Intercalation of an oxalatooxoniobate complex into layered double hydroxide and layered zinc hydroxide nitrate

A Zn/Al layered double hydroxide with molar ratio of 3 was prepared by coprecipitation in alkaline pH and used as a matrix to intercalate the ionic complex diaquadioxalatooxoniobate(V) (DDON), derived from NH₄[NbO(C₂O₄)₂(H₂O)₂]2H₂O. In a similar way, the layered zinc hydroxide nitrate, Zn₅(OH)₈(NO₃)₂2H₂O, was synthesized, preexpanded with azelate ions (⁻OOC(CH₂)₇COO⁻), and then intercalated with the niobium complex. For both layered matrices, the results from X-ray powder diffractometry, Fourier transform infrared spectroscopy, and thermal analysis (TG/s-DTA) indicate the presence of the oxalate ion. In addition, results from X-ray photoelectron and Raman spectroscopy indicate the presence of the niobium center bonded to oxygen atoms. Finally, diffuse reflectance UV–vis spectroscopy suggests that the niobium centers are coordinated to oxalate ions. This is the first report of the intercalation of niobium into a layered matrix.     

Intercalation assembly of kojic acid into Zn-Ti layered double hydroxide with antibacterial and whitening performances

The inhibitor of melanin and the bacteriostatic agent kojic acid was inserted into Zn-Ti layered double hydroxide (LDH) by anion-exchange reaction. The structure, slow release, antibacterial and skin whitening activity were studied.     

Sugar-anionic clay composite materials: intercalation of pentoses in layered double hydroxide

The intercalation of non-ionized guest pentoses (ribose and 2-deoxyribose) into the Mg-Al and Zn-Al layered double hydroxides (LDHs) was carried out at 298 K by the calcination-rehydration reaction using the Mg-Al and Zn-Al oxide precursors calcined at 773 K. The resulting solid products reconstructed the LDH structure with incorporating pentoses, and the maximum amount of ribose intercalated by the Mg-Al oxide precursor was approximately 20 times that by the Zn-Al oxide precursor. The ribose/Mg-Al LDH was observed to have the expanded LDH structure with a broad (003) spacing of 0.85 nm. As the thickness of the LDH hydroxide basal layer is 0.48 nm, the interlayer distance of the ribose/Mg-Al LDH is 0.37 nm. This value corresponds to molecular size of ribose in thickness (0.36 nm), supporting that ribose is horizontally oriented in the interlayer space of LDH. The maximum amount of ribose intercalated by the Mg-Al oxide precursor was approximately 5 times that of 2-deoxyribose. Ribose is substituted only by the hydroxyl group at C-2 position for 2-deoxyribose. Therefore, the number of hydroxyl group of sugar is essentially important for the intercalation of sugar molecule into the LDH, suggesting that the intercalation behavior of sugar for the LDH was greatly influenced by hydrogen bond between hydroxyl group of the intercalated pentose and the LDH hydroxide basal layers.     

Exfoliation of layered double hydroxide in polystyrene by in-situ atom transfer radical polymerization using initiator-modified precursor

Exfoliated nanocomposite, based on Zn, Al layered double hydroxide (LDH) and polystyrene (PS), has been achieved by in-situ atom transfer radical polymerization reaction from initiator-modified LDH. The exfoliated structure is characterized by X-ray diffraction and transmission electronic microscope. The results suggest that the exfoliated ZnAl(DS) LDH sheets with a thickness of less than 1 nm disperse individually in the PS matrix, and the thermal stability of the nanocomposite shows a marked improvement. When the 50 wt% weight loss is selected as a comparison point, the decomposition temperature of PS/LDH nanocomposite is about 45 °C higher than that of pure PS.     

Intercalation of paracetamol into the hydrotalcite-like host

Hydrotalcite-like compounds are often used as host structures for intercalation of various anionic species. The product intercalated with the nonionic, water-soluble pharmaceuticals paracetamol, N-(4-hydroxyphenyl)acetamide, was prepared by rehydration of the Mg-Al mixed oxide obtained by calcination of hydrotalcite-like precursor at 500 °C. The successful intercalation of paracetamol molecules into the interlayer space was confirmed by powder X-ray diffraction and infrared spectroscopy measurements. Molecular simulations showed that the phenolic hydroxyl groups of paracetamol interact with hydroxide sheets of the host via the hydroxyl groups of the positively charged sites of Al-containing octahedra; the interlayer water molecules are located mostly near the hydroxide sheets. The arrangement of paracetamol molecules in the interlayer is rather disordered and interactions between neighboring molecules cause their tilting towards the hydroxide sheets. Dissolution tests in various media showed slower release of paracetamol intercalated in the hydrotalcite-like host in comparison with tablets containing the powdered pharmaceuticals.     

