Quick-scanning X-ray absorption fine structure beamline at SSRF

The layout and characteristics of the hard X-ray spectroscopy beamline(BL11B)at the Shanghai synchrotron radiation facility are described herein.BL11B is a bending-magnet beamline dedicated to conventional and millisecond-scale quick-scanning X-ray absorption fine structures.It is equipped with a cylindrical collimating mirror,a double-crystal monochromator comprising Si(111)and Si(311),a channel-cut quick-scanning Si(111)monochromator,a toroidal focusing mirror,and a high harmonics rejection mirror.It can provide 5-30 keV of X-rays with a photon flux of~5×10^(11)photons/s and an energy resolution of~1.31×10^(-4)at 10 keV.The performance of the beamline can satisfy the demands of users in the fields of catalysis,materials,and environmental science.This paper presents an overview of the beamline design and a detailed description of its performance and capabilities.

X-ray absorption near the edge structure and x-ray photoelectron spectroscopy studies on pyrite prepared by thermally sulfurizing iron films

This paper reports how pyrite films were prepared by thermal sulfurization of magnetron sputtered iron films and characterized by X-ray absorption near edge structure spectra and X-ray photoelectron spectroscopy on a 4B9B beam line at the Beijing Synchrotron Radiation Facility. The band gap of the pyrite agrees well with the optical band gap obtained by a spectrophotometer. The octahedral symmetry of pyrite leads to the splitting of the d orbit into t2g and eg levels. The high spin and low spin states were analysed through the difference of electron exchange interaction and the orbital crystal field. Only when the crystal field splitting is higher than 1.5 eV, the two weak peaks above the white lines can appear, and this was approved by experiments in the present work.

Extended X-ray absorption fine structure (EXAFS) of FAPbI_(3) for understanding local structure-stability relation in perovskite solar cells

Perovskite solar cells (PSCs) employing formamidinium lead iodide (FAPbI_(3)) have shown high efficiency.However,operational stability has been issued due to phase instability of α phase FAPbI_(3) at ambient temperature.Excess precursors in the perovskite precursor solution has been proposed to improve not only power conversion efficiency (PCE) but also device stability.Nevertheless,there is a controversial issue on the beneficial effect on PCE and/or stability between excess FAI and excess PbI_(2).We report here extended X-ray absorption fine structure (EXAFS) of FAPbI_(3) to study local structural change and explain the effect of excess precursors on photovoltaic performance and stability.Perovskite films prepared from the precursor solution with excess PbI_(2)shows better stability than those from the one with excess FAI,despite similar PCE.A rapid phase transition from α phase to non-perovskite δ phase is observed from the perovskite film formed by excess FAI.Furthermore,the (Pb-I) bond distance evaluated by the Pb L_(III)-edge EXAFS study is increased by excess FAI,which is responsible for the phase transition and poor device stability.This work can provide important insight into local structure-stability relation in the FAPbI_(3)-based PSCs.

Landscape of s-triazine molecule on Si(100) by a theoretical x-ray photoelectron spectroscopy and x-ray absorption near-edge structure spectra study

The chemisorbed structure for an aromatic molecule on a silicon surface plays an important part in promoting the development of organic semiconductor material science. The carbon K-shell x-ray photoelectron spectroscopy（XPS） and the x-ray absorption near-edge structure（XANES） spectra of the interfacial structure of an s-triazine molecule adsorbed on Si（100） surface have been performed by the first principles, and the landscape of the s-triazine molecule on Si（100） surface has been described in detail. Both the XPS and XANES spectra have shown their dependence on different structures for the pristine s-triazine molecule and its several possible adsorbed configurations. By comparison with the XPS spectra, the XANES spectra display the strongest structural dependency of all of the studied systems and thus could be well applied to identify the chemisorbed s-triazine derivatives. The exploration of spectral components originated from non-equivalent carbons in disparate local environments has also been implemented for both the XPS and XANES spectra of s-triazine adsorbed configurations.

