The bending magnet beamline SOLABS will be dedicated to X-ray absorption spectroscopy (XAS) and related techniques in the energy range from 1 keV to ~12–15 keV, covering the K absorption edges of chemical elements between Mg and Se along with the L and M edges of many other elements. XAS is a non-destructive, element specific characterization method which can be applied to both crystalline and amorphous materials, liquids and samples in the gas phase. Moreover, XAS measurements can be performed under application relevant conditions (in situ). Both XANES (X-ray absorption near-edge structure) and EXAFS (extended X-ray absorption fine structure) data contain valuable structural information about the atomic environment of the absorber atoms in the materials under investigation. At SOLABS XAS spectra can be recorded in transmission or fluorescence mode.
The beamline SOLABS (XAS-HN) is intended for fundamental and applied research in:
- materials science, physics and chemistry (investigation of functional materials, esp. alloys, oxidic systems and catalysts, coatings, adhesives, etc.)
- biomedicine (investigation of metalloproteins, investigation of the stability, uptake and therapeutic mechanism of action of inorganic and bio-inorganic drugs, etc.)
- environmental protection (e.g., speciation of toxic elements during bioaccumulation).
In Spring 2021 commissioning will take place, and user operation will start in Summer 2021.
Extended X-ray Absorption Fine Structure (EXAFS)
EXAFS spectroscopy provides information about the average coordination number around the absorber atoms and bond distances
EXAFS - example 1
(a) Schematic illustration of Pt atoms deposited on nitrogen-doped carbon dots (Pt–NCDs) and (b) Fourier transformed Pt L3-edge EXAFS spectra of Pt–NCDs hybridized with TiO2 film, and of PtO2, PtCl2 and Pt foil as references for comparison (measured at beamline B18, Diamond Light Source).
The absence of a scattering peak in the region 2-3.5 Å, corresponding to a Pt-Pt bond, indicates that only isolated Pt atoms are bound to the NCD support, and the single peak at 1.6 Å reveals that they are coordinated to light atoms (4-5 carbon atoms) on the support.
This example shows that EXAFS data can be used to distinguish between single-atom catalysts and small clusters or nanoparticles bound to the support. Pt single-atoms are important as catalysts for photocatalytic hydrogen production.
Adapted from Hui Luo, Ying Liu, Stoichko D. Dimitrov, Ludmilla Steier, Shaohui Guo, Xuanhua Li, Jingyu Feng, Fei Xie, Yuanxing Fang, Andrei Sapelkin, Xinchen Wang and Maria-Magdalena Titirici, Pt single-atoms supported on nitrogen-doped carbon dots for highly efficient photocatalytic hydrogen generation, J. Mater. Chem. A, 2020, 8, 14690.
EXAFS - example 2
(left) Preparation of 17 atoms Pt clusters deposited on γ-Al2O3 (Pt17/γ-Al2O3)
(right) Fourier transform of Pt L3-edge EXAFS spectra of [Pt17(CO)12(PPh3)8]Cln, Pt17(CO)12(PPh3)8/γ-Al2O3, and Pt17/γ-Al2O3 together with EXAFS data of Pt foil and PtO2. In the spectrum of Pt17/γ-Al2O3 the peak at 1.7 Å is attributed to Pt–C or Pt–O bonds at the Pt17/γ-Al2O3 interface.
EXAFS data shows that in the Pt17/γ-Al2O3 system the supported Pt17 is not present in the form of oxide but has a framework structure like a metal cluster. Moreover, it was shown that supported Pt17 clusters are covered by CO molecules at normal temperature. CO molecules adsorbed on fine Pt17 supported clusters generally has a longer C–O bond compared to larger Pt supported nanoparticles, promoting the oxidation reaction and possibly contributing to the high catalytic activity of the Pt17/γ-Al2O3 system for carbon monoxide and propylene oxidation in comparison to γ-Al2O3-supported larger Pt nanoparticles (PtNP/γ-Al2O3)prepared by conventional impregnation.
Adapted from Yuichi Negishi, Nobuyuki Shimizu, Kanako Funai, Ryo Kaneko, Kosuke Wakamatsu, Atsuya Harasawa, Sakiat Hossain, Manfred E. Schuster, Dogan Ozkaya, Wataru Kurashige, Tokuhisa Kawawaki, Seiji Yamazoe and Shuhei Nagaoka, γ-Alumina-supported Pt17 cluster: controlled loading, geometrical structure, and size-specific catalytic activity for carbon monoxide and propylene oxidation, Nanoscale Adv., 2020, 2, 669-678. https://doi.org/10.1039/C9NA00579J