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…     

Fabrication of intercalated p-aminobenzoic acid into Zn-Ti layered double hydroxide and its application as UV absorbent

An organic ultraviolet (UV) ray absorbent, p-aminobenzoic acid (PABA) was intercalated into a Zn-Ti layered double hydroxide (LDH) precursor by an anion-exchange reaction to obtain ZnTi-PABA-LDH, a new organic-inorganic nanocomposite. The structure and the thermal stability of ZnTi-PABA-LDH were characterized by XRD, FT-IR and TG-DTA. The results indicate ZnTi-PABA-LDH, synthesized by this method, exhibit relatively high crystallinity, and markedly enhanced thermal stability of PABA after intercalation into ZnTi-LDH. The UV-vis-NIR spectrophotometric and ESR data show excellent UV ray resistance and greatly decreased photocatalytic activity when PABA is intercalated into the interlayers of the ZnTi-LDH. The studies suggest that ZnTi-PABA-LDH may have potential applications as safe sunscreen materials.     

Thermal characterization of the intercalation compound ofp-toluenesulfonate into a layered double hydroxide

On intercalation ofp-toluenesulfonate (PTS) into Mg/Al (0.73/0.27) layered double hydroxide (LDH), the layer expanded from 4.77 Å to 17.7 Å, indicating that the plane of PTS was perpendicular to the plane of the LDH layers. Thermal treatment of the PTS intercalate resulted in 82% of the included PTS being evolved as decomposition products. This value was higher than the value of 32.5% obtained with sodium PTS and 43.8% with a mixed sample of PTS and Mg/Al (0.73/0.27) LDH. It was considered that the intercalated PTS in Mg/Al (0.73/0.27) LDH was easy to decompose because interaction between intercalated PTS and Mg/Al (0.73/0.27) LDH was smaller than that between sodium and PTS in sodium PTS.     

Surface-charging behavior of Zn-Cr layered double hydroxide

A Zn-Cr layered double hydroxide (LDH) having the formula Zn(2)Cr(OH)(6)Cl(0.7)(CO(3))(0.15)2.1H(2)O was synthesized and characterized by powder X-ray diffraction, infrared spectroscopy, acid-base potentiometric titration, mass titration, electrophoretic mobility, and modeling of the electrical double layer. Adsorption of alizarin was also performed in order to show some particular features of the HDL. Net hydroxyl adsorption, which increases with increasing pH and decreasing supporting electrolyte concentration, takes place above pH 5. The electrophoretic mobility of the particles was always positive and it decreased when the pH was higher than 9. An isoelectric point of 12 could be estimated by extrapolating the data. The modified MUSIC model was used to estimate deprotonation constants of surface groups and different adsorption models were compared. Good fit of hydroxyl adsorption and electrophoresis could be achieved by considering both OH(-)/Cl(-) exchange at structural sites and proton desorption from surface hydroxyl groups. The modeling, in agreement with alizarin adsorption, indicates that most of the structural positive charge of the LDH is screened at the surface by exchanged anions and negatively charged surface groups. It also suggests that only structural charge sites initially neutralized by chloride ions are active for anion exchange. The remaining sites are blocked by carbonate and do not participate in the exchange.     

Studies on the intercalation of naproxen into layered double hydroxide and its thermal decomposition by in situ FT-IR and in situ HT-XRD

Layered double hydroxides, novel anionic clay, meet the first requirement as inorganic matrices for encapsulating functional drugs or biomolecules with negative charge in aqueous media. In this study, naproxen has been intercalated into Mg-Al layered double hydroxide by the methods of ion exchange. The structure and composition of the intercalated material have been studied by X-ray diffraction (XRD), UV-vis spectroscopy and inductively coupled plasma emission spectroscopy. A schematic model has been proposed. Furthermore, in situ Fourier transform infrared spectroscopy, in situ high-temperature XRD, and thermogravimetry (TG) have been used to characterize the thermal decomposition of the hybrid material. It has been found that the thermal stability of the intercalated naproxen is significantly enhanced compared with the pure form before intercalation, which suggests that this drug-inorganic layered material may have prospective application as the basis of a novel drug delivery system.     

