Al LDHs Research Articles

Kinetics of uptake of Cu 2+ and Cd 2+ by Mg–Al layered double hydroxides intercalated with citrate, malate, and tartrate

In this study, kinetics of the uptake of Cu 2+ and Cd 2+ by Mg–Al layered double hydroxides (Mg–Al LDHs) intercalated with citrate 3− (C 6H 5O 7 3−), malate 2− (C 4H 4O 5 2−), and tartrate 2− (C 4H 4O 6 2−) in the interlayer were examined. When the Mg–Al LDHs were added to Cu 2+ and Cd 2+ solutions of a constant pH of 5.0, the concentrations of Cu 2+ and Cd 2+ decreased with increasing temperature. The uptake was shown to occur as chelation between the heavy metal ions and the organic acid anions. The uptake rate equation was found to be dependent on the type of chelate formed.

Preparation of Mg–Al layered double hydroxides intercalated with alkyl sulfates and investigation of their capacity to take up N, N-dimethylaniline from aqueous solutions

This study examined the effect of the interlayer spacing of a Mg–Al layered double hydroxide (Mg–Al LDH) on the ability of the Mg–Al LDH to take up a nonionic organic material. Mg–Al LDHs, intercalated with 1-propanesulfonate (PS −), 1-hexanesulfonate (HS −), and 1-dodecanesulfonate (DS −), were prepared by coprecipitation, yielding PS·Mg–Al LDH, HS·Mg–Al LDH, and DS·Mg–Al LDH, respectively. The increase in the alkyl chain lengths of the Mg–Al LDHs (PS − < HS − < DS −) resulted in the perpendicular orientation of the organic acid anions in the interlayer of Mg–Al LDH, which in turn resulted in more organic acid anions being accommodated in the interlayer space. An organic acid anion with a large molecular length was more easily intercalated in the interlayer of Mg–Al LDH than one with a small molecular length. This was attributed to the hydrophobic interaction between the alkyl chains, affecting the intercalation of the organic acid anions. The uptake of N, N-dimethylaniline (DMA) by Mg–Al LDHs increased in the order PS·Mg–Al LDH < HS·Mg–Al LDH < DS·Mg–Al LDH. The uptake was attributed to the hydrophobic interactions between DMA and the intercalated PS −, HS −, and DS −. Thus, Mg–Al LDH, which has a lot of large interlayer spacings when intercalated with organic acid anions, can take up a large number of DMA molecules from an aqueous solution.

Hybrid inorganic/organic composites of Mg–Al layered double hydroxides intercalated with citrate, malate, and tartrate prepared by co-precipitation

Inorganic/organic composite materials composed of Mg–Al layered double hydroxides (Mg–Al LDHs) intercalated with citrate (C 6H 5O 7 3−), malate (C 4H 4O 5 2−), or tartrate (C 4H 4O 6 2−) anions were prepared by a co-precipitation technique and characterized by X-ray diffraction and compositional analyses. The molecular orientation of the organic component in the interlayer space was determined. At low intercalation levels, citrate ion was inclined at an angle of 26° relative to the brucite-like layers of Mg–Al LDH. At higher solution concentrations, both the Mg(C 6H 5O 7) − complex and free C 6H 5O 7 3− were isotropically oriented in the interlayer space. For both malate·Mg–Al LDH and tartrate·Mg–Al LDH, the organic anions were inclined at 26° relative to the Mg–Al LDH layers regardless of anion concentration.

