Solution decomposition of the layered double hydroxide (LDH) of Zn with Al

The layered double hydroxides (LDH) of Zn with Al containing intercalated CO₃²⁻ and NO₃⁻ ions undergo solution decomposition to yield a highly crystalline oxide mixture comprising ZnO and ZnAl₂O₄ at temperatures as low as 150–180 °C under hydrothermal conditions. In contrast solid-state decomposition takes place at a much higher temperature (240–315 °C) in air. Solution decomposition is not only guided by the low octahedral crystal field stabilization energy of Zn²⁺ ions, a factor that also affects solid-state decomposition, but also by solubility considerations. The LDHs of Mg and Ni with Al do not undergo solution decomposition.     

Synthesis and characterization of a UV absorbent-intercalated Zn-Al layered double hydroxide

Zn-Al-layered double hydroxides (LDHs) containing the organic anion of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (HMBA), a highly efficient UV absorber, have been synthesized by reaction in air of HMBA with an LDH-carbonate precursor obtained by a process involving separate nucleation and aging steps. The structural properties, photo- and thermal stability of the resulting Zn-Al-HMBA-LDHs were characterized by PXRD, FT-IR and UV-visible spectroscopy and laser particle-size analysis. The results obtained indicated that Zn-Al-HMBA-LDHs synthesized by this method were relatively highly crystalline and had a narrow distribution of particle size. Intercalation of HMBA in the LDH interlayer galleries resulted in an enhanced photo- and thermal stability without affecting its UV absorption capacity; this shows that the hybrid HMBA-LDH phase has potential applications as a UV absorber.     

Synthesis and characterization of 5-fluorocytosine intercalated Zn-Al layered double hydroxide

In this paper, the intercalation of 5-fluorocytosine (5-FC) into a layered inorganic host, Zn-Al layered double hydroxide (LDH), has been carried out using coprecipitation method to obtain 5-FC/LDH nanohybrids. The intercalated amount (A_In) of 5-FC into the LDH is remarkably dependent on the molar ratio (R_F/M) of 5-FC to metal ions and the pH of coprecipitation system. The morphology of 5-FC molecules in 5-FC/LDH nanohybrids is dependent on the A_In. It is interestingly found that the morphology of the nanohybrid particles may be changed with the increase of R_F/M from hexagonal plate particles to threadlike particles. The in vitro drug release from the nanohybrids is remarkably lower than that from the corresponding physical mixture and pristine 5-FC at either pH 4.8 or pH 7.5. In addition, the release rate of 5-FC from the nanohybrid at pH 7.5 is remarkably lower than that at pH 4.8, this is due to a possible difference in the release mechanism. The obtained results show these drug-inorganic nanohybrids can be used as a potential drug delivery system.     

Morphology and fracture behaviour of polyethylene/Mg-Al layered double hydroxide (LDH) nanocomposites

Fracture behaviour of polyethylene (PE)/Mg-Al layered double hydroxide (LDH) based nanocomposites has been studied by essential work of fracture (EWF) approach. Transmission electron microscopy (TEM and X-ray diffraction (XRD) analysis have been used to investigate the morphological features of these nanocomposites. A maximum in the non-essential work of fracture was observed at 5 wt.% LDH demonstrating enhanced resistance to crack propagation compared to pure PE. Morphological analyses of the nanocomposites show that the dispersed LDH platelets are partially exfoliated and also forms clusters with polymer chains remaining entrapped within. Rheological analyses show that the typical low-frequency Newtonian flow behaviour, as observed in unfilled polymer, shifts to shear-thinning behaviour with increasing LDH concentration. At 5 wt.% LDH a ductile-to-brittle transition has been observed. Fracture surface investigation by SEM reveals the arresting of the plastic crack growth by the LDH particle clusters, which is more significant at 5 wt.% LDH content. At higher LDH concentrations, the number of such particle clusters increases causing decrease in the average distance between them. As a result large-scale plastic deformation of the matrix at higher LDH concentration is effectively arrested favouring small strain failure and this in turn reaffirms the possible existence of a ductile-to-brittle transition. The study in general reveals that the resistance against crack initiation (essential work of fracture: EWF) and crack propagation (non-essential work of fracture: βw_p) in these nanocomposites are structurally correlated with the matrix behaviour and the morphology (state of LDH particle dispersion) respectively.     

