A von Hamos-type hard X-ray spectrometer at the PETRA III beamline P64.

The design and performance of the high-resolution wavelength-dispersive multi-crystal von Hamos-type spectrometer at PETRA III beamline P64 are described. Extended analyzer crystal collection available at the beamline allows coverage of a broad energy range from 5 keV to 20 keV with an energy resolution of 0.35-1 eV. Particular attention was paid to enabling two-color measurements by a combination of two types of analyzer crystals and two two-dimensional detectors. The performance of the spectrometer is demonstrated by elastic-line and emission-line measurements on various compounds.

Operando X-ray Absorption Spectroscopy (XAS) Observation of Photoinduced Oxidation in FeNi (Oxy)hydroxide Overlayers on Hematite (α-Fe2O3) Photoanodes for Solar Water Splitting.

An FeNi (oxy)hydroxide cocatalyst overlayer was photoelectrochemically deposited on a thin-film hematite (α-Fe2O3) photoanode, leading to a cathodic shift of ∼100 mV in the photocurrent onset potential. Operando X-ray absorption spectroscopy (XAS) at the Fe and Ni K-edges was used to study the changes in the overlayer with potential in the dark and under illumination conditions. Potential or illumination only had a minor effect on the Fe oxidation state, suggesting that Fe atoms do not accumulate significant amount of charge over the whole potential range. In contrast, the Ni K-edge spectra showed pronounced dependence on potential in the dark and under illumination. The effect of illumination is to shift the onset for the Ni oxidation because of the generated photovoltage and suggests that holes that are photogenerated in hematite are transferred mainly to the Ni atoms in the overlayer. The increase in the oxidation state of Ni proceeds at potentials corresponding to the redox wave of Ni, which occurs immediately prior to the onset of the oxygen evolution reaction (OER). Linear combination fitting analysis of the obtained spectra suggests that the overlayer does not have to be fully oxidized to promote oxygen evolution. Cathodic discharge measurements show that the photogenerated charge is stored almost exclusively in the Ni atoms within the volume of the overlayer.

Chromium (VI) in phosphorus fertilizers determined with the diffusive gradients in thin-films (DGT) technique.

Phosphorus (P) fertilizers from secondary resources became increasingly important in the last years. However, these novel P-fertilizers can also contain toxic pollutants such as chromium in its hexavalent state (Cr(VI)). This hazardous form of chromium is therefore regulated with low limit values for agricultural products even though the correct determination of Cr(VI) in these fertilizers may be hampered by redox processes, leading to false results. Thus, we applied the novel diffusive gradients in thin-films (DGT) technique for Cr(VI) in fertilizers and compared the results with the standard wet chemical extraction method (German norm DIN EN 15192) and Cr K-edge X-ray absorption near-edge structure (XANES) spectroscopy. We determined an overall good correlation between the wet chemical extraction and the DGT method. DGT was very sensitive and for most tested materials selective for the analysis of Cr(VI) in P-fertilizers. However, hardly soluble Cr(VI) compounds cannot be detected with the DGT method since only mobile Cr(VI) is analyzed. Furthermore, Cr K-edge XANES spectroscopy showed that the DGT binding layer also adsorbs small amounts of mobile Cr(III) so that Cr(VI) values are overestimated. Since certain types of the P-fertilizers contain mobile Cr(III) or partly immobile Cr(VI), it is necessary to optimize the DGT binding layers to avoid aforementioned over- or underestimation. Furthermore, our investigations showed that the Cr K-edge XANES spectroscopy technique is unsuitable to determine small amounts of Cr(VI) in fertilizers (below approx. 1% of Cr(VI) in relation to total Cr).

In vitro SOD-like activity of mono- and di-copper complexes with a phosphonate substituted SALAN-type ligand.

SALEN- and SALAN-based complexes with catalytically active metal centers are very promising small molecules to be utilized as part of antioxidant therapies. Here we discuss a modified SALAN-type molecule armed with two phosphonate groups that significantly increase its water solubility and aid to furnish mono- or dinuclear complexes with Cu2+ ions. The regulation of the SOD-mimicking (i.e., catalytic) disproportionation reaction of the superoxide radical anion (O2•-) at pH ~7.5 could be achieved by adjusting the metal-to-ligand stoichiometry as confirmed by McCord-Fridovich and pulse radiolysis tests. The higher antioxidant activity of the dicopper complex can be explained by the better access of O2•- to the copper centers and their more positive Cu(II)/Cu(I) redox potential. Simultaneously the analysis of in vitro effect on cells morphology indicates that cytotoxicity is also affected by the metal-to-ligand ratio, however, the active complex molecules do not show notable cytotoxicity that, together with the observed SOD-like activities, makes them potential candidates for antioxidant therapies.