Uptake of heavy metal ions from aqueous solution using Mg–Al layered double hydroxides intercalated with citrate, malate, and tartrate

Mg–Al layered double hydroxide (Mg–Al LDH) was modified with organic acid anions using a coprecipitation technique, and the uptake of heavy metal ions from aqueous solution by the Mg–Al LDH was studied. Citrate·Mg–Al LDH, malate·Mg–Al LDH, or tartrate·Mg–Al LDH, which had citrate 3− (C 6H 5O 7 3−), malate 2− (C 4H 4O 5 2−), or tartrate 2− (C 4H 4O 6 2−) anions intercalated in the interlayer, was prepared by dropwise addition of a mixed aqueous solution of Mg(NO 3) 2 and Al(NO 3) 3 to a citrate, malate, or tartrate solution at a constant pH of 10.5. These Mg–Al LDHs were found to take up Cu 2+ and Cd 2+ rapidly from an aqueous solution at a constant pH of 5.0. This capacity was mainly attributable to the formation of the citrate–metal, malate–metal, and tartrate–metal complexes in the interlayers of the Mg–Al LDHs. The uptake of Cu 2+ increased in the order malate·Mg–Al LDH < tartrate·Mg–Al LDH < citrate·Mg–Al LDH. The uptake of Cd 2+ increased in the order malate·Mg–Al LDH < tartrate·Mg–Al LDH = citrate·Mg–Al LDH. These differences in Cu 2+ and Cd 2+ uptake were attributable to differences in the stabilities of the citrate–metal, malate–metal, and tartrate–metal complexes. These results indicate that citrate 3−, malate 2−, and tartrate 2− were adequately active as chelating agents in the interlayers of Mg–Al LDHs.

Preparation and characterization of Mg–Al layered double hydroxides intercalated with benzenesulfonate and benzenedisulfonate

Mg–Al layered double hydroxides (Mg–Al LDHs) intercalated with benzenesulfonate (BS –) and benzenedisulfonate (BDS 2–) ions were prepared by coprecipitation and characterized by X-ray diffraction, FT-IR spectroscopy, and chemical analyses. The intercalated BS – and BDS 2– maintained their intrinsic molecular structures within the Mg–Al LDH interlayers. At low intercalation levels, the benzene ring of BS – in BS · Mg–Al LDH was inclined at 30° relative to the plane of the brucite-like layers of Mg–Al LDH. With increasing BS – content, the benzene ring adopted an additional configuration perpendicular to the Mg–Al LDH layers. In BDS-intercalated Mg–Al LDH, the benzene ring of BDS 2– was tilted at 26° relative to the plane of the Mg–Al LDH layers. Intercalation levels of BDS 2– were smaller than those of BS – despite the greater charge density of BDS 2–, which was likely attributable to a greater degree of electrostatic repulsion between intercalated anions.

Fabrication and characterization of a novel inorganic MnO 2/LDHs multilayer thin film via a layer-by-layer self-assembly method

Multilayer thin films comprising negatively charged MnO 2 sheets and positively charged Mg–Al LDHs sheets have been prepared by the electrostatic layer-by-layer adsorption technique. The resulting films were characterized by UV–vis spectra, scanning electron microscope (SEM), X-ray photoelectron spectra (XPS), and so on. UV–vis spectra show that the absorbance values at characteristic wavelengths of the multilayer films increase almost linearly with the number of LDHs/MnO 2 bilayers. SEM images indicate that the surface of the multilayer films is rather smooth and dense. XPS spectra confirm the incorporation of MnO 2 and Mg–Al LDHs into the films.

A composite of layered double hydroxides obtained through random costacking of layers from Mg–Al and Co–Al LDHs by delamination–restacking: Thermal decomposition and reconstruction behavior

A composite of dodecylsulfate intercalated Mg–Al and Co–Al LDHs in which the layers of the two LDHs are randomly costacked was prepared starting from the monolayer colloidal dispersions of the individual surfactant intercalated LDHs obtained through delamination in 1-butanol. The surfactant ion of the composite could be exchanged for acetate ions. The thermal decomposition and reconstruction behavior of the acetate-intercalated composite was found to be different from those of an LDH in which each layer contains Mg, Co and Al and a physical mixture of Mg–Al and Co–Al LDHs. While the composite shows partial reconstruction to LDH phase even after heating up to 1000 °C the other samples do not show reconstruction beyond 800 °C.

