Interlayer Space Of Clay Mineral Research Articles

NH3-probe X-ray photoelectron spectroscopy method to characterize solid acidity of clay minerals

Accurate determination of solid acidity is essential for evaluating the catalytic activity of clay minerals. However, the conventional Fourier-transform infrared (FTIR) method using NH3 as the probe encounters challenges in measuring the solid acidity owing to the presence of water on the surface or within interlayer spaces of clay minerals as well as the influence of environmental water during the detection process. To mitigate water interference, a NH3-probe X-ray photoelectron spectroscopy (XPS) approach was adopted as an alternative to the FTIR method for the identification and semi-quantification of solid acidity of clay minerals. Following NH3 adsorption, the types of solid acid sites in clay minerals were identified through the chemical shift in N1s XPS spectra. The ratio of Brønsted and Lewis acid sites in a given sample and the relative concentration of acid sites across different samples were determined by examining the specific N1s peak area ratio. According to the XPS data, the ratios of Brønsted and Lewis acid sites in Ca-montmorillonite (SAz-2) and Na-montmorillonite (SWy-2) were nearly 1:1, whereas that for the illite–smectite mixed-layer mineral (ISCz-1) was 4. The acid site contents in SAz-2 were more than twice those of SWy-2. This work highlights the promising application prospects of the NH3-probe XPS method in solid acidity investigations of clay minerals.

Study of montmorillonite modification technology using polyvinylpyrrolidone

In this work, a new method of modifying montmorillonite (Mt) with polyvinylpyrrolidone (PVP) was developed, which makes it possible to obtain modified Mt with different structures and modifier content simultaneously. The essence of the method consists in mixing colloidal solutions of Mt and PVP, processing the mixture with ultrasound, settling, and selecting individual layers of the final solution. Several methods, such as scanning electron microscopy (SEM), X-ray diffraction (XRD), thermal gravimetry (TG), differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy, have been used to characterize pure substances and to study the structure and thermal behavior of the composites. It was established that PVP macromolecules could both intercalate in the interlayer space of Mt and form exclusively exfoliated Mt. In addition, under certain conditions, Mt flocculated with PVP can be obtained. It is shown that during intercalation, PVP macromolecules displace and replace montmorillonite water in the interlayer space of clay mineral.

Two Forms of Ice Identified in Mars-like Clay Using Neutron Spectroscopy

The capacity of clay minerals to store large amounts of water is utilized in a number of industrial and environmental applications on Earth, for example, as components in geosynthetic clay liners in landfills or ingredients in water-based drilling fluids, and could prove important on Mars to identify future human landing sites where water could be harvested. The subzero behavior of water interacting within the interlayer space of clay minerals is of particular interest in most applications but remains poorly understood. To better understand the hydrothermal mechanism by which water ice bonds and separates from clay interlayers, we have utilized neutron spectroscopy, spectral analysis, and phonon band assignment. The inelastic neutron scattering from sodium montmorillonite, hydrated at 24, 73, and 166% water content, as well as an oven-dried sample, were measured to assess the vibrational density of states. The water contents studied provide a range of pore dimensions within clay gels that have varying degrees of confinement. The type of ice formed from water held in larger intra- and interparticle pores differs substantially from that confined within the interlayer (pseudo-two-layer hydrate), and the differences vary with hydration level. Spectral subtraction over an energy transfer range 50 < E < 550 cm–1 (8 < E < 70 meV) produces clearly two different forms of ice: hexagonal and cubic in the two wetter samples. A form of interfacial ice, presumably of a lower density, is observed in the vibrational density of states spectrum of the sample hydrated to a pseudo-two-layer hydrate (ie 24% gravimetric water content (GWC), 10 H2O/Na+). No hexagonal or cubic ice is observed in this sample. The four vibrational modes within the translation band of hexagonal ice are apparent within the sample hydrated to 166% gravimetric water content, in which pores greater than 20 nm are largely water-filled. By considering hydrogen bonding of the water to the clay surface, our data indicate an increase in the strength of the H-bond due to a shorter distance to the hydroxyl. We attribute this decrease to the pores in the clay generating a localized negative pressure or “suction” effect, thus attracting the water.

