Influence of Varying Synthetic Routes on the Physicochemical Properties of Mg-Al-CO3 and Zn-Al-CO3 Hydrotalcite-Like Compounds: A Comparative Study (original) (raw)
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Russian Journal of General Chemistry, 2017
A series of multi-component layered double hydroxides with hydrotalcite structure containing doubly charged magnesium and cobalt cations and triply charged aluminum and iron cations in the brucite-like layers have been synthesized by co-precipitation at variable pH. Formation of the hydrotalcite structure has been confirmed by X-ray diffraction analysis. Thermal behavior of the synthesized samples has been studied by IR spectroscopy, thermogravimetry, and differential thermal analysis.
Orbital: The Electronic Journal of Chemistry, 2018
The synthesis of layered double hydroxides has been investigated aiming innumerous applications, mainly as adsorbent, catalyst and catalyst support materials, due their ability to adsorb anionic species and several aqueous soluble compounds. The carbonated magnesium-aluminium hydrotalcites are known as the main class of the layered double hydroxides and new composition are often characterized under the view point of thermal stability, crystallinity and catalytic performance for many reactions. Few trivalent cations are able to replace the aluminum one due the severe restriction for oxidation state and ionic radii, but the iron (III) one seems to be high potential to improve some of the characteristics required for that materials, such as specificity for built-rebuilt bonds in organic molecules. In this work, we have synthesized carbonated magnesium-aluminum hydrotalcite samples through the coprecipitation at pH 11 and investigate the Fe(III) insertion at 10 and 20 mol%. Thermal analysis, FTIR spectrometry and X-ray diffractometry techniques were used to understand the influence of the Fe(III) co-substitution, keeping the Mg(II) molar fraction invariable among the samples. We show the iron (III) insertion affects the dehydration and dehydroxylation processes due the changes in M-OH bond energies Very homogeneous structures were obtained for all of the samples dried at 100 ºC and a consistent lattice volume expansion was observed as a function of iron (III) content, which can be required for catalyst or catalyst matrix applications.
In the present research work Mg 2 Al layered double hydroxide (LDH) intercalated with cubane-1,4-dicarboxylate anions was prepared by coprecipitation method, when solutions of Mg(II) and Al(III) nitrate salts, react with an alkaline solution of cubane-1,4-dicarboxylic acid .The successful preparation of nanohybrid of cubane-1,4-dicarboxylate(cubane-dc) anions with LDH was confirmed by powder X-ray diffraction, FTIR spectroscopy and thermal gravimetric analysis(TGA). The increase in the basal spacing of LDHs from 8.67 Å to 13.40 Å shows that cubane-dc anions were successfully located into the interlayer space. Thermogravimetric analyses confirm that the thermal stability of the intercalated cubane-dc anions is largely enhanced compared to the pure form before intercalation because of the host-guest interaction involving the hydrogen bonds. The interlayer structure, hydrogen bonding, and subsequent distension of LDH compounds containing cubane-dc anions were shown on the molecular simulation .The RDF (radial distribution function), mean square displacement (MSD), and self-diffusion coefficient were calculated using the trajectory files on the basis of molecular dynamics (MD) simulations, and the results indicated that the cubane-dc anions was more stable when intercalated into the LDH layers. A good agreement between calculated and measured X-ray diffraction patterns and between experimental and calculated basal spacing was obtained.
Hydrotalcite synthesis via co-precipitation reactions using MgO and Al(OH)3 precursors
Ceramics International, 2011
Hydrotalcite (Mg 6 Al 2 (OH) 16 (CO 3)Á4H 2 O), also known as aluminum-magnesium layered double hydroxide (LDH) or anionic clay, is a synthetic compound that was broadly investigated in the past decade due to its many potential applications, such as clinic anti-acid, catalyst support, adsorptive flotation, flame retardant, acid scavengers in polymer composites and as a raw material for high temperature insulating porous ceramics. This compound is usually produced by controlled chemical equilibrium shifting processes (such as co-precipitation) that requires various other purification steps (centrifugation, for example) and careful drying (freeze drying or ultrafiltration). In this paper, a novel route to synthesize hydrotalcite is presented, based on the hydration, dissolution and co-precipitation reactions carried out almost simultaneously in aqueous suspension containing reactive magnesium oxide and aluminum hydroxide. Compared to other methods (the regular co-precipitation, particularly), it presents various technological advantages such as low time-energy consumption, no further purification step requirement, high output and competitive production costs.