Uptake of Bisphenol A from Aqueous Solution by Mg&amp;ndash;Al-Layered Double Hydroxides Intercalated with 2-Naphthalene Sulfonate and 2,6-Naphthalene Disulfonate

Mg–Al-layered double hydroxides (Mg–Al LDHs) modified with aromatic anions were suspended in solutions of bisphenol A to investigate their properties as scavengers. The Mg–Al LDHs were intercalated with 2-naphthalene sulfonate (2-NS � ) and 2,6-naphthalene disulfonate (2,6-NDS 2� ) ions, which contain a naphthalene ring with one and two sulfonate (–SO3 � ) groups in their respective structures. The changes in the concentrations of the hazardous aromatic compounds in the suspensions with time were followed. The organic-modified Mg–Al LDHs decreased the bisphenol A concentrations very rapidly, which was attributable to the association between the aromatic ring of bisphenol A and the aromatic anions intercalated in the interlayer. Mg–Al LDH with lower content of aromatic anion in the interlayer was superior to that with the higher content for the uptake of bisphenol A. This was attributed to the larger spaces to accommodate more bisphenol A in the interlayer. [doi:10.2320/matertrans.M-MER2007873]

Intercalation behavior of l-ascorbic acid into layered double hydroxides

The intercalation of l-ascorbic acid (ASA) into three kinds of layered double hydroxides, such as Mg–Al, Mg–Fe and Zn–Al LDHs, has quantitatively been investigated by the calcination-rehydration (reconstruction) and coprecipitation methods. The amount of ASA intercalated was considerably different by the LDH systems that was estimated to be ca. 0.40 mol/mol-M 3+ for the Mg–Al and Mg–Fe systems by the reconstruction method. The Zn–Al system was hardly restored to the LDH structure by the rehydration reaction with the intercalation of ASA. ASA was also intercalated into the Mg–Al and Zn–Al LDHs by the coprecipitation method, while the intercalation of NO 3 − was observed in the Mg–Fe LDH. The basal spacing of the solid products were expanded to d 003 = 0.84 (Mg–Al) and 0.86 (Mg–Fe) nm by the reconstruction method, 0.97 (Mg–Al) and 1.06 (Zn–Al) nm by the coprecipitation method, respectively, suggesting that ASA was intercalated into the LDHs. A large fraction of ASA was intercalated as reduced form after the light and heat resistance tests of the ASA/LDHs. This result confirmed that ASA was stabilized by the intercalation of the LDHs interlayer space. Furthermore, the intercalated ASA was easily deintercalated from the LDH interlayer space by the ion exchange method using CO 3 2−. It is expected that LDHs will be good host materials for safe storage of vitamins.

Synthesis and characterization of new Mg(2)Al-paratungstate layered double hydroxides.

Layered double hydroxides (LDHs, or hydrotalcites) with Mg(2+) and Al(3+) cations in the mixed metal hydroxide layer and paratungstate anions in the interlayer have been prepared. Different methods have been followed: anion exchange with Mg,Al LDHs originally containing nitrate or adipate, reconstruction of the LDH structure from a mildly calcined Mg(2)Al-CO(3) LDH, and coprecipitation. In all cases, the tungsten precursor salt was (NH(4))(10)H(2)W(12)O(42). The prepared solids have been characterized by elemental chemical analysis, powder X-ray diffraction (PXRD), FT-IR spectroscopy, thermogravimetric (TG) and differential thermal (DTA) analyses, scanning electron microscopy (SEM) with EDX (energy-dispersive X-ray analysis), and nitrogen adsorption at -196 degrees C for surface area and surface texture. Most of the synthesis methods used, especially anion exchange starting from a Mg(2)Al-NO(3) precursor at low temperature and short reaction times, lead to formation of a hydrotalcite with a gallery height of 9.8 A; increasing the reaction temperature to 70-100 degrees C and maintaining short contact times leads to a solid with a gallery height of 7.8 A. Both phases have been identified as a result of the intercalation of W(7)O(24)(6)(-) species in different orientations in the interlayer space. If the time of synthesis or the temperature is increased, a more stable phase, with a gallery height of 5.2 A corresponding to a solid with intercalated W(7)O(24)(6)(-), is formed, probably with grafting of the interlayer anion on the brucite-like layers. All systems are microporous. Calcination at 300 degrees C leads to amorphous species, and crystallized MgWO(4) is observed at 700 degrees C.

