Evaluation of ionic conductivity for Mg–Al layered double hydroxide intercalated with inorganic anions

This study demonstrates that humidity, temperature, and the interlayer anions influence ionic conductivities of Mg–Al layered double hydroxides (LDHs) intercalated with inorganic anions. Results show that Mg–Al LDH intercalated with Br^? exhibited the highest ionic conductivity among Mg–Al LDHs intercalated with CO₃^2?, Cl^?, Br^?, NO₃^? and SO₄^2?. Its ionic conductivity was 1.1 × 10^? 2 S cm^? 1 at 80 °C under 80% relative humidity. The electromotive force for the hydroxide ion concentration cell using Mg?Al CO₃^2? LDH showed the same behavior with that using an anion exchange membrane, indicating that Mg–Al CO₃^2? LDH can be a hydroxide ion conductor.     

Influence of nature of precursors on the formation and structure of Cu-Ni-Cr mixed oxides from layered double hydroxides

Analogous layered double hydroxides (LDHs) with the Cu²⁺/Ni²⁺/Cr³⁺ molar ratio of 1/2/1 on the brucite-like layers and interlayer anions (viz sulfate, nitrate and carbonate, respectively) were synthesized by a coprecipitation method. For the first time, the effects of interlayer anions on the structural properties of as-synthesized LDHs and resulting calcined products at 773 K were investigated by means of powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), simultaneous thermogravimetric and differential thermal analysis (TG-DTA), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The results indicate that the nature of interlayer anions involved within the hydrotalcite (HT)-like structure has a larger influence on the thermal stability of LDHs precursors. Calcination of well-crystallized LDHs leads to the formation of mixed metal oxides including CuO, NiO and Cu²⁺-, Ni²⁺- and Cr³⁺-containing spinel phases, the composition distributions of which obtained from LDHs precursors depend on the nature of interlayer anions, thus resulting in the difference of the reducibility of reducible metal species in the calcined LDHs. Moreover, the surface basicity of the calcined material, which is related to the different behaviour of LDHs precursors during the thermal decomposition depending on the interlayer anions, increases progressively following the order of calcined LDHs from sulfate to nitrate and carbonate.     

Assessment of thermal and antimicrobial properties of PAN/Zn-Al layered double hydroxide nanocomposites

Polyacrylonitrile-based Zn–Al layered double hydroxide composites (PAN/LDH) have been synthesised with different LDH content by in situ polymerisation technique. The nanocomposites were systematically studied by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), thermo gravimetric analysis (TGA), field emission scanning electron microscope (FE SEM), high resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS) and antibacterial activity measurement. The successful formation of exfoliated nanocomposite was inferred from the XRD patterns and HRTEM images. The thermal decomposition of PAN was enhanced upon nanocomposite (PAN/LDH) formation. The antimicrobial activity of PAN/LDH nanocomposites is evaluated for antibacterial activity against some clinically important bacterial pathogens and the bacterial growth is monitored at different percentage of LDH. The PAN/LDH composites displayed considerable antibacterial activity, on the contrary the virgin PAN did not possess any antibacterial activity. The likely electrostatic interaction among LDH layers with charged surface of bacterial cell is assumed to be responsible for antimicrobial activity. The prepared nanocomposite has appreciable thermal stability in combination with antibacterial activities by which the material is suitable for packaging and fabrication in textile application.     

Pulsed laser deposition of Mg–Al layered double hydroxide with Ag nanoparticles

Powdered layered double hydroxides (LDHs)—also known as hydrotalcite-like (HT)—compounds have been widely studied due to their applications as catalysts, anionic exchangers or host materials for inorganic or organic molecules. Assembling thin films of nano-sized LDHs onto flat solid substrates is an expanding area of research, with promising applications as sensors, corrosion-resistant coatings, components in optical and magnetic devices. The exploitation of LDHs as vehicles to carry dispersed metal nanoparticles onto a substrate is a new approach to obtain composite thin films with prospects for biomedical and optical applications. We report the deposition of thin films of Ag nanoparticles embedded in a Mg–Al layered double hydroxide matrix by pulsed laser deposition (PLD). The Ag-LDH powder was prepared by co-precipitation at supersaturation and pH = 10 using aqueous solutions of Mg and Al nitrates, Na hydroxide and carbonate, and AgNO₃, having atomic ratios of Mg/Al = 3 and Ag/Al = 0.55. The target to be used in laser ablation experiments was a dry pressed pellet obtained from the prepared Ag-LDH powder. Three different wavelengths of a Nd:YAG laser (266, 532 and 1064 nm) working at a repetition rate of 10 Hz were used. X-Ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and secondary ions mass spectrometry (SIMS) were used to investigate the structure, surface morphology and composition of the deposited films.     