2005
Hydrotalcite-like compounds were co-precipitated with diluted sodium hydroxide from an unconventional aluminium source: the aluminium waste generated by the tertiary aluminium industry, with the assistance of ammonia and triethanolamine at pH 10. These products were characterised by several techniques (XRD, FT-IR, UV-vis-NIR, SEM, DTA-TG and BET methods) to compare results. The characterisation of products confirmed significant differences depending on basic reagent selected. Products co-precipitated with ammonia showed less crystal growth, a more significant iron content in the structure and higher internal surface area. Products from triethanolamine showed the entry of organic molecules into the layered structure. These findings were important for the improvement of methods based on waste treatment, transforming an aluminium hazardous waste into a value added product as layered double hydroxides.
Applied Clay Science, 2018
Magnesium-aluminum hydrotalcite-like compounds with molar ratios of Mg/Al ranging from 1.93 to 6.63 were synthesized and characterized with elemental analysis, XRD, SEM, TG/MS, XPS, 27 Al solid state MAS NMR, 13 C solid state CP MAS NMR, and vibrational spectroscopy (FTIR and Raman). The results of physico-chemical studies show that the materials are free of impurities and consistently point to the steady evolution of the interlayer anion composition upon increase of Mg/Al ratio. In particular, it is observed that the growing content of magnesium within the hydrotalcite layer is accompanied by the gradual substitution of dinegative interlayer carbonate anions with mononegative bicarbonates and/or nitrates. The observation contradicts the generally accepted view that the hydrotalcite-like structures have greater affinities for multivalent anions compared with monovalent ones. It is argued that in materials with low degree of Al for Mg substitution, hence larger distance between the charge generating sites, compensation by monovalent anions enhances Coulombic interactions within the hydrotalcite-like structure.
Cation selectivity during re-crystallization of Layered Double Hydroxides from mixed (Mg, Al) oxides
2015
The Layered Double Hydroxides (LDHs) with different cationic composition were obtained by regeneration process of mixed (Mg, Al) oxide (Mg:Al=2:1) with various regenerating solutions. Significant influence of pH on the cation composition of the LDH, obtained during regeneration process was found. The order of cation selectivity at pH 5-6 of regenerating solution is Zn > Fe 2+ > Co ≥ Ni > Cd > Mn > Mg >> Ca, while at high pH values (> 10) Mg-Al LDH is preferably formed. The change of cationic ratio M 2+ :Al depends on the composition of regenerating solution. The regeneration of mixed (Mg, Al) oxide with solutions of M 2+ Cl 2 or M 2+ (NO 3) 2 causes an increase in M 2+ :Al ratio from 2:1 to 2.5:1. The use of regenerating solutions containing an excess of both OH groups and M 2+ cations, such as Mg 4 (OH) 2 (CO 3) 3, Mg(OH) 2 , Ni(NH 3) 4 (H 2 O)Cl 2, etc., leads to formation of LDHs with M 2+ :Al ratio = 4. The obtained influences and dependences of solution composition, pH and the order of selectivity on the LDH composition are very important and useful data in the case of removing of hazardous or useful cations from solutions through regeneration of mixed (Mg,Al) oxide.
A study of crystallization of Mg-Al double hydroxides
Doklady Chemistry, 2002
Great recent attention has been focused on the development of methods for obtaining nanostructures and nanocomposites on their basis . One of the promising methods for synthesis of these nanocomposites is based on chemical modification of layered double hydroxides (LDHs) . LDHs are formulated as (OH) 2 [(anion n -) x / n · m H 2 O] , where M 2+ and M 3+ are metals in the oxidation states +2 and +3, respectively, and anion nstands for almost any anion or anionic complex . The LDHs consist of positively charged hydroxide [ (OH) 2 ] x + layers and anions located between these layers. The method for synthesizing nanocomposites is based on chemical modification of the anions placed in interlayers of LDHs. This method combines the ease of chemical methods of synthesis and the possibility of obtaining anisotropic and spatially confined nanostructures characteristic of the synthesis in nanoreactors .