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The adsorption behavior of Platinum nanoparticles was studied for the as-received catalyst (under inert gas), under hydrogen and CO atmosphere using our newly designed in-situ cell. X-ray Absorption Spectroscopy (XAS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) experiments were performed simultaneously with high data quality. Structural information and the type of adsorbate could be revealed via Extended X-ray Absorption Fine Structure (EXAFS) analysis, Δμ X-ray Absorption Near Edge Structure analysis (Δμ XANES) and in-situ DRIFTS. The as-received catalyst showed sub-surface oxygen and O(n-fold). Under CO atmosphere only CO(atop) was found. Reversible adsorbate induced changes of the Pt nanoparticle structure were derived from changes in the Pt-Pt coordination number and the corresponding bond distance. Under reducing conditions (H2, CO) a significant increase in both values occurred. Temperature dependent desorption of CO revealed a gradual shift from Pt-CO to Pt-O. Reoxidation was clearly assigned to strong metal support interaction from the SiO2 support.
The adsorption behavior of Platinum nanoparticles was studied for the as-received catalyst (under inert gas), under hydrogen and CO atmosphere using our newly designed in-situ cell. X-ray Absorption Spectroscopy (XAS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) experiments were performed simultaneously with high data quality. Structural information and the type of adsorbate could be revealed via Extended X-ray Absorption Fine Structure (EXAFS) analysis, Dl X-ray Absorption Near Edge Structure analysis (Dl XANES) and in-situ DRIFTS. The as-received catalyst showed sub-surface oxygen and O(n-fold). Under CO atmosphere only CO(atop) was found. Reversible adsorbate induced changes of the Pt nanoparticle structure were derived from changes in the PtAPt coordination number and the corresponding bond distance. Under reducing conditions (H2, CO) a significant increase in both values occurred. Temperature dependent desorption of CO revealed a gradual shift from PtACO to PtAO. Reoxidation was clearly assigned to strong metal support interaction from the SiO2 support.
Experimental N K-edge NEXAFS data of surface immobilized azide, 1,2,3-triazole and terpyridyl groups are interpreted with the help of DFT spectrum simulations. Assignments of π* resonances in experimental N K-edge NEXAFS spectra to nitrogen atoms within these functional groups have been made. The azide was immobilized on gold as the head group of a thiol SAM, 1,2,3-triazole was formed on this SAM by click reaction and terpyridyl groups were introduced as substituents of the acetylene used for the click reaction. For azide-terminated molecules, DFT spectrum simulations are found to be useful to find measurement conditions delivering experimental N K-edge NEXAFS data with negligible X-ray damage. The 1,2,3-triazole group is found to be rather stable under X-ray irradiation.
An ethynylterpyridine was 'clicked' to an azide-terminated self-assembled monolayer on gold and characterized by synchrotron radiation based surface analysis as NEXAFS and XPS. The detection of azide and terpyridine signatures confirmed a partial click reaction at room temperature. The absence of the azides after reaction at 50 °C indicates an almost complete conversion. For the latter case successful Pd(II) coordination has been proven. The Au–S interface of the SAMs has been characterized by S 1s and S 2p XPS.
The present study investigates early stages of ZIF-8 crystallization up to 5 minutes post mixing of precursor solutions. Dispersive X-ray Absorption Spectroscopy (DXAS) provides a refined understanding of the evolution of the coordination environment during ZIF-8 crystallization. Linear Combination Fiting (LCF) suggests tetrakis(1-methylimidazole)zinc2+ to be a suitable and stable mononuclear structure analogue for some early stage ZIF-8 intermediates. Our results pave the way for more detailed studies on physico-chemical aspects of ZIF-8 crystallization to better control tailoring ZIF-8 materials for specific applications.
Current time-resolved in situ approaches 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.
Bundling analytical capacities to understand phase formation in recycling of functional materials
(2019)
Transitioning from combustion engine-driven transportation to e-mobility demands a paradigm shift – from a system geared to maximize energy efficiency (i.e. fuel consumption) to a system that may be constrained by the availability of high technology (critical) metals required for electrical energy storage systems and drives. In the wake of these developments efforts in securing new resources of these metals from recycling of end-of-life products are increasing steadily.
Recycling of Li-Ion batteries has recently been evaluated. The results pinpoint to a critical need for understanding slag Formation and its dependence on metal components like Mn under extreme conditions. This will allow researchers to predict optimal Operation setting and to react quickly to changing market demands (which may be Li or Co at one point but may also shift to Ni or rare earth elements (REE)). The long-term goal is to control the formation of specific phases in slags allowing for a Maximum yield of elements of interest and optimal recovery in the separation processes that follows. The combination of data on the physical micro structure and local chemistry of the multi-Phase products during and after processing will help to understand and derive thermodynamic and kinetic data on its formation.
