In soils and sediments ferrihydrite often precipitates from solutions containing dissolved organic matter, which affects its crystallinity. To simulate this process we prepared a series of 2-line ferrihydrite-organic matter coprecipitates using water extractable organic matter (OM) from a forest topsoil. The products were characterized byX-ray diffraction, Mössbauer spectroscopy, N2-gas adsorption and transmission electron microscopy. With increasing C/Fe ratios of the initial solution the d-spacings of the two major XRD peaks increased, while peak shoulders at 0.22 and 0.16 nm weakened. The asymmetry of the 0.26 nm peak decreased and disappeared at a C/Fe ratio of 0.78. The quadrupole splitting of the Mössbauer spectra at 300 K increased from 0.78 to 0.90 mm s(-1), the mean magnetic hyperfine field at 4.2 K dropped from 49.5 to 46.0 T, and the superparamagnetic collapse of the magnetic hyperfine splitting was shifted toward lower temperatures. These data reflect a strong interference of OM with crystal growth leading to smaller ferrihydrite crystals, increased lattice spacings, and more distorted Fe(O,OH)6 octahedra. Even small amounts of OM significantly change particle size and structural order of ferrihydrite. Crystallinity and reactivity of natural ferrihydrites will therefore often differ from their synthetic counterparts, formed in the absence of OM.
Hydrochlorination of Acetylene Using Gold Catalysts: A Study of Catalyst Deactivation.-With a view to the importance of the title reaction in the industrial process for the production of vinyl chloride monomer, the effect of a range of parameters on the deactivation rate is discussed. In combination with 197Au Moessbauer spectroscopy and X-ray diffractometry deactivation mechanisms are investigated and it is shown that deposition of carbonaceous residues is a predominant process. -(NKOSI, B.; COVILLE, N. J.; HUTCHINGS, G. J.; ADAMS, M. D.; FRIEDL, J.; WAGNER, F. E.; J.
Iron oxide nanoparticles are of great scientific interest due to their huge versatility of applications. The oxidation process of magnetite to maghemite is difficult to monitor as both iron oxide polymorphs possess connatural chemical properties. Especially the surface composition and reactivity of these nanosystems, which are most relevant for interactions with their environment, are not completely understood. Here, the oxidation of magnetite is investigated under mild and harsh conditions in order to understand the oxidation behaviour and the chemical stability of transition forms. Therefore, the oxidation process, is investigated with Raman, Mössbauer and X-ray photoelectron spectroscopy as well as X-ray diffraction and magnetometry. The multi-analytical approach allows new insights into surface composition and rearrangement according to respective different depth profiles. For both conditions investigated, the ferrous iron components are oxidised prior to structural changes in the Fe-O vibrations and crystal structure. The process starts from the outer layers and is acid catalysed. Oxidation leads to a decrease of magnetisation which still remains higher than 54 emu g −1. The charge and surface reactivity can be affected by the different oxidation methods and the irreversible adsorption of acid molecules. Biocompatibility and catalytic properties of iron oxide nanoparticles open doors to future applications.
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