Interlayer Space Of Kaolinite Research Articles

The important role of surface hydroxyl groups in aluminum activation during phyllosilicate mineral acidification

Phyllosilicate minerals are the important components in soils and an important source of activated aluminum (Al) during soil acidification. However, the mechanisms for Al activation in phyllosilicate minerals were not understood well. In this paper, the effect of phyllosilicate surface hydroxyl groups on Al activation during acidification was studied after the minerals were modified with inorganic and organic materials. After modification of kaolinite, montmorillonite, and illite with fulvic acid (FA-), iron oxide (Fe-), Fe combined with FA (Fe-FA-), and siloxane (Si–O-), the interlayer spaces were altered. For instance, when modified with Fe, Fe entered the interlayer spaces of kaolinite and montmorillonite and changed the interlayer spaces of both minerals but did not affect that of illite. Also, the other modification methods had significant effects on the interlayer space of montmorillonite but not on kaolinite and illite. It was observed that all the modification strategies inhibited Al activation during acidification by reducing the number of hydroxyl groups on the mineral surfaces and inhibiting protonation reactions between H+ and hydroxyl groups. Nevertheless, the inhibition effect varies with the type of phyllosilicate mineral. For kaolinite (Kao), the inhibition effect of the different modification methods on Al activation during acidification followed: Fe-FA-Kao > Fe-Kao > Si–O-Kao > FA-Kao. Additionally, for montmorillonite (Mon), the inhibition effect was in the order: Si–O-Mon > Fe-Mon > Fe-FA-Mon > FA-Mon, while for illite, it was: Fe-illite > Si–O-illite ≈ Fe-FA-illite > FA-illite. Thus, the hydroxyl groups on the surfaces and edges of phyllosilicate minerals play an important role in the activation of Al from the mineral structure. Also, the protonation of hydroxyl groups may be the first step during Al activation in these minerals. The results of this study can serve as a reference for the development of new technologies to inhibit soil acidification and Al activation.

Enhanced adsorption performance of La(III) and Y(III) on kaolinite by oxalic acid intercalation expansion method

This paper reported a new method to enhance adsorption performance of La(III) and Y(III) on kaolinite by enlarging the interlayer space of kaolinite. The intercalation method could enlarge the interlayer space of kaolinite effectively in previous research literatures, whereas there were few studies on utilizing further reaction of intercalators to expand and exfoliate kaolinite by generating gas. The expanded kaolinite (EKH) involved in this study could enhance adsorption performance of La(III) and Y(III) significantly. The EKH in a state between extended and exfoliated was obtained undergoing two steps. Firstly, H2C2O4 was inserted into the kaolinite layers through the secondary substitution liquid phase intercalation method. Secondly, the Kaol-H2C2O4 (KH) intercalation complex was rapidly calcined with H2C2O4 and Na2CO3, the power provided by the neutralization reaction promoted the thermal decomposition of H2C2O4 between the kaolinite layers to produce a large amount of gas. XRD showed that the interlayer space of the KH intercalation complex expanded from 0.717 nm to 1.112 nm. The specific surface area and total pore volume of the EKH were 1.5 and 2.2 times higher than unmodified kaolinite respectively. The surface of EKH possessed higher zeta potential with more negative charges. The results of batch adsorption experiments showed that the adsorption capacity (101.5 mg/g and 78.9 mg/g) of EKH to La(III) and Y(III) was much higher than that of kaolinite (17.1 mg/g and 9.8 mg/g). Pseudo-second-order model and Langmuir model manifest the adsorption kinetics and isotherm. Therefore, the EKH prepared by the intercalation expansion method could be prospectively applied to the treatment of La(III) and Y(III) in industrial wastewater.

