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Anions

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Ray L Frost – One of the best experts on this subject based on the ideXlab platform.

  • a review of the removal of Anions and oxyAnions of the halogen elements from aqueous solution by layered double hydroxides
    Journal of Colloid and Interface Science, 2014
    Co-Authors: Frederick L Theiss, Godwin A Ayoko, Sara J Couperthwaite, Ray L Frost

    Abstract:

    The application of layered double hydroxides (LDHs) and thermally activated LDHs for the removal of various fluorine (F(-),BF4(-)), chlorine (Cl(-),ClO4(-)), bromine (Br(-),BrO3(-)) and iodine (I(-),IO3(-)) species from aqueous solutions has been reviewed in this article. LDHs and thermally activated LDHs were able to significantly reduce the concentration of selected Anions in laboratory scale experiments. The M(2+):M(3+) cation ratio of the LDH adsorbent was an important factor which influenced anion uptake. Though LDHs were able to remove some target anion species through anion exchange and surface adsorption thermal activation and reformation generally produced better results. The presence of competing Anions including carbonate, phosphate and sulphate had a significant impact on uptake of the target anion as LDHs typically exhibit lower affinity towards monovalent Anions compared to Anions with multiple charges. The removal of fluoride and perchlorate from aqueous solution by a continuous flow system utilising fixed bed columns packed with LDH adsorbents has also been investigated. The adsorption capacity of the columns at breakpoint was heavily dependent on the flow rate and lower than result reported for the corresponding batch methods. There is still considerable scope for future research on numerous topics summarised in this article.

  • Synthesis and Raman spectroscopic characterisation of hydrotalcite with CO3 2− and (MoO4)2− Anions in the interlayer: Synthesis and Raman spectroscopic characterisation of hydrotalcite
    Journal of Raman Spectroscopy, 2007
    Co-Authors: Sara J. Palmer, Ray L Frost, Godwin A Ayoko, Tai Nguyen

    Abstract:

    Raman spectroscopy has been used to characterise synthetic mixed carbonate and molybdate hydrotalcites of formula Mg6Al2(OH)16((CO3)2-,(MoO4)2-).4H2O. The spectra have been used to assess the molecular assembly of the cations and Anions in the hydrotalcite structure. The spectra may be conveniently subdivided into spectral features based upon the carbonate anion, the molybdate anion, the hydroxyl units and water units. Bands are assigned to the hydroxyl stretching vibrations of water. Three types of carbonate Anions are identified: (a) carbonate hydrogen-bonded to water in the interlayer, (b) carbonate hydrogen-bonded to the hydrotalcite hydroxyl surface, (c) free carbonate Anions. It is proposed that the water is highly structured in the hydrotalcite as it is hydrogen bonded to both the carbonate and the hydroxyl surface. The spectra have been used to assess the contamination of carbonate in an open reaction vessel in the synthesis of a molybdate hydrotalcite of formula Mg6Al2(OH)16((CO3)2-,(MoO4)2-).4H2O. Bands are assigned to carbonate and molybdate Anions in the Raman spectra. Importantly the synthesis of hydrotalcites from solutions containing molybdate provides a mechanism for the removal of this oxy-anion

  • Nitrate absorption through hydrotalcite reformation
    Journal of Colloid and Interface Science, 2006
    Co-Authors: Ray L Frost, Anthony W. Musumeci

    Abstract:

    Thermally activated hydrotalcite based upon a Zn/Al hydrotalcite with carbonate in the interlayer has been used to remove nitrate Anions from an aqueous solution resulting in the reformation of a hydrotalcite with a mixture of nitrate and carbonate in the interlayer. X-ray diffraction of the reformed hydrotalcites with a d(003) spacing of 7.60 A shows that the nitrate anion is removed within a 30 min period. Raman spectroscopy shows that two types of nitrate Anions exist in the reformed hydrotalcite (a) nitrate bonded to the ‘brucite-like’ hydrotalcite surface and (b) aquated nitrate anion in the interlayer. Kinetically the nitrate is replaced by the carbonate anion over a 21 h period. Two types of carbonate Anions are observed. This research shows that the reformation of a thermally activated hydrotalcite can be used to remove Anions such as nitrate from aqueous systems.

Toshikatsu Sata – One of the best experts on this subject based on the ideXlab platform.

  • Studies on anion exchange membranes having permselectivity for specific Anions in electrodialysis — effect of hydrophilicity of anion exchange membranes on permselectivity of Anions
    Journal of Membrane Science, 2000
    Co-Authors: Toshikatsu Sata

    Abstract:

    Abstract Recent studies on anion exchange membranes and electrodialysis methods to permeate specific Anions through the membranes are reviewed. The studies are classified: (1) to increase cross-linkage of the anion exchange membranes, (2) to form tight surface layers on the anion exchange membranes, (3) to decrease hydrophilicity of the anion exchange membranes or their surfaces by introducing specific anion exchange groups in the membranes, (4) to impregnate hydrophilic compounds in the anion exchange membranes to increase hydrophilicity of the membranes, (5) to control permselectivity of Anions by photoirradiation using membranes with a photoresponsive group and (6) to control permselectivity of Anions through thermally responsive anion exchange membranes with temperature. Permselectivity of specific Anions through the anion exchange membranes is governed mainly by the balance of hydration energy of Anions with hydrophilicity of the membranes, partially by hydrated ionic size of the Anions, except the membranes having an oppositely charged layer on the membrane surface.

