Double Hydroxides Of Mg Research Articles

Effects of the cation ordering in Mg:Al and Zn:Al layered double hydroxides on crystallographic and spectroscopical properties by means of first principles calculations

Layered double hydroxides (LDH) are interesting materials due to their high absorption and catalytic properties. Their applications in environment, agriculture and pharmaceutical fields are becoming widely important. The interlayer and intralayer cation ordering on layered double hydroxides of Mg:Al 2:1 and Zn:Al 2:1 are studied by means of different ordering models at Density Functional Theory level. The cation ordering in LDH is interesting for monitoring the synthesis of these solids and for the applications of LDH, however it is difficult to determine experimentally. We have explored several ordering arrangements of the cation distribution in Mg:Al 2:1 and Zn:Al 2:1 LDH and the effect of these cation arrangements on some crystallographic and spectroscopic properties.

Sorption of U(VI) onto Layered Double Hydroxides of Mg and Al with β-Cyclodextrin from Aqueous Solutions

Sorption of U(VI) onto Layered Double Hydroxides of Mg and Al with β-Cyclodextrin from Aqueous Solutions

Adsorption of Hexavalent Chromium on Granular Activated Carbon fortified with a layered double hydroxide of Mg and Fe in aqueous solutions

Adsorption of Hexavalent Chromium on Granular Activated Carbon fortified with a layered double hydroxide of Mg and Fe in aqueous solutions

Compared arsenic removal from aqueous solutions by synthetic mixed oxides and modified natural zeolites

Layered Double Hydroxides of Mg–Al–Fe and their mixed metallic oxides of high specific surface area were synthesized by the coprecipitation method. A natural zeolite from a regional quarry with high clinoptilolite content was conditioned and modified. Initially, an acid treatment was applied and subsequently Fe(III) was incorporated by the wet impregnation method. Then the prepared solid materials were characterized by XRD, N2 adsorption–desorption at 77 K, SEM, DRS UV–Vis, and MP-AES to determine their physicochemical properties. Finally, the solid materials were evaluated as adsorbents for arsenic removal in water. The tracking of As and its species concentration at trace levels was carried out by cathodic stripping Square-wave voltammetry, which has proved to be a highly selective and sensitive electrochemical method. High levels of effectiveness in terms of removal were achieved, particularly with the natural zeolites and mixed oxides of highest iron content.

Сорбция U(VI) на слоистых двойных гидроксидах Mg и Al, содержащих β-циклодекстрин, из водных растворов

Сорбция U(VI) на слоистых двойных гидроксидах Mg и Al, содержащих β-циклодекстрин, из водных растворов

Packed hybrids of gold nanoparticles and layered double hydroxide nanosheets for microextraction of triazine herbicides from maize.

This work describes a nanohybrid material consisting of gold nanoparticles (AuNPs) and nanosheets of layered double hydroxides (NLDHs) of Mg(II) and Al(III). Mono-disperse AuNPs were immobilized on the surface of the LDHs via Au-O bonding. The nanohybrid sorbent was packed in an organic filter along with a syringe and applied to the microextraction of triazine herbicides with the help of an injection pump. The collected hexane eluate was concentrated and directly injected into a HPLC column for quantification. The effects of the amount of Au/LDH nanohydrobrids, type, flow rate, volume of washing and eluting solvent were optimized. The method was validated by detecting four triazine herbicides (prometryn, atrazine, terbumeton and secbumeton) in spiked maize. The limits of detection range between 35 and 108pgg-1. The relative standard deviations range from 1.0-6.9% for repeatability and 4.6-7.8% for reproducibility (for n = 5). Graphical abstract Schematic presentation of a nanohybrid material consisting of gold nanoparticles and nanosheets of layered double hydroxides of Mg(II) and Al(III) (Au/LDH) for use as an adsorbent for microextraction in a packed syringe. Organic filter heads were used as the container of Au/LDHs nanohybrids, and were connected with the syringes installed on the injection pump for the semi-automatic microextraction and preconcentration of triazines in maize.

Sorption of U(VI) onto layered double hydroxides and oxides of Mg and Al, prepared using microwave radiation

Layered double hydroxides of Mg and Al, containing CО32– ions in the interlayer space (LDH-Mg-Al-CО3), and layered double oxides of Mg and Al (LDO-Mg-Al) were prepared using microwave radiation (MWR). The use of MWR allows not only acceleration of the synthesis of both LDH and LDO, but also preparation of compounds with high kinetic characteristics of the U(VI) sorption. The degree of U(VI) sorption (α) from 10–2 M aqueous U(VI) solutions at a sorption time of 4 h and V/m = 50 mL g–1 exceeds 99.0%. In sorption from more concentrated (10–1 M) aqueous U(VI) solutions under similar conditions, α on all the samples does not exceed 37.5%.

