Journal Publications

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Browsing Journal Publications by Subject "Absorption spectroscopy"

Now showing 1 - 9 of 9
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    Characterization of foliar manganese (Mn) in Mn (hyper)accumulators using x-ray absorption spectroscopy
    (Wiley-Blackwell, 2010-12-01) Fernando, DR; Mizuno, T; Woodrow, IE; Baker, AJM; Collins, RN
    Plant hyperaccumulation of the essential nutrient manganese (Mn) is a rare phenomenon most evident in the Western Pacific region, and differs from hyperaccumulation of other elements. Mn hyperaccumulators employ a variety of species-dependent spatial distribution patterns in sequestering excess foliar Mn, including primary sequestration in both nonphotosynthetic and photosynthetic tissues. This investigation employed synchrotron X-ray absorption spectroscopy (XAS) in a comparative study of Mn (hyper)accumulators, to elucidate in situ the chemical form(s) of foliar Mn in seven woody species from Australia, New Caledonia and Japan. Foliar Mn was found to predominate as Mn(II) in all samples, with strong evidence of the role of carboxylic acids, such as malate or citrate, as complexing ligands. Overall, the X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine-structure spectroscopy (EXAFS) data appeared weighted against previous observations that oxalate binds excess Mn in Mn-(hyper)accumulating species. © 2010, Wiley-Blackwell.
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    Comparison of the atomic structure of InP amorphized by electronic or nuclear ion energy-loss processes
    (American Physical Society, 2008-02) Schnohr, CS; Kluth, P; Byrne, AP; Foran, GJ; Ridgway, MC
    InP was amorphized by ion irradiation in two very different regimes: (i) 185 MeV Au irradiation, where the energy loss was predominantly via inelastic processes (electronic stopping), or (ii) Se irradiation in an energy range of 0.08-7 MeV, where elastic processes (nuclear stopping) were dominant. The structural parameters of the amorphous phase were determined for as-irradiated and thermally relaxed samples using extended x-ray absorption fine structure spectroscopy. Despite the fundamentally different energy transfer mechanisms, no significant difference in the atomic structure of the two amorphized samples was observed. We attribute this result to a common "melt and quench" process responsible for amorphization. In fact, the measured structural parameters for the amorphized samples, including the fraction of homopolar In-In bonding, were consistent with simulations of the amorphous phase produced by assuming a quench from the melt. © 2008, American Physical Society
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    Effect of amorphous Fe(III) oxide transformation on the Fe(II)-mediated reduction of U(VI).
    (American Chemical Society, 2011-02-15) Boland, DD; Collins, RN; Payne, TE; Waite, TD
    It has recently been reported that the Fe(II)-catalyzed crystallization of 2-line ferrihydrite to goethite and magnetite can result in the immobilization of uranium. Although it might be expected that interference of the crystallization process (for example, by the presence of silicate) would prevent uranium immobilization, this has not yet been demonstrated. Here we present results of an X-ray absorption spectroscopy study on the fate of hexavalent uranium (U(VI)) during the Fe(II)-catalyzed transformations of 2-line ferrihydrite and ferrihydrite coprecipitated with silicate (silicate−ferrihydrite). Two-line ferrihydrite transformed monotonically to goethite, whereas silicate−ferrihydrite transformed into a form similar to ferrihydrite synthesized in the absence of silicate. Modeling of U L(III)-edge EXAFS data indicated that both coprecipitated and adsorbed U(VI) were initially associated with ferrihydrite and silicate−ferrihydrite as a mononuclear bidentate surface complex. During the Fe(II)-catalyzed transformation process, U(VI) associated with 2-line ferrihydrite was reduced and partially incorporated into the newly formed goethite mineral structure, most likely as U(V), whereas U(VI) associated with silicate−ferrihydrite was not reduced and remained in a form similar to its initially adsorbed state. Uranium(VI) that was initially adsorbed to silicate−ferrihydrite did, however, become more resistant to reductive dissolution indicating at least a partial reduction in mobility. These results suggest that when the Fe(II)-catalyzed transformation of ferrihydrite-like iron oxyhydroxides is inhibited, at least under conditions similar to those used in these experiments, uranium reduction will not occur. © 2011, American Chemical Society