Mg–Al LDH reinforced PMMA nanocomposites: a potential material for packaging industry

Poly-methylmethacrylate/Mg–Al layered double hydroxide (PMMA/LDH) based nanocomposites have successfully been synthesised with varying LDH content by in situ polymerisation technique and systematically studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT IR), UV-Visible spectroscopy and microscopic (FE SEM and HR TEM) analysis. In particular, thermogravimetric analysis (TGA) and gas barrier properties measurement were carried out to assess the suitable application of these materials. The thermal property of PMMA/LDH composites was compared with neat PMMA and an enhancement in thermal stability was noticed with gradual increase in LDH content in the composite. Gas permeability measurement data showed significant decrease in oxygen permeability value of the PMMA/LDH nanocomposites in comparison to the pristine PMMA. Enhancement in thermal stability along with significant reduction in oxygen permeability of PMMA upon composite formation indicate the possible application of these materials in packaging industries.     

Synthesis,characterization and electrochemical study of layered double hydroxides intercalated with 2-thiophenecarboxylate anions

The synthesis, characterization, and electrochemical study of the Zn(II)–Al(III) and Zn(II)–Cr(III) Layered Double Hydroxides (LDHs) containing 2-thiopenecarboxylate as the interlayer anions are described. The LDHs were prepared by the constant pH coprecipitation technique followed by hydrothermal treatment for 72 h. The materials were analyzed by PXRD, FT-IR, ¹³C CP-MAS, EDX, TEM, and CV. The presence of the organic heterocyclic anions was confirmed by FT-IR and the related solid-state ¹³C NMR data strongly suggested that these were dimerised during coprecipitation. Accordingly, the basal spacing found by the X-ray technique was ∼15.3 Å, a distance coincident with the formation of bilayers of the intercalated anions. The structural organization of all the new materials was greatly enhanced by hydrothermal treatment, as shown by PXRD. The improved organization of the bilayered structures had a strong influence in the electrochemical behaviour of clay-modified electrodes produced with these materials, such as the diminished resistance to the ionic flow through the LDHs films.     

High‐pressure Raman spectroscopic and other structural studies of hydrotalcites containing intercalated dicarboxylic acid anions

The results of pressure‐tuning Raman spectroscopic, X‐ray powder diffraction and solid‐state ¹³C‐NMR studies of selected dicarboxylate anions intercalated in a Mg–Al layered double hydroxide lattice are reported. The pressure dependences of the vibrational modes are linear for pressures up to 4.6 GPa, indicating that no phase transitions occur. The interlayer spacings show that the oxalate, malonate and succinate dianions are oriented perpendicular to the layers, but the glutarate and adipate are tilted. The solid‐state ¹³C‐NMR spectra of these materials show full chemical shift anisotropy and, therefore, the anions are not mobile at room temperature. Copyright © 2011 John Wiley & Sons, Ltd.     

Magnetic Nanocomposites Formed by FeNi3 Nanoparticles Embedded in Graphene. Application as Supercapacitors

A general family of magnetic nanocomposites formed by FeNi₃ ferromagnetic nanoparticles (NPs) embedded in a graphitized carbon matrix is reported. The soft chemical approach used relies on the catalytic effect of the NPs resulting from the thermal decomposition of the layered double hydroxide precursor, which acts as a multilayered nanoreactor enabling the formation of a range of carbon nanoforms (CNFs). This is followed by acid treatment of the as‐prepared nanocomposites to isolate the different CNFs formed. These range from carbon nano‐onions to graphene depending on the temperature of the thermal decomposition. This synthetic process paves the way for the rational design of metal–carbon nanocomposites with controllable composition as precursors of nanocarbons or even graphene. The coexistence of metal NPs and nanostructured carbon is a major source of applications. As a proof of concept, the electrochemical performance of these metal–carbon hybrid supercapacitors is studied under high discharging current densities and they exhibit high values of specific capacitance and excellent rate capabilities.     

