MgAlCe水滑石的合成及其表征

采用共沉淀水热法合成了MgAlCe三元复合层状氢氧化物。详细探讨了x(Al)/x(Ce)、水热温度及pH值对合成产物物相的影响。通过XRD、TG/DTG、SEM及TEM对制备的水滑石进行分析。结果表明,当x(M2+)/x(M3+)=1.5,x(Al)/x(Ce)=16∶1,pH值=7.9条件下进行多种离子共沉淀,并经140℃、10h水热处理后,得出的产物结晶度较高,物相纯净,具有典型层状结构,并且其热稳定性较好,层间羟基硝酸根失去温度在300～500℃之间,表明其作为阻燃剂具有很大的潜力。     

Reconstitution effect of Mg/Ni/Al layered double hydroxide

Layered double hydroxide (LDH) having a different cation (Mg, Ni, Al) composition was successfully synthesized by the low supersaturation method. The sample was thermally decomposed and reconstituted in water and nitrate media at different temperatures. X-ray powder diffraction and X-ray fluorescence were used to investigate the differences between the obtained layered materials and those after the reconstitution process. To the best of our knowledge, there are only few studies where the influence of the third metal cation on the reconstitution process was analyzed.     

Layer-by-layer self-assembly of polyimide precursor/layered double hydroxide ultrathin films

The layer-by-layer (LBL) self-assembly has been extensively used as a simple and effective method for the preparation of polyelectrolyte multilayer films. In this work, we utilized this unique method to prepare polyimide precursor/layered double hydroxide (LDH) ultrathin films. Well-crystallized Co-Al-CO₃ LDH and subsequent anion exchanged Co-Al-NO₃ LDH were prepared and characterized by scanning electron microscopy and X-ray diffraction (XRD). By vigorous shaking of the as-prepared Co-Al-NO₃ LDH, positively charged and exfoliated LDH nanosheets were obtained. Atomic force microscopy and XRD investigations indicated the delamination of LDH nanosheets. The precursor of polyimide, poly(amic acid) tertiary amine salt (PAS) was prepared by the polycondensation of dianhydride and diamine, and subsequent amine salt formation. By using the LBL method, heterogeneous ultrathin films of PAS and LDH were prepared. The formation of the ordered nanostructured assemblies was confirmed by the progressive enhancement of UV absorbance and the XRD results.     

Preparation and characterization of melt processed poly(l-lactide)/layered double hydroxide nonocomposites

This work reports the fabrication and physical properties of biodegradable poly(l-lactide) (PLLA) composites containing a fraction of unmodified layered double hydroxides (LDH–NO₃) and γ-polyglutamate-modified layered double hydroxides (γ-LDH) by melt blending process. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) experimental results showed that the original LDH–NO₃ with the certain amount of aggregates was unevenly dispersed throughout the PLLA matrix. Conversely, γ-LDH allows the formation of an intercalated nanocomposite. Although the water vapor permeability of the PLLA/LDH systems was decreased with increasing the loading of LDH, the barrier property of PLLA reinforced with γ-LDH is superior to that of PLLA-L composites. The effects of both LDHs on mechanical and thermal properties of PLLA were also investigated.     

Intracellular drug delivery of layered double hydroxide nanoparticles

Intracellular drug delivery of layered double hydroxide (LDH) nanocarriers have been examined in human osteosarcoma Saos-2 cell culture line by both electron and confocal microscopies. For transmission electron microsopic (TEM) study, LDHs and anticancer drug, methotrexate (MTX) loaded LDHs were synthesized and the particle size was controlled. From the scanning electron microscopic (SEM) studies, morphologies of LDH nanoparticle and its MTX intercalated form were proven to be platelike hexagonal with an average size of approximately 150 nm. In order to understand the cellular penetration behavior, both nanoparticles were treated to human osteosarcoma Saos-2 cell culture lines and the cellular uptake pattern with respect to incubation time was observed by TEM and SEM. We observed that the nanoparticles are attached at the cellular membrane at first and then internalized into the cells via endocytosis within 1 h. Then are located in the intracellular vacuole (endosome). In order to examine the intracellular drug delivery mechanism of LDH nanoparticles, fluorescein 5-isothiocyanate (FITC) labeled MTX was intercalated into LDH and treated on Saos-2 cells. Laser scanning confocal microscopic studies revealed that the FITC-MTX molecules were first internalized with LDH nanocarriers via endocytosis, and located in endosome to deliver loaded drug to target cellular organ. It was, therefore, concluded that LDH could play a role as drug delivery nanocarriers.     

