The association of cobalt with iron and manganese (oxyhydr)oxides in marine sediment.

Formation and dissolution of authigenic Fe and Mn (oxyhydr)oxides influence cycling of trace metals in oxic/suboxic surface sediments.We used the diffusive gradients in thin films technique (DGT) to estimate the association of cobalt with iron and manganese oxides. We compared Co, Fe and Mn maxima measured by DGT in the pore waters of fresh and aged marine sediment cores and estimated the Co/Fe and Co/Mn ratios in the metal oxides. A Mn maximum was not visible in DGT concentration profiles of freshly collected sediment cores, but after ageing the sediment we observed a distinct Mn peak, presumably due to broadening of the depth range over which the various electron acceptors occur. Estimated Co/Mn ratios from both experiments are within the range of literature values for marine sediments, but the value from the aged experiment is at the lower end of the range. This is attributed to stimulation of sulphate reduction and precipitation of cobalt sulfides. The good correlation between Co and Fe maxima in the fresh sediments is attributed to the similarity of their reactions with sulphide rather than Co being released during authigenic Fe oxide reduction

Study of the magnetite to maghemite transition using microwave permittivity and permeability measurements

The microwave cavity perturbation (MCP) technique is used to identify the transition from magnetite (Fe3O4) to the meta-stable form of maghemite (γ-Fe2O3). In this study Fe3O4 was annealed at temperatures from 60 to 300 °C to vary the oxidation. Subsequent to annealing, the complex permittivity and magnetic permeability of the iron oxide powders were measured. The transition to γ-Fe2O3 was corroborated with x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM). XRD, XPS and VSM implied that the starting powder was consistent with Fe3O4 and the powders annealed at more than 200 °C were transitioning to γ-Fe2O3. The MCP measurements gave large differences in both complex permittivity and magnetic permeability of the two phases in the frequency range of 2.5–10.2 GHz. Magnetic permeability decreased with annealing temperature, though magnetic losses showed frequency dependent behaviour. Complex permittivity measurements showed a large decrease in both dielectric constant and losses at all measurement frequencies, as well as a prominent loss peak centred around the phase transition temperatures. We interpret the loss peak as being a consequence of field effects due to an intermediate multi-phase mixture. Additionally, almost no frequency dependence was observed. The reduction in complex permittivity implies that the $\text{Fe}_{\text{oct}}^{2+}$ cations in the lattice provide a significant contribution to polarization at microwave frequencies and the effects of $\text{Fe}_{\text{oct}}^{3+}$ are nominal in comparison. The change in loss can be explained as a combination of the differences in the effective conductivity of the two phases (i.e. Fe3O4 exhibits electron-hopping conduction whereas the presence of vacancies in γ-Fe2O3 nullifies this). This shows that the non-invasive MCP measurements serve as a highly sensitive and versatile method for looking at this phase transition in iron and potentially the effects of oxidation states on the polarization in other iron oxides

Associations between multimorbidity and neuropathology in dementia: a case for considering functional cognitive disorders, psychiatric illness, and dementia mimics

Cognitive impairment in older people has a variety of underlying causes. In addition to neurodegenerative causes such as Alzheimer's disease, a dementia-like cognitive disorder may appear due to non-degenerative factors. Multimorbidity has been previously associated with clinical dementia risk, though whether this was due to greater risk of dementia-related neuropathology, or other factors that mimic dementia, was unclear. We provide evidence that physical multimorbidity is not associated with greater pathological changes at autopsy. Other factors related to multimorbidity and cognitive impairments may be important targets for investigation, such as functional cognitive disorders, primary psychiatric disorders (depression, anxiety, psychosis) and polypharmacy

The selective oxidation of n-butanol to butyraldehyde by oxygen using stable Pt-based nanoparticulate catalysts: an efficient route for upgrading aqueous biobutanol

Supported Pt nanoparticles are shown to be active and selective towards butyraldehyde in the base-free oxidation of n-butanol by O2 in an aqueous phase. The formation of butyric acid as a by-product promoted the leaching of Pt and consequently the activity of the catalysts decreased upon reuse. Characterisation showed that the degree to which Pt leached from the catalysts was related to both the metal–support interaction and metal particle size. A catalyst active and stable (<1% metal leaching) in the aqueous reaction medium was obtained when Pt nanoparticles were supported on activated carbon and prepared by a chemical vapour impregnation method. The presence of n-butanol in the aqueous medium is required to inhibit the over oxidation of butyraldehyde to butyric acid. Consequently, high selectivities towards butyraldehyde can only be obtained at intermediate n-butanol conversion