Nanomaterials based upon silylated layered double hydroxides

A class of nanomaterials based upon the surface modification of layered double hydroxides (LDHs) have been synthesized by grafting silanes onto the surfaces of the LDH. By in situ coprecipitation, the surfaces of a LDH have been modified through grafting of 3-aminopropyltriethoxysilane (APTS) using the anionic surfactant Na-dodecylsulfonate (SDS). The synthesized nanomaterials were characterized by X-ray diffraction (XRD), attenuated total reflection Fourier-transform infrared spectroscopy (ATR FTIR), thermogravimetry (TG) and transmission electron microscopy (TEM). The grafted LDH (LDH-G) displays distinct XRD patterns proving the obtained materials are a new and different phase. The FTIR spectra of the silylated hydrotalcite show bands attributed to Si-O-M (M = Mg and Al) vibration at 996 cm⁻¹, suggesting that APTS has successfully been grafted onto the LDH layers. The TG curves prove the grafted sample has less M-OH concentration and less interlayer water molecules, as indicated by the M-OH consumption during the condensation reaction between Si-OH and M-OH on the LDH surface. The grafted sample displays a ribbon-like thin sheet in the TEM images, with the lateral thickness estimated as 2.5 nm.     

Layered double hydroxides as heterogeneous catalyst systems in the cross-coupling reactions: an overview

Molecular Diversity - Layered double hydroxides (LDHs) are recognized as two-dimensional (2D) clay materials, which comprise the interlayer anions and host layers with a positive charge...     

Near-infrared spectroscopy of palladium-containing layered double hydroxides used as catalysts

Three catalysts consisting of layered double hydroxides (LDHs) of magnesium and aluminum, and containing palladium in various forms, were synthesized and subsequently characterized by mid- and near-infrared spectroscopies. The results thus obtained are compared with those for a pure Mg/Al layered double hydroxide. The spectra for the Pd-containing LDHs (particularly the strength of the bands) were found to depend on the particular palladium form present. As a rule, the mid-infrared spectra contained a strong, broad band at 3800-2500 cm⁻¹ due to stretching vibrations of the different types of hydroxyl groups present in the solids and another signal at ca. 1370 cm⁻¹ due to the presence of carbonate ions in the interlayer region. These signals were the strongest in the near-infrared spectra, which were also quite similar, roughly, for all solids.     

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

Layered double hydroxides (LDHs) are a class of artificially constructed materials that have potential applications in a wide range of fields, including biomedical research and drug development. In this study, we have successfully intercalated folic acid into LDH using two different approaches: co-precipitation and ion exchange. The resultant LDH-folic acid constructs were then characterized by powdered sample X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM), thermogravimetry and differential thermal analysis (TG-DTA). XRD data demonstrated that folic acid molecules remained intact and stable between the hydroxide layers in LDH particles constructed by both co-precipitation and ion-exchange methods, with interlayer spacings of 15.3 and 16.0 Å, respectively. Particle size and surface topography were also determined using TEM. Cytotoxicity test revealed that neither LDH nor LDH-folic acid nanohybrids were toxic to the cell line 293T, suggesting that they can be used as a safe and noncytotoxic drug delivery system. Furthermore, the buffering effect of the intercalated LDH was evaluated. This work provides fundamental insights and technical details for utilizing biofunctional molecules that can form nanobiohybrid particles.     

三元LDH的改性及去除酸性橙II的光谱分析研究

吸附法由于具有效率高、成本低、无毒、简单等优点，具为最常见的废水处理方法。采用吸附法的关键是吸附剂的选择和制备。层状氢氧化物(LDH)作为一类新型吸附剂，拥有特殊的层状结构、层板元素的可调变性、层间阴离子的可交换性，近期备受关注，但其吸附能力的提升仍是亟需研究的问题。利用均苯四甲酸(PA)对三元层状氢氧化物(Ca-Mg-Al-LDH)进行插层改性，制备出新型的芳香酸阴离子改性层状氢氧化物(PA-LDH)，对其进行煅烧得到煅烧产物(PA-LDO)，并结合紫外分光光度法(UV-Vis)研究其对酸性橙II的吸附性能。通过红外光谱(FTIR)和氮气吸附-脱附实验对其进行结构表征。结果发现，PA-LDH相比LDH在1 717 cm-1处出现了一个新的峰，归属为ν(C═O)，且相对PA的C═O峰(1 668 cm-1)向高频方向移动，这可能是由于PA之间形成的缔合体被破坏，表明PA可能插层进入了LDH的间层。相比PA-LDH的红外光谱谱图，可以发现PA-LDO在3 000 cm-1附近的弱峰消失了，表明层间阴离子在煅烧过程中被破坏，但是在875和723 cm-1处与M—O和M—OH(M=Ca，Mg和Al)振动相对应的峰仍然存在，表明煅烧处理后其相似的结构依然得到了保持。通过氮气吸附-脱附实验测得PA-LDH和PA-LDO的比表面积分别为15.934 1和119.401 0 m2·g-1，说明在煅烧后，其比表面积增大，因此PA-LDO可能具有更好的吸附效果。以阴离子染料酸性橙Ⅱ为目标污染物，在pH 7.0，吸附剂用量5 mg，波长为484 nm的条件下，通过UV-Vis分析手段，分别考察了吸附时间、染料初始浓度等对PA-LDH、PA-LDO吸附性能的影响。结果表明，PA-LDH和PA-LDO对酸性橙Ⅱ的Q_max分别为561.322和1 401.639 mg·g-1，高于目前文献所报道的Q_max值。通过吸附等温实验，发现PA-LDH和PA-LDO对酸性橙II的吸附基本符合Langmuir模型，即单分子层吸附为该吸附过程的主导过程，且理论最大吸附容量分别可为588.235和1 428.571 mg·g-1，与上述实验值相接近，这说明制备的芳香酸阴离子改性层状氢氧化物对阴离子染料具有较好的吸附性能，在治理染料废水中具有一定的应用前景。     

