Thermal behaviour of montmorillonite pillared with different metal oxides

Natural montmorillonite was pillared by various polyhydroxy cations. The resulting pillared layer clays (PILCs) were characterized by X-ray fluorescence, X-ray diffraction (XRD) and infrared (IR) spectroscopies. The thermal behaviour of Al-PILC was investigated in detail by a combonation of XRD, derivatography IR spectroscopy and a comparison to natural montmorillonite is given. It was found that thermal stability of Al-PILC is lower than that of natural montmorillonite. However, heat treatment in the stability region results in significant sintering of natural montmorillonite, while the interlayer spacing of Al-PILC is hardly affected.     

Intercalation of a nonionic surfactant (C10E3) bilayer into a Na-montmorillonite clay

A nonionic surfactant, triethylene glycol mono-n-decyl ether (C(10)E(3)), characterized by its lamellar phase state, was introduced in the interlayer of a Na-montmorillonite clay at several concentrations. The synthesized organoclays were characterized by small-angle X-ray scattering in conjunction with Fourier transform infrared spectroscopy and adsorption isotherms. Experiments showed that a bilayer of C(10)E(3) was intercalated into the interlayer space of the naturally exchanged Na-montmorillonite, resulting in the aggregation of the lyotropic liquid crystal state in the lamellar phase. This behavior strongly differs from previous observations of confinement of nonionic surfactants in clays where the expansion of the interlayer space was limited to two monolayers parallel to the silicate surface and cationic surfactants in clays where the intercalation of organic compounds is introduced into the clay galleries through ion exchange. The confinement of a bilayer of C(10)E(3) nonionic surfactant in clays offers new perspectives for the realization of hybrid nanomaterials, since the synthesized organoclays preserve the electrostatic characteristics of the clays, thus allowing further ion exchange while presenting at the same time a hydrophobic surface and a maximum opening of the interlayer space for the adsorption of neutral organic molecules of important size with functional properties.     

Use of a polyhedral oligomeric silsesquioxane (POSS)-imidazolium cation as an organic modifier for montmorillonite

Recent studies on organically modified clays (OMCs) have reported enhanced thermal stabilities when using imidazolium-based surfactants over the typical ammonium-based surfactants. Other studies have shown that polyhedral oligomeric silsesquioxanes (POSS) also improve the thermal properties of composites containing these macromers. In an attempt to utilize the beneficial properties of both imidazolium surfactants and POSS macromers, a dual nanocomposite approach to prepare OMCs was used. In this study, the preparation of a new POSS-imidazolium surfactant and its use as an organic modifier for montmorillonite are reported. The purity, solubility, and thermal characteristics of the POSS-imidazolium chloride were evaluated. In addition, several OMCs were prepared by exchanging the Na+ with POSS imidazolium cations equivalent to 100%, 95%, 40%, 20%, and 5% of the cation exchange capacity of the clay. The subsequent OMCs were characterized using thermal analysis techniques (DSC, SDT, and TGA) as well as 29Si NMR to determine the POSS content in the clay interlayer both before and after thermal oxidation degradation. Results indicate the following: (1) the solvent choice changes the efficiency of the ion-exchange reaction of the clay; (2) self-assembled crystalline POSS domains are present in the clay interlayer; (3) the d-spacing of the exchanged clay is large (3.6 nm), accommodating a bilayer structure of the POSS-imidazolium; and (4) the prepared POSS-imidazolium exchanged clays exhibit higher thermal stabilities than any previously prepared imidazolium or ammonium exchanged montmorillonite.     

Hybridization of sugar alcohols into brucite interlayers via a melt intercalation process

We report the preparation of organic-brucite (BR) hybrids using harmless sugar alcohols (xylitol, XYL, and sorbitol, SOR). Since XYL and SOR are solid materials at room temperature, the hybridization was investigated by comparing two separate methods, hydrothermal treatment and melt mixing. BR-sugar alcohol hybrids were successfully prepared by a melt intercalation method at 175 °C. X-ray diffraction and Fourier transform infrared spectroscopy analyses indicated that organic molecules were intercalated into the brucite layers, overcoming the barrier of hydroxyl bonds between the BR layers. Moreover, X-ray photoelectron spectroscopy and thermal analyses showed that the intercalated materials at 175 °C resulted in the formation of covalent Mg-O-C bond linkages on the interlayer surface of BR.     