Local Structure Analysis of Lead Zinc Niobate-Barium Titanate Ceramic by X-Ray Absorption Spectroscopy and Density Functional Calculation

The local structure of an alternative Pb（Zn1/3Nb2/3）O3-based perovskite ceramic is investigated. The 0.07BaTiO33-0.93Pb（Zn1/3Nb2/3）O3 ceramic is synthesized using a combination of Zn3Nb2O8 B-site precursor and BaTiO33 perovskite phase stabilizer. Then, x-ray absorption spectroscopy and density functional theory are employed to calculate the local structure configuration and formation energy of the prepared samples. Ba2＋ is found to replace Pb2＋ in AA-site with Zn2＋ occupying BB-site in Pb（Zn1/3Nb2/3）O3, while in the neighboring structure, Ti4＋4＋ replaces Nb5＋5＋ in BB-site with Pb2＋2＋ occupying AA-site. With the substitution of BaTiO33 in Pb（Zn1/3Nb2/3）O3, the bond length between Zn2＋ and Pb2＋ is longer than that of the typical perovskite phase of Pb（Zn1/3Nb2/3）O3. This indicates the key role of BaTiO33 in decreasing the steric hindrance of Pb2＋ lone pair, and the mutual interactions between Pb2＋ lone pair and Zn2＋ and the formation energy is seen to decrease. This finding of the formation energy and local structure configuration relationship can further extend a fundamental understanding of the role of BaTiO33 in stabilizing the perovskite phase in PbZn13Nb23O3-based materials, which in turn will lead to an improved preparation technique for desired electrical properties.

Theoretical characterization of the adsorption configuration of pyrrole on Si(100)surface by x-ray spectroscopy

The possible configurations of pyrrole absorbed on a Si(100)surface have been investigated by x-ray photoelectron spectroscopy(XPS)and near-edge x-ray absorption fine structure(NEXAFS)spectra.The C-1s XPS and NEXAFS spectra of these adsorption configurations have been calculated by using the density functional theory(DFT)method and fullcore hole(FCH)approximation to investigate the relationship between the adsorption configurations and the spectra.The result shows that the XPS and NEXAFS spectra are structurally dependent on the configurations of pyrrole absorbed on the Si(100)surface.Compared with the XPS,the NEXAFS spectra are relatively sensitive to the adsorption configurations and can accurately identify them.The NEXAFS decomposition spectra produced by non-equivalent carbon atoms have also been calculated and show that the spectral features vary with the diverse types of carbon atoms and their structural environments.

Structural control of magnetic nanoparticles for positive nuclear magnetic resonance imaging

In addition to the tens of millions of medical doses consumed annually around the world,a vast number of nuclear magnetic resonance imaging(MRI)contrast agents are being deployed in MRI research and development,offering precise diagnostic information,targeting capabilities,and analyte sensing.Superparamagnetic iron oxide nanoparticles(SPIONs)are notable among these agents,providing effective and versatile MRI applications while also being heavy-metal-free,bioconjugatable,and theranostic.We designed and implemented a novel two-pronged computational and experimental strategy to meet the demand for the efficient and rigorous development of SPION-based MRI agents.Our MATLAB-based modeling simulation and magnetic characterization revealed that extremely small maghemite SPIONs in the 1-3 nm range possess significantly reduced transversal relaxation rates(R_(2))and are therefore preferred for positive(T_(1)-weighted)MRI.Moreover,X-ray diffraction and X-ray absorption fine structure analyses demonstrated that the diffraction pattern and radial distribution function of our SPIONs matched those of the targeted maghemite crystals.In addition,simulations of the X-ray near-edge structure spectra indicated that our synthesized SPIONs,even at 1 nm,maintained a spherical structure.Furthermore,in vitro and in vivo MRI investigations showed that our 1-nm SPIONs effectively highlighted whole-body blood vessels and major organs in mice and could be cleared through the kidney route to minimize potential post-imaging side effects.Overall,our innovative approach enabled a swift discovery of the desired SPION structure,followed by targeted synthesis,synchrotron radiation spectroscopic studies,and MRI evaluations.The efficient and rigorous development of our high-performance SPIONs can set the stage for a computational and experimental platform for the development of future MRI agents.

XAFS Study of Coordination Structure of Cu（L-His）2 in Solution

Multiple coordination modes are present copper coordination environment varies in the CuII-histidine complex in solution and the with pH. In this work, we have investigated the coordination geometry of Cu（His）2 complex using X-ray absorption fine structure （XAFS） analysis. Copper K-edge XAFS spectra were acquired on aqueous Cu2＋ samples with his- tidine at different pH values. The coordination environments were further confirmed by chemically modified histidine. Results show that the caboxylate groups coordinate at acidic condition, while amino and imidazole nitrogens get coordinated at higher pH. For the co- ordination geometry of Cu（His）2 in solution at physiological pH, the sixfold coordination is preferentially formed, while the fivefold coordination can co-exist in equilibrium.

