Intercalation Of Kaolinite Research Articles

Dielectric properties of intercalated kaolinite

Intercalation of kaolinite allows to locate guest polar molecules in the interlayer area. In the presented experiments, the kaolinite+potassium acetate, kaolinite+urea and kaolinite+N-methylformamide intercalates were investigated. An increase in electric permittivity at low frequencies is probably related to the interlayer water molecules. The increase in the high frequency permittivity and losses were explained as a movement of the polar intercalated molecules. The dielectric properties were discussed simultaneously with the results of thermogravimetric and X-ray experiments.

Reactivity of kaolinite in ionic liquids: preparation and characterization of a 1-ethyl pyridinium chloride–kaolinite intercalate

A novel class of organic–inorganic nanohybrid material was prepared by the intercalation in kaolinite of a molten organic salt (1-ethyl pyridinium chloride, EP) above its melting temperature. The intercalation proceeded at 170 °C under N2. It did not succeed when kaolinite was used as the starting material, whereas the melt intercalation process was possible when DMSO–kaolinite (DMSO-K) was used as the starting material. The amount of EP loaded in the galleries of kaolinite is 24.3% (0.574 mol of EP per unit-cell) which produces an increase of the basal spacing d001 from 1.10 nm in the case of DMSO-K to 1.35 nm. The melt intercalation process could be dramatically improved by the choice of the temperature of reaction as well as of the atmosphere. At lower temperatures (less than 140 °C), even if the reaction medium is the ionic liquid, the intercalation is not observed. This results from the non-release of DMSO from the interlamellar space of DMSO-K, a step essential for the intercalation of EP to proceed. This work indicates that the intercalation of EP and the displacement of DMSO from the interlamellar spaces of kaolinite take place concurrently, not in a sequential manner. However, the process is initially driven by the thermal removal of DMSO.

The effect of mechanochemical activation upon the intercalation of a high-defect kaolinite with formamide

The effect of mechanochemical activation upon the intercalation of formamide into a high-defect kaolinite has been studied using a combination of X-ray diffraction, thermal analysis, and DRIFT spectroscopy. X-ray diffraction shows that the intensity of the d(001) spacing decreases with grinding time and that the intercalated high-defect kaolinite expands to 10.2 Å. The intensity of the peak of the expanded phase of the formamide-intercalated kaolinite decreases with grinding time. Thermal analysis reveals that the evolution temperature of the adsorbed formamide and loss of the inserting molecule increases with increased grinding time. The temperature of the dehydroxylation of the formamide-intercalated high-defect kaolinite decreases from 495 to 470 °C with mechanochemical activation. Changes in the surface structure of the mechanochemically activated formamide-intercalated high-defect kaolinite were followed by DRIFT spectroscopy. Fundamentally the intensity of the high-defect kaolinite hydroxyl stretching bands decreases exponentially with grinding time and simultaneously the intensity of the bands attributed to the OH stretching vibrations of water increased. It is proposed that the mechanochemical activation of the high-defect kaolinite caused the conversion of the hydroxyls to water which coordinates the kaolinite surface. Significant changes in the infrared bands assigned to the hydroxyl deformation and amide stretching and bending modes were observed. The intensity decrease of these bands was exponentially related to the grinding time. The position of the amide CO vibrational mode was found to be sensitive to grinding time. The effect of mechanochemical activation of the high-defect kaolinite reduces the capacity of the kaolinite to be intercalated with formamide.