聚苯胺/ZnFe_2O_4纳米复合物的制备与表征

以Fe(NO3)3·9H2O和Zn(NO3)2·6H2O为原料,采用改进的柠檬酸盐前驱物法合成了片状ZnFe2O4,进一步通过原位聚合反应得到了聚苯胺(PANI)/ZnFe2O4纳米复合物。利用X射线粉末衍射、扫描电子显微镜、透射电子显微镜、红外光谱以及荧光光谱等测试技术对其进行了表征。实验结果表明,通过原位聚合反应PANI沉积在片状ZnFe2O4表面。X射线粉末衍射和红外光谱进一步证实了PANI/ZnFe2O4纳米复合物的生成。ZnFe2O4的引入提高了PANI的荧光发光性能和热稳定性。     

Vermiculite as a useful host for guest cyclic aliphatic amine intercalation, followed by cation adsorption

Two vermiculite hybrids containing aliphatic amines intercalated were synthesized. The amount of guest molecules intercalated resulted in 0.60 and 0.52 mmol g⁻¹ for pyperidine and pyperazine, respectively, which reflect the effectiveness of such kind of reactions. The processes were confirmed by elemental analysis and infrared spectroscopy. X-ray diffraction patterns suggested that the original crystallinity of matrix was maintained, however, the intercalation process is associated with the conformation of the guest molecule and the presence of the compensate cation inside the interlayer cavity. The intercalated inorganic hosts adsorb divalent lead, nickel, copper and cobalt cations, more effectively at basic pH value, from aqueous solution, which content of adsorption is higher than the precursor native vermiculite.     

Investigation of structure and thermal stability of surfactant-modified Al-pillared montmorillonite

For combining the properties of organoclays and pillared clays, inorganic–organic clays have attracted much attention in recent years. In this study, Al Keggin cation pillared montmorillonites (Al-Mts) were first prepared and parts of Al-Mts were calcined at different temperatures (C-Al-Mts). The inorganic–organic montmorillonites were synthesized by intercalating Al-Mts and C-Al-Mts with the cationic surfactant, hexadecyltrimethyl ammonium bromide (HDTMAB). The products were characterized by X-ray diffraction, X-ray fluorescence, and simultaneous thermogravimetric analysis. For HDTMAB-modified uncalcined Al Keggin cation pillared montmorillonites (H-Al-Mts), the basal spacing increased with the increment of surfactant loading level, but the Al content of H-Al-Mts decreased simultaneously, indicating that the intercalated surfactant replaced some Al Keggin cations in the interlayer space. However, in the case of C-Al-Mts, the interlayer spaces could not be further expanded after surfactant modification, implying that the neighboring montmorillonite layers were “locked” by the aluminum pillars which were formed by dehydroxylation of Al Keggin cation pillars during thermal treatment. The thermal stability of HDTMAB-modified C-Al-Mts (H-C-Al-Mts) was much better than that of H-Al-Mts. The major mass loss of H-C-Al-Mts occurred at ca. 410 °C, corresponding to decomposition of intercalated surfactant cations. In contrast, H-Al-Mts displayed two mass loss temperatures at ca. 270 and 410 °C, corresponding to the evaporation of surfactant molecules and the decomposition of surfactant cations in the interlayer space, respectively.     

Novel hybrids of Cu2+ ternary complexes of salicylidene-amino acid Schiff base with phenanthroline（or bipyridine） intercalated in Mg/Al-NO3-layered double hydroxide

Four Cu²⁺ complexes of salicylidene-amino acid Schiff base with 1,10-phenanthroline（Phen） or 2,2’- bipyridine（Bipy） were successfully intercalated in interlayer galleries of Mg/Al-NO₃-layered double hydroxide（LDH） by the swelling-restored method.The hybrids were characterized by elemental analysis,X-ray diffraction,FT-IR spectra,UV-vis DRS,TG-DTA and SEM observation.Good protection of the complexes by LDH in neutral and weak acidic solutions was revealed by UV spectra,cyclic voltammograms and luminescence spectra.     