Oxidation of antimony (Ⅲ) in soil by manganese (Ⅳ) oxide using X-ray absorption fine structure

The oxidation of antimony （Ⅲ） in soils was studied using X-ray absorption fine structure （XAFS） spectra. An andosol soft sample and artificial soil samples （SiO2 blended with iron （Ⅲ） hydroxide and manganese （Ⅳ） oxide） were used herein. After adding antimony （Ⅲ） oxide to all soil samples, the oxidation process was observed by recording the XAFS spectra of Sb K-edge, Fe Kedge, and Mn K-edge. The results indicated that manganese （Ⅳ） oxide played an important role in the oxidation of Sb（Ⅲ）; however iron （Ⅲ） hydroxide was not directly related to the reaction. During a 2-hr continuous Sb K-edge X-ray absorption near edge structure （XANES） measurement with an interval of I rain of one of the artificial soil samples （SiO2 ＋ MnO2 ＋ Sb2O3）, a pseudo-first-order reaction was determined with an average estimated rate of 0.52 ±0.04 hr-1. Compared to the lower oxidation rate of andosol, it is suggested that because of the low concentration of Mn（Ⅳ） in natural soils, the oxidation process of Sb（Ⅲ） might be relatively slow and require more time to convert Sb（Ⅲ） to Sb（V）.

Relating atomic local structures and Curie temperature of NdFeB permanent magnets:an X-ray absorption spectroscopic study

Relationship between atomic local structures and Curie temperature of NdFeB permanent magnets was investigated semi-quantitatively using synchrotron radiation technique. Fe K-edge X-ray absorption spectroscopy(XAS) was employed to study the local structure of Fe atoms for samples before and after doping Dy, Tb or Gd. It is found that the bond lengths and coordination numbers are changed. Thus, the exchange interaction between Fe atoms increases with Dy, Tb or Gd doping, resulting in the improvement of Curie temperature of NdFeB permanent magnets. The doping effect is proven by experimental measurement of the magnetic properties. Microstructural characterization using scanning electron microscopy(SEM) was also used to further analyze the effect of different rare earth elements doping on Curie temperature of NdFeB permanent magnets.

Synthesis, characterization and extended X-ray absorption fine structure of novel polynuclear copper complexes with new eighteen-membered macrocycle ligands

Macrocycle compounds have great importance in host-guest chemistry and moleculeidentifications. 4-acetyl-bispyrazolones are a new type of polydentate ligands. Whenthey react with diamine compounds, new compounds or complexes containing C=O andC=N groups can be obtained. These compounds can be used to study the relationship ofcoordination structure and its properties, energy transferring processes between metal

Structure and chemical valence study of Sr_(n+1)Ru_nO_(3n+1)(n= 1, 2, ∞) series

Effect of structure parameter n and its coupling with the connection mode among RuO6 octahedra of Srn＋1RUnO3n＋1 （n = 1, 2, ∞） are investigated. The gradually enhanced rotation and tilting effect with increasing n are observed in Srn＋1RUnO3n＋1. Besides, the chemical valence of Ru is not changed, while the one of Sr gradually varies with increasing n, which highlights the great contribution of connection mode to the chemical environment. Our results show a strong n dependence on the connection mode between octahedra in Srn＋1RUnO3n＋1 （n = 1, 2, ∞）.

X-ray Spectroscopically Probing Mo_(2)C@MoSe_(2)Heterojunction Electrodes

Due to their high electrical conductivity and layered structure,two dimensional MXene materials are re⁃garded as promising candidates for energy storage applications.However,the relatively low stability and specific ca⁃pacity of MXene materials limit their further utilization.In this study,these issues are addressed using a heterostruc⁃ture strategy via a one-step selenization method to form Mo_(₂)C@MoSe_(₂).Synchrotron radiation X-ray spectroscopic and high-resolution transmission electron microscopy(HRTEM)characterizations revealed the heterostructure consisting of in-situ grown MoSe_(2)on Mo_(2)C MXene.Electrochemical tests proved the heterojunction electrode’s superior rate perfor⁃mance of 289.06 mAh·g^(-1)at a high current density of 5 A·g^(-1)and long cycling stability of 550 mAh·g^(-1)after 900 cycles at 1 A·g^(-1).This work highlights the useful X-ray spectroscopic analysis to directly elucidate the heterojunction structure,providing an effective reference method for probing heterostructures.

