Anion-exchange properties of hydrotalcite-like compounds
TL;DR: Ion exchange isotherms between hydrotalcite-like (HT) ions were determined and the spacing and width of the 003 reflection were measured as a function of HT composition as mentioned in this paper.
Abstract: Ion-exchange isotherms between hydrotalcite-like (HT) of the NO3-, CI-, and SO4- forms and F , 0% Br , I , OH-, SO42-, CO3 z-, and Naphthol Yellow S (NYS 2-) ions were determined, and the spacing and the width of the 003 reflection were measured as a function of HT composition The ion-exchange equilibrium constant for HTs of monovalent anions are in the sequence OH- > F > Cl > Br- > NO3- > I , those for divalent anions are in the sequence CO3 ~- > NYS z- > SO42- The ion-exchange equilibrium constants tend to increase as the diameters of the anions decrease, and the crystallite size in the 001 direction tends to increase with anions having higher selectivity The OH-form of HT has the smallest basal spacing and the largest crystallite size in the 001 direction
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TL;DR: This paper describes a systematic study on the synthesis, anion exchange, and delamination of Co-Al layered double hydroxide (LDH), with the aim of achieving fabrication and clarifying the properties of LDH nanosheet/polyanion composite films.
Abstract: This paper describes a systematic study on the synthesis, anion exchange, and delamination of Co-Al layered double hydroxide (LDH), with the aim of achieving fabrication and clarifying the properties of LDH nanosheet/polyanion composite films. Co-Al-CO3 LDH hexagonal platelets of 4 mum in lateral size were synthesized by the urea method under optimized reaction conditions. The as-prepared CO3(2-)-LDH was converted to Cl- -LDH by treating with a NaCl-HCl mixed solution, retaining its high crystallinity and hexagonal platelike morphology. LDHs intercalated with a variety of anions (such as NO3-, ClO4-, acetate, lactate, dodecyl sulfate, and oleate) were further prepared from Cl- -LDH via an anion-exchange process employing corresponding salts. Exchanged products in various anion forms were found to show different delamination behaviors in formamide. Among them, best results were observed for NO3- -LDH in terms of the exfoliating degree and the quality of the exfoliated nanosheets. The delamination gave a pink transparent suspension containing well-defined nanosheets with lateral sizes of up to 2 microm. The resulting nanosheets were assembled layer-by-layer with an anionic polymer, poly(sodium styrene 4-sulfonate) (PSS), onto quartz glass substrates to produce composite films. Magnetic circular dichroism (MCD) measurements revealed that the assembled multilayer films exhibited an interesting magneto-optical response.
1,128 citations
TL;DR: Layered double hydroxides (LDHs) have been investigated for many years as host materials for a range of anion exchange intercalation reactions as mentioned in this paper and have been used extensively as ion-exchange materials, catalysts, sorbents and halogen absorbers.
Abstract: Layered double hydroxides (LDHs) have been investigated for many years as host materials for a range of anion exchange intercalation reactions. In this role they have been used extensively as ion-exchange materials, catalysts, sorbents and halogen absorbers. More recently, there have been a tremendous number of new developments using these materials to store and deliver biologically active materials in vivo. Significant advances have been made recently on the characterisation of these materials, including structural studies and on the mechanism of intercalation using in situ techniques.
1,030 citations
TL;DR: In this paper, the structure, main properties and preparation methods of cationic and anionic clays are reviewed in light of the versatility and potential of these materials, which may be useful tools in the move towards establishing environmentally friendly technologies.
791 citations
TL;DR: A number of approaches to the synthesis of a class of anionic clay minerals (M a 2+ M b 3+ (OH) 2 a +2 b (X − ) 2 b · x H 2 O; M 2+ = Mg, Ni, Co, Zn, Cu, etc., M 3+ = Al, Cr, Fe, Sc; m 2+ /M 3+ ∼ 1−5; X − = water and base stable anion; x = 0−6) have been sumarized.
772 citations
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TL;DR: The basic salts of this system were prepared and their structures and physico-chemical properties were studies by electron microscopy, chemical analysis, X-ray powder diffraction, thermal analysis, and acidity-basicity measurements as mentioned in this paper.
Abstract: The basic salts of this system were prepared and their structures and physico-chemical properties were studies by electron microscopy, chemical analysis, X-ray powder diffraction, thermal analysis, i.r. absorption spectra, BET absorption, and acidity-basicity measurements. The salts were found to be new compounds analogous to hydrotalcite. They can be expressed by the formula; [M
2+
M
3+
(OH)2(x+y))]y+ [A
1
−
, Az2- · mH2O]-(z1 + 2z2) where M2+ and M3+ denote di- and trivalent cations, A− and A2− denote mono- and divalent anions, respectively, and y = z1 + 2z2; z1 ≫ z2. The structures consist of positively charged Cd(OH)2-like basic layers and intermediate layers formed from anions and water molecules with the solid solution of divalent cation (M2+) and trivalent cation (M3+) being formed in the range of 0.6 > x/(x + y) > 0.9. The anions of Cl−, NO
3
−
and ClO
4
−
are easily substituted by CO
3
2−
. A large part of the NO
3
−
makes a monodentate-type bond and the ClO
4
−
a bridge-type bond.
