Browsing by Author "Yee, LH"

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    Effects of pH, competing ions and aging on arsenic(V) sorption and isotopic exchange in contaminated soils
    (Elsevier, 2019-06) Rahman, MS; Clark, MW; Yee, LH; Comarmond, MJ; Payne, TE; Burton, ED
    Cattle tick control in Australia using arsenicals from early 1900s to 1955 has led to the existence of some 1600 contaminated sites in northern New South Wales alone. Sorption processes play key roles in controlling arsenic (As) accessibility and subsequent mobility in these dip soils. As(V) sorption and accessibility in three As-contaminated soils and two uncontaminated soil types (ferralitic and sandy soils) are investigated utilizing batch sorption experiments and isotopic exchange techniques. The aged contaminated soils displayed little or no ability to sorb additional As(V), and increasing the soil pH caused a substantial reduction in As(V)-sorption and resulting in As(V)-release. Isotope exchange experiments further supported that any further exposure of the aged-contaminated-soils to additional As(V) increased As-mobilization potential. Amendments of phosphate greatly decreased As(V) sorption in aged-contaminated-soils where As-sorption sites were more highly saturated, whereas phosphate had little effect on As(V) sorption in pristine soils. Similarly, sulfate reduced As(V) sorption, but these effects were less marked than those for phosphate, hence, the application of both PO43− and SO42− in As(V)-contaminated-soils may lead to potential As(V)- mobilization. Conversely, Ca2+ increases As(V)-sorption, which is consistent with expected changes in the surface charge characteristics from Ca2+ sorption, and/or Ca-AsO4 precipitations, consequently Ca2+ amendments may improve As-retention, thereby decreasing As accessibility from cattle dip soils. Therefore, the detailed knowledge presented here provides new insights that may be useful for the assessment and management of the As-contaminated soils. © 2019 Elsevier Ltd.
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    Photochromic spirooxazines functionalized with oligomers: investigation of core-oligomer interactions and photomerocyanine isomer interconversion using NMR spectroscopy and DFT.
    (American Chemical Society, 2010-05-07) Yee, LH; Hanley, TL; Evans, RA; Davis, TP; Ball, GE
    Photochromic spirooxazines functionalized with poly(ethylene glycol) (PEG) and poly(dimethylsiloxane) (PDMS) oligomers were monitored using NMR spectroscopy at temperatures between 193 and 233 K before and after in situ exposure to UV irradiation. NOESY and ROESY experiments reveal the TTC (trans−s-trans−cis) isomer to be the dominant merocyanine isomer formed on photolysis, with some CTC (cis−s-trans−cis) isomer also present. Significant ROE cross peaks were observed between the “bulk” of the oligomeric units and protons across the entire photochromic core of the molecule, the intensity of these cross peaks suggesting that the interaction of the oligomer side chain and core of the molecule is significantly enhanced by the permanent attachment, especially with the PDMS side chain. The 2D NMR spectra indicate that there is exchange between the TTC and CTC isomers even at 193 K. This isomerization of the parent spirooxazine compounds, lacking the oligomeric side chains, was found to be acid-catalyzed, and DFT calculations support the strong possibility that it is the protonated merocyanine form that undergoes the facile isomerization process. Interconversion of the different merocyanine isomers is suggested to be fast on the NMR time scale under many experimental conditions, precluding the observation of different isomers using NMR spectroscopy at room temperature. © 2010, American Chemical Society