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Abstract: At the morphological and anatomical level the ionome, or the elemental composition of an organism, is an understudied area of plant biology. In particular, the ionomic responses of plant-pathogen interactions are scarcely described, and there are no studies on immune reactions. In this study we explored two X-ray fluorescence based ionome visualisation methods (benchtop and synchrotron-based micro XRF (µXRF), as well as the quantitative Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) method, to investigate the changes that occur in the ionome of compatible and incompatible plant-pathogen interactions. We utilised the agronomically important and comprehensively studied interaction between potato, Solanum tuberosum, and the late blight oomycete pathogen, Phytophthora infestans, as an example. We used one late blight susceptible potato cultivar and two resistant transgenic plant lines (only differing from the susceptible cultivar in one or three resistance genes) both in control and P. infestans inoculated conditions. In the lesions from the compatible interaction we observed rearrangements of several elements. This included, a decrease of the mobile macro nutrient potassium (K), and an increase of iron (Fe), and manganese (Mn) in the lesion versus the tissue outside the lesion. Interestingly, we observed distinctly different distribution patterns of accumulation at the site of inoculation in the resistant lines for calcium (Ca), Magnesium, Mn and silicon (Si) compared to the susceptible cultivar. The results reveal different ionomes in diseased plants compared to resistant plants. Our results demonstrate a technical advance and pave the way for deeper studies of the plant-pathogen ionome in the future.

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Abstract: Coal fly ash is an industrially useful by-product of coal combustion, with millions of tonnes held in repositories globally. This fine and cheaply-available waste material, is proven to sometimes be enriched in valuable elements/compounds, such as rare earth element (REE) minerals and actinides, alongside heavy toxic elements such as Cr, Pb, As and Cd, making coal fly ash both a potential unconventional source of valuable minerals and a hazardous material depending on the elemental trace chemistry of the parent coal body. The importance of REE and actinides for use in advanced electronics technologies and the nuclear industry, alongside concerns over geopolitics and instability in the global supply market, means there is now a renewed incentive for countries to secure native sources of economically-sustainable rare earth elements through research and development efforts. Unconventional sources of REE, such as coal fly ash, represent a potentially interesting value proposition, especially for developing countries. The work presented in this thesis provides a study of rare earth elements and actinides in Nigerian simulant coal fly ash from the perspective of resource recovery and environmental protection. A suite of advanced analytical laboratory techniques and novel synchrotron radiation techniques, alongside micromanipulation methods, were used in this study to understand the amounts and mineralogical association of REE and actinides in 3 different Nigerian coal deposits. Bulk and micro mineralogical analyses were first performed on the simulant coal fly ash using x-ray diffraction and scanning electron microscopy / with energy dispersive x-ray fluorescence and spectroscopy used for elemental analysis. It was observed that the Nigerian simulant coal fly ash samples were less complex in mineralogy than conventional rare earth ores (with quartz, mullite, haematite and cristobalite as the major mineral phases), composed of discrete micron-scale particles of rare earth mineral monazite ([Ce,La,Nd,Th]PO4), xenotime (YPO4) and zircon (ZrSiO4), alongside uraninite (UO2) and thorite (ThSiO4). Subsequent bulk elemental analysis performed using inductively-coupled plasma mass spectrometry, showed the simulant coal fly ash to be enriched in the rare earth elements, being more enriched in the higher-valued critical rare earth elements Nd, Eu, Tb, Dy, Y and Er, compared to conventional rare earth ores. Sequential extraction analysis of the simulant fly ash materials showed significant recoverability of rare earth elements in the acid-soluble fraction using cheap and environmentally-friendly ethanoic acid; the toxic heavy metals Cd and As were also significantly recovered in the acid-soluble fraction. Synchrotron radiation analysis of individual micro-particles of monazite and uraninite using micro-x-ray fluorescence mapping, micro-x-ray fluorescence tomography, micro-x-ray absorption near edge spectroscopy and micro-x-ray diffraction showed a zonation pattern in the monazite particles, with the rims rich in the rare earth elements, and the core rich in U and Th but depleted in the rare earth elements. In the uraninite particles, U was homogeneously-distributed, existing in the chemically reduced IV oxidation state. Gamma-ray spectrometry analysis of the bulk coal and simulant coal fly ash was also performed using a high-purity Ge gamma-ray detector. Compared to World mean levels, the radioactivity and associated hazard associated with the parent coal samples were insignificantly-low. However, the equivalent activity concentration and radiological hazard levels associated with the simulant coal fly ashes were significantly-high, above United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) World mean and recommended levels.