Dense Integration of Stable Aromatic Radicals within the Two-Dimensional Interlayer Space of Clay Minerals via Clay-Catalyzed Deamination of Arylammoniums

Here, we have successfully demonstrated the dense integration of aryl radical cations within two-dimensional interlayer nanospace of abundant magnesium aluminosilicate clay minerals via spontaneous...

Facile sample preparation method allowing TEM characterization of the stacking structures and interlayer spaces of clay minerals

Transmission electron microscopy (TEM) is an essential and irreplaceable technique for studying the micromorphology and microstructure of clay minerals. However, observing layer stacking and detecting the interlayer spaces of clay minerals by TEM are still major challenges, due to the difficulty of finding suitable fields of view for clay planes along the [00l] direction. A simple and effective sample pretreatment method was proposed here for TEM characterization of clay mineral stacking structures and interlayer spaces. Using this method, clay mineral-bearing ultrathin slices, in which clay minerals particles showed an orientated arrangement, were prepared based on the resin embedding method. The (00l) plane of clay minerals was exposed toward electron beams during TEM analysis, and fields of view along the [00l] direction were observed, accordingly. This method is thus particularly useful for the observation of stacking information and detection of interlayer regions in clay minerals. The validity of this method is exemplified by its application to pure kaolinite and clay mineral-rich shale samples which contains several clay minerals and the clay mineral-organic matter complexes.

A periodic DFT study of adsorption of water on sodium-montmorillonite (001) basal and (010) edge surface

Water molecules can be easily adsorbed on the surface or in the interlayer space of clay minerals. This process is named hydration which plays an important role in various application fields. In order to find how water interacted with surface through minimizing the interaction among multiple waters, the adsorptions of single water molecule on external surfaces of sodium-montmorillonite (Na-MMT), including (001) basal and (010) edge surface, were theoretically investigated based on periodic density functional theory (DFT) method. The adsorption energies and geometries as well as electronic properties were studied in the work. It was found that water molecule was adsorbed on Na-MMT (001) basal surface mainly through electrostatic interaction between water molecule and Na+ cation, and was adsorbed on (010) edge surface through hydrogen bonding between water and surface OH or OH2 groups. The adsorption energy Eads value of water molecule on (010) edge surface was larger than that on (001) basal surface. After adsorption, a part of electron density was transferred from both Na-MMT (001) and (010) surfaces to water molecule. Based on the PDOS, there was the bonding between Na 3s and Ow 2p orbitals on (001) basal surface and between H 1s and O 2p orbitals for hydrogen bonds on (010) edge surface.

Diffusion and adsorption of uranyl ion in clays: Molecular dynamics study

Molecular dynamics (MD) simulations were performed to study the diffusion and adsorption behaviors of aqueous uranyl species in interlayer space of clay minerals, which are key processes in the safety assessment for geological disposal of radioactive waste. The diffusion behaviors of UO22+, K+, CO32− and Cl− and H2O were evaluated for the aqueous solution system. The diffusion coefficients of these species decreased with increasing solutes concentration, and that of UO22+ was much smaller than others. In the aqueous solution with higher concentration of carbonate ions, uranyl carbonate complexes such as UO2CO3 and UO2(CO3)22− could be observed. For the clay-aqueous solution system (clay: montmorillonite or illite), the adsorption and diffusion behaviors of UO22+ and K+ were evaluated by MD calculations. The distribution coefficients (KD) of these solutes increased with the layer charge of clay, and the KD value of UO22+ might be smaller than that of K+. Further, the diffusion coefficients in the adsorption layer on the basal plane were relatively small and decreased with increasing the layer charge of clay.

Occurrence of stable and mobile organic matter in the clay-sized fraction of shale: Significance for petroleum geology and carbon cycle