Molecular configurations and orientations of hydrazine between structural layers of kaolinite

Hydrazine is one of the most commonly used entraining agents to penetrate kaolinite, yet the mechanism of intercalation of kaolinite by hydrazine is still in debate. The objectives of this study are to investigate the possible molecular configurations and orientations of hydrazine in the interlayer of kaolinite and the configuration changes induced by water molecules. Water molecules increased the intercalation rate and caused the expansion of the intercalation complex from 0.96 to 1.03 nm. The kinetic effect was likely the result of breaking the self-associations of hydrazine molecules and releasing more “free” hydrazine molecules for the intercalation. H-bonding caused large red shifts of the inner surface OH stretching bands from 3695 to 3626 cm −1 in the 0.96-nm kaolinite hydrazine intercalation (KHI) complex and to 3570 and 3463 cm −1 in the 1.03-nm KHI complex. The NH stretching bands of the hydrazine molecules in the KHI complexes became sharper and blue-shifted more than 20 cm −1 compared with the free liquids. The symmetric NH vibrations at 3365 and 3310 cm −1, and the NN vibration at 1092 cm −1 became infrared inactive in the 0.96-nm KHI complex. The frequency of the SiO bands of the kaolinite in the 1.03-nm KHI complex was slightly lower than in the 0.96-nm KHI complex (5 cm −1 shift). These IR band changes implied that hydrazine molecules have different configurations in the complexes: hydrazine molecules had an eclipsed form in the interlayer of the 0.96-nm KHI complex. The eclipsed configuration has a dipole moment of 3.31 D, which is higher than the gauche form (1.83–1.90 D). The molecule was oriented with the NN bond parallel or nearly parallel to the (001) surface of the mineral and the four H atoms of each hydrazine molecule reacted with the basal siloxane surface. When a suitable amount of water was present, it promoted the configuration change of the hydrazine molecules from the eclipsed form to the common gauche form. This gauche form was stabilized by transforming to a more polarized NH 3NH tautomer structure (5.4 D). To promote an optimal interaction between hydrazine and the mineral surface, the NN bond of the hydrazine was tilted about 30° from the (001) plane and caused the intercalation complex to expand from 0.96 to 1.03 nm. The eclipsed form and the tautomer were stabilized by the asymmetric interlayer environment of kaolinite. The two proposed models and reaction mechanisms match the high dipole moment requirement as found for other entraining agents. Further investigation is needed to confirm the exact configuration of hydrazine molecules and whether or not the tautomer exists.

Intercalation and interlamellar grafting of polyols in layered aluminosilicates. d-Sorbitol and adonitol derivatives of kaolinite

This paper reports the intercalation of alditols into the interlamellar spaces of kaolinite. The alditols were adonitol, a meso compound, and D-sorbitol. The grafting of hydroxy groups onto the aluminol internal surfaces of kaolinite followed the intercalation. The polyols were intercalated into kaolinite by displacing dimethyl sulfoxide (DMSO) from the DMSO–kaolinite intercalate (Kao–DMSO). This was done directly from the alditol melt at temperatures just above the melting point of the respective polyols. The intercalated polyols are arranged in a flattened monolayer arrangement, such that the interlayer expansion was 3.1 A (adonitol) and 4.6 A (D-sorbitol). Infrared spectroscopy showed that heating the intercalated materials at 200 °C for 1 h resulted in the grafting of the alditols on the inner aluminol surface of kaolinite. 13C CP and DD/MAS NMR indicated the complete replacement of the DMSO molecules by the alditol guests and that the alditols were rigidly constrained in the interlamellar spaces of kaolinite. The intercalation of adonitol was monitored with time. The reaction proceeds via a partial collapse of the Kao–DMSO intercalate before the intercalation of the adonitol.

The Effect of Kaolinite Intercalation on the Structural Arrangements of N-Methylformamide and 1-Methyl-2-pyrrolidone

N-methylformamide (NMF) and 1-methyl-2-pyrrolidone (NMP) were intercalated with kaolinite, characterized, and deintercalated for analysis (the NMP was intercalated after expansion of the kaolinite layers with NMF). The dynamics of guest molecules within the kaolinite lamellae was studied by means of FT-IR and liquid state 1H and 13C NMR on the NMF and NMP before intercalation and also on the deintercalated solutions. Both compounds were deintercalated using water. The FT-IR spectra show no significant differences before and after intercalation, for either NMF or NMP, indicating that there is no change in molecular arrangement as a result of intercalation. 1H and 13C NMR investigations supported the findings of the FT-IR and indicated that structural arrangement and orientation of the guest species remain the same after deintercalation. This work provides evidence that intercalation is due to weak physical bonding.