Syntheses of Mg–Al–NO3layered double hydroxides with high crystallinity in the presence of amines

In the present work, layered double hydroxides of Mg–Al were synthesized with nitrate interlayer anions in the presence of different types of amines such as ethylenediamine, dimethylamine, and trimethylamine, without a N2atmosphere, from a homogeneous solution using the coprecipitation method. The concentration of the different types of amines and pH of the solution were adjusted to produce high-purity and -crystallinity samples. The structure and morphology of layered double hydroxides were characterized and investigated by powder X-ray Diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and thermogravimetric analysis techniques. The analyses showed that with increasing amine concentration, both crystallinity and purity of the samples increase at pH 10.5.

Sorption of 60Co from aqueous solutions on layered double hydroxides of Mg, Al, and Nd

Sorption of U(VI) from aqueous solutions of various compositions on layered double hydroxides (LDHs) of Mg, Al, and Nd, and also on layered double oxides (LDOs) of Mg and Al was studied. Experiments on sorption of UO22+ carbonate complexes from aqueous solution on LDO-Mg-Al showed that [UO2(CO3)3]4− ions are weakly captured by LDH-Mg-Al formed by contact of LDO-Mg-Al with water. With an increase in the uranium concentration in solution, Kd of U(VI) decreases. For 3.3 × 10−3 M [UO2(CO3)3]4− solutions, after 24-h contact of the solid and liquid phases, the distribution coefficients do not exceed 1.0 ml g−1 at V/m = 50 ml g−1. From aqueous nitrate solutions, U(VI) is sorbed on LDH-Mg-Al-NO3 poorly: Kd of U(VI) does not exceed 1.0 ml g−1 at 24-h contact of the solid and liquid phases and V/m = 50 ml g−1. At the same time, U(VI) is efficiently sorbed from aqueous 10−3 M UO2(NO3)2 solutions on LDH-Mg-Al and LDH-Mg-Nd with CO32− and OH− ions in the interlayer space. After 15-min contact of the solid and liquid phases, Kd of U(VI) exceeds 5 × 103 ml g−1. With an increase in the UO22+ concentration to 10−1 M, Kd of U(VI) decreases considerably, becoming lower than 25 ml g−1, but increases to ∼150 ml g−1 with an increase in the contact time of the solid and liquid phases to 24 h. The effect of the Na+, Ca2+, Cl−, and SO42− ions and of pH of the initial solution on the U(VI) sorption from aqueous UO2(NO3)2 solutions on LDH-Mg-Al-CO3 was examined.

Effect of complexing anions on sorption of U(VI), 90Sr, and 90Y from aqueous solutions on layered double hydroxides of Mg, Al, and Nd

Sorption of 90Sr and 90Y from aqueous solutions on Mg-Al and Mg-Nd layered double hydroxides (LDHs) in various forms was studied. The distribution coefficients Kd of U(VI) and 90Sr on LDH-Mg-Al-EDTA are 100–120 ml g−1 in 15 min of contact of the solid and liquid phases at V/m = 50 ml g−1. At the same time, under similar conditions, U(VI) and 90Sr are not sorbed from aqueous solutions on LDH-Mg-Al-C2O4. The sorption of U(VI) from aqueous solutions containing H2EDTA2−, C2O42−, and CO32− on LDH-Mg-Nd-CO3 and LDH-Mg-Al-CO3 strongly depends on the concentration of the complexing anions in the solution. In particular, for 10−3 M aqueous UO22+ solutions, with an increase in [C2O42−] from 10−3 to 5 × 10−2 M, Kd of U(VI) decreases from >5 × 103 to 70 ml g−1 for LDH-Mg-Al-CO3 and from 170 to ∼0 ml g−1 for LDH-Mg-Nd-CO3. In the presence of 10−3 to 5 × 10−2 M CO32− in aqueous solution, U(VI) is not noticeably sorbed on LDH-Mg-Nd-CO3 (Kd does not exceed 16 ml g−1 at V/m = 50 ml g−1), and on LDH-Mg-Al-CO3 the sorption sharply decreases (Kd decreases from >5 × 103 to ∼0 ml g−1 at V/m = 50 ml g−1). The presence of complexing anions in the solution does not appreciably affect the 90Sr sorption, but noticeably affects the 90Y sorption. With an increase in their concentration, Kd of 90Y appreciably decreases. The effect exerted by Sr2+ ions on the sorption of microamounts of U(VI) and by UO22+ ions on the sorption of microamounts of 90Sr and 90Y from aqueous solutions on LDH-Mg-Nd-CO3 was also examined.

