Magnesium-aluminum Layered Double Hydroxide Research Articles

Photoactivation of Molecular Oxygen by an Iron(III) Porphyrin with a Magnesium Aluminum Layered Double Hydroxide for the Aerobic Epoxidation of Cyclohexene

AbstractThe photocatalytic aerobic epoxidation of cyclohexene proceeded under visible‐light irradiation only if 5,10,15,20tetrakis(pentafluorophenyl)porphyrin iron(III) chloride ([FeIII(TPFPP)Cl]) was combined with Mg‐Al layered double hydroxide (Mg‐Al LDH) as a solid base in chloroform. The OH groups in the Mg‐Al LDH exchanged with the axial Cl ligands in [FeIII(TPFPP)Cl] to afford [FeIII(TPFPP)OH], which functioned photocatalytically in the presence of Mg‐Al LDH but was inactive in its absence. The band in the action spectrum agreed well with the Soret band in the UV/Vis absorption spectrum of [FeIII(TPFPP)OH]. The spectral changes indicated the reduction of [FeIII(TPFPP)OH] to [FeII(TPFPP)] under visible‐light irradiation, which in turn activates O2 that could be used for the epoxidation of cyclohexene.

Bionanocomposite materials from layered double hydroxide/N-trimellitylimido-l-isoleucine hybrid and poly(vinyl alcohol)

Nanocomposites (NCs) of poly(vinyl alcohol) (PVA) with chiral-modified magnesium–aluminum-layered double hydroxides (LDHs) were prepared by solution intercalation method. A novel chiral organomodified LDH was synthesized from the coprecipitation reaction of the aluminum (III) nitrate nonahydrate, magnesium (II) nitrate hexahydrate, and bioactive N-trimellitylimido-l-isoleucine amino acid in aqueous solution via simple, fast, and green method under ultrasound irradiation for the first time. The morphology and structure of the obtained material are examined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), and field-emission SEM techniques. The TEM and XRD structure study revealed a coexistence of exfoliated and intercalated modified LDH in PVA matrix. The effects of modified LDH contents on the thermal property of PVA films were investigated by thermogravimetric analysis method, and the results show that by the addition of the modified LDH into the PVA causes an increase in the thermal decomposition temperatures of the novel NC materials.

Ionic elastomers based on carboxylated nitrile rubber (XNBR) and magnesium aluminum layered double hydroxide (hydrotalcite)

The presence of carboxyl groups in carboxylated nitrile butadiene rubber (XNBR) allows it to be cured with dif- ferent agents. This study considers the effect of crosslinking of XNBR by magnesium aluminum layered double hydroxide (MgAl-LDH), known also as hydrotalcite (HT), on rheometric, mechano-dynamical and barrier properties. Results of XNBR/HT composites containing various HT loadings without conventional curatives are compared with XNBR com- pound crosslinked with commonly used zinc oxide. Hydrotalcite acts as an effective crosslinking agent for XNBR, as is particularly evident from rheometric and Fourier transform infrared spectroscopy (FTIR) studies. The existence of ionic crosslinks was also detected by dynamic mechanical analysis (DMA) of the resulting composites. DMA studies revealed that the XNBR/HT composites exhibited two transitions - one occurring at low temperature is associated to the Tg of elas- tomer and the second at high temperature corresponds to the ionic transition temperature Ti. Simultaneous application of HT as a curing agent and a filler may deliver not only environmentally friendly, zinc oxide-free rubber product but also ionic elastomer composite with excellent mechanical, barrier and transparent properties.