Titania-triethanolamine-kaolinite nanocomposites as adsorbents and photocatalysts of herbicides

Kaolinite-titania adsorbents/photocatalysts were prepared by functionalizing a kaolinite with titanium(IV) triethanolaminate isopropoxide by the sol–gel route. These materials were characterized by various techniques and applied in adsorption studies (kinetic and equilibrium) of the herbicides diuron, hexazinone, and tebuthiuron. Photodegradation studies were also conducted with the materials submitted to heat-treatment at 400, 700, or 1000 °C. The basal spacing increased from 0.71 to 1.08 nm when pure kaolinite was functionalized with titanium triethanolaminate units. The materials displayed FTIR bands of –CH, –NH2, and Ti–OH groups, thereby confirming that titanium alkoxide was present in the kaolinite interlayer space. The pseudo second-order model was the best for describing the kinetic adsorption process. In the equilibrium study, the Langmuir model best described the adsorption mechanism. The photodegradation studies showed that the kaolinite-titania nanocomposites heat-treated at 400 and 700 degraded diuron, hexazinone, and tebuthiuron efficiently due to the presence of metakaolin and formation of the anatase phase.

A template approach for the multifunctionalization of the interlayer space of kaolinite

The interlayer space of kaolinite was functionalized with an ionic liquid (1-(2-hydroxyethyl)-3-methylimidazolium chloride (IL1)) by controlling the amount of grafted organic cation. The strategy used was to co-intercalate the compound to be grafted and a non-reactive template. The template was an IL (1-(propyl)-3-methylimidazolium chloride (IL2)) capable of intercalating in the interlayer space of kaolinite, without being grafted. This template when intercalated covers certain grafting sites and prevents them from reaction with other chemical species present in the interlayer space. Physicochemical characterizations confirm that the presence of the template effectively reduces the amount of grafted IL. This phenomenon was observed through the decrease of the d001-value of the nanohybrid kaolinite (from 13.1 Å to 9.6 Å) and the increase of the amount of physisorbed water which occupies the vacant space resulting from the partial grafting of the IL. Multifunctional materials were prepared by intercalating dimethyl sulfoxide (DMSO) or by grafting triethanolamine (TEA) molecules in the vacant space, using simple synthesis procedures. Several multifunctional materials can be produced using this approach, the main caution being the judicious choice of reagents. These materials can find promising applications in catalysis and in molecular recognition systems.

Luminescent properties of biohybrid (kaolinite-proline) materials synthesized by a new boric acid catalyzed route and complexed to Eu3+

The properties of Eu3+-biohybrid (kaolinite-proline) materials were investigated by powder X-ray diffraction, vibrational spectroscopy, scanning electron microscopy, nitrogen adsorption and photoluminescence to understand how Eu3+ interacts with the biohybrid matrices. Biohybrids were obtained through the conventional route and by two new catalytic routes for functionalization of clay minerals, and were then complexed to Eu3+ ions at a constant proline:Eu3+ molar ratio of 3:1, while the water molecules originally existing in the first coordination sphere of Eu3+ ions in the kaolinite-grafted complexes were replaced by 2-thenoyltrifluoroacetone (tta). The typical Eu3+ emission spectra for solids containing tta revealed the characteristic Eu3+ transitions from fundamental 5D0 state to excited 7FJ (J = 0, 1, 2, 3 and 4) states. The lifetime measurements also confirmed that water molecules were exchanged, increasing emission efficiency. The time-resolved spectra allowed to remove the matrix and ligand emissions and thus to evaluate their influence on the emission of the lanthanide ion. After incorporation of Eu3+, the thermal stability of the solids improved. The intercalated europium complexes did not show the same ligand/Eu3+ molar ratio as the free complexes, due to the restricted mobility of the ligands grafted within the interlayer spaces of kaolinite. On the contrary, these complexes showed high internal quantum yields, low luminescence suppression (after tta coordination), preserved the kaolinite layered structure. They also showed a low water molecules coordination number, which made them very attractive for luminescent applications, in addition to bringing high added value, due to a low cost, non-toxicity, non-polluting and high efficiency.