Al-stabilized α-nickel hydroxide prepared by electrochemical impregnation

The structure and electrochemical performance of Ni–Al-layered double hydroxides (LDHs) prepared by electrochemical impregnation (ECI) were studied. The ECI Ni–Al LDHs, having the same structure as that of α-3Ni(OH) 2·2H 2O, have a tapping density of about 1.55–1.8 g cm −3. This compound has larger discharge capacity and better cycle stability than β-Ni(OH) 2. It also shows good electrochemical behavior at large discharge rate and low temperature such as 0 °C.

Direct Intercalation of Amino Acids into Layered Double Hydroxides by Coprecipitation

First, the direct intercalation of amino acids into various layered double hydroxides (Mg–Al, Mn–Al, Ni–Al, Zn–Al, and Zn–Cr LDHs) by coprecipitation has been investigated using phenylalanine (Phe) as a guest amino acid. The degree of Phe coprecipitation was strongly influenced by the solution pH and kind of LDH system and reached a maximum in the pH 8–10 region. The solid products were found to have an expanded LDH structure, which supported the belief that Phe was intercalated into LDHs as an amphoteric ion or anion. Two kinds of configuration for Phe in the gallery, either vertical (Mn–Al, Zn–Al, and Zn–Cr LDHs) or horizontal (Mg–Al LDH) in orientation were observed. Only in the Ni–Al system was the solid product a mixture of Phe/Ni–Al LDH and Phe/Ni(OH)2 composite. Next, the thermal decomposition of the intercalated Phe was revealed to be accelerated by the catalytic action of metal ions in the host basal layer. The formation of Phe/Mg–Al, Mn–Al, and Zn–Al LDHs was also elucidated as being appreciably different by the kind of LDH system. Moreover, for various amino acids, the degree of coprecipitation was found to be strongly influenced by amino acid sidechains, i.e., length, structure, and physicochemical properties.

Spectroscopic Evidence for the Formation of Layered Ni−Al Double Hydroxides in Cement

X-ray absorption fine structure (XAFS) spectroscopy and diffuse reflectance spectroscopy (DRS) were applied to assess the solubility-limiting phase of Ni in cement systems. The study provides first direct spectroscopic evidence for the formation of Ni- and Al-containing hydrotalcite-like layered double hydroxides (Ni−Al LDHs) when cement material (a complex mixture of mainly CaO, SiO2, Al2O3, Fe2O3, MgO, and SO3) was treated with Ni in artificial cement pore water under highly alkaline conditions (pH = 13.3). The study shows that Ni−Al LDHs were formed in cement suspensions oversaturated with respect to β-Ni(OH)2 and aged at room temperature for 150 days. This finding indicates that Ni−Al LDHs and not Ni-hydroxides may determine the solubility of Ni in cement materials.

Syntheses and Thermal and Chemical Behaviors of Tartrate and Succinate Intercalated Zn(3)Al and Zn(2)Cr Layered Double Hydroxides.

Tartrate and succinate anions have been intercalated in Zn(3)Al and Zn(2)Cr LDHs. The preparations using either coprecipitation, anion exchange, or reconstruction methods are described. In the case of tartrate-containing LDH, coprecipitation and reconstruction methods have proved to be very limited to lead to pure materials due to the particular reactivity of tartrate anions. Intercalation of both anions under room-temperature conditions gives rise to expanded LDH with similar basal spacing. Moderate thermal treatments lead in all cases to a reorientation of the anions in the interlayer domains associated with an interlayer contraction occurring around 80 degrees C. The structural characterization, the thermal evolution, and the chemical stability of all the phases are studied by PXRD, FTIR, TGA, and DTA.