Preparation and thermal decomposition study of pyridinedicarboxylate intercalated layered double hydroxides

Supramolecular 2,3- and 2,5-pyridinedicarboxylate (PDC) intercalated ZnAl-layered double hydroxides (2,3- and 2,5-PDC–ZnAl–LDHs) have been prepared by ion exchange method. The structure and composition of the intercalated materials have been studied by X-ray diffraction (XRD) and inductively coupled plasma emission spectroscopy (ICP). The study indicates that the 2,3-PDC and 2,5-PDC anions are accommodated as interdigitated bilayer and monolayer arrangement respectively between the sheets of LDHs. Furthermore, their thermal decomposition processes were studied by the use of in situ high temperature X-ray diffraction (HT-XRD), and the combined technique of thermogravimetry-differential thermal analysis-mass spectrometry (TG-DTA-MS) under N2 atmosphere. Based on the comparison study on the temperatures of both decarboxylation and complete decomposition of interlayer PDC, it can be concluded that 2,5-PDC–ZnAl–LDHs has higher thermal stability than that of 2,3-PDC–ZnAl–LDHs.     

Flower‐like layered double hydroxide‐modified stainless‐steel fibers for online in‐tube solid‐phase microextraction of Sudan dyes

Layered double hydroxides are a family of inorganic crystals that have gained a lot of attention due to its special structure and properties such as high porosity, large specific area, and excellent anion exchange ability. In this work, flower‐like NiAl‐layered double hydroxides with high specific area were in situ immobilized onto the stainless steel fibers by bioinspired polydopamine modification method and packed into poly (ether ether) ketone tube for online solid‐phase microextraction with high performance liquid chromatography analysis. Thanks to the high specific surface area and excellent extraction ability of the NiAl‐layered double hydroxides, the fibers showed excellent extraction performance to three Sudan dyes with enrichment factors between 260 to 650 folds. After optimization of the reaction and extraction conditions, an online solid‐phase microextraction method was developed for determination of Sudan dyes in water samples and chili samples. The method has limits of detection of 0.01 to 0.02 ng/mL, good linearity and good reproducibility (≤1.45%).     

Synthesis pretreatment and characterization of a magnetic layered double hydroxides fluorescent probe

Using magnetic layered double hydroxide （MLDH） as carrier of fluorescein （FLU）, a fluorescent composite of MLDH-FLU was prepared via intercalation reaction of ion change. The crystal properties of MLDH-FLU were investigated through XRD, IR, TEM and TG-DSC characterization. It is shown that the crystal type of MLDH-FLU composite matched well with R-hexagonal crystal system of MLDH, with crystal cell parameters of a, c and channel height h equal to 0.3199, 2.411 and 0.3267 nm respectively. The superabundant pigment adsorbed outside the composite should be cleared before interference with cells, but excessive wash would decrease stability and cause crystal phase transformation of MLDH.     

Study on the coating of nano-scale SiO<Subscript>2</Subscript> film on the surface of nanocrystalline Mg-Al layered double hydroxides

Since the layered double hydroxides (abbreviatedas LDHs) were firstly reported to be used as precur-sors of new catalytic materials by S. Miyata[1] in 1971,their preparations, ion-exchanges with the balancinginterlayer anions, structure characteristics an…     

甲氨蝶呤柱撑水滑石超分子结构层柱材料的插层组装

用共沉淀和离子交换法将抗肿瘤类药物甲氨蝶呤(MTX)插层组装到水滑石层间,制备了一种新型的结晶度高、晶相单一且MTX在层间有序排列的超分子结构的药物-无机复合层柱材料.用XRD、原子光谱、元素分析、FT/IR、SEM及TG-DSC分析表征了超分子结构层柱材料的结构,并给出其结构模型.     

均匀沉淀法直接合成有机阴离子柱撑水滑石

以尿素为沉淀剂用均匀沉淀法直接合成有机阴离子柱撑水滑石(Layered Double Hydroxides，LDH)及CoAl水滑石等，并用XRD，FT—IR，TGA，TEM等分析手段对所合成的水滑石进行了表征．结果表明，尿素均匀沉淀法可以直接合成有机阴离子柱撑水滑石及CoAl水滑石等，并且可以方便地消除原料中阴离子的干扰，是合成有机阴离子柱撑水滑石及CoAl水滑石等的一个简便快速的新方法。     

Isothermal crystallization kinetics of poly(3‐hydroxybutyrate)/layered double hydroxide nanocomposites