Dispersion of organically modified clays within n-alcohols

A method for formation of polymer-clay nanocomposites involves dispersion of the nanometer silicate layers of clays into a solvent, followed by dispersion into polymers. The dispersion of layered silicates within solvents affects the structure and properties of the nanocomposites. We report the dispersion of organically modified clays, used for formation of nanocomposites with organic polymers, within a range of alcohol solvents. Experiments involved stirring a mixture containing approximately 1 wt% of alkylammonium-modified clays in n-alcohols with general molecular structure RnOH, where n represents the number of carbons of alkyl chains, varying from 2 to 8. The clays precipitated from the dispersion when RnOH solvents with n<5 were used, however, they formed gels for solvents with n5. The increased dispersion was related to the decrease of polarity and hydrogen bonding force within solvents. X-ray diffraction for the dispersed clays indicated that the interlayer spaces (1.8 nm), formed by regular stacking of the silicate layers, expanded to a maximum of 3.0 nm after treatment with RnOH with n5. The interlayer expansion was due to the intercalation of n-alcohol molecules within the interlayer spaces. It is suggested that the alkyl chains of n-alcohols remain parallel to the silicate surface in the intercalate. Preliminary experiments on the influence of these alcohol solvents on the intercalation of polyol (polyether) are also reported.     

Incorporation of fullerene derivatives into smectite clays: a new family of organic-inorganic nanocomposites

Three fulleropyrrolidine derivatives, characterized by the presence of positive charges, were introduced in the interlayer space of montmorillonite. The composites were characterized by powder X-ray diffraction and differential thermal and thermogravimetric (DTA-TGA) analysis, in conjunction with FTIR, UV-Vis, Raman, and (57)Fe-M?ssbauer spectroscopies. Organophilic derivatives were intercalated into organically modified clays, while water-soluble fulleropyrrolidines were introduced into the clay galleries through ion exchange. The experiments, complemented by computer simulations, show that not all the clay-clay platelets are intercalated by the fullerene derivatives and that a sizable amount of charge transfer takes place between the host and the guests.     

Surface modification of nanoclays by catalytically active transition metal ions

A unique class of nanoclays was prepared by modification of pristine clays or organoclays (Cloisite C20A) with transition metal ions (TMIs). The composition, structure, morphology and thermal properties of TMI-modified nanoclays were investigated by atomic absorption spectroscopy (AAS), elemental analysis (EA), scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray absorption near-edge structure (XANES) spectroscopy. The content of TMIs in modified clays was found to be close to the limiting value of ion exchange capacity. SEM and X-ray results confirmed that TMIs were located between the mineral layers instead of being adsorbed on the surface of clay particles. TGA results indicated that the TMI treatment of organoclays could significantly increase the thermal stability, which was more pronounced in air than in nitrogen. Temperature-resolved SAXS measurements revealed that the presence of TMIs increased the onset temperature of structural degradation. The higher thermal stability of TMI-modified organoclays can be attributed to the change in the thermal degradation mechanism, resulting in a decrease in the yield of volatile products and the formation of char facilitated by the presence of catalytically active TMIs.     

Sol–gel synthesis and enhanced properties of a novel transparent PMMA based organic–inorganic hybrid containing phosphorus,nitrogen and silicon

A novel flame-retardant silane containing phosphorus and nitrogen, tetramethyl(3-(triethoxysilyl)propylazanediyl) bis(methylene) diphosphonate (TMSAP), is firstly synthesized and then incorporated into poly(methyl methacrylate) (PMMA) matrix through sol–gel method to produce organic–inorganic hybrids. The chemical structure of TMSAP was confirmed by Fourier transform infrared spectra, ¹H nuclear magnetic resonance (NMR) and ³¹P NMR spectra. The hybrids obtained maintain relatively high transparency, and exhibit a significant improvement in thermal properties, mechanical performance and flame retardancy when compared to pure PMMA, including increased glass transition temperature (T _g ) by 11.4 °C, increased onset thermal degradation temperature (T_0.1) by 82.6 °C, increased half thermal degradation temperature (T_0.5) by 42.0 °C, increased hardness, increased limited oxygen index and decreased heat release rate. Morphological studies of hybrids by scanning electron microscopy (SEM) and ²⁹Si MAS NMR suggest that cross-linked silica network is formed in the hybrids and the inorganic silica particles are distributed well in the polymer matrix. Thermal degradation behaviors investigated by thermogravimetric analysis and char structure analysis studied by SEM and X-ray photoelectron spectroscopy demonstrate the catalytic charring function of TMSAP, and synergistic effect between phosphorus, nitrogen and silicon element. The formation of network structure, homogeneous distribution of silica and the char formation during degradation play key roles in these property enhancements. Detailed mechanisms for these enhancements are proposed.     

