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Instruments / Technical Area	Publication Details	Published
I08-Scanning X-ray Microscopy beamline (SXM)	Evidence for a core-shell structure of hydrothermal carbon Luke J. R. Higgins , Andy P. Brown , John P. Harrington , Andrew B. Ross , Burkhard Kaulich , Bhoopesh Mishra Carbon DOI: 10.1016/j.carbon.2020.01.060 Diamond Proposal Number(s): [19228, 22730] Open Access Show Abstract ▼ Abstract: Hydrothermal carbonisation (HTC) has been demonstrated to be a sustainable thermochemical process, capable of producing functionalised carbon materials for a wide range of applications. In order to better apply such materials, the local chemistry and reaction pathways governing hydrothermal carbon growth must be understood. We report the use of scanning transmission X-ray microscopy (STXM) to observe chemical changes in functionality of carbon between the interface and bulk regions of HTC. Spatially-resolved, element-specific X-ray photo-absorption spectra show the presence of differing local carbon chemistry between bulk “core” and interface “shell” regions of a glucose-derived hydrothermal carbon spherule. STXM provides direct evidence to suggest that mechanistic pathways differ between the core and shell of the hydrothermal carbon. In the shell region, at the water-carbon interface, more aldehyde and/or carboxylic species are suspected to provide a reactive interface for bridging reactions to occur with local furan-based monomers. In contrast, condensation reactions appear to dominate in the core, removing aryl-linking units between polyfuranic domains. The application of STXM to HTC presents opportunities for a more comprehensive understanding of the spatial distribution of carbon species within hydrothermal carbon, especially at the solvent-carbon interface.	Jan 2020
	Analytical electron microscopy of barium titanate and barium-strontium Omar Matar , Nicole Hondow , Olga Posada , Michael Routledge , David Hernandez-Maldonado , Christoph Walti , Claire Murray , Rik Brydson , Steven Milne , Andy Brown European Microscopy Congress 2016 DOI: 10.1002/9783527808465.EMC2016.5998 Show Abstract ▼ Abstract: Nanoparticles with non-centrosymmetric crystal structures exhibit second harmonic generation (SHG) of light when illuminated by a femtosecond pulsed laser. Such nanoparticles can be used as optical biomarkers to circumvent the drawbacks associated with fluorescent proteins and semiconductor quantum dots, such as photobleaching and fluorescent intermittency (blinking). Bulk barium titanate has a tetragonal crystal structure at room temperature however, reduction in particle sizes generally correlates with an increasing phase fraction of cubic material which does not exhibit SHG [1]. In this study we have produced barium titanate (BaTiO3) and barium-strontium titanate (Ba1-xSrxTiO3) nanoparticles by the hydrothermal method. These nanoparticles appear predominantly cubic by laboratory-XRD but Rietveld refinement on synchrotron X-Ray powder diffraction data suggests a mixture of tetragonal and cubic phases. Transmission electron microscopy (TEM) analysis techniques such as electron energy loss spectroscopy (EELS) and energy-dispersive X-ray (EDX) spectroscopy have been used to determine the inter- and intra-particle phase and composition of BaTiO3 and Ba1-xSrxTiO3 nanoparticles. Prior STEM-EELS work, suggests an intra-particle phase distribution of cubic and tetragonal phases [2]. STEM-EEL linescans by aberration corrected scanning transmission electron microscopy (SuperSTEM) confirm that these hydrothermal samples exhibit intra-particle phase distribution of a tetragonal core and a cubic shell (Figure 1 & 2). Multi-photon microscopy correlated with SEM demonstrates the SHG signals from the BaTiO3 and Ba1-xSrxTiO3 nanoparticles [3]. The cellular uptake and biocompatibility of the BaTiO3 and Ba1-xSrxTiO3 nanoparticles have been determined by cell viability (MTT) and genotoxicity (Comet) assays. Uptake was confirmed by backscattered Z-contrast imaging by SEM and EDX (Figure 3), along with bright field TEM and HAADF-STEM of resin embedded cell sections. Direct correlation between electron microscopy (SEM & TEM) and multi-photon microscopy will be used to determine SHG characteristics at the individual particle level when taken up by cells.	Dec 2016
B18-Core EXAFS I22-Small angle scattering & Diffraction	Formation of stable uranium(VI) colloidal nanoparticles in conditions relevant to radioactive waste disposal Pieter Bots , Katherine Morris , Rosemary Hibberd , Gareth Law , Fred Mosselmans , Andy Brown , James Doutch , Andy Smith , Sam Shaw Langmuir 30 (48) DOI: 10.1021/la502832j Diamond Proposal Number(s): [5975, 8544] Open Access Show Abstract ▼ Abstract: The favored pathway for disposal of higher activity radioactive wastes is via deep geological disposal. Many geological disposal facility designs include cement in their engineering design. Over the long term, interaction of groundwater with the cement and waste will form a plume of a hyperalkaline leachate (pH 10–13), and the behavior of radionuclides needs to be constrained under these extreme conditions to minimize the environmental hazard from the wastes. For uranium, a key component of many radioactive wastes, thermodynamic modeling predicts that, at high pH, U(VI) solubility will be very low (nM or lower) and controlled by equilibrium with solid phase alkali and alkaline-earth uranates. However, the formation of U(VI) colloids could potentially enhance the mobility of U(VI) under these conditions, and characterizing the potential for formation and medium-term stability of U(VI) colloids is important in underpinning our understanding of U behavior in waste disposal. Reflecting this, we applied conventional geochemical and microscopy techniques combined with synchrotron based in situ and ex situ X-ray techniques (small-angle X-ray scattering and X-ray adsorption spectroscopy (XAS)) to characterize colloidal U(VI) nanoparticles in a synthetic cement leachate (pH > 13) containing 4.2–252 μM U(VI). The results show that in cement leachates with 42 μM U(VI), colloids formed within hours and remained stable for several years. The colloids consisted of 1.5–1.8 nm nanoparticles with a proportion forming 20–60 nm aggregates. Using XAS and electron microscopy, we were able to determine that the colloidal nanoparticles had a clarkeite (sodium–uranate)-type crystallographic structure. The presented results have clear and hitherto unrecognized implications for the mobility of U(VI) in cementitious environments, in particular those associated with the geological disposal of nuclear waste.	Oct 2014

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