Tandem X-ray absorption spectroscopy and scattering forin situtime-resolved monitoring of gold nanoparticle mechanosynthesis

Current time-resolvedin situapproaches limit the scope of mechanochemical investigations possible. Here we develop a new, general approach to simultaneously follow the evolution of bulk atomic and electronic structure during a mechanochemical synthesis. This is achieved by coupling two complementary synchrotron-based X-ray methods: X-ray absorption spectroscopy (XAS) and X-ray diffraction. We apply this method to investigate the bottom-up mechanosynthesis of technologically important Au micro and nanoparticles in the presence of three different reducing agents, hydroquinone, sodium citrate, and NaBH4. Moreover, we show how XAS offers new insight into the early stage generation of growth species (e.g.monomers and clusters), which lead to the subsequent formation of nanoparticles. These processes are beyond the detection capabilities of diffraction methods. This combined X-ray approach paves the way to new directions in mechanochemical research of advanced electronic materials.Peer reviewe

Inner relaxations in equiatomic single phase high entropy cantor alloy

The superior properties of high entropy multi functional materials are strongly connected with their atomic heterogeneity through many different local atomic interactions. The detailed element specific studies on a local scale can provide insight into the primary arrangements of atoms in multicomponent systems and benefit to unravel the role of individual components in certain macroscopic properties of complex compounds. Herein, multi edge X ray absorption spectroscopy combined with reverse Monte Carlo simulations was used to explore a homogeneity of the local crystallographic ordering and specific structure relaxations of each constituent in the equiatomic single phase face centered cubic CrMnFeCoNi high entropy alloy at room temperature. Within the considered fitting approach, all five elements of the alloy were found to be distributed at the nodes of the fcc lattice without any signatures of the additional phases at the atomic scale and exhibit very close statistically averaged interatomic distances 2.54 2.55 with their nearest neighbors. Enlarged structural displacements were found solely for Cr atoms. The macroscopic magnetic properties probed by conventional magnetometry demonstrate no opening of the hysteresis loops at 5 K and illustrate a complex character of the long range magnetic order after field assisted cooling in 5 T. The observed magnetic behavior is assigned to effects related to structural relaxations of Cr. Besides, the advantages and limitations of the reverse Monte Carlo approach to studies of multicomponent systems like high entropy alloys are highlighte

Determining Structure Activity Relationships in Oxide Derived Cu Sn Catalysts During CO2 Electroreduction Using X Ray Spectroscopy

The development of earth abundant catalysts for selective electrochemical CO2 conversion is a central challenge. Cu amp; 63743;Sn bimetallic catalysts can yield selective CO2 reduction toward either CO or formate. This study presents oxide derived Cu amp; 63743;Sn catalysts tunable for either product and seeks to understand the synergetic effects between Cu and Sn causing these selectivity trends. The materials undergo significant transformations under CO2 reduction conditions, and their dynamic bulk and surface structures are revealed by correlating observations from multiple methods X ray absorption spectroscopy for in situ study, and quasi in situ X ray photoelectron spectroscopy for surface sensitivity. For both types of catalysts, Cu transforms to metallic Cu0 under reaction conditions. However, the Sn speciation and content differ significantly between the catalyst types the CO selective catalysts exhibit a surface Sn content of 13 at. predominantly present as oxidized Sn, while the formate selective catalysts display an Sn content of amp; 8776;70 at. consisting of both metallic Sn0 and Sn oxide species. Density functional theory simulations suggest that Sn amp; 948; sites weaken CO adsorption, thereby enhancing CO selectivity, while Sn0 sites hinder H adsorption and promote formate production. This study reveals the complex dependence of catalyst structure, composition, and speciation with electrochemical bias in bimetallic Cu catalyst

Recent developments of X ray absorption spectroscopy as analytical tool for biological and biomedical applications

X ray absorption spectroscopy XAS , in its various modalities, has gained exponential attention and applicability in the field of biological and biomedical systems. Particularly in this field, challenges like low concentration of analyte or proneness to radiation damage have certainly settle the basis for further analytical developments, when using X ray based methods. Low concentration calls for higher sensitivity by increasing the detection limits DL ; while susceptibility for radiation damage requires shorter measurement times and or cryogenic sample environment possibilities. This manuscript reviews the latest analytical possibilities that make XAS more and more adequate to investigate biological or biomedical systems in the last 5 amp; 8201;year

Increasing the Efficiency of Optimized V SBA 15 Catalysts in the Selective Oxidation of Methane to Formaldehyde by Artificial Neural Network Modelling