Poly(3‐hydroxybutyrate) (PHB)/layered double hydroxides (LDHs) nanocomposites were prepared by mixing PHB and poly(ethylene glycol) phosphonates (PEOPAs)‐modified LDH (PMLDH) in chloroform solution. Both X‐ray diffraction data and TEM micrographs of PHB/PMLDH nanocomposites indicate that the PMLDHs are randomly dispersed and exfoliated into the PHB matrix. In this study, the effect of PMLDH on the isothermal crystallization behavior of PHB was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. Isothermal crystallization results of PHB/PMLDH nanocomposites show that the addition of 2 wt % PMLDH into PHB induced more heterogeneous nucleation in the crystallization significantly increasing the crystallization rate and reducing their activation energy. By adding more PMLDH into the PHB probably causes more steric hindrance of the diffusion of PHB, reducing the transportation ability of polymer chains during crystallization, thus increasing the activation energy. The correlation among crystallization kinetics, melting behavior and crystalline structure of PHB/PMLDH nanocomposites can also be discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3337–3347, 2006     

乙二胺四乙酸柱撑镁锌铝三元水滑石的制备与表征

采用共沉淀法合成了Mg2ZnAl-CO3水滑石;以其为前驱体,利用离子交换法进行插层组装得到Mg2ZnAl-EDTA三元柱撑水滑石;采用X射线衍射仪和傅立叶变换红外光谱仪对产物进行了表征.结果表明,合成的Mg2ZnAl-CO3水滑石纯度高、晶型良好,其层间CO32-可被乙二胺四乙酸(EDTA)阴离子取代形成Mg2ZnAl-EDTA三元柱撑水滑石;柱撑水滑石的层间距离明显增加,EDTA阴离子在层间倾斜排列.     

用焙烧复原法插层组装有机层柱双氢氧化物

有机酸根插层双氢氧化物(简记为:LDHs OA)是制备具有特殊性质和功能的层柱材料的一类重要前驱体[1 3]。本文以Mg6Al2(OH)16CO2-3·6H2O(简记为MgAl CO2-3)和Zn6Al2(OH)16CO2-3·4H2O(简记为ZnAl CO2-3)为前体,用焙烧复原法将十四酸根(简记为14A)和十八酸根(简记为18A)分别插层组装到了MgAl LDHs和ZnAl LDHs层板间而制得了具有大的层间距、良好的结晶度和规整的层状结构的14A(18A)插层LDHs层柱材料(分别简记为MgAl 14A,mgAl 18A,ZnAl 14A,ZnAl 18A),用XRD谱、IR谱表征了插层交换产物的结构。1　实验部分1.1　仪…     

Flammability and thermal degradation behavior of ethylene‐vinyl acetate/layered double hydroxides/zinc borate composites

Mg‐Al‐Fe ternary‐layered double hydroxides (LDHs) were synthesized by a calcination‐rehydration method using Bayer red mud. The products were characterized using X‐ray diffraction and thermogravimetric analysis. The flammability and thermal degradation of ethylene‐vinyl acetate/layered double hydroxides/zinc borate (EVA/LDHs/ZB) composites were studied with limiting oxygen index, UL 94, cone calorimeter test, smoke density test, and thermogravimetry‐Fourier transform infrared spectrometry. Although limiting oxygen index value of the composites decreased with increasing ZB amount, a suitable addition of ZB can apparently improve the UL 94 rating of the material. The heat release rate of the 5% ZB containing ternary composites decreased compared with the EVA/LDHs composites. It is obtained from smoke density test that ZB could help smoke suppression. The ternary composites possessed a higher thermal stability than the EVA/LDHs composites. Copyright © 2016 John Wiley & Sons, Ltd.     

Treatment of heavy metal ions in wastewater using layered double hydroxides: A review

Heavy metal ions are toxic, and their toxicities change with different valence states, charges, and radii. Among the methods used for heavy metal ion removal, adsorption is widely employed due to its low cost and simple operation. As natural anionic clays, layered double hydroxides (LDHs) have drawn considerable attention for their use in the removal of anionic pollutants (such as heavy metal anions) due to their high removal efficiency and environmental friendliness. This article reviews the effects of the charge, type, and radius of the cations in the laminates of LDHs and the anions in the LDH interlayers, as well as the charge and radius of the heavy metals and the conditions (such as pH, coexisting ions, and temperature) on removing heavy metal ions with LDHs. The removal mechanisms have also been discussed. LDHs are hugely promising as an application for removing heavy metal ions that exist in different ionic forms by controlling the type and condition of LDHs.     

