Hyperfine interaction in Zn–Al layered double hydroxides intercalated with conducting polymers

: In this study the preparation of layered double hydroxide (LDH)/sugar nanocomposites using an exfoliated MgAl-lactate LDH (Mg: Al = 3:1) and a sugar (sucrose and maltose) as precursors is described. The products have been characterised by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The properties of the composite materials have been further studied using differential scanning calorimetry (DSC). The expanded interlayer spacing of the lactate LDH suggests the intercalation of lactate ions within the gallery region. Stirring of the MgAl-lactate LDH in water for 24 hours at room temperature resulted in a clear colloidal dispersion. Upon solvent evaporation, the resulting material consisted of a disorganized restacked LDH phase. The most significant evidence for the formation of nanocomposites from the exfoliated clay materials is suggested by the absence of reflections associated with the LDH in the PXRD patterns. DSC results suggest that the glass transition temperatures of the composite materials with 5%, 10% and 20% LDH loading are superior to the parent maltose. Therefore, the LDH nanolayers give the LDH filled sugar nanocomposites better thermal stability than the pristine sugar, thus these composites could be used as drug excipients in the pharmaceutical industry. Keywords : Amorphous sugar, exfoliation, layered double hydroxides, nanocomposites, thermal stability. Doi: 10.4038/jnsfsr.v39i2.3171 J.Natn.Sci.Foundation Sri Lanka 2011 39 (2): 113 - 119

Zn–Cr layered double hydroxide: Visible light responsive photocatalyst for photocatalytic degradation of organic pollutants

Study on the sorption–desorption–regeneration performance of Ca-, Mg- and CaMg-based layered double hydroxides for removing phosphate from water

Two different approaches to synthesizing Mg–Al-layered double hydroxides as folic acid carriers

Mechanism of boron removal and stabilization by in-situ formation of layered double hydroxides: Insight from spectroscopy and DFT studies.

The aim of this work is to explore the possibility of use of layered double hydroxides (LDH) as a photocatalyst for the selective oxidation of toxic nitrogen oxides, NO and NO2 (NOx ), to nitrate. Recent studies suggest that layered double hydroxides could be suitable for this aim. LDH consists of brucite-like layers, with a partial MII/MIII substitution, which causes a positive charge in the layer. The excess of charge generated is replaced by the intercalation of anions in the interlayer space. LDHs are layered materials with general formula [MII1-xMIIIx(OH)2]Xn-x/n·nH2O where MII = Mg2+, Zn2+, etc; MIII = Al3+, Fe3+, etc; and Xn- an interlayer anion which could be a great variety of inorganic and organic species depending on the preparation method. Calcination at 500 ºC converts the LDHs into mixed oxides, rehydration of which restores the original LDH structure by interaction anions from aqueous solution (reconstruction). Thus, we synthesized MgAl-CrO4 LDH by reconstruction method, from the precursor MgAl-CO3 with Mg/Al ratio of 3, obtained by coprecipitation method, and compared these two LDH as photocatalysts for decomposition of NOx gases (deNOx). Techniques such as XRD, FT-IR and UV-Vis spectroscopy have been used to characterize the samples. Compared to the pristine LDH system, the textural characteristics, optical and electronic properties of chromium containing LDH samples exhibited a better harvesting of sunlight and the highest specific surface area (> 50 m2. g-1). In addition, the photocatalytic results showed high efficiency of LDH (60%) towards the complete oxidation of NOx.

A new series of Cu/Zn/Mn/Fe/Al hydrotalcite-like layered double hydroxides (LDHs) with the Cu/(Zn + Mn)/(Fe + Al) atomic ratios of 1/1/1 in synthesis mixture were synthesized by the coprecipitation method. The chemical composition of multicomponent precursors was identified by chemical analyses. The thermal stability, structure, and texture changes of these as-synthesized LDHs were studied by in situ high-temperature X-ray diffraction (HT-XRD), thermogravimetric-differential thermal analysis combined with mass spectrometry (TG-DTA-MS) in different atmosphere, transmission electron microscopy (TEM), and N2 adsorption–desorption experiments. The results exhibit that the incorporation of Fe3+ and Mn2+ into the lattices of Cu-containing LDHs in sequence decreases the crystallinity, water content, and thermal stability of corresponding compounds, and the thermal treatment of LDHs results in the formation of thermodynamically stable composite metal oxide associated with a small amount of simple metal oxide and also changes in texture of calcined solid. Under mild experimental conditions (atmospheric pressure and 25 °C), the catalytic liquid-phase oxidation of aqueous phenol solutions is related to the composition, oxidation states, composite forms and synergy of transition metal cations in calcined LDHs, and calcined LDH with Cu/Zn/Mn/Fe/Al atomic ratio of 1/1/0/0.3/0.7 at 500 °C achieves the highest conversion of phenol mainly owing to the formation of a larger amount of composite metal oxide with some residual carbonate in the solid.