Chemical modification of zinc hydroxide nitrate and Zn-Al-layered double hydroxide with dicarboxylic acids

A zinc hydroxide nitrate (ZHN), Zn5(OH)8(NO3)2.2H2O, and a layered double hydroxide (LDH), Zn/Al-NO3 were doped with 0.2 mol% of Cu2+ during alkaline chemical precipitation. Both compounds were intercalated with adipate ((-)OOC(CH2)4COO(-)), azelate ((-)OOC(CH2)7COO(-)), and benzoate (C6H5COO(-)) ions through ion exchange reactions. Solid state 13C nuclear magnetic resonance spectroscopy showed only one signal of carboxylic carbon for adipate and azelate intercalated into LDH, indicating that the carboxylic ends of both acids were equivalent, whereas the signal split when the intercalation was into the ZHN matrix. The electron paramagnetic resonance (EPR) spectrum of copper in octahedral cation sites of LDH layers showed a Hamiltonian parameter ratio g ||/A ||=170 cm and, after intercalation of adipate, the change was not significant: g ||/A ||=174 cm. This result indicates that the carboxylate ions did not coordinate with copper centers. Nonetheless, the intercalation of azelate increased the ratio to g ||/A ||=194 cm, similar to the spectra of ZHN modified with adipate, g ||/A ||=199 cm, and azelate, g ||/A ||=183 and 190 cm, which are associated with the coordination of copper by weak carboxylate anion ligands. Copper occupies octahedral or tetrahedral sites in ZHN layers, and the EPR spectra indicate that the dicarboxylate anions reacted preferentially with octahedral sites, whereas benzoate reacted with both sites.     

Synthesis and selective IR absorption properties of iminodiacetic-acid intercalated MgAl-layered double hydroxide

An MgAl-NO₃-layered double hydroxide (LDH) precursor has been prepared by a method involving separate nucleation and aging steps (SNAS). Reaction with iminodiacetic acid (IDA) under weakly acidic conditions led to the replacement of the interlayer nitrate anions by iminodiacetic acid anions. The product was characterized by XRD, FT-IR, TG-DTA, ICP, elemental analysis and SEM. The results show that the original interlayer nitrate anions of LDHs precursor were replaced by iminodiacetic acid anions and that the resulting intercalation product MgAl-IDA-LDH has an ordered crystalline structure. MgAl-IDA-LDH was mixed with low density polyethylene (LDPE) using a masterbatch method. LDPE films filled with MgAl-IDA-LDH showed a higher mid to far infrared absorption than films filled with MgAl-CO₃-LDH in the 7-25 μm range, particularly in the key 9-11 μm range required for application in agricultural plastic films.     

Stabilization of antioxidant gallate in layered double hydroxide by exfoliation and reassembling reaction

As for the stabilization of chemically sensitive bioactive molecule in this study, gallic acid (GA) with antioxidant property was intercalated into interlayer space of layered double hydroxide (LDH), which was realized by exfoliation and reassembling reaction. At first, the pristine nitrate-type Zn₂Al-LDH in solid state was synthesized via co-precipitation followed by the hydrothermal treatment at 80 °C for 6 h, and then exfoliated in formamide to form a colloidal solution of exfoliated LDH nanosheets, and finally reassembled in the presence of GA to prepare GA intercalated LDH (GA-LDH) desired, where the pH was adjusted to 8.0 in order to deprotonate GA to form gallate anion. According to the XRD analysis, GA-LDH showed well-developed (00l) diffraction peaks with a basal spacing of 1.15 nm, which was estimated to be larger than that of the pristine LDH (0.88 nm), indicating that gallate molecules were incorporated into LDH layers with perpendicular orientation. From the FT-IR spectra it was found that gallic acid was completely deprotonated into gallate, and stabilized in between LDH lattices via electrostatic interaction. The content of GA in GA-LDH was determined to be around 23 wt% by UV–vis spectroscopic study, which was also confirmed by HPLC analysis. According to the in-vitro release of GA out of GA-LDH in PBS solution (pH 7.4) at 4 °C, GA was sustainably released from GA-LDH nanohybrid up to 86% within 72 h. The antioxidant property of GA-LDH was almost the same with that of intact GA which was examined by DPPH. The photostability of GA-LDH under UV light irradiation was immensely enhanced compared to intact GA. It is, therefore, concluded that the present GA-LDH nanohybrid can be considered as an excellent antioxidant material with high chemical- and photo-stabilities, and controlled release property.     

A novel nanocomposite material prepared by intercalating photoresponsive dendrimers into a layered double hydroxide

A novel combination for an inorganic-organic nanocomposite material was demonstrated. Anthryl dendron, i.e., poly(amidoamine) dendron with an anthracene chromophore group at the focal point, was incorporated in the interlayer space of ZnAl-NO₃ type layered double hydroxide (LDH) through an anion-exchange reaction. The photoabsorption and fluorescence properties of the resulting material were different from those of the bare anthryl dendron molecule. It was suggested that the change in photochemical properties was due to the organization and π-π interaction of anthracene chromophores within the interlayer of the LDH.     