激光驱动的多层膜复合靶M带辐射光谱研究

时间分辨X射线吸收精细结构谱技术需要产生高亮度、均匀、宽光谱的X射线源。单一靶材产生的M带辐射源亮度高,但均匀性较差,因此提出了一种使用多种金属材料制备的多层膜复合靶产生M带辐射的方案。针对Si的K边X射线吸收谱实验,根据前期单一靶材M带光谱实验数据理论计算了最优的材料比例,制备了Au、Yb、Dy三种材料组成的多层膜复合靶,并在神光II激光装置上开展了脉冲激光驱动的多层膜复合靶辐射光谱测量,实验结果和理论计算基本一致。相比单一靶材,多层膜复合靶产生的M带辐射源具有光谱宽、整体亮度均匀的优点,在时间分辨X射线吸收精细结构谱中具有较大的应用潜力。

硫化零价铁去除水中钼酸盐的效能与机理

钼矿的开采及含钼产品的生产与使用导致水中钼污染问题日益突出.为明确硫化零价铁(S-ZVI^(bm))去除水中钼酸盐的效能及作用机理,采用球磨法制备S-ZVI^(bm),进而探究S-ZVI^(bm)在有氧条件下去除Mo(VI)的反应动力学,并采用同步辐射技术等表征手段分析其反应机理.结果表明:硫化可显著加速零价铁的吸氧腐蚀过程,进而可将Mo(VI)的去除速率及去除容量分别提高3.6~42.3倍及1.7~3.2倍.与未改性零价铁相比,S-ZVI^(bm)可对抗Mo(VI)的致钝作用,进而可在更高的Mo(VI)浓度及更宽的pH值范围内实现Mo(VI)的有效去除.同步辐射技术表征结果显示,尽管硫化预处理可提高零价铁去除Mo(VI)的效能,但并未改变零价铁去除Mo(VI)的作用机理,即S-ZVI^(bm)仍主要通过化学吸附来实现Mo(VI)的去除.

Research Article Local structure and magnetic properties of a nanocrystalline Mnrich Cantor alloy thin film down to the atomic scale

The huge atomic heterogeneity of high-entropy materials along with a possibility to unravel the behavior of individual components at the atomic scale suggests a great promise in designing new compositionally complex systems with the desired multifunctionality.Herein,we apply multi-edge X-ray absorption spectroscopy(extended X-ray absorption fine structure(EXAFS),Xray absorption near edge structure(XANES),and X-ray magnetic circular dichroism(XMCD))to probe the structural,electronic,and magnetic properties of all individual constituents in the single-phase face-centered cubic(fcc)-structured nanocrystalline thin film of Cr_(20)Mn_(26)Fe_(18)Co_(19)Ni_(17)(at.%)high-entropy alloy on the local scale.The local crystallographic ordering and componentdependent lattice displacements were explored within the reverse Monte Carlo approach applied to EXAFS spectra collected at the K absorption edges of several constituents at room temperature.A homogeneous short-range fcc atomic environment around the absorbers of each type with very similar statistically averaged interatomic distances(2.54-2.55Å)to their nearest-neighbors and enlarged structural relaxations of Cr atoms were revealed.XANES and XMCD spectra collected at the L2,3 absorption edges of all principal components at low temperature from the oxidized and in situ cleaned surfaces were used to probe the oxidation states,the changes in the electronic structure,and magnetic behavior of all constituents at the surface and in the sub-surface volume of the film.The spin and orbital magnetic moments of Fe,Co,and Ni components were quantitatively evaluated.The presence of magnetic phase transitions and the co-existence of different magnetic phases were uncovered by conventional magnetometry in a broad temperature range.