Stability and mobility of organic matter (OM) in shale is of great significance for the carbon cycle and petroleum exploration and exploitation. To examine the stability and mobility of OM occurrence in shales, clay-sized fractions (<2μm) were separated from shales physically and chemically treated with different reagents. These fractions were followed by pyrolysis and measurements of specific surface area (SSA) and Fourier transform infrared spectrophotometry (FTIR). It is revealed that after wet chemical oxidation and organic solvent extraction, there exist: a) changes in total organic carbon (TOC), hydrogen index (HI) and oxygen index (OI); b) appreciable decrease in absorption intensity of –CH2– stretching vibration bands at 2924 and 2853cm−1; and c) dramatic increase of SSAs after wet chemical oxidation. These characteristics suggest that the TOC in the clay-sized fraction can be categorized into physical mobile-OC (PmOC), chemical mobile-OC (CmOC) and stable-OC (SOC), which account for 43.3%, 17.1% and 39.6% of TOC on average in the studied samples, respectively. The OM in the clay-sized fraction mainly occurs on mineral internal surface, and the occurrence of OM determines the stability and mobility of OC. The PmOC mainly accumulates in the pores and at the mouth and/or edge of the interlayer spaces of clay minerals, the CmOC chiefly adsorbs on the mineral external surface, and the SOC mainly occurs on the mineral internal surface. These occurrence characteristics of different OCs indicate that the mobility and stability of OM occurrence in a sample have different levels. The occurrence of stable and mobile OM in the clay-sized fraction of shale as investigated can improve the understanding of the occurrence of OM in shales, and provide a new insight for carbon cycle research and petroleum exploration and exploitation.

Influence of synthesis method in preparation of HDTMA+- and HDPy+-illites/smectites

Intercalation of cationic surfactants hexadecylpyridinium (HDPy+) and hexadecyltrimethylammonium (HDTMA+) into the interlayer space of homoionic (Na+-, Ca++- and Zn++-) illites/smectites using three methods (solution intercalation, solid–solid reaction and microwave irradiation) was investigated in this study. The changes in the surfaces and structures of the organo-illites/smectites with cationic surfactant were characterized using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR).The results showed that the intercalation of surfactant cations was complete within 24h, 15min and 2min by conventional method, solid–solid reaction and microwaves irradiation, respectively. HDPy+t and HDTMA+ surfactants were retained by Zn++-illites/smectites suggesting important surface properties (CEC=80meq/100g clay, SBET=116.5m2/g) and developed acid–base properties (point of zero proton charge PZC, density charge σH). HDPy+ cation loading was effective suggesting that the aromatic polar group is favored for intercalation. Different configurations of surfactants within interlayer space of clay mineral were proposed based on the basal spacings which increased with surfactant loading. The presence of symmetrical and asymmetrical vibration bands of the –CH2 group in the IR spectrum of the modified illites/smectites and the variation of their frequencies and their intensities confirmed the results obtained by XRD.

Thermal degradation of organic matter in the interlayer clay–organic complex: A TG-FTIR study on a montmorillonite/12-aminolauric acid system

The storage of natural organic matter within the interlayer space of layered silicate is an important type of clay–organic association in sediment. However, the role of the interlayer space of clay minerals in the thermal degradation of organics and the generation of hydrocarbons has not been well understood. In this study, an interlayer clay–organic complex was synthesized using montmorillonite (Mt) and 12-aminolauric acid (ALA). An Mt–ALA complex in which Mt and ALA were simply mixed was also prepared for comparison. Thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR) was applied to monitor the thermal events and the corresponding products during the thermal degradation of the Mt–ALA complexes. In the absence of Mt, ALA decomposed at 467°C via the cleavage of CC bonds, producing aliphatic hydrocarbon, N-containing compounds, and carboxylic acid. The decomposition temperatures of organic matter in the mixed Mt–ALA complex and the interlayer Mt–ALA complex decreased to 402 and 342°C, respectively. The most characteristic products of the interlayer Mt–ALA complex were NH3 and saturated hydrocarbons. The Brønsted acid sites in the interlayer space of Mt, arising from the dissociated interlayer water, initiated the deamination of ALA via the Hoffmann elimination pathway and significantly promoted the cracking of hydrocarbons via a carbonation mechanism. Lewis acid sites had little effect on the thermal degradation of ALA. This work indicated that the interlayer space of clay minerals provided the storage space for organic matter. Moreover, the active sites within the interlayer space strongly promoted the thermal degradation of organics.