Modification of the surfaces of Wyoming montmorillonite by the cationic surfactants alkyl trimethyl, dialkyl dimethyl, and trialkyl methyl ammonium bromides

Surfaces of a Wyoming SWy-2 sodium montmorillonite were modified using microwave radiation through intercalation with the cationic surfactants octadecyl-trimethyl ammonium bromide, dimethyldioctadecylammonium bromide, and methyl-tri-octadecyl ammonium bromide by an ion exchange mechanism. Changes in the surfaces and structure were characterized using X-ray diffraction (XRD), thermal analysis (TG) and infrared (IR) spectroscopy. Different configurations of surfactants within montmorillonite interlayer are proposed based on d(001) basal spacings. A range of surfactant molecular environments within the surface-modified montmorillonite are proposed based upon their thermal decomposition. IR spectroscopy using a smart endurance single bounce diamond attenuated total reflection (ATR) cell has been used to study the changes in the spectra of CH asymmetric and symmetric stretching modes of the surfactants to provide more information of the surfactant molecular configurations.     

Fourier Transform Infrared Spectra of Naphthalene Disulfonates between Layers of Mg and Al double Hydroxide: Intercalation by Means of Coprecipitation and Direct Observation of Coordination from the Interlayer Anion to the Metal Cation in the Layer

A Mg/Al-layered double hydroxide with interlayernaphthalene-2,6-disulfonate having a basal spacing of1.68 nm was prepared by means of the coprecipitationmethod. The results of powder X-ray diffractionare compared with those of other intercalates whichhave interlayer naphthalene disulfonates. Fouriertransform infrared spectra of the LDH intercalatedcompounds reveal that the organic molecules located inthe interlayer region are stable. Coordinationfrom the oxygen atom in the –SO₃ ^- group of the interlayer molecules to the metal cation in the layeris observed.     

Comparison of solution-blending and melt-intercalation for the preparation of poly(ethylene-co-acrylic acid)/organoclay nanocomposites

Ethylene-acrylic acid copolymers (EAAs) and commercial montmorillonite clays organically modified with dimethyldihydrogenatedtallowammonium ions (Cloisite^® 15A and 20A) were used for the synthesis of nanocomposites by melt-compounding, static melting of polymer/clay mixtures and solution-intercalation in order to compare the effectiveness of these procedures and to shed light on the thermodynamics and the kinetics of the intercalation process. The preparation from solution was made by the use of several solvents, such as toluene, xylene, chloroform, etc., which were then removed from the hybrids by precipitation in different non-solvents or by evaporation. Particular attention was paid to the effect of the thermal treatments which are often used when processing the composites prepared from solution. X-ray diffraction (XRD) of the solution-blended composites showed that no intercalation of the EAAs inside the clay galleries can be achieved if solvent removal is made by precipitation in non-solvents or by room-temperature evaporation. On the contrary, intercalation was found to occur very rapidly (in less than 1 min) when both the hybrids prepared from solution and the mechanical blends of powdered components were melted in the absence of shear. Polymer intercalation was also found to occur, though with a lower rate, upon annealing the powder mixtures at temperatures lower than the EAA melting point. Microscopic observations made by polarized optical microscopy, scanning electron microscopy and transmission electron microscopy showed that the clay particles dispersion is appreciably lower for the composites prepared from solution, compared to those produced in the melt under shear flow conditions. The hybrids obtained by static melting of powder mixtures, on the other side, were expectedly found to comprise micron sized clay agglomerates, although intercalation was demonstrated also for these materials by XRD. The structure of the intercalated silicate layers stacks, characterized by an interlayer spacing of 4.0 nm, was shown to be independent of the preparation procedure and to correspond to thermodynamic equilibrium.     

Nanocomposites of polystyrene-b-polyisoprene copolymer with layered silicates and carbon nanotubes

Nanocomposites of polystyrene-b-polyisoprene (PS-b-PI) copolymer with layered-smectite clays (organically modified montmorillonite) and nanostructured clay-carbon nanotube hybrids were prepared. The diblock copolymer was synthesized by anionic polymerization using high-vacuum techniques and was molecularly characterized by size exclusion chromatography. Carbon nanotubes were developed on clay-supported nickel nanoparticles by the CCVD method. Nanotubes attached on the clay platelets were then chemically modified to create ester groups on their surfaces. PS-b-PI nanocomposites at various polymer to reinforcement loadings were prepared by solution intercalation. The final nanocomposites were characterized by powder X-ray diffraction, FT-IR spectroscopy, thermal analysis, and scanning electron microscopy. The experiments complemented with viscometry measurements reveal the successful incorporation of the reinforcements in the polymer mass.     