Electrochemical behaviors of iron-based layered double hydroxide thin-films

The ordered ultrathin films based on the fabrication of Mg/Fe-LDHs ([Mg₆Fe₂(OH)₁₆CO₃·(H₂O)_4.5]_0.375) nanosheets and hexacyanoferrate(III) anions via the self-assembly procedure were prepared. The electrodes modified by the films demonstrated a couple of well-defined reversible redox peaks attributed to [Fe(CN)₆]^3?/4? and Fe^2+/3+ couples. The effects of cycle number, scan rate and Mg/Fe molar ratio on the CV performance of the thin-film electrodes were observed in K₃[Fe(CN)₆] electrolyte. The [Fe(CN)₆]^3? pillared Mg/Fe-LDHs with Mg/Fe molar ratio of 3 (LDH-(CN)-3) demonstrated an excellent electrochemical behavior with a potential window between ??0.2 and 1.0 V, high specific capacitance and sensitivity, indicating that the high crystallinity, large specific surface area and plentiful [Fe(CN)₆]^3? anions in interlayer spaces were necessary. Especially, the interlayer [Fe(CN)₆]^3? anions significantly affected the electrochemical behavior of the electrode, where the electrode reaction was controlled by the diffusion of [Fe(CN)₆]^3?/4? and Fe^2+/3+ couples. Under current density of 2.5 A g^?1, the optimized LDH-(CN)-3 electrode exhibited high specific capacitance of 250.81 F g^?1 with good cycling stability. This facile synthesis strategy and the good electrochemical properties indicated that the LDH-(CN)-3 was a potential economical alternative material for supercapacitor application.     

Structural characterization, thermal and mechanical properties of polyurethane/CoAl layered double hydroxide nanocomposites prepared via in situ polymerization

Dodecyl sulfate (DS), one kind of sulfate anion, was intercalated in the interlayer space between CoAl layered double hydroxide (CoAl-LDH) layers, and then polyurethane (PU) based nanocomposites were prepared by in situ intercalation polymerization with different amounts of the organo-modified CoAl-LDH. An exfoliated dispersion of CoAl-LDH layers in PU matrix was verified by the disappearance of the (0 0 3) reflection of the XRD results when the LDH loading was less than 2.0 wt%. Tensile testing indicated that excellent mechanical properties of PU/LDH nanocomposites were achieved. The weak alkaline catalysis of DS to polyurethane chains, combined with the dehydration and structural degradation of the LDH below 300 °C, accounted for the process of proceeded degradation as shown in TGA results. The real-time FTIR revealed that the as-prepared nanocomposites had a slower thermo-oxidative rate than neat PU from 160 °C to 340 °C, probably due to the barrier effect of LDH layers. These results suggested potential applications of CoAl-LDH as a promising flame retardant in PUs.     

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.     

A simple method to synthesize layered double hydroxide nanoscrolls

Layered double hydroxide (LDH) is a promising drug carrier, ion exchanger, absorbent, and catalyst or even catalyst support due to its inimitable sandwich structure. If the LDH could be synthesized into the nanoscrolls, it will be promising ion channels for the biomolecule transfer, ion exchange, or catalysis. In this report, a simple technique has been developed to prepare layered double hydroxide nanoscrolls on a large scale. The composition of LDH nanoscrolls can be conveniently adjusted through experiment conditions. We proved the “rolling mechanism” to explain the formation of LDH nanoscrolls. Moreover, we unambiguously proposed the driving force for “rolling mechanism”, which is the change of the forces between the brucite-like sheets and the interanions and between the cations and cations in the brucite-like sheets.     

Intercalation of collagen and soybean peptides into Zn-Al layered double hydroxide

In order to develop a new type biocompatible organic/inorganic nanohybrid material, an intercalation of collagen peptides (CP) and soybean peptide (SP) into Zn-Al layered double hydroxide (LDH) by the coprecipitation reaction has been investigated. The peptide/LDH has been characterized by chemical analysis, powder X-ray diffraction (XRD), Raman spectroscopy, thermal gravimetric analysis (TG) and transmission electron microscopy (TEM). According to the XRD patterns and Raman spectra, the solid products were found to contain peptide and to show broad diffraction peaks with LDH structures. The CP/LDH and SP/LDH possess the expanding LDH structure, d(00l) = 2-3 nm, confirming that both peptides were intercalated into the LDH interlayer space with low organized stacking arrangement.     