Effect of Structural Stress on the Intercalation Rate of Kaolinite

Particle size in kaolinite intercalation showed an inverse reactivity trend compared with most chemical reactions: finer particles had lower reactivity and some of the fine particles cannot be intercalated. Although this phenomenon was noted in the early 1960s and several hypotheses have been reported, there is no widely accepted theory about the unusual particle size response in the intercalation. We propose that structural stress is a controlling factor in the intercalation and the stress contributes to the higher reactivity of the coarser particles. In this study, we checked the structural deformation spectroscopically and indirectly proved the structural stress hypothesis. A Georgia kaolinite was separated into nine size fractions and their intercalations by hydrazine monohydrate and potassium acetate were investigated with X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analyses. The apical Si–O band of kaolinite at 1115 cm−1 shifted to 1124 cm−1 when the mineral was intercalated to 1.03 nm by hydrazine monohydrate, and its strong pleochroic properties became much weaker. Similar reduction in pleochroism was observed on the surface OH bands of kaolinite after intercalation. Both the bending vibrations of the inner OH group at 914 cm−1 and of the surface OH group at 937 cm−1 shifted to 903 cm−1 after intercalation by hydrazine. A new band for the inner OH group appeared at 3611 cm−1 during the deintercalation of the 1.03 nm hydrazine kaolinite complex. Pleochroism change in the apical Si–O band suggested the tetrahedra had increased tilt with respect to the (001) plane. The tilt of the Si–O apical bond could occur only if the octahedra had also undergone structural rearrangement during intercalation. These changes in the octahedral and tetrahedral sheets represent some change in the manner of compensation for the structural misfit of the tetrahedral sheet and octahedral sheet. As the lateral dimensions of a kaolinite particle increases, the cumulative degree of misfit increases. Intercalation breaks the hydrogen bonds between layers and allows for the structure to reduce the accumulated stress in some other manner. The reversed size effect on intercalation probably was not caused by crystallinity differences as reported in the literature, because the Hinckley and Lietard crystallinity indices of the four clay fractions were very close to each other. Impurities, such as dickite- or nacrite-like phases are not significant in the studied sample as suggested by the XRD and IR results, they are not the main reasons for the lower reactivity of the finer particles.

Modification of the Hydroxyl Surface in Cesium Acetate Intercalated Kaolinite

Changes in the hydroxyl surfaces of cesium acetate intercalated kaolinite have been studied over the ambient to predehydroxylation temperature range using a combination of FTIR and Raman spectroscopy, combined with X-ray diffraction. Upon intercalation of a low-defect kaolinite with cesium acetate, the kaolinite layers expanded to 14.0 A. Upon heating the intercalate to 50 °C, the kaolinite expands to 17.0 A. Over the temperature range 100−200 °C, a third phase with a d(001) spacing of 12.80 A was observed. These expansions are reversible, and upon cooling the intercalation complex and upon exposure to air for sufficient lengths of time, the d(001) spacing returned to 14.0 A. These expansions are in harmony with thermal decomposition measurements. Diffuse reflectance spectroscopy shows that the cesium acetate intercalated kaolinite is almost completely intercalated and that the thermal treatment of the intercalate is reversible. The Raman spectrum of the hydroxyl stretching region of the intercalated kaol...