Synthesis of Cu-Al layered double hydroxides from aluminum saline slags

Ca–Al–NO3 layered double hydroxides (LDHs) with its layer structure presents potential to inhibit the ion transport process in the host matrix due to the increased tortuosity. In this study, the transport properties of lightweight concrete containing Ca–Al–NO3 layered double hydroxides (LDHs) are investigated. A co-precipitation method is applied to synthesize the Ca–Al–NO3 LDHs and the effect of the synthesis environment on the size and particle shape is investigated. The synthesized Ca–Al–NO3 LDHs are analytically characterized by XRD, SEM and FTIR analyses. A lightweight concrete (LWC) is designed applying the modified Andreasen and Andersen model and a natural expansive pumice as lightweight aggregates. The synthesized LDHs are applied to the LWC with a fixed volume amount but different sizes. The effect of the LDHs on the mechanical properties and transport properties of the designed LWC are investigated and furthermore the effect of the size of the LDHs on these properties is discussed.

Layered Double Hydroxides (LDHs) have been studied by many researchers for their interesting properties such as ion exchangers, adsorbents, polymer stabilizer, catalyst, and so on. LDHs are well known as anionic clays include anion species and water molecules in the interlayer which consist of positively charged metal hydroxide layers. It was reported that some types of LDHs prepared by co-precipitated method have high OH- conductivity and high performance as electrolyte for Alkaline Fuel Cells (AFCs)1). On the other hand, it is necessary to develop a newly industrial LDH synthesis method which enables to synthesize the particle and the composition uniformly. Homogeneous precipitation method with Urea is one of the general and promising LDH synthesis method to prepare the uniform LDH, in which pH controlled by hydrolysis of Urea. However only CO3 2- type LDHs are formed by the method. Therefore, we developed the new type synthesis named “decarboxylation method” that enables to synthesize LDH with high crystallinity and selective anion species in inner layer from precursor compounds in one pot. Prepared samples were measured by ICP and XRD to determine the compositions and structures, respectively, and observed by FE-SEM. Several intercalated anion (CO3 2-, SO4 2-, NO3 -, and Cl-) type M(II) (Zn2+, Co2+, and Ni2+)-Al(III)LDHs were successfully prepared by the decarboxylation method with highly crystallinity and uniform particle size distribution. The ionic conductivities on prepared LDHs were measured by the AC impedance method. Each NO3 - type LDH has remarkably higher ionic conductivity than another type LDHs. The NO3 - type Zn-Al LDH has highest conductivity than another cation type LDHs, and its conductivity is via 16 mS/cm at 80 oC under R.H.80%. 1) Y. Furukawa, K. Tadanaga, A. Hayashi, and M. Tatsumisago, Solid State Ionics, 192, 185-187 (2011).

In the present work, the hydrotalcite-like materials known as layered double hydroxides (LDHs) were synthesized. The Ni–Al and Ni–Fe materials with different Ni/Fe ratio were obtained by coprecipitation method at variable pH. The LDH structure was verified by X-ray diffraction, Fourier transform infrared, and Raman spectroscopy. No secondary extra phases were observed for any material. The electronic properties were evaluated by UV–vis spectroscopy, while the magnetic ones were followed by electron paramagnetic resonance (EPR). The results suggested that sample H/Ni–Fe2 (Ni/Fe = 2) has a ferrimagnetic behavior as a result of the combined action of NiII–OH–NiII, FeIII–OH–NiII, and FeIII–OH–FeIII pairs across the layers and ferromagnetic interactions operating between layers. Furthermore, the material H/Ni–Fe1 (Ni/Fe = 1.5) showed a combination of paramagnetic and ferromagnetic interactions which favors a superexchange interaction among metal centers through the OH bridges across the cationic sheets; the su...

High-entropy hexacationic layered double hydroxides of the cationic composition MgNiCoAlFeY were obtained by five different methods: coprecipitation at constant pH, coprecipitation at constant or variable pH followed by hydrothermal treatment, microwave assisted solvothermal, hydrothermal, mechanochemical method followed by hydrothermal treatment. All samples, except for the one obtained by coprecipitation at variable pH, are phase pure, with a uniform distribution of cations. The samples were characterized by X-ray diffraction, infrared spectroscopy, Raman spectroscopy, transmission electron microscopy. Thermal transformations of the samples were studied. The synthesis method affects the characteristics of the samples. The sample obtained by hydrothermal synthesis at variable pH possesses magnetic properties. The largest particles and those morphologically close to the hexagonal shape are formed by coprecipitation followed by hydrothermal treatment. The sample obtained by the microwave assisted solvothermal method is characterized by lower thermal stability.

The role of dispersion of LDH in fire retardancy: The effect of different divalent metals in benzoic acid modified LDH on dispersion and fire retardant properties of polystyrene– and poly(methyl-methacrylate)–LDH–B nanocomposites

Systematic screening of layered double hydroxides for phosphate removal and mechanism insight

In situ oligomerization of 2-(thiophen-3-yl)acetate intercalated into Zn2Al layered double hydroxide