Synthesis Of Hydrotalcite Research Articles

Microwave Synthesis of Hydrotalcite by Urea Hydrolysis

Hydrotalcite, layered double hydroxides (LDH), with hexagonal morphology has been rapidly synthesized by microwave reaction within 1 hour by urea hydrolysis from homogeneous solution. Different synthesis parameters, Mg/Al molar ratio, microwave reaction temperature and microwave power were systematically investigated. Pure hydrotalcite phase was obtained for Mg/Al ratios of 2:1 and 3:1, and higher reaction temperature gave higher crystallinity. The hydrotalcite synthesized at 600W power shows the highest crystallinity and more homogeneous crystal size distribution. The hydrotalcite samples were characterized by powder X-ray diffraction (XRD), simultaneous thermogravimetric/differential thermal analysis (TG/DTA), Fourier Transform Infrared (FT-IR) and Scanning electron micrograph (SEM).

Tuning Nanomaterials' Characteristics by a Miniaturized In‐Line Dispersion–Precipitation Method: Application to Hydrotalcite Synthesis

Tuning Nanomaterials' Characteristics by a Miniaturized In‐Line Dispersion–Precipitation Method: Application to Hydrotalcite Synthesis

Sol-gel synthesis of hydrotalcite — like compounds

Sol-gel hydrotalcite-like compounds were prepared using two different magnesium precursors, on the one hand magnesium ethoxide and on the other magnesium acetylacetonate. The aluminum precursor was always aluminum acetylacetonate. The resulting interlayer anions were ethoxide–acetylacetonate and acetylacetonate, respectively. Instead of the conventionally accepted thermal autoclave treatment, a new gelling and crystallization method is proposed using microwave irradiation. The solids were characterized by X-ray diffraction, nitrogen physisorption, thermogravimetric analysis, infrared spectroscopy and transmission electron microscopy. It is found that the acetylacetonate precursors determine surface area and crystallinity. Microwave irradiation guarantees a high surface area for an irradiation time as low as 10 min.

Microwave power effect on hydrotalcite synthesis

Hydrotalcite-like compounds, also referred as double layered hydroxides, are anionic clay-like compounds. They are microporous minerals with a layered structure. As they are scarcely found in nature they are usually synthesized through co-precipitation methods. A remarkable improvement in time and solution concentrations has been attained by microwaving the synthesis solutions. The obtained materials are original and different from those provided by the co-precipitation method. In this work, we correlate the features of the obtained hydrotalcite-like compounds, Mg/Al and Zn,Mg/Al, with the microwave intensity, the anion and cation nature, among others. When magnesium is incorporated at 200 W it remains in the outer layers of the hydrotalcite inhibiting the Zn diffusion which, then, forms zinc oxide. The irradiation power determines the homogeneity of the obtained materials as at 600 W the obtained hydrotalcite is more homogeneous than the one synthesized at 200 W.

Synthesis of Hydrotalcite from Wastes Discharged in Aluminum Regeneration Process and its Physical Properties

アルミドロスを原料として，無機陰イオン交換体の一種であり層状複水酸化物構造を有するハイドロタルサイトの合成を行った．得られた反応生成物に対して，結晶構造，表面構造，熱重量変化などの物性，pH緩衝作用，リン酸イオンの除去能力について検討した．ハイドロタルサイトの合成は，アルミドロスおよびMgCl2含有廃液を用いてAlとMgの複水酸化物の共沈法により行った．反応生成物には少量のSiO2, Al2O3, Fe2O3などが不純物として残存していた．得られた反応生成物の層間距離は約0.3 nmであった．ハイドロタルサイトを773 Kで3 h焼成するとMg–Al酸化物に変化し，焼成後に再水和操作を行うと再びハイドロタルサイトに復元した．反応生成物の物性は，試薬から合成したものとほぼ同一であった．得られたハイドロタルサイトは，pH緩衝作用とリン酸除去能力を併せもつものであった．

Influence of external field to wet chemical synthesis of Hydrotalcite

Influence of external field to wet chemical synthesis of Hydrotalcite

Urea method for the synthesis of hydrotalcites

Mg-Al, Zn-Al and Ni-Al hydrotalcite-like compounds with high crystallinity were synthesized by using the decomposing property of urea at high temperature. The crystallinity and the regularly of the samples were much preferable to those synthesized by other methods.