From Zn-Al layered double hydroxide to ZnO nanostructure:Gradually etching by sodium hydroxide

Zn-Al layered double hydroxide(LDH) was used as precursor to produce ZnO nanostructures through dissolution of aluminum hydroxide in caustic soda.The Zn-Al LDH could transform into different nanostructures of ZnO on LDH nanosheets and even pure ZnO nanorods under various NaOH concentration.The formed ZnO nanorods vertically aligned on both LDH sides.UV-vis diverse reflectance spectra show that the obtained ZnO nanorods have a band gap of approximately 3.05 eV.Such ZnO/LDH nanostructures might be used as photocatalyst in the organic pollutant decomposition.     

Facile and large-scale production of ZnO/Zn-Al layered double hydroxide hierarchical heterostructures

ZnO/Zn-Al layered double hydroxide (ZnO/Zn-Al LDH) hierarchical architecture, a new type of ZnO-based heterostructure, has been synthesized directly on an Al substrate via a facile solution phase process. The firecracker-like heterostructures consist of uniform ZnO nanorods orderly standing at the edges of two-dimensional (2D) surfaces of Zn-Al LDH nanoplatelets. Experimental result obtained from the early growth stage indicates that the underlying Zn-Al LDH nanoplatelet arrays are well constructed with their (00l) planes perpendicular to the surface of Al substrate. We propose that the "edge effect" of Zn-Al LDH and the "lattice match" between ZnO and Zn-Al LDH are vital to the growth of such heterostructures. The effects of total solution volume and NH3.H2O concentration on the formation of heterostructures are investigated. It is found that other LDH-based complex structures can also be achieved controllably by varying the mentioned experimental factors. Our work is the first demonstration of fabricating intricate ZnO/Zn-Al LDH heterostructures as well as well-defined Zn-Al LDH arrays on an Al substrate, for which several promising applications such as optoelectronics, biosensors, and catalysis can be envisioned.     

Concomitant synthesis of highly crystalline Zn-Al layered double hydroxide and ZnO: phase interconversion and enhanced photocatalytic activity

Metal oxide/hydroxide with hierarchical nanostructures has emerged as one of the most promising materials for their unique, attractive properties and feasibility of applications in various fields. In this report, a concomitant synthesis of crystalline zinc aluminum layered double hydroxide (ZnAl-LDH) nanostructure and ZnO is presented using Al substrate as template. Studies on interconversion of ZnO to LDH phase in bulk solution under hydrothermal conditions produced Al-doped ZnO (AZO) in one case, and in other, it improves the crystallinity of LDH film templated on Al substrate. In presence of Al salt, the self-limiting growth nature of plate LDH turned to non-self-limiting. Materials obtained during phase transition, AZO in bulk solution and crystalline porous ZnAl-LDH on substrate, have been demonstrated as effective photocatalysts for decomposition of congo red in aqueous medium.     

Preparation of ultrathin membranes by layer-by-layer deposition of layered double hydroxide (LDH) and polystyrene sulfonate (PSS)

Nanofilms were prepared by consecutively alternating adsorption of Mg–Al (2:1) layered double hydroxide (LDH) and polysodium 4-styrenesulfonate (PSS). The charge density of oppositely charged materials strongly affect film properties like thickness and ordering. The specific charge of the colloid particles (LDH) and macromolecules was determined with the particle charge detector. The sequential build-up of the thin films was followed by spectrophotometry and X-ray diffraction. The surface morphology of the multilayers was characterized by atomic force microscopy. The influence of the charge density of the applied materials and of the mass ratio of LDH/PSS on the film thickness were studied.     