Fluorescence of Mg-Al-Eu Ternary Layered Double Hydroxide Sensitivity to Phenylalanine

We reported for the first time the fluorescence sensitivity of a Mg-Al-Eu ternary layered double hydroxide (LDH) to phenylalanine (Phe). As shown in fluorescent spectra, the red emissions resulted from ⁵D₀-⁷F_J transition (J = 1, 2) of Eu³⁺ were quenched by Phe, and a strong peak around at 492 nm emerged. A strong interaction between the Mg-Al-Eu LDH and Phe was manifested by markedly different chemical shift positions of the Mg 2p, Al 2p, Eu 4d, O 1 s, and C 1 s peaks in the XPS spectra from those of the LDHs. These results showed that the charges transfer from Phe to the trivalent Eu ions may be taken place.     

Adsorption and photodegradation properties of anionic dyes by layered double hydroxides

The adsorption and photodegradation behavior of methyl orange (MO) and fast green (FG) over ZnAl- and MgAl-based layered double hydroxide (LDH) adsorbents have been examined. ZnAl-LDHs were prepared with Zn/Al ratios of 2 to 4 by co-precipitation at pH 8. The ZnAl-LDHs and a commercial MgAl-LDH with a Mg/Al ratio of 3 were evaluated for their ability to adsorb MO and FG and for the photodegradation behavior of these dyes under UV irradiation. Structure analysis of the LDH-dyes-adsorbed complexes revealed that the adsorption produced two types of structures, an intercalation complex for MO and a surface-adsorbed complex for FG. The maximum adsorption of MO on the LDHs was significantly higher (more than tenfold) than FG. Results indicated the adsorption isotherms for the retention of both dyes by ZnAl- and MgAl-LDHs could be fitted to a Freundlich equation, showing a higher affinity for dyes on MgAl-LDH compared to those on ZnAl-LDH. The catalytic degradation ability of dye-LDH complex solid films on a quartz plate was superior to pure dye films under UV irradiation. The FG non-intercalated LDH complexes showed much faster photodegradation under UV irradiation than the MO-intercalated LDH complexes, which pointed to the important role of the LDH materials containing sensitized dyes in enhancing the generation of labile hydroxyl ions from the hydrophilic LDH surface.     

Utilization of Mg2Al–layered double hydroxide as an effective sequestrator to trap Cu(II) ions from aqueous solution impacted by water quality parameters

Recently, Mg₂Al–layered double hydroxide (Mg₂Al–LDH) has been extensively studied as promising candidates to trap metal ions due to their high complexation and adsorption capacity. Herein, Mg₂Al–LDH was utilized as an effectiveness sequestrator to trap Cu(II) ions from aqueous solution by an adsorption process using batch technique under ambient conditions. The results showed that Cu(II) adsorption on Mg₂Al–LDH increases with pH increasing and maintains a high level at pH>7.0. The adsorption of Cu(II) was obviously affected by ionic strength at low pH, which was not dependent on ionic strength at high pH. The presence of HA or FA promotes the adsorption of Cu(II) on Mg₂Al–LDH at low pH values, while reduces the adsorption of Cu(II) at high pH values. The adsorption isotherms of Cu(II) on Mg₂Al–LDH at three different temperatures were simulated by the Langmuir, Freundlich, and Dubinin-Radushkevitch (D–R) models very well. The thermodynamic parameters were determined from the temperature-dependent adsorption, and the results showed that Cu(II) adsorption on Mg₂Al–LDH was exothermic and the process was favored at high temperature. The results suggest that Mg₂Al–LDH is suitable as a sorbent material for the recovery and attenuation of Cu(II)-polluted wastewater.     