Immobilization of l-alanine into natural kaolinite via amidation catalyzed by boric acid for the development of biohybrid materials

The natural amino acid l-alanine was immobilized on the interlayer space and surface of the natural Brazilian São Simão’s kaolinite using two different routes. In the first 3-aminopropyltriethoxysilane was previously grafted into kaolinite interlayer space resulting into aminofunctionlized kaolinite that was further employed as reactive sites on kaolinite surfaces to bond l-alanine via amidation reaction. In the second route 3-aminopropyltriethoxysilane was first modified by l-alanine via amidation reaction catalyzed by boric acid and the modified alkoxide grafted into kaolinite using kaolinite-dimethylsulfoxide resulting on the biohybrid. In both strategies the amino acid was covalently bounded using the carboxylic acid from the amino acids and amine groups present on the kaolinite surfaces resulting in amide bonds. In both routes, the reaction was catalyzed by boric acid. Results confirms that the nature and loading of immobilized l-alanine changes depending of the route employed. X-ray diffraction confirmed the expansion of the interlayer spaces of the grafted solids resulting in 8.3 ​Å and 10.8 ​Å respectively for grafted materials routes one and two respectively. Reaction effectivity was kinetically evaluated by infrared vibrational spectroscopy that confirms the presence of amide bonds in both products due to the bands at 1560 ​cm−1, due to carbonyl (N–CO) stretching, and 1490 ​cm−1, ascribed to N–H plane vibrations and C–N stretching. The typical vibration of inner surface aluminol groups at 938 ​cm−1 (for purified kaolinite) is absent for both routes employed after grafting reactions confirming the attachment of the modified alkoxide into aluminol groups via covalent bonds resulting in bonds type Al–O–Si. Thermal analysis showed the typical reduction of dehydroxylation temperature from 510 ​°C on pure kaolinite to 480 and 450 ​°C, respectively, on the biohybrid materials and confirmed the functionalization in both routes, the amount of organic content was quantified and was 0.193 and 0.298 ​mol of organic unit per 1 ​mol of kaolinite minimal formulae using route of previous grafting of kaolinite with amine groups and direct grafting of modified alkoxide into kaolinite dimethyl sulfoxide respectively. Specific surface area analysis by N2 adsorption-desorption isotherms (BET method), cationic exchange capacity, and total specific surface area by the methylene blue method also confirmed the reduction of specific surface area from kaolinite grafted derivatives induced by amidation reaction. The solids obtained was tested as matrix to incorporate acetyl salicylic acid and ibuprofen and reveal that grafted clays incorporate a higher amount of both drugs (qt ​= ​210 ​mg/g) The model that explain the adsorption kinetic mechanism was the pseudo-second order that reveal the higher affinity between adsorbent and acetyl salicilSalicylic acid and ibuprofen using the grafted kaolinite with alanine.

Voltammetric Determination of Pb(II) Ions at a Modified Kaolinite-Carbon Paste Electrode

We report a novel application of a carbon paste electrode modified with sodium dodecyl sulphate (SDS) intercalated kaolin clay for the electrochemical detection of Pb2+in aqueous medium using square wave voltammetry. SDS was used to modify a chemically purified kaolin clay via intercalation process to prepare a carbon paste electrode. The SDS kaolin clay was obtained by intercalation of SDS into the interlayer spaces of kaolinite in the presence of heat. The purified kaolinite and its SDS intercalate were characterised using techniques such as X-ray powder diffraction (XRD), X-ray fluorescence (XRF), thermogravimetric analysis (TGA), attenuated total reflection Fourier transform infrared (ATR-FTIR), scanning electron microscopy (SEM), BET and CHNS elemental analysis. These techniques proved the successful intercalation of SDS into the interlayer spaces of the clay adsorbent. Various parameters affecting the electrochemical detection of Pb2+ were optimised. A linear current response was obtained in the concentration range of 1–100 ppb. The limit of detection was found to be 2.48 ppb. The proposed sensor also demonstrates good reproducibility after series of 10 repetitive measurements with a relative standard deviation (RSD) of about 6.30%. The interfering effects of some ions on the detection of Pb2+ were evaluated. The proposed sensor was applied for the determination of Pb2+ in a real water sample.