Influences of polyhydric alcohol co-solvents on the hydration and thermal stability of MgAl-LDH obtained via hydrothermal synthesis

Magnesium–aluminum layered double hydroxides (MgAl-LDH) was prepared by hydrothermal synthesis. Five kinds of solvents, including pure water, water/ethanol, water/ethylene glycol, water/glycerin, and water/pentaerythritol, were respectively employed to synthesize the LDH grains. The microstructures and thermal stabilities of the obtained LDH were then contrastively investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectra (FT-IR), differential scanning calorimetry (DSC), and thermogravimetry (TG). It was shown that the incorption of polyhydric alcohol co-solvents benefit in the combination of crystal water through in-situ reaction. In comparison with the water molecules entered via diffusion, the in-situ combined crystal waters are characterized with high hydration level. But the excessive electrostatic interactions results in the decrease of crystallinity. With the increase of the hydroxyl group numbers in the co-solvents, the crystallinity of the obtained LDH became worse. At the same time, the dehydration temperatures of combined crystal water were elevated, while the deprivation of CO2 from intermediate layers and the dehydration of basic layers should occurred at relative lower temperatures. In the case of the LDH prepared by using pentaerythritol as co-solvents, the crystallinity and thermal stability were the worst because of the poor stacking of the layer structure.

Characterization and Film Properties of Electrophoretically Deposited Nanosheets of Anionic Titanate and Cationic MgAl-Layered Double Hydroxide

Anionic hydrated titanate (H(n)TiO(m): HTO) nanosheets and cationic magnesium-aluminum layered double hydroxide (Mg-Al LDH) nanosheets were electrophoretically deposited on positively and negatively charged indium tin oxide (ITO)-coated glass substrates, respectively. The HTO nanosheets and Mg-Al LDH nanosheets obtained were identified in neutral water as H(2)Ti(4)O(9)·nH(2)O with a ζ-potential of -23 mV and Mg(6)Al(2)(OH)(18)·4.5H(2)O with a ζ-potential of +41 mV, respectively. Dense and smooth HTO and Mg-Al LDH films with layered structures with thicknesses of about 10-15 μm were prepared in 300 s at 7.5 V by electrophoretic deposition (EPD) from the nanosheet suspensions. Both EPD HTO and LDH films showed elasticity because of their layered laminate structures. The HTO thick films demonstrated large adsorption properties and high photocatalytic activity, while the Mg-Al LDH thick films showed relatively high ionic conductivity of 10(-5) S cm(-1) at 80 °C and 80% relative humidity.

Transformation of alunite residuals into layered double hydroxides and oxides for adsorption of acid red G dye

For efficient utilization of alum sludge residuals, transformation of them into magnesium-aluminum layered double hydroxides (Mg-Al-LDHs) by the coprecipitation method was studied. The adsorption of Acid Red G (ARG) in aqueous solution onto the calcined LDHs was then investigated. The structure of synthesized materials was characterized by using X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), thermal analysis (TG-DTA) and scanning electron microscopy (SEM). The results showed that high crystalline hexagonal LDHs were synthesized from alum sludge. The particle size of LDHs synthesized from the direct use of alum sludge was much larger than that of LDHs synthesized from the use of alum sludge pretreated by acid or alkali. There existed the silicon in the LDHs synthesized from alum sludge pretreated by alkali. The LDO obtained by calcination of LDHs synthesized from alum sludge pretreated by acid was purer than that of LDO synthesized from alum sludge pretreated by alkali. The results of adsorption experiments indicated that the removal percentage of ARG with an adsorbent dose of 0.05 g was about 93.1% at pH=10 in room temperature for 150 min. The regenerated LDO for reuse was feasible within two cycles and ARG might be mainly absorbed on the surface of LDO.

