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, Godwin A Ayoko, Ray L Frost, 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.

  • Separation of Anions by Use of the Surface Modified Anion Exchange Resin.
    Analytical Sciences, 1997
    Co-Authors: Koji Matsusaki, Noriaki Hasimoto, Toshikatsu Sata
    Abstract:

    The surface of gel-type anion exchange resin was modified by the adsorption of an anionic polyelectrorite: polycondensation product of sodium naphthalene sulfonate and formaldehyde (trade name, Demol N). After the adsorption of the polymer, ion exchange capacity decreased and the rate of ion exchange reaction became slow though ion exchange equilibrium constants between two Anions did not changed. Especially, the ion exchange rate of divalent Anions was slower than that of the monovalent Anions. Because an anionic polyelectrorite layer was formed on the resin particle, the ion exchange of Anions with anion exchange site was retarded by sieving effect with the layer and the divalent Anions were difficult to ion exchange compared with the monovalent anion due to existence of the opposite charged layer to ion exchange groups. Using the modified anion exchange resin in the hydroxide ion form, separation of nitrate ion from sulfate ion was attempted. The modified resin was immersed in the mixture solution of nitrate and sulfate ions, and the solution was shaken for definite time. The nitrate ion was preferentially adsorbed on the resin. The resin was separated and introduced in the potassium perchlorate solution. After shaking for 90 minutes, the nitrate ion in the solution was determined by use of ion-chromatography. The separation and enrichment of nitrate ion from 50-fold amount of sulfate ions was accomplished.

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, Godwin A Ayoko, Ray L Frost, 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

Pablo Ballester - One of the best experts on this subject based on the ideXlab platform.

  • different nature of the interactions between Anions and hat cn 6 from reversible anion π complexes to irreversible electron transfer processes hat cn 6 1 4 5 8 9 12 hexaazatriphenylene
    Journal of the American Chemical Society, 2013
    Co-Authors: Gemma Aragay, Antonio Frontera, Vega Lloveras, Jose Vidalgancedo, Pablo Ballester
    Abstract:

    We report experimental evidence indicating that the nature of the interaction established between HAT(CN)6, a well-known strong electron acceptor aromatic compound, with mono- or polyatomic Anions switches from the almost exclusive formation of reversible anion−π complexes, featuring a markedly charge transfer (CT) or formal electron-transfer (ET) character, to the quantitative and irreversible net production of the anion radical [HAT(CN)6]•– and the dianion [HAT(CN)6]2– species. The preferred mode of interaction is dictated by the electron donor abilities of the interacting anion. Thus, weaker Lewis basic Anions such as Br– or I– are prone to form mainly anion−π complexes. On the contrary, stronger Lewis basic F– or –OH Anions display a net ET process. The ET process can be either thermal or photoinduced depending on the HOMO/LUMO energy difference between the electron donor (anion) and the electron acceptor (HAT(CN)6). These ET processes possibly involve the intermediacy of anion−π complexes having stro...

  • Recognition of Anions - Recognition of Anions
    Structure and Bonding, 2008
    Co-Authors: Ramón Vilar, Pablo Ballester
    Abstract:

    G.W. Bates, P.A. Gale: An Introduction to Anion Receptors Based on Organic Frameworks.- S.R. Bayly, P.D. Beer: Metal Based Anion Receptor Systems.- S.-I. Tamaru, I. Hamachi: Recent Progress of Phosphate Derivatives Recognition Utilizing Artificial Small Molecular Receptors in Aqueous Media.- P. Ballester: Anions and Pi-Aromatic Systems. Do they Interact Attractively?.- R. Vilar: Anion Templates in Synthesis and Dynamic Combinatorial Libraries.- S.L. Ewen, J.H. G. Steinke: Molecularly Imprinted Polymers Using Anions as Templates

Philip A. Gale - One of the best experts on this subject based on the ideXlab platform.

  • anion transport and supramolecular medicinal chemistry
    Chemical Society Reviews, 2017
    Co-Authors: Philip A. Gale, Jeffery T Davis, Roberto Quesada
    Abstract:

    New approaches to the transmembrane transport of Anions are discussed in this review. Advances in the design of small molecule anion carriers are reviewed in addition to advances in the design of synthetic anion channels. The application of anion transporters to the potential future treatment of disease is discussed in the context of recent findings on the selectivity of anion transporters.

  • Anions in Supramolecular Chemistry
    Fundamentals and Applications of Anion Separations, 2004
    Co-Authors: Philip A. Gale
    Abstract:

    Recent developments in the area of anion recognition and sensing have produced a variety of new selective receptors for Anions.1 However, the great variety of anionic species and their importance in the environment (pollutant Anions from over use of agricultural fertilizers cause eutrophication of lakes and inland waterways2), biological systems (mis-regulation of anion transport is responsible for a number of medical conditions including cystic fibrosis3) and in medicine (the maintenance of sulfate anion concentration in dialysis patients continues to be problematic4) presents a continuing challenge to the suprarnolecular chemist to design selective receptors for specific guest species. This chapter will discuss the efforts of our group and our collaborators in the areas of recognition and sensing of anionic species and of the roles of Anions in assembly processes in solut ion and in the solid state. As such, this review does not provide a comprehensive overview of this area of supramolecular chemistry.1

  • Anion coordination and anion-directed assembly: highlights from 1997 and 1998
    Coordination Chemistry Reviews, 2000
    Co-Authors: Philip A. Gale
    Abstract:

    Abstract This review article highlights advances made in anion coordination chemistry in 1997 and 1998. The first section of the review examines anion receptors that do not contain metal ions. This is followed by a review of metal containing anion receptors in which the metal can function as (i) a coordination site for the anion; (ii) a non-coordinating reporter group that signals the presence of the anion by a perturbation of its physical properties; (iii) an element of a receptor designed to withdraw electron density from a π-electron system and so increase the affinity of a hydrophobic receptor for Anions or (iv) part of a self-assembled array that is binding an anionic guest. The role of Anions in directing the self-assembly of complex molecular architectures will also be examined.