Calcined Mg–Al Layered Double Hydroxides for Uptake of Trace Levels of Bromate from Aqueous Solution

Layered double hydroxides of Mg and Al (Mg–Al LDH) were synthesized with OH–, Cl–, or CO32– as charge compensating anions. The materials were calcined at 500 °C in air. The bromate uptakes of calcined and uncalcined LDH materials were investigated from 0.78 μmol/dm3 bromate solution. Results show that uncalcined LDH exhibited no bromate uptake, although calcined LDH exhibited bromate uptake: the initial bromate concentration of 0.78 μmol/dm3 decreased to less than 0.078 μmol/dm3, the maximum contaminant level established for bromate in drinking water. The rate of bromate uptake of calcined LDH was slow to attain equilibrium in 48 h. The bromate uptake data of calcined LDH agreed well with the Freundlich model.

Structure and Composition of the Layered Double Hydroxides of Mg and Fe: Implications for Anion‐Exchange Reactions

AbstractPartial cation exchange of Mg2+ ions with Fe3+ ions employing solid Mg(OH)2 as precursor yielded an ordered layered double hydroxide of Mg and Fe in the presence of carbonate anions. Structure refinement revealed that the compound adopts the polytype structure 3R1 (space group R$\bar {3}$m, a = 3.108 Å, c = 23.08 Å) and does not show any signs of cation order. It crystallizes with a unique cation ratio of [Mg]/[Fe] = 4. At this ratio, the compound shows a single sharp absorption in its electronic spectrum at 280 nm. Attempts to prepare the LDH with a higher Fe content resulted in the phase separation of excess Fe into X‐ray amorphous binary compounds, the existence of which can be discerned only by the appearance of absorptions at λ > 350 nm, a characteristic of oxide–hydroxides of Fe3+. The nitrate‐containing compound also forms with a similarly low Fe content. At this composition, the compound does not exhibit any anion‐exchange properties as the nitrate ions intercalated in layered hydroxides of low layer charge are not labile. This explains the paucity of information on anion‐exchange reactions of layered double hydroxides of Mg and Fe.

Sorption of U(VI) from aqueous solutions on layered double hydroxides of Mg, Al, and Nd

Sorption of U(VI) from aqueous solutions on layered double hydroxides of Mg, Al, and Nd

Synthesis of a novel layered double hydroxides [MgAl 4(OH) 12](Cl) 2·2.4H 2O and its anion-exchange properties

A novel layered double hydroxide of Mg and Al with composition [Mg 0.96Al 4.00(OH) 12]Cl 1.86(CO 3) 0.03·2.4H 2O, designated as MgAl 4–Cl, was synthesized by mixing crystalline gibbsite (γ-Al(OH) 3) and solid MgCl 2·6H 2O with subsequent hydrothermal treatment at 160 °C for 72 h. The MgAl 4–Cl exhibited a crystalline material of a layered structure, as evidenced from X-ray diffraction. Anion uptake experiments with the MgAl 4–Cl showed that Cl − in the interlayer space can be exchanged with anions such as Br −, H 2PO 4 −, CO 3 2− or dodecyl sulfate (DS −) from aqueous solutions with preservation of the layered structure. Uptake of NO 3 −, BrO 3 − or SO 4 2− on the MgAl 4–Cl showed different behavior; these anions can be exchanged within 1 h maintaining the layered structure, but a release of Mg 2+ cations from the sample was observed with increased reaction time, resulting in collapse of the layered structure and formation of the gibbsite phase, as determined from chemical analyses and X-ray diffraction.

Sorption of Cs, Sr, and Y radionuclides on mixed layered double hydroxides of Mg, Al, and Nd from the aqueous phase

Sorption of 137Cs, 90Sr, and 90Y radionuclides from aqueous solutions on the solid phase of layered double hydroxides (LDHs) of Mg, Al, and Nd was studied. Sorption of 137Cs from 10−5 M aqueous CsNO3 solutions on the LDH-Mg-Al-Nd solid phase is extremely weak. At the same time, 90Sr and 90Y are efficiently sorbed on the LDH-Mg-Al-Nd solid phase from 10−5 M aqueous Sr(NO3)2 solutions. After 5-min contact of the solid and liquid phases, Kd of 90Sr and 90Y exceeds 103 ml g−1. With an increase in the Nd content in LDHs of mixed composition, their sorption properties toward 90Sr and 90Y are enhanced.

Chromate uptake characteristics of the pristine layered double hydroxides of Mg with Al

The layered double hydroxides (LDHs) of Mg with Al readily scavenge dissolved chromate ions under a wide range of conditions. While the chromate uptake is quantitative in the LDH containing 33 mol% Al, the uptake is only 58% of the stoichiometric value in the LDH containing 25 mol% Al. This indicates that the lower symmetry of the NO 3 − ions in the LDH with 33 mol% Al facilitates the intercalation of chromate ions even under conditions of equilibration with excess dissolved nitrate ions. The chromate uptake obeys the Langmuir adsorption isotherm suggesting that the entire interlayer region of the LDH behaves like a surface. This surface is structural rather than morphological as the chromate uptake correlates negatively with the BET surface area of the LDHs.