Preparation,characterization, structure‐property relationships,and thermal degradation kinetics of poly (lactic acid)/amidated potassium hydrogen phthalate intercalated layered double hydroxides nanocomposites

A novel nucleating agent, amidated potassium hydrogen phthalate intercalated layered double hydroxides (AP‐LDHs) were prepared using an amidation reaction. Through the structural characterization, it was found that AP‐LDHs had been successfully prepared. Meanwhile, the antibacterial activity of AP‐LDHs was studied. In order to improve the performance of poly (lactic acid) (PLA), PLA/AP‐LDHs nanocomposites were prepared by melt blending. Morphological analysis showed that PLA nanocomposites had an exfoliated structure. Mechanical properties test showed that the mechanical properties of PLA nanocomposites were enhanced. And the fracture scanning electron microscope analysis indicated that the PLA/AP‐LDHs nanocomposites exhibited ductile fracture characteristics. Moreover, differential scanning calorimetry and polarized optical microscopy analysis results demonstrated that the crystallization rate, nucleation density, and crystallinity of PLA/AP‐LDHs were improved. Thermogravimetric analysis and thermal degradation kinetics showed that the thermal stability of the PLA nanocomposites was significantly improved.     

磷钨酸插层MgAl水滑石层间距的调变及催化酯化脱酸性能

通过改变离子交换温度和时间合成了具有不同层间距的磷钨酸(H_3PW_(12)O_(40),HPW)插层MgAl水滑石(LDHs),采用XRD、FT-IR、Raman、~(31)P MAS NMR、ICP-AES和Hammett指示剂-正丁胺滴定法等表征其性质,并研究其对模型原油的催化酯化脱酸性能。高的离子交换温度有利于形成较大的层间距(d_(003)约1.46 nm),较长的交换时间有利于形成较小的层间距(d_(003)约1.05 nm)。不同的层间距源自HPW在层间不同的存在形式,P_2W_(18)O_(62)~(6-)以C_2轴倾斜于层板和PW_(11)O_(39)~(7-)以C_2轴垂直于层板的方式排列于层间时,形成d_(003)约1.46 nm的层间距;PW_(12)O_(40)~(3-)与层板发生嫁接,并以C_2轴垂直于层板的方向排列于层间时,形成d_(003)约1.05 nm的层间距。层间P_2W_(18)O_(62)~(6-)和PW_(11)O_(39)~(7-)能产生更高比例的中强酸中心,同时大的层间距有利于反应物扩散进入层间与酸中心接触,能够提高LDHs的催化酯化脱酸性能。     

Fiber‐in‐tube solid‐phase microextraction of caffeine as a molecular tracer in wastewater by electrochemically deposited layered double hydroxide

Modified stainless‐steel wires with a layer of polyaniline conductive polymer were coated by electrochemical deposition with Zn/Al layered double hydroxide to make solid‐phase microextraction fibers. The coating layer was also electrochemically deposited on the inner surface of a stainless‐steel tube. Then, ten prepared fibers were put inside the inner coated tube to make a fiber‐in‐tube solid phase microextraction device. The device was applied for the extraction of caffeine (1,3,7‐trimethylxanthine) from domestic wastewater samples. Extraction conditions including extraction and desorption times, pH and ionic strength of the sample solution, and content of the organic desorption solvent were investigated and optimized. Under the optimized conditions, the fiber‐in‐tube solid phase microextraction exhibited excellent extraction efficiency toward caffeine. The precision of the method was evaluated. Average relative standard deviation of 5.7% (n = 6) for intraday analysis and 8.3% (n = 5) for interday analysis was obtained. The limits of detection and limits of quantification of the method (at signal to noise ratio of 3 and 10) were obtained as 0.14 and 0.37 ng/mL, respectively. The current study can provide new prospective applications of layered double hydroxide conductive polymer fiber coatings.     

Immobilization of lipase from Candida rugosa on layered double hydroxides for esterification reaction

Synthesis of layered double hydroxides (LDHs) of Zn/Al-NO3- hydrotalcite (HIZAN) and Zn/Al-diocytyl sodium sulfosuccinate (DSS) nanocomposite (NAZAD) with a molar ratio of Zn/Al of 4:1 were carried out by coprecipitation through continuous agitation. Their structures were determined using X-ray diffractometer spectra, which showed that basal spacing for LDH synthesized by both methods was about 8.89 A. An expansion of layered structure of about 27.9 A was observed to accommodate the surfactant anion between the interlayer. This phenomenon showed that the intercalation process took place between the LDH interlayer. Lipase from Candida rugosa was immobilized onto these materials by physical adsorption method. It was found that the protein loading onto NAZAD is higher than HIZAN. The activity of immobilized lipase was investigated through esterification of oleic acid and 1-butanol in hexane. The effects of pore size, surface area, reaction temperature, thermostability of the immobilized lipases, storage stability in organic solvent, and leaching studies were investigated. Stability was found to be the highest in the nanocomposite NAZAD.     

