Synthesis and UV absorption properties of 2,3-dihydroxynaphthalene-6-sulfonate anion-intercalated Zn-Al layered double hydroxides

An organic UV absorbent has been intercalated into a layered double hydroxide (LDH) host by ion exchange of a Zn-Al-LDH-nitrate precursor with a solution of 2,3-dihydroxynaphthalene-6-sulfonic acid (DNSA) sodium salt in water. After intercalation of the UV absorbent, the powder X-ray diffraction (XRD) pattern shows that the interlayer distance in the LDHs increases from 0.90 to 1.59 nm. The possible structure is that the interlayer DNSA anions arrange in a monolayer and in a perpendicular orientation toward the hydroxide layers. Infrared spectra and TG-DTA curves reveal the presence of a complex system of supramolecular host-guest interactions between layers. The thermal stability of the intercalated UV absorbent was investigated by TG-DTA and it was found that this material is more stable than the original organic UV absorbent at high temperature, showing that the thermostability is markedly enhanced after intercalation into the LDH host. The UV absorbent-intercalated LDHs exhibit excellent UV photostability in polypropylene composites.     

The role of the trivalent metal in an LDH: Synthesis, characterization and fire properties of thermally stable PMMA/LDH systems

Two layered double hydroxides (LDHs), calcium aluminum undecenoate (Ca₃Al) and calcium iron undecenoate (Ca₃Fe), have been prepared by the co-precipitation method. XRD analysis of these LDHs reveals that they are layered materials and FT-IR and TGA confirmed the presence of the undecenoate anions in the material produced. The PMMA composites were prepared by bulk polymerization and the samples were characterized by XRD, TEM, TGA and cone calorimetry. Both additives greatly enhance the thermal stability of PMMA, while the calcium aluminum LDH gives better results when the fire properties were examined using the cone calorimeter.     

Recent progress in functionalized layered double hydroxides and their application in efficient electrocatalytic water oxidation

Layered double hydroxides(LDHs), a class of anionic clays consisting of brucite-like host layers and interlayer anions, have been widely investigated in the last decade due to their promising applications in many areas such as catalysis, ion separation and adsorption. Owing to the highly tunable composition and uniform distribution of metal cations in the brucite-like layers, as well as the facile exchangeability of intercalated anions, LDHs can be modified and functionalized to form various nanostructures/composites through versatile processes such as anion intercalation and exfoliation, decoration of nanoparticles, selfassembly with other two-dimensional(2D) materials, and controlled growth on conductive supports(e.g.,nanowire arrays, nanotubes, 3D foams). In this article, we briefly review the recent advances on both the LDH nanostructures and functionalized composites toward the applications in energy conversion, especially for water oxidation.     

Investigation of layered double hydroxides intercalated by oxomolybdenum catecholate complexes

Oxomolybdenum(VI) complexes of 3,4-dihydroxybenzoic acid (3,4-H 2dhb) have been incorporated into layered double hydroxides (LDHs) by treatment of the LDH-nitrate (Zn-Al, Mg-Al) or LDH-chloride (Li-Al) precursors with aqueous or water/ethanol solutions of the complex (NMe 4) 2[MoO 2(3,4-dhb) 2].2H 2O at 50 or 100 degrees C. The texture and chemical composition of the products were investigated by elemental analysis and scanning electron microscopy (SEM) with coupled energy dispersive spectroscopy (EDS). Microanalysis for N and EDS analysis for Cl showed that at least 90% of nitrate or chloride ions were replaced during the ion exchange reactions. The final Mo content in the materials varied between 6.5 and 11.6 wt %. Mo K-edge EXAFS analysis, supported by IR, Raman, UV-vis, and (13)C{ (1)H} CP/MAS NMR spectroscopic studies, showed the presence of cointercalated [MoO 2(3,4-dhb) 2] ( m- ) and [Mo 2O 5(3,4-dhb) 2] ( m- ) complexes in proportions that depend on the type of LDH support and the reaction conditions. The binuclear bis(catecholate) complex, with a Mo...Mo separation of 3.16 A, was the major species intercalated in the Zn-Al and Li-Al products prepared using only water as solvent. The X-ray powder diffraction (XRPD) patterns of all the Mo-containing LDHs showed the formation of an expanded phase with a basal spacing around 15.4 A. High-resolution synchrotron XRPD patterns were indexed with hexagonal unit cells with a c-axis of either 30.7 (for Li-Al-Mo LDHs) or 45.9 A (for a Zn-Al-Mo LDH). Fourier maps ( F obs) calculated from the integrated intensities extracted from Le Bail profile decompositions indicated that the binuclear guest species are positioned such that the Mo --> Mo vector is parallel to the host layers, and the overall orientation of the complex is perpendicular to the same layers. The thermal behavior of selected materials was studied by variable-temperature XRPD, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC).     