A mechanochemical approach to get stunningly uniform particles of magnesium–aluminum-layered double hydroxides

A mechanochemical approach is developed in preparing a series of magnesium–aluminum-layered double hydroxides (Mg–Al-LDHs). This approach includes a mechanochemical process which involved manual grinding of solid salts in an agate mortar and afterwards peptization process. In order to verify the LDHs structure synthesized in the grinding process, X-ray diffraction (XRD) patterns, transmission electron microscopy (TEM) photos and thermogravimetry/differential scanning calorimetry (TG–DSC) property of the product without peptization were characterized and the results show that amorphous particles with low crystallinity and poor thermal stability are obtained, and the effect of peptization is to improve the properties, more accurately, regular particles with high crystallinity and good thermal stability can be gained after peptization. Furthermore, the fundamental experimental parameters including grinding time, the molar ratio of Mg to Al element (defined as R value) and the water content were systematically examined in order to control the size and morphologies of LDHs particles, regular hexagonal particles or the spherical nanostructures can be efficiently obtained and the particle sizes were controlled in the range of 52–130nm by carefully adjusting these parameters. At last, stunningly uniform Mg–Al-LDHs particles can be synthesized under proper R values, suitable grinding time and high degree of supersaturation.

Layered Double Hydroxide Intercalated with Sodium Dodecyl Sulfate

The study investigates the intercalation of magnesium-aluminum layered double hydroxide with sodium dodecyl sulfate. Monolayer intercalation of the LDH-carbonate was achieved using an acetic acid-assisted ion exchange reaction. The carboxylic acid is believed to assist intercalation of dodecyl sulfate by facilitating the elimination of the carbonate ions present in the anionic clay. Bilayer intercalation was achieved by a coprecipitation method and this resulted in a highly crystalline product. However, in this case the interlayer contains a mixture of dodecyl sulfate anion, sodium dodecyl sulfate and the hydrolysis product dodecanol. The organic phase in the latter product shows an order-disorder transition between 100°C and 120°C, with thermal degradation and volatilization commencing above 170°C.

Preparation and investigation of the combustion behavior of polypropylene/organomodified MgAl-LDH micro-nanocomposite

Layered double hydroxides (LDHs) are considered as a new emerging class of clays and they have a promising future in the field of nanocomposites due to their highly tunable properties. In this research, polypropylene/organomodified magnesium–aluminum LDH (PP/O-MgAl-LDH) composites were prepared by direct melt compounding. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the samples. Both XRD and TEM images of the composites illustrate the formation of a mixed morphology of micro and nano scale dispersion of MgAl-LDH in the matrix. Its combustion behaviors were examined via microscale combustion calorimeter (MCC), and char residues investigated by SEM. The MCC results show that the addition of Mg-Al-LDH into PP can efficiently decrease the specific heat release rate (HRR), the heat release capacity (HRC), and total heat release (THR), indicating the flame retardancy of the composite are improved. Flame retardant properties of PP/O-MgAl-LDH micro-nanocomposite were further enhanced with the increasing amounts of MgAl-LDH concentration.

Structural Evolvement of Heating Treatment of Mg/Al-LDH and Preparation of Mineral Mesoporous Materials

Abstract Although hydrotalcite, or layered double hydroxides (LDHs), is not a common mineral, it is an important material that can be easily synthesized in laboratory. In this study, structural evolvement and BET surface area changes of heat treated Mg/Al-LDH is evaluated by XRD, TEM and N2-BET analyses. The results indicate that the magnesium-aluminum LDH with carbonate as interlayer anion, periclase-like oxides was formed at temperatures of 400–800°C. Meanwhile, 2–3 nanometer mesoporous were formed during decomposition of LDH. However, the heat treated samples still preserve the morphology of the original LDH plates. Periclase-like formed from LDH heat treatment may re-hydrolyze and recover the structure of LDH. However, crystallinity of the recovered LDH is lower than that of the original LDH. This heat treatment will result in formation of (Mg, Al)-oxide nano-crystals and nanopores among the nano-crystals. When heating temperature exceeds 1000, the periclase-like (Mg, Al)-oxide is transformed into a composite with periclase (MgO) and spinel phases. The periclase can be re-hydrolyzed and dissolved in HCI solution. After acid treatment, the sample with a high surface area is composed of spinel nano-crystals and nanopores among them. Our results will provide a new and economic way to synthesize mesoporous materials through pathways of phase transformation of precursor materials with different composition.