Kaolinite Clay Mineral Reactivity Improvement through Ionic Liquid Functionalization

AbstractSince the intercalation of 1‐ethylpyridinium chloride in the interlayer space of kaolinite in 2005, several other ionic liquids (ILs) have been successfully intercalated. Unlike other clay minerals that display charged structural units, kaolinite is almost neutral. ILs intercalation in kaolinite results in both the cation and the anion in the interlayer space. The confinement of ILs in this two‐dimensional polarized space is of numerous interests, with certainly the most important to be discovered. Moreover, kaolinite interlayer space is decorated by a dense network of hydroxyl functions that can be easily functionalized. Recent study demonstrates that it is possible to synthesize ILs from simple organic molecules whose cations can be permanently grafted into the interlayer space of kaolinite. This review presents the results obtained in kaolinite functionalization by ILs, by focusing on the synthesis, applications and potential perspectives offered by these new nanohybrid materials.

Preparation of Methyl Viologen-Kaolinite Intercalation Compound: Controlled Release and Electrochemical Applications.

This work reports the preparation of novel kaolinite nanohybrid material obtained by intercalation of methyl viologen (MV) in the interlayer space of kaolinite, using methoxykaolinite (K-M) as starting material. Characterization of the resulting material (K-MV) confirmed the presence of MV units in the interlayer space of K-M with lateral orientation, associated with a high amount of water molecules due to the hydrophilic nature of MV. The resulting structural formula of this organoclay based on thermogravimetric analysis was Si2Al2O5(OH)3.72(OCH3)0.28(MV)0.17(H2O)0.82. The release of MV from the K-MV composite was studied in order to evaluate the advantages of using this material for pesticide formulation with MV as active ingredient. The localization of MV in the interlayer space of K-M significantly slows its release in water. However, the interactions that retain MV in the interlayer space remain sufficiently less intense to ensure a complete release of MV in a relatively short time (2 h). On the basis of the interactions that ensure MV intercalation in methoxykaolinite, K-M was used as electrode modifier and applied for the electrochemical determination of MV. The electrochemical signal of MV on the K-M modified electrode was 2 times more intense compared to the pristine kaolinite modified electrode. After optimization of experimental parameters, a sensitivity of 3.91 μA M-1 and a detection limit of 0.14 nM were obtained at the K-M modified electrode. This performance represents one of the most important reported so far in the literature during the electrochemical determination of MV. The sensor was also found very efficient for MV determination in real water systems (well, spring, and tap water) despite the decrease of sensitivity due to the presence of interfering species.

Sensitive Amperometric Determination of Thiocyanates at Ionic Liquid Nanohybrid Kaolinite Modified Glassy Carbon Electrode

AbstractElectrochemical sensors have been developed by modifying a glassy carbon electrode with organo‐kaolinite hybrid materials. These materials were obtained by the grafting of four ionic liquids (1‐(2‐hydroxyethyl)‐4‐benzylpyridinium chloride, 1‐(2‐hydroxyethyl)‐4‐(tert‐butyl)pyridinium chloride, 1‐(2‐hydroxyethyl)‐4‐ethylpyridinium chloride and 1‐(2‐hydroxyethyl)‐4‐methylpyridinium chloride) on the interlayer aluminol surfaces of kaolinite. With the presence of ionic liquids in the interlayer space of kaolinite, the hybrid materials acquired anion exchange properties and were successfully applied as electrode modifier for the electroanalysis of thiocyanate (SCN−), an anion of medical and environmental concern. A pre‐concentration/detection strategy was used to overcome the interfering effect of the electrolytic solution. After the optimisation of some key experimental parameters (sodium nitrate as electrolyte, 5 min of accumulation time) calibration curves were plotted. Excellent linearity was obtained in the low concentration region (1×10−6 M to 4×10−5 M). The lowest detection limit (15 nM) was obtained with the benzylpyridinium functionalized kaolinite and the highest (60 nM) with the methylpyridinium functionalized kaolinite. Interfering anions (NO3−, Cl−, SO42− and CH3COO−) present in the pre‐concentration solution were found to interfere with SCN− but the sensors remained stable and produced reproducible signals. The most sensitive sensor was successfully applied for the amperometric determination of SCN− in human saliva samples.