Modification of the Hydroxyl Surface in Potassium-Acetate-Intercalated Kaolinite between 25 and 300 °C

Changes in the hydroxyl surfaces of potassium-acetate-intercalated kaolinite have been studied over the ambient to predehydroxylation temperature range using a combination of X-ray diffraction (XRD) and Raman spectroscopy. Upon intercalation, the kaolinite expanded along the c-axis direction to 13.88 Å. When the intercalation complex is heated over the 50 to 300 °C range, X-ray diffraction shows the existence of three additional intercalation phases, with d spacings of 9.09, 9.60, and 11.47 Å. The amount of each phase is temperature-dependent. Thermal analysis shows three phase changes, at 88, 293, and 364 °C. These expansions are reversible, and upon cooling, the intercalation complex returned to its original spacing. The 13.88 Å phase existed only in the presence of water. It is proposed that the expanded kaolinite intercalation phases result from the orientation of the acetate within the intercalation complex. The completely intercalated kaolinite showed a single Raman band at 3607 cm-1 attributed to the inner-surface hydroxyl hydrogen bonded to the acetate ion. This band corresponds to the 13.88 Å phase. Mild heating of the intercalated complex at 50 °C caused a rearrangement of the surface structure, with Raman hydroxyl-stretching bands being observed at 3594, 3604, and 3624 cm-1. Further thermal treatment at 100 °C caused these bands to shift to 3599, 3605, and 3624 cm-1. At the predehydroxylation temperature for potassium-acetate-intercalated kaolinite (250 °C), two bands were observed, at 3601 and 3633 cm-1. At this temperature, only the 11.62 Å phase existed, suggesting that the 3601 cm-1 band is related to the 11.62 Å phase. Above this temperature, no hydroxyls are spectroscopically evident. When the complex is cooled to room temperature, the Raman spectra of the hydroxyl surfaces are identical to those of the initial intercalation complex, showing that the thermal modification of the kaolinite surfaces is reversible.

Effect of water on the formamide-intercalation of kaolinite

The molecular structures of low defect kaolinite completely intercalated with formamide and formamide–water mixtures have been determined using a combination of X-ray diffraction, thermoanalytical techniques, DRIFT and Raman spectroscopy. Expansion of the kaolinite to 10.09 Å was observed with subtle differences whether the kaolinite was expanded with formamide or formamide–water mixtures. Thermal analysis showed that greater amounts of formamide could be intercalated into the kaolinite in the presence of water. New infrared bands were observed for the formamide intercalated kaolinites at 3648, 3630 and 3606 cm −1. These bands are attributed to the hydroxyl stretching frequencies of the inner surface hydroxyls hydrogen bonded to formamide with water, formamide and interlamellar water. Bands were observed at similar positions in the Raman spectrum. At liquid nitrogen temperature, the 3630 cm −1 Raman band separated into two bands at 3633 and 3625 cm −1. DRIFT spectra showed the hydroxyl deformation mode at 905 cm −1. Changes in the molecular structure of the formamide are observed through both the NH stretching vibrations and the amide 1 and 2 bands. Upon intercalation of kaolinite with formamide, bands are observed at 3460, 3344, 3248 and 3167 cm −1 attributed to the NH stretching vibration of the NH involved with hydrogen bonded to the oxygens of the kaolinite siloxane surface. In the DRIFT spectra of the formamide intercalated kaolinites bands are observed at 1700 and 1671 cm −1 and are attributed to the amide 1 and amide 2 vibrations.