Synthesis and Characterization of Poly(ethylene terephthalate)/Modified Lithium‐Aluminum‐Layered Double Hydroxide Nanocomposites Prepared Using In‐situ Polymerization

Layered double hydroxides are a type of layered stacked compound, which can be intercalated with organic‐molecule modifiers. An ion‐exchange process for layered double hydroxide (LDH) was used to intercalate water‐soluble sulfanilic acid salt (SAS) and dimethyl 5‐sulfoisopthalate (DMSI) into lithium aluminum layered double hydroxides (LiAl LDHs). In this work, a hydrothermal process was used to modify LiAl LDHs, and the modified LiAl LDHs were treated with either SAS or DMSI through an ion‐exchange process and were then intercalated using bis‐hydroxyethylene terephthalate (BHET). The results indicate that the modified LiAl LDHs improved the interlayer compatibility between the PET and LiAl LDH layers; thus, enabling the oligomer molecules to more easily enter the gallery of the LiAl LDH layers so that polymer chains could be included between the LDH layers during polymerization of the matrix. The better barrier, mechanical properties, and thermal stability of these new types of PET nanocomposites are discussed.     

Tungstocobaltate-pillared layered double hydroxides: Preparation, characterization, magnetic and catalytic properties

A new polyoxometalate anion-pillared layered double hydroxide (LDH) was prepared by aqueous ion exchange of a Mg-Al LDH precursor in nitrate form with the tungstocobaltate anions [CoW₁₂O₄₀]⁵⁻. The physicochemical properties of the product were characterized by the methods of powder X-ray diffraction, elemental analysis, infrared spectroscopy, thermogravimetric analysis and cyclic voltammetry. It was confirmed that [CoW₁₂O₄₀]⁵⁻ was intercalated between the brucite-type layers of the LDHs without a change in the structure. Magnetic measurement shows the occurrence of antiferromagnetic interactions between the magnetic centers. The investigation of catalytic performance for this sample exhibits high activity for the oxidation of benzaldehyde by hydrogen peroxide.     

Embedded high density metal nanoparticles with extraordinary thermal stability derived from guest-host mediated layered double hydroxides

A chemical precursor mediated process was used to form catalyst nanoparticles (NPs) with an extremely high density (10(14) to 10(16) m(-2)), controllable size distribution (3-20 nm), and good thermal stability at high temperature (900 °C). This used metal cations deposited in layered double hydroxides (LDHs) to give metal catalyst NPs by reduction. The key was that the LDHs had their intercalated anions selected and exchanged by guest-host chemistry to prevent sintering of the metal NPs, and there was minimal sintering even at 900 °C. Metal NPs on MoO(4)(2-) intercalated Fe/Mg/Al LDH flakes were successfully used as the catalyst for the double helix growth of single-walled carbon nanotube arrays. The process provides a general method to fabricate thermally stable metal NPs catalysts with the desired size and density for catalysis and materials science.     

12-磷钨酸插层MgAl水滑石的合成、表征及催化酯化原油脱酸性能

采用离子交换法合成了不同Mg/Al物质的量比的12-磷钨酸(H_3PW_(12)O_(40),HPW)插层水滑石(LDHs),采用XRD、FT-IR、Raman、ICP-AES、TG-DSC等分析手段表征其物化性质,Hammett指示剂-正丁胺滴定法测定其酸强度和酸量分布。进一步将其用于原油催化酯化脱酸反应,并与NO_3型LDHs对比,探讨酯化活性与催化剂性质之间的关系。结果表明,催化剂的活性主要受酸性和比表面积的影响。HPW插层LDHs的酯化活性明显优于NO3型LDHs,归因于增强的酸性和增大的比表面积。对于弱酸性的NO_3型LDHs,酯化活性与比表面积呈正向关系,Mg/Al物质的量比为4时,具有最大的比表面积和脱酸活性。而对于较强酸性的HPW插层LDHs,酯化活性主要受到酸量的影响,Mg/Al物质的量比为2的催化剂具有最高的酸量和脱酸活性。     