Functional Kaolinite.

The world resources of all clays are extremely large. Among the various types of clays, the world mine production of kaolin in 2016 was 37.0 Mt, the largest mined clay. Kaolin is traditionally used in ceramics, refractories and as paper coating and filling. But kaolin, as it is demonstrated in this paper, has a bright potential for use in non-traditional, high value-added, applications. This is particularly true for its principal component: the mineral species kaolinite which has a chemical structure allowing its functionalization, leading to a variety of potential applications. Kaolinite is a layered 1 : 1 clay mineral, the layer being made of two different sheets, a tetrahedral silica sheet and an octahedral alumina sheet. Large dipole-dipole interactions, in addition to a network of H-bonds, link the siloxane surface of a layer to the aluminol surface of another layer, making intercalation of guest species in kaolinite challenging. There is however a limited number of molecular units (molecules or salts) that can directly intercalate in kaolinite to form "pre-intercalates". Once intercalated these molecular units can be exchanged by a large number and variety of guests, providing access to the interlayer space of kaolinite, and to its reactive aluminol internal surfaces. The intercalation of molecules of pharmacological interest showed the potential of kaolinite to act as a slow-releasing agent for drugs, and the intercalation of polymers resulted in the creation of intercalated nanocomposites. The intercalation of ionic liquids gave materials with ionic conductivity properties in the solid-state. Intercalates are however unstable in water. One needed to make these organo-inorgano nanohybrid materials resistant to hydrolysis and more thermally stable. The network of aluminol groups on the internal surfaces of kaolinite offers the opportunity to design and create controlled organo-inorgano nanohybrid materials, taking advantage of their reactivity, in particular with hydroxyl groups of organic compounds, to form Al-O-C bonds. A functional, two-dimensional, spatially restricted, environment can be created with controlled nanoarchitecture. The grafting of organic groups on the aluminol internal carpets has allowed applications in catalysis, in sensing, in heavy metals adsorption, in exfoliated nanocomposite, in luminescence, and in structural modifications to form nanoscrolls or nanorolls. This paper shows how the future of the use of kaolinite will shift from its traditional uses in ceramics, tiles and paper coating to more sophisticated, high value-added, uses. In particular, research should amplify in the years to come to design an efficient and cost-effective method to produce kaolinite with nanotubular morphology. One can foresee also that efficient, easy-to-use, electrochemical devices based on modified kaolinite, will be created to quantify selectively a variety of pollutants in waste waters.

Simulation study of intercalation complexes of kaolinite with simple amides as primary intercalation reagents

Delamination/exfoliation of book-like kaolinite particles is one of the most promising ways to produce aluminosilicate nanoscrolls. For the delamination of the kaolinite layers, multi-step intercalation/deintercalation procedures are used. In the first, direct intercalation step, the intercalation reagents are typically small organic molecules possessing high dipole moment. We modeled, evaluated and compared the incorporation features of formamide, urea and N-methylformamide molecules into the interlayer space of kaolinite by classical molecular simulations using realistic CHARMM-based atomic force fields. Besides the determination of characteristic basal spacings of the intercalation complexes, we compared the density and orientation distributions of the guest molecules, as well as atomic pair correlation functions. From the simulations we also calculated the typical intermolecular interaction energies and estimated the translational mobility of the different substances. Our results show that urea has some preference over the other substances in multi-step, heat-treating intercalation/deintercalation procedures with kaolinite.