Preparation of Glycy- l-Tyrosine intercalated layered double hydroxide film and its in vitro release behavior

This paper describes the preparation of films of peptide (Glycy- l-Tyrosine, denoted as GlyTyr) intercalated layered double hydroxide (LDH) and its release performances. GlyTyr has been intercalated into a magnesium–aluminum LDH, and the resulting film was fabricated by solvent evaporation method in order to exploit new formulation in drug carrier especially used in skin medicament. Based on the results of XRD, FT-IR, FT-IR-ATR, UV–vis, 13C NMR, ICP and elemental analysis, it was found that GlyTyr has been successfully intercalated into LDH gallery. TG/DTA, in situ FT-IR, in situ XRD and polarimetry indicate that the chemical stability of GlyTyr was enhanced significantly in the confined region of LDH galleries compared with its pristine form. SEM reveals that the film thickness is about 12.6 μm with c-orientation of LDH platelets ( ab plane parallel to the substrate). In vitro release tests of the GlyTyr-LDH film in pH 7.4 phosphate buffered saline (PBS) showed that no burst release phenomenon occurred at the beginning stage and a high release ratio of GlyTyr (91%) was obtained, exhibiting controlled release behavior. Furthermore, the parabolic diffusion model was used to simulate the release kinetics of GlyTyr from the LDH carrier, indicating that the external surface diffusion or the intraparticle diffusion via ion-exchange is the rate-determining step in the release process. Therefore, this work demonstrates that Mg/Al-LDH is an effective inorganic matrix for the peptide storage and controlled delivery at the required time.

Synthesis and characterization of biodegradable poly( l-lactide)/layered double hydroxide nanocomposites

This study reports the preparation and physical properties of biodegradable nanocomposites fabricated using poly( l-lactide) (PLLA) and magnesium/aluminum layered double hydroxide (MgAl-LDH). The MgAl-LDH with molar ratio of Mg/Al = 2 were synthesized by the co-precipitation method. In order to improve the chemical compatibility between PLLA and LDH, the surface of LDH was organically-modified by polylactide with carboxyl end group (PLA–COOH) using ion-exchange process. Then, the PLLA/LDH nanocomposites were prepared by solution intercalation of PLLA into the galleries of PLA–COOH modified LDH (P-LDH) in tetrahydrofuran solution. Both X-ray diffraction data and Transmission electron microscopy images of PLLA/P-LDH nanocomposites indicate that the P-LDHs are randomly dispersed and exfoliated into the PLLA matrix. Mechanical properties of the fabricated 1.2 wt.% PLLA/P-LDH nanocomposites show significant enhancements in the storage modulus when compared to that of neat PLLA. Adding more P-LDH into PLLA matrix induced a decrease in the storage modulus of PLLA/P-LDH nanocomposites, probably due to the excessive content of PLA–COOH moleculars with low mechanical properties. The thermal stability and degradation activation energies of the PLLA and PLLA/P-LDH nanocomposites can also be discussed.

Variation of benzyl anions in MgAl-layered double hydroxides: Fire and thermal properties in PMMA

Magnesium aluminum layered double hydroxides (MgAl-LDHs) intercalated with a range of benzyl anions were prepared using the coprecipitation method. The benzyl anions differ in functionality (i.e. carboxylate, sulfonate, and phosphonate) and presence or absence of an amino substituent. Various methods for preparing LDHs (i.e. ion exchange, coprecipitation and rehydration of the calcined LDH methods) have been compared with the MgAl-benzene phosphonate and their effect on fire and thermal properties was studied. After characterization, the MgAl-LDHs were melt-blended with poly(methyl methacrylate) (PMMA) at loadings of 3 and 10% by weight to prepare composites. Characterization of the LDHs and the PMMA composites was performed using FTIR, XRD, TGA, transmission electron microscopy (TEM) and cone calorimetry. FTIR and XRD analyses confirmed the presence of the charge balancing benzyl anions in the galleries of the MgAl-LDHs. Improvements in fire and thermal properties of the PMMA composites were observed. The cone calorimeter revealed that the addition of 10% MgAl-LDHs reduces the peak heat release rate by more than 30%.