Deintercalation of Hydrazine-Intercalated Low-Defect Kaolinite

AbstractThe deintercalation of a low-defect kaolinite intercalated with hydrazine was studied by X-ray diffraction, diffuse reflectance infrared spectroscopy (DRIFT), and Raman microscopy over 30 d. X-ray diffraction showed that the kaolinite was fully intercalated. More than 120 h were required for the hydrazine-intercalate to decompose. The Raman spectra of the hydrazine intercalate showed only a single band at 3620 cm−1, which was attributed to the innerhydroxyl group. Upon deintercalation, additional Raman bands were observed at 3626 and 3613 cm−1. These bands decreased in intensity with further deintercalation. As deintercalation proceeded, the bands assigned to the inner-surface hydroxyl groups at 3695, 3682, 3670, and 3650 cm−1 occurred and increased in intensity. DRIFT spectra showed two bands at 3620 and 3626 cm−1 for the fully intercalated kaolinite only. Upon deintercalation, an additional band assigned to intercalated water was observed at 3599 cm−1 and increased in intensity at the expense of the 3626-cm−1 band. Bands attributed to the innersurface hydroxyl groups increased in intensity with deintercalation. Both the Raman and DRIFT spectra showed complexity in the NH-stretching region with two sets of NH-symmetric and antisymmetric stretching bands. Deintercalation was followed by the loss of intensity of these bands. Significant changes were also observed in the hydroxyl deformation and water-bending modes as a result of deintercalation. A model of hydrazine intercalation of kaolinite based on the insertion of a hydrazine-water unit is proposed. The hydrated end of the hydrazine molecule hydrogen bonds with the innersurface hydroxyl groups resulting in the formation of a band at 3626 cm−1 in the DRIFT spectra.

Preparation of Kaolinite-Amino Acid Intercalates Derived from Hydrated Kaolinite

AbstractIntercalation of amino acids into 10.0-Å hydrated kaolinite was studied by powder X-ray diffraction (XRD), differential thermal analysis-thermal gravimetry (DTA-TG), and infrared (IR) spectroscopy. Intercalation was found to be dependent on the chain-length, pH, and the concentration of the amino acid zwitterion. Near the isoelectric point, fully intercalated phases were obtained in solutions of concentration >0.5–1 M for glycine (Gly), 2–3 M for β-alanine (β-Ala), and 12 M for both γ-aminobutyric acid (γ-Aba) and δ-aminovaleric acid (δ-Ava). ∊-aminocaproic acid (∊-Aca) with a long chain (C = 6) was only partially intercalated. Intercalated amino acid formed a mono-molecular arrangement with the alkyl chain tilting toward the layer at an angle related to H2O content. The compositions of the intercalates of the Gly and β-Ala are Al2Si2O5(OH)4·(Gly)0.67·0.24H2O and Al2Si2O5(OH)4·(β-Ala)0.63·0.25H2O, respectively, based on TG data. From IR data, Gly and β-Ala molecules are found intercalated as zwitterions and these molecules form hydrogen bonds with both the Al-OH and Si-O surfaces of kaolinite. Washing the intercalate with water produced a hydrated kaolinite, which may form a second amino-acid intercalate of high order. Thus, hydrated kaolinite intercalates or deintercalates amino acids depending on concentration and conditions.

NMR Study of Kaolinite Intercalation Compounds with Formamide and Its Derivatives. 2. Dynamics of Guest Molecules

Dynamics of guest molecules in kaolinite intercalation compounds with formamide (FA), formamide-N,N-d2 (FA-d2), N-methylformamide (NMF), and N,N-dimethylformamide (DMF) has been investigated through 2H NMR spectra and 2H and 13C spin−lattice relaxations. 2H NMR spectra of kaolinite/FA-d2 in the temperature range 200−350 K are composed of a narrow central peak, a resolved Pake doublet (RD1), and a distribution of Pake doublets (RDs). Quadrupole coupling constants and asymmetric factors obtained by fitting the spectral patterns indicate that RD1 is ascribed to the host hydroxyl group formed through H−D exchange during the synthesis and RDs to the guest molecules in the interlayer. Temperature dependence of the quadrupole coupling constant reveals that the guest molecules undergo librational motions and that the librational amplitude increases with temperature. Spin−lattice relaxations of 1H and 29Si spins are due to paramagnetic impurities. 29Si spins relax through direct dipole−dipole interaction with electron spins, and spin diffusion plays a role in the 1H relaxation. Variable-temperature 13C spin−lattice relaxation times T1 of kaolinite intercalates with FA, FA-d2, NMF, and DMF were recorded at two magnetic fields. T1 decreases with increasing temperature in all the samples and increases at the higher magnetic field in the order of FA > FA-d2 > NMF > DMF, where it is almost independent of the field in kaolinite/DMF. 13C spins relax through dipole−dipole interactions with 1H and 14N by the librational motions of the molecules. The field dependence indicates that the correlation times are of the order of nano-seconds, and that they are in the order of FA > FA-d2 > NMF > DMF. The temperature dependence of the relaxation time is caused by the amplitude change of the librational motions. 2H spins relax mainly through paramagnetic impurities being assisted by spin diffusion at low temperatures, and fluctuation of quadrupole interaction caused by the librational motions contributes to the relaxation at higher temperatures.