Role of the interlayer space of montmorillonite in hydrocarbon generation: An experimental study based on high temperature–pressure pyrolysis

The interlayer clay–organic complex is an important clay–organic association in sedimentary environments. However, the effects of organic matter storage in the interlayer space of clay minerals on the thermal degradation of organics and the generation of hydrocarbons have not been investigated. In this study, montmorillonite (Mt) and 12-amoniolauric acid (ALA) were used to prepare an interlayer Mt–ALA complex and a Mt–ALA complex in which Mt and ALA were simply mixed. Pyrolysis experiments on the ALA and Mt–ALA complexes were conducted in a confined gold capsule system at a fixed temperature and pressure of 350°C and 36MPa, respectively. X-ray diffraction, elemental analysis and Fourier transform infrared spectroscopy were used to characterize the Mt–ALA complexes, and automatically controlled gas chromatography along with a pyrolysis furnace was used to detect the volatile components released during pyrolysis. In the absence of Mt, the pyrolysis of ALA yielded only a small amount of C1–5 hydrocarbons and CO2. The amounts of C1–5 hydrocarbons released from the pyrolysis of the interlayer Mt–ALA complex and the mixed Mt–ALA complex are approximately 43 and 5 times greater than the amounts released from ALA alone, respectively. The Brønsted acid sites in the interlayer space of Mt, which arise from the interlayer dissociated water, significantly promote the cracking of hydrocarbons through a carbocation mechanism, the isomerization of normal hydrocarbons and alkene–alkane conversion through hydrogenation, resulting in high i-alkane/n-alkane and alkene/alkane ratios in the pyrolysis products. The Lewis acid sites of Mt are primarily involved in the decarboxylation of ALA during pyrolysis and are responsible for CO2 generation.

Acidities of confined water in interlayer space of clay minerals

The acid chemistry of confined waters in smectite interlayers have been investigated with first principles molecular dynamics (FPMD) simulations. Aiming at a systematic picture, we establish the model systems to take account of the three possible controlling factors: layer charge densities (0 e, 0.5 e and 1.0 e per cell), layer charge locations (tetrahedral and octahedral) and interlayer counterions (Na + and Mg 2+). For all models, the interlayer structures are characterized in detail. Na + and Mg 2+ show significantly different hydration characteristics: Mg 2+ forms a rigid octahedral hydration shell and resides around the midplane, whereas Na + binds to a basal oxygen atom and forms a very flexible hydration shell, which consists of five waters on average and shows very fast water exchanges. The method of constraint is employed to enforce the water dissociation reactions and the thermodynamic integration approach is used to derive the free-energy values and the acidity constants. Based on the simulations, the following points have been gained. (1) The layer charge is found to be the direct origin of water acidity enhancement in smectites because the neutral pore almost does not have influences on water dissociations but all charged pores do. (2) With a moderate charge density of 0.5 e per cell, the interlayer water shows a p Ka value around 11.5. While increasing layer charge density to 1.0 e, no obvious difference is found for the free water molecules. Since 1.0 e is at the upper limit of smectites’ layer charge, it is proposed that the calculated acidity of free water in octahedrally substituted Mg 2+-smectite, 11.3, can be taken as the lower limit of acidities of free waters. (3) In octahedrally and tetrahedrally substituted models, the bound waters of Mg 2+ show very low p Ka values: 10.1 vs 10.4. This evidences that smectites can also promote the dissociations of the coordinated waters of metal cations. The comparison between the two Mg 2+-smectites reveals that different layer charge locations do not lead to obvious differences for bound and free water acidities.

Interlayer Spaces Associated with Hydration and Dehydration in Synthetic Saponite

Positron annihilation lifetime spectroscopy was conducted for a synthetic saponite to investigate hydration and dehydration behaviour occurring in nanoscale interlayer spaces. Long positron lifetime of ∼ 24 ns was observed with the intensity of ∼ 8 % when the sample is evacuated at ∼ 10−5 Torr. The radius of open nanospace evaluated from the positron lifetime is ∼ 10 Å, which corresponds to the interlayer spaces of saponite. The open nanospace increases up to 13 % after baking at 423 K for 8 h under the vacuum. The present results imply that positron annihilation spectroscopy is powerful tool to investigate hydration and dehydration behavior through the local structural changes in the interlayer spaces of clay minerals.