Electric quadrupole interaction of 100Rh in antimony, hafnium and rhenium

The effects of the Mg(II)/Fe(III) ratio on the structure and Fe microenvironments in MgFe LDH substances were investigated. The LDHs were prepared by the co-precipitation method with Mg(II)/Fe(III) ratios from 2:1 to 6:1. The materials were characterized by ⁵⁷Fe Mössbauer spectroscopy and powder X-ray diffractometry. The ⁵⁷Fe Mössbauer spectra exhibited asymmetric doublet corresponding to high-spin Fe(III) microenvironments in all LDH structure. It was found that the quadrupole splitting decreased with increasing Mg(II)/Fe(III)ratio reflecting change in the electric field gradient due to the incorporation of different amounts of iron into the Mg-containing layers.     

Synthesis and photochemical properties of zinc–aluminum layered double hydroxide/organic UV ray absorbing molecule/silica nanocomposites

Organic ultraviolet (UV) ray absorbents have been used as sunscreen materials, but may pose a safety problem when used at high concentration. In order to prevent direct contact of organic UV ray absorbent to the human skin several organic UV absorbents such as 4-hydroxy-3-methoxybenzoic acid, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, 4-hydroxy-3-methoxycinnamic acid, 4,4′-diaminostilbene-2,2′-disulfonic acid, p-aminobenzoic acid and urocanic acid were intercalated into Zn₂Al layered double hydroxides (Zn₂Al-LDHs) by anion-exchange and/or co-precipitation reaction. Thereafter, the obtained nanocomposites were coated with amorphous silica. Significant amounts (20–40 mass%) of organic UV absorbers were intercalated as univalent and/or divalent anions. The UV ray absorption ability of the organic UV absorbents increased and their catalytic activity for the air oxidation of castor oil greatly decreased when they were intercalated into the interlayer spaces of the Zn₂Al-LDHs. The deintercalation of organic molecules from LDHs by the anion exchange reaction with carbonate ion could be greatly depressed by coating the nanocomposite powder with amorphous silica.     

有机硼酸盐插层Zn/Al-LDH的红外和拉曼光谱特征

研究了碳酸根和硼酸根的二元锌铝水滑石的X射线衍射,拉曼和红外光谱特征。采用一步水热共沉淀法,分别制得结晶良好的层间为碳酸根和硼酸根的二元锌铝水滑石。X射线衍射分析显示,硼酸根插层后水滑石（003）特征衍射峰向小角度移动,峰型尖锐,水滑石通道高度从0.28 nm增加至0.42 nm;红外光谱和拉曼光谱特征表明,硼酸根插层后,碳酸根的红外和拉曼特征峰消失。层间硼酸根以B₃O₃(OH)-₄,B₄O₅(OH)2-₄和B(OH)-₄三种形式存在。随层间离子的不同,与羟基相关的红外光谱和拉曼光谱峰位均有所改变。研究结果表明以硼酸三正丁酯为插层剂,可获得单一相、纯度较高的硼酸根型锌铝水滑石,拉曼光谱可准确探测水滑石层间阴离子变化对其结构和性能的影响。     

Self-assembly of metal–organic frameworks and graphene oxide as precursors for lithium-ion battery applications

We fabricated composites of Fe₂O₃/reduced graphene oxide as lithium-ion batteries anode material with controlled structures by employing self-assembly of metal–organic frameworks (MOFs) and polymer-functionalized graphene oxide as precursors. By electrostatic interaction, the negatively charged MOFs, Prussian Blue (PB), are assembled on poly(diallyldimethylammonium chloride) (PDDA)-functionalized graphene oxide (positive charge). Then the PB cubes become FeOOH nanosheets when treated with sodium hydroxide. Upon further annealing, the FeOOH nanosheets transform to Fe₂O₃ nanoparticles while the graphene oxide become reduced graphene oxide simultaneously. It was found that the composites have good performance as anode of lithium-ion battery. This work shows a new way for self-assembling MOFs and 2D materials.