NMR Study of Kaolinite Intercalation Compounds with Formamide and Its Derivatives. 1. Structure and Orientation of Guest Molecules

Local structures and orientations of guest molecules in kaolinite intercalation compounds of kaolinite/formamide (FA), kaolinite/formamide-N,N-d2 (FA-d2), kaolinite/N-methylformamide (NMF), and kaolinite/N,N-dimethylformamide (DMF) have been studied by means of solid-state NMR. 29Si magic-angle-spinning (MAS) NMR spectra identify the original kaolinite and the intercalates, while 13C MAS NMR spectra distinguish interlayer and outersurface adsorbed guest molecules. Quantitative analyses of 29Si and 13C NMR spectra combined with thermogravimetric analysis result in a formula of one interlayer guest molecule per Al2Si2O5(OH)4 host unit for all the intercalates. Intercalation causes high-frequency shift in the 13C resonance of the guest molecules. Strength in the guest−host interaction as revealed by changes in the 13C chemical shift of the carbonyl group upon intercalation is in the order of FA > NMF ∼ DMF. The 13C chemical shift of the methyl group confirms a cis conformation for NMF in the kaolinite interlayer space, and changes in the methyl chemical shift upon intercalation are DMF (trans) > NMF (cis) > DMF (cis). The magnitude of the temperature dependence in the 13C chemical shift is on the order of FA < NMF < DMF, and the 13C line width is FA > NMF > DMF. These facts reveal that the mobility of the guest molecules is in the order of FA < NMF < DMF. Kaolinite/NMF shows a second methyl peak whose amount increases with decreasing temperature, demonstrating the presence of molecules with a different orientation. The 1H chemical shifts confirm hydrogen-bonding interactions between the amide protons and the kaolinite host in kaolinite/FA and no such hydrogen-bonding interactions in kaolinite/NMF at room temperature. The chemical shift value of the hydroxyl groups in the host kaolinite structure is not affected by intercalation. The 1H line widths of carbonyls are FA > NMF > DMF, and those of methyls are NMF > DMF, which confirms again that the mobility of the guest molecules is FA < NMF < DMF.

Intercalation of kaolinite with acetamide

Upon intercalation of both ordered (low defect) and disordered (high defect) kaolinites with acetamide, two types of interaction are observed. Firstly, hydrogen bonding between the NH2 groups of the acetamide with the siloxane oxygens is formed, as evidenced by the formation of two new bands at 3400 and 3509 cm–1. Secondly, the appearance of additional bands at ∼3600 cm–1 in both the infrared and Raman spectra of the acetamide intercalates is attributed to a second type of hydrogen bonding by the interaction of the C=O group and the inner surface hydroxyls. Changes in the intensity of the hydroxyl deformation modes in the 895 to 940 cm–1 region are attributed to the changes in the hydrogen bonding of the kaolinite surfaces. It is proposed that the hydrogen bonding between the adjacent kaolinite layers is replaced with hydrogen bonding between both kaolinite surfaces and the acetamide molecule. Changes in the molecular structure of acetamide are observed upon intercalation. The amide 1 band is lost and replaced with a well-defined NH2 deformation vibration. The loss of the amide 1 band is attributed the hydrogen bond formation between the amide hydrogens and the siloxane surface. The bands of the C=O group at 1680 and 1740 cm–1 become a single band at 1680 cm–1. The amide 2 band remains unchanged. The lack of intensity of the 1740 cm–1 band is attributed to the formation of hydrogen bonding between the inner surface hydroxyl groups and the carbonyl group.

