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Abstract: Iron (oxyhydr)oxide nanoparticles are known to sorb metals, including radionuclides, from solution in various environmental and industrial systems. Effluent treatment processes including the Enhanced Actinide Removal Plant (EARP) (Sellafield, UK) use a neutralisation process to induce the precipitation of iron (oxyhydr)oxides to remove radionuclides from solution. There is a paucity of information on mechanism(s) of U(VI) removal under conditions relevant to such industrial processes. Here, we investigated removal of U(VI) from simulated effluents containing 7.16 mM Fe(III) with 4.2 × 10-4-1.05 mM U(VI), during the base induced hydrolysis of Fe(III). The solid product was ferrihydrite under all conditions. Acid dissolutions, Fourier Transform infrared spectroscopy and thermodynamic modelling indicated that U(VI) was removed from solution by adsorption to the ferrihydrite. The sorption mechanism was supported by X-ray Absorption Spectroscopy which showed U(VI) was adsorbed to ferrihydrite via a bidentate edge-sharing inner-sphere species with carbonate forming a ternary surface complex. At concentrations ≤0.42 mM U(VI) was removed entirely via adsorption, however at 1.05 mM U(VI) there was also evidence for precipitation of a discrete U(VI) phase. Overall these results confirm that U(VI) sequestered via adsorption to ferrihydrite over a concentration range from 4.2 × 10-4-0.42 mM confirming a remarkably consistent removal mechanism in this industrially relevant system.

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Abstract: Deposition of gold on supports can produce catalytically active forms of gold as well as spectators, but previous understanding of the nature of active immobilized precursors is poor. By using synchrotron X-ray powder diffraction (SXRD) and X-ray absorption spectroscopy (XAS) techniques, we report a novel synthesis and structural elucidation of atomically dispersed gold species anchored to the internal surface of TS-1 as K+Au(OH)2Na+(Of)3 (“f” signifies the framework atoms of TS-1 in the formula.). It is found that the choice of alkali ions plays a crucial role in nucleation and stabilization of the atomic precursor. These anchored single Au upon controlled reduction in H2 can form uniform gold clusters in direct contact with the TS-1 surface containing isolated Ti sites: their interface exhibits excellent specificity and stability towards epoxidation of propylene in H2/O2 due to synergetic effect.

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Abstract: The activity of oxides towards the oxygen evolution reaction (OER) is usually tuned by changing the transition metal components and/or the surface facets. An important yet less studied feature is the repercussion of the lattice oxygen content of the oxide in the active site's coordination and catalytic performance. This is illustrated here for the Ba-Ni-O system. We synthesized two oxides with Ni in different coordination and oxidation states, namely BaNiO2 with Ni2+ in square-planar positions, and BaNiO2.78(2) with Ni3+ and Ni4+ in octahedral positions. We show that the square-planar configuration of Ni endows BaNiO2 with high intrinsic OER activity, comparable to the best catalysts in the literature. DFT indicates that progressively lowering the lattice oxygen content from BaNiO3 to BaNiO2 increases the Ni sites' affinity for the reaction intermediates, thereby lowering the OER overpotential. Thus, oxygen content is an important parameter in oxide catalysts, as it modulates the coordination, orbital splitting, oxidation number, and catalytic activity of the active sites.

Open Access

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Abstract: Monoclinic vanadium(IV) oxide [VO2(M)] is a widely studied material due to its thermochromic properties and its potential use for energy-efficient glazing applications. VO2(M) nanoparticles can be a great advantage for energy-efficient glazing as below 50 nm the nanoparticles poorly interact with visible wavelengths – resulting in an increase in visible light transmittance whilst maintaining the thermochromic response of the material. The direct synthesis of VO2(M) nanoparticles with effective thermochromic properties will be a step forward towards industrial applications of this material. Unfortunately, many of the synthesis processes reported so far involve multiple steps, including post-treatment, and the synthesis is not always reproducible. In this study, we present the first direct synthesis of pure monoclinic VO2 nanoparticles by continuous hydrothermal flow synthesis (CHFS). TEM images showed that nanoparticles in the size range of 30-40 nm were produced. The VO2(M) nanoparticles also showed good thermochromic properties with a solar modulation (∆Tsol) of 3.8%, as established by UV/Vis spectroscopy. A range of analytical methods was used to characterise the materials, including X-ray absorption spectroscopy (XANES and EXAFS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The influence of niobium (Nb) doping on the physical and thermochromic properties of the VO2 nanoparticles was also explored. Previous work has shown a sharp metal-to-semiconductor transition of VO2 upon incorporation of Nb dopant. The results of the current work suggested these changes are likely due to changes on the local structure of the oxide.

Open Access

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Abstract: Spin crossover (SCO) complexes are an example of potential molecular bistability. This effect describes the ability of a system to undergo a transition from a low spin (LS) to a high spin (HS) state by an external perturbation, e.g. temperature or pressure. The exact mechanisms underlying a spin transition are not completely understood yet, since complex processes take place both at the structural and the electronic level. With the known standard methods, these changes cannot be investigated simultaneously in one experiment (Structure change: XRD, XAS, spin state: Mößbauer, SQUID). Therefore, subject of this thesis is the in-depth analysis of existing methods and their improvement by development of new approaches for the analysis of temperature-dependent SCO processes with hard X-ray absorption and emission spectroscopic techniques. With these methods, it is possible to follow the structural and electronic changes in one experiment quasi-simultaneously without changing the experimental conditions. Temperature-dependent EXAFS, HERFD-XANES, CtC, and VtC XES experiments were performed on a mononuclear Fe (II) complex with a gradual SCO behaviour. All spectra showed interesting behaviour caused by the transition from the LS to the HS state. The spectral changes were quantified by several approaches and the results were compared to magnetization data obtained by SQUID magnetometry. It was shown that in principle all methods are well suited for the investigation of SCO processes.