Formation of titanium dioxide nanostructures in the interlayer space of clay minerals

Kaolin and montmorillonite are intercalated through their consecutive two-stage treatment with dimethyl sulfoxide (DMSO) and TiCl4 vapors. It is established that, at 293 K, this process is kinetically hindered irrespective of the mobility of adjacent structural layers in the minerals. As the temperature is elevated to 393 K, the first stage markedly accelerates, thus making it possible to synthesize kaolin-DMSO and montmorillonite-DMSO intercalates in real time with interplanar spacings d 001 = 11.4 and 23.18 A, respectively, and the degree of intercalant incorporation up to 40 wt %. The replacement of DMSO by TiCl4 leads to the formation of kaolin-TiCl4 (d 001 = 13.1 A) and montmorillonite-TiCl4 (d 001 = 15.3 A) intercalates, amorphization of the minerals, subsequent hydrolysis of intercalated TiCl4, and the formation of hydrated titanium dioxide. The thermal transformation of the latter within a temperature range of 573–673 K is accompanied by the formation of anatase nanoclusters possessing high photocatalytic activity.

Assessment of potentially reactive pools of aluminium in poor forest soils using two methods of fractionation analysis

The research was carried out in a pine-covered area of the Wielkopolski National Park (Poland), for years exposed to acid rain. The soils under study are sands and loamy sands with a pH of 3.3–4.4. To assess potentially reactive pools of aluminium in those soils, two methods were employed: sequential and single extraction. For the exchangeable form the results obtained by single extraction using KCl greatly exceeded the figures yielded by sequential extraction, in which the conditions under which the process was executed (pH 7) led to an underestimation of the results. The soil profile displayed a lithogenically dichotomous structure which was reflected in the aluminium content, especially in Al extracted by pyrophosphate (single extraction) and in the so-called oxidisable fraction (sequential extraction). In both cases there was a jump in Al concentrations resulted from the release of aluminium from interlayer spaces of clay minerals. The labile percentage obtained for mean values in the profile amounted from 8.1% for single extraction to 12.1% for sequential extraction, which may indicate the metal’s considerable pool of potentially reactive aluminium. Single extraction seems to be more reliable in evaluating Al forms.

Preparation and characterization of poly(tetramethyl-p-phenylenediamine)/clay hybrids via intercalative polymerization

New noncovalent bonding polymer/clay hybrids were prepared, including the polymer poly(tetramethyl-p-phenylenediamine) (poly-TMPD). Polymerization occurred in the interlayer space of clay mineral successively after intercalation of monomers. Two types of clay minerals with different surface properties—a hydrophilic lithium fluorotaeniolite (TN) and four kinds of organophilic fluorotaeniolites (org-TNs)—were used as the hosts. Powder x-ray diffraction results showed an increase of 0.7–1.0 nm in the basal spacings, indicating the formation of poly–TMPD in the interlayer space of the hosts. Intercalative polymerization was also supported by Fourier transform infrared spectroscopy. The orientation of the poly-TMPD and thermal behavior were also discussed.

Fractionation of light hydrocarbons through GC columns packed with rocks and minerals-Implications for natural gas migration.

To understand the effect of rock types on the fractionation of light hydrocarbons in natural gases during migration in sedimentary rocks, the retention time of each hydrocarbon (C1, C2, C3, i-C4, i-C5 and n-C5) was measured using gaschromatografic columns packed with various rock and mineral samples. The fractionation occurred when the samples contained expandable clay minerals or zeolites. The order of retention times depended on the kind of clay minerals or zeolites present in the column. When montmorillonite, halloysite, vermiculite and mordenite were used, the order was C1 < C2 < C3 < i-C4 < n-C4 < i-C5 < n-C5. When clinoptilolite was used, the order was C1 < i-C4 < C2 < i-C5 < C3 < n-C4, probably because the pore size of clinoptilolite is somewhere between the cross-sectional diameters of n-alkanes and i-alkanes. The fractionation became larger as the columns packed with mineral samples aged. When not aged, only small fractionation was observed. These results show that the dehydrated state of the interlayer spaces of clay minerals or the pore spaces of zeolites play an important role in fractionation. Furthermore, these results suggest that the large fractionation by clay minerals or zeolites does not occur under normal subground condition where these minerals are hydrated.

Silicate Materials for Storage of Hydrogen

Advantages of using hydrogen as a source of energy and silicate materials for its storage, in place of metal hydrides, have been explained. The silicates studied are vermiculites (from France, Spain and artificially prepared), montmorillonite, chlorite (USA) and zeolites (artificially prepared). It has been shown that finely divided metal particles (15–100 Å) can be formed in the interlayer space of clay minerals or in the structural voids of zeolite under suitable conditions and these can serve for storing hydrogen.