Intercalation effects in LDPE/o-montmorillonites nanocomposites

Typical montmorillonite clays (Cloisite^® Na⁺, Cloisite^® 30B) were modified by treatment with octadecyl ammonium chloride (ODC) and successive additions of octadecylamine (ODA). XRD analyses of the modified clays indicated an increase of the basal spacing of the (0 0 1) planes depending on the ODC or ODA additions.Nanocomposites were prepared by dispersing the modified clays (3% w/w concentration) in LDPE, using a Brabender mixer. XRD measurements of the obtained products indicated in some cases the achievement of intercalation effects, which were confirmed by TEM analysis.Some thermal, mechanical, dynamic-mechanical and rheological properties were evaluated and correlated to the degree of intercalation.     

Novel multilamellar mesostructured molybdenum oxide nanofibers and nanobelts: synthesis and characterization

One-dimensional molybdenum oxide nanostructures with layered mesostructures were prepared directly from commercial bulk MoO3 crystals by a surfactant-templated hydrothermal process. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, infrared spectra, and thermal analyses have been used to characterize the obtained molybdenum oxide nanomaterials. By use of cetyltrimethylammonium bromide as the structure-directing template, novel molybdenum oxide nanofibers with triple interlayer distances of 2.84, 2.66, and 2.46 nm have been obtained. The nanofibers have diameters of 20-100 nm and length up to 20 microm. The growth of multilamellar molybdenum oxide nanofibers can be interpreted by the combination of surfactant/inorganic self-assembly process and host/guest intercalation chemistry. On the basis of the X-ray diffraction and infrared results, a possible arrangement of surfactant in the interlayer space of molybdenum oxide by bilayer micelles with different tilt angles has been proposed. In addition, the thermal stability of surfactant has been improved by intercalation. Moreover, molybdenum oxide nanobelts with two kinds of interlayered structures were also produced in the presence of n-alkylamines (n = 12, 14, 16, and 18) following a similar method, these nanobelts show length up to more than 10 microm, width ranging between 200 and 600 microm, and width-to-thickness ratios of about 3-12. A linear relationship is observed between the interlayer distance and the number of carbon atoms in n-alkyl chains.     

Intercalation of salicylic acid into ZnAl and MgAl layered double hydroxides for a controlled release formulation

Salicylic acid was intercalated into an inorganic host consisting of ZnAl/MgAl-layered double hydroxides lamella by reconstruction method. Powder X-ray diffractograms showed that the basal spacing of the layered double hydroxide bearing salicylate as the intergallery anion expanded from 7.6 and 7.8 Å in the precursors to 14.49 Å and 14.85 in ZnAl and MgAl layered double hydroxide, respectively. These values suggest that the organic molecules form bilayers in the interlayer space. Fourier transform infrared study further confirmed intercalation of salicylate into the interlayer’s of the layered double hydroxides. The thermal stability of the intercalated salicylic acid is significantly enhanced compared with the pure form before intercalation. Using the XRD results combined with a molecular simulation model, a possible representation of the salicylate anion positioning between the lamellar layers has been proposed. The in vitro drug release from intercalated material was remarkably lower than that from the corresponding physical mixture at pH 7.5. The kinetic analysis showed the importance of the diffusion through the particle in controlling the drug release rate. The obtained results show that hydrotalcite may be used to prepare modified release formulations.     

基于氟碳表面活性剂插层水滑石的聚酰亚胺纳米复合材料的制备与性能

以氟碳表面活性剂全氟辛基磺酸钾为插层剂, 通过离子交换制备插层水滑石, 并以其为填料, 通过原位插层聚合方法, 制备了水滑石/氟碳表面活性剂/聚酰亚胺纳米复合材料. 用X射线衍射、 红外光谱和热失重等方法分析插层水滑石结构. 结果表明, 全氟辛基磺酸钾插层水滑石后, 水滑石的层间距由0.76 nm增加到2.52 nm, 在水滑石层间构建了氟碳链的微环境. 这种氟化水滑石可剥离分散于聚酰亚胺基体中, 改善了纳米复合材料的气体阻隔性能、 介电性能和机械性能. 这种影响不仅体现无机纳米片层的杂化效果, 而且展示出氟碳链的特点.