Unveiling structural evolution of Fe single atom catalyst in nitrate reduction for enhanced electrocatalytic ammonia synthesis

Atomic transition metal–nitrogen–carbon electrocatalysts exhibit outstanding activity in various electrocatalytic reactions.The challenge lies in predicting the structure of the active center,which may undergo changes under applied potential and interact with reactants or intermediates.Advanced characterization techniques,particularly in-situ X-ray absorption spectroscopy(XAS),provide crucial insights into the structural evolution of the metal active center during the reaction.In this study,nitrate reduction to ammonia(NO_(3)RR)was selected as a model reaction,and we introduced in-situ XAS to reveal the structural evolution during the catalytic process.A novel single atom catalyst of iron loaded on three-dimensional nitrogen–carbon nanonetwork(designated as Fe SAC/NC)was successfully synthesized.We unraveled the structural transformations occurring as pyrrole-N_(4)-Fe transitions to pyrrole-N_(3)-Fe throughout the NO_(3)RR process.Notably,the Fe SAC/NC catalyst exhibited excellent catalytic activity,achieving a Faradaic efficiency of 98.2% and an ammonia generation rate of 22,515μg·h^(−1)·mgcat−1 at−0.8 V versus reversible hydrogen electrode.Theoretical calculations combined with in-situ spectroscopic characterization showed that pyrrole-N_(3)-Fe reduced the energy barrier from *NO to*NHO and improved the selectivity of ammonia.This provides a robust reference for the design of efficient nitrate-to-ammonia synthesis catalysts.

土壤中砷吸附机理及其影响因素研究进展

土壤中砷(As)的生物可利用性、迁移、转化及归宿在很大程度上依赖于其在土壤中的吸附反应。本文首先概述了土壤中As污染物的主要形态、价态及其与吸附的关系,较为系统地介绍了土壤中As吸附的主要影响因素和土壤中As吸附机理等方面的最新研究进展,并重点对X-射线吸收精细结构光谱(XAFS)、红外光谱(IR)等现代分析技术和方法在As吸附研究中的应用和进展进行了论述。由于土壤组分与结构的复杂性,As在环境介质中的吸附机理研究目前仍集中在单纯矿物上的吸附行为,为As在土壤中的吸附研究提供了理论基础。X-射线吸收精细结构光谱及红外光谱研究结果证明As在土壤中的吸附主要与含Fe、Al等矿物结合,形成以双齿双核结构为主的配位结构:其吸附机理与土壤矿物及As污染物的价态、吸附浓度等有关,主要包括表面络合反应和表面沉淀作用;但是土壤中As吸附机理研究还需要进一步深入研究。文章最后分析了有关土壤中As吸附研究的发展趋势和重要动向。

还原条件对CO_2加氢用Fe/TiO_2催化剂结构的影响

考察了 5 %Fe/TiO2 催化剂在CO2 加氢制低碳烃中的催化活性 .最佳结果显示 ,CO2 转化率为 19 1% ,C2 +烃选择性为 5 0 1% .用X射线粉末衍射、激光拉曼光谱、穆斯堡尔谱及FeK 吸收边扩展X射线吸收精细结构等研究了该催化剂在还原条件下的体相及表面结构 .结果表明 ,在Fe/TiO2 中 ,主要存在超顺磁的Fe0 ,α Fe,配位不饱和的Fe2 +物种及体相FeTiO3.还原温度对Fe/TiO2 催化剂的体相和表面结构及催化性能有显著的影响 .高温还原会破坏催化剂的表面结构 ,导致催化活性显著下降 .将催化活性与体相及表面结构相关联 ,提出Fe0 与配位不饱和的Fe2 +物种之间的协同作用是催化剂显示较高活性的重要原因 .

近边X射线吸收精细结构光谱法研究土壤腐殖质组分含碳官能团组成及磷酸根影响

应用同步辐射近边X射线吸收精细结构(NEXAFS)光谱技术研究了土壤腐殖质各组分(富里酸、胡敏酸及胡敏素等)的含碳官能团组成信息,并通过分析PO43-存在条件下胡敏酸、胡敏素的官能团组成变化特征,探讨了PO43-与土壤腐殖质之间的微观作用机制。结果表明,土壤腐殖质不同组分的官能团分布具有类似的光谱特征,但组成比例存在明显差异。随着腐殖质组分的酸不溶性增加,胡敏酸、胡敏素疏水性脂肪基官能团比例显著高于富里酸,芳构化程度也明显增加,而亲水性羧基官能团比例趋于降低;PO43-通过静电作用、取代反应可以选择性释放胡敏酸中部分小分子羧基官能团,从而改变胡敏酸官能团的组成特征。此研究结果对于应用NEXAFS研究有机碳官能团形态、结构及理解PO43-在土壤微界面上的反应机制具有重要意义。