Suppression of the Reversible Thermal Behavior of the Layered Double Hydroxide (LDH) of Mg with Al: Stabilization of Nanoparticulate Oxides

The layered double hydroxide of Mg with Al decomposes below 600 degrees C with the loss of nearly 48% mass, resulting in the formation of an oxide residue having the rock salt structure and nanoparticulate morphology. However, this product reconstructs back into the parent LDH, owing to its compositional and morphological metastability. The oxide can be kinetically stabilized within an amorphous phosphate network built up through an ex situ reaction with a suitable phosphate source such as (NH4)H2PO4. This oxide transforms into a thermodynamically more stable phase with a spinel structure on soaking in an aqueous medium. The oxide residue has a nanoparticulate morphology as revealed by the Scherrer broadening of the Bragg reflections as well as by electron microscopy. This work shows that the hydroxide reconstruction reaction and spinel formation are competing reactions. Suppression of the former catalyzes spinel formation as the excess free energy of the metastable oxide residue is unlocked to promote the diffusion of Mg2+ ions from octahedral to tetrahedral sites, which is the essential precondition to the formation of a normal spinel. This reaction taking place as it does at ambient temperature and in solution helps in the retention of a nanostructured morphology for the spinel. Another way of stabilizing the oxide is by incorporating the thermally stable borate anion into the LDH. This paves the way for an in situ reaction between the cations of the host LDH and the borate guest. The in situ reaction directly leads to the formation of an oxide with a spinel structure.

Anion substitution of nitrate-saturated layered double hydroxide of Mg and Al

In the context of producing industrial-grade hydrotalcite-like (HT) materials containing phosphate and sulfate for use as slow-release fertilizers, the ease with which nitrate-HT can be converted to phosphate-HT and sulfate-HT has been examined. Graded amounts of di-ammonium hydrogen phosphate and ammonium sulfate were added to nitrate-HT, while maintaining pH at 9.5, to produce substitutions ranging from approximately 50% to 100%. Chemical and X-ray diffraction analysis of the products confirmed that the substitution could be easily effected by simple topotactic exchange.

Nanohybrids for controlled antibiotic release in topical applications

New polymeric composite materials containing a nanohybrid to be used for the controlled release of an antibiotic molecule, chloramphenicol succinate, have been formulated, prepared and characterised. The nanohybrid consists of a layered double hydroxide of Mg–Al hydrotalcite-type, in which the nitrate anions present in the host galleries were replaced with chloramphenicol succinate anions (CFS −) by a simple ion-exchange reaction. Different amounts of the hybrid material were incorporated in polycaprolactone and processed as films of 0.15 mm thickness. The composite materials were analysed by X-ray diffractometry and thermogravimetry and their mechanical properties were determined. They showed properties even better than those of the pristine polymer. The release process of the antibiotic molecules was found to be very interesting and promising for tuneable drug delivery. It consists of two stages: an initial stage of a very rapid burst, in which a small fraction of drug is released; and a second stage that is much slower, extending for a longer and longer time. This behaviour is profoundly different and much slower than that of a sample in which the antibiotic molecule is directly incorporated into the polymeric matrix. The parameters influencing drug release have been individuated and discussed.

Selective adsorption of phosphate from seawater and wastewater by amorphous zirconium hydroxide

Phosphate adsorption from single electrolyte (NaH 2PO 4), phosphate-enriched seawater, and model wastewater was studied using amorphous zirconium hydroxide, ZrO(OH) 2⋅(Na 2O) 0.05⋅1.5H 2O, as an adsorbent. Batch experiments were carried out to investigate the adsorption of phosphate. The effect of pH on phosphate adsorption from seawater showed that the uptake of phosphate increased with an increase in pH up to 6, and then decreased sharply with a further increase in pH of the solution. The equilibrium data of phosphate adsorption were followed with a Freundlich isotherm. The uptake of phosphate at the adsorbent/solution ratio 0.05 g/2 L was 10 and 17 mg-P/g for the phosphate-enriched seawater and the model wastewater, respectively. A much higher adsorptivity toward phosphate ions in seawater was observed on ZrO(OH) 2⋅(Na 2O) 0.05⋅1.5H 2O than on other representative adsorbents based on layered double hydroxides of Mg(II)–Al(III), Mg(II)–Fe(III), and Ni(II)–Fe(III). The effective desorption of phosphate ions on ZrO(OH) 2⋅(Na 2O) 0.05⋅1.5H 2O could be achieved using a 0.1 M NaOH solution. The usefulness of experimental data for practical applications in removing phosphate in seawater and wastewater is discussed.