Acidic and basic gas adsorption properties in composites of layered double hydroxide/aluminosilicate xerogels

Composites of Mg-Al LDH and ASG were prepared by various methods, and their acidic and basic gas adsorption properties were investigated by CO₂ and NH₃ gas TPD. Of the various preparation methods, composite samples prepared by precipitation of LDH in an ASG sol solution showed a superior adsorption for both acidic and basic gases. The adsorption was higher than the arithmetic mean of the LDH, which mainly adsorbs acidic gas and the ASG, which mainly adsorbs basic gas. These composites could be good candidates as adsorbents and deodorants for the simultaneous uptake of acidic and basic adsorbates, i.e. materials with dual function adsorption properties.     

Sepiocite, sepiolite-like nanoclay derived from hydrotalcite-like layered double hydroxide

Sepiocite, a synthetic sepiolite-like nanoclay, was derived from hydrotalcite-like Mg2Al(CO3)0.5-layered double hydroxide (LDH) under phase transformation at 270 +/- 3 degrees C. The crystal structure of sepiocite is conceptually very similar to that of sepiolite derived from montmorillonite clay because sepiocite is formed through the alternation of the blocks and tunnels along the crystallographic c-axis, with a partial dehydroxylation of the octahedral Mg-(OH)-Al configuration into tetrahedral ones. Three important findings regarding sepiocite were arrived at: (i) its high specific surface area of 128.25 m2/g with an average particle size of 200 nm, which is approimately equal to 3.5 times larger than the specific surface area of the pristine LDH (34.21 m2/g); (ii) its non-swelling property; and (iii) its strongly reduced anion-exchange capacity.     

层状双金属氢氧化物的原位改性及其吸附性能

为了改善层状双金属氢氧化物(LDHs)材料对水体中碘离子的吸附性能,通过共沉淀法制备铜基LDH材料,利用煅烧及煅烧后还原分别制得层状双金属氧化物(CLDH)和Cu-Cu_2O-CLDH材料,并探究这3种LDHs材料对水体中I-的吸附性能。扫描电镜观察到Cu-Cu_2O-CLDH的表面上长出了小颗粒,X射线衍射结果证明这些小颗粒为Cu及Cu_2O,比表面积测试结果表明Cu-Cu_2O-CLDH的比表面积达到了316. 76 m~2/g,远远大于LDH及CLDH材料。吸附实验结果显示:LDH和CLDH对I-的饱和吸附容量分别为23. 8、84. 8 mg/g,而改性后的CuCu_2O-CLDH对I-的饱和吸附容量提升到了134. 5 mg/g。根据I-的吸附实验结果及吸附后的样品表征,发现Cu、Cu_2O能够与I-反应生成Cu I,加上与CLDH的协同作用,使得材料对I-的吸附效率进一步提高。     

Preparation and wetting properties of layered double hydroxide colloidal nano/microspheres with tunable flower-like morphologies

Layered double hydroxides (LDHs), known as a type of multifunctional anionic layered clay, typically exhibit stability and intrinsic hydrophilicity at neutral and alkaline pH. We herein report a polymer bead-templated preparation of flower-like LDH shell microspheres with the LDH platelets tuned under different aging durations and temperatures. Thickness of LDH shell walls was tuned readily by varying preparation conditions such as aging durations and temperatures. After a simple chemical surface modification using fluorine-silane molecule, the flower-like LDH nano/microspheres show the distinctly different transitions from the intrinsic hydropholicity to the superhydrophobicity at pH 2 and neutral pH. In contrast, at alkaline condition of pH 12 small flower-like spheres were formed atop of the parent microspheres, which may be argued in terms of a process of desorption of silane molecule at the alkaline condition combined with dissolution and reassembly of LDH platelets. Our finding of the superhydrophobic LDH spheres may find useful applications in chemical and biosensors against harsh acidic conditions.     