Unique layered double hydroxide morphologies using reverse microemulsion synthesis

We report the first controlled synthesis of a layered double hydroxide (LDH) in a water-in-oil reverse microemulsion system. This synthesis of Mg2Al-LDHs was carried out in the reverse microemulsion of NaDDS (sodium dodecyl sulfate)-water-isooctane with water/surfactant molar ratio = 24. This enables us to obtain nanometer sized LDH platelets typically with a 40-50 nm diameter and 10 nm thickness. Further modification of the reverse microemulsion using triblock copolymers during crystallization allowed us to express different growth orientations of the LDH structure. These data show that the aspect ratio of LDHs can be flexibly adjusted over a wide range.     

基于层状氢氧化物衍生复合氧载体的生物质化学链气化实验研究

通过低饱和共沉淀法合成了类水滑石结构的层状氢氧化物(Layered Double Hydroxide,LDH)前驱体,经煅烧获得衍生Cu/Al/Zn、Cu/Al/Ni、Cu/Al/Ni/Zn高分散复合氧载体。采用XRD、XRF、H2-TPR、SEM及BET等分析手段对氧载体的结构及反应性能进行了表征,并通过固定床反应器开展了氧载体与生物质化学链气化实验。结果表明,合成的三种前驱体都具有典型的水滑石特征衍射峰,且层板稳定。Cu/Al/Zn前驱体层间厚度为0.264 2 nm,Ni2+引入后,层间距减小。前驱体煅烧后形成的复合氧载体中元素含量与制备试剂基本一致。氧载体中Zn、Ni元素的引入可提升Cu O的反应活性,降低H2还原的反应温度,Zn元素与Cu具有更好的协同作用。Cu/Al/Ni/Zn氧载体在固定床化学链气化中具有较好的碳转化率和气体产率,其碳转化率为82.03%。反应后氧载体比表面积为5.995 m2/g,具有较好的可再生性与抗烧结性,是生物质化学链气化反应较为理想的氧载体。     

Stoichiometric synthesis of a pure ferrite from a tailored layered double hydroxide (hydrotalcite-like) precursor

Calcination of a layered double hydroxide precursor containing MgII, FeII and FeIII cations with an Mg2+:(FeII + FeIII) ratio of 0.5 affords a pure ferrite spinel, MgFe2O4, which has a higher saturation magnetization than samples of the same material produced by conventional ceramic routes.     

Water-swellable MgAl-LDH (layered double hydroxide) hybrids: synthesis, characterization, and film preparation

LDH hybrids were synthesized from Cl (-)MgAl-LDHs by anion exchange with short-chain alkyl carboxylate intercalants: C n H 2 n+1 COO (-) ( n = 0-3). Among them, LDH3 (LDH with Mg/Al = 3) hybrids containing acetate ( n = 1) and propionate ( n = 2) exhibited swelling behavior in water. The action of water on acetate-LDH3 (AcO-LDH3) and propionate-LDH3 (PrO-LDH3) led to semitransparent suspensions via a viscous gel state. From the X-ray diffraction profiles of the gels, only a broad feature was observed by the loss of the sharp reflections. The reflections reappeared for the films obtained by drying the gel, indicating the restacking of the LDH nanosheets into the original stacked structure. Observation using atomic force microscopy revealed delaminated nanosheets with a thickness of 1.1-1.5 nm with the same morphological features as the starting LDHs. XRD measurement and AFM observation supported the formation of unilamellar LDH sheets. Semitransparent self-standing LDH films were obtained by peeling off the films formed on a PE (polyethylene) substrate by drying the colloidal suspension thereon. The thickness of the obtained flexible films ranged from 10 to 25 microm, and they could be anion exchanged with inorganic and organic anions in the film state.     

Hollow nanoshell of layered double hydroxide

Hollow nanoshells of layered double hydroxide (LDH) have been fabricated using exfoliated LDH nanosheets as a shell building block and polystyrene beads as a sacrificial template.     