Synthesis of Hydrotalcite from Seawater and Its Application to Phosphorus Removal

10.0 wt% milk of lime was added to seawater containing AlCl 3 at Mg/Al molar ratio of 3.0 until pH 10.5 with stirring, and kept at 25;C for 1 h. Hydrotalcite (HT) was precipitated as a single phase, and Mg 2+ and Al 3+ were quantitatively precipitated. The chemical composition was [Mg 0.75 Al 0.25 (OH) 2 ][(SO 4 ) 0.06 (Cl) 0.02 (OH) 0.11 *];0.27H 2 O* (*Balance). A 100 mg-P/L Na 2 HPO 4 solution and the HT were shaken at 25;C. Phosphate removal increased with increasing time and the HT quantity, and was the highest at pH 7-9. Phosphate ion could be quantitatively removed, adding 8 times the stoichiometric quantity of the HT at pH 8.7 for 6 h.

Hydrotalcite synthesis using calcined dolomite as a magnesium and alkali resource

Hydrotalcite synthesis using calcined dolomite as a magnesium and alkali resource

Clean route for the synthesis of hydrotalcites and their property of selective intercalation with benzenedicarboxylate anions

Layered double hydroxides (LDHs or hydrotalcites) have received considerable attention because of their many potential applications, as ion-exchangers, catalysts and molecular recognition [1, 2]. Clean synthesis technology has been greatly promoted in recent years because of the environmental benefits. LDHs are usually prepared by coprecipitation methods [1]. The disadvantage of it is that a large volume of waste liquor containing salts is produced during the synthesis processes. An alternative synthesis route for LDHs was first reported by Misra et al. [3]. This method should be more economical and environmentally friendly than the traditional process. Here, we discuss the conditions required for pure hydrotalcites formation and the possibility of utilizing the waste liquors to make the process even more “green.” Intercalation of guest species into lamellar LDHs has been found to be an effective low temperature method to modify the materials in a controllable manner [2]. Here, we report intercalation of benzoate and 1,2-, 1,3or 1,4-benzenedioate ions into LDHs by the reaction of calcined LDHs with solutions of the organic acids.

On the stability of mixed M2+/M3+ oxides

The stability of Mg(Al)O formed by calcination of Mg–Al-containing hydrotalcites has been studied under steam-rich conditions (H2O:N2=1:1) at 600–650°C and 1atm. It was found that the MgO structure as well as a high specific surface area are maintained after calcination at temperatures up to 800°C. It has further been observed that the steam stability of Mg(Al)O towards sintering is improved after calcination of hydrotalcite at higher temperatures: calcination at 800°C gave an improved stability of Mg(Al)O compared to calcination at 700°C. Further, the stability towards sintering was influenced by the Mg/Al ratio of the hydrotalcite. Mg(Al)O materials formed from hydrotalcites with a Mg/Al ratio of 5 exhibit better long-term stabilisation characteristics compared to a Mg/Al ratio of 3 after calcination at 800°C. A partial or full substitution of aluminum with gallium in the oxide did not improve the steam stability. Changing the hydrotalcite synthesis procedure from co-precipitation to the alkoxide route did not significantly alter the steam stability after calcination.

Anionic Clay and Hydrotalcite Synthesis

Anionic Clay and Hydrotalcite Synthesis

Synthesis of Hydrotalcite using Magnesium from Seawater and Dolomite

Three methods of synthesizing hydrotalcite(HT) have been developed using magnesium from seawater and dolomite(MgCa(CO3)2). In the first process, 1.0M Na2CO3solution was added to calcium ion free artificial seawater containing AlCl3 with an initial Mg/Al molar ratio of 2.0∼3.7 until a pH of 10 was obtained. The solution was then continuously stirred for Ih at 60°C. CO3 2--HT was precipitated as a single phase, and the initial Mg/Al molar ratio, which each recovery of Mg2+and Al3+ from the solution was above 98%, was 2.0–2.3. In the second process, a Ca(OH)2 slurry was added to artificial seawater containing AlCl3 with an initial Mg/Al molar ratio of 1.0∼5.0 until a pH of 10.5 was obtained, and then was stirred for Ih at 60°C. HT was also precipitated as a single phase with initial Mg/Al molar ratio 2.0∼4.0. The initial Mg/Al molar ratio, which each recovery of Mg2+ and Al3+ from the solution was above 98%, was 2.2∼3.3, but SO4 2- and Cl− were contained in the precipitated HT. When HT was produced using initial Mg/Al molar ratio of 3.0 at 25°C, SO4 2- and Cl−in the HT were ion-exchanged with CO3 2- in a 0.05M Na2CO3solution for 24h at 25°C, and SO4 2- and Cl− content of the HT were decreased to 0.5 and 0.05wt%, respectively. In the third process, dolomite calcined at 1000°C was added to an AlCl3 solution with an initial Mg/Al molar ratio of 1.0∼2.0, and the solution was stirred for 1∼4h at 25∼90°C. HT was precipitated with the smallest amount of MgO and Mg(OH)2 when the initial Mg/Al molar ratio was 1.5 and the solution was stirred for 4h at 90°C.