熔融插层法制备LLDPE/MgAl-LDH 剥离型纳米复合材料及其热性能研究

The interlayer surface of MgAl layered double hydroxide （MgAl-LDH） was modified by exchanging about half of the interlayer nitrate anions by dodecyl sulfate anions （DS） to get MgAl（H-DS） LDH, and then the MgAl（H-DS） was melt intercalated by LLDPE to get the LLDPE/MgAl-LDH exfoliation nanocomposites. The samples were characterized by Fourier transform infrared （PTIR） spectroscopy, X-ray diffraction （XRD）, ion chromatography, transmission electron microscopy （TEM）, and thermogravimetry analysis （TGA）. The nanoscale dispersion of MgAl-LDH layers in the LLDPE matrix was verified by the disappearance of （001） XRD reflection of the modified MgAl-LDH and by the TEM observation. The TGA profiles of LLDPE/MgAl-LDH nanocomposites show a faster charring process between 210 and 370 ℃ and a higher thermal stability above 370 ℃than LLDPE. The decomposition temperature of the nanocomposites with 10 wt% MgAl（H-DS） can be 42 ℃ higher than that of LLDPE at 40% weight loss.     

Layered nanoparticles modified by chain end functional PE and their nanocomposites with PE

Layered materials (MMT,LDH) were successfully modified by chain end functionalized polyethylene via an ion exchange method.The samples were characterized by using elemental analysis,Fourier transform infrared (FTIR) spectrum,X-ray diffraction (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM) and thermogravimetric analysis (TGA).The XRD results demonstrated that MMT was successfully exfoliated with the disappearance of [001] peak.For the LDH,the peak [003] moved to a low angle and greatly weakened,indicating that LDH was successfully functionalized and completely intercalated or exfoliated.HDPE/layered nanocomposites were obtained between HDPE and different content of functional layered materials.The SEM and TEM results of nanocomposites showed the layered materials were well dispersed in the HDPE matrix,with a particle size of 100-200 nm.     

Synthesis and adsorption properties of p-sulfonated calix[4 and 6]arene-intercalated layered double hydroxides

The intercalation of water-soluble p-sulfonated calix[4 and 6]arene (CS4 and CS6) in the interlayer of the Mg-Al and Zn-Al layered double hydroxide (LDH) by the coprecipitation method has been investigated, as well as the adsorption properties of the resulting CS/LDHs for benzyl alcohol (BA) and p-nitrophenol (NP) to prepare new microporous organic-inorganic hybrid adsorbents. The amount and arrangement of CS intercalated was different by the kind of the host metal ions. CS4 cavity axis was perpendicular for the Mg-Al LDH basal layer and parallel for the Zn-Al LDH basal layer, while CS6 cavity axis was perpendicular for both the LDH basal layers. In the BET surface area measurement, the surface area of the Zn-Al/CS4/LDH was four times than that of the Mg-Al/CS4/LDH, expecting that the former has higher adsorption capacity than the latter. In fact, the adsorption ability of the CS/LDHs for BA and NP in aqueous solution was found to be larger in the Zn-Al/CS4/LDH than in the Mg-Al/CS4/LDH. In addition, the adsorption ability of both the LDHs was larger in the CS6/LDHs than in the CS4/LDHs. These results were explained by the difference in the amount and arrangement of CS intercalated in the LDH interlayer space.     

Synergistic effects of layered double hydroxide with phosphorus-nitrogen intumescent flame retardant in PP/EPDM/IFR/LDH nanocomposites

<正>Synergistic effects of layered double hydroxide(LDH) with intumescent flame retardanct(IFR) of phosphorus-nitrogen (NP) compound in the polypropylene/ethylene-propylene-diene/IFR/LDH(PP/EPDM/IFR/LDH) nanocomposites and related properties were studied by X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),limiting oxygen index(LOI),UL-94 test,cone calorimeter test(CCT) and thermo-gravimetric analysis (TGA).The XRD and TEM results show that the intercalated and/or exfoliated nanocomposites can be obtained by direct melt-intercalation of PP/EPDM into modified LDH and that LDH can promote the IFR additive NP to disperse more homogeneously in the polymer matrix.The SEM results provide positive evidence that more compact charred layers can be obtained from the PP/EPDM/NP/LDH sample than those from the PP/EPDM/LDH and PP/EPDM/NP samples during burning.The LOI and UL-94 rating tests show that the synergetic effects of LDH with NP can effectively increase the flame retardant properties of the PP/EPDM/NP/LDH samples.The data from the CCT and TGA tests indicate that the PP/EPDM/NP/LDH samples apparently decrease the HRR and MLR values and thus enhance the flame retardant properties and have better thermal stability than the PP/EPDM/LDH and PP/EPDM/NP samples.     