Electrochemical synthesis of cobalt hydroxide films with tunable interlayer spacings

An electrochemical synthetic condition is developed to produce cobalt hydroxide films with significantly increased basal spacings (d(001)>or= 25.0 A) by incorporating anionic surfactants (i.e. sodium dodecyl sulfate and 1-hexadecanesulfonate) into the interlayer regions via electrodeposition.     

Synergistic effects of layered double hydroxide with hyperfine magnesium hydroxide in halogen-free flame retardant EVA/HFMH/LDH nanocomposites

The synergistic effects of layered double hydroxide (LDH) with hyperfine magnesium hydroxide (HFMH) in halogen-free flame retardant ethylene-vinyl acetate (EVA)/HFMH/LDH nanocomposites have been studied by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), thermogravimetric analysis (TGA), limiting oxygen index (LOI), mechanical properties' tests, and dynamic mechanical thermal analysis (DMTA). The XRD results show that the exfoliated EVA/HFMH/LDH can be obtained by controlling the LDH loading. The TEM images give the evidence that the organic-modified LDH (OM-LDH) can act as a disperser and help HFMH particles to disperse homogeneously in the EVA matrix. The TGA data demonstrate that the addition of LDH can raise 5-18 °C thermal degradation temperatures of EVA/HFMH/LDH nanocomposite samples with 5-15 phr OM-LDH compared with that of the control EVA/HFMH sample when 50% weight loss is selected as a point of comparison. The LOI and mechanical tests show that the LDH can act as flame retardant synergist and compatilizer to apparently increase the LOI and elongation at break values of EVA/HFMH/LDH nanocomposites. The DMTA data verify that the T_g value (−10 °C) of the EVA/HFMH/LDH nanocomposite sample with 15 phr LDH is much lower than that (T_g = −2 °C) of the control EVA/HFMH sample without LDH and approximates to the T_g value (−12 °C) of pure EVA, which indicates that the nanocomposites with LDH have more flexibility than that of the EVA/HFMH composites.     

Mechanochemical synthesis of PbS/Ni–Cr layered double hydroxide nanocomposite

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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.     

Temperature-controlled electrochemical switch based on layered double hydroxide/poly(N-isopropylacrylamide) ultrathin films fabricated via layer-by-layer assembly

In this paper we report the fabrication of layered double hydroxide (LDH) nanoparticles/poly(N-isopropylacrylamide) (pNIPAM) ultrathin films (UTFs) via the layer-by-layer assembly technique, and their switchable electrocatalytic performance in response to temperature stimuli was demonstrated. X-ray diffraction and UV-vis absorption spectroscopy indicate a periodic layered structure with uniform and regular growth of the (LDH/pNIPAM)(n) UTFs; an interaction based on hydrogen bonding between LDH nanoparticles and pNIPAM was confirmed by X-ray-photoelectron spectroscopy and Fourier transform infrared spectroscopy. Temperature-triggered cyclic voltammetry and electrochemical impedance spectroscopy switch for the UTFs was obtained between 20 and 40 °C, accompanied by reversible changes in surface topography and film thickness revealed by atomic force microscopy and ellipsometry, respectively. The electrochemical on-off property of the temperature-controlled (LDH/pNIPAM)(n) UTFs originates from the contraction-expansion configuration of pNIPAM with low-high electrochemical impedance. In addition, a switchable electrocatalytic behavior of the (LDH/pNIPAM)(n) UTFs toward the oxidation of glucose was observed, resulting from the temperature-controlled charge transfer rate. Therefore, this work provides a facile approach for the design and fabrication of a well-ordered command interface with a temperature-sensitive property, which can be potentially applied in electrochemical sensors and switching.     

Resettable fluorescence logic gate based on calcein/layered double hydroxide ultrathin films

A fluorescent logic gate was fabricated based on calcein/layered double hydroxide ultrathin films (UTFs) via alternate assembly technique, which exhibits high stability, reversibility, and resettability. The logic gate was manipulated by utilizing pH value, Hg(2+) and Cl(-) ion as inputs, and the fluorescence emission of the (calcein/LDH)(16) UTF as output, serving as a three-input logic gate that combines the YES and INHIBIT operation.