Preparation of Layered Double Hydroxide Microspheres by Spray Drying

In order to fully exploit their attractive properties in actual practical applications, layered double hydroxide (LDH) materials should be fabricated into macroscopic form. A magnesium−aluminum layered double hydroxide (MgAl-LDH) containing interlayer carbonate anions has been obtained using a synthesis route involving separate nucleation and aging steps, and microspheres of the material formed in a subsequent spray drying process. The resulting products are composed of nanosized LDH particles aggregated into solid microspheres with a diameter of 10−50 μm, a sphericity of 0.84, modal pore access diameter of 87.9 nm, surface area of 43 m2/g, and total pore volume of 1.29 cm3/g. The presence of an accessible diffusion pathway in the macropore domain of the LDH microspheres offers the possibility of enhanced performances in a wide range of applications. Furthermore, the spherical morphology of the materials was retained when the LDHs were converted into solid base catalysts by calcination and subsequent rehy...

Thermal Degradation of Novel Exfoliated PLLA/LDH Nanocomposites

In this article, we report the fabrication of novel poly(L-lactide) (PLLA) nanocomposites based on PLLA and magnesium-aluminium layered double hydroxides (MgAl-LDH) which were mixed the polylactide with carboxyl end group (PLA-COOH) in acetone . Both the X-ray diffraction data and transmission electron microscopy images of the PLLA/LDH nanocomposites indicate that most of the LDH layers were disorderly exfoliated into the PLLA matrix. The thermal degradation behaviors of PLLA and its nanocomposites were studied using thermal gravimetric analysis (TGA) under nitrogen atmosphere at heating rates from 5 to 40 °C/min. The TGA profiles of the PLLA/LDH nanocomposites show less thermal stability than that of neat PLLA due to the presence of Mg and Al which has a drastic influence on thermal stability of PLLA. The activation energy of PLLA, 1 wt% and 3 wt% PLLA/LDH nanocomposites were 158, 140 and 130 kJ/mol, respectively.

Preparation of macrospherical magnesia-rich magnesium aluminate spinel catalysts for methanolysis of soybean oil

In order to fully exploit the green characteristics of solid base catalysts they should be fabricated into macrostructured rather than powder form. Magnesia-rich magnesium aluminate spinel ( MgO · MgAl 2 O 4 ) framework catalysts with tunable basicity have been prepared by using γ ‐ Al 2 O 3 macrospheres (0.5–1.0 mm in diameter) as a hard template. The process involves in situ growth of magnesium–aluminum layered double hydroxides (MgAl-LDHs) in the channels of the γ ‐ Al 2 O 3 macrospheres by the urea hydrolysis method, followed by calcination, tuning of the basicity through etching of excess aluminum with aqueous alkali and a final calcination step. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), elemental analysis and low temperature N 2 adsorption–desorption studies demonstrate that the composite MgO · MgAl 2 O 4 materials are composed of nanosized rod-like particles aggregated into a spherical framework. Catalytic reactivity was investigated by using methanolysis of soybean oil as probe reaction. The MgO · MgAl 2 O 4 composite shows a higher biodiesel yield compared to an MgO / MgAl 2 O 4 / γ ‐ Al 2 O 3 material with the same loading of magnesium prepared by a conventional impregnation method. The enhanced catalytic activity of the former material can be ascribed to its higher basicity, specific surface area, pore volume and pore size.