A composite of layered double hydroxides obtained through random costacking of layers from Mg–Al and Co–Al LDHs by delamination–restacking: Thermal decomposition and reconstruction behavior

A composite of dodecylsulfate intercalated Mg–Al and Co–Al LDHs in which the layers of the two LDHs are randomly costacked was prepared starting from the monolayer colloidal dispersions of the individual surfactant intercalated LDHs obtained through delamination in 1-butanol. The surfactant ion of the composite could be exchanged for acetate ions. The thermal decomposition and reconstruction behavior of the acetate-intercalated composite was found to be different from those of an LDH in which each layer contains Mg, Co and Al and a physical mixture of Mg–Al and Co–Al LDHs. While the composite shows partial reconstruction to LDH phase even after heating up to 1000 °C the other samples do not show reconstruction beyond 800 °C.     

Structure-property relationships of new polystyrene nanocomposites prepared from initiator-containing layered double hydroxides of zinc aluminum and magnesium aluminum

Polystyrene/layered double hydroxides (PS/LDHs) nanocomposites were prepared by free radical polymerization of styrene monomer in the presence of LDHs intercalated with 4,4′-azobis(4-cyanopentanoate) anions (LDH-ACPA). XRD and ATR-IR are used to confirm that the materials produced are layered and the presence of the azo-initiator anions in these LDHs. These LDHs were used successfully to polymerize styrene and both XRD and TEM images of the composites support the formation of a mixed exfoliated-intercalated nanocomposite for ZnAl-ACPA but a microcomposite for MgAl-ACPA. The magnesium-containing LDHs decreased the glass transition temperature (T_g) of the composites while ZnAl-ACPA did not affect T_g significantly. The T_g depression is related to enhanced polymer dynamics due to the extra free volume at the LDH additive-polymer interface. A reduction in the onset of thermal decomposition temperature was observed in PS/LDH compared to neat PS, likely due to the early decomposition of the LDH. The fire performance, as evaluated by the cone calorimeter, reveal that PS-ZnAl-ACPA shows enhanced fire properties compared to PS-MgAl-ACPA.     

Preparation of 5-benzotriazolyl-4-hydroxy-3-sec-butylbenzenesulfonate anion-intercalated layered double hydroxide and its photostabilizing effect on polypropylene

An organic UV absorber has been intercalated into a layered double hydroxide (LDH) host by ion-exchange method using ZnAl-NO₃-LDH as a precursor with an aqueous solution of the sodium salt of 5-benzotriazolyl-4-hydroxy-3-sec-butylbenzenesulfonic acid (BZO). After intercalation of the UV absorber, the interlayer distance in the LDHs increases from 0.89 to 2.32 nm. Infrared spectra and thermogravimetry and differential thermal analysis (TG-DTA) curves reveal the presence of a complex system of supramolecular host-guest interactions. The thermostability of BZO is markedly enhanced by intercalation in the LDH host. ZnAl-BZO-LDHs/polypropylene composite materials exhibit excellent UV photostability.     

醇水介质中共沉淀法制备甲氨蝶呤/层状双氢氧化物纳米材料的研究

采用乙醇-水混合溶液为溶剂,以NaOH为沉淀剂制备了甲氨蝶呤(MTX)-镁铝层状双氢氧化物(Mg-Al-LDH)纳米复合材料,利用X-射线衍射(XRD)、透射电镜(TEM)和傅里叶变换红外(FT-IR)光谱等表征手段,对其结构及形貌进行了系统研究.研究表明,与传统的水溶液共沉淀法相比,醇水共沉淀法制备的MTX/LDH纳...     