Role of Water in the Intercalation of Kaolinite with Hydrazine

A low-defect kaolinite of 7.18-Å basal spacing was expanded upon intercalation with hydrazine. The 001d-spacing was broad and the peak resolved into components at 10.28, 9.48, and 8.80 Å. It was found that the ordered kaolinite predominantly expanded to 9.48 Å with 31.2% and 10.28 Å with 38.0% of the total peak area. A high-defect kaolinite showed expansion by hydrazine in identical steps withd-spacings of 10.27, 9.53, and 8.75 Å. It is proposed that the intercalation of the kaolinite by hydrazine occurs according to the orientation of the hydrazine molecule and that water plays an integral part in the process of kaolinite expansion. For the hydrazine-intercalated kaolinite, hydroxyl stretching bands attributed to water are observed at 3413, 3469, and 3599 cm−1for the low-defect kaolinite and at 3600 and 3555 cm−1for the high-defect kaolinite. Upon the exposure of the low-defect hydrazine-intercalated kaolinite to air, an additional water band is observed at 3555 cm−1. Water bending modes are observed at 1578, 1598, 1612, 1627, 1650, and 1679 cm−1for the hydrazine-intercalated low-defect kaolinite and at 1578, 1598, 1613, 1627, 1652, and 1678 cm−1for the hydrazine-intercalated high-defect kaolinite. The intensities of these bands are a function of the exposure to air and measurement time. The 1650- and 1679 cm−1bands increased in intensity as the intensity of the 1612 cm−1band decreased. Even after exposure to air for 24 h, water remained in the kaolinite interlayer space and only after heating was the water removed. The 1578, 1598, and 1612 cm−1bands as well as the 1627 cm−1band are attributed to (a) free or non-hydrogen-bonded water held in the interlayer spaces of the kaolinite, (b) water in the hydration spheres of the hydrazine, and (c) adsorbed water on the kaolinite surface. In kaolinites additional bands at 1650 and 1679 cm−1are attributed to water coordinated to the siloxane surface.

Modification of the Kaolinite Hydroxyl Surfaces through Intercalation with Potassium Acetate under Pressure

Kaolinite hydroxyl surfaces have been modified upon intercalation with potassium acetate under a range of conditions. Modification is observed by changes in the hydroxyl stretching region using Raman and infrared spectroscopy. Upon the intercalation of low defect kaolinite with potassium acetate under a pressure of 20 bars and 220°C, the Raman spectra showed additional bands at 3590, 3603, and 3609 cm−1. The DRIFT spectra of this intercalate showed new bands at 3595 and 3605 cm−1. These bands are attributed to the inner surface hydroxyls hydrogen bonded to the acetate anion. Intercalation under 20 bars pressure at 220°C caused the differentiation of the inner surface hydroxyl groups, resulting in these additional bands. By using milder conditions of 2 bars and at 120°C, additional Raman bands were found at 3592, 3600, and 3606 cm−1. If the kaolinite was intercalated at 1 bar and 100°C, a new broad Raman band was found at 3605 cm−1. It is proposed that the effect of intercalation of the low defect kaolinite under pressure caused the kaolinite to become disordered and this disordering was dependent upon the temperature of intercalation.