Characterization and Applications of Kaolinite Robustly Grafted by an Ionic Liquid with Naphthyl Functionality.

Functionalization of the kaolinite (K) interlayer space is challenging. In this work, a new kaolinite-based nanohybridmaterial (K-NI) was successfully synthesized by grafting on the interlayer aluminol surfaces the ionic liquid, 1-(1-methylnaphthyl)-3-(2-hydroxyethyl) imidazolium chloride (NI), using a guest displacement strategy. A substantial increase of the basal spacing (10.8 Å) was obtained. This is a grafted derivative of kaolinite possessing one of the largest d-values. Washing in water for several days and other vigorous treatments such as sonication showed a minor effect on the integrity of the material. FTIR and 13C NMR confirmed the conservation of the structure of the ionic liquid after the grafting. Thermal analysis confirmed the presence of grafted material and was used to estimate the abundance of the grafted ionic liquid (0.44 mole per mole of kaolinite structural formula, (Al2Si2O5(OH)4)). By using cyclic voltammetry, the permeability of a film of K-NI for the bulky ferricyanide ions was demonstrated. The accumulation of nitrophenolate anions was effective (maximum capacity of 190 μmol/g), but was less important than what was expected due to the steric hindrance of the bulky grafted NI. Although the presence of chloride anions reduced the adsorption capacity, the affinity of the modified kaolinite interlayer space for the nitrophenolate anions was demonstrated.

Kaolinite-polymer compounds by grafting of 2-hydroxyethyl methacrylate and 3-(trimethoxysilyl)propyl methacrylate

Novel kaolinite-polymer solids containing methacrylate groups were prepared by functionalization of the Brazilian São Simão kaolinite with the monomers 2-hydroxyethyl methacrylate (HEMA) and 3-(trimethoxysilyl)propyl methacrylate (TMSPM). Functionalization involved reflux of the monomers in the presence of kaolinite previously intercalated with dimethylsulfoxide (DMSO). HEMA and TMSPM effectively displaced DMSO molecules from the clay mineral interlayer, forming AlOC bonds in organic-inorganic hybrid matrices. The resulting materials were characterized by powder X-ray diffraction, thermal analysis, infrared spectroscopy and TEM analysis. Powder X-ray diffraction evidenced the intercalation of DMSO, and its substitution by HEMA and TMSPM. Thermal analyses indicated that HEMA- and TMSPM-functionalized kaolinite materials were thermally stable up to 300°C. The shift of the infrared bands due to interlayer hydroxyl groups and the presence of bands due to characteristic vibrations of the methacrylate groups (3349, 3331, 3290, and 1589cm−1) also confirmed the functionalization of the kaolinite with the monomers. The ability of both monomers to graft methacrylate groups onto kaolinite interlayer space was also analyzed. The solids obtained were used as adsorbents of dye methylene blue (MB), showing that the clay nanocomposites could remove the dye more efficiently than the isolated precursors (pure kaolinite and the polymers) separately. The kinetics of the process followed a pseudo-second order model and equilibrium fitted well to the Freundlich model.

Effect of reaction temperature on intercalation of octyltrimethylammonium chloride into kaolinite

The structural property, thermal behavior, and morphology of octyltrimethylammonium chloride–kaolinite complexes prepared at different reaction temperatures were studied by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry–differential scanning calorimetry, and scanning electron microscope. The present study demonstrated that the arrangement model of octyltrimethylammonium cations (OTAC+) within the kaolinite interlayer space was independent of reaction temperature. The alkyl chains adopted a similar rigid paraffin-bilayer arrangement with different tilted angles. Although the intercalation led to an increased number of gauche conformers, the number of nonlinear conformers remained constant with increasing temperature. With increasing temperature, the number of trans conformers continuously augmented and resulted in decreased gauche/trans ratio. Therefore, the molecular environment remained solid like. Simultaneously, the surfactant packing density gradually increased, along with the decreasing water content in the organoclays. This effect improved thermal stability and hydrophobicity. The thermal decomposition processes of the kaolinite–OTAC+ complex can be divided into four steps. Furthermore, SEM images showed that the morphology of these complexes was strongly dependent on the given temperature. In general, increasing the temperature within the limited given temperature (≤70 °C) promoted the transformation from platy layers to nanoscrolls. Most of the transformed nanoscrolls were acquired in the products prepared at 70 °C, and further increasing in temperature decreased the nanoscrolls yield. Nevertheless, the packing density increased in the process, thereby demonstrating that the packing density not only promoted nanoscrolls transformation but also prevented the progress.