933 citations
"Anion-exchange properties of hydrot..." refers background or methods or result in this paper
...These compounds are similar to the mineral hydrotalcite, MgnAIz(OH)16CO3"4H20 (Miyata and Kumura, 1973; Taylor, 1973; Miyata, 1975)....
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...EXPERIMENTAL Hydrotalcite-like compounds corresponding to the above mentioned formula in which x is about 0.3 and A"-is NO3 , CI-, or SO42-were prepared by the meth- Copyright 9 1983, The Clay Minerals Society od described by Miyata (1975) and Miyata et al. (1977)....
[...]
...These results also agree with the conclusion of Miyata (1975) in that the basal spacing is substantially determined by the sum of the thickness of the basic layer (which decreases with an increase in x but at a smaller rate than that of the interlayer ) and the size of the anion in the interlayer....
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TL;DR: Ahstraet et al. as discussed by the authors used coprecipitation followed by hydrothermal treatment between 150 ~ and 250~C. Based on the structural formula [Mgl_xAlx(OH)~lX+l(COz)x/2 �9 mH20] x-, pure solid solutions were formed in the range Al/(Al + Mg) = 0.2 to 0.33, where m = (1 - 3x/ 2).
Abstract: Ahstraet--Hydrotalcite solid solutions were prepared by coprecipitation followed by hydrothermal treatment between 150 ~ and 250~C. Based on the structural formula [Mgl_xAlx(OH)~lX+l(COz)x/2 �9 mH20] x-, pure solid solutions were formed in the range Al/(Al + Mg) = 0.2 to 0.33, where m = (1 - 3x/2). Maximum crystallite size was achieved by hydrothermal treatment between 180 ~ and 200~ with x = 0.337 to 0.429. Crystal strain was also minimized at these values of x. The adsorption c~pacity for Naphthol Yellow S increased as x increased and reached a maximum (1.56 x 10 6 moles/m 2) when x = 0.287, a value eight times larger than that of Mg(OH)~. A weak endothermic DTA peak at about 350~ is probably due to the loss of structural water in the main layer of the structure. On calcination between 400 ~ and 700~ only periclase was detected, probably containing A1 in solid solution. Hydration of the calcined product resulted in the reconstruction of the original hydrotalcite structure.
812 citations
"Anion-exchange properties of hydrot..." refers background or methods in this paper
...HT is stable to 400~ but transforms into a MgO-AI203 solid solution (Mg,-3x/zAlxO) by heating to 500~176 This solid solution rehydrates and combines anions to form HT in the presence of water and anion (Miyata and Okada, 1977; Miyata, 1980)....
[...]
...Prior to measuring ion-exchange isotherms the stability of HT-NO3 in NaF and NaOH solutions was determined by examining the molar ratio of Mg to AI in the HT-NO3 using the lattice parameter a (Miyata, 1980) before and after contact with the solution....
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TL;DR: In particular, the effects of the solvent, which is considered as an independently variable component, are taken explicitly into account in this paper, where expressions for thermodynamic equilibrium constants are set up for the ion exchange equilibria of models defined in terms of operational variables.
Abstract: Expressions for thermodynamic equilibrium constants are set up for the ion‐exchange equilibria of models defined in terms of operational variables. Formulas summarizing the methods for the computation of the requisite activity coefficients are given. In particular, the effects of the solvent, which is considered as an independently variable component, are taken explicitly into account.
791 citations
"Anion-exchange properties of hydrot..." refers methods in this paper
...The equilibrium constant (Ke) was calculated by using the method of Gaines and Thomas (1953) from the following equation ft HT)A=I log Ke = log K~o 3 d(HT)A, (HT)A=0 in which (HT)A is the mole fraction of anion A on the HT....
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487 citations
"Anion-exchange properties of hydrot..." refers background in this paper
...HT consists of positively charged brucite-like layers [Mg, xAI~(OH)2] ~+ alternating with disordered, negatively charged interlayers [A@BULLET mHzO] • 9 Mg and AI are randomly distributed among the octahedral positions, and the OH layer sequence is -BC-CA-AB-BC-(Allmann, 1968)....
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TL;DR: In this paper, three groups of minerals are discussed, which are typified by pyroaurite and sjogrenitc, hydrocalumite, and ettringite.
Abstract: Three groups of minerals are discussed, which are typified by pyroaurite and sjogrenitc, hydrocalumite, and ettringite. All show interesting structural features. In the pyroaurite-sjogrenite group, brucite-likc layers carrying a net positive charge alternate with layers in which the oxygen atoms of carbonate groups and water molecules are statistically distributed on a single set of sites; other anions may replace the carbonate, especially in synthetic phases. Hydrocalumite and related synthetic phases also have layer structures in which positively charged main layers alternate with intermediate layers containing anions and water molecules; the anions occur in cavities and their nature can again vary widely. In the ettringite group, the structures are based on positively charged columns, between which occur channels containing anions and sometimes also water molecules. This group includes thaumasite, the only natural mineral known to contain silicon six-coordinated by oxygen that is not a high-pressure phase. The thermal dehydration behaviour in each group is briefly considered.
470 citations
"Anion-exchange properties of hydrot..." refers background in this paper
...These compounds are similar to the mineral hydrotalcite, MgnAIz(OH)16CO3"4H20 (Miyata and Kumura, 1973; Taylor, 1973; Miyata, 1975)....
[...]