二氟尼柳/水滑石插层组装结构、氢键及水合特性的分子动力学模拟

采用分子动力学方法模拟二氟尼柳插层水滑石(DIF/LDHs)的超分子结构, 研究复合材料主客体间形成的氢键以及水合膨胀特性.结果表明, 当水分子总数与DIF分子总数之比Nw≤3时, 层间距dc保持基本恒定, 约1.80 nm; 当Nw≥4时, 层间距逐渐增大, 且符合dc=1.2611Nw+13.63线性方程. 随着水分子个数增加, 水合能驻UH逐渐增大. 当Nw≤16时, 由于⊿UH<-41.84 kJ·mol-1, LDHs-DIF可以持续吸收水, 从而使材料层间距不断膨胀. 但当Nw≥24时, ⊿UH>-41.84 kJ·mol-1, 此时LDHs-DIF层间不能再进一步水合, 因此LDHs-DIF在水环境中膨胀具有一定的限度. 水滑石层间存在复杂的氢键网络. DIF/LDHs水合过程中, 水分子首先同步与层板和阴离子构成氢键; 当阴离子趋于饱和后, 水分子继续与层板形成氢键, 并逐步发生L-W型氢键取代L-A型氢键, 驱使阴离子向层间中央移动, 与层板发生隔离; 最后水分子在水滑石羟基表面形成有序结构化水层.     

LDPE/Mg-Al layered double hydroxide nanocomposite: Thermal and flammability properties

Layered double hydroxides (LDHs) are new nanofillers which exhibit improved thermal and flammability properties in various kinds of polymer matrices. These materials have certain advantages over conventional metal hydroxides and also layered silicates so far as the flame retardancy is concerned. In this article, flammability and thermal properties of the nanocomposite based on low density polyethylene (LDPE) and Mg-Al based layered double hydroxide (Mg-Al LDH) are reported in detail. The nanocomposites containing different LDH concentrations were prepared by melt-compounding using a tightly intermeshing co-rotating twin-screw extruder. The morphological analysis reveals an exfoliated/intercalated type LDH particle morphology in these nanocomposites. The thermogravimetric analysis (TGA) shows that even a small amount of LDH improves the thermal stability and onset decomposition temperature in comparison with the unfilled LDPE. The heat release rate (HRR) and its maximum (PHRR) during cone-calorimeter investigation are found to be reduced significantly with increasing LDH concentration. The nanocomposites not only exhibit reduced total heat released (measure of propensity to produce long duration fire), but also lower tendency to fast fire growth (measured by the ratio of PHRR and time of ignition). The limited oxygen index (LOI) and the dripping behavior are also improved with increasing LDH concentration.     

Synthesis of ionic liquid intercalated layered double hydroxides of magnesium and aluminum: A greener catalyst of Knoevenagel condensation

Due to their structural merits that arise from their stability and high surface area, the layered double hydroxide (LDH) materials have caused strong attention. These characteristics provided intriguing possibilities with improved efficiency for catalytic applications. In this work, the preparation of 1-butyl-3-methylimidazolium hydroxide ([BMIM]⁺OH⁻) intercalated by a facile approach in a layered double hydroxide (LDH) matrix is reported and its implementation as a greener catalyst is shown. Different physico-chemical techniques such as XRD, FTIR, TGA, and N₂-physisorption, HRTEM, and CO₂ adsorption are implemented to characterize the structure of the fabricated catalysts. The [BMIM]⁺OH⁻/LDH exhibit outstanding catalytic performance in Knoevenagel condensation, resulting from the high LDH surface area and synergistic effects between both the intercalated ionic liquid and LDHs matrix. Knoevenagel’s fabricated catalysts can be exploited to catalyze different condensations and can be reused well. This work therefore generates good opportunities in the field of catalysis for the preparing and implementation of LDH-based catalysts.     

微波法合成乙二醇插层镍铝层状双金属氢氧化物

乙二醇(EG)插层层状双金属氢氧化物(LDH)可作为层间催化反应器,用于原油中环烷酸与EG的酯化脱酸反应,但其合成过程需要较长时间。 以硝酸根型镍铝LDH为前体,在KOH促进下,采用微波辅助的离子交换法合成EG插层LDH,省时节能,提高效率。 考察了微波时间、微波温度和微波功率对EG插层LDH结构的影响。 并用XRD、FT-IR和TG-DSC等比较了微波法和常规方法合成的EG插层LDH的性质。 结果表明,微波辐射能提供高能量,促进待交换阴离子向层间的扩散,并减弱层板与层间原有阴离子间的作用力,在微波温度为120 ℃,微波时间为10 min和微波功率550 W的条件下,即可得到结晶度高的EG插层LDH。 微波法合成的EG插层LDH与常规方法合成的具有相似的性质和更高的结晶度,而合成时间可由12 h大幅缩短至10 min。