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    Experimental observation and computational study of the spin-gap excitation in Ba3BiRu2O9
    (American Physical Society, 2016-11-01) Ling, CD; Huang, Z; Kennedy, BJ; Rols, S; Johnson, MR; Zbiri, M; Kimber, SAJ; Hudspeth, J; Adroja, DT; Rule, KC; Avdeev, M; Blanchard, PER
    Ba3BiRu2O9 is a 6H-type perovskite compound containing face-sharing octahedral M2O9 (M=Ir, Ru) dimers, which are magnetically frustrated at low temperatures. On cooling through T∗=176 K, it undergoes a pronounced magnetostructural transition, which is not accompanied by any change in space group symmetry, long-range magnetic ordering, or charge ordering. Here, we report the first direct evidence from inelastic neutron scattering that this transition is due to an opening of a gap in the excitation spectra of dimers of low-spin Ru4+ (S=1) ions. X-ray absorption spectroscopy reveals a change in Ru-Ru orbital overlap at T∗, linking the emergence of this spin-gap excitation to the magnetostructural transition. Ab initio calculations point to a geometrically frustrated magnetic ground state due to antiferromagnetic interdimer exchange on a triangular Ru2O9 dimer lattice. X-ray total-scattering data rule out long-range magnetic ordering at low temperatures, consistent with this geometrically frustrated model. ©2016 American Physical Society
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    A layered wide-gap oxyhalide semiconductor with an infinite ZnO2 square planar sheet: Sr2ZnO2Cl2
    (Royal Society of Chemistry, 2017-03-13) Su, Y; Tsujimoto, Y; Miura, A; Asai, S; Avdeev, M; Ogino, H; Ako, M; Belik, AA; Masuda, T; Uchikoshi, T; Yamaura, K
    A new square-planar zinc oxyhalide, Sr2ZnO2Cl2, was successfully synthesized using a high-pressure method. Absorption spectroscopy revealed an indirect band gap of 3.66 eV. Electronic structure calculations indicated a strong hybridization between Zn 3dx2−y2 and O 2p orbitals, which is distinct from tetrahedrally coordinated ZnO. © Royal Society of Chemistry 2021
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    Solid phases responsible for Mn II, Cr III, Co II, Ni, Cu II and Zn immobilization by a modified bauxite refinery residue (red mud) at pH 7.5
    (Elsevier, 2014-01-15) Collins, RN; Clark, MW; Payne, TE
    Although modified bauxite refinery residues (MBRR) immobilize trace metals, the retention mechanisms in this complex multiphase material have not been examined in detail. In this study, X-ray absorption spectroscopy was used to investigate the host minerals, and retention mechanisms, responsible for binding MnII, CrIII, CoII, Ni, Cu and Zn in MBRR. High metal loadings (∼10 mM at pH 3) in aqueous phases simulated highly contaminated mine drainage environments, whereas a final pH of 7.5 represents the typical MBRR pH buffering providing surface loadings of 1.7–2.6 wt%. Under these conditions, CrIII precipitated as a solid phase similar to γ-CrOOH and/or amorphous Cr(OH)3, regardless of host mineral, whereas MnII immobilization was associated with (partial) oxidation in all cases. Cobalt and Ni precipitated primarily as hydrotalcite-like solids when in contact with the MBRR, and sodalite, gibbsite and hydrotalcite tended to dominate this process. Cu uptake by MBRR resulted from the precipitation of Cu(OH)2 although sorption processes may have made an additional contribution, whereas Zn precipitated as a solid phase similar to that of hydrozincite. The nature of the trace metal precipitate formed was often influenced by the host mineral constituent of MBRR, indicating that specific minerals in the MBRR can be primarily responsible for its metal immobilization properties, with gibbsite, hematite and hydrotalcite featuring prominently. © 2013 Elsevier B.V.
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    Stabilization of triam(m)inechloridoplatinum complexes by oxidation to PtIV.