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Abstract: Biominerals are widespread in Nature and they precipitate to respond to different physiological purposes. A broad knowledge of their chemical and structural properties offers a unique opportunity to improve our capability to reconstruct actual and paleoenvironment. In this work, we show two case studies, bivalves and foraminifera grown in polluted sites that were characterized by applying different and complementary synchrotron radiation-based investigation techniques, mainly focused on the investigation of Zn incorporation in the biomineralized shells. Using scanning transmission X-ray microscopy (STXM) and X-ray micro-fluorescence (µ-XRF), we found the colocalization of elements across the shells, while we obtained information on chemical speciation of Zn by applying X-ray absorption spectroscopy (XAS). Noticeably, instead of metal dispersion in the Ca-carbonate shells, we found traces of several independent phases, in particular for Zn, dispersed generally as microscopic minerals. This work provides fundamental insight into the structural properties, coordinative and chemical environment of some marine biominerals. This new knowledge is fundamental to understand the biogeochemical processes and to develop effective environmental proxies.

Open Access

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Abstract: The high-energy release of plutonium (Pu) and uranium (U) during the Maralinga nuclear trials (1955–1963) in Australia, designed to simulate high temperature, non-critical nuclear accidents, resulted in wide dispersion µm-sized, radioactive, Pu–U-bearing ‘hot’ particles that persist in soils. By combining non-destructive, multi-technique synchrotron-based micro-characterization with the first nano-scale imagining of the composition and textures of six Maralinga particles, we find that all particles display intricate physical and chemical make-ups consistent with formation via condensation and cooling of polymetallic melts (immiscible Fe–Al–Pu–U; and Pb ± Pu–U) within the detonation plumes. Plutonium and U are present predominantly in micro- to nano-particulate forms, and most hot particles contain low valence Pu–U–C compounds; these chemically reactive phases are protected by their inclusion in metallic alloys. Plutonium reworking was observed within an oxidised rim in a Pb-rich particle; however overall Pu remained immobile in the studied particles, while small-scale oxidation and mobility of U is widespread. It is notoriously difficult to predict the long-term environmental behaviour of hot particles. Nano-scale characterization of the hot particles suggests that long-term, slow release of Pu from the hot particles may take place via a range of chemical and physical processes, likely contributing to on-going Pu uptake by wildlife at Maralinga.

Open Access

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Abstract: Halide perovskite/crystalline silicon (c-Si) tandem solar cells promise power conversion efficiencies beyond the limits of single-junction cells. However, the local light-matter interactions of the perovskite material embedded in this pyramidal multijunction configuration, and the effect on device performance, are not well understood. Here, we characterize the microscale optoelectronic properties of the perovskite semiconductor deposited on different c-Si texturing schemes. We find a strong spatial and spectral dependence of the photoluminescence (PL) on the geometrical surface constructs, which dominates the underlying grain-to-grain PL variation found in halide perovskite films. The PL response is dependent upon the texturing design, with larger pyramids inducing distinct PL spectra for valleys and pyramids, an effect which is mitigated with small pyramids. Further, optimized quasi-Fermi level splittings and PL quantum efficiencies occur when the c-Si large pyramids have had a secondary smoothing etch. Our results suggest that a holistic optimization of the texturing is required to maximize light in- and out-coupling of both absorber layers and there is a fine balance between the optimal geometrical configuration and optoelectronic performance that will guide future device designs.