Fabrication of layered double hydroxide/photoresponsive dendron nanocomposite multilayer film by electrostatic layer-by-layer assembly

A novel inorganic–organic nanoscopic multilayer film consisting of exfoliated MgAl-type layered double hydroxide (LDH) nanosheets and anthryl dendrons [i.e., poly(amidoamine) dendrons with an anthracene chromophore group at the focal point] was fabricated using an electrostatic layer-by-layer (LbL) assembly. UV–vis spectroscopy and X-ray diffraction analysis indicated the successful LbL growth of dendron/LDH multilayer films. Furthermore, fluorescence spectroscopic analysis indicated that the dendrons are present as a monolayer between LDH nanosheets in the film.     

An intercalated hybrid of polyacrylamide/layered double hydroxide prepared via in situ intercalative polymerization

A new intercalated hybrid of polyacrylamide (PAM)/layered double hydroxide (LDH) prepared via in situ intercalative polymerization procedure is reported. LDH with counterion ion of nitrate or dodecyl sulfate anion was employed for comparison. The obtained PAM/LDH hybrid was characterized by X-ray diffraction, infrared spectra, differential scanning microcalorimetry and X-ray photoelectron spectrum. The results reveal that the LDH modified with dodecyl sulfate anion can be used to obtain an intercalated hybrid, whereas PAM polymer chains can not enter the interlayer space of LDH with nitrate anion as counterion ion.     

Photocatalytic activity and stability of TiO2/ZnAl layered double hydroxide based coatings on mortar substrates

The surface properties and photocatalytic activity of the cement and pozzolanic mortar samples coated with TiO₂/ZnAl layered double hydroxides were studied with the intention to design suitable protective, hydrophilic coatings. In order to underline the existing correlation between the water uptake characteristics and the surface features, the coated mortars were subjected to water absorption test by capillarity, to photo-induced surface water absorption test and to photo-induced hydrophilicity test by contact angle measurements. The self-cleaning behavior of the mortar systems was evaluated by monitoring the photocatalytic rhodamine B removal efficiency in correlation with the development of photo-induced surface hydrophilicity. The coating durability was assessed towards the weathering effect of rain (essential for the coating self-cleaning properties). The positive result of the coating deposition was the improvement of photocatalytic activity, photo-induced hydrophilicity and the decrease of mortar systems surface roughness. The study revealed that the developed coating promotes self-cleaning effect.     

Preparation and characterization of bio-nanocomposites based on poly(3-hydroxybutyrate-co-4-hydroxybutyrate) and CoAl layered double hydroxide using melt intercalation

In this study, the exfoliated bio-nanocomposites based on poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3,4)HB) and cobalt-aluminum layered double hydroxide (LDH) were prepared via melt intercalation. The thermal stability, thermal combustion and thermo-mechanical properties for these bio-nanocomposites were systematically investigated. The formation of an exfoliated structure was confirmed by X-ray diffractometry and transmission electron microscopy analysis. The microscale combustion calorimetry results show that the heat release capacity (HRC) of the bio-nanocomposites is an important parameter of the fire hazard which is significantly reduced with the addition of LDH. The storage modulus of the bio-nanocomposites with small amount of LDH is remarkably enhanced measured by dynamic mechanical analysis.     

Oxidizing synthesis of Ni–Mn layered double hydroxide with good crystallinity

Ni²⁺–Mn³⁺ layered double hydroxide (LDHs) with good crystallinity and uniform morphology has been hydrothermally synthesized at 180 °C for 2 days using urea as hydrolysis agent and ammonium peroxodisulfate as oxidant. The obtained Ni²⁺–Mn³⁺ LDHs material has been characterized by XRD, SEM, XPS, FT-IR, and TG–DTA. Ammonium peroxodisulfate as oxidant plays an important role for the formation of Ni²⁺–Mn³⁺ CO₃²⁻ LDHs material, and Mn²⁺ ions are oxidized into Mn³⁺ ones during the precipitation of Mn²⁺ ions, giving rise to layered hydroxide with the hydrotalcite structure. Ni²⁺–Mn³⁺ LDHs material with Ni/Mn molar ratio of 4 has a layered structure with a basal spacing of 0.739 nm. The morphology, size, and uniformity of the as-prepared materials connect with the hydrothermal treatment temperatures, and uniform and regular flowerlike spheres with a mean lateral size of 3.5 μm are observed for Ni²⁺–Mn³⁺ LDHs material with good crystallinity and uniform morphology.