Characterization of kaolinite-cetyltrimethylammonium chloride intercalation complex synthesized through eco-friend kaolinite-urea pre-intercalation complex

Because of its suitability for producing kaolinite nanoscrolls, the kaolinite-cetyltrimethylammonium chloride intercalation complex is of interest in the research area of kaolinite nanocomposites. Experimental and molecular simulation analyses are used to investigate this intercalation complex, revealing its real structure formed through partially methoxy-modified kaolinite. Cost-efficient homogenization method is applied to synthesize the eco-friend kaolinite-urea pre-intercalation complex, which was found to be favorable to intercalate cetyltrimethylammonium chloride into the interlayer space of kaolinite. The influence of the pre-intercalated urea molecules, the partial modification of kaolinite structure with methoxy groups, and the presence of methanol molecules in the interlayer space of kaolinite on the intercalation of cetyltrimethylammonium chloride is characterized experimentally by X-ray diffraction, thermal analysis, Fourier transform infrared spectroscopy, and electron microscopy. The kaolinite-cetyltrimethylammonium chloride complex is identified at the basal spacing of 3.82nm with the chemical formula of Al2Si2O5(OH)3.7(OCH3)0.3(CTAC)1.6(Me)1.6. Our molecular simulations predict methanol-containing structures between methoxy-functionalized kaolinite layers with diffuse guest molecular arrangements.

Thermal decomposition behavior and de-intercalation kinetics of kaolinite/quaternary ammonium salt complexes

Kaolinite/quaternary ammonium salt complexes were prepared by intercalation and displacement of kaolinite–N-methylformamide (Kaol–NMF) with methanol (Me) and quaternary ammonium salt. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry and differential scanning calorimetry (TG–DSC) analysis. The d-values of the kaolinite/quaternary ammonium salts complexes increase with the alkyl chain length of the quaternary ammonium salts. Based on the results and the available evidence pointing toward the interlayer structure of kaolinite intercalation complexes, the most possible structural model for the kaolinite/quaternary ammonium salt intercalation complexes was proposed. For the kaolinite–dodecyl trimethyl ammonium chloride, kaolinite–trimethyl tetradecyl ammonium chloride and kaolinite–hexadecyltrimethylammonium chloride, the intercalation molecules are oriented perpendicular to the kaolinite surface in a single layer. However, for kaolinite–stearyl trimethyl ammonium chloride, the cationic head of intercalated stearyl trimethyl ammonium chloride molecules may be partially hydrated and arrayed aslant in the interlayer space of kaolinite with an inclination angle of 35°. Thermal analysis results revealed that the thermal decomposition of kaolinite/quaternary ammonium salt complexes occurs in two main steps. The function of the most probable mechanism, activation energy E and pre-exponential factor were obtained by mutual authentication using KAS and Ozawa methods, Satava integral method and Achar–Brindley–Sharp–Wendworth methods. The average activation energy E of four kaolinite/quaternary ammonium salt intercalation complexes is 108.147, 153.478, 125.723 and 88.008 kJ mol−1, respectively. The optimized mechanism function for de-intercalation process of quaternary ammonium salt is f(α) = 1 − α and G(α) = −ln(1 − α).