Molecular Structure of Dimethyl Sulfoxide Intercalated Kaolinites

Upon the intercalation of kaolinite with DMSO, new Raman bands at 3660, 3536, and 3501 cm are observed for the low-defect kaolinite and at 3664, 3543, and 3509 cm for the high-defect kaolinite. An additional band at 3598 cm was observed for the high-defect kaolinite. The band at 3660 cm was assigned to the inner-surface hydroxyls hydrogen bonded to the S=O group. The other three bands are attributed to the hydroxyl stretching frequencies of water in the intercalation complex. The hydroxyl deformation region is characterized by one intense band in both the FTIR and Raman spectra at 905 cm. Significant changes in the Raman spectra of the intercalating molecule are observed. Splitting of the C-H symmetric and antisymmetric stretching vibrations occurs. Two Raman bands at 2917 and 2935 cm and four bands at 2999, 3015, 3021, and 3029 cm are observed. The in-plane methyl bending region shows two Raman bands at 1411 and 1430 cm. The DRIFT spectra show complexity in these regions. The S=O stretching region shows bands at 1066, 1023, and 1010 cm upon intercalation with DMSO for the low-defect kaolinite and 1058, 1028, and 1004 cm for the high-defect kaolinite. The 1058 cm band is signed to the free monomeric S=O group and the 1023 and 1010 cm bands to two different polymeric S=O groups. Bands attributed to the C-S stretching vibrations, the in-plane and out-of-plane S=O bending and the CSC symmetric bends all move to higher frequencies upon intercalation. It is proposed that intercalation with DMSO depends on the presence of water and that the additional bands at 3536 and 3501 cm are due to the presence of water in the intercalate.

The Role of Water in the Intercalation of Kaolinite with Potassium Acetate

Water in intercalated kaolinites is observed first as bands inthe hydroxyl-stretching region at 3300 to 3550 cm−1and bythe water H–O–H bending vibrations in the 1560 to 1680-cm−1region. For potassium-acetate-intercalated kaolinite, hydroxyl-stretching bands attributed to water are observed at ∼3540,∼3475, ∼3430, and ∼3380 cm−1. Water bending modes areobserved at 1560, 1586, 1610, and 1679 cm−1. These bands are attributed to (a) water molecules adsorbed on the kaolinite surface, (b) zeolitic water, (c) molecular first layer water, and (d) orderedwater on the hydroxyl surface, respectively. The intensities ofthe bands are a function of the method of preparation of the intercalated kaolinite. As the kaolinite was washed for varying time intervals, the 1560 cm−1band decreased in intensity more rapidly than the 1610 cm−1band. Even after washing for 24 h significant concentrations of water remained on the kaolinite and only heating removed the water. The 1560, 1586, and 1610 cm−1bands are attributed (a) to free or non-hydrogen-bonded water held in the interlayer spaces of the kaolinite, (b) to water in the hydration sphere of the potassium ion, and (c) to surface-adsorbed water on the kaolinite layers. In kaolinites intercalated under pressure, an additional band was observed at 1679 cm−1. It is proposed that this band is due to water coordinated to the kaolinite surface.

Infrared Study of the Intercalation of Kaolinite by Caesium Bromide and Caesium Iodide

CsBr- and CsI-kaolinite intercalation complexes were synthesized by gradually heating caesium halide disks of the DMSO–kaolinite intermediate up to 330°C. Infrared spectroscopy revealed two types of complexes with the caesium salts: almost nonhydrous, obtained during thermal treatment of the DMSO complex, and hydrated, produced by regrinding the disk in air. Comparison of band positions for CsBr–kaolinite and CsI–kaolinite with those for the CsCl complex (observed in a previous study) shows that the strength of the hydrogen bond between the intercalated halide and the inner surface hydroxyl decreases on the order CsCl > CsBr > CsI. The nonreactivity of CsI in mechanochemical intercalation may arise from weak interaction between I−and inner surface hydroxyl groups, resulting from the fact that caesium is a very soft acid and iodide is a very soft base. Consequently, the very strong interaction between the two ions in the crystal is not disrupted during mechanochemical treatment.