The present study investigates the possibility of improving the selective oxidation of methane to formaldehyde over V SBA 15 catalysts in two different ways. In a classical approach of catalyst optimization, the in situ synthesis of V SBA 15 catalysts was optimized with regard to the applied pH value. Among the set of catalysts synthesized, a higher amount of incorporated vanadium, a higher content of polymeric VOx species as well as a less ordered structure of the support material were observed by increasing the pH values from 2.0 to 3.0. An optimum in performance during the selective oxidation of methane to formaldehyde with respect to activity and selectivity was found over V SBA 15 prepared at a pH value of 2.5. With this knowledge, we have now evaluated the possibilities of reaction control using this catalyst. Specifically, artificial neural network modelling was applied after the collection of 232 training samples for obtaining insight into the influence of different reaction parameters temperature; gas hourly space velocity GHSV ; and concentration of O2, N2 and H2O onto methane conversion and selectivity towards formaldehyde. This optimization of reaction conditions resulted in an outstanding high space time yield of 13.6 kgCH2O amp; 8729;kgcat amp; 8729;h amp; 8722;

Evaluation of the Specific Activity of M N Cs and the Intrinsic Activity of Tetrapyrrolic FeN4 Sites for the Oxygen Reduction Reaction

M N C electrocatalysts are considered pivotal to replace expensive precious group metal based materials in electrocatalytic conversions. However, their development is hampered by the limited availability of methods for the evaluation of the intrinsic activity of different active sites, like pyrrolic FeN4 sites within Fe N Cs. Currently, new synthetic procedures based on active site imprinting followed by an ion exchange reaction, e.g. Zn to Fe, are producing single site M N Cs with outstanding activity. Based on the same replacement principle, we employed a conservative iron extraction to partially remove the Fe ions from the N 4 cavities in Fe N Cs. Having catalysts with the same morphological properties and Fe ligation that differ solely in Fe content allows for the facile determination of the decrease in density of active sites and their turn over frequency. In this way, insight into the specific activity of M N Cs is obtained and for single site catalysts the intrinsic activity of the site is accessible. This new approach surpasses limitations of methods that rely on probe molecules and, together with those techniques, offers a novel tool to unfold the complexity of Fe N C catalyst and M N Cs in genera

Investigation of polycapillary half lenses for quantitative confocal micro X ray fluorescence analysis

The use of polycapillary optics in confocal micro X ray fluorescence analysis CMXRF enables the destruction free 3D investigation of the elemental composition of samples. The energy dependent transmission properties, concerning intensity and spatial beam propagation of three polycapillary half lenses, which are vital for the quantitative interpretation of such CMXRF measurements, are investigated in a monochromatic confocal laboratory setup at the Atominstitut of TU Wien, and a synchrotron setup on the BAMline beamline at the BESSY II Synchrotron, Helmholtz Zentrum Berlin. The empirically established results, concerning the intensity of the transmitted beam, are compared with theoretical values calculated with the polycap software package and a newly presented analytical model for the transmission function. The resulting form of the newly modelled energy dependent transmission function is shown to be in good agreement with Monte Carlo simulated results for the complete energy regime, as well as the empirically established results for the energy regime between 6 amp; 8197;keV and 20 amp; 8197;keV. An analysis of possible fabrication errors was conducted via pinhole scans showing only minor fabrication errors in two of the investigated polycapillary optics. The energy dependent focal spot size of the primary polycapillary was investigated in the laboratory via the channel wise evaluation of knife edge scans. Experimental results are compared with data given by the manufacturer as well as geometric estimations for the minimal focal spot size. Again, the resulting measurement points show a trend in agreement with geometrically estimated results and manufacturer dat

Dispersive X ray Absorption Spectroscopy for Time Resolved In Situ Monitoring of Mechanochemical Reactions

X ray absorption spectroscopy XAS provides a unique, atom specific tool to probe the electronic structure of solids. By surmounting long held limitations of powder based XAS using a dynamically averaged powder in a Resonant Acoustic Mixer RAM , we demonstrate how time resolved in situ TRIS XAS provides unprecedented detail of mechanochemical synthesis. The use of a custom designed dispersive XAS DXAS setup allows us to increase the time resolution over existing fluorescence measurements from amp; SIM;15 min to 2 s for a complete absorption spectrum. Hence, we here establish TRIS XAS as a viable method for studying mechanochemical reactions and sampling reaction kinetics. The generality of our approach is demonstrated through RAM induced i bottom up Au nanoparticle mechanosynthesis and ii the synthesis of a prototypical metal organic framework, ZIF 8. Moreover, we demonstrate that our approach also works with the addition of a stainless steel milling ball, opening the door to using TRIS DXAS for following conventional ball milling reactions. We expect that our TRIS DXAS approach will become an essential part of the mechanochemical tool bo