Structural Model and De-Intercalation Kinetics of Kaolinite-Methanol-Sodium Stearate Intercalation Compound

Kaolinite-methanol-sodium stearate intercalation compound (Ka-MeOH-SS) was prepared by intercalation of kaolinite with dimethyl sulfoxide (DMSO) followed by displacing of DMSO with methanol and methanol by sodium stearate. The sample was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal analysis (thermogravimetry (TGA) and differential scanning calorimetry (DSC)) and transmission electron microscopy (TEM). The results show that the basal spacing of Ka-MeOH-SS was enlarged to 45.5-47.9 A and parts of its layers cocked and curled. Stearate ions were grafted on the methoxy groups and arrayed aslant in the interlayer space of kaolinite with an inclination angle of 47.45o to 52.17o. Sodium ions were adsorbed around the SiO4 tetrahedron and interlayer carboxylate anions, whereas some of them entered into the ditrigonal hole of tetrahedral sheets. The thermal de-intercalation of Ka-MeOH-SS includes three steps and the activation energy E is 98.3 kJ mol−1, logarithm of pre-exponential factor lg(A / s-1 is 9.71 and the mechanism function is f(α) = −ln (1 − α) and G(α) = 1 − α.

Synthesis and investigation of proton conductivity for intercalated kaolinite with 4-amidinopyridinium chloride

The proton-conducting materials have potential application in devices such as fuel cells. In this study, a mineral kaolinite-based proton conducting material, kaolinite-4-amidinopyridinium hydrochloride (K-4-APy–HCl), was synthesized by the intercalated compound kaolinite-4-amidinopyridine (K-4-APy) adsorbing volatilizing HCl. The thermogravimetric analysis (TG), powder X-ray diffraction (PXRD) and IR spectrum confirmed the HCl successfully inserting into the interlayer space of kaolinite and the 4-aminopyridine being protonated. The intercalation efficiency is estimated to be ca. 85.6%. With respect to K-4-APy, the interlayer space expends by 1.53Å. The thermal decomposition mechanism was studied by PXRD and TG techniques. The K-4-APy–HCl shows proton conductivity with σ=3.379×10−8Scm−1 at 373K and Ea=1.159eV in the anhydrous condition, which are comparable to MOFs-based proton conducting materials.

Thermal decomposition behavior and de-intercalation mechanism of acetamide intercalated into kaolinite by thermoanalytical techniques

De-intercalation is the inverse of the intercalation process, which can be easily and rapidly determined by thermal analysis. Research on the de-intercalation process is beneficial to exploring the intercalation mechanism that is still unclear in the case of kaolinite intercalation. The objectives of this study were (a) to investigate the thermal decomposition behavior of the intercalation compound of kaolinite and (b) to determine the kinetics of de-intercalation process by thermal analysis to study the mechanism of de-intercalation reaction in kaolinite. Here, the kaolinite–acetamide intercalation compound that was prepared by the direct intercalation method was investigated. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy results showed that acetamide molecules were inserted into the interlayer space of kaolinite and apparently formed new hydrogen bonds with the inner surface hydroxyl groups of kaolinite. The basal spacing of kaolinite increased from 0.721 to 1.102nm upon intercalation with acetamide. The thermogravimetric (TG) and differential scanning calorimetry (DSC) curves indicated that the decomposition process of the intercalation compound could be divided into two steps. The first step was attributed to the de-intercalation of the intercalated molecules at a temperature of about 181°C, and the second step corresponded to the dehydroxylation of kaolinite at a temperature of about 502°C. The completed kinetic triplet of the de-intercalation reaction was obtained through thermal analysis kinetics methods. The apparent activation energy Ea of the de-intercalation process was calculated to be about 73.6kJmol−1 by an iterative procedure. The pre-exponential factor A was estimated to be in the range of 1.06×1010s−1 to 7.92×1010s−1 by the Dollimore method. The optimized mechanism function of the de-intercalation process of acetamide was determined to be an nth-order chemical reaction through the Malek method. The mechanism function is G(α)=[1−(1−α)1−n]/(1−n), f(α)=(1−α)n and experiments showed that the value of n increased with increased heating rate.