Computer Simulation Study of the Structural Stability and Materials Properties of DNA-Intercalated Layered Double Hydroxides

The intercalation of DNA into layered double hydroxides (LDHs) has various applications, including drug delivery for gene therapy and origins of life studies. The nanoscale dimensions of the interlayer region make the exact conformation of the intercalated DNA difficult to elucidate experimentally. We use molecular dynamics techniques, performed on high performance supercomputing grids, to carry out large-scale simulations of double stranded, linear and plasmid DNA up to 480 base pairs in length intercalated within a magnesium-aluminum LDH. Currently only limited experimental data have been reported for these systems. Our models are found to be in agreement with experimental observations, according to which hydration is a crucial factor in determining the structural stability of DNA. Phosphate backbone groups are found to align with aluminum lattice positions. At elevated temperatures and pressures, relevant to origins of life studies which maintain that the earliest life forms originated around deep ocean hydrothermal vents, the structural stability of LDH-intercalated DNA is substantially enhanced as compared to DNA in bulk water. We also discuss how the materials properties of the LDH are modified due to DNA intercalation.

Adsorption of phenylalanine on layered double hydroxides: effect of temperature and ionic strength

In this work we report the adsorption of phenylalanine (Phe) on Magnesium Aluminum Layered Double Hydroxides (Mg–Al–CO3-LDH) at two different temperatures (298 and 310 K) and under two distinct ionic strength conditions (with and without the addition 0.1 M of NaCl). The adsorption isotherms exhibit the same profile in all conditions, and they only differ in the amount of removed Phe. At lower ionic strength, the isotherms are almost identical at both temperatures, except for the last points, where the increase in temperature causes a decrease in the amount of adsorbed Phe. An increase in ionic strength results in a decrease in Phe adsorption. The electrokinetic potential decreases as the amount of adsorbed Phe increases, and only positive values are observed. This indicates that the surface of the adsorbent is not totally neutralized and suggests that more Phe could be removed by adsorption. The presence of Phe on the solid is confirmed by FTIR spectra, which present the specific bands assigned to Phe. The hydrophobicity of the amino acid probably contributes to its extraction, thus enabling the removal of a great amount of Phe. In conclusion, LDH is potentially applicable in the removal of Phe from wastewater.

Synthesis of magnesium aluminium layered double hydroxides in reverse microemulsions

Reverse microemulsions have been used to control the nucleation and growth of magnesium aluminium layered double hydroxides (LDH). The reactants were prepared in aqueous solution and then dispersed in an isooctane–sodium dodecyl sulfate (DDS) microemulsion. Under these conditions magnesium aluminium LDH phases were obtained containing DDS as the charge-balancing interlayer anion. By adjusting the water : surfactant molar ratio (w = [H2O]/[Surf.]) of the microemulsion we were able to control the nucleation and growth of the LDH phases. In some cases LDH nanoplatelets exhibiting a uniform 14 Å monolayer thickness could be isolated and characterized by AFM.

Influence of nano-LDHs on char formation and fire-resistant properties of flame-retardant coating

Flame-retardant nano-coatings were prepared by adding flame-retardant nano-concentrates to APP/PER/EN coating. Dispersion morphology and stability principle of nano-size magnesium aluminum-layered double hydroxides (nano-LDHs) have been studied by using transmission electron microscopy (TEM). Relation of added amount of nano-concentrates in flame-retardant coating to flame-retardant properties for APP/PER/EN system has been studied by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), differential thermal analysis (DTA), thermogravimetry (TG) and fire protection test. It was indicated that nano-LDHs could catalyze the esterification reaction between ammonium polyphosphate and pentaerythritol, and IPN network formed by nano-size thermal-decomposed products of LDH could efficiently enhance char formation and structure of char layer. Only specific content (1.5%) of nano-LDHs in flame-retardant coating could efficiently improve its char layer structure and fire-resistant properties. Nano-LDHs (1.5%) greatly improve mechanical properties (bonding strength, bending resistance and resistance to freeze–thaw cycle) of flame-retardant coating.