Microwave Irradiation Effect on Hydrotalcite Synthesis

New synthesis method of hydrotalcites using microwave irradiation is presented, which avoids the autoclave high temperature treatment as well as the long crystallization time. The crystallite size of the obtained solids is smaller than in the conventionally prepared hydrotalcites. The highest irradiation time provided the lowest aluminium incorporation to the hydrotalcite network. Diminishing microwave irradiation time produces purer hydrotalcites. If the gel is irradiated only for two minutes a well crystallized hydrotalcite is obtained.

Synthesis of hydrotalcite with high layer charge for CO2 adsorbent

Synthesis of hydrotalcite with high layer charge for CO2 adsorbent

Synthesis of Hydrotalcites Using Microwave Irradiation

ABSTRACTHydrotalcites are mineral anion exchangers whose exchange capacity is determined by the amount of structural magnesium atoms (octahedrally coordinated) substituted by aluminium atoms. In this work we study the synthesis of hydrotalcites using a domestic microwave oven at room pressure. The effect of the oven power on the composition and on the resulting structure of two hydrotalcites differing on their nominal Al/Al+Mg ratio is presented.

Synthesis of hydrotalcite with high layer charge for CO 2 adsorbent

Hydrotalcite-like compounds (HT) with 24% to 48% Al 3+-substitution have been synthesized in the Mg 2+-Al 3+-Fe(CN) 6 4- system. Conditioning of the synthesized and air-dried compound with K 4Fe(CN) 6 4- solution at 80°C was essential to obtain the 80–90% pure ionic Fe(CN) 6 4- form on an equivalent basis. A linear decrease in a o with an increase in the mole ratio of R=Al 3+/(Mg 2++Al 3+) was extended to R=0.48. The CO 2 adsorption profiles were dependent upon both the interlayer distance and the Al 3+-substitution. The expanded space with the large anion Fe(CN) 6 4- can accommodate more effectively CO 2 gas in comparison with the NO 3 − and mixed ionic forms. The optimum space and charge density in the interlayer as a CO 2 adsorption field could be found on the hydrotalcite with the Al 3+-substitution of 37%. The isosteric heat of CO 2 adsorption was 43.3 kJ mol −1 in the range of adsorption of 20 to 40 cm 3 g −1 at 298 K and 0.1 MPa.

Investigation of the surface structure and basic properties of calcined hydrotalcites

In this work, we investigated the influence of preparation method, calcination temperature, and Mg : Al atomic ratio on the basic properties of calcined hydrotalcites. The steady-state decomposition of 2-propanol at 593 K and atmospheric total pressure was studied to compare the surface reactivities of the mixed oxides with those of pure MgO and Al 2O 3. In general, the activity and selectivity to propanone formation followed the order MgO ≥ calcined hydrotalcities ⪢ alumina, indicating that catalytically active basic sites are present on the calcined hydrotalcites. However, the selectivity to propanone is influenced significantly by the method of hydrotalcite synthesis. In addition, the observed activation energies and pre-exponential factors for propanone formation compensated each other over mixed oxides of different Mg : Al atomic ratios, resulting in similar areal reaction rates. The observed compensation effect can be explained by a shift in the rate-determining elementary step on a nonuniform surface. No significant influence of calcination temperature on the surface area and 2-propanol reactivity of hydrotalcite was observed for temperatures of 723–923 K, whereas calcination of hydrotalcite at 1173 K resulted in lower surface area, decreased selectivity to propanone, and formation of separate oxide phases. Temperature-programmed desorption (TPD) of CO 2 from calcined hydrotalcites indicated that the incorporation of aluminum into MgO suppresses the formation of high-strength base sites normally associated with pure MgO; however, low-strength base sites are still present on the mixed oxide. Based on results from 27Al NMR, XPS, CO 2 TPD, and 2-propanol reaction, we speculate that some Al is located at the surface but is in a local oxidic environment not favorable for acid-catalyzed reactions that typically occur over pure alumina.