In this paper we are giving an overview on the analytical challenges and approaches to provide robust data on local element concentration and species (especially Mn which is a common component of next generation Li-ion batteries cathodes), spanning the dimensions from the nanometer scale to the bulk material. The complementary interactions of X-rays and electrons make them ideal probes to collect Interface and “in-depth” information. Before- and -after studies as well as in situ structural changes and Phase (trans)formation, changes in elemental and elemental species (e.g. oxidation state) distribution may be tracked by X-ray diffraction (XRD), X-ray fluorescence microscopy and X-ray Absorption spectroscopy. The application of such advanced analytical tools will not only provide essential clues during early lab-based experiments towards the development of new recycling technologies, but may also be deployed for on-line and in-line monitoring of industrial processes.
This paper focuses on the scandium speciation in bauxite residues of different origin. Insights into mineralchemical similarities and differences of these materials will be presented and links to their natural geological background discussed. The presented research should provide fundamental knowledge for the future development of efficient and viable technologies for Sc-recovery from bauxite residues derived from different bauxites and accumulating at different localities. In total, five bauxite residues were investigated which originated from Greece, Germany, Hungary and Russia (North Ural & North Timan) using a combination of different analytical tools. Those included: laser ablation inductively coupled plasma mass spectrometry, X-ray absorption near Edge structure (XANES) spectroscopy, μ-Raman spectroscopy as well as scanning electron microscopy and electron microprobe analyses. X-ray fluorescence and inductively coupled plasma mass spectrometry were used to determine the overall chemical composition. The investigated samples were found to exhibit a relatively homogenous distribution of Sc between the larger mineral particles and the fine-grained matrix except for Al-phases like diaspore, boehmite and gibbsite. These phases were found to be particularly low in Sc. The only sample where Sc mass fractions in Al-phases exceeded 50 mg/kg was the Russian sample from North Ural. Fe-phases such as goethite, hematite and chamosite (for Russian samples) were more enriched in Sc than the Al-phases.
In fact, in Greek samples goethite showed a higher capacity to incorporate or adsorb Sc than hematite. Accessory minerals like zircon, rutile/anatase and ilmenite were found to incorporate higher mass fractions of Sc (>150 mg/kg), however, those minerals are only present in small amounts and do not represent major host phases for Sc. In Russian samples from North Ural an additional Ca–Mg rich phase was found to contain significant mass fractions of Sc (>500 mg/kg). μ-XANES spectroscopy was able to show that Sc in bauxite residue occurs adsorbed onto mineral surfaces as well as incorporated into the crystal lattice of certain Fe-phases. According to our observations the bauxite type, i.e. karstic or lateritic, the atmospheric conditions during bauxitization, i.e. oxidizing or reducing, and consequently the dominant Sc-bearing species in the primary Bauxite influence the occurrence of Sc in bauxite residues. In karstic bauxites, underlying carbonate rocks can work as a pH-barrier and stabilize Sc. This prevents the Sc from being mobilized and removed during bauxitization. Hence, karstic bauxites are more prone to show a Sc enrichment than lateritic bauxites. Reducing conditions during bauxitization support the incorporation of Sc into clay minerals such as chamosite, which can dissolve and reprecipitate during Bayer processing causing Sc to be redistributed and primarily adsorb onto mineral surfaces in the bauxite residue. Oxidizing conditions support the incorporation of Sc into the crystal lattice of Fe-oxides and hydroxides, which are not affected in the Bayer process. The genetic history of the bauxite is therefore the major influential factor for the Sc occurrence in bauxite residues.
We report on the formation of polymer-stabilized superparamagnetic single-core and multi-core maghemite nanoparticles. The particle formation was carried out by coprecipitation of Fe(II) and Fe(III) sulfate in a continuous aqueous process using a micromixer system. Aggregates containing 50 primary particles with sizes of 2 nm were formed at a reaction temperature of 30 °C. These particles aggregated further with time and were not stable. In contrast, stable single-core particles with a diameter of 7 nm were formed at 80 °C as revealed by small-angle X-ray scattering (SAXS) coupled in-line with the micromixer for particle characterization. X-ray diffraction and TEM confirmed the SAXS results. X-ray absorption near-edge structure spectroscopy (XANES) identified the iron oxide phase as maghemite.