Methotrexate intercalated ZnAl-layered double hydroxide

The anticancerous drug methotrexate (MTX) has been intercalated into an ZnAl-layered double hydroxide (LDH) using an anion exchange technique to produce LDH-MTX hybrids having particle sizes in the range of 100-300 nm. X-ray diffraction studies revealed increases in the basal spacings of ZnAl-LDH-MTX hybrid on MTX intercalation. This was corroborated by the transmission electron micrographs, which showed an increase in average interlayer spacing from 8.9 Å in pristine LDH to 21.3 Å in LDH-MTX hybrid. Thermogravimetric analyses showed an increase in the decomposition temperature for the MTX molecule in the LDH-MTX hybrid indicating enhanced thermal stability of the drug molecule in the LDH nanovehicle. The cumulative release profile of MTX from ZnAl-LDH-MTX hybrids in phosphate buffer saline (PBS) at pH 7.4 was successfully sustained for 48 h following Rigter-Peppas model release kinetics via diffusion.     

Heck reaction catalyzed by colloids of delaminated Pd-containing layered double hydroxide

A novel ligand-free catalyst, Pd(II)-doped colloidal layered double hydroxide (LDH) has been prepared from delamination of glycinate-intercalated ternary-component MgPdAl-LDH ([Mg_0.95Pd_0.05Al_1/3(OH)₂][Gly_1/3·mH₂O]) in formamide. The catalytic performance of these mono-dispersed ultrathin nanosheets of LDH for Heck reaction was evaluated. Owing to the largely enhanced accessibility for reactant molecules resulting from the nature of high inner surface area of LDHs, these palladium-bearing nanosheets showed excellent efficiency in Heck reactions in a wide range of substrate molecules. The presence of Mg, Al and OH⁻ ions in the LDH-lamellas favors control the size growth of the in situ formed Pd(0) species implanted in the LDH layer matrixes, helping to prevent the formed Pd(0) from extraction from the lamellas followed by Pd-black formation. Moreover, the Pd sites and basic sites on the brucite-like nanosheets are combined at a molecular level and interact with each other closely because of the co-precipitation method employed; so the basic sites on the LDH monolayers might function as basic ligands. This new catalyst, delaminated MgPdAl-LDH, was characterized by XRD, TEM, HRTEM and EDX analysis.     

An optical sensor based on H-acid/layered double hydroxide composite film for the selective detection of mercury ion

A novel optical chemosensor was fabricated based on 1-amino-8-naphthol-3,6-disulfonic acid sodium (H-acid) intercalated layered double hydroxide (LDH) film via the electrophoretic deposition (EPD) method. The film of H-acid/LDH with the thickness of 1 μm possesses a well c-orientation of the LDH microcrystals confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The fluorescence detection for Hg(II) in aqueous solution was performed by using the H-acid/LDH film sensor at pH 7.0, with a linear response range in 1.0 × 10⁻⁷ to 1.0 × 10⁻⁵ mol L⁻¹ and a detection limit of 6.3 × 10⁻⁸ mol L⁻¹. Furthermore, it exhibits excellent selectivity for Hg(II) over a large number of competitive cations including alkali, alkaline earth, heavy metal and transitional metals. The specific fluorescence response of the optical sensor is attributed to the coordination between Hg(II) and sulfonic group in the H-acid immobilized in the LDH matrix, which was verified by NMR spectroscopy and UV–vis spectra. In addition, density functional theory (DFT) calculation further confirms that the coordination occurs between one Hg²⁺ and two O atoms in the sulfonic group, which is responsible for the significant fluorescence quenching of the H-acid/LDH film. The results indicate that the H-acid/LDH composite film can be potentially used as a chemosensor for the detection of Hg²⁺ in the environmental and biomedical field.     

Intercalation of dodecyl sulfate into layered double hydroxides

The intercalation of sodium dodecyl sulfate and exchange of dodecyl sulfate anion into layered double hydroxides has been examined by means of X-ray diffraction, infrared and thermogravimetric procedures. Three types of derivatives were obtained having mean interlayer spacings of 26 Å, 36 Å and 47 Å, respectively. These interlayer distances did not correlate with the amount of organic incorporated between the layers but, as shown by computer simulations, depended upon the orientation of the chains within the interlamellar space. In several reactions both intercalation of neutral sodium dodecyl sulfate as well as exchange of the dodecyl anion took place. Attempts to remove the alkyl sulfate chains with dilute acid resulted in dissolution of the more basic metals producing non-stoichiometric layered products.     

Production and utilization of amino acids.

The amino acid industry has been steadily expanding since monosodium glutamate was first marketed as a flavoring material in 1909. Its production has recently reached almost the 1 billion dollar level. Amino acids are produced by extraction from protein hydrolyzates, by fermentation with the aid of microorganisms, by enzymatic processes, and by chemical synthesis. To obtain natural L-amino acid, chemical synthesis generally requires two additional steps, i.e. optical resolution and racemization of the D isomer. The most important applications of amino acids include the fortification of plant food and feeds by supplementation of the deficient essential amino acid(s). Apart from their uses in the food industry, medical applications of amino acids (nutritional preparations and therapeutic agents) are becoming increasingly important.