  • studies on anion exchange membranes having permselectivity for specific Anions in electrodialysis effect of hydrophilicity of anion exchange membranes on permselectivity of Anions
    Journal of Membrane Science, 2000
    Co-Authors: Toshikatsu Sata

    Abstract:

    Abstract Recent studies on anion exchange membranes and electrodialysis methods to permeate specific Anions through the membranes are reviewed. The studies are classified: (1) to increase cross-linkage of the anion exchange membranes, (2) to form tight surface layers on the anion exchange membranes, (3) to decrease hydrophilicity of the anion exchange membranes or their surfaces by introducing specific anion exchange groups in the membranes, (4) to impregnate hydrophilic compounds in the anion exchange membranes to increase hydrophilicity of the membranes, (5) to control permselectivity of Anions by photoirradiation using membranes with a photoresponsive group and (6) to control permselectivity of Anions through thermally responsive anion exchange membranes with temperature. Permselectivity of specific Anions through the anion exchange membranes is governed mainly by the balance of hydration energy of Anions with hydrophilicity of the membranes, partially by hydrated ionic size of the Anions, except the membranes having an oppositely charged layer on the membrane surface.

  • change in transport properties of anion exchange membranes in the presence of ethylene glycols in electrodialysis
    Journal of Colloid and Interface Science, 1998
    Co-Authors: Toshikatsu Sata, Kouichi Mine, Koji Matsusaki

    Abstract:

    To change permselectivity between two Anions through anion-exchange membranes in electrodialysis, the hydrophilicity of the anion-exchange membranes was increased by impregnation of hydrophilic compounds, ethylene glycols with varying molecular weights, into the membranes. Ethylene glycols have good affinity to the anion-exchange membranes and were selectively impregnated into a domain where anion-exchange groups exist. The change in the transport numbers of bromide, fluoride, sulfate, and nitrate ions relative to chloride ions was evaluated in the presence of the glycols (because the glycols dissolved from the membrane matrix to the salt solutions, electrodialysis was carried out using the salt solutions containing the glycols). Permeation of the strongly hydrated Anions, fluoride and sulfate ions, was increased compared with chloride ions, and permeation of the less hydrated Anions, bromide and nitrate ions, became difficult to achieve through the membranes in the presence of ethylene glycols. This was due to the increase in the uptake of more hydrated Anions into the membrane and not due to the change in mobility ratio between Anions through the membrane. Increasing the hydrophilicity of the anion-exchange membranes was an effective method for changing the permeation behavior of Anions through membranes in electrodialysis.

Godwin A Ayoko – One of the best experts on this subject based on the ideXlab platform.

  • a review of the removal of Anions and oxyAnions of the halogen elements from aqueous solution by layered double hydroxides
    Journal of Colloid and Interface Science, 2014
    Co-Authors: Frederick L Theiss, Godwin A Ayoko, Sara J Couperthwaite, Ray L Frost

    Abstract:

    The application of layered double hydroxides (LDHs) and thermally activated LDHs for the removal of various fluorine (F(-),BF4(-)), chlorine (Cl(-),ClO4(-)), bromine (Br(-),BrO3(-)) and iodine (I(-),IO3(-)) species from aqueous solutions has been reviewed in this article. LDHs and thermally activated LDHs were able to significantly reduce the concentration of selected Anions in laboratory scale experiments. The M(2+):M(3+) cation ratio of the LDH adsorbent was an important factor which influenced anion uptake. Though LDHs were able to remove some target anion species through anion exchange and surface adsorption thermal activation and reformation generally produced better results. The presence of competing Anions including carbonate, phosphate and sulphate had a significant impact on uptake of the target anion as LDHs typically exhibit lower affinity towards monovalent Anions compared to Anions with multiple charges. The removal of fluoride and perchlorate from aqueous solution by a continuous flow system utilising fixed bed columns packed with LDH adsorbents has also been investigated. The adsorption capacity of the columns at breakpoint was heavily dependent on the flow rate and lower than result reported for the corresponding batch methods. There is still considerable scope for future research on numerous topics summarised in this article.

  • Synthesis and Raman spectroscopic characterisation of hydrotalcite with CO3 2− and (MoO4)2− Anions in the interlayer: Synthesis and Raman spectroscopic characterisation of hydrotalcite
    Journal of Raman Spectroscopy, 2007
    Co-Authors: Sara J. Palmer, Ray L Frost, Godwin A Ayoko, Tai Nguyen

    Abstract:

    Raman spectroscopy has been used to characterise synthetic mixed carbonate and molybdate hydrotalcites of formula Mg6Al2(OH)16((CO3)2-,(MoO4)2-).4H2O. The spectra have been used to assess the molecular assembly of the cations and Anions in the hydrotalcite structure. The spectra may be conveniently subdivided into spectral features based upon the carbonate anion, the molybdate anion, the hydroxyl units and water units. Bands are assigned to the hydroxyl stretching vibrations of water. Three types of carbonate Anions are identified: (a) carbonate hydrogen-bonded to water in the interlayer, (b) carbonate hydrogen-bonded to the hydrotalcite hydroxyl surface, (c) free carbonate Anions. It is proposed that the water is highly structured in the hydrotalcite as it is hydrogen bonded to both the carbonate and the hydroxyl surface. The spectra have been used to assess the contamination of carbonate in an open reaction vessel in the synthesis of a molybdate hydrotalcite of formula Mg6Al2(OH)16((CO3)2-,(MoO4)2-).4H2O. Bands are assigned to carbonate and molybdate Anions in the Raman spectra. Importantly the synthesis of hydrotalcites from solutions containing molybdate provides a mechanism for the removal of this oxy-anion