Thermal degradation kinetics of biodegradable poly(3‐hydroxybutyrate)/layered double hydroxide nanocomposites

The thermal degradation behaviors of biodegradable poly(3‐hydroxybutyrate) (PHB) and PHB/poly(ethylene glycol) phosphonates (PEOPAs)‐modified layered double hydroxide (PMLDH) nanocomposites have been investigated using thermogravimetric analysis. Effects of PMLDH contents on the isothermal degradation kinetics of PHB were explored. These experimental results show that the degradation kinetics of PHB/PMLDH nanocomposites is the chain‐scission process of cyclic β‐elimination reaction with the following autocatalytic reactions, which is very similar to that of pure PHB matrix. Further calculated data based on the autocatalytic model can fit very well with the experimental data. The E_a value of PHB/PMLDH nanocomposites is increased as the content of PMLDH increases. This can be attributed to the incorporation of more PMLDH loading to PHB induced a decrease in the degradation rate and an increase in the residual weight for PHB/PMLDH nanocomposites. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1207–1213, 2008     

A comparative study of thermal decomposition behaviour of Zn-Cr,Zn-Cr-Al and Zn-Al type layered double hydroxides

Hydrolysis of ZnO in acidic pH provides a facile route for synthesis of layered double hydroxides (LDH) bearing Zn²⁺ with Cr³⁺ and Al³⁺ without having carbonate ion in the inter-layer position. The thermal decomposition of the prepared LDH show that with the increase of Cr³⁺ content in the system there is an increase in the thermal stability of the compounds. In case of Zn-Cr LDH there is a non-mass loss transition around 420°C. Segregation of parent LDH structure to a bivalent oxide and a spinel takes place in both Zn-Cr and Zn-Al LDH only at temperatures above 550°C.Authors are grateful to Director R. R. L. Jorhat for his kind permission to publish the work, as well as acknowledgement is due to Prof. Herbert Poellmann of University of Halle, Germany for some powder XRD runs. Also, acknowledgement is due to Ministry of Environment and Forests, Govt. of India for some financial assistance.     

Development of a γ‐alumina‐ nanoparticle‐functionalized porous polymer monolith for the enrichment of Sudan dyes in red wine samples

Monolithic materials were synthesized in capillaries by in situ polymerization with N‐isopropylacrylamide, glycidyl methacrylate, and ethylene dimethacrylate as the monomers, and methanol and PEG as the porogens. With γ‐alumina nanoparticles attached to the surface of the porous monolithic column via epoxide groups, a novel polymer monolith microextraction (PMME) material was prepared with a good mechanical stability and a high extraction capacity. SEM and X‐ray photoelectron spectroscopy were employed to characterize the modified monolithic column, demonstrating that γ‐alumina nanoparticles were effectively functionalized onto the monolithic column. In addition, a new method was developed for the analysis of Sudan I–IV dyes using PMME coupled with HPLC. In order to obtain the optimum extraction efficiency, the PMME conditions including desorption solvent type, sample pH, sample volume, sample flow rate, and eluent flow rate were investigated. Under the optimum conditions, we obtained acceptable linearities, low LODs, and good intra‐ and interday RDSs. When applied to the determination of Sudan I–IV dyes in red wine samples, satisfactory recoveries were obtained in the range of 84.0–115.9%.     

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。     

Poly(L‐lactide)/layered double hydroxides nanocomposites: Preparation and crystallization behavior

Novel nanocomposites from poly(L ‐lactide) (PLLA) and an organically modified layered double hydroxide (LDH) were prepared using the melt‐mixing technique. The structure and crystallization behavior of these nanocomposites were investigated by means of wide‐angle X‐ray diffraction (WAXD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and polarized optical microscopy (POM). WAXD results indicate that the layer distance of dodecyl sulfate‐modified LDH (LDH‐DS) is increased in the PLLA/LDH composites, compared with the organically modified LDH. TEM analysis suggests that the most LDH‐DS layers disperse homogenously in the PLLA matrix in the nanometer scale with the intercalated or exfoliated structures. It was found that the incorporation of LDH‐DS has little or no discernable effect on the crystalline structure as well as the melting behavior of PLLA. However, the crystallization rate of PLLA increases with the addition of LDH‐DS. With the incorporation of 2.5 wt % LDH‐DS, the PLLA crystallization can be finished during the cooling process at 5 °C/min. With the addition of 5 wt % LDH‐DS, the half‐times of isothermal melt‐crystallization of PLLA at 100 and 120 °C reduce to 44.4% and 57.0% of those of the neat PLLA, respectively. POM observation shows that the nucleation density increases and the spherulite size of PLLA reduces distinctly with the presence of LDH‐DS. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2222–2233, 2008