    (CSIRO Publishing, 2011-03-11) Daly, HL; Hall, MD; Failes, TW; Zhang, M; Foran, GJ; Hambley, TW
    PtIV analogues of the active end groups {PtClN3} of multinuclear Pt anticancer drugs have been investigated. The crystal structure of trans,mer-[PtCl(OH)2(dien)]Cl shows that the bond lengths are similar to those in the dihydroxidoplatinum(iv) analogue of cisplatin. The axial ligands are shown to be the predominant influence on reduction potentials with the dihydroxido complex trans,mer-[PtCl(OH)2(NH3)3]Cl being the most resistant to reduction. X-ray absorption near-edge spectroscopy is shown to be suitable for monitoring the oxidation state of these complexes and reveals that trans,mer-[PtCl(OH)2(NH3)3]+ survives for more than 2 h in cancer cells. © 2011, CSIRO Publishing
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    Structural chemistry and magnetic properties of the hexagonal double perovskite Ba2CoOsO6
    (American Chemical Society, 2020-04-14) Kayser, P; Orlandi, F; Avdeev, M; Zhang, Z; Kimpton, JA; Kennedy, BJ
    The double perovskite Ba2CoOsO6, synthesized using solid-state methods at ambient pressure, is shown as a rare example of an oxide adopting the 6L-trigonal (S.G.: P3̅m1) perovskite structure. The structure, refined using a combination of X-ray and neutron diffraction data, showed the Co and Os were ordered over the two dimer sites with additional ordering over the corner-sharing sites. Bond valence calculations show the presence of the Co(II) and Os(VI) valence states, and the latter was confirmed using X-ray absorption spectroscopy. Bulk magnetic susceptibility measurements show Ba2CoOsO6 to undergo antiferromagnetic ordering near 100 K, and neutron diffraction showed an ordered moment on the Co3, Co4, and Os2 sites; whereas the Os1/Co1 remained disordered. © 2020 American Chemical Society
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    Understanding the supramolecular self-assembly of zirconium titanate mesophases formed from the poly(ethylene oxide) surfactant brij-58
    (American Chemical Society, 2010-07-13) Luca, V; Drabarek, E; Griffith, CS; Hanley, TL
    The evaporation-induced self-assembly of mesoporous zirconium titanium oxide thin films prepared from precursor solutions with the composition ZrxTi1−xCl4:40 EtOH:0.005 Brij 58:h H2O (where x = 0.28, h = 10, and Brij 58 = diblock copolymer C16H33PEO20) by dip coating has been studied as a function of the mole fraction of zirconium (x), the relative humidity (RH), and the drying conditions. Extremely well-ordered mesophases and compositional homogeneity on the atomic scale were consistently obtained when the films were prepared at relative humidities above 60%, under which conditions a cubic phase was identified. The influence of humidity was monitored using a combination of in situ small-angle X-ray diffraction (SAXD) and small-angle X-ray scattering (SAXS). These techniques showed the existence of nanocrystalline phases during the initial drying process for films prepared from precursor solutions with x in the range of 0.20−0.60. The nanocrystalline phases were evidenced as multiple X-ray reflections above 8° 2θ. These reflections were ascribed to relatively crystalline nano building units of the mesophase and displayed only a transient stability in humid air, disappearing after 1 h of film conditioning in any humidity. A clear dependence of the primary d-spacing observed in the SAXD on composition for films dried at 65% RH, stabilized at 200°C, and calcined at 350°C provided strong evidence of the ability to form a complete solid solution of Zr and Ti in the oxide mesophase prepared from the precursor solutions. This compositional homogeneity was confirmed by transmission electron microscopy and further corroborated using Ti K-edge X-ray absorption spectroscopy, which probed the local chemical environment of the embedded Ti atoms. The data provided here are in stark contrast to studies of zirconium titanium mixed oxide film systems using similar preparation procedures but triblock copolymer porogens such as F-127. A hypothesis is tendered to explain the dramatic difference in the products obtained using these distinct but related copolymer templates. © 2010, American Chemical Society