‐ferropericlase on decomposition of the spinel‐structured olivine [γ‐(Mg,Fe)₂SiO₄] at 78 (3) GPa after laser heating at 2200 (100) K.     

铅锌矿区浮萍中铅的XANES形态分析

南京栖霞山铅锌矿是华东地区最大的铅锌矿床之一,已开采50多年,由此引发的环境问题日益突出。当地环境中铅含量较高,但铅的迁移和毒性机理不明。为此在该地区开展了铅锌矿生物地球化学研究,借助ICP-MS铅含量分析和Pb-LⅢ边XANES形态分析技术,在该污染区发现了耐受并富集重金属的浮萍样品,浮萍中铅的含量为39.4 mg·kg-1。XANES分析和形态拟合结果显示其含硬脂酸铅65%和硫化铅36.9%,从而揭示浮萍样品中铅以含硫的有机酸铅形式存在。     

用XANES实验方法研究Cr的价态

用改进的XANES(X射线吸收近边结构谱)方法对不同比例Cr(Ⅲ)和Cr(Ⅵ)的酵母制剂进行Cr价态研究,该方法与传统方法的区别是用一个电离室同时进行透射和荧光XANES实验.此实验方法简单,快捷,特别适用于在相同的实验条件下,以一个已知标样为标准,对一系列未知价态样品进行的比较分析.实验结果表明酵母对Cr有很强的还原能力,它几乎能将所有的Cr(Ⅵ)还原成Cr(Ⅲ).Cr的K边XANES谱在掺入酵母剂前后有所变化,说明不同样品中的Cr原子近邻结构有所不同     

Magnesium K‐edge XANES spectroscopy of geological standards

Magnesium K‐edge X‐ray absorption near‐edge structure (XANES) spectra have been investigated to develop a systematic understanding of a suite of Mg‐bearing geological materials such as silicate and carbonate minerals, sediments, rocks and chemical reagents. For the model compounds the Mg XANES was found to vary widely between compounds and to provide a fingerprint for the form of Mg involved in geologic materials. The energy positions and resonance features obtained from these spectra can be used to specify the dominant molecular host site of Mg, thus shedding light on Mg partitioning and isotope fractionation in geologic materials and providing a valuable complement to existing knowledge of Mg geochemistry.     

A Li K‐edge XANES study of salts and minerals

The first comprehensive Li K‐edge XANES study of a varied suite of Li‐bearing minerals is presented. Drastic changes in the bonding environment for lithium are demonstrated and this can be monitored using the position and intensity of the main Li K‐absorption edge. The complex silicates confirm the assignment of the absorption edge to be a convolution of triply degenerate p‐like states as previously proposed for simple lithium compounds. The Li K‐edge position depends on the electronegativity of the element to which it is bound. The intensity of the first peak varies depending on the existence of a 2p electron and can be used to evaluate the degree of ionicity of the bond. The presence of a 2p electron results in a weak first‐peak intensity. The maximum intensity of the absorption edge shifts to lower energy with increasing SiO₂ content for the lithium aluminosilicate minerals. The bond length distortion of the lithium aluminosilicates decreases with increasing SiO₂ content, thus increased distortion leads to an increase in edge energy which measures lithium's electron affinity.     

XANES and EXAFS in Cu-Ti and Ni-Zr glasses

X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements have been done at the K-edge of Cu in Cu-Ti glasses and on the K-edges of Ni and Zr in Ni-Zr glasses using a synchrotron radiation source. The results are discussed in terms of the shape shift and intensity of the absorption edge as well as the principal absorption maximum. The values of bondlength calculated by the one-electron multiple scattering XANES theory as well as the graphical analysis EXAFS technique show good agreement.     

Local structure investigation of the active site of the imidazolonepropionase from Bacillus subtilis by XANES spectroscopy and ab initio calculations

Imidazolonepropionase is an important enzyme that plays a crucial role in the degradation of the histidine in mammals and bacteria. In this contribution a detailed structural investigation is presented of the imidazolonepropionase from Bacillus subtilis at the zinc site by X‐ray absorption near‐edge structure (XANES) spectroscopy combining experimental data with ab initio calculation in the framework of the multiple‐scattering theory. The resolved local structure leads to a modification of the data set in the Protein Data Bank (PDB) (PDB code 2BB0). Actually, data suggest that the carboxyl of the Asp324 moves far away from the zinc ion at the center, while the water molecule and the nearest‐neighbor histidines move towards it. This new conformation and the occurrence of a short water‐to‐zinc bond length support the nucleophilic attack catalytic mechanism proposed for this enzyme.     

Manganese speciation in Diplodon chilensis patagonicus shells: a XANES study

X‐ray absorption near‐edge spectroscopy (XANES) at the Mn K‐edge was used to investigate the environment of Mn in situ within the growth increments of the long‐lived freshwater bivalve species Diplodon chilensis patagonicus. Single XANES spectra and Mn Kα fluorescence distributions were acquired at submillimetre resolution (up to 100 µm × 50 µm), at Mn concentrations below the weight percent range (100–1000 µg g^?1) in a high Ca matrix. The position and intensity of the pre‐edge feature in the shell spectrum resembles best that of the Mn(II)‐bearing reference compounds, suggesting that this is the oxidation state of Mn in the bivalve shells. By comparison with the XANES spectra of selected standard compounds, hypotheses about Mn speciation in the shell are also reported. In particular, different factors, such as provenance, ontogenetic age, variable Mn‐concentrations or seasonal shell deposition seem not to influence the speciation of the metal in this bivalve species.     

Investigation of sulfur speciation in particles from small coal-burning boiler by XANES spectroscop

Sulfur K-edge X-ray absorption near-edge structure （XANES） spectroscopy was employed to study the speciation of sulfur in raw coal, ash by-product and fine particulate matter from a small coal-burning boiler. By means of least square analysis of the XANES spectra, the major organic and inorganic sulfur forms were quantitatively determined. The results show that about 70% of the sulfur in raw coal is present as organic and a minor fraction of the sulfur occurs as other forms： 17% of pyrite and 13% of sulfate. While in bottom ash, fly ash, and PM2.5, the dominant form of sulfur is sulfate, with the percentage of 80,79 and 94, respectively. Moreover, a number of other reduced sulfur including thiophenic sulfur, element sulfur and pyrrhotite are also present. During coal combustion, most of organic sulfur and pyrite were oxidized and released into the atmosphere as SO2 gas, part of them was converted to sulfate existing in coal combustion by-products, and a small part of pyrite was probably reduced to elemental sulfur and pyrrhotite. The results may provide information for assessing the pollution caused by small boiler and developing new methods for the control of SO2 pollution.